Institute of Fundamental Technological Research

This paper introduces a first-time investigation into the impact of power ultrasound (PUS)-assisted preparation on the physicochemical and mechanical properties of cement-granulated blast furnace slag (GBFS) composite pastes. Pastes containing deposited GFBS with varying particle size fractions, partially replacing Portland cement, were prepared using PUS (ultrasonic horn tip, 20 kHz, 700 W) in pulse mode in a vertical jacketed glass sonoreactor with closed-circuit cooling. Cement paste incorporating 20 wt.% GBFS as mass substitution with varying particle size fractions was characterized by several physicochemical techniques at different curing ages. Exploring the cement and GBFS interaction induced by PUS, the compressive and flexural strength, the elastic modulus and indentation hardness, the heat of hardening, the mineral composition of hydration products, and the specific surface area BET were evaluated for a curing time of up to 28 days. The grain size distribution of GFBS and the reaction mixture's pH were measured. Both mechanical properties, heat of hydration and nanoporosity exhibited strong sensitivity to PUS treatment. Sonofragmentation of GBFS particles (especially the 125–250 μm fraction) increased with increasing sonication time, resulting in a relative increase of fraction <63 μm and a decrease of fraction >125 μm by 275 % and 60 %, respectively. Using the obtained SEM-EDS data, a simplified mechanism is proposed to explain the effects induced by PUS treatment.

Power ultrasound treatment, Portland cement, Granulated blast furnace slag, Early strength development, C-S-H/C-A-S-H, Seeding effect

An alkali–silica reaction (ASR) is a chemical process that leads to the formation of an expansive gel, potentially causing durability issues in concrete structures. This article investigates the properties and behaviour of ASR products in mortar with the addition of low-purity calcined clay as an additional material. This study includes an evaluation of the expansion and microstructural characteristics of the mortar, as well as an analysis of the formation and behaviour of ASR products with different contents of calcined clay. Expansion tests of the mortar beam specimens were conducted according to ASTM C1567, and a detailed microscopic analysis of the reaction products was performed. Additionally, their mechanical properties were determined using nanoindentation. This study reveals that with an increasing calcined clay content, the amount of the crystalline form of the ASR gel decreases, while the nanohardness increases. The Young’s modulus of the amorphous ASR products ranged from 5 to 12 GPa, while the nanohardness ranged from 0.41 to 0.67 GPa. The obtained results contribute to a better understanding of how the incorporation of low-purity calcined clay influences the ASR in mortar, providing valuable insights into developing sustainable and durable building materials for the construction industry.

alkali–silica reaction, ASR products, calcined clay, mortar, expansion

The paper presents and discusses the results of a study of the thermal properties of cement composites with different contents of magnetite aggregate (0%, 20%, 40% and 60% by volume). The effect of grain size on the evaluated thermal properties was also investigated. For this purpose, concrete containing 50% by volume of magnetite aggregate with four different fractions (1–2 mm, 2–4 mm, 4–8 mm and 8–16 mm) was used. Thermal parameters were evaluated on specimens fully saturated with water and dried to a constant mass at 65 °C. The series with varying grain sizes of magnetite achieved thermal conductivity values in the range of 2.76–3.03 W/(m·K) and 2.00–2.21 W/(m·K) at full water saturation and after drying to a constant mass, respectively. In the case of the series with 20% magnetite by volume, the thermal conductivity was 2.65 W/(m·K) and 1.99 W/(m·K) for the material fully saturated with water and dried to a constant mass, respectively. The series with a 60% volume share of magnetite obtained values of this parameter of 3.47 W/(m·K) and 2.66 W/(m·K), respectively, under the same assumptions.

shielding concrete, thermal properties, magnetite aggregate

Concrete used in nuclear applications faces significant durability challenges due to degradation from radiation, thermal stresses, and chemical reactions. These issues highlight the critical need for impermeable concrete shields to prevent radioactive leaks and protect against harmful radiation. This study examines how concrete composition affects gas permeability and gamma radiation shielding properties. Three coarse aggregates—amphibolite (reference), magnetite, and serpentine—and two cement types (ordinary and slag) were tested, with concrete densities ranging from 2309 to 3538 kg/m3. Gas permeability was measured using a Cembureau-type constant head permeameter, and gamma shielding was assessed through the linear attenuation coefficient (µ) and half-value layer (HVL) at 137Cs decay energies. The results revealed significant variations in gas permeability and gamma ray shielding based on aggregate and cement type, with observable relationships between gas permeability, HVL, and concrete density. The results obtained from the presented research will contribute to increasing the safety, durability and cost-effectiveness of concrete constructions and maintenance of nuclear facilities.

Heavyweight aggregate, Hydrogen-bearing aggregate, Shielding concrete, Gas permeability, Gamma ray attenuation, Microstructure, ITZ

The article presents the diagnostic results on surface-hardened industrial concrete floors. Selected examples of floors showcased premature damage to surface layers, characterized by intense dusting, delamination, and local spalling, while the structural system remained unaffected. Quantitative petrographic analysis of concrete was applied to core specimens from the floors, involving the examination of digital images from a polarizing optical microscope and a scanning electron microscope. The hardening compound and powdered specimens of the cement matrix were characterized using differential thermal analysis and X-ray diffraction. A multiple microindentation method was employed to assess local variations in mechanical properties. Concrete cross-section analysis revealed areas with a non-uniform distribution of air voids, identified regions exhibiting increased porosity, highlighted areas of cracking in the concrete, indicated local variability in the phase composition of cement hydration products, and pointed out the presence of carbonated areas. The causes of the damage were discussed based on these findings,. The crucial role of quantitative petrographic analysis in diagnosing premature surface damage to industrial floors was demonstrated.

concrete, delamination, quantitative microscopy, porosity, industrial floors, dusting, surface hardening

Przedstawiono wyniki oceny diagnostycznej posadzki przemysłowej przy wykorzystaniu metodyki ilościowej oceny mikrostruktury betonu. Objawy uszkodzeń obejmowały pylenie powierzchniowe i delaminację warstwy utwardzonej. Przeprowadzono analizę petrograficzną składu betonu w próbkach-odwiertach. Zaobserwowano nadmierne napowietrzenie betonu, gromadzenie się porów powietrznych i występowanie ukierunkowanych spękań, miejscową zmienność składu fazowego produktów hydratacji cementu, w tym występowanie obszarów o intensywnej karbonatyzacji, co wpływało na przedwczesne uszkodzenia powierzchniowe.
Diagnostic assessment of industrial floor using the methodology of quantitative evaluation of concrete microstructure is presented. Symptoms of damage included surface dusting and delamination of the top layer. A petrographic analysis of the concrete composition in core specimens was carried out. Excessive air content, accumulation of air voids and the occurrence of oriented cracks, local variability of the phase composition of cement hydration products, including the occurrence of carbonated areas were observed and associated with the premature surface damage.

delaminacja, mikroskopia ilościowa, porowatość, posadzki betonowe, utwardzenie powierzchniowe, delamination, quantitative microscopy, porosity, concrete floors, surface hardening

Results of experimental investigation on the mitigation of alkali–silica reaction (ASR) by low-grade calcined clay are presented. Domestic clay with an Al2O3 content equal to 26% and SiO2—58% was used. The calcination temperatures were as follows: 650 °C, 750 °C, 850 °C and 950 °C, which were chosen much more widely than presented in previous studies. Pozzolanity of the raw and calcined clay was determined with the Fratini test. The performance of calcined clay to mitigate ASR was evaluated according to ASTM C1567 using reactive aggregates. A control mortar mixture was prepared with 100% Portland cement (Na2Oeq = 1.12%) as a binder with reactive aggregate, and test mixtures were made with 10% and 20% of calcined clay as a cement replacement. The microstructure of the specimens was observed on the polished sections using scanning electron microscope (SEM) operated in backscattered mode (BSE). The results of expansion of mortar bars with reactive aggregate showed that replacing cement with calcined clay reduced the expansion of the mortar bars. The greater the cement replacement, the better results in terms of ASR mitigation. However, the influence of the calcination temperature was not as clear. The opposite trend was found with the use of 10% or 20% calcined clay.

alkali–silica reaction (ASR), expansion, low grade calcined clay, mitigation, Fratini test, microscopic analysis

Despite ongoing efforts to prevent the damaging effects of alkali-silica reaction (ASR) in concrete structures, this phenomenon still exists and causes significant degradation. This study aims to investigate the role of various deicing agents in provoking ASR by examining volume expansion, cracks, and microstructure of mortar and concrete containing aggregates identified as non-reactive by standard ASR test methods. To achieve this, the concrete specimens undergo simulated operating conditions testing to induce ASR expansion, with an external supply of alkali from chloride- and formate-based deicers. The findings suggest that the configuration and concentration of the deicing agent used, as well as the mineral composition of the aggregate that was previously identified as non-reactive, can significantly impact the expansion and damage caused by ASR. The results indicate that existing methods for testing aggregates for ASR may have limitations when formate-based agents are used.

Alkali-silica reaction, Concrete, Aggregate, Expansion, Deicing agents, Microscopy

The combination of MCNP6 and the FISPACT codes was used to predict inventories of radioisotopes produced by neutron exposure of a sample in a research reactor. The detailed MCNP6 model of the Budapest Research Reactor and the specific irradiation geometry of the NAA channel was established, while realistic material cards were specified based on concentrations measured by PGAA and NAA, considering the precursor elements of all significant radioisotopes. The energy- and spatial distributions of the neutron field calculated by MCNP6 were transferred to FISPACT, and the resulting activities were validated against those measured using neutron-irradiated small and bulky targets. This approach is general enough to handle different target materials, shapes, and irradiation conditions. A general agreement within 10% has been achieved. Moreover, the method can also be made applicable to predict the activation properties of the near-vessel concrete of existing nuclear installations or assist in the optimal construction of new nuclear power plant units.

MCNP6,Monte Carlo simulations,FISPACT,Isotope inventory,Radioisotope production,Neutron activation analysis,Mineral aggregate,Radiation shielding concrete

A thorough petrographic evaluation of aggregates from igneous rocks in terms of their alkali–silica reaction (ASR) potential is crucial in ensuring the durability and long-term performance of concrete structures, especially those where access to additional alkalis is possible, such as from de-icing agents. The aim of the research was to assess the potential reactivity of aggregates from igneous rocks, as only such aggregates are used for concrete airport pavements in Poland. Petrographic analysis was conducted to identify the reactive minerals in the aggregate, and it was extended by quantitative image analysis. The strained, microcrystalline and cryptocrystalline quartz were found to be reactive components but significantly differed in content. It was found that aggregates from igneous rocks were characterized by different susceptibility to ASR and that methods to mitigate the occurrence of ASR should be considered to be used in airfield concrete. A relationship between the content of analyzed reactive minerals and the expansion of mortar bars in AMBT, as well as of the concrete prism in the CPT method, was revealed.

igneous rocks, granite aggregate, mineral composition, thin sections, digital image analysis, petrographic analysis, alkali–silica reaction, concrete durability

The long term durability of concrete pavements in wet-freeze climate is influenced by deicing salts used for winter maintenance of roads. Alkaline deicers could also be an external source of alkalis therefore their role in respect to development of deleterious alkali-silica reaction (ASR) should be considered. The performance of mineral aggregate mixtures in concrete was studied using RILEM test procedure ‘60°C concrete test with external alkali supply’. Air entrained concrete specimens were exposed to cyclic temperature changes, wetting-drying and NaCl solution immersion. Tests revealed the development of concrete expansion in time and associated changes of its elastic modulus for 31 mixtures of fine and coarse aggregate and Portland and fly ash or slag blended cements. The expansive behavior of air entrained concrete was strongly influenced by the presence of micro- and cryptocrystalline silica in aggregates. A replacement of nonreactive limestone sand by moderately reactive quartz sand resulted in a substantial enhancement of concrete expansion by a factor of three. Observed reduction of elastic modulus was correlated with more abundant presence of alkali-silica reaction products in concrete. Effects of cement type (CEM I, CEM II/A-V and CEM II/B-S) on the ASR performance of concrete with crushed coarse aggregate and quartz sand are discussed.

