胶量和水泥用量：高掺量橡胶有利于提高拌和物的可加工性和混凝土强度，但不利于混凝土的体积稳定性和开裂。从经济效益的角度出发，在满足施工要求的前提下，应尽量少用橡胶材料。根据设计强度等级的要求，确定最小橡胶材料用量不小于460 kg/m3，用量范围为460～500 kg/m3，水泥用量为300～340 kg/m3。
Mixing ratio design mainly considers water binder ratio, sand rate, rubber dosage, variety and dosage of admixture. The workability, mechanical properties, durability and volume stability, construction period and economic benefit of concrete mix are taken into account, and the water glue ratio, sand rate, the amount of glue material and the amount of admixture are controlled in the proper range to achieve the balanced development of the concrete performance.
The ratio of water to binder is larger than that of water binder ratio, which is beneficial to improving the workability of concrete mixture, but it will reduce the strength and durability of concrete. According to the requirement of the design strength grade, the maximum water binder ratio is not more than 0.30, and the low water glue ratio can be realized by using high performance polycarboxylic acid water reducing agent and adding mineral admixture.
Sand ratio: high sand rate can improve concrete performance, but it is not conducive to concrete strength, it will increase the possibility of shrinkage and cracking of concrete. In order to meet the requirements of construction, the sand rate can be reduced as much as possible. The workability of the condensate can be improved by mixing gas. The sand rate is controlled from 36 to 39%. The precast box girder of Xiangshan harbour bridge is a marine concrete. The gas content of the concrete is 3 + 1%.
The amount of glue and cement: the high dosage of rubber is beneficial to the improvement of the workability and concrete strength of the mixture, but it is not conducive to the volume stability and cracking of concrete. From the perspective of economic benefits, the rubber material should be used as little as possible under the premise of satisfying construction requirements. According to the requirement of the design strength grade, it is determined that the minimum rubber material dosage is not less than 460 kg/m3, the dosage range is 460~500 kg/m3, the cement dosage is 300~340 kg/m3..
The variety and dosage of mineral admixture: adding a proper amount of active mineral admixture can not only adjust the gradation of cement particles, but also improve the effect of thickening, plasticizing and water reducing, and can improve the effect of aggregate interface and improve the permeability resistance of concrete. It is easy to cause shrinkage and cracking of concrete due to excessive volume of admixture and accelerate deterioration of concrete, which is not conducive to durability of concrete. The range of mineral admixture is controlled at 30 to 40%.