Rehabilitation of Urban Streets Using Engineered Asphalt Emulsion-Cement Full Depth Strengthening Systems

Many urban centres across Canada are experiencing significant deterioration of their streets, particularly aged streets constructed on weak subgrade materials that were not originally designed for modern traffic load conditions. Benefits of cold in-place recycling on urban service roads include reduced consumption of new source aggregates, reduced rehabilitation costs, and significant reductions in weather exposure during construction. Additional benefits of cold in-place recycling include significant reduction in load induced damages to surrounding streets, and reduced total construction energy required to rehabilitate streets, which reduces vehicle emissions released in urban environments associated with street rehabilitation projects. This paper demonstrates the use of mechanistic-climatic laboratory characterization applied to the rehabilitation of two cold in-place recycled City of Regina streets. The City of Regina streets employed in this study were chosen as typical urban pavements requiring structural rehabilitation. This study presents the material characterization results of the composite recycled surfacing and granular base materials strengthened with an engineered blend of cement and asphalt emulsion. The mechanistic laboratory characterization was performed across the spectrum of multiaxial stress states and load frequencies typical of urban field state conditions. The a priori ground penetrating radar profiles were used to quantify the spatial quantities of in situ recyclable composite surfacing and granular materials. Based on the ground penetrating radar profiles, significant variation in recyclable granular layer thickness was identified across both pavement structures. The thickness information proved critical in the full depth recycling design process to accurately quantify the reclamation thickness, as well as material stabilization design. This research also presents the use of structural asset management performance measurements taken before and after strengthening of the Regina pilot test sites. The non-destructive falling weight deflection structural asset measurements performed in this study demonstrated a significant increase in structural asset value as a result of the full depth cement-asphalt emulsion strengthening systems employed. The field structural responses concurred with the increase in mechanistic laboratory material properties obtained in the material design phase of this project. This research also demonstrated cold in-place recycling to be similar in cost to conventional full depth remove and replace street rehabilitation systems. It is believed that the cost to perform cold in-place recycling and full depth strengthening will decrease over time as the technology becomes more reliable and more commonly deployed, whereas the costs of conventional street rehabilitation are believed to continue to increase over time. Additional holistic benefits of cold in-place recycling include reduced construction time, and therefore interruption to homeowners; reduced emissions and energy consumption; as well as recycling of in situ materials and conservation of aggregate sources in the Regina area. KEY WORDS: asphalt emulsion, urban road stabilization, cold in-place recycling