Water Diffusion Behavior and Shrinkage Characteristics of Internal Curing Pavement Concrete

Super absorbent polymer (SAP) internal curing agent exhibits applicable water compensation capabilities in response to declining internal relative humidity (IRH) of cement concrete during the initial curing period, thereby inhibiting the generation of shrinkage cracks and enhancing the hydration degree of the cementitious materials. This paper explores the water diffusion behavior and shrinkage characteristics of SAP internal curing pavement concrete. In accordance with the characteristics of pavement concrete, the influence of SAP particle sizes, dosages, and curing conditions on the internal relative humidity (IRH) of concrete was examined by using the MIC-TD-TM temperature and humidity integrated sensor. Additionally, the spatial distribution of IRH at various vertical depths within the concrete was clarified. Moreover, the relationships between different types of shrinkage strain and IRH, temperature with time were also analyzed. The equivalent water diffusivity coefficient (DH) for the internal curing pavement concrete was determined, leading to the establishment of a DH-IRH model. Results indicate that at 28 days, the IRH of C30 and C40 internal curing pavement concrete reached 93.12% RH and 89.78% RH, respectively, representing an increase of 14.21% and 13.82% compared to the control group. Furthermore, the shrinkage reduction rates for the C30 and C40 internal curing groups were 69.83% and 87.62%, respectively, demonstrating that SAP significantly enhances curing effects in concrete with lower water-binder ratios. The incorporation of SAP effectively mitigates the vertical humidity gradient in pavement concrete, leading to a more uniform IRH across all layers, which positively influences the suppression of humidity-induced warping stresses in the road slab. Based on results concerning shrinkage strain, IRH, temperature, and the calculated internal curing water content, three main stages during the 28-day curing period were identified. Notably, the initial DH of the internal curing group was higher than that of the control group, and the decrease rate of DH with IRH was attenuated.