Long-term performance of recycled asphalt mixtures containing high RAP and RAS

The application of reclaimed asphalt pavement(RAP)and reclaimed asphalt shingles(RAS)on asphalt pavement can reduce the asphalt paving cost,conserve energy and protect the environment.However,the use of high contents of RAP and RAS in asphalt pavement may lead to durability issues,especially the fatigue cracking and thermal cracking.It is necessary to conduct a series of analyses on asphalt mixtures containing high RAP and RAS,and seek methods to enhance their long-term performance.This paper provides a comprehensive over-view of the long-term performance of recycled asphalt mixtures containing high contents of RAP and RAS.The findings in this research show that rutting resistance of high recycled asphalt mixtures is not a concern,whereas their resistance to fatigue and thermal cracking is not conclusive.Recycling agents can be used to improve the thermal cracking resistance of high recycled asphalt mixtures.An optimum decision on recycling agents will improve the durability properties of high recycled asphalt mixtures.It is recommended that to use a balanced mixture design approach with testing of the blended asphalt binders will provide better understanding of long-term performance of recycled asphalt mixtures containing high RAP and RAS.

Cement-fly Ash Stabilization of Cold In-place Recycled (CIR) Asphalt Pavement Mixtures for Road Bases or Subbases

For lack of laboratory and field performance data on stabilization of reclaimed asphalt pavement （RAP） aggregate and stabilized soil （S） for road bases and subbases construction, the influences of RAP/S ratio, cement and fly ash content, modifying agent （MA） on the compact, unconfined compressive strength, indirect tensile strength and water stability of the CIR mixtures were investigated. The experimental results showed that the maximum dry density and the optimum moisture content of the mixture changed significantly with the RAP/S ratio and cement-fly ash content. Unconfined compressive strength, indirect tensile strength and water stability were improved significantly by the addition of MA, and the water stability was improved by nearly 20% on average. Scanning electron microscopy（SEM） images indicated that MA accelerated the hydration of cement-fly ash system. Needle-like AFt and fibrous C-S-H gel were observed in the mixtures, which resulted in the cementation effect among the CIR mixture particles and a more compact microstructure. All these could be the cause of high strength of the CIR mixtures with MA.

On the Use of Recycled Asphalt and Trinidad Lake Asphalt(TLA)for the Preparation of High Modulus Asphalt Concrete

Rutting of asphalt pavement occurs earlier and is more serious under the increasingly heavy traffic load conditions that can be found in subtropical monsoon climate regions.High modulus asphalt concrete(HMAC)with excellent anti-rutting and anti-fatigue properties is generally used to mitigate this issue.Given the relatively high cost of the additives used in this type of asphalt,in this study the feasibility of using recycled asphalt mixture(RAP)and Trinidad lake asphalt(TLA)for the preparation of HMAC is considered.The mineral composition of the RAP is first analyzed,then the TLA modified asphalt with different levels of RAP content is used to assess the effect of RAP on the performance of the mixture.Finally,the high-temperature rheological properties of extracted bitumen and the adhesion characteristic between mineral and bitumen are analyzed.The results show that after RAP combustion,the yellowish and greyish minerals display different alkalinity values,while the greyish mineral exhibits an improved ability to combine with bitumen.Thus,RAP can significantly enhance the high-temperature rutting resistance of TLA modified asphalt mixtures.The aged bitumen in RAP makes the mixed binder harder and improves its rheological properties at high temperatures.