Air entrained concrete,alkali-silica reaction,external alkalis,NaCl solution,performance test

During the wintertime, concrete pavements experience harsh exposure conditions due to the presence of both the freezing–thawing and wetting–drying cycles. Airport concrete pavements are commonly de-iced using chloride-free organic salts such as potassium formate or potassium acetate. However, these materials contain alkali ions which can have harmful effects on both the cement matrix and the aggregate. Specifically, there is an increased risk of occurrence of the alkali–silica reaction (ASR). The goal of this research was to estimate the influence of potassium formate on the potential of causing alkali–silica reaction in aggregates with different categories of reactivity (R0, R1, R2). The accelerated mortar bar test and its modification (which involves replacing sodium hydroxide solution with a potassium formate solution) were used. Detailed SEM-EDS examinations were performed to confirm the presence of alkali–silica reaction and to analyze the influence of potassium formate on the microstructure of mortar.

alkali–silica reaction,potassium formate,de-icing agent,reactive aggregate

This article presents the results of an experimental investigation into the mitigation of the alkali–silica reaction (ASR) resulting from using low-grade clay calcined at 850 °C. The clay used in the experiment was domestic clay with an Al2O3 content equal to 26% and a SiO2 content of 58%. The performance of calcined clay in ASR mitigation was evaluated according to ASTM C1567 using reactive aggregates. The control mortar mixture consisted of 100% Portland cement (Na2Oeq = 1.12%) binder and reactive aggregate. The test mixtures used the same reactive aggregate and binders, in which part of the cement was replaced with either 10%, 20% or 30% calcined clay. The microstructure of specimens was examined on the polished sections using a scanning electron microscope (SEM) operated in the backscattered mode (BSE). The results of expansion obtained from the mortar bars made with the reactive aggregate showed that replacing cement by calcined clay reduced their expansion, with the level of expansion decreasing with the increase in the level of cement replacement.

calcined clay, alkali–silica reaction, expansion, mitigation, microstructure

Alkali-silica reaction (ASR) is a phenomenon that causes irreversible damage to concrete structures. Since 1940, research has continued to investigate the possibility of eliminating these negative effects. The lack of availability of non-reactive aggregates requires the use of reactive aggregates, characterized by satisfactory physical and mechanical properties, with the introduction of innovative solutions to mitigate the effects of ASR expansion. Recently, fibre-reinforcement has shown to be a promising approach, even if the type and the volume of fibres used to reduce, or eliminate, the deleterious effects of expansion are not well established. For this reason, Miniature Concrete Prism Tests (MCPT) were performed on 4 series of expansive concrete prisms without any fibres and with 0.5% in volume of polypropylene fibres, steel fibres, and recycled carbon fibres, respectively. In addition, 4 series of non-expansive mortar prisms, with and without fibres, were tested in bending. As a result, by using recycled carbon fibres a moderate expansion can be observed after 56 days, in contrast to the high expansion of un-reinforced concrete. The same positive effect cannot be observed in concrete reinforced with steel or polypropylene fibres. This is due to the absence of the deflection hardening capacity of the fibre-reinforcement, as confirmed by both mechanical tests on non-expansive mortars, and by the analysis of microstructure on the post-mortem specimens.

Mortar, Concrete, Bending tests, Miniature Concrete Prism Tests (MCPT), Expansion Microstructure

Concrete mix design for radiation shielding is mainly based on selection of aggregate materials of specified elemental composition. Serpentinite aggregate could be a desirable component of concrete for mixed-radiation attenuation and for high temperatures, however its durability performance needs further attention. The objective of the study is to reveal the influence of serpentinite aggregate on the microstructure and transport properties of baryte-serpentinite concrete. Mix design was developed for low-heat Portland cement and slag cement by using a combination of serpentinite aggregate and baryte aggregate. The compressive strength, chloride migration coefficient, carbonation resistance were experimentally investigated. The durability tests were compared with open porosity, mercury intrusion porosimetry measurement and examination of thin section of concrete by optical microscope. The results revealed increased porosity of contact zone of serpentinite aggregate with cement matrix. Open and capillary porosity of concrete was found to increase with increase of serpentinite aggregate content. Consequently, an increase of the chloride migration coefficient up to 2.5 times, the rate of carbonation up to 4 times were observed.

baryte, serpentinite, carbonation, chloride ion permeability, durability, microstructure, mix design, interfacial transition zone, porosity, radiation shielding concrete

A viable prediction of service life of reinforced concrete structures exposed to irradiation environment is necessary to support a license extension for currently operating nuclear power plants as well as to support concrete mix optimization for new builds. An experimental study was carried out to evaluate the corrosion performance of mild steel reinforcing bars under gamma irradiation at environmental conditions favoring accelerated carbonation. in elevated temperature. The electrochemical impedance spectroscopy and potentiodynamic electrochemical tests were performed to assess the corrosion rates on the rebar surfaces. Effects of irradiation were also examined in regard to capillary pore size distribution by mercury intrusion porosimetry and mesopore distribution based on nitrogen desorption data. Companion tests were performed to determine the compressive and flexural strength of mortar exposed to gamma irradiation. Relative effects of gamma irradiation are reported for mortar specimens containing fly ash or limestone powder used for partial replacement of Portland cement up to 40% by mass. Gamma irradiation dose up to 2 MGy was found to affect the properties of passive layer of steel in comparison to non-irradiated specimens. A decrease of corrosive potential and passivation potential was found. An increase of corrosion current density by an order of magnitude due to gamma irradiation was observed. Parameters of polarization curves of steel indicated unstable passive layer on steel reinforcement in irradiated mortars.

gamma irradiation, steel corrosion, supplementary cementitious materials, modification, electrochemical impedance spectroscopy, corrosion potential, Barrett-Joyner-Halenda porosity

Prediction of carbonation progress in concrete exposed to ionizing radiation is important for the durability assessment of nuclear power plants, eventually needed for operational license extension. The objective of this work is to reveal the influence of gamma irradiation on the carbonation development and resulting microstructural features of cement mortar. The composition of mortar was varied by using mineral additions. Canned specimens at elevated CO2 concentration environment were exposed to gamma irradiation up to the absorbed dose of 1.6 MGy in the vicinity of spent nuclear fuel rods in pool of research reactor. Micromechanical properties of carbonation reaction products were determined using nanoindentation tests. The carbonation depth was found to increase with increasing absorbed γ dose. The size of calcite crystals was about three times greater in irradiated specimens. Gamma irradiation improved the micromechanical properties of carbonation products. Effects of mineral additives on the characteristics of irradiated mortar are discussed.

calcite, carbonation, cement mortar, gamma irradiation, microstructure, mineral additions, nanoindentation

Diagnostic tests were carried out on specimens drilled from a section of jointed, unreinforced highway pavement after 15 years of service. The section of highway was exposed to heavy road traffic, environmental actions of wet-freeze climate zone and associated winter maintenance including application of deicing salt. Premature pavement damage was manifested by visible cracking, mostly along transverse joints and in slab corners. Tests performed on core specimens included petrographic analysis of concrete and its components, using optical and scanning electron microscopy, also evaluation of elastic and transport properties, expansion potential, cracks and air void system. Numerous cracks in the grains of coarse quartzite aggregate were found. Reactive forms of quartz in quartzite aggregate - microcrystalline and cryptocrystalline quartz - were abundant. The gel-like products in cracks in quartzite grains and in surrounding cement paste were identified as alkali-silica reaction products. Expansion of specimens exposed to an alkali-silica reaction-promoting environment indicated the potential for further development of such reaction. Substantial cracking and reduction of modulus of elasticity was correlated with the presence of reactive quartz in quartzite aggregate. The role of additional destructive factors, such as the impact of heavy vehicles traffic and freeze-thaw aggression was indicated by greater cracks in the slow traffic lane compared than in the emergency lane, associated with local marginal air entrainment of concrete.

alkali-silica reaction, concrete, cracking, durability, highway pavement

After 15 years of exploitation, numerous instances of damage to the concrete pavement motorway located in northern Germany were observed. Detailed macro and microscopic analysis and determination of mechanical properties were performed on the collected cores. It was found that cracks in the coarse and fine aggregate resulted from advanced alkali-silica reaction. No impact of de-icing agents on the destruction of the concrete pavement was found, while attention was paid to the potential intensification of concrete degradation resulting from the increase in traffic on motorways. The results obtained are a detailed supplement to the German research, as this region (Rostock) has not been analysed before.

Alkali-silica reaction, Concrete, Aggregate, Petrographic analysis, Microstructure

Premature damage to the concrete pavement of a trunk road section after 15 years of its service life was noticed. The damage manifested itself in cracking along transverse joints and in the corners of slabs. Diagnostic investigations, covering a petrographic analysis of concrete and mineral aggregates by means of optical and scanning microscopy, an evaluation of the elastic properties, the degree of cracking and air-void parameters and an identification of the alkali-silica reaction products, were carried out on core samples. Multiple cracks in coarse quartzite aggregate particles and in cement matrix were found. A significant presence of microcrystalline and cryptocrystalline quartz in quartzite particles was detected. Typical alkali-silica reaction products were unambiguously identified. The considerable cracking and the substantial decrease in the modulus of elasticity were correlated with the presence of reactive quartz in the quartzite aggregate and the alkali-silica reaction was found to be the main cause of the damage. Additional damaging factors, such as heavy traffic loads and frost aggression, are discussed.

concrete, road pavement, pavement evaluation, aggregate, quartzite, alkali-silica reaction, cracks, service life

Sand used as fine aggregate in concrete may, under unfavorable environmental conditions, cause alkali-silica reaction and the consequent deterioration of durability and functional properties of concrete. The aim of this work is to compare alkali-silica reactivity of 18 natural sands of various origin. The potential reactivity of sands was tested according to the procedures PB/1/18 and PB/3/18 established in the Technical Guidelines issued by the General Directorate for National Roads and Motorways. Mineral composition of aggregate was analyzed in order to identify reactive minerals. Mortar bar expansion tests and microscopic analyses of the products of alkali-silica reaction were performed. The research indicated that 6 (33%) out of 18 tested aggregates should be classified as “moderately reactive” and 12 (67%) aggregates should be classified as “non-reactive”. It was demonstrated that the origin of sand affects its susceptibility to alkali-silica reaction.

alkali-silica gel, expansion, fine aggregate, reactive minerals, sand

The design of concrete for radiation shielding structures is principally based on the selection of materials of adequate elemental composition and mix proportioning to achieve the long-term durability in nuclear environment. Concrete elements may become radioactive through exposure to neutron radiation from the nuclear reactor. A selection of constituent materials of greatly reduced content of long-lived residual radioisotopes would reduce the volume of low-level waste during plant decommissioning. The objective of this investigation is an assessment of trace elements with a large activation cross section in concrete constituents and simultaneous evaluation of susceptibility of concrete to detrimental alkali-silica reaction. Two isotopes 60Co and 152Eu were chosen as the dominant long-lived residual radioisotopes and evaluated using neutron activation analysis. The influence of selected mineral aggregates on the expansion due to alkali-silica reaction was tested. The content of 60Co and 152Eu activated by neutron radiation in fine and coarse aggregates, as well as in four types of Portland cement, is presented and discussed in respect to the chemical composition and rock origin. Conflicting results were obtained for quartzite coarse aggregate and siliceous river sand that, despite a low content, 60Co and 152Eu exhibited a high susceptibility to alkali-silica reaction in Portland cement concrete. The obtained results facilitate a multicriteria selection of constituents for radiation-shielding concrete.

alkali-silica reaction, concrete durability, low-level radioactive waste, neutron activation analysis, radiation shielding concrete, trace elements

Three series of tests performed on fibre-reinforced gypsum composites are described herein. Sheep wool fibres and hemp fibres were used as reinforcement. The aim was to evaluate the capability of these biomaterials to enhance the fracture toughness of the gypsum matrix. The mechanical properties were measured by means of flexural tests on small specimens, whereas scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction were used to analyse the microstructure and composition of the fibres and of the gypsum composites. As a result, wool fibres were shown to improve the mechanical performance of the gypsum matrix, better than hemp fibres. This is due to the high adhesion at the interface of the fibre and gypsum matrix, because the latter tends to roughen the surface of the wool and, consequently to increase the bond strength. This preliminary research carried out shows that this type of biofiber—a waste material—can be considered a promising building material in sustainable and environmentally friendly engineering.

organic waste material, fibre-reinforced gypsum, mechanical properties, microstructure

The alkali-silica reactivity of granites may significantly affect the durability of road and airfield concrete pavements. The aim of the study was to evaluate the reactivity of granites commonly used as an aggregate in concrete pavements, with particular emphasis on microscopic methods. The research was focused on petrographic diagnosis of reactive minerals in granites, their quantitative analysis and comparison of the obtained results with standard measurements. The strained quartz was recognized as a reactive component and the linear relationship between its content and specimens expansion was found.

alkali-silica reaction, concrete, durability, granite, image analysis, microscopy, pavements, slow-reacting aggregates, expansion

The effect of gamma-ray irradiation on cement mortar properties is investigated in this study in order to understand the mechanism behind the strength and stiffness reduction, which may be significant according to the available researches. 60Co irradiation facility with the generating dose rate of 0.1–10 Gy/s and the total activity of 4.4·10^15 Bq (120 kCi) was used to perform the irradiation, so that the total observed dose of the irradiated samples reached the values ranging from 12.0 to 15.0 MGy. An identical set of control samples was placed in the same laboratory conditions away from gamma radiation. The results of nanoindentation, X-ray diffraction analysis and mercury intrusion porosimetry of the irradiated and the control samples are shown and explained in detail in this study. The nanoindentation creep compliance and the nanoindentation elastic modulus of the irradiated and the control samples do not show any significant difference. The mineral composition obtained using the X-ray diffraction analysis of the irradiated and the control samples is also similar. The pore structure rearrangement and microcrack occurrence, which were evidenced by the mercury intrusion porosimetry and scanning electron microscopy, led to the porosity increase and may be attributed to the significant decrease of compressive strength.

cement mortar, drying, experiment, gamma-ray, nanoindentation, porosity, X-ray diffraction

The effects of gamma irradiation on concrete properties during early hardening were studied towards radioactive waste storage or accelerated processing at precast plants. Concrete mixtures containing different mineral aggregates (baryte, magnetite, amphibolite) were investigated. During initial 16 hours of hardening the mixes were irradiated using 60Co gamma source at the rate of 3.5 kGy/h. The mechanical properties and microstructural features of irradiated early-age concrete were tested: the secant elastic modulus, the compressive strength, the porosity and pore size distribution. XRD and SEM analysis were also performed. The results indicate both the stiffening and pore refinement in concrete due to early gamma irradiation. Effects of early irradiation on microstructural features of cement matrix were found in the subsurface layer up to the depth of 2 mm. The influence of different mineral aggregates in concrete on the radiation-induced changes of early age properties is discussed.

