Research On Influencing Factors Of Hydration Degree Of Cementitious Materials Under Constant Low And Negative Temperature Environment

Portland cement have to hydrate in low temperature environment during the construction of bored pile in permafrost area,a better understanding of the effects of low temperature and water-cement ratio on the hydration heat of cement will be beneficial to the application of cement-based materials in permafrost areas.In this study,the effects of water-cement ratio and low temperature on hydration heat of cement were investigated using solution calorimetry tests.According to the results,when curing at 20?,the lower water-cement ratio resulted in a higher cumulative hydration heat and hydration heat evolution rate at 24 hours but reduced after that.The lower water-cement ratio lead to a lower cumulative hydration heat curing at 5? and 0?.Different from curing under positive temperature,the higher water-cement ratio cause a lower cumulative hydration heat curing at-5?.The cumulative hydration heat of cement paste increases with the curing temperature,and the influence of negative temperature on the cumulative hydration heat of cement paste increases with the water-cement ratio.The compound exponential model is used to predict the hydration heat of cement paste maintained above 0?,while the logarithmic function model is in good agreement with the experiment data curing at negative temperature.Based on the test of the effect of constant low and negative temperature environment on the degree of hydration of cement paste,this article further carried out an experiment on the effect of mold temperature and water-binder ratio on the degree of hydration of cement paste under adiabatic temperature rise environment,and Based on the obtained test data,the calculation formula of cement hydration affected by water-cement ratio and mold temperature was fitted and analyzed.The results show that: under the same hydration environment of the same mold temperature,the cement paste has a lower water-to-binder ratio,and the accelerated age is earlier,and the peak of the heat release rate is larger,resulting in higher hydration in the first 24 hours.Degree and heat release rate,but then the heat release rate is faster,and eventually the degree of hydration decreases.The higher mold temperature will lead to the accelerated age,but the exothermic peak size will be basically unchanged,resulting in a higher degree of 24-hour hydration,but then it will also decline,and the final degree of hydration will be lower.The fitting result of the composite index model considering the influence of the mold temperature is in good agreement with the test data as a whole,but the test data of the first 24 hours have a high consistency with the Boltzmann function fitting result.Finally,by comparing and analyzing three different ways to characterize the degree of hydration: hydration heat method,chemically combined water method,calcium hydroxide content determination method,explore the correlation between different measurement methods,and further explain how to more accurately characterize cement The degree of hydration of the pulp.At the same time,the effects of constant temperature hydration environment and adiabatic heating environment on the degree of hydration of cement paste are analyzed,and it is further clarified that the constant low and negative temperature hydration environment has a greater effect on cement paste than semi-adiabatic or even adiabatic environment.Differential effects of hydration.