DEVELOPMENT OF LABORATORY AND FIELD PERFORMANCE TESTS FOR CHIP SEAL

Angelique Umutoniwase

doi:10.7273/000004455

Chip seal, also known as bituminous surface treatment (BST) or seal coat, is frequently used as a preventive or reactive maintenance technique for roads. Chip seal often consists of a layer of asphalt binder or emulsion sprayed on the existing pavement followed by a one-stone thick layer of aggregate, followed by compaction, and sweeping. Raveling and bleeding are the two of major distresses that affect the performance of chip seal. Studies have shown that these distresses are related to the embedment depth. Embedment depth is the depth that rock is lodged into a binder and is a key parameter that significantly affects the performance of the chip seal. Currently, embedment depth is evaluated by pulling out the rock from the binder (often by a plier) and visually estimating the percentage of embedment. However, this method is subjective and does not provide accurate and reliable results. In this study, a methodology is developed to estimate the embedment depth or percent embedment of chips based on the unembedded height measured from sand patching or laser texture scanner. In addition, novel methods were developed to quantify the raveling and bleeding performance of chip seal, based on Cantabro test and Hamburg Wheel Tracking tests, respectively. These two methods were then used to evaluate factors that could affect the performance of chip seal, such as emulsion application rate, chip application rate, choke application rate, chip/choke moisture condition, aggregate gradation, emulsion type, etc. The mean profile depth (MPD) and percent embedment in the field are measured with the laser scanner and are used to correlate with the chip seal performance, in terms of raveling and bleeding. The shoulder MPD value of chip seal after sweeping and fog seal should be at a minimum of 0.15" to prevent raveling or bleeding from happening. When the MPD in wheel path drops below 0.05", either raveling or bleeding has occurred. Moreover, long-term performance of chip seal was retrieved from Washington pavement management system (WSPMS). It was found that chip seal greatly reduced the cracking and slowed down the cracking growth when compared to hot mix asphalt overlay. However, no improvement of rutting or international roughness index (IRI) by the chip seal was found.

DEVELOPMENT OF LABORATORY AND FIELD PERFORMANCE TESTS FOR CHIP SEAL

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