Long-term Performance Of Cement-stabilized Reclaimed Asphalt Pavement(RAP) Base

In recent years,a large number of highways need to be rebuilt or maintained while there are about 2 million tons of Reclaimed Asphalt Pavement(RAP)produced annually in the process of maintenance and reconstruction.If these waste asphalt mixtures are treated by simple pit burying and stacking,it is bound to be a great waste of resources,at the same time,it will have a great negative impact on the protection of the natural environment.Therefore,how to effectively utilize these waste asphalt mixtures has become an urgent problem and task faced by road researchers in recent years.The goal of this study is to develop the cement-stabilized RAP as the base layer of expressway,exploring the strength and long-term durability of the cement-stabilized RAP,especially the influence of the content of RAP on its strength and durability.The following experiments were carried out:(1)The performances of raw materials used for the cement-stabilized RAP were tested,including sieve test of new aggregate,apparent density test,water absorption test.In addition,the extraction test of RAP and gradation test of RAP aggregate were performed;(2)Four RAP dosages of 0%,20%,40% and 60% and four cement contents of 2.5%,3%,3.5% and 4% were selected for compaction tests;(3)Unconfined compressive strength tests of cement-stabilized RAP for 7 days and 28 days were carried out with RAP dosage and cement content as variables,respectively.The relationships between unconfined compressive strength and one of the RAP content and cement content was analyzed.respectively.(4)In addition,the shrinkage,frost resistance and water stability of cement stabilized RAP were discussed as long-term performance.The results were as follows:(1)The fine aggregate content in the extracted waste asphalt mixture increases.After the long-term effect of vehicle load and milling process,mineral aggregate has been broken and refined,and crushed stone coarse aggregate needs to be added to meet the standard requirements of dense skeleton gradation.(2)With the increase of cement content,the optimum water content and maximum dry density of the mixture with the same RAP content increase gradually;with the increase of RAP content,the optimum water content and maximum dry density of the mixture with the same cement content decrease gradually.(3)The results of unconfined compressive strength of cement-stabilized RAP for 7 and 28 days are consistent,that is,the unconfined compressive strength of mixtures with different RAP content increases with the increase of cement content;for mixtures with the same cement content,the compressive strength increases first and then decreases with the increase of RAP content.(4)According to thechange of water loss rate of cement-stabilized RAP,it can be found that the water loss rate increased rapidly in the first 7 days,accounting for 60%~70% of the total water loss;the water loss rate increased slowly in the middle 7-20 days,accounting for 20%~30% of the total water loss rate;after 20 days,the water loss rate tended to be stable,accounting for about 5% of the total.(5)The cement-stabilized RAP has better frost resistance than those without RAP,and the mass loss rate was less than 5% after five freeze-thaw cycles.The higher the cement content,the better the frost resistance of cement stabilized RAP.(6)Water stability test showed that cement stabilized RAP has good water stability.