Bryan Wilson

Decision-making Tool for the Selection of Pavement Preservation Treatments in General Aviation Airport Pavements

Adequate planning for airfield pavement preservation is required for efficient mitigation of pavement deterioration due to loading and environmental conditions. Large airports generally have trained staff for managing their pavement network and a significant budget for routine maintenance. However, there are many general aviation (GA) airports in the United States (U.S.) which may lack these resources. Therefore, technical rules for pavement preservation need to be simplified for GA airport managers. While the typical approach to managing these pavements is reactive, which requires costly rehabilitation/reconstruction, proactive preservation uses more frequent, low-cost treatments. In this paper, a tool for the selection of durable and cost-effective treatments for pavement preservation, and steps and database used for development of this tool are introduced. This tool can be used by non-technical decision makers in general aviation. The results for selection of treatments vary depending on different climate zones and airport traffic reflected on airport categories.

Evaluating Tack Properties of Trackless Tack Coats Through Dynamic Shear Rheometer

Tracking of traditional tack coat materials is a common concern during hot-mix asphalt overlay construction. This problem can be avoided by using trackless tacks, which are recently developed tack products that resist sticking to tires. Thus loss of tack materials from the paving surface is preventable. Various trackless tack products have been introduced to the market; however, there is still a lack of evaluation on their tracking resistance. The objective of this study was to measure the rheological and tack properties of trackless tack materials through the dynamic shear rheometer. Six trackless tacks and a traditional tack were evaluated. To identify rheological characteristics, the dynamic shear rheometer frequency sweep test was performed on the tack residues. Also, the modified dynamic shear rheometer tackiness test was conducted on both tack emulsions and residue at different temperatures. The emulsion samples were tested throughout the curing period. The tack samples were categorized into soft and stiff binder groups with respect to complex shear modulus obtained from the frequency sweep test. The tack energy was estimated to quantify the stickiness in the tackiness test. A significant difference in tack energy was observed between soft and stiff group binders. The stiffness of the investigated tack materials with respect to the complex shear modulus is well correlated with the tack material properties.

Chemical-Mechanical Interaction of Non-Tracking Tack Coat and Aggregate on Bond Strength

The effectiveness of a hot-mix asphalt (HMA) overlay is largely dependent on the quality of its bond to the existing surface. A good bond will evenly disperse traffic loads from one layer into the next, while a poor bond will concentrate stresses within relatively thin upper layer. This condition will expedite premature distresses like fatigue cracking, slippage cracking and delamination. All of these problems are then exacerbated by moisture accumulating at the bonded interface. Non-tracking tacks, recently introduced to the paving industry, bond asphalt layers together while avoiding the tracking problems under traffic associated with traditional tacks. While traditional tack has been well studied, these new products require further evaluation. Of particular concern is the loss of adhesion between exposed aggregate on the existing road and asphalt binder. The objectives of this study were to characterize existing non-tracking products, and measure the bonding potential of different types of aggregate from a chemo-mechanical perspective. For this purpose, the rheological properties of the emulsion residues and base binder of five non-tracking tacks and one conventional tack were characterized. The bonding potential between the tack and different aggregate substrates was measured with a pneumatic adhesion tester. The results show significant differences in bond strength of aggregates with rough surface and the control binder or emulsion residue at different testing temperatures. The control binder and emulsion residue at different testing temperatures were also found to develop different bond strength with any given aggregate. The results show that the control binder and emulsion residue have different degrees of sensitivity to aggregate type in terms of their bond strength.

Development of Test Procedures to Measure Tracking Resistance of Non-Tracking Tack Coat

Non-tracking tacks, recently introduced to the paving industry, bond pavement layers while avoiding the tracking problems associated with traditional tacks. Initially, there was only one supplier of non-tracking tack in Texas, but now multiple producers are bringing products to the market. Performance to date has been good, but there are no established methods to test tackiness/tracking resistance of current and new products. The objective of this research, therefore, was to develop and assess three tests for measuring tracking resistance: the modified no-pick-up time test, the Texas Transportation Institute (TTI) sand adhesion test, and the modified dynamic shear rheometer (DSR) tackiness test. These methods were evaluated on four tack materials, three curing temperatures, and at 10-minute curing time intervals. The results from the modified no-pick-up time test were clearly influenced by curing time and curing temperature. The TTI sand adhesion test could discern among different tack materials. Track free time may be defined as less than 2 g of sand adhesion. The modified DSR tackiness test showed measurable differences among the tack types and different temperatures and times. Of these test methods, the researchers recommend adoption of the modified no-pick-up time test for routine tracking resistance testing. “Track-free time” should be defined as less than 10% tracking in 40°C curing. Testing of this and other tests should continue, especially with other conventional and non-tracking tacks.

Benefit–Cost Analysis of Florida High-Friction Surface Treatments

High-friction surface treatments (HFSTs) are effective at reducing crashes on horizontal curves; however, HFST effectiveness on other roadway sections (e.g., tangents, intersections, intersection approaches) is not well documented. The crash reduction effectiveness of HFSTs in Florida was assessed, and the benefit–cost (BC) ratios for these section types were calculated. The researchers identified 23 HFST projects in Florida and attempted to collect data for each project, including bidding records, roadway geometry, and crash statistics. The cost data were based on the average comprehensive HFST unit cost and scaled by the size of the application. The benefit was estimated on the basis of 5-year extrapolations of average total and wet weather crash reductions. Savings were estimated on the basis of Florida Department of Transportation KABCO severity distribution of the crashes and an average cost per crash. On average, HFST applications on tight curves reduced the total crash rate by 32% and the wet weather crash rate by 75%. The average BC ratio on tight curve sections was between 18 and 26, depending on the benefit calculation method. Wide curve and tangents sections had few accidents initially, and HFST had negligible impact. From a crash perspective, wide curve and tangent HFST applications are not cost-effective. The effectiveness of HFST on intersection and approach applications is still inconclusive. Half the sections had good BC ratios and the other sections had negative benefit (increased crash rates). When considering the application of HFST, the engineer should consider whether there is an existing crash problem and whether it is skid related.

Tackiness Properties of Non-Tracking Tack Coats

Non-tracking tacks are introduced to improve the bonding of pavement layers by preventing the tracking problems associated with conventional tacks. However, the evaluation of the non-tracking tacks has not been well-established as compared with the traditional tack coats. The goal of this research was to measure the rheological properties, the bonding potentials and tack properties of non-tracking tack materials. For this purpose, the dynamic shear rheometer (DSR) frequency sweep test was performed on the tack residues for investigating their rheological properties. Also, a pneumatic adhesion tester was used to measure the pull-off strength of the interaction between the residues and aggregate. The DSR tackiness test was conducted to identify the tracking resistance and quantify the tack energy. Three non-tracking tack coats and a traditional tack coat were used. The results of the DSR frequency sweep test showed that the non-tracking tack materials are stiffer than the traditional tack coat. The results from the pull-off testing and the DSR tackiness test demonstrated that the effect of tack type on the bond strength and tackiness was significant. Furthermore, it was shown in the tackiness test that the testing temperature had a major impact on the change of tack energy for the non-tracking tacks.