Compressive creep behavior of alkali-activated slag recycled aggregate concrete under non-uniform humidity field

The creep deformation of alkali-activated slag recycled aggregate concrete (AAS-RAC) under long-term loading is significantly affected by its internal humidity field, but the mechanism of humidity diffusion on its creep under complex boundaries lacks systematic research. To reveal the coupling regulation laws of internal humidity on the AAS-RAC creep behavior, this paper carried out compressive creep tests and internal relative humidity monitoring of AAS-RAC under completely dry, completely sealed, and locally exposed conditions. The results show that when the water-to-binder ratio increases from 0.40 to 0.60, the proportion of harmful pores inside the material increases by 45.1%, leading to a 17.1% decrease in internal relative humidity, which in turn increases the AAS-RAC creep coefficient by 11.4%. For AAS-RAC with a water-to-binder ratio of 0.50, the basic creep accounts for 52.1% of the total creep, which is higher than the proportion of basic creep in ordinary concrete under the same water-to-binder ratio. In addition, the local humidity diffusion condition (single-sided exposure rate of 0.25%) will cause the internal relative humidity loss rate to increase by 39.4%, making the creep coefficient of AAS-RAC increase by 32.9%. An AAS-RAC creep prediction model considering the coupling effect of humidity diffusion and mechanical response was established. The research results can provide a scientific basis for evaluating the long-term mechanical properties of concrete structures under non-uniform humidity fields in relevant codes.