Admixtures Relevant to Precast Concrete
General Purpose polycarboxylate-based HRWRs – A HRWR for high flow (≤10 in.) and/or low w/c ratio concretes (≥ 0.40). These superplasticizers would not necessarily be applied for a special performance such as high early strength or self consolidation.
High Early Strength – A polycarboxylate-based HRWR designed and formulated to enable increased strength at early ages.
Extended Slump Life HRWR – These admixtures are typically blends of different polycarboxylates, which are engineered to activate or increase slump at different times. The goal of these polycarboxylate-blended products is to maintain concrete mixtures at target workability levels until concrete is placed and consolidated without delaying set times. Several HRWR products have been recently introduced, comprised solely of slowly activating polycarboxylates, which can be added to almost any concrete mix to extend slump life as desired.
Rheology Modifying Admixtures – These admixtures are designed to impart lubricity to the concrete, especially at very low slumps, resulting in improved formed finish, increased productivity and improved surface texture.
Viscosity Modifying Admixtures (VMAs) – Viscosity modifying admixtures are most commonly used in SCC when the batch-to-batch variations in aggregate gradation, particle shape and density, and water content make it difficult to consistently produce a stable, non-segregating SCC mix. VMAs function by building a network structure within the pore water that helps minimize water and paste movement, especially once the concrete is in a static state. VMAs have also been used with conventional concrete mixes where the concrete mix may have a tendency to segregate.
Shrinkage Reducing Admixtures (SRAs) – SRAs help provide some measure of reducing the potential for autogenous shrinkage cracking with high-performance concrete (w/c ratio < 0.40).