Abstract: In order to reduce the shrinkage of recycled sand concrete, the effects of pre-wetting recycled sand on working performance, compressive strength, autogenous shrinkage, dry shrinkage and internal relative humidity of concrete were studied. On this basis, three kinds of expansion agents were mixed into the concrete, and the effects of the synergistic action of pre-wetting recycled sand and expansion agents on the autogenous shrinkage and dry shrinkage of concrete were studied. The results show that under the condition of the same additional water consumption, compared with concrete prepared with recycled sand in absolute dry condition, the working performance of the concrete prepared by using pre-wetting recycled sand is reduced, the strength is increased, and the internal relative humidity can be maintained at a higher level, which effectively reduces its autogenous shrinkage and dry shrinkage. Among the three kinds of expansion agents mixed into the concrete, calcium expansive has the best inhibition effect on the autogenous shrinkage of concrete, and calcium magnesium complex expansion agents have the best inhibition effect on the dry shrinkage of concrete. At 100% pre-wetting degree, compared with concrete without expansion agents, the autogenous shrinkage of the 10% calcium specimen of the fully recycled sand concrete is reduced by 83.2%, and the dry shrinkage of the 6% calcium magnesium complex specimen of the fully recycled sand concrete is reduced by 36.1%.

Key words: recycled sand concrete, pre-wetting recycled sand, expansion agent, internal relative humidity, autogenous shrinkage, dry shrinkage