Natural wool is a good insulating material, both thermal and acoustic. Nevertheless, with the increase in demand for the use of waste materials, other applications, such as the use of wool as a fibre-reinforcement in mortars and concretes, have been found. Unfortunately, wool, like other natural organic materials, dissolve in alkaline environment and, consequently, the performances of the reinforcement cannot be guaranteed for a long time. To solve the above issue, three series of reinforced mortar beams, with various contents of alkalis in cement, are investigated herein. The chemical compatibility, and the effects of alkalinity on the mechanical performances, are investigated by testing the beams in three point bending and, subsequently, by analysing the microstructure of the mortars through a scanning electron microscope equipped with energy dispersive X-ray spectroscopy. The results reveal that the lower the alkalinity of the cement paste, the better the resistance of wool fibres in cementitious matrix, which guarantees larger post-cracking residual stresses in the wool reinforced mortars.

fibre-reinforcement, fracture & fracture mechanics, microstructure, waste valorisation

In this paper, an overview of the latest research activities in the field of cement-based composites incorporating sheep wool reinforcement is presented. First, the characteristics of this type of natural fibre are described. Then, the current use of sheep wool fibres in cement-based composites is discussed. The research problems regarding the properties of cement matrix composites reinforced with sheep wool are divided into four groups: thermal and acoustic properties, mechanical behavior, durability issues, and microstructure aspects. The latter two groups are analysed separately, because both durability and microstructure are of particular importance for future applications of wool reinforcement. Finally, the main directions of future researches are presented.

natural fibres, sheep wool fibres, mechanical properties, durability, microstructure

Calcined clays are the only potential materials available in large quantities to meet the requirements of eco-efficient cement-based materials by reducing the clinker content in blended cements or reducing the cement content in concrete. More than 200 recent research papers on the idea of replacing Portland cement with large amounts of calcined clay are presented and discussed in detail. First, the fundamental information about the properties and structure of clay minerals is described. Then, the process of activation and hydration of clays is discussed, including the methods of pozzolanic activity assessment. Additionally, various testing methods of clays from different worldwide deposits are presented. The application of calcined clay in cement and concrete technology is then introduced. A separate chapter is devoted to lime calcined clay cement. Then an influence of calcined clay on durability of concrete is summarized. Finally, conclusions are formulated.

calcined clay, binder, supplementary cementitious materials, cement-based materials

The assessment of the aggregate suitability for concrete pavements applies mainly to coarse aggregate. However, even fine aggregate can significantly affect the long-term durability of concrete when it is susceptible to alkali-silica reaction (ASR). The sustainable use of available fine aggregates for the production of concrete, while reducing the effects of ASR, requires special preventive measures. The paper proposed different procedures to determine the chemical composition of aggregate and the related ASR risk. The study covers various properties of natural fine aggregates from glacial deposits. The experiments included determination of chemical composition by prompt gamma activation analysis (PGAA), quantitative mineralogical characterisation on thin sections using digital image procedure (DIP) and expansion measurements in mortar bar test (MBT). The strong correlation of sand origin and its susceptibility to ASR was observed. Content of micro- and cryptocrystalline quartz in siliceous sand was found to have a crucial effect on its performance in AMBT.

fine aggregate, alkali-silica reaction, mineral composition, prompt gamma activation analysis, digital image procedure, glacial deposit

Durability of concrete designed for radiation shielding structures is an important issue in nuclear power plant safety. An investigation of the permeability of concrete containing heavyweight aggregates and water-bearing aggregates was performed with respect to gaseous and liquid media. Mix design was developed using Portland and slag cement, crushed magnetite and serpentine aggregate. The use of slag cement in concrete containing magnetite and serpentine aggregates resulted in the substantial improvement of the compressive strength in comparison with Portland cement concrete. The application of slag cement was found to reduce the chloride ingress, regardless of the special aggregate use. The coefficient of chloride migration was within the range 5 ÷ 8 × 10^−12 m^2/s and 17 ÷ 25 × 10^−12 m^2/s for slag cement concrete and Portland cement concrete, respectively. At the same time, the carbonation depth was increased twice for slag cement concrete in comparison to Portland cement concrete. However, the maximum carbonation depth after one year of exposure to 1% CO2 was only 14 mm for slag cement concrete, and 7 mm for reference concrete. The total pore volume evaluated using mercury intrusion porosimetry was influenced by the type of special aggregate used. It was shown that concrete with various contents of magnetite aggregate and slag cement achieved the smallest total pore volume. While serpentine coarse aggregate caused an increase in total pore volume in comparison to concrete with magnetite aggregate.

chloride permeability, carbonation, slag cement, radiation shielding concrete, microstructure, MIP, mix design, Portland cement, magnetite

It is known that natural wool is a good thermal insulating material, but recent results suggest another application: the use of wool as a fiber-reinforcement in mortars and concretes. Indeed, the mechanical properties of wool filaments are comparable to those of some synthetic polymeric fibers (e.g., made with polypropylene). However, wool can dissolve in alkaline environments and, therefore, the performances of reinforced cement-based matrixes cannot be guaranteed for a long time. Accordingly, three series of reinforced mortar beams have been made with low alkali, high alkali, and sulfoaluminate cements. To investigate the chemical compatibility, and the subsequent effects on the mechanical performances, the beams have been tested in three point bending. As a result, the lower the alkalinity of the cement paste, the better the post-cracking capability of wool fibers to arrest the growth of cracks.

wool reinforcement, low alkali cement, high alkali cement, sulfoaluminate cement

Fly ashes from coal combustion in circulating fluidized bed boilers in three power plants were tested as a potential additive to cement binder in concrete. The phase composition and microstructure of cement pastes containing fluidized bed fly ash was studied. The fractions of cement substitution with fluidized bed fly ash were 20% and 30% by weight. X-ray diffraction (XRD) tests and thermal analyses (derivative thermogravimetry (DTG), differential thermal analysis (DTA) and thermogravimetry (TG)) were performed on ash specimens and on hardened cement paste specimens matured in water for up to 400 days. Quantitative evaluation of the phase composition as a function of fluidized bed fly ash content revealed significant changes in portlandite content and only moderate changes in the content of ettringite.

clean coal combustion, fluidized bed fly ash, microstructure, phase composition, portlandite, unburned carbon

The paper presents the results of investigations into the reactivity of domestic aggregates produced from selected sedimentary rocks, carried out using the new testing methods, consistent with the RILEM and ASTM methods, implemented by GDDKiA (Polish General Directorate for National Roads and Motorways) documents. The range of the investigations covered coarse crushed aggregates produced from limestone, dolomite, sandstone and greywacke rocks, potentially suitable for making strong and durable concrete. No reactive forms of quartz were found in the mineralogical composition of the limestone aggregates and the dolomite aggregates. Micro- and cryptocrystalline quartz occurred in the particles of the greywacke aggregates and the sandstone aggregates. On the basis of the expansion of mortar and concrete specimens the aggregates produced from the sedimentary rocks were classified into the reactivity categories: R0, R1 and R2. A sodium-potassium-calcium silicate gel, whose composition (consistent with that reported in the literature) was characteristic of the alkali-silica reaction products, was found. The investigations resulted in a consistent assessment of the reactivity of the aggregates.
W pracy przedstawiono wyniki badań reaktywności krajowych kruszyw z wybranych, litych skał osadowych przy wykorzystaniu nowych metod badawczych wdrożonych w dokumentach technicznych Generalnej Dyrekcji Dróg Krajowych i Autostrad (GDDKiA), zgodnych z metodami RILEM i ASTM. Zakres badań obejmował kruszywa grube łamane o potencjalnej przydatności do wykonania wytrzymałego i trwałego betonu, wyprodukowane ze skał wapienia, dolomitu, piaskowca i szarogłazu. W składzie mineralnym kruszyw z wapieni i dolomitu nie stwierdzono obecności reaktywnych form kwarcu; w ziarnach kruszywa z szarogłazów i piaskowca występował kwarc mikro- i kryptokrystaliczny. Na podstawie wydłużenia próbek określono następujące kategorie reaktywności wybranych krajowych kruszyw ze skał osadowych: R0, R1 i R2. Zaobserwowano występowanie żelu krzemianu sodowo-potasowo-wapniowego o składzie charakterystycznym dla produktów reakcji alkalia-kruszywo, zgodnym z danymi literaturowymi. Uzyskano spójną ocenę reaktywności kruszyw.

alkali-aggregate reaction, cement, concrete, dolomite aggregate, expansion, greywacke, limestone, quartz, reactive minerals, sandstone / beton, cement, kruszywo dolomitowe, kruszywo wapienne, kwarc, minerały reaktywne, piaskowiec, reakcja alkalia-kruszywo, szarogłaz, wydłużenie

The paper presents investigations into the reactivity of aggregates from igneous rock, carried out in accordance with the procedures contained in the GDDKiA General Technical Specification "Concrete pavements". The aim of the investigations was evaluation of the suitability of the aggregates for road structures and pavements built using cement based concrete technology. Aggregates produced from extrusive rocks (basalt, melaphyre and porphyry) and from intrusive rocks (granite and gabbro) were analysed. The mineral composition of the aggregates was evaluated with regard to their reactive SiO2 content. Expansion tests on mortar bar and concrete prism specimens with analysed aggregates and a microscopic analysis of the alkali-aggregate reaction products were carried out. A considerable amount of reactive minerals: chalcedony, tridymite and microcrystalline quartz and volcanic glass were found in the grains of the porphyry and melaphyre aggregates. On the basis of the conducted investigations the two aggregates made of igneous rocks (melaphyre and porphyry) were classified into category R1 (moderately reactive). The basalt aggregate, the granite aggregate and the gabbro aggregate were assigned to category R0 (non-reactive).
W artykule przedstawiono badania reaktywności kruszyw ze skał magmowych przeprowadzone zgodnie z procedurami ujętymi w instrukcjach GDDKiA OST "Nawierzchnie betonowe" w celu oceny ich przydatności do stosowania w technologii betonu cementowego na drogowe konstrukcje inżynierskie i nawierzchnie. Analizie poddano kruszywa ze skał wylewnych: bazalt, melafir i porfir oraz ze skał głębinowych: granit i gabro. Przeprowadzono ocenę składu mineralnego kruszyw z uwagi na zawartość reaktywnych minerałów krzemionkowych. Przeprowadzono badania wydłużenia próbek zapraw i betonów z kruszywami oraz analizę mikroskopową produktów reakcji alkalia-kruszywo. Stwierdzono występowanie znacznej ilości reaktywnych minerałów w ziarnach kruszywa z porfiru i melafiru: chalcedonu i trydymitu oraz kwarcu mikrokrystalicznego i szkliwa wulkanicznego. Na podstawie przeprowadzonych badań dwa kruszywa ze skał magmowych (melafir oraz porfir) zaklasyfikowano do kategorii R1 - umiarkowanie reaktywne. Kruszywo bazaltowe, granit oraz gabro przypisano kategorii R0 - niereaktywne.

aggregate, alkali reactivity, alkali silica gel, cristobalite, igneous rocks, microcrystalline quartz, reactive minerals / alkaliczny żel krzemionkowy, kruszywo, krystobalit, mikrokrystaliczny kwarc, minerały reaktywne, reaktywność alkaliczna, skały wulkaniczne

