Dowel Bar Retrofit Research Articles

Comparative evaluation of mitigation methods for traffic-induced reflective cracking in airport composite pavement

Composite pavement provides an effective and quick solution to restore structural and functional capacity of airfield pavement. However, discontinuities of concrete slabs cause initiation and propagation of reflective cracking in asphalt overlay. This study aims to evaluate and compare the effectiveness of mitigation methods for traffic-induced reflective cracking in airport composite pavements. Finite element (FE) models were developed and validated to predict pavement responses under heavy weight deflectometer (HWD) and aircraft tire loading. The load transfer efficiency (LTE) of existing rigid pavement were evaluated under common deterioration scenarios like base erosion and concrete damage. The crack potential was indicated by pseudo J-integral considering stress intensity factors (SIFs) of different fracture modes. The results show that thicker asphalt overlay, stress absorbing interlayer, and increase of LTE can help mitigate reflective cracking. Increasing 51-mm overlay (from 76 mm to 127 mm) and applying 25-mm interlayer show the similar reduction in reflective cracking fracture potential by about 35% at early crack stage. However, applying interlayer has more benefit on cost effectiveness and pavement elevation control. On the other hand, dowel bar retrofit and base treatment can improve LTE and thus reduce the crack potential at early crack stage of 76-mm overlay by 40% on doweled pavement and 60% on un-doweled pavement, respectively.

Study on Dowel Bar Retrofit on Rigid Pavement to Load Transfer Restoration

Finite element model analysis was performed with respect to patterns of load transfer relying on the action of aggregate interlocking and on the concurrent action of aggregate interlocking and dowel bars. The best timing for dowel bar retrofit was determined by way of increase in load transfer efficiency and maximum tensile stress borne at joints. The situation of dowel bar retrofit to restore load transfer efficiency was verified by way of onsite tests and economic analysis performed before we came to the conclusion that the way of dowel bar retrofit to restore load transfer efficiency is fairly cost effective. The construction technique of dowel bar retrofit to restore load transfer efficiency is finally summarized in light of engineering practice.

Rehabilitation Assessment of Jointed Concrete Pavement Using the Rolling Dynamic Deflectometer and Ground Penetrating Radar

Abstract Transportation authorities need tools to characterize the structural conditions of jointed concrete pavements (JCPs) to minimize or, in the best case, prevent premature failures of rehabilitated JCPs. Applications of the rolling dynamic deflectometer (RDD) and ground penetrating radar (GPR) in pavement forensic studies and rehabilitation investigations are presented. The continuous RDD deflection profiles allow the evaluation of mid-slab behavior and load transfer conditions of joints/cracks, while GPR surveys assist in detecting adverse subsurface conditions such as voids and increased moisture. In this paper, the patterns in RDD deflection profiles that represent the four different structural conditions in JCPs are presented and discussed. Then, the results from combined RDD and GPR surveys on two rehabilitation projects are presented. In the first project, the problematic slabs with poor load transfer and high vertical differential deflections are identified in the RDD profile. The GPR survey is used to identify the cause of the high differential deflections, voids filled with water under the slabs. The recommendation is to fill the existing voids by using under-sealing techniques and install dowel-bar retrofit prior to a new overlay. In the Grogans Mill project, the RDD profile shows that the southbound lane has a significant number of slabs with a strong potential for reflective cracking. The GPR data indicated that there is moisture beneath the deteriorated slabs. A reconstruction of the southbound lane is recommended. On the other hand, the northbound lane consists of three subsections that require different rehabilitations: Slab replacement, asphalt overlay, and reconstruction. The success of rehabilitation generally depends on the selection of appropriate treatments. By providing 100 % coverage, both RDD and GPR are effective tools in evaluating existing conditions, and the combination of these tools significantly assists in selecting the optimum rehabilitation treatment.

Dowel Bar Retrofit (DBR) performance in Texas

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.

