No abstract

Lumbar spondylolysis and spondylolisthesis are common spinal disorders that most of the times are incidental findings or respond favorably to conservative treatment. In a small percentage of the patients, surgical intervention becomes necessary. Because too much attention has been paid to novel surgical techniques and new modern spinal implants, some of fundamental concepts have been forgotten. Identifying that small but important number of patients with lumbar spondylolysis or spondylolisthesis who would really benefit from lumbar surgery is one of those forgotten concepts. In this paper, we have developed an algorithmic approach to determine who is a good candidate for surgery due to lumbar spondylolysis or spondylolisthesis.

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Due to the increased use of recycled materials in pavement, the crack resistance of asphalt mixtures has become a major concern. This study evaluated the crack resistance of asphalt mixtures containing up to 40% reclaimed asphalt pavement (RAP) at intermediate temperatures. Three groups of materials consisting of seven plant-produced hot-mix asphalt mixtures were evaluated. A suite of test methods with various mechanistic backgrounds were employed, namely: semi-circular bend, simplified viscoelastic continuum damage, indirect tension, Texas overlay, and Illinois flexibility index tests. The corresponding parameters obtained for assessing crack resistance were: critical strain energy release rate Jc, material fatigue sensitivity, dissipated creep strain energy, number of cycles to failure Nf,OT, the interaction plot of critical fracture energy versus crack progression rate, and the flexibility index, respectively. Test results indicated that mixtures with higher RAP content exhibited higher stiffness and indirect tensile strength with lower compliance than the counterpart materials. In addition, all evaluation parameters, except for the use of the interaction plot from the Texas overlay test, provided consistent observations that incorporation of more RAP deteriorated the materials’ crack resistance. The mixture-discriminating capabilities of all test methodologies were also investigated using the paired t-test on the experimental data of each mixture group. The results presented herein were part of Pooled Fund TPF-5(294) study titled Develop Mix Design and Analysis Procedures for Asphalt Mixtures Containing High-RAP and/or RAS Contents.