Long-term exposure of concrete to nuclear reactor environments may enhance the ageing phenomena. An investigation concerning a possible deleterious alkali-silica reaction (ASR) in concrete containing high-density aggregates is presented in this paper. The scope of this investigation was limited to heavy aggregates that could be used for the construction of the first Polish nuclear power plant (NPP). Five different high-density aggregates were selected and tested: three barites, magnetite, and hematite. Mineralogical analysis was conducted using thin section microscopic observation in transmitted light. The accelerated mortar beam test and the long-time concrete prism test were applied to estimate the susceptibility of heavy aggregates to ASR. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted on aggregates and mortars. The quartz size in aggregate grains was evaluated using image analysis. Application of the accelerated mortar beam method confirmed the observations of thin sections and XRD analysis of high-density aggregates. The microcrystalline quartz in hematite aggregate and cristobalite in one of barite aggregate triggered an ASR. The composition of ASR gel was confirmed by microscopic analysis. The long-term concrete test permitted the selection of innocuous high-density aggregates from among the other aggregates available, which showed practically no reactivity.

alkali-silica reaction, heavyweight concrete, high-density aggregate, quartz size, radiation shielding, reactive minerals

The microscopic analysis of the different cellulose fibre cement composites is presented. The observations of the fibres in optical microscope in transmitted light and in scanning electron microscope are described. The micro computed tomography (micro-CT) and SEM were used to determine the distribution of the fibres in the matrix. The investigated fibre cement boards were produced by extrusion process and panels were cured in natural conditions. The main goal of the research was application of different microscopic methods to analyze the fibres distribution as a result of a different methods of their production. Micro-CT was used for 3D visualization of fibres distribution in three different fibre cement boards. It was possible to determine the average diameter of the fibres and their concentration using the high-resolution mode of micro-CT scanning procedure. Finally, a procedure which can be applied as a useful tool for analysis of the different procedures used in production of fibre cement boards is described. This procedure can be successfully used in the quality control system of cellulose fibre distribution in cement composites

Cellulose fibre reinforced cement boards, Microstructure, Fibre distribution, X-ray microtomography, SEM-EDS analysis

nuclear reactor, concrete shield, radiation influence

Two different barite ore (barium sulfate BaSO4) specimens from different localizations were tested and described in this paper. Analysis of the microstructure was performed on polished sections, and on thin sections using X-ray microtomography (micro-CT), and optical microscopy (MO). Microtomography allowed obtaining three-dimensional images of the barite aggregate specimens. In the tomograms, the spatial distribution of the other polluting phases, empty space as well as cracks, pores, and voids – that exceeded ten micrometers of diameter-were possible to visualize. Also, the micro-CT allowed distinguishing between minerals of different density, like SiO2 and BaSO4. Images obtained and analyzed on thin sections with various methods using the optical microscopy in transmitted light delivered additional information on the aggregate microstructure, i.e. allow for estimation of the different kinds of inclusions (like the different density of the minerals) in the investigated specimens. Above methods, which were used in the tests, completed each another in order to supply a set of information on inclusions' distribution and to present the important differences of the barite aggregate specimens microstructure.

barite ore, barite aggregate, microstructure, optical microscopy, thin sections analysis, X-ray tomography

Considering the long-time durability of concrete in road infrastructure it is important to control the threat of expansive reaction between sodium and potassium hydroxides in the pore solution and the reactive minerals present in the aggregate. Petrographic analysis is the basis for the qualification of aggregates to appropriate classes of reactivity according to ASTM C1778 and RILEM recommendations. This paper presents the results of petrographic analyses of thin sections made from twenty different domestic aggregates. The tested crushed aggregates were obtained from bedrock and glacial deposits. The evaluation of the mineral composition of aggregates included identification of deleterious components and determination of the content of reactive forms of silica. This enabled preliminary classification of aggregate in one of the three classes of reactivity according to RILEM. Obtained results provide an initial assessment of potential reactivity of aggregates and can assist in making decisions to undertake further accelerated or long-term laboratory testing or to modify the concrete mix design.

aggregate, alkali-aggregate reaction (AAR), petrographic analysis, reactive minerals, thin sections

Przedstawiono wyniki analizy petrograficznej 20 kruszyw łamanych z rożnych regionów Polski, przeprowadzonej na cienkich szlifach analizowanych pod mikroskopem w świetle przechodzącym. Próbki kruszyw grubych frakcji do 16 mm pochodziły ze skał litych oraz ze złóż polodowcowych z zakładów produkcji kruszyw, łamanych stosowanych do betonu. Ocenę składu mineralnego kruszyw, mającą na celu rozpoznanie składników szkodliwych, przeprowadzono z uwagi na zawartość reaktywnych minerałów krzemionkowych, m.in. opalu, krystobalitu, trydymitu, chalcedonu, wielkość kryształów (skryto- i mikrokrystaliczny kwarc) oraz kwarcu w stanie naprężeń. Zastosowanie metody petrograficznej na cienkich szlifach pozwoliło na wstępną kwalifikację do kategorii potencjalnie reaktywnej lub reaktywnej. Uzyskane wyniki badań stanowią wstępną informację o przydatności kruszyw jako składników betonu bądź o skierowaniu ich do dalszych szczegółowych badań lub ich odrzucenia

analiza petrograficzna, kruszywo, minerały reaktywne, reakcja alkaliczna kruszywa (AAR)

W artykule opisano podstawowe wyniki uzyskane w trakcie realizacji projektu badawczego „Trwałość i skuteczność betonowych osłon przed promieniowaniem jonizującym w obiektach energetyki jądrowej” [1]. Przedstawiono też wytyczne techniczne i kryteria oceny betonu osłonowego. Uzyskane wyniki mogą stanowić podstawę dalszych prac przy projektowaniu obiektów elektrowni jądrowych, składowisk materiałów radioaktywnych i innych miejsc powstawania, stosowania lub przechowywania materiałów wytwarzających promieniowanie jonizujące. Artykuł obejmuje zagadnienia związane z wymaganą skutecznością betonowych konstrukcji osłonowych przez zapewnienie bezpieczeństwa personelu i otoczenia przed oddziaływaniem promieniowania jonizującego. Rozpatrzono również trwałość osłon betonowych, tzn. zachowanie właściwości mechanicznych i nieprzepuszczalności w okresie przewidzianej eksploatacji pod wpływem przewidywanych oddziaływań zewnętrznych i procesów starzenia, a także przy podwyższonej temperaturze i promieniowaniu jonizującym. Artykuł nie obejmuje zagadnień integralności osłon pod obciążeniami wyjątkowymi, spowodowanymi awarią reaktora, uderzeniem samolotu, działaniami terrorystycznymi itp.

In this paper a method of X-ray microtomography (micro-CT) was employed for a direct insight into a microstructure of fibre cement boards of different quality. Four specimens were subjects of examination. Two parameters were determined to characterize the level of compaction of fibres in concrete matrix: mean-square displacement of migrating virtual particles after 500,000 of time steps and a diffusive tortuosity. The results of the investigation had revealed that fibre cement boards differing in density produce different images after processing with micro-CT method. The effect of microstructure tightening due to saturation using dying agent was also detectable.

Fibre cement boards, Delamination of fibres, Computational modelling, X-ray microtomography

The influence of blended cements containing calcareous fly ash (W) on the strength and permeability of air entrained concrete was studied. Moderately active calcareous fly ash of CaO content of 26% and loss on ignition of 2%, obtained from lignite fired power station in Poland, was selected. Ternary cement compositions including siliceous fly ash (V) and ground granulated blast furnace slag (S) were also studied. Air void analysis in hardened concrete was used to evaluate the effectiveness of air entraining process. Pore size distribution was characterized by mercury intrusion porosimetry (MIP). The presence of calcareous fly ash in cement resulted in a moderate increase in the compressive strength of concrete and an increase of the category of resistance to chloride ion migration. Test results revealed a linear relationship between the capillary porosity measured by MIP and the chloride migration coefficient (Dnssm). The permeability was lower for increased clinker replacement level which was due to formation of smaller diameters of the capillary pores.

Air entrained concrete, Air void characteristics, Calcareous fly ash, Chloride ion migration, Multicomponent cements, Pore size distribution, Strength

The objective of this paper is to examine the possible use of new blended cements containing calcareous fly ash in structural concrete, potentially adequate for structural elements of nuclear power plants. The investigation included five new cements made with different contents of non-clinker constituents: calcareous fly ash, siliceous fly ash, ground granulated blastfurnace slag, and a reference cement—ordinary Portland cement. The influence of innovative cements on the resistance of concrete to chloride and carbonation exposure was studied. Additionally, an evaluation of the microstructure was performed using optical microscopy on concrete thin sections. Test results revealed a substantial improvement of the resistance to chloride ion penetration into concrete containing blended cements. The resistance was higher for increased clinker replacement levels and increased with curing time. However, concrete made with blended cements exhibited higher depth of carbonation than the Portland cement concrete, except the Portland-fly ash cement with 14.3% of calcareous fly ash. The thin sections analysis confirmed the values of the carbonation depth obtained from the phenolphthalein test. Test results indicate the possible range of application for new cements containing calcareous fly ash.

blended cements, calcareous fly ash, chloride migration, carbonation, durability, nuclear shielding concrete, thin sections

Alkali-silica reaction (ASR) is considered as a potential aging-related degradation phenomenon that might impair the durability of concrete in nuclear containments. The objective of this paper is the application of digital analysis of microscopic images to identify the content and size of quartz grains in heavy mineral aggregates. The range of investigation covered magnetite and hematite aggregates, known as good absorbers of gamma radiation. Image acquisition was performed using thin sections observed in transmitted cross-polarized light with λ plate. Image processing, consisting of identification of ferrum oxide and epoxy resin, and the subsequent application of a set of filtering operations resulted in an adequate image reduction allowing the grain size analysis. Quartz grains were classified according to their mean diameter so as to identify the reactive range. Accelerated mortar bar tests were performed to evaluate the ASR potential of the aggregates. The SiO2 content in the heavyweight aggregates determined using the image analysis of thin sections was similar to XRF test result. The content of reactive quartz hematite was 2.7%, suggesting that it would be prone to ASR. The expansion test, according to ASTM C1260, confirmed the prediction obtained using the digital image analysis.

alkali-silica reaction, grain size, heavyweight aggregate, image analysis, radiation shielding concrete, reactive aggregate, quartz

The results of studies of concretes from the special cements, destined to the production of shields against the radiation. The study included Portland cement, Portland fly ash cement, and cements with different content of granulated blastfurnace slag. The application of special cements decreased the possibility of ASR occurrence. CEM I 42.5N LH/SR3/NA and CEM III/A 42.5N LH/HSR/NA usage in heavy concrete of gravity in the range of 3200-3600 kg/m3, the compressive strength was in the range of 45-62 MPa and 62-81 MPa after 28 and 90 days, respectively. The comparison of the effect of CEM III/A 42,5N LH/HSR/NA usage instead of CEM I 42,5N LH/SR3/NA for heavy concrete production the systematic decrease of the rate of water absorption, decrease of coeffi cient of chloride ions diffusion, but increased the carbonation rate, was shown.

special cements, concrete shields

Możliwość wystąpienia reakcji alkalicznej wodorotlenków sodu i potasu (Alkali Silica Reaction, ASR) w betonowych osłonach reaktorów wymaga szczególnej ostrożności przy doborze składników betonów do realizacji programu energii jądrowej w Polsce. Uszkodzenia osłon reaktorów w USA i w Belgii wskazują kierunki niezbędnych badań, [1-3]. W badaniach przedstawionych w artykule zastosowano kruszywa o dużej gęstości (osłabianie promieniowania gamma): magnetytowe, barytowe oraz hematytowe oraz kruszywo o wysokiej zawartości wody związanej (absorpcja promieniowania neutronowego) – kruszywo serpentynitowe. Przeprowadzono badania mikroskopowe kruszyw na cienkich szlifach w celu identyfikacji potencjalnie szkodliwych minerałów z uwagi na zagrożenie ASR, oraz przyspieszone i długotrwałe badania w celu określenia potencjalnej reaktywności alkalicznej tych kruszyw. Wyniki badań wykluczyły możliwość stosowania kruszywa hematytowego do betonów osłonowych. Wyniki badań odnośnie do wykorzystania dostępnych kruszyw specjalnych tworzą podstawy projektowania bezpiecznych osłon w warunkach krajowych

reakcja krzemionki z wodorotlenkami sodu i potasu (ASR), ekspansja, beton osłonowy, kruszywo specjalne

The paper presents a method of pore connectivity analysis applied to specimens of cement based composites differing in water to cement ratio. The method employed X-ray microtomography (micro-CT). Microtomography supplied digitized three-dimensional radiographs of small concrete specimens. The data derived from the radiographs were applied as an input into the application based on the algorithm called ‘random walk simulation’. As the result a parameter called diffusive tortuosity was established and compared with estimated porosity of examined specimens.

