Ten-Year Performance Review of In Situ Hot-Mix Recycling in Ontario

In today’s climate of environmental and economic constraints coupled with a diminishing aggregate supply, in situ hot-mix recycling provides an important alternative to conventional pavement rehabilitation. In situ hot-mix recycling, including hot in-place recycling (HIR) and cold inplace recycling (CIR), is proving to be an economical rehabilitation technique that conserves granular materials and energy and results in zero waste. The Ministry of Transportation and the Regional Municipality of Ottawa–Carleton have rehabilitated in excess of 80 projects using in situ hot-mix recycling techniques since 1987. The HIR process is suitable for roadways exhibiting a variety of surficial nonstructural distresses. The HIR process involves heating the existing pavement surface, scarifying, adding rejuvenator, fine aggregates, or beneficiating hot-mix (admixture) as required, mixing, reprofiling, and compacting this hot mixture in a continuous operation. CIR is suitable for roadways with moderate to severe distresses where reflection cracking is a concern. CIR involves milling the existing pavement, screening for oversize, addition of asphalt emulsion, and mixing; then this cold renewed material is spread, reprofiled, and compacted on the roadway in one continuous operation. An overview on the design, construction procedures, test results, and pavement performance to date of in situ recycling is presented. Ten years of performance monitoring of the in situ recycling projects has resulted in the evolution of design strategies and performance specifications. Their effectiveness, limitations, and future utility on highway contracts are discussed.