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Over the years, thicknesses of continuously reinforced concrete pavement (CRCP) increased to accommodate rising truck traffic. With a fixed percentage of longitudinal reinforcement relative to the concrete cross-sectional area, thicker slabs necessitate more reinforcement and reduced bar spacing, potentially hindering consolidation. To address this issue, two-mat steel design was implemented in Texas for pavements with thickness of 330 mm (13 in.) or larger. Performance evaluations of thick CRCPs revealed that horizontal cracking developed at the depth of reinforcement where one-mat steel was placed, while no horizontal cracking was observed where two-mat steel was used. Pavement responses with one-mat and two-mat reinforcements with different depths were analysed by three-dimensional modelling with a finite element analysis (FEA) programme for the wide range of environmental loadings. Maximum concrete vertical tensile stresses around longitudinal reinforcement at transverse crack area are a good indicator of horizontal cracking potential; those stresses were evaluated, along with concrete stresses at top of the slab, which are responsible for top-down transverse cracking. The results show that the two-mat design causes higher concrete stresses at the top of the concrete slab and lower concrete stresses around the longitudinal reinforcement, leading to increased transverse cracks and a reduction in horizontal cracking potential. [ABSTRACT FROM AUTHOR]

Permeable pavements are often developed as alternatives to traditional pavement (TP) systems for the mitigation of urban stormwater runoff impairment. The objective of this study was to evaluate the stormwater runoff and pollutant load-reduction performance of an enhanced permeable interlocking concrete pavement system with enlarged joints filled with gravel. This system was compared with an adjacent TP application located in La Feria, Texas. Both pavements were monitored for 2 years through a total of 65 storm events. Both pavement systems received some run-on stormwater flows from surrounding areas that included sediment and nutrients. Runoff volume was 80% lower than the TP. Furthermore, total suspended solids, 5-day biochemical oxygen demand, and Escherichia coli exhibited average reductions of 76% for 23 samples, 56% for 19 samples, and 12% for 11 samples, respectively. Field data were used to develop a Windows Source Loading and Management Model (WinSLAMM) method, which was in good agreement with the observed values. [ABSTRACT FROM AUTHOR]

Over the years, the design of thin and ultra-thin concrete overlays (TWT and UTW) has improved. The performance of TWT and UTW sections built with various designs in Texas has been evaluated, with the goal of further improving design standards and construction specifications. Distresses observed in TWT and UTW sections built prior to 2005 were associated with (1) panel size and layout, (2) transition areas, (3) sliding of slab panels, and (4) defects in existing HMA. Design improvements were made in 2011 to mitigate those distresses, which included placing joints away from wheel paths and the use of continuously reinforced concrete pavement (CRCP) or thickened slabs at transition areas. Regardless of the slab thicknesses used, the panel layout should be 1.83- × 1.83-m (6- × 6-ft). The goal is to have saw-cut joints away from the wheel paths, and thus reducing wheel load stresses in concrete slabs. The increase in curling stresses due to the use of this slab size compared with smaller size slabs appears to be offset more by reduced wheel load stresses. Comprehensive characterization of the existing HMA condition should be made to identify and address hidden defects before the TWT or UTW overlays. Even with some distresses, TWT and UTW sections in Texas have performed satisfactorily with oldest sections having been in service for more than 14 years with minimal repairs required. No distresses have been observed in two TWT projects built in 2011 and 2012 with the improved design practices. [ABSTRACT FROM AUTHOR]

Abstract: In the last 10years, 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 25mm has been successfully corrected by DBR and DG on the US287 project, which still provides good ride quality after 6years 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 6.4mm–9.4mm developed in less than 2years. 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 9.5mm–12.7mm was not a critical factor for the consolidation of the grout. Although slot width above 63.5mm 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, 20s 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. [Copyright &y& Elsevier]

A section of jointed concrete pavement on U.S. 75, which was built from 1982 to 1985, in the Paris District of the Texas Department of Transportation (TxDOT) experienced severe pumping and settlement, even though two types of treatment (full depth repair and polyurethane foam injection) were performed. An extensive field investigation was conducted using ground penetrating radar, falling weight deflectometer, dynamic cone penetrometer, and coring to identify the causes of the continued pumping and settlement problems, and develop an optimal repair strategy. The pavement evaluation included tie bar condition, load transfer efficiency (LTE) at transverse and longitudinal construction joints, and base support conditions. Some of the tie bars failed in shear due to corrosion, which resulted in substantially low LTEs (<40%) at longitudinal construction joints. Pumping and settlement problems were more pronounced where the tie bars failed; the resulting large deflections exacerbated the pumping and settlement problems. The results demonstrate the importance of adequate LTEs (>80%) provided by tie bars, base and subgrade support, in providing satisfactory JCP performance. Inadequate design or construction of any of these critical elements could lead to performance problems, potentially including severe settlement, which is quite difficult to repair. To repair this pavement section, the Paris District of TxDOT is planning to retrofit tie bars by the “slot stitching” method, along with filling the voids under the slab using grout, followed by thin overlay using latex modified concrete to correct the differential elevation problems at longitudinal construction joints. It is expected that this repair strategy will address the distress problems and extend the pavement life. [ABSTRACT FROM AUTHOR]

