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Evaluation of Stone/RAP Interlayers under Accelerated Loading
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2007-04-01
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[PDF-1.14 MB]
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and Performance;NTL-HIGHWAY/ROAD TRANSPORTATION-Materials;
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Abstract:A common method used by the Louisiana Department of Transportation and Development (LADOTD) for pavement design of noninterstate highways is to lime treat the subgrade and place a stabilized layer of soil cement over it followed by a layer of hot mix asphalt. One consistent problem with this method of construction is the appearance of reflection cracking in the asphalt layer. This is due to naturally-occurring shrinkage cracking in the soil cement, which propagates upward through the asphalt layer and then forms a combination of transverse and block cracking. As the pavement ages, the cracks accelerate the deterioration of the pavement structure. The results of the first ALF experiment indicated that placing a crushed stone layer either on top of the cement stabilized layer or beneath the asphalt layer would increase the pavement load carrying capacity by five fold when compared to conventional pavement structures with only soil cement base course layer. This concept is generally known as stone interlayer or inverted pavement design. This experiment sought to evaluate alternative materials such as reclaimed asphaltic pavement (RAP) to make the stone interlayer system more economical. Hot mix asphalt pavements built on equivalent thicknesses (3.5 inches) of RAP and crushed limestone base courses built on top of 6 inches of soil layer stabilized with 10 percent cement were evaluated side by side under the accelerated traffic loading test. A third test lane also evaluated the performance of RAP placed on a thicker (10 inch) but weaker cement (5 percent) treated layer. The test results showed that the crushed stone and RAP had very similar pavement performance under accelerated loading. Therefore, the researchers concluded the RAP is a suitable alternative for crushed stone in a stone interlayer system. They also found that in a stone interlayer system, thicker layers of cement treated layers with lower cement content performed better than thinner soil stabilized layers.
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