Study On Strengthening Treatment And Application Of Cement Stabilized Aggregate Milling Material

In recent years,China's highway construction has gradually changed from focusing on new road construction to paying equal attention to both new road construction and old road maintenance,overhaul and medium repair.A large number of roads need to be overhauled or refurbished each year,and a large amount of cement stabilized aggregate milling material will be produced.Milling material of cement stabilized aggregate are generally discarded or used as fillers to fill the roadbed,or used in road sub-base or low-grade road base.Whether it is abandoned or used as a filler,the value of cement stabilized aggregate milling material is low.However,the application of untreated milling material directly to low-grade road sub-base or base has many problems,such as great variability of material,difficult quality control,many hidden dangers of pavement structure and long-term performance guarantee.Therefore,how to make full use of milling material and ensure the good performance of the base material has become the key point for the recovery and utilization of milling material.In this paper,the density,crushing value,water absorption and needle flake content of cement stabilized aggregate milling material are measured.The surface morphology of milling material is observed by SEM scanning,and the main composition of surface material is analyzed by EDS.The difference between milling material and natural aggregate is obtained,that is,the surface of milling material is covered with a layer of cement mortar.The strengthening test includes physical and chemical strengthening.The physical strengthening is mechanical grinding.The relationship between milling material performance index and grinding work is obtained by parallel experimental design of the number of grinding bodies and grinding times.Chemical strengthening mainly includes acid treatment,silane coupling agent and sodium silicate treatment.Through orthogonal test,the effects of acid concentration,soaking time and types of acid on the strengthening effect of milling material were obtained.The optimum solution concentration of silane coupling agent and sodium silicate for milling material was obtained by controlling the solution concentration.The results show that in mechanical grinding,the crushing value and water absorption of milling material show a trend of decreasing first and then increasing with the increase of grinding work,and there is the best grinding work.In the acid treatment test,the acid concentration has the greatest influence on the acid treatment effect,followed by the acid type,and the influence of the soaking time is small.The best treatment condition is 0.3 mol/L hydrochloric acid(strong acid)soak for 12 h.The water absorption and crushing value of milling material decrease first and then stabilize with the increase of silane coupling agent concentration.When the concentration of silane coupling agent is 2%,the treatment effect is better.The water absorption and crushing value of milling material decrease with the increase of sodium silicate concentration.When the concentration of sodium silicate is 40%,the treatment effect of sodium silicate is better.Comparing the four strengthening methods,it can be concluded that the mechanical grinding can improve the milling material properties better.When the strengthening treatment parameters are 8 steel balls and 200 revolutions,the crushing value of milling material decreases from 32.7% to 24.2%,and the water absorption rate decreases from 5.04% to 1.12%.In this paper,Milling material is treated by mechanical grinding with strengthening treatment parameters of 8 steel balls and 200 revolutions.The treated milling material is used as recycled aggregate in the experimental study on the properties of cement stabilized recycled aggregate.The experimental cement dosage is 4%,5%,6%,and the recycled aggregate dosage is 0%,20%,40%,60%,80%,100% respectively.Parallel experimental design is carried out to study and analyze the relationship between the compressive strength,splitting strength,compressive rebound modulus,drying shrinkage of cement stabilized recycled aggregate and cement dosage,recycled aggregate dosage.The results show that the strength,crack resistance of cement stabilized recycled aggregate increase with the increase of cement dosage and decrease with the increase of recycled aggregate dosage.When the cement dosage is 6%,the aggregates are all recycled aggregates,and the 7d unconfined compressive strength of the mixture still meets strength requirement of highway and first-class highway base under medium or light traffic loads and in secondary and below road base under heavy traffic loads.