Gravel aggregates have been used extensively in the Houston District for continuously reinforced concrete (CRC) pavements construction for many years. However, some of these pavements have been subject to early-age delamination and eventual spalling damage. A series of studies since the early 1990's have been conducted to gain a better understanding of mechanisms, material properties, and construction practices related to delamination and spalling. This paper describes a systematic and methodical approach for selecting construction measures to counter the negative effects of using gravel aggregates in concrete paving as it pertains to minimizing early-age delamination distress. The approach was developed based on laboratory measures and practices, numerical approaches for assessing delamination potential, and test sections established in the Houston District, Texas. The testing programs in the laboratory and the field, as well as the analytical results, are presented in this paper. The analysis of the results leads to a step-by-step approach for evaluating and selecting construction measures. [ABSTRACT FROM AUTHOR]

In Texas, many miles of plain jointed concrete pavement (JCP) were constructed without proper load transfer devices such as dowels. After a number of years of service, some JCP sections without dowels showed distresses in the form of faulting at transverse joints. Some of the sections were designed in accordance with the AASHTO 1986 Guide, which required 50–75 mm thicker slabs in exchange for not using dowels. This pavement design did not work, with faulting at transverse joints that cause poor ride. Dowel bar retrofit (DBR) was performed on four projects to restore the pavement condition. Overall, DBR restored load transfer efficiency and resulted in improvement of ride quality. Even where the subbase stiffness is 5–10 times less than the minimum value required for proper performance of JCPs, properly installed DBR effectively restored pavement condition with minimum faulting after decades of service. Therefore, it indicated that DBR is able to minimize the faulting even where there is poor base/subgrade support. This is significant in that there are no effective and practical methods to improve subbase conditions in existing concrete pavement, whereas DBR can restore pavement conditions at a reasonable cost. However, not all DBR projects were successful. In one DBR project, faulting in the range of 6.4–9.5 mm occurred after less than 2 years of treatment. Forensic investigation revealed voids under the dowel bars, which indicates poor consolidation of the grout material. Efforts are currently underway in TxDOT to improve specifications for grout materials and DBR construction. [ABSTRACT FROM AUTHOR]

The main objective of the forensic study was to identify the cause(s) of the pavement failure on a temporary detour of an interstate highway in Austin, Texas. Ground penetrating radar (GPR), falling weight deflectometer (FWD), coring, trenching, and comprehensive laboratory tests were performed. It was found that the main cause of the premature failure was attributed to material and construction practices. The base material used on this project did not meet the Triaxial class 1 requirement; it tested as a class 2.3 material. The base material was found to be highly moisture susceptible; it did not meet the Texas Department of Transportation's (TxDOT's) compressive strength requirements when subjected to capillary soaking. In addition, the repetitive triaxial test results revealed that the stiffness and load-carrying capability and resistance to permanent deformation became inadequate when the base material was exposed to moisture. It is believed that moisture entered this pavement primarily through poorly compacted AC layers and longitudinal joints. Cores taken in March 2004 from the original type B and C layers confirmed that the majority of cores have air voids exceeding 9%. The lower type B layer was also badly segregated and debonded from the upper type C layer at some locations. GPR results also indicated that the joints in the pavement were excessively porous. Further tests on the recovered binder for the type B layer indicated that the binder was prematurely aged, most probably from overheating during production. [ABSTRACT FROM AUTHOR]

Reflective cracking through jointed concrete pavement overlays has been a persistent problem. Several different rehabilitation strategies have been used in Texas. This paper is a summary of the performance of strategies used in the past 10 years. The performance of the crack-retarding grid has been disappointing as it has been related to several premature failures. Only one project has realized a benefit of the crack-retarding grid, where the reflective cracking was delayed by about 1 year. The writers believe the small openings in the crack-retarding grid and the lack of an effective bond may be the causes of the layer separation. A proprietary crack-retarding asphalt material has been performing well over two years of monitoring. In one experimental project, 100% of the cracks reflected through conventional overlay material in the first year. Both Petromat fabric underseal and crack-retarding asphalt material have been performing satisfactorily to retard reflective cracking. However, there is a large cost difference between these two treatments. Seven experimental treatments on a major section of US 59 were evaluated. The worst-performing section on the US 59 project was the break-and-seat method, which failed due to weak subgrade support. The weak subgrade is unable to support cracked concrete, which leads to a rocking action under traffic loads. It is concluded that for future projects, the break-and-seat method should not be applied on subgrade with a dynamic cone penetrometer penetration rate exceeding 25 mm per blow. A flexible base overlay with thin asphalt surfacing and the Arkansas (large stone) mix have performed well. Flexible base overlays were able to absorb the joint movement and eliminate the reflective cracking. The flexible base should be of top quality with very low moisture susceptibility. In Texas, this involves specifying a Texas triaxial Class 1 material with classification of “good” in suction/dielectric tests. It is also critical to provide an effective seal for the flexible base. A chip seal followed by a thin 75-mm hot mix layer is recommended. [ABSTRACT FROM AUTHOR]