Experimental Study On Material Properties Of Prestressed Concrete At Low Temperatures

Our country has the vast cold region, including 13 provinces, cities and autonomous regions in the three Norths, covering more than 50% of the total area of the whole country. In Heilongjiang Province, the normal temperature construction time is only 4-6 months. For pre-stressed concrete simply-supported girder bridges, the main problem of the construction under low temperature is the early stage cold damage of concrete and the winter tension of pre-stressed steel strand. As the early stage cold damage has great destructive effect on concrete and such destructive effect cannot be recovered even after the standard curing of later stage, it will bring permanent damage to the later stage functional performance of concreate. In the construction under low temperature, people usually carry out the construction according to the strength and transformation theory for pre-stressed steel strand under normal temperature. However, with the impact of low temperature, both its elasticity modulus and elongation will change. If it is still controlled according to the elongation value under normal specification, the tension control stress cannot be controlled correctly. Therefore, it is necessary to analyze the critical anti-freeze strength of low temperature concreate and influencing factors and analyze the mechanical properties of steel strand under low temperature.This paper mainly researched the change rules of mechanical properties for cement mortar and concrete of different strength grades under low temperature, found the critical anti-freeze strength of concrete of different strength grades under different temperatures according to the definition of general critical anti-freeze strength, identified the main factors influencing the critical anti-freeze strength of concrete through the analysis on factors influencing the critical anti-freeze strength, carried out the orthogonal experiment with the help of SPSS statistical analysis software, and found the subjective effect of each influencing factor in order to improve and guide the construction under low temperature.This paper carried out the mathematic fitting of ultimate strength, elasticity modulus and elongation value of pre-stressed steel strand with Origin 9.0 through the test on mechanical properties of pre-stressed steel strand under low temperature. Then, the paper took the tension of 40m pre-stressed T girder steel strand used in the approach bridge of Mulan Bridge as the example to give the modifier formulas to the tension of steel strand under low temperature.