Research on water transport behaviors and hydration characteristics of internal curing pavement concrete

This paper presents the influence of internal curing agent (super absorbent polymer, SAP) on the water transport behaviors and hydration characteristics of pavement concrete. The H-1 nuclear magnetic resonance (NMR) test was performed to quantitatively analyze the transformation rule of different forms of water, and the variation rule of relative humidity in different vertical depths of concrete slab was also studied. Moreover, the isothermal calorimetry and thermogravimetry method were adopted to study the hydration process of internal curing pavement concrete. The flexural strength of specimens with SAPs were evaluated by the four-point bending method. Finally, the enhancement mechanism of SAP on the properties of pavement concrete was revealed through analyzing the water transport behaviors, hydration characteristics and microstructure characteristics. The results show that specimens with SAPs of smaller particle size could keep the humidity compensating and hydration enhancing process for a long time. The humidity gradient in the slab could be significantly reduced that might mitigate the humidity warping stress distributed in the slab. Although SAP delayed the hydration process of binding materials in the early age, it could greatly improve the hydration degree in the long term, which helps improving the crack resistance and the compactness of pavement concrete. The adhesion of aggregate-cement matrix interfacial transition zone (ITZ) and the compactness of microstructure was improved during the internal curing process. (C) 2020 Elsevier Ltd. All rights reserved.