Study On The Influence Of Composite Early-strength Agent And Cement Particle Size On The Early Strength Of Low-temperature Concrete

Concrete is a common,mixed from the cementing components and filling components of the building materials.Into the 21st century,with the progress of China’s construction industrialization,the demand for concrete is not only manifested in quantity and quality,but also in the increasing demand for concrete functionality.There are large areas of high latitude and low temperature in China,concrete in low temperature environment shows a slowdown in hydration reaction or even stagnation,greatly reducing the flow rate of the formwork,which restricts the application of concrete,thereby reducing the efficiency of the economy and the environment impact.Improving the hydration reaction of concrete at low temperature,increasing the hydration rate,and enabling concrete to reach the required strength as soon as possible at low temperature are very valuable directions in concrete research.For the problem of slow hydration rate of concrete in low temperature environment,this paper focuses on two directions of admixtures and cementing materials.Compound early strength agent is a common admixture in modern concrete,it has the characteristics of low cost,low dosage,and obvious effect.Different types of early strength agents have different effects in the application of concrete,chose different mechanisms of early strength agents in low temperature environment（5℃,10℃）for testing,and chose calcium formate（C₂H₂O₄Ca）,anhydrous sodium sulfate（Na₂SO₄）,triethanolamine(C₆H₁₅O₃N),calcium bromide（Ca Br₂）,triisopropanolamine(C₉H₂₁NO₃),etc.These different types of early strength agents were mixed into C40 concrete at low temperatures of 5℃and 10℃,respectively,to find out the best type of early strength agent and the optimal ratio in single-mixed experiments,and the optimal ratio of compound early strength agent in double-mixed experiments.The effects of early strength agents on the macroscopic properties of cement mortar were studied by dry shrinkage,fluidity,setting time and strength tests.The effects of early strength agents on the macroscopic properties of cement mortar were studied by X-ray diffraction and X-ray fluorescence.Diffraction technique and X-ray fluorescence spectroscopy were used to analyze the types of hydration products of concrete at different ages.Thermogravimetric analysis was used to determine the percentage of hydration products of concrete at different ages.Scanning electron microscopy was used to observe the types and morphology of hydration products of concrete at different ages,and mercury piezoelectric method was to study the effect of early strength agent on the development of concrete pores.The results of macroscopic and microscopic studies are combined to analyze the early strength effect and mechanism of the compound early strength agent in concrete,and to investigate and evaluate the effect of the compound early strength agent in low temperature environment by using it in common concrete under different conditions.Cementitious material is an important part of concrete,which is related to the workability,durability and strength of concrete.According to research,it is found that the particle size distribution of cementitious material has a certain degree of influence on the early strength of concrete.When the cement particles with diameter distribution are used in combination with the low-temperature early strength agent,the effect on the early strength of concrete under the low-temperature environment.In terms of cementitious materials,the effect of cement particle size on the early strength of concrete was studied.Ultra-fine cement with different particle sizes was selected,and the cement particle size was studied through strength comparison test,X-ray diffraction technology,TG/DSC analysis technology and SEM analysis in a low temperature environment.The distribution affects the macroscopic properties of concrete and the microscopic hydration products.The test results show that the early strength of 0.08%triethanolamine and 2%sodium formate is the best in low temperature environment,and it has a beneficial effect on volume stability,fluidity,and setting time.The C40 concrete mixed with calcium formate and triethanolamine double-mixed early strength agent was cured for18 h,1 d,3 d,7 d under simulated natural conditions at 5℃,and its strength was increased by 700%,540%,11.4%and 10%respectively compared with the control group;curing at 10℃under simulated natural conditions for 18 h,1 d,3 d,and 7 d,the intensity was increased by 991%,400%,19.6%and 11%respectively,compared with the control group.The concrete strength of the period is close to the normal temperature standard curing strength.The addition of low-temperature early strength agent reduces cement fluidity and final setting and initial setting time,and has a good effect on the porosity of early concrete.The mixing of 5～30μm cement and composite early strength agent improves early hydration reaction speed,which makes the early strength of concrete higher.The use of 5～30μm ultra-fine cement in low temperature environment can further improve the early strength of concrete on the basis of the use of composite early strength agent.The increase in strength is the most obvious at 1d,which is increased by 14%at 5°C and 14.8%at 10°C.