Study Of Concrete Strength Under Constant Minus-temperature And Varied Minus-temperature And Calculation Formula Optimization Of Early Strength Of Concrete

With the social development and the update of concrete technology, the demand for high-performance concrete is increasing day by day. Winter comes relatively earlier and lasts a rather longer duration in most of the North areas of China, In order to accelerate the pace of the construction of infrastructure, winter construction becomes an inevitable stage in concrete construction. The average geothermal temperature of QingHai-Tibet Railway and QingHai-Tibet Highway vary from 0~3.5?, in order to stride over Permafrost Region, bridges with base of the concrete-grouted piles are usually adopted. Formulating reasonable concrete curing temperature and time, clearing all sorts of influencing factors, grasping the strength development and deducing earlier strength will affect the engineering quality and progress directly. It is meaningful to explore its' frost resistance, impermeability and durability performance only when the strength of concrete structure itself is satisfied.This article aims at the concrete of winter construction in Permafrost Region and North areas, in view of some not yet settled problems on the basis of summarizing the predecessors' research, systematically studies the strength increasing mechanism and early compressive strength of speculation of high-performance concrete under constant minus-temperature and varied minus-temperature, main contents are listed as follows:(1) Respectively calculated the hydration heat and degree of hydration through net cement slurry hydration heat test with different water-cement ratio and constant minus-temperature(-3 ?), analyzed how temperature and water-cement ratio influence hydration heat.(2) Cement stone occupies about a quarter of concrete volume, and its' performance decides the performance of concrete to a certain degree, the cement stone compressive strength test is conducted under constant minus-temperature(-3 ?) and varied minus-temperature with different water-cement ratio so as to analyze the influence from temperature, water-cement ratio and age towards the performance of cement stone, combined with the hydration degree of net cement slurry under constant minus-temperature, quantitatively analyzed the connection between hydration degree and cement stone performance from the angle of hydration, then explored the influence to concrete strength.(3) Analyzed the changing law of concrete strength and pore structure through concrete compressive strength and pore structure test with different mixing proportion under constant minus-temperature(-3?) and varied minus-temperature; Explored the connection between mesoscopic structure and the strength of concrete, then explained how temperature, water-cement ratio and age influence macroscopic compressive strength of concrete from the perspective of meso level.(4) Measured the concrete curing temperature in detail along with the concrete compressive strength test under constant minus-temperature and varied minus-temperature, then calculated the maturity of concrete in different curing conditions, predicted the early strength of concrete based on the maturity theory and perfected the calculation formula of the early strength of concrete.