Artykuł prezentuje metodę wyznaczania parametru charakteryzującego intensywność połączeń mikroporów w zastosowaniu do próbek kompozytów z matrycą cementową, różniących się stosunkiem wodnocementowym. Metoda bazuje na wynikach badań z zastosowaniem mikrotomografii rentgenowskiej. Analizowano zdigitizowane zestawy danych, opisujące trójwymiarową reprezentację mikrostruktury niewielkich próbek wykonanych z betonu. Przygotowane w ten sposób skany mikrostruktury zastosowano jako dane wejściowe wprowadzone do oprogramowania wykorzystujacego algorytm ‘przypadkowo migrujących cząstek wirtualnych’. W ten sposób wyznaczono parametr mikrostruktury znany jako krętość dyfuzyjna. Parametr ten porównano z porowatością obserwowaną wyznaczoną dla zbadanych próbek przy wykorzystaniu analizy jasności voxeli w analizowanych próbkach.

X-ray tomography, concrete microstructure, diffusive tortuosity

The results of microstructural characterization of mortars containing fly ash class C (High Calcium Fly Ash) from combustion of lignite are presented. The evaluation of the microstructure was performed using scanning electron microscope, optical, and confocal microscope. The tested beams were bent till the crack and microcracks opening, which were healed during the different curing time. The results showed that the replacement of cement with fly ash class C influenced the process of crack healing. The addition of HCFA, at both 30% and 60%, speeds up the self-healing process in cracks and particularly in micro-cracks. In the research, the completely filling up of the cracks by new phases has not been observed, only the beginning of such process has been noticed.

self-healing, cement matrix, stereomicroscope, SEM-EDX analysis

In the paper two advanced methods for testing cement based composites are described and compared. These are X-ray microtomography and optical microscopy. Microtomography supplies three-dimensional images of small concrete specimens. In the tomograms all cracks, pores and other voids and inclusions, that exceed a few micrometers, are shown. Such visualisation can become a valuable tool for analysis of the basic material properties. Images obtained on thin sections and analysed with various methods on optical microscopes supply additional information on material microstructure that cannot be obtained in tomograms. For example it is relatively easy to determine zone penetrated by CO2 ingress. These two methods, presented on examples of tests, complete each another in order to supply a set of information on composition and defects of tested composite materials.

cement matrix composites, concrete deterioration, X-ray tomography, microscopic analysis, concrete microstructure

Concretes for the shields against ionizing radiation should be executed with particular care to satisfy all requirements, not only effective attenuation of different radiation but also sufficient durability. In the paper fundamental problems are presented that are related with designing of such protective concretes in order to avoid alkali-aggregate reaction. The results of preliminary investigations are presented that indicate how to select barite aggregate and to define composition of concrete mix. Present knowledge in that area of materials engineering should be completed before initiation of construction of nuclear power stations at industrial scale in Poland.

Alkali Aggregate Reaction (AAR), heavy aggregate, ionizing radiation

Concrete is used universally as a basic material for shields against ionizing radiation in various buildings related to nuclear energy plants and for other applications of fission materials, e.g. for material testing, therapeutic treatment installations and radioactive materials deposits. In order to fulfil their structural functions, concrete containment walls should have sufficient durability and the control of the ageing of concrete is necessary in all conditions of their functioning. Apart from climatic actions there are serious problems related to the influence of radiation on concrete microstructure and properties during many years of exploitation, particularly in the case of high doses of irradiation with neutrons and rayons gamma (γ).

concrete shields, nuclear power plant, special aggregate, ionizing radiation

The purpose of this research was to determine the carbonation depths in concrete containing calcareous fly ash. Eleven concrete mixes with the same water-binder ratio w/b and with different amounts of calcareous fly ash have been prepared in laboratory. In the test series I the mixes were produced with five blended cements containing different amounts of the following supplementary cementitious materials: calcareous fly ash, siliceous fly ash and granulated blast furnace slag. The second test series was produced with calcareous fly ash replacing 30% of the cement by weight. The maximum depth of carbonation in concrete was determined using the phenolphthalein method. The progress of the carbonation front was established by analysing polished thin sections of concrete under a polarizing microscope in transmitted light. The most resistant to carbonation was the concrete containing, beside clinker, 14.3% of calcareous fly ash as a cementitious material. The specimens of concrete containing different amounts of calcareous fly ash were compared and no significant variations were found both in the rate and depth of carbonation. On the other hand, the rate of advancement of carbonation front was higher in concrete containing calcareous fly ash as compared to the reference concrete without admixtures.

blended cements, calcareous fly ash, carbonation, particle size separation of fly ash

The objective of this investigation was to develop rules for automatic assessment of concrete quality by using selected artificial intelligence methods based on machine learning. The range of tested materials included concrete containing nonstandard waste material—the solid residue from coal combustion in circulating fluidized bed combustion boilers (CFBC ash) used as an additive. Performed experimental tests on the surface scaling resistance provided data for learning and verification of rules discovered by machine learning techniques. It has been found that machine learning is a tool that can be applied to classify concrete durability. The rules generated by computer programs AQ21 and WEKA by using the J48 algorithm provided a means for adequate categorization of plain concrete and concrete modified with CFBC fly ash as materials resistant or not resistant to the surface scaling.

Machine learning, Automatic classification rules, Database, Concrete durability, Scaling resistance, Circulated fluidized bed combustion fly ash (CFBC fly ash)

The objective of this investigation was to develop rules for automatic categorization of concrete quality using selected artificial intelligence methods based on machine learning. The range of tested materials included concrete containing a new waste material - solid residue from coal combustion in fluidized bed boilers (CFBC fly ash) used as additive. The rapid chloride permeability test - Nordtest Method BUILD 492 method was used for determining chloride ions penetration in concrete. Performed experimental tests on obtained chloride migration provided data for learning and testing of rules discovered by machine learning techniques. It has been found that machine learning is a tool which can be applied to determine concrete durability. The rules generated by computer programs AQ21 and WEKA using J48 algorithm provided means for adequate categorization of plain concrete and concrete modified with CFBC fly ash as materials of good and acceptable resistance to chloride penetration.

concrete durability, chloride ions migration, circulated fluidized bed combustion fly ash (cfbc fly ash), machine learning, classification rules, database

Salt solutions are used on pavement surfaces during wintry weather events to guarantee safe driving conditions. In addition to sodium chloride (NaCl) which continues to be traditionally used as deicer, the usage of solutions of calcium chloride (CaCl2) and magnesium chloride (MgCl2) is on the increase due to need provide a more consistent ice and snow control and thus ensure safety of the travelling public. This paper assesses the effects of three different salt solutions (NaCl, CaCl2, and MgCl2) on several physical and mechanical properties of pavement concretes. These deicing solutions were used under simulated wetting-drying (WD) and freezing-thawing (FT) exposure regimes with total ion concentration of the deicers was 10.5 molal for WD exposure and 5.5 molal for FT exposure.
Two types of concretes were used in the study; the ordinary portland cement concrete and the fly ash concrete (20% of cement replacement by mass). The prismatic and cylindrical specimens were used to monitor physical changes due to these exposure regimes. The physical changes of cylindrical specimens subjected to the WD regime were monitored by taking ultrasonic pulse velocity (UPV) measurements after every 2 weeks of exposure and crushing these cylinders at the end to obtain the compressive strength. The effects on prismatic specimens were monitored by measuring mass and resonant frequencies after every 2 weeks of exposure and using these data to calculate changes in the relative dynamic modulus of elasticity (RDME). The test results obtained from the RDME and UPV measurements, combined with visual observations were used to assess the effects of deicers on concretes. It was observed that CaCl2 solution is more harmful as compared to MgCl2 solution for both plain and fly ash modified concretes.

Deicing Salt Solutions, Pavement Concretes

The objective of this investigation was to test the effectiveness of the Acoustic Emission (AE) measurements in determining the critical stresses during four-point bending of mortar beams. Within the measuring procedure the parameter σcr/σ300 was calculated and analysed. Additionally, the influence of cement replacement by high calcium fly ash (HCFA) on the process of crack healing was discussed. Mortar beams with different content of HCFA and reinforced by steel microfibres were prepared for tests. After curing in standard conditions the beams were subjected to four-point bending test in order to introduce the pre-cracking. Thereafter the beams were cured in the lime water and loaded after 56 and 112 days in the same way as for the first time. Additionally the microstructure of mortars was studied in a stereo optical microscope as well in an electron scanning microscope including the Energy Dispersive X-ray analysis (EDX). The results of microstructural characterization of mortar containing HCFA from lignite combustion are presented. The applied load level slightly exceeded the critical stress, producing intense crack growth processes however did not significant affected the load capacity of the beams. During the consecutive loading the decreasing tendency of σcr/σ300 ratio was noted. The obtained results confirm that the latter parameter can be applied as a measure of the composite degradation level for the elements carrying the repeated loads of amplitude close to the critical stress of the structure and also that the cement replacement with HCFA influences the process of crack healing.

critical stress, Acoustic Emission, microcracking, self-healing, concrete microstructure, fly ash

Mortar beams were cast with various content of high calcium fly ash as a partial replacement of Portland cement. The results of microstructural characterization of mortar containing fly ash class C (High Calcium Fly Ash – HCFA) from lignite combustion are presented. The evaluation of the microstructure was performed using SEM and optical microscopy. At the age of 28 days the beams were subjected to 4-point bending until opening of a system of microcracks and cracks. Then, the beams were cured in lime water for 56 and 112 days after precracking and again subjected to loading. The results in a form of partial self-healing were recorded with load-deflection curves and using optical methods. The results show the percentage of replacement of cement by fly ash influenced the process of crack healing.

Microcracking, Self-healing, Microstructure, Fly Ash

The objective of this investigation was comparing the penetration of chloride ions in ordinary and air-entrained concretes containing a waste material Fluidized Bed Combustion Fly Ash (FBCFA). All concretes were tested with 15% and 30% cement replacement by FBCFA, with the same water-binder ratio of 0.45. Two kinds of fly ash coming from fluid bed combustion in two power plants in Poland have been used.
In this study the rapid chloride permeability test - Nordtest Method BUILD 492 method - was used. The microstructure of the concrete was analyzed on thin polished sections and the measurement of air voids sizes and their distribution, using digital image analysis, was carried on according to PN-EN 480-11:2008.
Obtained results have shown a significant influence of partial cement replacement by FBCFA on the chloride ions movements in concrete. It has been found that this kind of addition reduced considerably the chloride ion penetration. The influence of air entrainment on the chloride diffusion coefficients was also measured and it was shown that application of air-entraining admixture for concretes with FBCFA reduce the chloride diffusion coefficient but it should be used with caution.

Fluidized Bed Combustion Fly Ash (FBCFA), Pore Size Distribution, Chloride Permeability, Concrete, Durability

Tematem referatu jest ocena mikrostruktury, mikrotwardości i wczesnej wytrzymałości zapraw wykonanych z cementów wieloskładnikowych, zawierających różne ilości dodatku popiołu lotnego wapniowego. Zakres badań objął prototypowe cementy CEM II i CEM V wykonane w skali laboratoryjnej. Do badań mikrostruktury zapraw i składników wyjściowych zastosowano mikroskopię optyczną z wykorzystaniem cyfrowej analizy obrazu, mikroskopię skaningową z mikrosondą i metodę mikroindentacji. Wytrzymałość zapraw z cementów wieloskładnikowych z udziałem popiołów wapiennych po 28 dniach twardnienia oznaczona zgodnie z normą była niższa od zaprawy przyjętej za wzorzec, wykonanej z cementu CEM I bez dodatków. Obniżenie wytrzymałości w stosunku do wzorca zawierało się w granicach od 11 do 41% i było wyraźnie zależne od ilości dodatków popiołu lotnego wapiennego, krzemionkowego czy żużla wielkopiecowego. Wzrost ilości dodatku powodował obniżenie wytrzymałości. W mikrostrukturze matrycy cementowych zapraw badanych techniką SEM stwierdzono, że tworzące ją uwodnione krzemiany wapnia typu C-S-H mają we wszystkich zaprawach zbliżona budowę tzw. plastra miodu, wśród których są obecne heksagonalne kryształy portlandytu i relikty nieuwodnionych ziarn cementu oraz ziarna kuliste, pochodzące z dodatku popiołu.

mikrostruktura, popiół lotny wapienny, cementy wieloskładnikowe, wytrzymałość, SEM, mikroskopia optyczna

In this review paper the structure of concrete investigated as a composite material is analyzed on different levels from the viewpoint of its diagnosis. The diagnosis of a complex structure of concrete should cover identification and estimation of existing damages and possible failures. The aim is to ensure adequate durability and high quality of concrete in infrastructure works. The most effective methods that are actually available are shortly described. Beside various non destructive techniques, the optical and scanning electron microscopy that is applied on specimens representing material used in a diagnosed structure, are shortly described. The importance of quantitative results of material analysis and of image processing is stressed. On the basis of a thorough structural analysis of the concrete treated as a multicomponent material it is possible to determine its quality, to check correct execution of the designed diverse composition and to verify used components. All these data form necessary basis for a diagnosis of concrete quality and conformity with requirements. The review is partly based on research developed and realized at IPPT PAN during past several years in the scope of concrete treated as a structural composite material.

