Experimental Study On Spontaneous Heating Mix Ratio Of Prestressed Passage Grouting Material In Plateau Area

With the continuous progress of social economy,the requirements for existing and new projects are getting higher and higher,and ordinary materials have been difficult to meet the requirements of special projects.For example,bridges and other projects require some parts to obtain higher strength performance in a short time under negative temperature environment to prevent special damage caused by negative temperature environment.Based on the research background of prestressing grouting process in the negative temperature environment of Pubarong Bridge,this paper chooses sulphoaluminate cement combined with spontaneous heating material to prepare a kind of grouting material which can depend on its own heat source to raise the temperature of slurry under the negative temperature environment,thus speeding up hydration reaction and quickly obtaining the strength of grouting material.The grouting material has the characteristics of moderate setting time,high early strength and good frost resistance under negative temperature environment.It is suitable for the project of prestressing grouting under negative temperature environment.Through reading domestic and foreign literatures,this paper has a deep understanding of post-tensioned prestressing grouting technology.Based on the analysis of the properties of common grouting materials,the materials which can rapidly solidify and spontaneously heat under negative temperature environment are selected and the feasibility analysis is carried out.According to the factors of water cement ratio,water reducing agent,early strength agent,retarder and horizontal orthogonal test,the initial fluidity,30 min fluidity,initial setting time,flexural strength and compressive strength of grouting materials are obtained.Strength performance indicators are ranked as the basis of adjusting performance indicators under negative temperature.Adding silica fume to adjust the fluidity and strength index of grout to achieve the optimal effect.Calcium oxide and nano-silica are used to increase the system temperature and reaction rate of grout under negative temperature environment.At the same time,ordinary calcium oxide is chemically coated to reduce the "agglomeration" effect of calcium oxide,and nano-particles are used to fill the voids to improve the strength of grout.The early performance and durability of negative temperature grout were studied.The results show that the material can still reach 13 MPa in 1D compressive strength and 2 MPa in 1D flexural strength at the extreme temperature of-10℃.The volume of the material will not shrink in negative temperature environment and has the characteristics of micro-expansion.The material has excellent sulfate resistance.It is cured in negative temperature environment for 3 days and then immersed in saturated sulfate solution for 102 days.The minimum compressive strength of immersion section can still exceed 60 MPa,which is only 9.3% lower than that of exposed section.When the material is injected into the pore model at-10 C,the maximum expansion stress is 4.7 MPa near 2 h,which increases with the decrease of external temperature,but does not cause cracking of concrete around the pre-stressed pore.