Using SAP to control the deformation of shrinkage-compensating concretes at early age

To reduce the cracking of concrete as induced by early -age shrinkage, it is a common practice to prepare shrinkage -compensating concretes (ShCCs) by introducing expansive agents (EAs). However, some problems remain unresolved in the use of EAs, and the quantitative relationship between the dosage of EAs and the expected expansion is still unclear up to now. Therefore, superabsorbent polymer (SAP) is further introduced into ShCCs in this experimental study, in order to understand the effect of SAP on the free deformation of ShCCs with an increasing dosage of EA. Besides, the working mechanism between EA and SAP is studied by monitoring the concrete internal relative humidity (RH) and temperature and by testing the drying water loss ratio and the pore structures. According to the research results, SAP has a significant promoting effect on the expansive effect of EA in ShCCs, and the combined use or double -introduction of EA and SAP reduces the early -age shrinkage of concrete significantly. As indicated by the experimental results, the introduction of 6% EA and 6% internal curing water using SAP by mass to cementitious materials in ShCCs is the best scheme and shows a good synergistic effect. Whatsoever, the drying shrinkage of all ShCCs without or with SAP could not be eliminated at early age. However, it is noteworthy that drying shrinkage shows a linear correlation with the loss ratio of drying water. For all ShCCs, the expansive deformation induced by EA and SAP becomes more significant with their dosage and the relationship between them obeys a strengthened exponential equation. Therefore, the dosage of the EA and SAP should be determined according to the target introduction of expansive deformation in practical applications. Finally a similar two -stage mode is shown by the development of shrinkage and internal RH with curing time at the early age.