Lessons Learned from Field and Laboratory Testing of a DBR Project

Where faulting takes place due to the absence of dowel bars and inadequate subbase support in jointed concrete pavement (JCP), dowel bar retrofit (DBR) is used to improve load transfer efficiency (LTE) and to prevent further faulting of slabs at transverse joints. Even though DBR generally improves LTEs and overall performance of JCPs, not all DBR projects have been successful. Faulting reoccurred within 2 years after DBR treatment on US59 in Texas. An investigation from the cores taken in the project revealed excessive voids under a dowel bar due to poor consolidation of the grouting material. A laboratory investigation was performed to determine the most critical factors for adequate consolidation of grouting materials in DBR. Typical rapid-setting grout materials widely used in DBR were selected and full-scale specimens were made for evaluations. Four testing variables for consolidation performance were investigated: time of placement after mixing, vibration time, slot width, and maximum aggregate size. Maximum aggregate size and slot width were not critical factors for consolidation performance of grout. The most significant factor was vibration time. Twenty s of vibration is recommended. Placement time was also an important factor, with grout materials placed after initial set performing poorly. Delayed placement of grout materials without vibration led to the most voids under the dowel bars.

Performance of Dowel Bar Retrofit Projects in Texas

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...

Field Performance Monitoring of Repair Treatments on Joint Concrete Pavements

Abstract This paper presents the performance of three rehabilitation methods on six highways to restore the condition of concrete pavement: (1) polyurethane foam injection (PFI), (2) dowel bar retrofit (DBR), and (3) full depth repair (FDR). PFI was able to raise the slabs to the target levels; however, it was not able to maintain the slabs at the target levels and thus prevent slabs from further settlement. In addition, new cracks have been observed in some slabs and it was believed that PFI might have created uneven supports that allowed the truck traffic to shatter the slabs. Long-term benefits of DBR were demonstrated on a project with 10 years of traffic, where asphalt overlay was placed. Only minimum reflective cracks were observed on the DBR sections as compared to severe reflective cracks on sections without DBR. In another project, DBR effectively restored the ride quality that reduced the International Roughness Index (IRI) from 2.83 m/km to 1.26 m/km. The poor ride of this pavement section before DBR was due mainly to severe faulting. This illustrates that dowel bars provided excellent load transfer at transverse contraction joints, which minimized the potential for faulting. FDR has been used to repair localized pavement distresses. However, subsidence of slabs and cracks reappeared on the slabs that received FDR, due partly to the inadequate base support. Currently, there are no objective test methods and criteria for base preparation in the FDR specifications. To improve the effectiveness of FDR, current FDR specifications need to be revised.

Application of Rolling Dynamic Deflectometer to Forensic Studies and Pavement Rehabilitation Projects

Characterization of the load transfer of jointed plain concrete pavements requires proper tools. The rolling dynamic deflectometer (RDD) has been used successfully on many Texas Department of Transportation projects for this purpose. Applications of the RDD in forensic studies and pavement rehabilitation projects are presented. RDD deflection profiles were used to assist in diagnosing the causes of reflective cracks on SH87a, where a reflective crack relief interlayer was placed in a rehabilitation project to minimize reflective cracking. However, frequent and severe reflective cracks still occurred on SH87a in the turning and inside lanes, where traffic is lighter than in the outside lane. It was concluded that poor load transfer at joints (indicated by high relative vertical movements) was one of the main contributing factors to the reflective cracking in these two lanes. Two rehabilitation projects are also presented to show how continuous RDD deflection profiles were critical to the success of the projects. In the BU287 project, RDD profiles were used to identify successfully locations for full-depth repair in Subsection 1 and recommend a different rehabilitation strategy (remove and reconstruct) in Subsection 2 because of the significant number of joints that have a severe potential for reflective cracking. In the SH87b rehabilitation project, the RDD was employed to identify locations that need dowel bar retrofit and other locations that need full-depth repair. It is concluded that RDD data not only are able to provide 100% coverage but also offer quantifiable and objective information for forensic and rehabilitation studies in terms of relative movements at joints and cracks.

