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EVALUATION OF THE CAPE SEAL PROCESS AS A PAVEMENT REHABILITATION ALTERNATIVE

A 1-year research project was conducted to evaluate the Cape seal process as a pavement rehabilitation technique. During the course of this research project, most of the Cape seal projects that have been constructed within the state were visited as part of the evaluation. Projects documented during the visits included both successes and failures. Of the failed projects, most of the problems could be attributed to the underlying chip seal failing as a result of aggregate loss or insufficient chip seal-pavement bond. As part of this investigation, the researchers performed a series of laboratory tests. Specifically, permeability tests, shear tests, and loaded wheel tests were performed on laboratory-made Cape seal specimens. Permeability tests were also conducted using field cores. The results indicated that the permeability of microsurfacing does not exceed that of typical hot mix asphalt overlays. If properly constructed, microsurfacing can result in a permeability lower than that associated with coarse hot mix asphalt concrete mixes. The shear tests were performed in a repeated mode at 58 deg C, a typical hot pavement temperature for Texas. The tests indicated that debonding failure most often occurs at the interface of the chip seal and the underlying pavement, rather than at the interface of the chip seal and the microsurfacing. However, partial movement of the microsurfacing and the chip seal - though not as severe as the first mode discussed - could be observed. Excellent performance was observed for microsurfacing specimens under loaded-wheel tests. However, specimens prepared as Cape seals failed after a limited number of cycles. This finding indicates that the test setup is not well suited for the chip seal/microsurfacing combination (i.e., it is not necessarily indicative of a bad mixture). This is the case because of the very smooth frictionless surface of the specimen mounting plate under the chip seal. However, the test underscores the significance of a good bond between the chip seal and the underlying layer. Based on the field observations and the laboratory results, a set of guidelines are provided that can improve Cape seal performance.