Research And Application Of Magnesium Oxychloride Cement Concrete In Road Engineering

The climate in western region in China is characterized by arid-cold,great temperature difference,long time with low temperature,great water evaporation,which is unfavorable to hydration process and early strength development of cement concrete.And the common cement concrete pavement is prone to shrinkage cracking and frost damage with harsh weather.Magnesium oxychloride cement is a kind of air hardening condensed material,which is condensed and hardened by hydrated magnesium oxychloride under alkaline condition.It has the advantages of high coagulation hardening,high early strength,simple curing and durable.With the rapidly exploitation of salt lake in western region,the environment is polluted by large amount brine.In view of this,this paper systematically studies the key technologies of design and application of magnesium oxychloride cement in the road engineering instead of traditional Portland cement.Based on the mechanism of hydration reaction of magnesium oxychloride cement and the theory of phase transition,the basic materials of magnesium oxychloride cement are selected,the proper composition is determined,and the mechanical properties and water resistance indexes are proposed.Four types of composite magnesium oxychloride cements are developed,including fly ash magnesium chloride cement,limestone powder magnesium chloride cement,dolomite powder magnesium cement and water-resistant magnesium cement.The impact of admixtures on magnesium oxychloride cement is studied,reasonable method,content and indexes of mixing are also determined.The low temperature compatibility test method was used to evaluate the low temperature adaptability of the magnesium chloride cement.Aiming at the climatic characteristics of Qinghai Province,this paper focuses on the influence of the key parameters of the magnesium oxychloride cement concrete on the working performance and mechanical properties after replacing the ordinary Portland cement,and determines the proper range of the key parameters of the concrete.In order to solve the problems of high strength and easy cracking of magnesium oxychloride cement concrete,the strengthening and toughening are carried out by means of fiber reinforcement technology.Based on the existing water reducer which isn't meet the needs of concrete construction,retarded polycarboxylic water reducer was developed by molecular structure design technology.With design framework of Portland cement concrete,the paper puts forward the technical requirements and composition design method of the magnesium chloride cement concrete material based on the requirements of workability,mechanical properties and water resistance,and verifies the road performance.According to the analysis of the water resistance of the magnesium chloride cement concrete and the distribution of the wet coefficient in Qinghai Province,water resistance indexes of the magnesium chloride cement concrete in different climate areas of Qinghai Province are proposed.The paper also puts forward the preparation technology of magnesium oxychloride cement concrete with the composition characteristics of magnesium oxychloride cement concrete and the preparation technology of ordinary cement concrete.Based on the practice of demonstration engineering,with determined technical measures,including technology process,time control and concrete retarding materials,and combined with the optimization of existing cement concrete construction process,the construction technology of magnesium oxychloride cement concrete pavement and culvert is finally formed.In this paper,the effect of 2 years operation is tracked,and the economic benefits are evaluated with performance-cost ratio.