The long-term re-cementation of recycled concrete aggregate in road sub-base and its impacts on pavement performance

Recycled concrete aggregate (RCA) can be used as a pavement sub-base or base material, but the re-cementation of RCA raises concerns about its engineering properties and its impacts on pavement performance. This study investigated the long-term re-cementation phenomenon of RCA that has served for 13 years in road pavements, and the effects of this phenomenon on the RCA's physical, chemical and mechanical properties. Subsequently, the study also examined the impacts of RCA re-cementation on pavement response and performance using a novel random modulus field technique. It was found that the RCA modulus rises roughly in a power law with the increase of service time, indicating a continuous re-cementation process of this material. The re-cemented RCA particle has a porosity of about 7.8 %, anticipated to be lower than that of new unbound RCA. The net-shaped structures were found near the air voids, which is caused by the newly generated cementation crystals in re-cementation. The new mortar has a lower hardness value than that of the ordinary concrete mortar, but the overall strength of the re-cemented RCA is comparable to that of the cement-treated base. In a pavement structure, re-cementation decreases asphalt layer strain and subgrade strain, helping lower the bottom-up cracking and permanent deformation. However, severe re-cementation increases the risk of reflective cracking. In addition, large-size re-cemented particles increase the variations of pavement responses and thus bring additional uncertainties to pavement performance predictions. To mitigate this concern, limiting the fine aggregate (<0.6 mm) content in RCA is an effective solution since this component is closely related to re-cementation.