Accounting for Water Stored in Superabsorbent Polymers in Increasing the Degree of Hydration and Reducing the Shrinkage of Internally Cured Cementitious Mixtures

The use of superabsorbent polymers (SAPs) in cementitious materials has attracted much attention recently due to the potential benefits associated with internal curing. In this study, a commercially produced SAP is characterized using pore solution absorption and desorption measurements. The SAP helps maintain higher internal relative humidity in the pastes, resulting in a reduction in autogenous shrinkage. This paper explores the effects of partial SAP replacements and compares the results to those obtained using a previously developed relationship based on pore size distribution and relative humidity measurements, which aims to predict the reduction in shrinkage coming from additional internal curing water. Using this approach reduces the amount of SAP used for internal curing, as compared to the more conventional design methodology, which is based on providing a volume of internal curing water that is equivalent to the total chemical shrinkage. Experimental data showed that only a fraction of the provided internal curing water ends up filling the pores and reducing the autogenous shrinkage. Other factors, such as increased degree of hydration and partial desorption of the internal curing agent, account for the sharing of the available internal curing water. The aforementioned approach was modified to consider these factors. It can be concluded that using lower amounts of SAP results in substantial reduction of autogenous shrinkage at early ages, and the developed relationship predicts this shrinkage reduction.