Effects of W/P ratio and limestone filler on permeability of cement pastes

摘要

Because of environmental and economic benefits, a fraction of cement is increasinglyreplaced by limestone fillers raising a question on to what extent limestone fillers affect thedurability of cementitious materials. This work aims at understanding the effects ofwater/powder (w/p) ratio and limestone filler replacement on water permeability of cementpastes. A newly proposed technique using a controlled constant flow concept was applied tomeasure permeability of hardened cement paste samples following a factorial experimentaldesign. It was observed that both limestone filler and w/p ratio significantly influence thewater permeability. At a given w/p ratio, adding limestone filler made the microstructurecoarser, especially for high w/p ratio. Nevertheless, if the comparison is based on a givenwater/cement (w/c) ratio instead of w/p ratio, the limestone filler replacement refined themicrostructure in terms of capillary porosity and pore size distribution, resulting inpermeability decreases of cement pastes. Furthermore, a modified Carmen-Kozeny relationwas established which enables prediction of the permeability from capillary porosity and thecritical pore diameter.