The thin overlay mix (TOM) and ultrathin overlay mix (UTOM) specifications in Texas test falling head water flow as a surrogate measure of density. Current flow time criterion has never been correlated to density; furthermore, there is no maximum flow time to prevent overcompaction. A rolling density meter (radar) and a circular track meter may also be used to measure thin lift density. These tests and traditional core testing were used on three projects, and the correlations between tests were analyzed. Correlations were strong on a project-by-project basis but generally poor when data sets were combined. Flow time and mean profile depth, flow time and core voids, and surface dielectric and core voids were the strongest correlations overall; measured voids were unusually high. The reliability of taking core measurements on such thin samples is questionable and may be overly influenced by the surface texture. The flow test should continue to be used as a surrogate measure of density. No minimum flow time was recommended because of unusually high void measurements. To avoid overcompaction in TOMs, flow time should be less than 6 min on higher-speed or critical sections and less than 10 min on lower-speed, noncritical sections. From the standpoint of macrotexture in the UTOM, no upper limit is recommended for flow time. The rolling density meter should be employed on project-specific issues when full-coverage density measurements are desired. Further testing should be conducted on the reliability of measuring voids on very thin cores.
The specific objectives of this research were to quantify the effects of certain environmental factors on the relative strength loss of soil–cement subjected to compaction delay and to develop a numerical tool that can be easily used by engineers and contractors for determining a maximum compaction delay time for a given project. These objectives were addressed through extensive laboratory work and statistical analyses. The laboratory work involved testing an aggregate base material and a subgrade soil, each treated with two levels of cement. Environmental factors included in the experimentation were wind speed, air temperature, and relative humidity; three levels of each factor were evaluated in combination with three compaction delay times. The primary response variables in this research were relative compaction and relative strength. The findings indicate that relative strength is sensitive to variability among the selected independent variables within the ranges investigated in this research, while relative compaction is not. Inferring relative strength from relative density is therefore not a reliable approach on soil–cement projects. Consistent with theory, higher wind speed, higher air temperature, lower relative humidity, and higher compaction delay time generally result in lower relative strength. With the nomographs developed in this research, the maximum delay time permitted for compaction of either a base or subgrade material similar to those tested in this research can be calculated. Knowing in advance how much time is available for working the soil–cement will help contractors schedule their activities more appropriately and ultimately produce higher-quality roads.
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.
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.
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