The Effect of SAP on Volumetric Changes and Microstructural Alterations in PC-GGBS Matrices

Abstract

Despite their growing popularity in construction, cement-based materials containing ground granulated blast-furnace slag (GGBS) may suffer from various deteriorative actions, including development of early cracks caused by shrinkage processes. Moreover, the degree of GGBS reaction (at later stages) can be limited by lack of space already filled by early products of Portland cement (PC) hydration. In attempt to reduce these negative effects, Superabsorbent polymers (SAP) can be used as internal curing agents and facilitate hydration processes. This paper intends to evaluate and correlate shrinkage behaviour and microstructural features of SAP-GGBS mortars during the first 90 days. Six sets of mortars (with 0% and 50% GGBS) modified by two SAPs were analysed. Autogenous, plastic and drying shrinkages were tested, and microstructural characteristics were analysed by the MIP technique. The experimental results showed significant effect of SAPs on shrinkage reduction in GGBS matrices. The paper argues that deposition of later GGBS hydration products in pores below 20 nm, triggered by SAP water, leads to a relative expansion of SAP-PC-GGBS mortars. In this context, the role of SAPs in GGBS-PC matrices is twofold: firstly, a provision of additional water for hydration and, secondly, a provision of the required space for later products formation.