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This study investigates the thermal conductivity of fly ash concrete. Experiments were conducted to obtain the thermal conductivity of fly ash-cement pastes and mortars. Pastes were prepared to investigate the effect of fly ash, and mortar specimens were prepared for studying the effect of aggregates. It was found from the test that the replacement of cement by fly ash resulted in lower thermal conductivity. Thermal conductivity of mortar was higher than that of the cement paste. A simple parallel model for predicting thermal conductivity of fly ash concrete was proposed as a time-, material-and mix-proportion-dependent function. Thermal conductivity of concrete was computed based on the volumetric fractions and respective thermal conductivity values of each ingredient including the hydrated and pozzolanic products. Thermal conductivity of all ingredients in concrete are obtained from other studies except for the fly ash powder and hydrated products. In this study, thermal conductivity of hydrated product was obtained by the use of regression analysis together with the test results of cement paste, and thermal conductivity of fly ash powder was derived from the test results of cement-fly ash paste. The model was satisfactorily verified with various experimental results for pastes, mortars and concretes.

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ABSTRACT:The coefficient of thermal expansion (CTE) of cementitious paste at various ages was studied. Pastes were prepared with various water to binder and fly ash to binder ratios. The CTE of paste increased with age, and decreased with fly ash content, particularly at an early age. A model for predicting the CTE of paste was proposed as a time, material, and mix proportion dependent function. The model was verified with various experimental results and the verification results were satisfactory.

Damage in a reinforced concrete column subjected to long-term elevated temperature (approximately 1508C) was studied by conducting detail inspection as well as finite element analysis. The damage information was collected through visual inspection, non-destructive tests, coring, and chemical analysis. Inspection results illustrated more damage level in the portion exposed to high temperature. Chemical analysis as well as cracking patterns indicated that the damage was not the same as the damage caused by fire attack and was not caused by chloride penetration, carbonation or sulphate attack. The mechanism of the damage was clarified by using finite element analysis with a condition of sudden drop of surface temperature. It was found from the analysis that cracking can be induced on the surface of the column due to temperature gradient if there is a substantial surface temperature drop.