MONITORING ASPHALT CONCRETE PERFORMANCE AT HIGH ALTITUDES IN THE PERUVIAN ANDES

Thermal cracking in Peru usually occurs in roads with elevations higher than 3,700 meters above sea level (MASL). Asphalt pavements at elevations between 3,700 and 4,300 MASL usually develop thermal cracking, but this type of distress is more severe at even higher altitudes, especially with the combined effects of the large amount of solar radiation, daily temperature cycle, and relatively large amounts of precipitation. The asphalt concrete (AC) thickness of 8 to 12 cm in the La Oroya-Cerro de Pasco Road was designed to carry traffic of approximately 1,000 trucks per day. When the asphalt mixture was designed and constructed according to standard practice and specifications, severe longitudinal cracking appeared 5 to 8 months after completion of construction. In order to reduce this thermal cracking, the following material characteristics and construction procedures were analyzed: (a) engineering properties of the top crude and the asphalt cement; (b) engineering properties of aggregates, particularly those used for fines and filler materials; (c) optimum heating temperature of the asphalt aggregates before mixing; (d) minimum air temperature at which AC can be laid and compacted; (e) measures taken to protect the prime coat and base course; (f) types of asphalt cements used and their respective engineering properties; (g) tensile strength and workability characteristics of the AC mixture; and (h) types and quantities of additives. Preliminary conclusions of specification modification have been adopted by the Peruvian road authorities to improve asphalt performance at high altitudes.