Experimental Study On Early Strength Of Precast Concrete

As China continues to promote industrialization and called for building a resource-saving and environment-friendly society construction, precast concrete industry has gradually become the dominant trend of the future development of concrete, and it is more widely used in many engineering fields and applications (such as Municipal Engineering and construction engineering). But the main problem of the current concern is production efficiency and production cycle, and early strength precast concrete is the key issues that must be addressed. According to a survey of many precast concrete plant on the domestic production, in order to improve the early strength, shortening cycle and accelerate the template turnover, many manufacturers generally use steam curing process in precast concrete production, it consumes a lot of coal resources, while generating a lot of greenhouse gases. Therefore Free precast concrete steam curing technology to improve the early strength is imperative.This paper address the problem in two ways:Firstly, starting from admixtures, experimental study synthesized a early strong Polycarboxylate PCE1; secondly, the gypsum. This paper gets laws of the influence of its late strength on mortar early by studing the four gypsum plant produced seven anhydrite and hemihydrate gypsum. And it determines a gypsum which is conducive to improve the early strength of pre-cast concrete, then determines the optimal dosage in mortar plaster and partial complex admixture of content through each test and orthogonal test verification methods. In the concrete orthogonal experiment, we find that this plaster and the corresponding optimal dosage can optimize the preparation of the C40 precast concrete, and we find that the early detection 1-3d strength can be increased by more than 50%, full realizing the early form removal standards. Finally, from the point of the principle, this paper analyzes the causes and mechanism of that plaster improves precast concrete s early strength.Adding an appropriate amount of gypsum in concrete can significantly reduce hydration rate of the clinker containing aluminum (C3A) and iron-bearing mineral phase, so that the cement hydration time becomes longer, ensuring that it has sufficient plasticity in full time, and it is conducive to the development of the early strength. The right amount of gypsum reacting with the chemical composition of cement can form an appropriate amount of AFt, which can fill the internal porosity of cement, increase the density level, and form a strong structural framework, enhancing the early strength. However, if adding too much cement plaster, concrete will form a lot of expansive material, decreasing the strength. Therefore gypsum content has a best proportion. For ordinary portland cement concrete, this study determines the optimal dosage of hemihydrate gypsum. At the basis of several experiments, we can conclude that when we change the cement for the manufacturer or species, and the content of each component changes, leading to the content is not applicable. So the quantity of hemihydrate gypsum ash is related to cement’s chemical composition and proportion. This study also find that when the admixture of anhydrous gypsum and the group content of cement achieve the best proportion, concrete s early and late strength may exceed the hemihydrate, but the optimum ratio remains to be further study.