Institute of Fundamental Technological Research

W artykule przedstawiono wyniki badań parametrów termicznych procesu twardnienia mieszanek betonowych, z których dwie wykonano z wykorzystaniem kruszyw stosowanych w produkcji betonów osłonowych (kruszywo magnetytowe oraz serpentynitowe), a trzecią, referencyjną, z wykorzystaniem kruszywa amfibolitowego. Na podstawie analizy dokonanych pomiarów temperatury wyznaczono parametry procesu twardnienia betonu (m.in. maksymalny przyrost temperatury, maksymalny gradient i in.). Jednocześnie rozwiązując numerycznie tzw. zagadnie-nie odwrotne wyznaczono parametry cieplne betonu w trakcie pierwszych 72 godzin twardnienia. Tą samą metodą wyznaczono również wartości funkcji źródła ciepła, a następnie na jej podstawie oszacowano ilość ciepła wydzieloną w procesie hydratacji cementu. Uzyskano dobrą jakościową zgodność postaci funkcji źródła ciepła oraz wykresów zmian temperatury w mieszankach. W toku analiz uzyskanych wyników wyraźnie zaznaczył się wpływ zróżnicowania parametrów cieplnych zastosowanych kruszyw. W przypadku mieszanki z kruszywem serpentynitowym dały się także zauważyć istotne różnice w przebiegu przyrostu temperatury (opóźnienie) w stosunku do pozostałych mieszanek

młody beton, beton osłonowy, ciepło hydratacji, ciepło właściwe, współczynnik przewodzenia ciepła

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

Concrete manhole covers of underground cable networks, placed into pavements of roadways and footways, are often subjected to premature damage posing a threat to traffic safety. That is why the investigation was undertaken to increase the durability of precast concrete covers. New concrete mixtures for precast elements as well as the structure of elements (the type of a chassis, the number and arrangement of reinforcement bars) were designed. Experimental research into the load bearing capacity of concrete elements manufactured in multiple precast plants according to the assumed mix design was carried out. The impact of the type of cement, chemical admixtures and fibre reinforcement on the load capacity of precast concrete elements was assessed. The high effectiveness of fibre reinforcement enhancing the load bearing capacity of concrete covers was found.

concrete, concrete precast elements, fibre-concrete, load capacity, manhole covers

The paper presents the results of investigation of the specific heat and the thermal conductivity of shielding concrete and the specific heat of selected crushed aggregates used to produce them. The results of the specific heat were obtained by two methods: a stationary method, using a calorimeter, and a non-stationary method. The obtained results were compared to the results available in the literature. In addition, in the case of measuring the specific heat, the results obtained with the two methods were compared and attempt has been made to explain the differences between them.

shielding concrete, heavy aggregates, specific heat, thermal conductivity