Effect of additional water or superplasticizer on key characteristics of cement paste made with superabsorbent polymer and other shrinkage mitigating materials

The use of superabsorbent polymer (SAP) coupled with expansive agent (EA) or shrinkage-reducing admixture (SRA) can effectively reduce shrinkage of cement-based materials. However, SAP particles at high contents can adversely affect rheological and mechanical properties. Securing proper workability can be accomplished by additional water or adjusting the superplasticizer (SP) demand. There is an uncertainty about the efficiency of these approaches to workability compensation. This study evaluates the effect of additional water or SP on key properties of cement paste made with SAP and relatively high content of EA or SRA. Macro and micro mecha-nisms underlying the effect of combined shrinkage mitigating strategies on the performance of cement paste made with 0.4 water-cementitious materials ratio are investigated. Results indicate higher efficiency of increasing SP demand by 0.6% versus the addition of water by 30 g per gram of SAP. Up to 80% higher compressive strength is obtained for the mixtures made with additional SP, which is attributed to up to 33% reduction in capillary porosity and smaller pore-size distribution of the hydrated cement paste. In the presence of high EA content, the use of additional SP prevents excessive initial expansion in the paste with additional water.