No abstract

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 fresh concrete state for a long time, and then adding an activator the following day to produce R-concrete, the concrete can be reused in the same manner as ordinary concrete. By adding a superplasticizer to the concrete to obtain sufficient consistency with slump of 22 cm, an 18 cm slump can be obtained the next day. The properties of R-concrete, such as compressive strength, freeze resistance and change in length are equivalent to ordinary concrete. 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 other hand, R-concrete made by mixing returned concrete with new concrete exhibits an equal setting time to ordinary concrete.