Research On Mix Proportion Design Of Concrete Based On Workability

For ready-mixed concrete, to realize the designed strength and durability requirement, the most important fundamental parameter is water/binder ratio, and then the workability of fresh concrete is crucial. The variations of raw materials, which always occur in production process, would impact properties and performance of concrete, thus it needs to readjust the proportion. The principle for readjusting is to ensure workability to satisfy the construction requirement on the premise of given water/binder ratio. The present method for mix proportion design of concrete and quality control in ready-mix plants in China can not easily adapt to such variation. The present specification for mix proportion design of concrete does not have the method of proportioning concrete based on workability design.A model of suspension with coarse particles for fresh concrete with superplasticiser is established based upon the theory of theology. Three factors for mix proportion design of concrete based on the workability of fresh concrete are indentified. They are the water/bider ratio (W/B), the surplus coefficient of paste (V_p/V_os) and the surplus coefficient of mortar(V_m/V_og). The relation between those factors and the workability of fresh concrete are tested and analyzed, and a method for mix proportion design of concrete mixture based on workability requirement of fresh concrete is established, with the prerequisites of the satisfaction of strength and durability.The relation between mortar and concrete on workability and strength is studied with a lot of mix proportions used in construction projects and additional tests are added. The analysis shows that under the condition of the saturated dosage of superplasticiser, there is a good relevance between the surplus coefficient of mortar and workability of fresh concrete. There is a corresponding relationship among the three factors, W/B, V_p/V_os and V_m/V_og. The saturation dosage of superplasticiser determined by mortar experiments is close to the dosage in the targeted concrete.This method for mix proportion design of concrete has been used for proportioning concrete mixture in ready-mix plants. The tests of slump and W/B ratio of fresh concrete, compression strength of hardened concrete shown that the concrete mixtures were in conformity with strength and workability demands. The study has shown that the mix proportion design of concrete based on workability is simple, convenient and rapid due to motar experiments. The three parameters for trial mix proportion of concrete can be easily determined by starting with accumulated data that has been used in the past or by experiment on mortar,which means that the mix proportion design of concrete is no longer mainly depend on the experience. The experiments for testing the W/B ratio of fresh concrete shown that the Japanese apparatus is reasonably accurate and convenience and can be used as an effective method for the production quality control of ready-mix plants.