COLD RECYCLING OF ASPHALT PAVEMENTS ON LOW-VOLUME ROADS

Abstract

Cold recycling can play a major role in the upgrade of secondary low-volume roads. Many farm-to-market roads exist in Pennsylvania that are good candidates for cold recycling with emulsified asphalt. Many roads have been built up over the years with open-graded cold mixtures (travel plant mix) or layer after layer of seal coats and surface treatments. These roads are also heavily patched. It is necessary to obtain a uniform, strengthened base course if these so-called pancake roads are to be upgraded and widened at the same time. Cold recycling is a good upgrading strategy to accomplish this. The Pennsylvania Department of Transportation had completed about 90 cold-mix recycling projects by the end of 1985. All three modes of cold-mix recycling have been attempted: central plant mixing, mobile plant mixing, and in-place mixing. The Pennsylvania Department of Transportation's guidelines for selecting suitable candidate projects and standard specifications for a cold recycled base course are provided. The current mix design procedures, which are at a developmental stage, are also provided. The optimum emulsion content is selected by considering (a) bulk specific gravity of the compacted specimen, (b) initial resilient modulus, and (c) resilient modulus after vacuum saturation with water. Case histories are included of some projects that were completed by use of mobile mixing plant and in-place mixing in which different equipment was used. Experience in cold recycling indicates a need for obtaining optimum moisture content in the reclaimed asphalt pavement material so that the emulsified asphalt can be dispersed effectively in the mix. The recycled mixtures are usually susceptible to damage from moisture intrusion and abrasion by traffic. It is therefore necessary to cover the mixtures with at least two applications of a surface treatment to avoid ravelling and potholing.