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.
This study is aimed to elucidate the influence of ambient relative humidity on the compressive strength of fly ash cement paste. The ambient relative humidity has an influence on both the internal relative humidity and the hydration reaction, and further influences the compressive strength development. The experiment results revealed that the compressive strength of paste decreases with a reduction in ambient relative humidity. The same tendency can be found on the internal relative humidity and the hydration reaction as well. The detriment of strength development at low ambient relative humidity is affected by the retardation of the hydration reaction of C 2 S and C 4 AF. Moreover, the internal relative humidity at the time of test also has an influence on the compressive strength. The compressive strength decreased with the reduction in the relative humidity below the relative humidity lower than 95%. In addition, the compressive strength can be expressed as a function of the internal relative humidity and the hydrated gel volume derived from the degree of hydration of cement and the degree of pozzolanic reaction of fly ash.
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