The benefits of using recycled materials in highway pavements was assessed quantitatively by conducting life-cycle analysis and life-cycle cost analysis on pavements consisting of conventional and recycled materials for a highway construction project in Wisconsin. Results of the analysis indicate that using recycled materials in the base and subbase layers of a pavement can result in reductions in global warming potential (20%), energy consumption (16%), water consumption (11%), and hazardous waste generation (11%) while also extending the service life of the pavement. In addition, using recycled materials in the base and subbase layers can result in a life-cycle cost savings of 21%. The savings are even greater if landfill avoidance costs are considered for the recycled materials incorporated in the pavement. Extrapolation of the benefits to conditions nationwide indicates that modest changes in pavement design to incorporate recycled materials can contribute substantially to the emission reductions required to stabilize greenhouse gas emissions at current levels.
Bottom-up cracking may be due to CSL surface raveling or fatigue of the CSL, as follows:(a) Bottom-up cracking due to CSL surface raveling Based on accelerated pavement testing, studies show that the surface of a stabilized base layer can ravel, creating a layer of loose material between the HMA and base CSL (Figure A-8). Raveling of the base increases the strain level at the bottom of the HMA, which can result in alligator cracking. In addition, pumping was observed in these cases. The pumping is caused by the loss of fines in the loose material layer. This phenomenon may be linked to the erodibility of stabilized materials, which often happens when relatively fine raw materials are treated (De Beer 1985). reported the loose layer is about 0.8 in. thick and is believed to be due to shear failure within the CSL as a result of horizontal loading, which in turn causes alligator cracking.
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