Comparison of the effects that supplementary cementitious materials replacement levels have on cementitious paste properties

Modified R-3 testing has been used to classify four different SCMs, namely, limestone, pumice, slag, and densified silica fume. Cementitious pastes were prepared by replacing ordinary portland cement with SCMs at different replacement levels - 20%, 40%, and 60% for limestone, pumice, and slag and 5%, 10%, and 15% for silica fume. The influences of SCM replacement level on heat flow, heat release, calcium hydroxide consumption, bound water contents, compressive strength, and bulk resistivity for a period of 56 days were quantified. The SCMs have widely varying effects on these properties as a function of replacement levels, however, in general, inert and reactive SCMs show little difference in properties at early ages and lower replacement levels (20%). The impacts of SCMs on cementitious paste properties are more apparent at higher replacement levels (40%-60%) and at later ages (28 and 56 days). These findings have important implications in practice and suggest that standard ASTM strength activity index testing could be improved by testing at higher replacement levels. In addition, bulk resistivity shows ability to differentiate inert and reactive materials and could be a potential candidate for standardization. The ratio of heat release to calcium hydroxide consumption obtained from the modified R-3 test shows a strong correlation with the relative compressive strength of SCMs at different replacement levels and could be used to explore links between reactivity testing, SCM replacement, and paste property evolution.