Determination of cement hydration and pozzolanic reaction extents for fly-ash cement pastes

This article intends to quantify the reaction extents of cement grains and fly-ash (FA) particles in blended cement pastes during their hardening process. To this aim, a synthetic model for cement hydration extent in blended pastes is established taking into account the dilution effect, local w/c augmentation effect as well as heterogeneous nucleation effect of FA particles. Then the cement hydration and FA reaction extents of blended cement pastes with two w/b ratios (0.3, 0.5) and four FA contents (0%, 20%, 40%, 60%) are investigated. The non evaporable water content (Wn) and calcium hydroxide content (CH) were measured by thermal gravity analysis (TGA) and the FA reaction extent was quantified by the selective dissolution method. On the basis of these experimental data, the cement hydration extent and FA pozzolanic reaction extent are determined from both experimental approach and model-based approach. From the results, it is observed that local w/c, heterogeneous nucleation effects and FA hydration have comparable contribution to the total Wn content in blended pastes while the FA hydration dominates in CH content. Furthermore, the good agreement between the experimental hydration extents and model-based extents validates the established synthetic model for cement hydration extent in blended pastes.

We establish a synthetic model for cement hydration extent with the presence of FA. This model incorporates the pure dilution effect, the local w/c augmentation effect and the heterogeneous nucleation effect of FA on cement hydration extent (see figure). The TGA and selective dissolution method were employed to quantify the cement hydration extent and pozzolanic reaction extent of FA respectively. The results obtained from experiment and agree well with those from synthetic model.Figure optionsDownload as PowerPoint slideHighlights
► We propose a synthetic model for cement hydration extent in blended pastes.
► We quantify cement-FA hydration extents by TGA analysis on Wn and CH.
► Synthetic model meets with experimental quantifications with good agreements.
► Dilution, w/c, nucleation and reaction effects of FA contribute all to Wn content.
► FA reaction effect dominates in CH content evolution in blended pastes.