W James Wilde

Monitoring Curing of Emulsion-stabilized Roadways Using the Dynamic Cone Penetrometer

Several counties in Minnesota have used an emulsified asphalt to stabilize unimproved gravel highways in rural areas. This has been done in hopes of reducing dust on such roads, reducing the frequency and extent of maintenance, and improving ride quality. As applications of such a stabilization technique increase, the need to investigate and quantify the benefits of this technique is becoming more important. Several county roads in rural Blue Earth County, in south central Minnesota, were stabilized and monitored during the fall of 2005. Dynamic Cone Penetrometer measurements were taken periodically for several months following the stabilization of two gravel roads using emulsified asphalt. Due to the nature of the emulsion compound, the stabilized material was expected to increase in stiffness with time as curing of the emulsion occurred. The Dynamic Cone Penetrometer results verified that the stiffness did increase with time as expected with this stabilization process.

Thickness Design Method for Bituminous-Stabilized Aggregate-Surfaced Roads

Many low-volume roadways in the county road system in Minnesota consist of unpaved aggregate surfaces. It is the responsibility of the county engineer to make determinations regarding the design and maintenance of such roads, as well as determinations regarding specific criteria such as weight restrictions. One method used by several counties in Minnesota is to construct a bituminous-stabilized layer by adding several inches of new aggregate and stabilizing it with an engineered, water-based asphalt emulsion through mix-in-place methods. There is a need, however, for a design method to provide highway engineers and their staffs with technical backing for the designs selected. This paper describes the results of an ongoing research project to develop a design method for determining the required thickness of stabilized and unstabilized layers in this type of aggregate-surfaced road. The basic design method is based on the material properties and a correlation between layered elastic analysis, dynamic cone penetrometer testing, and falling weight deflectometer testing. Results of the materials testing and layered elastic analysis are presented, as well as the correlation between the analysis and measured falling weight deflection data. The load rating analysis uses the Minnesota Department of Transportation methodology of estimating load rating on low-volume roads on the basis of falling weight deflectometer data. This method of design will allow county and other agency engineers to determine the appropriate thickness of the stabilized layer in order to obtain the desired load rating.

Sustainability of Using Recycled Concrete Aggregates as Coarse Aggregate in Concrete Pavements

Conservation and reuse of resources are important aspects of sustainability. It is common practice in the U.S. to crush old concrete pavements at the end of their service lives into recycled concrete aggregate and then reuse them in the base course of new pavements. It is not, however, common to use the recycled concrete aggregate (RCA) in the new concrete pavement itself. This paper examines the sustainability and, in particular, the economics of using RCA in the construction of new concrete pavements. Life cycle cost analyses were performed for various hypothetical pavement construction scenarios including RCA both in the base and in the concrete layer and compared with conventional options. If RCA is simply substituted for natural aggregate in a concrete mixture, the concrete is likely not to perform as well as a concrete made without RCA. This can be compensated for by decreasing the water–cement ratio and/or increasing the cement content. Despite this fact, the results of the life cycle cost analyses show that it can be very economical to use RCA in new concrete pavement construction. As the natural aggregate used for concrete may be more expensive than the natural aggregate used for base courses, it may make good economic sense to substitute RCA for natural aggregate in concrete. Life cycle analysis also shows that concrete with RCA may have better environmental impact.

Open-graded Aggregate Base (OGAB) Controlling Subsurface Moisture Regime and Structural Stability from MnROAD Instrumentation Data

Open-graded aggregate base courses have been increasingly used in Portland cement concrete (PCC) pavements as one of the effective strategies for improving subsurface drainage efficiency and thus pavement longevity. In addition to maintaining adequate permeability, these layers are also required to remain stable during pavement construction, performance period and future rehabilitation activities. In an effort to study subsurface drainage and stability of a new open-graded aggregate base material (OGAB Special) under construction, PCC pavement test sections (Cells 306 and 406) were constructed by the Minnesota Department of Transportation (MnDOT) on the 3.5-mile mainline interstate roadway segment at the MnROAD test facility in 2011. Both test cells consist of 6-in. thick PCC slab, 6-in. thick OGAB Special layer and 7-in. Class 5 (MnDOT traditional dense-graded) unbound aggregate underlain by clay subgrade. This paper presents the findings from analyzing field instrumentation data and Falling Weight Deflectometer (FWD) test results to assess the effectiveness of the OGAB Special layer in controlling subsurface moisture regime and providing structural stability. For comparison, field test data were also collected and analyzed from MnROAD Cells 38, 53, and 54 that are located in the low-volume roadway segment and consist of PCC slabs of similar thickness and traditional dense-graded base layers (Class 5 or 6) underlain by clay subgrade. It was concluded from analysis results that the OGAB Special layer cannot only reduce the subsurface moisture content significantly but also provide comparable structural stability, as compared to traditional dense-graded (Class 5/6) base layers.

Effect of Crack Sealant Material and Reservoir Geometry on Surface Roughness of Bituminous Overlays

Many state, county, and municipal highway agencies have experienced the formation of bumps when placing single-lift overlays or the first lift of a multiple-lift overlay. These bumps are produced at the location of a previously existing crack, and even then almost exclusively when the crack has been sealed in advance of the overlay. When such bumps are not covered with a subsequent lift, what remains is often a rough ride on a newly overlaid roadway. The effects of crack sealant material type and geometry (shape) of the routed cracks in the existing surface on the formation of bumps in bituminous overlays are described. A matrix of four sealant type treatments and six geometries was designed and implemented in a test section in Jackson County, Minnesota. The overlay on the test section was constructed in September 2007. Results of this investigation indicate that cooler pavement surface temperatures, no over-band, hot-poured crumb rubber, and hot-poured elastic sealants provide the best resistance to the formation of bumps in overlays.