Abstract
Because of environmental consideration and variety of required performance for concrete, the kinds of constituent materials used for concrete have been increased. For this reason the bleeding of concrete has shown a high value in some cases. It is said that higher bleeding has some harmful effects on the properties of concrete and reinforcement but the method for control of bleeding have not been proposed.
This paper presents the results of experimental study and the literature survey on the simple prediction model of bleeding of concrete.
The experiment was composed of four series and the bleeding test of concrete was conducted in accordance with JIS A 1123 except for the interval of taking the rising water. In series 1, unit water content and the kind of chemical admixtures were varied under the constant water cement ratio. In series 2, the variation of bleeding in the different 7 batches was checked. In series 3, unit water content, water cement ratio and the kind of chemical admixtures were varied. In series 4, the variation of 7 bleeding test samples in the same batch was checked. Based on the series 2 a simple prediction equation of bleeding was established.
And a literature survey on bleeding of concrete in Japan was conducted and the data of experiments in which unit water content or water cement ratio are varied under the other condition is constant were set in order.
Moreover the comparison of the existing three prediction equations and the equation model of bleeding of concrete proposed in this paper was conducted.
At the last stage the effect of bleeding in the cases in which this proposed equation was adapted to those using with other chemical admixtures were considered based on the data provided by some organizations, because the concretes using with air-entraining agent and air-entraining and water-reducing agent were treated in this experiment.
The conclusions of this study are summarized as follows.
(1) It was confirmed that bleeding amount reduces linearly with the reduction of unit water content or water cement ratio.
(2) The data of variation in the different batches and that in the same batch were obtained, and in the latter case the variation of plain concrete was larger than that of concrete with air-entraining agent or air-entraining and water- reducing agent.
(3) The prediction equation of bleeding considering unit water content and water cement ratio was established, and it compares favorably with existing equations.
(4) The empirical constant coefficient in the prediction equation of bleeding had wide range of 3 or 4 times due to the lots of used materials even if the brand or district was the same. In other words, it was found that bleeding mass had the same range. Accordingly, it is necessary to study the influence of the quality of cement and fine aggregate on the empirical constant coefficient in the future.
(5) In the case where chemical admixtures were used, the coefficients which multiplies the empirical constant coefficient of plain concrete were shown in each kind of chemical admixture. The compatibility of experimental values and calculated values in the case of air-entraining and water-reducing agent or air-entraining and high range water-reducing agent was not so good compared to air-entraining agent or water-reducing agent.
