Recycling the decasting concrete catches more attention in the world. It depends on the strength for construction bearing to utilize recycled concrete (RC). Mixture ratio is one key factor deciding strength, which is supported by a crucial parameter: water-cement ratio. So the calculation of unit water use in RC is the hot topic, it is crucial that additional adsorbed water should be determined. It is appropriate to adopt the form of full (or part) coarse aggregate adding natural sand. In the case of mixed coarse aggregate adding natural sand, the water in each stere of RAC should increase its percentage corresponding to the ordinary concrete in the mix proportion design, the calculating formula for the additional adsorbed water is put forward, by which the additional adsorbed water coincides better with the experimental data through verification, and which can provide a reference for the designer in RC mixed ratio.
