An improved mechanistic empirical design procedure for unbonded concrete overlays of existing concrete pavements (UBOLs) should account for the effect of the interlayer on the structural response of the pavement. One approach is to use the Totsky model to characterize the interlayer. The Totsky model treats the interlayer as a bed of springs between two plates and is currently incorporated into the rigid pavement finite element software ISLAB. A difficulty encountered in implementing this model is that there are currently no guidelines as to what the interlayer k-value should be for different types of interlayers. The interlayer can be constructed of new or aged asphalt (open or dense graded) or a nonwoven geotextile fabric. To establish the k-values that accurately characterize each of these materials, an ISLAB model of a laboratory test was created so the k-values could be established by matching the measured and calculated difference between the deflections in the overlay and existing pavement. To supplement the use of the laboratory data in establishing the Totsky interlayer k-value, an analysis was carried out using falling weight deflectometer (FWD) data from UBOLs at the Minnesota Road Research Facility (MnROAD). Analyses were then performed to determine if the difference between k-values for different interlayer materials are statistically significant, and if the results from the laboratory analysis match those obtained from the MnROAD field data. The Totsky k-value recommended for use when modeling the response of an UBOL with an asphalt interlayer is 3500 psi/in and 425 psi/in for a fabric interlayer.
State departments of transportation began using recycled concrete aggregate (RCA) as aggregate in portland cement concrete pavement in the United States in the late 1970s. Although RCA is rarely used in current U.S. rigid pavement slabs, the impetus for its continued use remains the same: a lack of landfill space, a shortage of nearby quality natural aggregates, or both. However, as American pavement engineers and researchers place a greater emphasis on sustainable, reusable roadways, the status quo for RCA in American roadways should be reconsidered along with these new priorities. This study proposes to revisit the use of recycled concrete as aggregate in rigid pavement slabs by using overlooked research to address the concerns that prevented the wide-scale adoption of recycled concrete as an aggregate in pavement slabs by state departments of transportation. Experiences encountered in countries (mostly restricted to Europe) where the use of RCA in rigid pavement is more common are also described. New opportunities for the use of RCA as a structural component in pavement concretes are detailed.
In recent decades, state, local, and federal use of asphalt concrete overlays to rehabilitate portland cement concrete pavements has increased significantly. This growth has increased the attention given to mechanistic– empirical modeling of reflective cracking. This paper describes recent research that assessed and modified the state of the art in mechanistic– empirical modeling of reflective cracking. The research reviewed the original Mechanistic–Empirical Pavement Design Guide model and the CalME reflective cracking model. The paper also details research in which the CalME model was modified to facilitate its integration into the design guide for pavement projects of composite asphalt concrete over portland cement concrete.
The Minnesota Department of Transportation began construction on the Minnesota Road Research Project (MnROAD) in 1991 and opened the full-scale pavement research facility to live traffic in 1994. Since the time of its construction, MnROAD, the first major test track since the AASHO Road Test of the 1950s and 1960s, has provided many lessons in pavement testing and pavement engineering on behalf of the greater pavement community. Researchers at the University of Minnesota reviewed these lessons from the first phase of MnROAD (the facility's first 10 years of operation) for a project titled MnROAD Lessons Learned. The Lessons Learned project involved more than 50 interviews; 300 published and unpublished reports, papers, and briefs; and an online survey of pavement professionals. This paper, based on the Lessons Learned project, presents a sample of the lasting benefits of MnROAD at the local, state, and national levels. Furthermore, the paper provides extensive references for these benefits in the hope of increasing awareness of this pavement test facility's underpublicized contributions to pavement engineering.
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