Roles of packing density and water film thickness in strength and durability of limestone fines concrete

Recent studies have revealed that the use of limestone fines (LF) to replace an equal volume of cementitious paste in concrete could improve the strength and durability of the concrete and reduce the carbon dioxide footprint of concrete production. However, there are different views on how and why the use of LF as a cementitious paste replacement without changing the mix composition of the paste could increase the performance of hardened concrete, bearing in mind that LF are not inherently cementitious. In this work, the effects of the addition of LF on the packing density and water film thickness (WFT) of concrete mixes were investigated, and the roles of packing density and WFT were studied by correlating the strength and durability to the voids ratio (determined from the packing density) and WFT. Based on the results of this study, it is suggested that the use of LF as a cementitious paste replacement improves strength and durability mainly through increasing the packing density (the same as decreasing the voids ratio) and decreasing the WFT of the concrete mix.