Investigation on the Internal Relative Humidity of Superabsorbent Polymer–Modified Concrete Exposed to Various Ambient Humidities at Early Age

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The drop in internal relative humidity (IRH) affects the early-age cracking risk of concrete. Superabsorbent polymers (SAPs), an internal curing material, are usually used to decrease the drop rate of IRH in concrete and the shrinkage-induced cracking risk of concrete. This study investigated the changes in IRH and distribution of IRH in SAP-modified concrete under sealed conditions and exposed to various ambient humidities. The test results showed that the use of SAPs and additional internal curing water can compensate for water consumption caused by self-desiccation and moisture diffusion (MD) and increase the IRH of concrete exposed to various ambient humidities. However, the degree to which SAPs mitigated the drop in IRH of concrete exposed to outside ambient decreased with increasing ambient humidity. The IRH of SAP-modified concrete increased, and the MD coefficient decreased nonlinearly with increasing ambient humidity. A model for predicting IRH of SAP-modified concrete exposed to various ambient humidities under the influence of self-desiccation and MD was proposed.