Search

Road agencies are increasingly incorporating performance-related specifications (PRS) in construction contracts to specify quality in terms of parameters related to desired long-term performance. PRS provides a means to account for the value lost or gained by the variances of the designed performance parameters from the specified target values. The use of PRS for pavement preservation treatments (e.g. chip seals) has been generally non-existent. The objective of this paper is to establish a step-by-step procedure for formulating chip seals PRS guidelines. The percent embedment (PE) of aggregates into emulsified asphalt was selected as the acceptance quality characteristic (AQC). Chip seal specimens with varying percent embedment levels were prepared using aggregate and emulsion types in Michigan. Aggregate loss and bleeding were selected as performance indicators. Laboratory tests were conducted to compute PE, aggregate loss and bleeding for the chip seal specimens. Relationships were developed between quality measures, service life, and pay factors. The expected pay curves were developed based on quality measures and were used to establish acceptable and unacceptable quality levels. The pay factors were evaluated to ensure fair payments for the quality of work produced. The work presented will provide the general guidelines for developing PRS for chip seal projects. [ABSTRACT FROM AUTHOR]

Chip seals are mostly designed on the basis of empirical methods, which fail to account for the effect of microstructural factors (i.e. percent embedment of aggregates and aggregate shape) on chip seal performance. Two-dimensional (2-D) viscoelastic Finite Element (FE) analyses coupled with laboratory-based sweep tests as per ASTM D7000 were performed to evaluate the impact of such factors on the performance of chip seals. The factors considered in this study were percent embedment, two different aggregate shapes (cubical and flaky), temperature, and aggregate application rates. The 2-D FE models were developed from actual images of the chip seal specimens with cubical and flaky aggregates. The analyses revealed that the maximum tensile strain at the aggregate-binder interface for the chip seals with cubical aggregates follows an asymptotic trend after the percent embedment level of 50%. The trend was not evident in the case of the chip seals with flaky aggregates. The FE simulations also indicated that the chip seals with cubical aggregates outperformed the chip seals with flaky aggregates, which was also observed through the laboratory tests. Furthermore, it was determined that excess aggregate application rates, i.e. higher than that of the optimum design rates, are detrimental to the chip seal performance. [ABSTRACT FROM AUTHOR]

• Percent Embedment and aggregate orientation: important microstructure parameters. • Chip seal microstructure analyzed through image processing methodology. • Adding excessive aggregates detrimental to chip seal microstructure and performance. Relationship between the internal microstructure of chip seals (e.g., the percent embedment, aggregate shape and orientation) and their performance is not well understood. In an effort to improve understanding of the relationship between binder/aggregate application rates and the microstructure of chip seals, image processing and analysis techniques were developed to quantify percent embedment (PE) and aggregate orientation. A new parameter called "Effective Percent Embedment" was introduced for improved quantification of the effect of application rates on aggregate loss during the sweep test. It was observed that aggregates orient on their flattest side as the binder application rate increases and aggregate application rate decreases. These results are expected to serve as a basis for performance-based chip seal design guidelines focusing on compacted chip seal aggregate structure. [ABSTRACT FROM AUTHOR]