Effect of SAP on hardening process and development of microstructure in high performance concrete : a review

The main purpose of Super Absorbent Polymer (SAP) added into high performance concrete is to prevent or reduce self-desiccation (or autogenous shrinkage) of concrete. The mechanism behind is free water release from saturated SAP lead to an increase of relative humility and to promote further hydration. Compared to plain cement paste, the added SAPs change hydration process and the development of microstructure in concrete. In this contribution, the degree of hydration of cement in cement composites containing SAP are reviewed. The influence of SAP on the development of microstructure properties, i.e. porosity, pore size distribution, morphology and connectivity of bulk cement paste and interface transition zone between cement paste and SPA, the voids introduced by SAP are discussed. It is concluded that the addition of SAP in the mixture increases the hydration degree of cement particle, this leads to a reduction of capillary porosity in the matrix and increase gel pore in the paste. The additional of SAP meanwhile increase the void in the ITZ between SAP and matrix. Micro-computer tomography image shows that the voids introduced by SAP in the mixture are homogenously distributed with an average diameter of 150 µm