Evaluation of superplasticizer performance in concrete

Superplasticizers are an essential component in modern concretes, providing workability enhancement at low water to cement ratios, and resulting in the production of durable and sustainable concrete. Although the mechanisms leading to superplasticizer performance are well understood, issues of cement - superplasticizer incompatibility are regularly seen in field applications. In this paper, laboratory investigations on cement concrete from a recently concluded research project are reported. The experimental program was divided into two phases: (i) evaluation of the influence of ambient conditions, and (ii) study of the influence of mix parameters - size of mix and speed of mixing - on superplasticizer effectiveness. In both studies, concrete designed for strength of 40 MPa at 28 days (representing typical ready mix composition) with ordinary Portland cement (OPC) and Portland pozzolan cement (PPC) was evaluated for its early age properties, using SNF and PCE based superplasticizers. The results of the investigations reveal the complex nature of interactions between cement and superplasticizers in concrete.