Concrete, Durability, Image analysis, Microstructure

Celem przeprowadzonych badań była ocena przepuszczalności betonu zawierającego popiół lotny wapienny pochodzący ze spalania węgla brunatnego, w stanie surowym i po dodatkowym domieleniu. W badaniach skoncentrowano się na określeniu wpływu ilości popiołu jako dodatku do betonu na wnikanie mediów agresywnych. Określono podstawowe właściwości mieszanki betonowej oraz wytrzymałość na ściskanie. Oznaczono współczynnik migracji jonów chlorkowych przy nieustalonym ich przepływie, głębokość penetracji wody pod ciśnieniem oraz współczynnik gazoprzepuszczalności betonu. Mikrostrukturę badanych betonów przeanalizowano na cienkich płytkach w mikroskopie polaryzacyjnym do światła przechodzącego. Stwierdzono, że zastąpienie cementu przez dodatek popiołów lotnych wapiennych do betonu w ilości 15% lub 30% przy w / s =0,55 powoduje poprawę ich wodo- i gazoszczelności, z tą jednak różnicą, że do zmniejszenia gazoprzepuszczalności betonu odpowiedniejsze jest stosowanie popiołów domielonych. Niższe wartości współczynnika migracji jonów chlorkowych otrzymano w betonach zawierających popiół lotny wapienny, wzrost w / s zwiększył przenikalność jonów chlorkowych. Analiza obrazów na cienkich szlifach betonowych wykazała, że w miarę wzrostu zawartości popiołu w betonie wzrasta również ilość niespalonych cząstek węgla w matrycy, których wielkość jest zależna od czasu mielenia popiołu

gazoprzepuszczalność, migracja chlorków, mikrostruktura, popiół lotny wapienny, wodoprzepuszczalność

Industrial utilization of fly ash from various kinds of fuel plays an important role in the environmentally clean and cost effective power generation. The primary market for fly ash utilization is as a pozzolanic addition in concrete production. The paper concerns the concretes containing fly ash called Fly Ash from Biomass (FAB) from co-combustion of hard coal and wood biomass (wood chips). Characterization of the fly ash was carried on by means of X-ray diffractometry and E-SEM/EDS analysis. The results of laboratory studies undertaken to evaluate the influence of FAB on concrete resistance to surface scaling due to cyclic freezing and thawing in the presence of NaCl solution were presented. The tests were carried out for concretes containing up to 25% of fly ash related to cement mass. Additionally, the microstructure of air-voids was described.
It was concluded that the FAB has significant effect on concrete freeze/thaw durability. The replacement of cement by fly ash from co-combustion progressively transformed the concrete microstructure into less resistant against freeze/thaw cycles and excessive dosage (over 15%) may dangerously increase scaling.

concrete, durability, fly ash from co-combustion of coal and biomass, scaling resistance, microstructure

W artykule opisano historię wiaduktu Kolei Kaliskiej a także stan zachowania konstrukcji. Omówiono aktualny stanu jakości betonu z wiaduktu sklepionego parabolicznego Drogi Żelaznej Warszawsko-Kaliskiej – najprawdopodobniej jednej z dwóch najstarszych budowli inżynierskich o konstrukcji betonowej na terenie Warszawy. Zamieszczono opis przygotowywania cienkich szlifów betonowych oraz przedstawiono wyniki analizy cienkich szlifów uzyskane za pomocą mikroskopu optycznego do obserwacji mikrostruktury betonu w świetle spolaryzowanym i w świetle ultrafioletowym. Scharakteryzowano rodzaj i wielkość kruszywa (analiza petrograficzna), a także przeprowadzono analizę jednorodności współczynnika wodno-cementowego ocenianą na podstawie rozkładu intensywności barwnika fluoroscencyjnego w świetle UV.

mikrostruktura, cienkie szlify, stuletni beton, wiadukt sklepiony

W pracy naszkicowano aktualny stan wiedzy na temat mechanizmów, powodujących powierzchniowe łuszczenie betonów. Uzupełniając opis zjawisk powierzchniowych przytoczono również podstawowe hipotezy, dotyczące wewnętrznej destrukcji betonu, spowodowanej działaniem mrozu, a także przedstawiono pomysł zastosowania „inteligentnego” materiału, tj. nawilżonych drobnych frakcji kruszywa lekkiego jako alternatywy w stosunku do tradycyjnych środków napowietrzających. Ponadto, opisano rodzaje porów występujących w betonie oraz sposób ich wypełnienia przez wodę.

beton nawierzchniowy, odporność na powierzchniowe łuszczenie, wewnętrzna pielęgnacja

Praca jest kontynuacją artykułu ‘’Zapobieganie łuszczeniu powierzchni betonowych przy użyciu nawilżonego kruszywa lekkiego. Cz. I – stan wiedzy”. W części II artykułu przedstawiono wyniki badań betonów zawierających nawilżone drobne frakcje kruszywa lekkiego, określono strukturę porów oraz odporność na powierzchniowe łuszczenie (według SS 13 72 44) i mrozoodporność (badaną wg PN-88/B-06250 i przy pomocy pomiaru oporu elektrycznego, według ASTM C 666 A).

beton, mrozoodporność, odporność na powierzchniowe łuszczenie, nawilżone kruszywo lekkie

The subject of the investigation was the influence of pre-wetted lightweight aggregate on damage of the concrete surface due to cyclic freezing and thawing in the presence of de-icing salts tested according to the Swedish Standard SS 13 72 44 (the Borås method). Six series of concrete specimens were made with the same water/binder (w/b) ratio 0.32, cement volume 400 kg/m3 and content of superplasticiser 8.8 kg/m3. One series, S3/2, contained an air-entraining agent. Series S4/7 and S4/8 were made with water/cement ratio equal to 0.45 and a lower cement content 340 kg/m3. In a few series the sand fraction 0-2 mm and basalt fraction 2-4 mm were partly or totally replaced by wetted lightweight aggregate. Concretes S3/1, S3/3, S4/7 and S4/8, failed the test. The best results were obtained for concrete S3/6 (with the 2-4 mm fraction replaced by half) and S3/2 (air-entrained). The application of an air-entraining agent is more expensive than LWA, and at a construction site it is not always easy to control. It seems that the replacement of a part of aggregate by LWA could be a more effective way to improve the scaling resistance.

concrete, scaling resistance, internal curing, expanded clay

Projektowanie betonu na osłony przed promieniowaniem jonizującym polega przedewszystkim na selekcji kruszyw o określonym składzie pierwiastkowym. Kruszywo serpentynitowe o dużej zawartości wody związanej chemicznie, zwłaszcza w układzie z kruszywem ciężkim (np. barytem), może być pożądanym składnikiem betonu w osłonach przed promieniowaniem mieszanym (neutronowym i gamma), narażonych również na oddziaływanie podwyższonej temperatury. Celem przeprowadzonych badań było rozpoznanie wpływu mieszaniny specjalnych kruszyw grubych o zmiennej proporcji kruszywa serpentynitowego i barytowego na wytrzymałość, mikrostrukturę i przepuszczalność betonu z cementem żużlowym. Badano wytrzymałość na ściskanie i współczynnik migracji jonów chlorkowych. Wyniki badań trwałościowych przedstawiono w kontekście wyników pomiaru porowatości otwartej, porowatości kapilarnej wraz z obserwacjami mikrostruktury na cienkich szlifach. Zaobserwowano zwiększoną porowatość warstw kontaktowych kruszywa z zaczynem cementowym. Wzrost porowatości otwartej i kapilarnej betonu okazał się skorelowany ze wzrostem współczynnika migracji jonów chlorkowych.

cement, durability, fracture toughness, microstructure analysis, natural fibers

The paper presents results of the microstructural analysis of the expressway pavements concrete exhibiting signs of potential alkali-silica reaction (ASR). The analysis was performed on cores drilled from pavements from the northern part of Germany. Specimens were selected from regions of the pavements representing the highest degree of distress. The results obtained during microstructural characterization performed in the laboratory are presented and discussed. The microstructure of concretes was investigated using microscopy in both transmitted and reflected light as well as in scanning electron microscope (SEM) operated in the backscattered (BSE). The chemical compositions of the phases of interest were determined using the Energy Dispersive X-ray analysis (EDS). The thin sections were analyzed using petrographic microscope (under plane, crosspolarized light and with gypsum plate). The petrographic analysis of aggregates was conducted to determine the presence of potentially reactive minerals. During the microstructural analysis particular emphasis was placed on establishing exactly the type of the reaction and the distribution and the composition of the resulting gel. In addition, the Damage Rating Index method has been used to ascertain the degree of concrete pavement damage caused by ASR. During the microstructural analysis particular emphasis was placed on establishing exactly the type of the reaction and the distribution and the composition of the resulting gel. The results of the analysis revealed the presence of the deleterious reactions in pavements. Concrete showed evidence of the ASR. The reactive components were identified as schist and sandstone in the coarse aggregate and reactive siliceous fine aggregate. The resulting gel was predominantly of Si-Ca-K-Na composition.

aggregate, alkali-silica reaction (ASR), gel, petrographic analysis, reactive minerals, SEM analysis

Results of experimental investigations on the reactivity of crushed aggregates produced from sedimentary and igneous rocks are presented. Applied test methods, consistent with RILEM and ASTM standards are implemented in technical specifications of Polish national highway administration. The range of the investigations covered coarse aggregates produced from crushed limestone, dolomite, sandstone and greywacke rocks, as well as from basalt, melaphyre, porphyry, granite and gabbro. The aggregates were selected on the basis of their mechanical and physical properties to be adequate for making durable concrete for highway applications. The mineral composition of the aggregates was evaluated with regard to their reactive SiO2 content. A considerable amount of reactive minerals: chalcedony, tridymite and microcrystalline quartz were found in the grains of the porphyry and melaphyre aggregates. No reactive forms of quartz were found to be present in the mineralogical composition of the limestone aggregates and the dolomite aggregates. Micro- and cryptocrystalline quartz occurred in the particles of the greywacke aggregates and the sandstone aggregates. On the basis of the expansion of mortar and concrete of specimens, the coarse aggregates produced from crushed rocks were classified into three reactivity categories. A sodium-potassium-calcium silicate gel was found and its composition was consistent with that reported in the literature as characteristic of the alkali-aggregate reaction products. The tests revealed consistent assessment of the reactivity of the aggregates.

alkali silica gel, expansion tests, microcrystalline quartz, petrographic analysis, technical specifications

Depending on the intended use, some cement-based construction materials, such as paste, mortar and concrete, need to be fibre reinforced. In these materials, fibres play the same mechanical role as ossein, the elastic collagen fibres in animal bones that guarantees the resistance to fracture. Although commonly used fibres are made of various materials, such as steel, glass, polymers etc., animal and plant fibres can also be used in building materials. Among them, wool of sheep, a waste material in several countries, can effectively reinforce pastes, mortars and concretes. In addition to the research already performed in the field of cement-based composites, the use of sheep wool as reinforcement of gypsum-based composite is experimentally investigated herein for the first time. As a result, sheep wool reinforcement provides high fracture toughness, due to an excellent adhesion, and could be a valid alternative to the current industrial fibres in reinforced gypsum manufacts.

sheep wool fibres, gypsum-based composite, mechanical properties, microstructure

During the decommissioning of nuclear power plants, a significant amount of cement based composites should be disposed as radioactive waste. The use of material with low-activation constituents could effectively reduce radioactivity of concrete. The subject of the paper is the content of trace elements with large activation cross section in concrete constituents due to their ability to be activated in radiation shielding structures. Various Portland cement specimens were subjected to elemental analysis by neutron activation analysis and prompt gamma activation analysis to assess the dominant long-lived residual radioisotopes. Concentrations of the radionuclides, such as Europium-152, Cobalt-60 and Caesium-134 were assessed. Their half-life time is 13.5, 5.27, and 2.07 years, respectively. On the basis of the obtained results, recommendations for cement selection for low-activation concrete are proposed in order to economize decommissioning cost by reducing a radioactive concrete waste.

