Study On Optimization Design And Performance Of SMA Using Steel Slag And Reclaimed Asphalt Pavement

Stone mastic asphalt(SMA)is the most widely used surface layer material in China.However,SMA has consistently been expensive due to the scarcity of high-quality stones such as basalt.On the other hand,there is an abundance of steel slag and reclaimed asphalt pavement(RAP)in China,and steel slag exhibits excellent strength and abrasion performance.Studies have shown that steel slag can replace basalt aggregates in SMA.However,due to steel slag’s porous nature,the asphalt needed is increased.In contrast,fine RAP contains much asphalt,which can be used in SMA to partially fill voids in steel slag and reduce the need for new asphalt and fine aggregates.In this way,steel slag and RAP can be fully utilized in SMA,reducing engineering costs,saving resources,and preserving the environment at the same time.Currently,steel slag and RAP in SMA are designed mainly through empirical methods without further optimizing methods,performance evaluations,or comparative analyses.Therefore,further in-depth research is needed.According to a survey and analysis of domestic and foreign literature,this article tested and evaluated selected materials such as steel slag,RAP,and aggregates and found that all materials met standard laboratory requirements.Due to the porous nature of steel slag,a method for determining the effective relative density of steel slag aggregate was proposed.Subsequently,the VCA variation rules for steel slag coarse aggregate,basalt coarse aggregate,and steel slag+basalt coarse aggregate were studied through coarse aggregate compaction tests,and three multivariate coarse aggregate VCA prediction models were established.The application of the prediction models showed that the reverse S-shaped gradation had a smaller VCA value,the forward S-shaped gradation had a larger VCA value for the coarse aggregate,and the coarse aggregate with the theoretical maximum density line as the gradation was between the two.Moreover,the differences in VCA between coarse aggregates under the same gradation curve were also investigated.This research has provided a foundation and basis for the gradation optimization design of different aggregate types.In addition,based on previous research of the research group,a simplified analytical formula was developed through theoretical analysis.This formula described the relationship between the skeleton dense grading coarse-fine boundary particle size(or sieve)passing rate and VCA.Moreover,a design method for grading optimization for the SMA13 mixture has been proposed based on the concept that overall mineral grading is a combination of coarse aggregate grading and fine aggregate grading.This method was used to carry out the grading optimization design and determine the optimal asphalt-aggregate ratio for three different types of SMA13 mixtures,namely,steel slag+RAP SMA13(SR-SMA13),steel slag+basalt SMA13(BS-SMA13),and basalt SMA13(B-SMA13).The optimized gradings for each type of SMA13 were obtained.Next.SR-SMA13 was systematically studied and compared with BS-SMA13 and B-SMA13 regarding basic performance,creep characteristics at low temperatures,skid resistance,and fatigue performance.The experimental results showed that the dynamic stability of the optimized mixtures for all types of SMA13 was maximum,with the SR-SMA13 having the highest dynamic stability,followed by the BS-SMA13 and the B-SMA13,proving the superiority of the proposed optimization design method.The water stability and skid resistance performance were in the order of BS-SMA13>B-SMA13>SR-SMA13,with SR-SMA13 having relatively poor water stability performance.However,its residual stability and freeze-thaw splitting strength met the requirements of the specifications,and the skid resistance performance of SR-SMA13 was only slightly inferior to that of basalt SMA13.The order of low-temperature performance was BS-SMA13>SR-SMA13>B-SMA13,and the order of fatigue performance was B-SMA13>BS-SMA13>SR-SMA13.Finally,the performance of various SMA13 types was comprehensively evaluated and a brief economic analysis was conducted.Based on the results,the SR-SMA13 has excellent comprehensive road performance and performs better at high and low temperatures than the commonly used basalt-SMA13.Additionally,it saves approximately 23.0%on materials per kilometer,which results in significant economic benefits.This study can provide a theoretical basis and technical reference for promoting and applying steel slag and reclaimed asphalt pavement(RAP)in SMA.