Influence of Relative Humidity on Compressive Strength of Fly Ash Cement Paste

Abstract

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.

Effect of fly ash on the kinetics of Portland cement hydration at different curing temperatures

“…Since the hydration data for early curing ages is not provided in [12], it is assumed here that the fly ash in [12] would display similar influences on the early age hydration of the cement as those established in our study. Therefore, the model coefficients 20 B and 20 C obtained earlier for this study were applied to [12].…”

“…However, there is very little data in the literature that reports both the kinetics of hydration and the pozzolanic reaction together. One report however, Warangkana et al [12], provides both kinds of data, quantitatively, and from here the data there will be used to discuss the applicability of our model in the paper.…”

“…In [12], the degree of hydration and pozzolanic reaction in cement pastes with fly ash replacement ratios of 0%, 25%, and 50% (by volume) were studied at a water to binder ratio of Tables 1 and 2.…”

“…Therefore, the model coefficients 20 B and 20 C obtained earlier for this study were applied to [12]. Only the Based on the above and with the material properties of [12], the hydration kinetics of cement was simulated by our model, and the results of the simulation are shown with curves in Figure 10.…”

“…Termkhajornkit [11] and Saengsoy [12] have pointed out that the degree of hydration of the cement in fly ash-cement paste was higher than that in pure Portland cement paste. This suggests that to simulate the hydration kinetics of the cement in fly ash-cement blends using this model, hydration data for the cement in pure Portland cement paste is not suitable for model calibration.…”