Research On Technical Of Industrial Waste Gypsum Impedance Semi-Rigid Base Cracking

Since the reform and opening up,China's economy has developed rapidly,and highway traffic has entered a period of rapid development.Especially for high-grade highways,traffic mileage,traffic volume and heavy vehicles have rapidly increased,placing ever-increasing demands on highway materials.In order to better adapt to the rapid development of highway traffic,semi-rigid base asphalt pavement is widely used in high-grade highway,and gradually becomes the main structure of the base.The semi-rigid base layer has a certain plate body,high rigidity,strong bearing capacity,good load diffusion capacity and good water stability,plays a major bearing role in the asphalt pavement,guarantees the stability of the base layer,but the semi-rigid base also has its fatal shortcomings-shrinkage cracking and the resulting reflective cracks in the asphalt surface,which lead to the structural damage of the pavement,and affect the road performance and service life of the asphalt pavement.At present,the method of preventing and controlling the cracking of semi rigid base is mainly to optimize the design of gradation,limit the amount of cement,add the crack resistance layer and control the quality of the construction,but the effect is not ideal.On the basis of "Study on the cracking resistance mechanism and application of semi-rigid base which mixed with titanium gypsum(2013A16-05)" in Shandong province traffic science and technology innovation project,we start with the shrinkage cracking mechanism of the semi-rigid base,and add a certain proportion of industrial waste gypsum and fly ash in the cement stabilized macadam.The two will react with the cement to produce ettringite expansive body,which counteract the initial shrinkage of the semi-rigid base and control the cracking of the semi-rigid base.Based on the above theoretical basis,we have designed the blending ratio of the three materials,and made corresponding tests according to the proportion of mixing.First,the formation law of the ettringite expansion was analyzed by the composite cementitious material test and scanning electron microscope(SEM),and the deformation law of cement stabilized macadam was determined by the dry shrinkage and temperature shrinkage test.Subsequently,determined the the change rule of strength and durability of cement stabilized macadam through the road performance test.Finally,setting up a small test section to verify the results of indoor tests.Through comprehensive analysis,it is concluded that adding industrial waste gypsum will reduce the strength,modulus and fatigue performance of semi-rigid base to a certain extent,but it can effectively improve the problem of shrinkage and cracking of semi-rigid base,prolong the overall working time of semi-rigid base,improve the road performance and service life of asphalt pavement.Considering the deformation and road performance of the semi-rigid base,the optimum mixing ratio of cement,industrial waste gypsum and fly ash is 1:0.2:0.3.