Humidity field and moisture transfer of concrete with different pre-saturated recycled sand

The water absorption/desorption process of two kinds of recycled sand with parent concrete strength grade C20 and C50 respectively was tested. The influence of the pre-saturated recycled sand on the internal relative humidity development of concrete with strength grades of C30, C50, and C80 was tested. A critical water loss Wc of each concrete with pre-saturated recycled sand was calculated. The theoretical calculation model of concrete humidity considering the effect of pre-saturated recycled sand was established. The results show that the desorption process of recycled sand is closely related to its parent concrete strength grade (pore structure). The recycled sand with a weaker parent concrete induces a greater water release during the decline of ambient humidity. The use of recycled sand can prolong the humidity saturation period and improve the final humidity level of concrete. The effects are related to the pore size of the recycled sand and the new casting concrete. The recycled sand with a weaker parent concrete has stronger effect on the humidity of concrete. For the same recycled sand, it has a better effect on the humidity of high-strength concrete. The use of recycled sand can significantly increase the critical water loss of concrete. The introduction of pre-saturated recycled sand will increase the diffusion coefficient of concrete.