Study Of Mechanism And Technology Of Rapid Repair Of Frost Damage Ballastless Track Based On Interface Treatment Of Magnesium Phosphate Cement

The concrete base plate is an important part of the high-iron plate type ballastless track structure,which will be damaged first in the severe cold area due to freezing and thawing damage.The concrete of the base plate will cause the internal aggregate and cement stone to be powdered,peeled off and exposed the steel,when it is frozen.There is a hidden danger of driving safety,resulting in economic loss and casualties.The skylights operation time of the high-speed railway line is required to be repaired within 4 hours after the early morning,so the key to solve this problem is preparation of repair materials with good durability,low-temperature fast operation,convenient construction and low-cost.Generally,the high-speed railway base repair cycle is repaired every half a year.The fundamental problem is that the interface is not properly handled.In this paper,the characteristics of high early strength and partial neutrality of magnesium phosphate cement are used as concrete interface treatment materials to reduce or eliminate the phenomena of CH enrichment,orientation and crystallization at the interface to solve the defects in the interface transition zone,and improve the old concrete repair efficiency by chemical bonding.In this way,the repair cycle is extended,the maintenance cost of high-speed rail is reduced,and the operational safety is guaranteed.The main research results obtained are as follows:The best match was obtained through the single factor analysis of magnesium phosphate cement M:P ratio,borax dosage,water-solid ratio,sodium gluconate dosage,cellulose ether content,fly ash content,silica fume content.The mechanism was studied by hydration heat analysis,XRD and SEM.Magnesium phosphate cement-based concrete interface treatment material is prepared with the setting time of 26 min and the fluidity of 233 mm,which compressive strengths and tensile bond strengths reached to 50.1/2.5 and 63.3/3.4 and 70.5/4.3 MPa after l d,7 d and 28 d,respectively.The repairing material was selected from sulphate aluminate cement and Portland cement with 8.5:1.5 and blended with 1%gypsum.First of all,through the single factor test and analysis of the repairing materials as retarders,superplasticizers,fine stone powders,silica fumes and early strength agents.Then select the three factors and three levels of orthogonal test for the factors,which had a great influence on performance,to obtain the best formulation of low temperature fast repair material.The low temperature fast repair materials is prepared with the setting of 50 min,flexural strengths and compression strengths reach to 5.48/35.0 MPa,7.67/51.5 MPa,8.39/55.7 MPa,9.61/60.1 MPa after 2 h,d,7 d,28 d respectively,and tensile bond strength reachs to 2.33 MPa after 28 d.25 freeze-thaw cycles were carried out on the repaired concrete with and without magnesium phosphate cement-based interface materials,which tensile bond strength loss rate was 13.75%and 38.19%,respectively.After the concrete substrate was treated by the interface treatment material,the loss rate of the tensile bond strength of the repair material after 25 cycles of freezing and thawing could be reduced.The SEM-EDS analysis show that the interface treatment material will form a calcium phosphate gel at the interface of the matrix,which can effectively reduc the CH enrichment at the interface of the concrete.and the width of the interface transition zone leading to improve the repair bonding effect and repair durability.