Institute of Fundamental Technological Research

This paper features the development of a probabilistic model linking freeze–thaw (F-T) performance of concrete mixtures to their composition. A sensitivity analysis was performed on several concrete mixture parameters to identify the factors that have strong correlations with F-T resistance of concrete. The F-T performance level was defined as a discrete measure of the frost resistance of concrete. Finally, a new model to predict F-T damage incorporating the variability in concrete mix parameters (as selected from sensitivity analysis) was developed. This model was developed using only those data sets that contained the results of the relative dynamic modulus of elasticity (RDME) testing performed according to ASTM and AASHTO specifications. Concrete mixtures containing only ordinary portland cement (OPC) as the sole binder (i.e., mixtures that did not contain any supplementary cementitious materials) were considered. The reliability of the model was demonstrated using several examples of concrete mixtures of various compositions. Accordingly, this model provides the opportunity to optimize the concrete mix proportion for the required performance level of concrete under F-T exposure condition.

Freeze–thaw, Durability, Concrete, Pavement, Sensitivity analysis, Probabilistic design

The use of recycled aggregates in concrete is on the rise, driven by economic and environmental concerns. However, most of the existing models to predict the value of elastic modulus of concrete were developed for virgin aggregates and, as a result, they may often be inaccurate when applied to concrete made with recycled aggregate. In this study, the M5′ model tree algorithm was used to predict the elastic modulus of recycled aggregate concrete. The main advantages of the model tree algorithms are: (a) they output relatively simple mathematical models (formulas) and (b) are more convenient to develop and employ compared with other soft computing methods. To develop the model tree presented in this paper, over 450 data records were collected from internationally published literature. Error measures were used to compare the performance of the M5′ algorithm output to the output from other existing models. The results showed that the model developed using the M5′ algorithm has accuracy over 80 percent, which is well above the accuracy the other models.

M5′ model tree, Modulus of elasticity, Recycled aggregate, Concrete

The recent mechanistic-empirical pavement design guide (MEPDG) put more emphasis on the effects of thermal curling stresses on rigid pavement analysis and design. Mix design of concrete has significant influence on its thermal properties such as thermal conductivity, coefficient of thermal expansion, and specific heat. Aggregate type and content significantly alter the thermal properties of concrete incorporating them. The moisture state of the concrete increases its specific heat and thermal conductivity. A review of the effect of temperature of fresh concrete on early age properties is also presented. The performance of rigid pavements exposed to seasonal and daily fluctuations in temperature is discussed. Airfield concrete pavements which are subjected to jet engine exhausts experience heat cycles micro-cracking, coarsening of microstructure and loss of compressive and flexural strength. These effects are mostly the result of the dehydration and decomposition of paste matrix in concrete. Heat cycles result in concrete deterioration similar in appearance to freezing and thawing deterioration.

coefficient of thermal expansion, temperature gradient, thermal conductivity, thermal properties, concrete pavement

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)

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

This paper features the development of a probabilistic model linking freeze-thaw (F-T) performance of concrete mixtures to their composition. As part of the process of model development, a sensitivity analysis was performed on several concrete mixture parameters to identify these factors that have strong correlations with the F-T resistance of concrete. This sensitivity analysis was performed on 128 sets of experimental F-T test results collected from the literature. The F-T performance level was defined as a discrete measure of the frost resistance of concrete. Finally, a new model to predict the F-T damage of concrete incorporating the variability of the concrete mix parameters (as selected from sensitivity analysis) was developed. This model was developed using only these data sets which contained the results of the relative dynamic modulus of elasticity (RDME) testing performed according to the ASTM C 666 (AASHTO T 161) specifications. Furthermore, only mixtures containing ordinary portland cement (OPC) as a sole type of the binder (i.e., mixtures that did not contain any supplementary cementitious materials) were considered. Additional experimental test results were utilized to validate the model. The reliability of the model was further demonstrated using several examples 1 of concrete mixtures of various compositions. Furthermore, the effects of the number of F-T cycles, air content, paste content, and w/c ratio on the F-T performance of the concrete mixes were demonstrated using the developed model. Accordingly, this model provides the opportunity to optimize the concrete mix proportion for the required performance level of concrete under F-T exposure condition.

Freeze-thaw, durability, concrete, pavement, sensitivity analysis, probabilistic design

Construction industry demands large quantity of recycled materials for sustainable development. The use of recycled aggregate (RA) as a replacement for natural aggregate (NA) represents a sensible approach from technical, environmental, and economic points of view. Due to the substantial differences in the properties of RA and NA, predicting the performance of recycled aggregate concrete has been a concern in many design applications. In this study, M5´ model tree algorithm was used to develop a new model to predict the compressive strength of recycled aggregate concrete. Compared to other soft computing methods, the model tree algorithms offer the following advantages: (a) greater transparency with respect to development of model equations and (b) relative ease of development and implementation. To develop the model tree, 270 data sets were collected from international published literature. The results show that the developed model tree algorithm can well predict the compressive strength of recycled aggregate concrete.

M5´ model tree, modulus of elasticity, recycled aggregate, concrete

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 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