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Effect of Powder-to-Voids Ratio on Bleeding Process of Fresh Concrete

Part of free water in fresh concrete bleeds out and results in problems of hardened concrete. In order to explore the determinant factors to control bleeding process and effecting mechanism, a series of mix samples in various water-to-cement ratios and sand ratios for different slump requirements were prepared to test their bleeding rates. Then the parameters to control bleeding process of fresh concrete and their influencing factors were investigated by regression analysis. The results reveal that percent volume of powder in mix (βp) and the ratio of powder to voids between sand particles (p/v) are key factors to control bleeding speed, and p/v also controls the dormant time of bleeding. The sand ratio influences the bleeding process by changing the value of p/v. Both βp and p/v have their critical values and optimum ranges. When p/v=0.78~0.87, the bleeding can be regulated to Late-Slow type with the least harm to properties of hardened concrete.