Effect of binder composition on time-dependent stability and robustness characteristics of self-consolidating mortar subjected to prolonged agitation

Segregation in highly flowable cement-based materials leads to heterogeneous properties of hardened material with direct impact on mechanical properties and durability. An experimental program was undertaken to evaluate the effect of binary and ternary cementitious systems of fly ash (FA) and Metakaolin (MK) on time-dependent stability and robustness characteristics of self-consolidating mortar subjected to prolonged agitation. The effect of prolonged mixing on air content, packing density, and water film thickness (WFT) covering solid particles was investigated. Test results indicate that the coupled effect of changes in level of fluidity and drag force resulting from the use of different SCMs types and replacement rates affect the time-dependent stability characteristics. Mechanical properties and durability of self-consolidating mortars were found to be closely related to stability characteristics. Self-consolidating mortars subjected to 60 min prolonged agitation exhibited higher fluidity and lower stability compared to similar mixtures without prolonged mixing. The prolonged agitation results in an increase in packing density and excess water thickness covering solid particles, thus reflecting higher risk of bleeding and segregation over time (i.e. hidden potential of instability). The incorporation of MK was found to be effective in enhancing robustness of concrete when subjected to the prolonged agitation, given higher drag force exerted by paste on aggregate.