Alkali silica reaction (ASR) is a harmful phenomenon occurring as a result of chemical interactions between sodium and potassium hydroxides in the pore solution and reactive minerals contained in the aggregate. Reactive minerals like microcrystalline, cryptocrystalline or strained quartz dissolve in the alkaline solution and form an expansive gel product. Proper selection of concrete constituents is necessary to ensure the durability of concrete structures. The proper recognition of the aggregate mineralogical composition is a very important element in the process of selection of concrete components due to the risk of ASR occurrence. This paper presents the results of detailed microscopic analysis of alkali-silica reactivity of domestic fine aggregates of various origins. Six siliceous sands from different locations in Poland and one limestone sand were tested. Detailed petrographic analysis was performed on thin sections. In all siliceous sands micro- and cryptocrystalline quartz was recognized as a reactive mineral. Digital image analysis was performed for quantitative assessment of the potential of reactivity of sands. It revealed, that siliceous river sands were the most susceptible to an alkali-silica reaction, which was confirmed by mortar bar expansion test performed according to the standard test method.

In the present study the potential of alkali-silica reaction (ASR) in fine fraction of aggregate was analyzed. The investigation was focused on mineral composition of siliceous sand and its influence on ASR. Three siliceous sands from different origin and localization in Poland were tested. Petrographic analysis on thin sections was conducted. The automatic image analysis was used to estimate the content of reactive minerals (micro- and crypto-crystalline quartz). The XRD measurements were performed. Alkali-silica reactivity of fine aggregate was tested by mortar-bar test according to ASTM C1260 Standard. Petrographic analysis showed that all tested siliceous sands contained reactive form of quartz, micro- and cryptocrystalline. Mortar-bar tests according to ASTM C1260 indicated that one from the selected sands exceeded expansion over the limit and was considered as reactive. The content of reactive minerals in sands estimated by automatic image analysis corresponded to ASTM C1260 results. The higher content of reactive form of quartz in siliceous sand, the larger expansion of mortar-bar test.

Siliceous sand, Alkali-Silica Reaction (ASR), digital image analysis, micro- and cryptocrystalline quartz, expansion

It is known that natural wool is a good thermal insulating material, but recent results suggest another application: the use of wool as a fiber-reinforcement in mortars and concretes. Indeed, the mechanical properties of wool filaments are comparable to those of some synthetic polymeric fibers (e.g., made with polypropylene). However, wool can dissolve in alkaline environments and, therefore, the performances of reinforced cement-based matrixes cannot be guaranteed for a long time. Accordingly, three series of reinforced mortar beams have been made with low alkali, high alkali, and sulfoaluminate cements. To investigate the chemical compatibility, and the subsequent effects on the mechanical performances, the beams have been tested in three point bending. As a result, the lower the alkalinity of the cement paste, the better the post-cracking capability of wool fibers to arrest the growth of cracks.

Wool reinforcement, low alkali cement, high alkali cement, sulfoaluminate cement

The risk of occurrence of deleterious alkali-silica reaction (ASR) in concrete should be properly minimized in major highway pavements and bridges. Real-life experiences show that even in concrete made with aggregates potentially not susceptible to ASR, it may occur under unfavourable conditions of external alkali supply at wet conditions and heavy traffic load. An experimental investigation was performed to study the susceptibility of selected Polish mineral aggregates to ASR at external alkali supply. The test method „60°C concrete test with external alkali supply” covered by draft procedure RILEM AAR-12 was implemented at IPPT PAN laboratory. Air entrained concrete specimens were exposed to cyclic temperature changes and wet-dry exposure as well as NaCl solution exposure. Several combinations of coarse crushed aggregate and fine natural aggregate were tested in concrete designed as for heavy duty highway pavement. SEM evaluation of microstructure of concrete with glacial deposit aggregate revealed visible alkali-silica gel. The effects of fine aggregate on the expansion of concrete were also revealed.

air entrained concrete, alkali-silica reaction, cyclic exposure, external alkali, highway pavement

Salt solutions are used to ensure safe driving conditions during winter. NaCl deicer is the most often used brine in Polish climatic zone. The chemical effects of this type of chloride-based deicer in wetting and drying (WD) and temperature cycles on concrete need to be better understood. This research was focus to study the microstructure of air-entrained pavement concrete after combined chemical (10% of NaCl) and physical (WD and 60°C) exposure conditions. The adopted WD and temperature regime was designed to verify the hypothesis that regularly alternating wetting and drying cycles with external alkali supply from deicer salt will provoke the Alkali-Silica Reaction (ASR). The aggregates varied their origin and mineralogical composition. The microscopic examination was carried out on concrete specimens using SEM with EDX. The microscopic analysis has shown that main reason for concrete deterioration during cyclic chemical and physical exposure conditions was both physical influence - WD cycles and the chemical influence – ASR (primarily, the fine aggregate which lead to form of alkali-silica gel). The expansive gel was shown to be capable of destroying the test specimens. Also differences in mineralogical composition of coarse aggregates influenced on the concrete prism expansion due to ASR.

The long term performance of concrete pavements can be reduced due to improper selection of aggregates, thus prevention of damage due to alkali-silica reaction (ASR) requires a detailed examination of minerals in aggregates. The amount of reactive silica in the aggregate is an important factor governing the severity of ASR, which depends critically on the nature of the reactive aggregate. In the present study the potential for ASR in selected rocks in Poland was evaluated using petrographic methods. The tests were performed on crushed aggregates from different regions, covering a variety of rock origin and their geological structure. The optical microscopy in transparent light on thin sections was used as a principal tool to assess the mineral composition of aggregates. The content of reactive siliceous minerals was assessed. The petrographic examination concerned different forms of silica. Quartz grains were classified according to their mean diameter so as to identify the reactive range. The application of the petrographic method allowed for classification of aggregate for ASR potential using RILEM recommendation. The results of the study allow to make a quick and responsible decision to direct the aggregates to further detailed tests, reject or accept them as concrete components for concrete pavements.

alkali-silica reaction, polymineral grains, petrographic analysis

Penetration of external alkalis from deicing salts into concrete pavement can promote deleterious alkali-silica reaction (ASR) and therefore reduce its long-term performance. In severe exposure conditions (wet and heavy traffic load) the susceptibility of aggregates to ASR may be aggravated. To study this phenomenon on concrete specimens the combined cyclic exposure method was developed at VDZ Düsseldorf. Such a cyclic wet-dry-external alkali exposure was used on air entrained concrete specimens to investigate its influence on the microstructure and the permeability of concrete. Air voids characteristics, mercury intrusion porosimetry, porosity accessible to water and water absorption of concrete was tested. Concrete microstructure was observed in scanning electron microscope to reveal the specific features. The applied cyclic wetdry-external alkali exposure induced a marked decrease of total porosity of concrete and the appearance of ASR gel in cement matrix. An increase of the rate of water absorption of concrete was also found.

alkali-silica reaction, VDZ test, microstructure, permeability, water absorption

Crushed granite aggregates due to good physical and mechanical properties are widely accepted for production of durable concrete. This kind of aggregates are considered as not alkali-silica reactive (ASR). However, all of them contain silica. In some of them SiO2 occurs in a strained form or the crystals are small enough to be treated as microcrystalline, so they can be prone to ASR. Various granite aggregates taken from largest exploited Polish quarries were tested. Petrographic analysis on thin sections and accelerated mortar-bar test were carried out to assess potential of the alkali-silica reactivity. The petrographic analysis revealed differences in mineral composition of the tested granites. The strained quartz and microcrystalline quartz were the main potentially deleterious mineral in analyzed granite aggregates. Also the myrmekites were particularly visible in the granitic rocks. The results of the mortar-bar tests confirmed such predictions. The mortar beams showed expansion more than 0.1% after 28 days of exposition in 1M NaOH and 80°C. The bars made with RILEM cement showed fast and large elongation. In all cases the increase in mortar beam elongation was linear. The SEM-EDS analysis confirmed the presence of the ASR gel both, in the aggregate and in the matrix.

The addition of natural fibers residue in cement based materials can be a sustainable technological alternative for traditional dispersed reinforcement, and can improve the performance of brittle matrix materials. The presence of a wool reinforcement can increase the fracture toughness and, at the same time, can reduce the environmental impact of cementitious mortars. The beneficial effects are similarly to those observed in presence of vegetal fibers (e.g., hemp), which have been largely investigated in the literature. However, there are some limits in the use of wool fibers due to their chemical compatibility with the cement matrix, as they can dissolve in alkaline environments. In the present paper, to investigate the compatibility between wool fibers and cementitious mortars, laboratory prototypes have been taken into consideration. Three series of wool-reinforced mortar beams have been cast and cured in water (20°C) or in dry conditions (temp. 20 °C, 50% R.H.) for some days. Portland-limestone cement CEM II has been used, whereas the content of fibers has been limited to about 1% in volume to maintain the workability of the mortars. To investigate the chemical compatibility, and the subsequent effects on the mechanical performances, prototypes have been tested in three point bending. After the mechanical test, the mortars microstructure was evaluated through SEM images and by thin section in transmitted light, in order to individuate a possible relationship between the dissolution of wool and curing conditions. The microstructure observation revealed the capability of wool fibers to bridge the cracks, and to reduce the brittleness of plain mortars. The differences in the mortars microstructure due to alternative curing conditions were also observed and described in the paper. Accordingly, wool could be effectively used to reduce the plastic shrinkage of cementbased composites, like the industrially manufactured polypropylene fibers.

Wool fibers, Plain cement-based mortar, Fiber-reinforced mortar, Polypropylene fibers, Three point bending tests, SEM analyses

In the present study, the potential for the alkali–silica reaction (ASR) in radiation shielding concrete containing special aggregates is presented. The tests were performed on two kinds of aggregate: (1) high-density aggregate to absorb the gamma radiation (barite, magnetite, and hematite) and (2) mineral with high bound water content to attenuate the neutron flux (serpentinite). The optical microscopy in transparent light on thin sections, XRD and XRF method, was used to assess the mineral composition of aggregates. ASTM C1260 test method for potential alkali reactivity of aggregates was applied also to investigate the effect of different content and crystal size of silica on the expansion due to ASR. The tests revealed that all tested aggregates, such as barite, magnetite, hematite, and serpentinite, were characterized by low solubility at high pH. The XRD and XRF results have shown presence of silica in all tested aggregates, but the microscopic observations enhanced size and composition of SiO2 crystals. The aggregates were not deleterious themselves, but the different content and size of SiO2 crystals in the aggregate influenced their potential for alkali–silica reaction. The quartz in heavy kinds of rocks and in the serpentinite used for radiation shielding was just as much potentially susceptible to deleterious ASR as quartz in common rocks used in concrete technology. In the hematite, silica crystals were classified as microcrystalline, so it should be considered as potentially reactive. The expansion tests confirmed that hematite was highly reactive. Other aggregates after 14 days of testing did not exceed 0.1% elongation limit. The microstructural analysis of thin sections prepared from mortars after ASTM C1260 test confirmed expansion of aggregate grains due to ASR.

Alkali-Silica Reaction (ASR), ionizing radiation, high density aggregate

The use of exposed aggregate concrete (EAC) in the upper layer of two-lift pavements is spread over many European countries including Poland. However, the EAC technology is considered difficult to apply because of inevitable dependence on operator's experience to control the whole process properly. The proper timing of technological operations is critical. The investigation on the performance of EAC was performed to gain a better understanding of material and environmental factors involved. EAC slabs were manufactured in the laboratory following the procedure applied at the construction site. Air entrained concrete mix design included a variable water to cement ratio and cement type while the type and the content of aggregate was constant. The effects of curing intensity were studied. The strength properties, air void characteristics of hardened concrete, the freeze-thaw resistance and the salt-scaling resistance were tested of specimens cored from the slabs, using the European standard methods. EAC permeability was also evaluated using the methods covered by ASTM C1585 and NT Build 492. Such permeability indicators and frost durability were applied to evaluate the differences in EAC layers performance. The environmental vulnerability of EAC mixes used in the upper layer of two-lift pavements is discussed.

air entrainment, blended cement, concrete durability, curing technology, highway pavement, mix design, permeability

In the paper a method of X-ray microtomography (micro-CT) was employed for a direct insight into a microstructure of concrete with a practical resolution of approx. 10 micrometers3. Two sets of specimens were subjects of examination. The spatial concentration of air pores was investigated in three concretes differing in the amount of the supplement of high calcium fly ash (HCFA). The parameter of pore connectivity called diffusive tortuosity was determined in three other concretes made of the same ingredients but differing in water to cement ratio. The quantitative results obtained with application of described procedures are applicable in material characterization.

