Development of an Economic Dust Palliative for Limestone Surfaced Secondary Roads, HR-297, Progress Report, 1988

Research activities during this period concentrated on continuation of field and laboratory testing for the Dallas County test road. Stationary ditch collection of dust was eliminated because of inconsistent data, and because of vandalism to collectors. Braking tests were developed and initiated to evaluate the influence of treatments on braking and safety characteristics of the test sections. Dust testing was initiated for out of the wheelpath conditions as well as in the wheelpath. Contrary to the results obtained during the summer and fall of 1987, the 1.5 percent bentonite treatment appears to be outperforming the other bentonite treated sections after over a year of service. Overall dust reduction appears to average between 25 to 35 percent. Dallas County applied 300 tons per mile of class A roadstone maintenance surfacing to the test road in August 1988. Test data indicates that the bentonite is capable of interacting and functioning to reduce dust generation of the new surfacing material. Again, the 1.5 percent bentonite treatment appeared the most effective. The fine particulate bonding and aggregation mechanism of the bentonite appears recoverable from the environmental effects of winter, and from alternating wet and dry road surface conditions. The magnesium chloride treatment appears capable of long-term (over one year) dust reduction and exhibited an overall average reduction in the range of 15 to 30 percent. The magnesium chloride treatment also appears capable of interacting with newly applied crushed stone to reduce dust generation. Two additional one mile test roads were to have been constructed early this year. Due to an extremely dry spring and summer, construction scheduling was not possible until August. This would have allowed only minimal data collection. Considering this and the fact that this was an atypically dry summer, it was our opinion that it would be in the best interest of the research project to extend the project (at no additional cost) for a period of one year. The two additional test roads will be constructed in early spring 1989 in Adair and Marion counties.

Impact of Curling and Warping on Concrete Pavement, TR-668, 2016

Portland cement concrete (PCC) pavement undergoes repeated environmental load-related deflection resulting from temperature and moisture variations across the pavement depth. This phenomenon, referred to as PCC pavement curling and warping, has been known and studied since the mid-1920s. Slab curvature can be further magnified under repeated traffic loads and may ultimately lead to fatigue failures, including top-down and bottom-up transverse, longitudinal, and corner cracking. It is therefore important to measure the “true” degree of curling and warping in PCC pavements, not only for quality control (QC) and quality assurance (QA) purposes, but also to achieve a better understanding of its relationship to long-term pavement performance. In order to better understand the curling and warping behavior of PCC pavements in Iowa and provide recommendations to mitigate curling and warping deflections, field investigations were performed at six existing sites during the late fall of 2015. These sites included PCC pavements with various ages, slab shapes, mix design aspects, and environmental conditions during construction. A stationary light detection and ranging (LiDAR) device was used to scan the slab surfaces. The degree of curling and warping along the longitudinal, transverse, and diagonal directions was calculated for the selected slabs based on the point clouds acquired using LiDAR. The results and findings are correlated to variations in pavement performance, mix design, pavement design, and construction details at each site. Recommendations regarding how to minimize curling and warping are provided based on a literature review and this field study. Some examples of using point cloud data to build three-dimensional (3D) models of the overall curvature of the slab shape are presented to show the feasibility of using this 3D analysis method for curling and warping analysis.