Research On Crack Resistance Mechanism And Performance Of Semi-rigid Steel Slag Pavement Subgrade

Semi-rigid base is widely used in asphalt pavement base of high-grade highway in China due to the advantages of high overall strength,good stability and low cost,but the problem of cracks in semi-rigid base is still not solved.As an industrial waste residue,steel slag is a potential excellent road building material.Using steel slag instead of crushed stones as semi-rigid base aggregate can not only reduce the cost,but also turn waste into treasure.However,the high content of f-CaO in steel slag leads to poor volume stability,which is easy to cause structural expansion and cracking when used in engineering,resulting in low utilization rate of steel slag.Therefore,if we can make use of the expansibility of steel slag and reasonably control the content of f-CaO to restrain the shrinkage cracks of the base course,the durability of pavement will be greatly improved.In the current research,the steel slag with different f-CaO content was studied,and the steel slag,instead of crushed stones,were mixed into the cement stabilized crushed stone base to improve the anti-cracking performance of the base on the premise of meeting the basic mechanical properties.The main research contents are as follows:1)The feasibility of using steel slag instead of crushed stones in the base course was analyzed,the control index of steel slag was selected,several steel slags with different fCaO contents were strictly selected and their physical and mechanical properties were examined,focusing on the determination of the expansion rate of steel slag with different f-CaO contents.2)The factors affecting the cracking of cement stabilized crushed stone base were analyzed,and different grades and cement contents were selected to proportion design the ratio of cement stabilized steel slag crushed stone base,and the ratio was optimized by 7-day unconfined compression strength.3)The unconfined compressive strength test,indirect tensile strength test,and compressive resilience modulus test were conducted to study the influence of steel slag with different f-CaO contents on the mechanical properties of the base course under different steel slag content and different particle sizes.4)After analyzing the shrinkage mechanism of the base layer,the drying shrinkage test and temperature shrinkage test were conducted to study the influence of steel slag with different f-CaO content on the shrinkage performance of the base course with the change of the amount of steel slag and the particle size of the mixed steel slag.The research shows that the addition of steel slag can improve the unconfined compressive strength,indirect tensile strength and compressive resilience modulus of the base layer,and the strength of the base layer is the highest when the steel slag content is60% in the early stage of the test,and the steel slag content is 80% in the later stage of the test.When the content of steel slag reaches 80%,the expansion of the steel slag is larger,which causes the internal stress of the base to increase,resulting in a lower base strength;the addition of steel slag It is beneficial to the dry shrinkage performance of the base layer,and the higher the content of f-CaO in the steel slag,the more coarse-grained steel slag is added,the more the dry shrinkage coefficient of the base layer decreases,but the content of f-CaO in the steel slag 3 is too high with the addition of the steel slag.The base layer has a tendency to expand in the later stage of the test with the increase of the amount of steel slag;the addition of steel slag will increase the temperature shrinkage coefficient of the base layer,and the higher the content of f-CaO in the steel slag,the higher the content of steel slag,the higher the temperature shrinkage coefficient of the base layer,and the easier the base layer to produce temperature shrinkage.crack.In the case of using steel slag as much as possible,this study believes that the steel slag 2 with f-CaO content of2.20% is mixed with coarse-grained steel slag under 80% steel slag content for the best mechanical properties and shrinkage performance of the base.