Research On The Anti-freeze Critical Strength And Microstructure Of Negative Temperature Concrete

The main problem of winter construction is the concrete damage, due to early frost damage has greatly the destructive effects on concrete, early frost damage protection on durability of concrete is essential. As concrete construction in the negative temperature, if the damage on the cold concrete in the young, that does not meet the cold and frost damage to the critical intensity the most, how to ensure the concrete from freezing while in the Young, and make concrete strength at negative temperature continue to increase, post strength and durability improve is issue of common concern at today’s international engineering field. To minimize or avoid the damage of early frost damage of concrete, not only to early frost damage by means of tests to understand the extent of damage of concrete, but also should be aware of the internal microstructure of concrete at early development and early frost damage on the microstructure, which can to increase awareness of the negative temperature concrete.Domestic and foreign experts and scholars have had a large number of studies on the mechanism of freeze-thaw damage of concrete and how to improve the frost resistance of concrete and other aspects. The theoretical end of the age of frost damage of concrete mechanism and freezing tolerance has made significant progress, but early cold concrete and the changes of the microstructure have not system studies. This article for the problem that early frost damage of concrete structure and its post-impact strength, by changing the temperature system and the way of pre-curing time to study the effects on compressive strength of concrete that different curing conditions have, antifreeze critical strength of concrete calculated value. By using X-ray diffraction, differential thermal analysis and scanning electron microscopy, qualitatively analyze that different curing age the composition of hydration products of concrete, and SEM /EDXS assisted proof of the microstructure of concrete section.Firstly, by changing the concrete temperature system, raising the time to test different pre-6d and 31d compressive strength of concrete, pre-maintenance time and with different systems at different temperatures on concrete strength of early and late. The results show that the concrete pre-raising period should be more than 60h, or the cold strength is greater than the value of standard curing 31d strength of about 35.3%, and then experienced a constant negative temperature freezing, a changing negative temperature freezing, constant negative temperature air freeze-thaw cycles , changing negative temperature air freeze-thaw cycles, four different conditions of negative temperature, the early strength of concrete strength with the standard curing conditions, a decline of small, late strength is generally higher than the strength of standard curing conditions. Air freezing and water thawing cycles at constant negative temperature and changing negative temperature, under the two conditions, pre-raising time is greater than 24h, 31d strength of concrete were higher than those of standard curing strength more than 20%.Secondly, using the broad engineering calculation antifreeze critical strength and the maturity method, according to the standard curing age of each concrete strength value, calculated a constant negative temperature freezing, changing a negative temperature freezing constant negative temperature air freeze-thaw cycles, changing negative temperature air freeze-thaw cycles, constant negative temperature air freezing and water thawing cycles and changing negative temperature air freezing and water thawing cycles, the six different antifreeze critical strength value. The results showed that the antifreeze critical strength value by using maturity method is much higher than the value of antifreeze critical strength by using the direct determination method, for the winter, the safety of concrete in construction has a higher guaranteed rate. However, due to different conditions on the maturity method known formula for calculating the parameters to be determined in a large degree of dispersion, resulting in large deviations of calculation results, so the projects need careful application of the maturity method to determine the parameters of the formula.Finally, by using X-ray diffraction, differential thermal analysis and scanning electron microscopy micro-analysis tools, from a different point of view to analyze concrete hydration process and microstructure. Proposed a "concrete hydration process hypothesis" and its application at negative temperature. According to the hypothesis to explain the concrete admixture mechanism on antifreeze and early strength composition.The results showed that the concrete at early times by the various different types of pre-support system of curing temperature on concrete will produce different results. If concrete reach a certain pre-curing time, this time microstructure and hydration products corresponds to a structure, go through the negative temperature environment, will not damage early strength of concrete, the late strength will be higher than the strength of standard curing late concrete values. In this paper, the "hydration process of concrete hypothesis" and the application of the hypothesis at negative temperature .It may explain the antifreeze component, early strength and composition, the role of concrete admixture mechanism. On one hand, it provide a new platform and idea for the studies, on the other hand it can explain that concrete exist a variety of phenomena and problems.