| As an important part of construction industrialization in China,precast concrete technology has the advantages of centralized production and standardized process.Current steam curing methods have technical defects in the late performance deterioration of precast concrete,and will produce environmental problems such as high energy consumption and carbon emission.In this dissertation,ordinary and ceramsite internal curing concrete were taken as the research object.Based on the idea of using the hydration heat of cement to promote the early hydration reaction and exploring the new self-heating curing mechanism of precast concrete,the curing method of precast concrete based on cement hydration heat and related issues were studied.In this study,the relationship between hydration degree and equivalent age of ordinary and pre-absorbent ceramsite cementitious systems were verified by experiments,and a calculation model of hydration degree of ordinary and internally cured concrete based on equivalent age method was established.The common action mechanism of ceramsite internal curing materials and thermal insulation cover self-heating curing was expounded.A three-dimensional temperature field calculation model of concrete based on finite difference method was established,and the accurate temperature change process of ordinary and internal curing concrete under the condition of thermal insulation covering was described.Finally,the engineering application of precast concrete curing method based on cement hydration heat was developed.The main innovations and conclusions of this study are as follows:(1)The internal curing mechanism of the pre-absorbent ceramsite was expounded from the point of view of hydration heat in this study,a calculation model of concrete hydration degree with the consideration of the release process of internal curing water was established,and the influence of ceramsite internal curing materials on the hydration and exothermic of Portland cement cementitious system was determined.The thermal insulation cover self-heating curing method based on heat of hydration was proposed,in which the temperature of concrete increased by 8.7-20.9℃,and the temperature gradient decreased by 61%-80%compared with the ambient temperature condition.(2)Based on the finite difference method,a three-dimensional temperature field calculation model of concrete considering the hydration heat of cementitious materials and the heat exchange with the environment was developed and the applicability of the existing finite difference calculation model to the calculation of complex boundary conditions was improved.Compared with the existing one-dimensional model,the fitting difference of the maximum temperature of the example was reduced from 21.2%to 0.9%.(3)Adding the ceramsite internal curing material into the thermal insulation cover self-heating curing system further improved the early compressive strength and 28d compressive strength of concrete,and the 28d cumulative pore volume and the most probable aperture were obviously reduced.Compared with standard curing,the 1d compressive strength of thermal insulation cover self-heating curing was improved by24%-67%;Compared with high temperature curing,the growth rate of 28d compressive strength was 8.8%.The maximum temperature stress on the surface of concrete with thermal insulation cover self-heating curing method decreased by 30%-62%.Compared with ordinary concrete,the residual temperature stress at the central point of ceramsite internal curing concrete decreased by 16%-66%,and the decrease rate increased with the strength grade.(4)Compared with the current steam curing method,the precast concrete curing method based on cement hydration heat has obvious advantages in economy and environmental protection.The analysis results of the optimization example show that energy consumption of 9.08kg standard coal and carbon emission of 6.17kg can be reduced for 1m~3 C80 internal curing precast concrete. |
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