Effect of Various Admixture-Binder Combinations on Workability of Ready-Mix Self-Consolidating Concrete

This paper describes an experimental investigation that was carried out in order to evaluate the effects of high range water reducing admixture (HRWRA), viscosity-enhancing admixture (VEA), and binder type on key workability characteristics of self-consolidating concrete (SCC), including retention of deformability, passing ability, and stability. Concrete-equivalent mortar (CEM) mixtures were prepared to evaluate the effect of admixture-binder combinations on flow characteristics, including minimum water content (MWC) to initiate flow and relative water demand (RWD) to increase a given fluidity. Four polycarboxylate-based HRWRAs, a polynaphthalene sulfonate-based HRWRA, four types of VEAs, and three blended cements were evaluated. In total, 16 SCC mixtures with initial slump flow consistency of 660 +/- 20 mm and air volume of 6.5 +/- 1.5%, and 17 CEM mixtures were investigated. Flow characteristics of SCC and CEM mixtures made with a number of admixture-binder combinations indicate that the efficiency of admixture-binder combination depends on water-to-cementitious material ratio (w/cm), type of binder, and type of admixtures. The CEM approach can be used to evaluate the effect of admixture-binder combination on flow characteristics because the increase in MWC to initiate flow of CEM corresponds to higher demand in HRWRA in SCC mixtures. Binder type was shown to have marked influence on the retention of slump flow, L-box and V-funnel passing ability, filling capacity, and surface settlement characteristics. The binder type also affects HRWRA and air-entraining admixture (AEA) demand. As established from CEMs, B3 quaternary cement with the smallest 50% passing diameter had the highest MWC (lowest packing density) needed to initiate flow and the highest RWD (highest robustness to changes in water). SCCs made with such quaternary cement and polycarboxylate-based HRWRA also exhibited the highest HRWRA demand compared those prepared with other blended cements. Both sets of SCCs made with 0.35 w/cm and 0.42 w/cm plus VEA had similar HRWRA demand and static stability when the polycarboxylate-based HRWRA was used.