Dailey, Jay

This poster was created to accompany Report 2017-25, "Comprehensive Field Evaluation of Asphalt Patching Methods and Development of Simple Decision Trees and a Best Practices Manual."

This brochure was created to accompany Report 2017-25, "Comprehensive Field Evaluation of Asphalt Patching Methods and Development of Simple Decision Trees and a Best Practices Manual."

Asphalt mixtures are commonly specified using volumetric controls in combination with aggregate gradation limits; like most transportation agencies; MnDOT also uses this approach. Since 2010 onward; several asphalt paving projects for MnDOT have been constructed using coarser asphalt mixtures that are manufactured with lower total asphalt binder contents. Due to the severe cold climate conditions in Minnesota; there are concerns of premature cracking and inferior durability in asphalt mixtures with lower asphalt binder contents. This research project evaluated 13 low asphalt binder content mixes from 10 actual field projects to determine whether there is potential for poor cracking performance and high permeability. Assessment of field performance indicated an average of 7.75 years of life until 100% transverse cracking level is reached. The pavement structure played a significant factor in controlling the cracking rates. Thin overlays showed almost ten times inferior transverse cracking performance as compared to asphalt wearing courses on full-depth reclamation. Asphalt mixture volumetric factors did not show a statistically significant effect on cracking rates; however; the asphalt binder grade did show a strong effect. Eight out of the 13 coarse asphalt mixtures evaluated in this study have higher permeability than the typical dense graded asphalt mixtures. Performance evaluations using lab measured properties predicted poor thermal cracking performances. No discernable trends were observed between measured or predicted cracking performance and mix volumetric measures. Use of performance tests based on specifications for design and acceptance purposes is reinforced through this study.

The long-term performance of pothole patches largely depends on the selection of the patching method. A number of pothole patching methods are in practice in Minnesota and other nearby states. However; pavement maintenance crews often encounter problems in selecting the most appropriate patching method because proper guidelines are not available. The objective of this project was to investigate the effectiveness of different pavement patching methods and to develop simple decision trees and a best practices manual. The performance of 20 different pothole patches; which were patched with four different types of patching methods and located at five different construction sites; were monitored for approximately two years. Based on the observed performance of the pothole patches considered in this study; two forms of decision trees and a best practices manual have been developed for selecting the most appropriate patching method for a given pothole condition. The developed decision trees can be used to select the patching method based on the location of the pothole (e.g.; along longitudinal joints; localized potholes; etc.); construction season; condition of the pothole; and pothole area and depth. The best practices manual provides guidelines on the selection of patching method; pothole preparation; placement of patching materials; and compaction.

The asphalt mixture design and acceptance procedures for Minnesota Department of Transportation are currently governed primarily by the mixture composition requirements put forth through use of various volumetric measures (such as, air content, asphalt film thickness, aggregate gradation etc.). The asphalt binder has been required to meet performance criteria through the Superpave asphalt binder specifications. This study looked at use of laboratory performance test for asphalt mixtures. The study was conducted in three phases, first phase focused on merging the asphalt mix design records with the pavement performance data to determine effects of mix design parameters on asphalt pavement cracking performance. Second and third phase used a series of field sections across Minnesota to conduct field performance evaluations as well as laboratory tests on field cored samples. The testing for second an third phase of the study focused on using disk-shaped compact tension (DCT) fracture energy test as a laboratory performance test. The findings form he first phase of study indicated that the asphalt binder type as defined by the Superpave performance grade (PG) plays an important role in affecting the field cracking performance, majority of mixture design parameters did not indicate a consistent effect on field cracking performance, this reinforces the need for use of laboratory performance test as a mixture design tool as well as acceptance parameter. The DCT testing results showed trends consistent with previous and other on-going research studies, whereby the asphalt mixtures with higher fracture energies corresponded with pavements with lower amount of transverse cracking.

Partial-depth patching mixes must rapidly gain strength to allow the roadway to be reopened to traffic quickly. A patch should also bond well to the substrate to prevent the patch from separating from the existing material and be durable enough to withstand harsh winters. The objective of the research described in this report is to develop improved guidelines for evaluation of pre-bagged commercial patching mixtures and to recommend effective construction practices. To achieve these objectives, 13 different cementitious materials were selected and tested to determine key properties including strength gain, shrinkage, bond strength, and durability. The impact of the proposed research will be a better performing patch material as well as performance criteria that can be used to compare the materials tested in this program to new materials that will certainly be developed in the future. This research was conducted in four main phases, literature review and development of a testing plan and three phases of laboratory testing campaigns. The most commonly available acceptance specification for partial-depth patching materials is the ASTM C928. This specification was followed and the outcomes of each of the recommended tests were evaluated in context of the performance of the patching materials. Several additional tests were developed and conducted to evaluate the bonding properties of patching materials; correlations between lab measured properties were also evaluated. Through aforementioned testing and analysis, a laboratory testing based acceptance procedure was developed for partial-depth patching materials to be used by MnDOT.