X-ray microtomography, concrete, microstructure

In the present study the potential appearance of the alkali-silica reaction (ASR) in heavy aggregates was studied. ASTM C1260 Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) was applied. In order to investigate the effect of the content of alkalies in cement on the expansions due to ASR, three levels of total and soluble alkali content of cement were studied. Three portland cements Type I with different alkali content were selected. Two ordinary portland cements, which are commonly available in the market and one special cement were tested. That cement was specially made for the purpose of the nuclear shielding concrete CEM I NA-SR-LH of low-alkali, increased sulphate resistance and low heat of hydration. For the tests according to ASTM C 1260 the high-density aggregates, known as absorbing gamma radiation were selected: barite, magnetite and hematite. The expansion test revealed that hematite was highly reactive, regardless of the type of cement. Already after four days of storage in 1 N NaOH and 80°C the mortar bar expansion exceeded the limit of 0.1%, and after next four days was more than 0.2%., which qualifies it extremely reactive aggregate. Other aggregates after 14 days of testing did not exceed 0.1% elongation limit, but the influence of the type of cement was noticed. There was a noticeable tendency for increasing the total expansion with increasing the alkali content of cement.

Alkali-Silica Reaction (ASR), high density aggregate, cement composition

The results of microscopic analysis on thin sections of aggregates intended for nuclear shielding concrete are presented. The petrographic analysis was performed on different barite, magnetite and hematite aggregates used as the high-density aggregate to absorb gamma radiation. Both optical microscopy and accelerated expansion tests were used to recognise the potential for alkali-reactivity of the aggregates. The mineral composition of the tested aggregates was analysed on thin sections in transmitted cross-polarized light and XRD tests were additionally performed. Expansion tests of mortar bars exposed to 1 N NaOH solution at the temperature of 80°C were also performed following ASTM C1260. The high-density aggregates contained ore deposits - metallic opaque phases providing the required shielding properties. These aggregates also contained various amounts of non-metallic phases, with both innocuous non-ore minerals and deleterious, potentially reactive materials. Barite aggregates contained siderite, fluorite and hawleyite in varying amounts, apart from the barium sulphate being the principal component. Moreover, particularly reactive cristobalite and muscovite were identified in barite aggregates from certain quarries. Tests according to ASTM C1260 performed on mortars showed the expansion above the accepted criterion for non-reactive aggregate and confirmed the threat due to the presence of cristobalite in barite aggregates.

high-density aggregate, heavy concrete, alkali-silica reaction, thin section, XRD

The construction of Żarnowiec Nuclear Power Plant (NPP) facilities was discontinued in 1989, despite the high level of work advancement. Already a large part of the concrete structures was built, now submerged in water from Żarnowieckie Lake. These structures were exposed over 30 years to the environmental conditions (rain, and varying high and low temperatures) without any special maintenance treatment. The technological documentation archives are not available. Experimental testing of specimens drilled out from different concrete structure elements was performed in September 2014.
The goal of the research was the identification of the composition of concrete and its present properties, especially the recognition of the effects of long-term environmental impact. The scope of the research covered macroscopic and microscopic analysis of concrete, compressive strength test, permeability test defined as the rate of chloride ions migration and water absorption. Unfortunately, the most important parts of the concrete structure are not available for testing because they are under water level. The obtained results allowed to classify the concrete structural elements in nuclear power plants buildings as of a quite good quality.

durability, old concrete, strength, microstructure, permeability

The application of fibre reinforced concrete (FRC) in the various constructions in Nuclear Power Plants and particularly in the shields for protection against y and neutron radiation seems possible and useful. A few examples of shields built with FRC are described and rewieved and the question is formulated why this kind of cement based composites are rather infrequently used in that area.

fibre reinforced concrete (FRC), nuclear power plant (NPP), special concrete

In the paper the barite aggregate has been analyzed as a potential source of ASR in heavy concrete. Special attention was paid to BaSO4 and minor mineral components in aggregates and their influence on ASR development in tested mortars

heavy aggregate, Alkali Silica Reaction (ASR), ionizing radiation

Salt solutions are employed on pavement surfaces throughout wintry weather environment to guarantee safe driving conditions. Recently, deicing solutions of CaCl2 or MgCl2 (or sometimes rock salt (NaCl) pretreated with CaCl2 or MgCl2 brines,) are used to provide a more consistent ice and snow control. This paper assesses the effects of more prevalently used salt solutions on the microstructure and physical parameters (strength, expansion and mass) of pavement concretes. Deicing solutions of NaCl, CaCl2, and MgCl2 were used for wetting-drying (WD) and freezing-thawing (FT) conditions with total ion molality of 10.5 and 5.5 respectively.
The prismatic and cylindrical specimens were used to monitor physical changes due to these regimes and later on microstructural analysis was performed on them after the completion of exposure. The changes on cylindrical specimens due to WD regime were monitored by taking UPV measurements and crushing these cylinders at the end for compressive strength. The effects on prismatic specimens were monitored by measuring mass and resonant frequencies after every 2 weeks and used for calculating relative dynamic modulus of elasticity.
To study unidirectional penetration of deicers, several 3 in. (76 mm) diameter concrete cylinders were ponded with the deicing solutions in WD environment. These cylindrical specimens were used for SEM analysis and chloride profile grinding after end of the exposure. The microstructure of prismatic concretes specimens exposed to 350 FT cycles was observed using personnel SEM from two locations (one from the center and other from the edge) of the after conclusion of the both exposure conditions.

Physical Parameters, Pavement Concretes, Salt Solutions

The possibility of using the high calcium fly ash (HCFA) as type II concrete additive is not well established, especially in relation to the durability of concrete structures in aggressive environment. The paper presents results of microstructural characterization of air-entrained concrete containing high calcium fly ash from lignite combustion. Frost resistant concretes were designed with different content of fly ash use for cement replacement by 15% and 30%. Different kinds of HCFA were used: raw (unprocessed) and grinded during 10, 15 and 28 minutes. The evaluation of the microstructure was performed using SEM and optical microscopy on thin sections and plane sections. All thin sections were impregnated with epoxy containing fluorescent dye and were examined using ordinary light, crossed polarized light and UV light. The thin section evaluation involved petrographic characterization of aggregates and examination of paste quality. Automatic air-void analysis on plane sections revealed air-content, specific surface, spacing factor and the content of micropores in the hardened concrete. Significant differences in particle shape and size before and after grinding of the HCFA were revealed by SEM analysis. The results of thin section analysis of the high calcium fly ash concrete showed that its microstructure was more dense than that of the ordinary concrete. The influence of specific surface of fly ash on air void content in HCFA concrete was found.

high calcium fly ash (HCFA), air-entrained concretes, microstructural characterization

The deicing/anti-icing chemicals are routinely used during cold weather to ensure safe driving conditions. Traditionally, solid rock salt (NaCl) or NaCl brines have been used for these purposes but their efficiency is reduced at lower temperatures. In order to provide a more reliable means of ice and snow control, chemicals with lower freezing points, such as CaCl2 or MgCl2 (or sometimes rock salts pretreated with CaCl2 or MgCl2 brines) are increasingly being applied. The extent and magnitude of chemical reactions of these “new-generation” deicers with pavement concrete is still somewhat unclear. This paper presents the results of investigation of the physicochemical changes in the microstructure of pavement concrete exposed to different deicers and subjected to both wetting/drying (W/D) and freezing/thawing (F/T) regimes.
Plain concretes (PC) and fly ash modified concretes (20% mass replacement of cement) with water-to-cementitious materials ratio of 0.42 were exposed to three different types of deicing solutions, with total ion molality of, respectively, 10.5 for W/D and 5.5 for F/T regimes. For comparison purposes, additional set of specimens was kept in deionized water under similar exposure regimes. The companion controlled specimens were kept in saturated limewater at 23oC. The physical changes taking place in the prismatic (3” x 3” x 11.5”) specimens were monitored weekly and included measurements of dynamic modulus of elasticity (RDME) and mass changes. After 154 W/D cycles prismatic specimens exposed to 28% CaCl2 solution exhibited considerable visual distress, reduction in mass, and reduction in DME. The same deicer also caused reduction in mass and in DME after only 35 F/T cycles. The performance of fly ash modified concretes was better than that of PC in all deicing solutions under both W/D and F/T regimes.
To ensure a unidirectional penetration of deicers, several 3–in. diameter concrete cylinders were ponded with the same deicing solutions as the prismatic beams while being exposed to W/D cycles. These cylinders were used to prepare the SEM analysis samples.

plain concrete, fly ash concrete, deicing salts, pavement concrete

W referacie przedstawiono wyniki oceny mikrostruktury betonów z dodatkiem popiołów fluidalnych (pf) po badaniu mrozoodporności i odporności na powierzchniowe łuszczenie. Metodą cienkich szlifów przeprowadzono analizę mikrostruktury betonu przed i po badaniu trwałości mrozowej. Wszystkie cienkie szlify były zaimpregnowane żywicą z fluorescencyjnym barwnikiem i analizowane w świetle przechodzącym spolaryzowanym, przy równoległych i skrzyżowanych nikolach oraz w świetle UV. Na cienkich szlifach betonowych przeprowadzono analizę petrograficzną kruszywa i ocenę jakości zaczynu cementowego (łącznie ze sprawdzeniem rzeczywistego współczynnika wodno-spoiwowego). Analiza cienkich szlifów betonów z pf przed badaniem trwałości mrozowej, wykazała, że ich mikrostruktura jest bardziej zwarta niż betonu bez popiołu. Jednak, po cyklicznym zamrażaniu i odmrażaniu, betony z dodatkiem popiołu wykazały na cienkich szlifach liczne spękania w odróżnieniu do betonu bez popiołu fluidalnego. W betonie bez pf w strefie kontaktowej kruszywo-zaczyn zaobserwowano strefy umiejscowione pod kruszywem grubym z mniej zwartą strukturą zaczynu. Wyniki analizy cienkich szlifów wykazują, że zastosowana metoda badania mrozoodporności, oparta na pomiarze zmiany wytrzymałości na ściskanie, powinna być skorygowana aby lepiej odwzorowywała zniszczenie zachodzące w mikrostrukturze betonu.

popiół fluidalny, beton, trwałość, mrozoodporność, mikrostruktura, cienkie szlify

Celem rozpoczętych badań jest ocena przepuszczalności betonu zawierającego popiół lotny wapienny pochodzący ze spalania węgla brunatnego w energetyce zawodowej, w szczególności jakościowe rozpoznanie i określenie ilościowe wpływu składnika popiołowego w cemencie lub dodatku popiołu do betonu na wnikanie mediów agresywnych. W referacie przedstawiono podstawowe koncepcje badawcze oraz wyniki określania szczelności betonu na podstawie literatury. Stwierdzono, że można oczekiwać korzystnych efektów stosowania popiołu lotnego wapiennego, ujawniających się znaczącą redukcją współczynnika dyfuzji i współczynnika migracji chlorków, a także efektów niekorzystnych polegających na zwiększeniu przepuszczalności powietrza i ewentualnie podwyższeniu szybkości karbonatyzacji.

popiół lotny wapienny, trwałość, beton

AgriculturalWaste, Animal Origin Fibres, Cement-BasedMaterials, Microstructure, Mechanical Properties

kruszywa łamane, reakcja AAR, analiza petrograficzna

The durability of concrete in outdoor structures is closely related to its resistance against the aggressive gaseous actions coming from the environment and including influence of oxygen, nitrogen, carbon dioxide. The pore system and its interconnectivity in the concrete matrix directly influence the possibility of penetration of various aggressive gaseous media into concrete structure. The X-ray microtomography (micro-CT) is a modern, non-invasive technique enabling for determination of existing pores in the microstructure of concrete matrix. In the paper the results of investigation of two different concretes by the application of micro-CT method to micro-cores are presented. The quantitative information on the parameters of the analysed microstructure can improve the methods of material characterization available up to now.

X-ray microtomography, concrete, microstructure

The focus of this paper is on the microstructure, microhardeness and early strength of mortars made with different blended cement containing high calcium fly ash. The research was concerning prototype cements CEM I and CEM V made in the laboratory conditions. Optical microscopy with image analysis, scanning electron microscopy with EDX analysis and depth-sensing indentation were applied. The compressive and tensile strength was determined according to appropriate standards. The compressive strength of mortars made with blended containing high calcium fly ash after 28 days of hardening was lower than compressive strength of reference mortar with cement CEM I. The strength was lower in comparison with the reference mortar by 11 and 41% and it was clearly dependent on the content of high calcium fly ash, siliceous fly ash or ground granulated blastfurnance slag in the cement. The compressive strength was decreasing with increase of content of additions in cement. All the pastes were characterized by a similar C-S-H structure, so-called “honey comb”, the presence of the portlandite plates, relicts of the nonhydrated cement grains and spherical grains from fly ash.

microstructure, microhardeness, early strength, high calcium fly ash