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Baton Rouge, LA, United States

Yu X.B.,Case Western Reserve University | Yu X.B.,Louisiana Transportation Research Center | Yu X.,Case Western Reserve University
Canadian Geotechnical Journal | Year: 2011

Bridge scour is a major threat to the safety of bridges. There is a high risk of scour-induced damage due to the catastrophic nature of bridge foundation failure. The development of an innovative bridge scour monitoring system is a pressing task for the research community. Such a system needs to be fieldworthy, which is a characteristic assessed in terms of accuracy, ruggedness, and automation. Among these criteria, an automatic signal analysis algorithm is generally a prerequisite for deploying a long-term field monitoring program. This paper describes the development and validation of an algorithm for a scour monitoring system based on the principles of guided radar: time-domain reflectometry (TDR). This algorithm is based on the extension of the classic dielectric mixing model to layered systems. The performance of this algorithm is evaluated using experiments designed to simulate different field scour conditions. These include different types of sediments and the variation of river conditions (i.e., salinity of river water, air entrainment, and amount of suspended sediments). The experiment results indicate that the developed analyses algorithm is robust and accurate for scour-depth estimation under these investigated conditions. Source

Mohammad L.N.,Louisiana State University | Cooper S.B.,Louisiana Transportation Research Center | Elseifi M.A.,Louisiana State University
Journal of Materials in Civil Engineering | Year: 2011

The objective of this study was to evaluate the use of crumb rubber (CR) from waste tires and engineered additives as a rejuvenator to high reclaimed asphalt pavement (RAP) content asphalt mixtures. Six asphalt mixtures were prepared by mixing aggregate blends with four asphalt binders, an unmodified asphalt binder classified as performance grade (PG) 64-22, two polymer-modified binders classified as PG 70-22M and PG 76-22M, and a PG 76-22 crumb-rubber-modified binder. The RAP content was varied from 0-40% and crumb-rubber additives were blended with the unmodified binder by using wet and dry processes. Hot-mix asphalt (HMA) mixture testing included an evaluation of rutting susceptibility, moisture resistance, and resistance to cracking using the flow number test, the loaded-wheel tracking test, the dynamic modulus test, the modified Lottman test, the dissipated creep strain energy test, and the semi-circular bending test. Results of the experimental program indicated that the addition of the CR additives rejuvenated the blended asphalt binder for the HMA mixture with high RAP content. The use of high RAP content with crumb rubber as a rejuvenator in the preparation of HMA is expected to provide adequate moisture resistance and superior rutting resistance as compared to conventional mixtures. However, because of the hardening properties of the mix prepared with high RAP content, the fracture and cracking resistance of the produced mixture was reduced compared with polymer-modified mixes. © 2011 American Society of Civil Engineers. Source

Yang X.,Louisiana Transportation Research Center | Yang X.,University of Kansas | Han J.,University of Kansas | Pokharel S.K.,Access Inc. | And 6 more authors.
Geotextiles and Geomembranes | Year: 2012

Accelerated pavement testing (APT) is an effective method in evaluating pavement performances by applying controlled wheel loading under environmental conditions. This note presents the findings from an accelerated pavement test on unpaved road sections involving geocell reinforcement of sand bases. A total of four unpaved road sections were constructed. Sections 1 and 4 were unreinforced sections first with sand bases and then replaced with aggregate bases after failure. Sections 2 and 3 were sand sections reinforced with novel polymeric alloy (NPA) geocell under an aggregate cover layer. Rut depths developed in each section were measured after a certain number of wheel passes. Horizontal strains at different locations in the NPA geocell were monitored by strain gages. Test results demonstrated that the NPA geocell had a significant effect in improving the stability of unpaved roads and reducing the permanent deformation. Under the particular test condition, the NPA geocell-reinforced sand layer behaved equivalently to the A-1-a aggregate of the same thickness. The deformations of the geocell-reinforced road sections were analyzed. The test also revealed the importance of keeping the geocell structure intact to ensure the adequate performance of NPA geocell-reinforced bases. Strain gage measurements showed that the NPA geocell beneath the wheel path experienced tensile stresses whereas the geocell outside the wheel path experienced compressive stresses. © 2011 Elsevier Ltd. Source

Saber A.,Louisiana Tech University | Alaywan W.,Louisiana Transportation Research Center
Journal of Bridge Engineering | Year: 2011

Continuity diaphragms used in prestressed girder bridges on skewed bents have caused difficulties in detailing and construction. The results of the field verification for the effectiveness of continuity diaphragms for skewed, continuous, and prestressed concrete girder bridges are presented. The current design concept and bridge parameters that were considered include skew angle and the ratio of beam spacing to span (aspect ratio). A prestressed concrete bridge with continuity diaphragms and a skewed angle of 48°was selected for full-scale test by a team of engineers from Louisiana Department of Transportation and Development and the Federal Highway Administration. The live load tests performed with a comprehensive instrumentation plan provided a fundamental understanding of the load transfer mechanism through these diaphragms. The findings indicated that the effects of the continuity diaphragms were negligible and they can be eliminated. The superstructure of the bridge could be designed with link slab. Thus, the bridge deck would provide the continuity over the support, improve the riding quality, enhance the structural redundancy, and reduce the expansion joint installation and maintenance costs. © 2011 ASCE. Source

Ji G.,Louisiana State University | Li G.,Louisiana State University | Li G.,Southern University and A&M College | Alaywan W.,Louisiana Transportation Research Center
Construction and Building Materials | Year: 2013

Fiber reinforced polymer (FRP) composites, as a mature technology, have been widely used to repair/retrofit/reinforce damaged/degraded concrete structures such as steel reinforced concrete (RC) beams or columns by externally bonding FRP sheet(s) onto the surface of substrate concrete structures. However, the performance of FRP systems exposed to fire is a serious concern due to the combustibility of FRPs. The objective of this study is to understand and develop a new fire resistant technology with nanoclay reinforced intumescent coating. RC beams were prepared, damaged, and repaired by FRP with the new coating. The repaired RC beams were subjected to fire hazard again, and re-evaluated for its residual structural capacity. The effectiveness of the developed new coating for fire resistance was evaluated based on the test results. It is believed that this coating system would enhance fire resistance of the FRP, and safety and reliability of FRP repaired concrete structures. © 2013 Elsevier Ltd. All rights reserved. Source

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