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Austin, TX, United States

Chen D.H.,Changsha University of Science and Technology | Scullion T.,Texas A&M University | Hong F.,203 Bull Creek and 39 | Lee J.,AECOM Technology Corporation
Journal of Performance of Constructed Facilities | Year: 2012

A stretch of State Highway (SH) 6in Texas has been experiencing poor ride quality problems caused by continuous pavement swelling and heaving. Because of this, the Texas Department of Transportation (TxDOT) Waco District annually spent hundreds of thousands of dollars to overlay the pavement to keep it smooth. This study is motivated to identify the root causes and solutions to the critical problem. During the forensic study, a systematic approach is employed, which includes nondestructive and destructive tests. On the basis of the overall test results, it is revealed that the problem was initiated within the lower portion of the pavement structure (i.e.,subgrade) rather than in the upper pavement structure (i.e.,asphalt concrete and flexible base). It was further found that the major factors contributing to the subgrade problem include (1)swelling soils, (2)water penetrating into the expansive clay soils, (3)high organics content in the soil, (4)loss of strength of the lime stabilized layer, and (5)high levels of sulfates in the soils. Performance surveys of various potential treatments for remediating the problem associated with swelling subgrade soil and increased moisture were conducted. These performance histories provide input and guidance for the selection of the pavement rehabilitation strategies. On the basis of the past performance histories, a variety of short-term and long-term strategies were recommended to the Waco District office for solving the problem. © 2012 American Society of Civil Engineers. Source


Chen D.-H.,Changsha University of Science and Technology | Won M.,Texas Tech University | Hong F.,203 Bull Creek and 39
Construction and Building Materials | Year: 2011

In the last 10 years, TxDOT has utilized Dowel Bar Retrofit (DBR) in five projects. International Roughness Index (IRI), Falling Weight Deflectometer (FWD), Rolling Dynamic Deflectometer (RDD), and coring were employed to evaluate DBR effectiveness in those five projects. Different versions of special specifications were utilized for each DBR project. The main variables in different versions of the specifications are grout material and slot width requirements. Out of the five projects, four projects (SH73, SH73/SH87, US69, and US287) have performed to the designers' satisfaction. Those four projects demonstrated that DBR was able to improve Load Transfer Efficiency (LTE) and minimize reflective cracking on an AC overlay. The US69 project reveals that after DBR, Diamond Grinding (DG) should be applied to restore the ride quality. Faulting of greater than 25 mm has been successfully corrected by DBR and DG on the US287 project, which still provides good ride quality after 6 years of service. The experiences from these four projects suggest that DBR with either DG or an AC overlay can be used effectively to extend pavement life and restore the ride if it is done properly. However, on the US59 project, the DBR performance is unsatisfactory. Visible faulting of 6.4 mm-9.4 mm developed in less than 2 years. It was found that the primary cause for the unsatisfactory performance was excessive voids under the dowel bar, which prevented proper load transfer at the joint. X-ray tomography results indicate that approximately 50% of the area under the dowel was void. The following four main variables were investigated in the laboratory for potential causes for voids around dowels: (1) time of placement after grout mixing, (2) vibration time of grout, (3) slot width, and (4) maximum aggregate size. It was found that maximum aggregate size, in the range of 9.5 mm-12.7 mm was not a critical factor for the consolidation of the grout. Although slot width above 63.5 mm may be beneficial, it was not a critical factor for grout consolidation either. The factors that had significant effects on consolidation of the grout were time of placement after mixing and vibration time. Delayed placement of the grout without vibration led to substantial voids. These two factors might be the causes for the voids under dowels that led to poor performance of DBR on US59. The most significant factor for the consolidation of grout materials is vibration. Although vibration has been included in the current Texas Department of Transportation (TxDOT) special specifications for DBR, it should be properly enforced to ensure optimum consolidation. Based on the test results, 20 s of vibration is recommended for each slot. In addition, it is preferable to place grout into the slots before the initial set takes place, or within the manufacturers' recommended working time. © 2010 Elsevier Ltd. All rights reserved. Source


Chen D.-H.,Changsha University of Science and Technology | Hong F.,203 Bull Creek and 39 | Zhou F.,Texas Transportation Institute
Journal of Performance of Constructed Facilities | Year: 2011

A forensic study was conducted to investigate the premature cracking distress on an ongoing construction project on State Highway (SH) 24. Transverse cracks occurred at approximately every 9-15m (30-50ft) along the 9.6km (5.9mi) project. The field tests involved both destructive tests, including trenching and coring, and nondestructive tests, including falling weight deflectometer (FWD) and ground-penetrating radar (GPR) tests. The laboratory tests mainly included cement-treated base material and asphalt mixture material series tests. By integrating all the test results, it was concluded that the premature cracking was originating from the cement-treated base (CTB). Although CTB is not a new concept in pavement construction, stabilization of base materials is a complex process, which, if not handled properly, may lead to premature failures. The two primary factors that contributed to the premature failure are (1)an excessive amount of cement in the CTB, and (2)a high moisture content when the CTB was compacted (almost 2% above optimum moisture). It was believed the possibility of premature failure could be reduced significantly, if the lab verification tests were conducted on the CTB before construction started. Pavement life analysis was conducted to evaluate the current structure adequacy to sustain future traffic. In addition, extensive material design was conducted for the final wearing course asphalt mixture, which was intended to mitigate the effect of existing cracks by resisting crack propagation from the underlying structure. © 2011 American Society of Civil Engineers. Source


Chen D.-H.,Central South University of forestry and Technology | Hong F.,203 Bull Creek and 39 | Zhou W.,Huazhong University of Science and Technology | Ying P.,Central South University of forestry and Technology
NDT and E International | Year: 2014

Traditionally, in-place air voids are obtained based on field cores. Coring is a destructive and time-consuming process. This study presents a high speed Non-Destructive Testing (NDT) technique with Ground Penetrating Radar (GPR) to characterize the in-place air voids. A total of 92 cores were retrieved from three field projects to establish relationship between the air voids and the measured dielectric by GPR. A statistical model was developed to express the air void value as a function of dielectric and other variables. Contour air void maps could also be produced for the entire pavement sections. The results from the underlying studies have been used as the basis for the repair strategy selections. ©2014 Elsevier Ltd. All rights reserved. Source


Chen D.H.,Central South University of forestry and Technology | Hong F.,203 Bull Creek and 39
Canadian Journal of Civil Engineering | Year: 2014

A cost-effective strategy is needed to remedy the decaying jointed concrete pavements (JCP). The distress problems continue to cause poor ride quality and continued expense and delay to the traveling public. To explore the bonded concrete overlay (BCO), a half mile section was constructed with a 178 mm continuously reinforced concrete (CRC) overlay. Two other nearby sections were monitored along with the CRC BCO section, over the following 3 years. Over the 3 year period, the CRC BCO section was far less expensive to maintain than the other sections that continued to receive conventional full-depth repair (FDR). The ride quality of the CRC BCO section is also improved by approximately 60-100 inches/mile over conventionally FDR sections. It is believed that the CRC BCO offers a cost advantage over the conventional FDR strategy, and should be considered for future JCP rehabilitation projects. Source

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