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.
Through adding different additional water use, the compressive strength, splitting tensile strength and fluidity of recycled concrete of three aggregate combination forms were studied by experiment respectively. The experimental results show that with the increase of adding additional water use, the compressive strength and splitting tensile strength of recycled coarse aggregate concrete decrease, but that of recycled fine aggregate concrete and recycled all aggregate concrete increase firstly then decrease. When additional water use is added more 15% or 20% than that of basic ordinary concrete, the recycled coarse aggregate concrete and fine one can get pretty good fluidity. When it is added more 30%, the recycled all aggregate concrete has fluidity that is just satisfied.
The frostbite situation of recycled concrete suffered one-time freezing was analyzed, and was then compared with that of the normal concrete. In order to improve the frost resistance of recycled concrete, antifreeze was used and good effect was obtained. The results show that the frost resistance of recycled concrete is inferior to that of recycled concrete. Differences exist in the microstructures of the recycled concrete and normal one, which makes the decrease of frost resistance. Antifreeze can improve the microstructure of recycled concrete, so the frost resistance of it is improved as well.
Conservation of natural resources and preservation of environment are the essence of any development. The use of recycled aggregate concrete(RAC) is an attempt and an answer to some of the problems in constructional engineering. So recycling the decasting concrete catches more attention in the world. It depends on the strength for construction bearing to utilize recycled concrete(RC), but the strength calculation formula of RC has not been put forward yet. There is a linear relation between the common concrete compression strength and cement strength with cement-water mass ratio, whether this relationship also exists in recycled concrete or not it should be verified by experiment. Based on some experiments, the relationship between recycled concrete compression strength and its cement-water mass ratio was established, and the method to determine A′ and B′ values in Bolomey Formula was discussed.
The circumstance of fluid of fresh mixing concrete is analogous to Bingham fluid with pumping pressure in pipeline. The rheological characteristic of fresh mixing concrete along the pipeline wall in the action of push force with high pressure pumping is analysed. The results show that under the action of the concrete for pumping as long as the shear stress τ >τ 0 at the position of pipeline wall, the fresh mixing concrete begins to flow, but in an arbitrary radius, the flowing stops before the concrete for pumping to take place. The pull force of concrete for pumping produced by the shear stress is greater than cement paste's (or cement sand paste ) yield stress 0 τ ′ , the flowing may take place, therefore 0 0 τ τ ′ > , it is advantaged to the fresh mixing concrete for pumping.
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