Eller, Andrew

In Minnesota, concrete pavements are finished by dragging an inverted turf or a stiff-bristled broom longitudinally on the surface of freshly placed concrete pavements, right behind the paving machine. Prior to 1998, most concrete pavements were finished with a combination of the burlap-drag and transverse-tining. Subsequently those pavements were reconstructed and finished with current broom or turf drag. The study sought to ascertain if current texturing techniques resulted in higher wet weather accident events. A Minnesota Department of Transportation (Mn/DOT) study selected segments in the network where current texturing techniques replaced previous textures. Annual wet weather accidents data from the Mn/DOT database were analyzed. By examining annual wet weather accident counts, total accident counts and crash rates for a ten year period, current textures were compared to previous textures. The paper discusses how 3 statistical tools were used to compare wet weather accident data from previous texturing to data from current texturing. Statistical tools showed that current texturing practices did not cause increase in the annual wet weather accidents, crash rates as well as ratio of wet to dry weather accidents in the chosen test sections. This paper was submitted to the Transportation Research Board for the 2008 Annual Meeting.

During the Arab Oil Embargo of 1973, the price of crude oil quadrupled to $12 per barrel. Subsequently the price of asphalt, the bottom of the crude oil barrel, also increased significantly during this time and the cost of highway construction and rehabilitation rose dramatically. Contractors and equipment manufacturers quickly recognized that recycling reclaimed asphalt pavement (RAP) could provide many benefits and opportunities. Milling machines were developed, hot mix asphalt plants were modified to allow the addition of RAP to mixes, and soil stabilization equipment was redesigned to reclaim existing pavements in-place.

Full Depth Reclamation (FDR) is a particularly useful method for rehabilitating structurally failed pavements. City streets, once beyond their design life, tend to fail due to structural problems such as moisture damage in the base layer or alligator cracking. FDR is a relatively low-cost, energy saving method that is capable of solving pavement problems associated with the deeper layers of the base. It has been adopted as the preferred recycling technique in the USA and many other parts of the world. In addition, introducing an injected emulsion to the FDR materials further improves the overall pavement strength and resistance to moisture ingress. In this sense, FDR with injected emulsion is an ideal technique for rehabilitating or reconstructing low-volume roads that do not require a thick mat of hot mix asphalt (HMA), but could use some improvement of the pavement structure to resist moisture and improve strength.

This annual report details the testing and observations from Cells 39 Porous Concrete Overlay, 85 Pervious Concrete on Granular Subgrade, and 89 Pervious Concrete on Cohesive Subgrade of the LVR at MnROAD. Permeable pavements are useful to help solve some of the drainage problems that roadway facilities encounter. However, these pavements must also provide for other user needs in addition to the drainage aspect. Drainability should be measured along with friction, ride (IRI), noise, textural, and structural properties. Once these properties and their relation to service life are quantified, a design guide or recommendations can be made to optimize the pavement properties relative to the user's needs.

Foamed asphalt was discovered in Iowa by Csanyi in 1956, and has become a useful road rehabilitation tool when used in conjunction with cold in-place recycle (CIR) and full-depth reclamation (FDR) processes. The advance of pavement recycling and foaming technology has made foamed asphalt a common rehabilitation technique in many parts of the world including Europe, Asia, Africa, Canada, and parts of the United States. Iowa has used the technique extensively and has developed specifications for the construction of foamed asphalt FDR and CIR stabilized roadways. The intention of this research project, Investigation 873, is to develop FDR and CIR foamed asphalt specifications and report data and information that will assist engineers in Minnesota with successfully implementing foamed asphalt recycling techniques. There are already several foamed asphalt CIR projects in Minnesota that have been completed on low volume roads. The roadways were rehabilitated in Fillmore and Olmsted Counties from 2004 to 2008, and are performing quite well to date. The Minnesota Department of Transportation (Mn/DOT) has taken Falling Weight Deflectometer (FWD) and core data from these projects in order to examine the in-situ properties of the stabilized pavement layer, as well as the material properties of the foamed asphalt itself. The FWD data analysis reveals that the recycled pavement layer develops a relatively uniform strength despite the high variability inherent in most low-volume roads. Core data indicates that the foamed asphalt forms a cohesive matrix when mixed with the fines from the reclaimed material, which does not disintegrate when cored. Overall PG grade of the recycled layer changed significantly from the original mix in some cases, but not in others. The cause of this is unknown, however, differences in the procedures used and materials present at the different projects may help explain this. It is recommended that FWD, ground penetrating radar (GPR), and core analysis be performed before and after foamed asphalt projects to more accurately define these differences.

This report evaluates the first year performance of the Pervious Concrete test cell #64 located in the parking lot on the south side of the MnROAD pole barn. Performance measures utilized for this report include examination of stress-strain response through loading from the 80 kip MnROAD truck and Falling Weight Deflectometer (FWD). The FWD deflection basins were compared to those obtained for normal concrete of similar thickness design. The second performance measure was the vibrating wire strain gauge sensor response. Elastic modulus values were computed from the sensor data. In addition, petrographic analyses of cores taken from the test pad and pavements were performed to determine the macroscopic and microscopic characteristics of pervious concrete pavement after the first year. Furthermore, a surface rating of the pavement was performed to corroborate petrographic and freezethaw data in order to ascertain the cause of any structural anomalies within the pervious concrete structure. Overall, the pervious concrete cell #64 is performing well after its first year. Normal sanding and salting operations do not appear to have impacted the pore structure within the pervious concrete to date. However, a more quantitative method of measuring flow through the cell and base materials is needed before a final conclusion can be made about the enduring ability of pervious concrete to pass water. Such a quantitative flow measurement method is currently under development.