Study on the reuse of returned concrete

A method to reuse concrete that has been returned from the job site either entirely or partially unused is studied. By adding a stabilizer to returned unused and returned concrete to cease cement hydration, leaving it in a fr esh concrete state for a long time, and then adding an activator the follow ing day to produce R-concrete, the concrete can he reused in the same manne r as ordinary concrete. By adding a superplasticizer to the concrete to obt ain sufficient consistency with skimp of 22 cm, an 18 cm slump can be obtai ned the next day. The properties of R-concrete, such as compressive strengt h, freeze resistance and change in length are equivalent to ordinary concre te. The longer the setting time of the returned unused concrete, the longer the setting time of R-concrete made by adding stabilizer to it. On the oth er hand, R-concrete made by mixing returned concrete with new concrete exhi bits an equal setting time to ordinary concrete.