Evaluation of Vertebral derotation in the correction of Adolescent Idiopathic Scoliosis

Background Adolescent idiopathic scoliosis (AIS) represents a complex three-dimensional deformity. The rotation of the apical vertebrae is primarily responsible for the rib hump that represents the main cosmetic problem for adolescent patients. Correcting rotational deformity and maintaining the normal sagittal profile of the spine is more important than onlycorrecting coronal deformity. Aim of the Work to evaluate the efficacy of vertebral derotation using Single Concave Rod Rotation (SCRR) maneuver in the treatment of patients with Adolescent Idiopathic Scoliosis (AIS) by clinical and radiological follow up for 1 year. Patients and Methods This prospective analysis was done on 30 patients with AIS, who underwent one stage posterior only corrective surgery with SCRR maneuver between 2016 and 2019 at Ain Shams University Hospitals in order to correct their deformities. All patients included in this study had idiopathic curve between 40 and 80 degrees, with flexibility index < 50%, and their ages were between 10 and skeletal maturity. Results Compared to the results obtained by other studies using the same technique, our study included patients with relatively large curve magnitude and the lowest flexibility index, had average coronal correction rate by about 65.5% and minimal correction loss during follow up (-1°). Furthermore, our study included the largest mean preoperative RA. The axial correction rate was average (32.7%) and has the lowest complication rate and better clinical outcome and patient satisfaction among other studies that used SCRR maneuver. However, the mean operating time in our series in the present study was longer than the mean operating time in the literature. The mean amount of blood loss in our study was more than the mean amount in other studies. Conclusion Simple concave rod rotation is a good option for correction of the deformed curve in AIS. We can state that simple concave rod rotation with pedicle screw instrumentation and without the use of DVD maneuver could successfully correct both coronal and axial deformity with minimal complication. Adding DVD technique offers a better correction of apical vertebra rotation.

Rheology-Chemical Based Procedure to Evaluate Additives/Modifiers Used in Asphalt Binders for Performance Enhancements: Phase 2

The increased use of softer binders in Illinois over the past decade is primarily attributed to the increased use of recycled materials in asphalt pavement construction. The shift in demand of using PG 58-28 over PG 64-22 has resulted in potential alternative methods to produce softer binders more economically using proprietary products. However, there are challenges in using these proprietary products for asphalt modification because of uncertainty in their long-term performance and significant variability in binder chemistry. The current SuperPave performance grading specification for asphalt binders is insufficient in differentiating binders produced from these modifiers. Therefore, the objective of this study is to evaluate the performance of various softener-type asphalt binder modifiers using a wide array of rheological and chemistry tests for their integration into the Illinois Department of Transportation’s material specifications. The small-strain rheological tests and their parameters allowed for consistent grouping of modified binders and can be used as surrogates to identify performing and nonperforming asphalt binders. A new parameter, Δ|G*|peak τ, was developed from the linear amplitude sweep test and showed potential to discriminate binders based on their large-strain behavior. Chemistry-based parameters were shown to track aging and formulation changes. The modifier sources were identified using fingerprint testing and were manifested in the modified binder chemical and compositional characteristics. The two sources of base binders blended with the modifiers governed the aging rate of the modified binders. Mixture performance testing using the Illinois Flexibility Index Test and the Hamburg Wheel-Track Test were consistent with the rheological and chemical findings, except for the glycol amine-based modified binder, which showed the worst cracking performance with the lowest flexibility index among the studied modifiers. This was contrary to its superior rheological performance, which may be attributed to lower thermal stability, resulting in high mass loss during mixing. According to the characterization of field-aged binders, laboratory aging of two pressurized aging vessel cycles or more may represent realistic field aging of 10 to 15 years at the pavement surface and is able to distinguish modified binders. Therefore, an extended aging method of two pressurized aging vessel cycles was recommended for modified binders. Two different testing suites were recommended for product approval protocol with preliminary thresholds for acceptable performance validated with field-aged data.

Laboratory and Field Evaluation of Pre-Treated Dry-Process Rubber-Modified Asphalt Binders and Dense-Graded Mixtures

Pre-treatment of ground tire rubber is emerging as a popular method to incorporate rubber particles in dense-graded asphalt mixtures. This study investigates the effects of a chemically engineered Dry-Process Ground Tire Rubber (DP-GTR) modification in asphalt binders and mixtures. The DP-GTR is comprised of rubber particles measuring 400 to 600 µm in diameter (minus #30 mesh) coated with a non-elastomeric liquid. No change in aggregate gradation is necessary in DP-GTR modification of asphalt mixtures. In this study, the effects of DP-GTR modification on binder properties were measured by dynamic shear rheometer, Multiple Stress Creep and Recovery (MSCR), and bending beam rheometer tests. Additionally, mixture properties measured by three cracking tests: Disk-shaped Compact Tension (DC[T]) test, Illinois Flexibility Index, and indirect tensile asphalt cracking test and one rutting test (Hamburg wheel track test) were evaluated. Results showed: (a) 10–12°C bump on binder high temperature performance grade with 10% DP-GTR modification by weight of binder; (b) improvement in non-recoverable compliance in MSCR test indicated higher rut resistance; (c) increase in DC(T) fracture energy at low temperatures; (d) decrease in rut depth; and (e) decrease in flexibility index and cracking test index. Field performance of the chemically treated DP-GTR sections located in different states was examined to address discrepancies observed in the cracking tests. The cracking and rutting performance of all the field sections was good-to-excellent, suggesting that some of the currently popular simple cracking tests may not be able to properly assess the cracking resistance inherent in GTR-modified asphalt mixtures.