Evaluation of Dowel Bar Retrofit Alternatives Using Accelerated Pavement Testing

This paper presents the results of accelerated pavement testing using the heavy vehicle simulator (HVS) to evaluate the performance of dowel bar retrofit (DBR) joints and cracks as measured by deflections and load transfer efficiency (LTE). Four HVS sections were constructed and tested: one with four epoxy-coated steel dowels per wheelpath, one with three epoxy-coated steel dowels per wheelpath, one with four fiber-reinforced polymer (FRP) dowels per wheelpath, and one with one joint with four epoxy-coated steel dowels per wheelpath and the other with four hollow stainless steel dowels per wheelpath. HVS and falling weight deflectometer (FWD) testing indicated that DBR significantly improved the LTE and reduced deflections compared with the undoweled pavement. Previous HVS trafficking damaged LTE on undoweled joints, but no significant loss of LTE was found after heavy HVS trafficking on DBR joints or originally doweled joints. Under FWD testing, the LTE from DBR joints (four steel dowels per wheelpath) was typically between 85 to 90% at lower temperatures before trafficking and greater than 95% for joints with originally installed dowels. The configuration using three dowels per wheelpath was found to have significantly lower LTE than that using four dowels per wheelpath. FRP and grout-filled hollow stainless steel dowels had similar performance to epoxy-coated steel dowels. The equivalent built-in temperature difference values of after-DBR sections are lower than those of before-DBR sections, likely as a result of the time of construction when the slabs were expected to be flattest. This finding indicates that tensile stresses in the concrete slabs could also be decreased by DBR.

Evaluation of Dowel Bar Retrofit Alternatives Using Accelerated Pavement Testing

This paper presents the results of accelerated pavement testing using the heavy vehicle simulator (HVS) to evaluate the performance of dowel bar retrofit (DBR) joints and cracks as measured by deflections and load transfer efficiency (LTE). Four HVS sections were constructed and tested: one with four epoxy-coated steel dowels per wheelpath, one with three epoxy-coated steel dowels per wheelpath, one with four fiber-reinforced polymer (FRP) dowels per wheelpath, and one with one joint with four epoxy-coated steel dowels per wheelpath and the other with four hollow stainless steel dowels per wheelpath. HVS and falling weight deflectometer (FWD) testing indicated that DBR significantly improved the LTE and reduced deflections compared with the undoweled pavement. Previous HVS trafficking damaged LTE on undoweled joints, but no significant loss of LTE was found after heavy HVS trafficking on DBR joints or originally doweled joints. Under FWD testing, the LTE from DBR joints (four steel dowels per wheelpath) was typically between 85 to 90% at lower temperatures before trafficking and greater than 95% for joints with originally installed dowels. The configuration using three dowels per wheelpath was found to have significantly lower LTE than that using four dowels per wheelpath. FRP and grout-filled hollow stainless steel dowels had similar performance to epoxy-coated steel dowels. The equivalent built-in temperature difference values of after-DBR sections are lower than those of before-DBR sections, likely as a result of the time of construction when the slabs were expected to be flattest. This finding indicates that tensile stresses in the concrete slabs could also be decreased by DBR.

Performance of Dowel Bar Retrofitted Concrete Pavement Under Heavy Vehicle Simulator Loading

The California Department of Transportation uses dowel bar retrofit (DBR) as a rehabilitation strategy for concrete pavements. Two test sections were retrofitted with dowel bars and a third section was designated as a control on US-101 near Ukiah, California. All three sections were subjected to accelerated pavement testing by using the Heavy Vehicle Simulator (HVS). The results obtained with the HVS demonstrated a large improvement in load transfer efficiency (LTE) and decreases in maximum vertical deflections and vertical deflection differences from DBR. LTE was not damaged by trafficking on the sections with DBR and was less sensitive to temperature changes than the control section. Falling weight deflectometer testing showed damage to the interlock at the joint on the control section and no damage on the sections with DBR. Joint and crack deflections and deflection differences increased with trafficking. A total equivalent loading of approximately 11,000,000 equivalent single-axle loads was applied to each of the sections with DBR without failure occurring.

Ten-Year Performance of Dowel-Bar Retrofit: Application, Performance, and Lessons Learned

The Washington State Department of Transportation (WSDOT) has been rehabilitating its aged portland cement concrete pavements over the last 10 years by using dowel-bar retrofit, panel replacements, and diamond grinding. These pavements have been rehabilitated, with dowel-bar retrofit, to extend the performance life beyond the original design life of 20 years. The first dowel-bar retrofit application in Washington was constructed as a test section in 1992. Since then, WSDOT has dowel-bar retrofitted more than 350 lane-kilometers. Dowel-bar retrofit performance and application are described, and lessons learned in the last 10 years are discussed.