Recycling PEMs Back To TLPAs: Is That Possible Notwithstanding RAP Variability?

Porous European mixes, PEMs, are porous asphalts which when compacted have an air void content usually in excess of 20%. PEMs points of strength are reduction of splash and spray, mitigation of outdoor noise, optimization of skid resistance at high speeds in wet conditions. Conversely, PEMs have quite low bearing properties, clogging, variation of volumetrics over the time, variation of noise, texture, friction, and permeability performance over the time. Furthermore, at the end of their lifecycle many issues arise: RAP variability, uncertainties on the potential for high percentage recycling, potential for recycling a surface layer back to a surface layer. Based on the abovementioned facts, objectives and scopes were then focused into the analysis of the feasibility of a two-layer porous asphalt (TLPA) by recycling from-PEM RAP, when highly variable rap stockpiles are involved. The following main issues were addressed: mitigating the clogging and its related consequences (acoustic and drainability performance over the time); preserving traditional (bearing properties, skid resistance) and premium (silentness, drainagebility) performance; recycling high percentages of from-PEM RAP. Materials selection was followed by mixtures production. Traditional and advanced tests on RAP and recycled mixes were carried out. RAP variability was examined and a method for facing its consequences was proposed. Mechanical performance was adequate and environmental compatibility was achieved. Functional performance resulted very promising. Results are encouraging about the possibility of achieving a satisfactory level of surface performance. Practical applications and perspectives in rehabilitation, maintenance, and research are outlined.