If dowel placement deviates from the desired position, it is said to be misaligned. These bars are mainly used in jointed plain concrete pavement jpcp to carry the additional stress and load induced due to the moving vehicle. Any negligence during the construction process may lead to premature distresses in concrete pavement slabs. Dowel bars are typically placed at the middepth of the slab and should be parallel to the pavement surface and parallel to the direction of travel. Pierce jeff uhlmeyer state pavement engineer pavement design engineer jim weston pavement technology technician prepared for washington state transportation commission department of transportation and in cooperation with u. Course description concrete pavement preservation series. After drilling, secure dowel bars and tie bars into the existing pavement with either an. Repair of minor cracks these are very low small width cracks or hairline cracks. Dowel bar insertion for load transfer at mid panel crack kansas department of transportation video vh393b this is a noncommercial video report on a kansas shrp test section of concrete. This involves cutting a slot in the concrete where each dowel bar is to go, and the dowel bars are placed in special chairs to ensure they are at the correct position and alignment within the slot. Other specialized repairs in clude continually reinforced concrete pavement crcp, retrofitting load transfer with dowel bars and texture planing concrete surfaces to restore ride diamond grinding.
Dowel bar is a terminology used in concrete pavements in general. Methodologies for repair of cracks in pqc in concrete. In normal concrete pavement construction, the width of the concrete placement varies and can be as wide as 50 ft. Performance of dowel bar retrofitted concrete pavement under hvs loading. Based on the concrete pavement climate region, verify the types of reinforcement, tie bars, dowel bars, tie bar baskets, and dowel bar baskets to be used within the concrete pavement, refer to section 401. The temperature and moisture gradient that exists between top and bottom of the concrete pavement slabs causes the curling and warping of the slab. T0 protect the bars from corrosion dowel bars are either stainless steel or epoxy coated.
Typically, dowel baskets span an entire lane width and are fabricated from thick gauge wire. Missouri and minnesota use dbr for working transverse cracks in jointed reinforced concrete pavement jrcp. First, at each mid panel crack the pavement is sawn and cleaned, and. Dowel bar is short round, smooth steel bar used to provide a mechanical connection between slab without restricting horizontal joint movement. Improper placement embedment of dowels leads to decrease in load transfer efficiency, which can result in faulting and other pavement distresses. National highway institute national highway institute. These distresses may appear in the form of uncontrolled cracking, plastic shrinkage cracking, settlement cracking mainly over pipe culverts and near slab culverts, popouts, crack over dowel bars etc. Evaluation of joint and crack load transfer khazanovich and gotlif 2002 2.
This rehabilitation technique is only applicable to cpcd, not crcp. Load transfer is defined as the ability of a joint or crack to transfer wheel load from one slab to the next. Effect of dowel bar arrangements on performance of jointed plain. Longitudinal cracking at transverse joints caused by dowel bars in. A dowel bar retrofit dbr is a method of reinforcing cracks in highway pavement by inserting steel dowel bars in slots cut across the cracks. The concrete pavement guide cpg provides a comprehensive overview of current new construction reconstruction, preservation, and rehabilitation strategies used by the department for concrete pavement. Dowel bar retrofit dbr is a concrete pavement restoration cpr tool that restores load transfer across joints and cracks by installing dowel bars linking the adjoining slabs. In this video, we will discuss about the use of dowel bar in rigid pavement pqc with the diagram. Structural distresses such as concrete spalling and cracking increased in severity with the number of misaligned dowel bars at the joint. Placed across transverse joints at the middepth of the slab transfer load from one slab to another without preventing the joint from opening commonly made of round, smooth, epoxy coated steel bars reduce joint faulting and corner cracking. Guidelines for dowel alignment in concrete pavements. The sawcut depth of a longitudinal contraction joint should be of the slab thickness.
Staying connected with dowel bars pavement interactive. A dowel bar assembly figure 72, commonly called a basket, is placed on the subgrade before paving at the location of the contraction joint. Dowel bar retrofit construction practices pavement. Significantly misaligned dowels may lead to joint locking which can cause slabs to crack.
Dowel bar insertion for load transfer at mid panel crack youtube. The existing concrete should be removed from the dowel bar slot using jackhammers weighing 30 pounds or less. Department of transportation federal highway administration. Practices vary from state to state, but dowel bars are typically required in eightinch or thicker pavements. Joint spacing longer than jpcp and up to a maximum of about 15. In this case, the crack should be dowel bar retrofitted and not the joint.
Good load transfer improves concrete pavement performance by reducing tensile stresses in concrete, reducing corner deflection, and reducing differential deflection. Concrete pavement preservation the national center for. Concrete dowel drills concrete construction magazine. Concrete pavement construction basics placing dowel baskets dowel bars transfer heavy loads across joints in the pavement, preventing faulting at the joint that can lead to pavement damage. Retrofit dowel bars in jointed concrete pavement 163 th 52, zumbrota project description the first retrofit dowel bar project in minnesota was constructed in 1994 on minnesota trunk highway 52 th 52 near zumbrota.
In a retrofit, dowel bars are inserted at joints of existing concrete slabs that did not have them before. Practices for concrete pavements dowel and tie bar misplacement. Debris should be cleaned out of the slot prior to placement, after which gap around the. Retrofit dowel bars in jointed concrete pavement long. The information in the cpg applies to all concrete pavement.
Precast concrete pavement technology washington dc the national academies press doi 101722622710 the installation work included removal of the existing concrete at crack locations preparation of the base and bedding drilling of the dowel bar holes in the exist ing slabs panel placement and sliding of the dowel bars into the. I had tried to give the clear picture about the utilization and importance of dowel bar. Theoretical and practical studies of concrete pavement have determined that the optimal spacing between joints depends on the slab thickness, subbase stiffness, and concrete strength. Dowel bars are commonly used in jointed plain concrete pavements jpcp as a. A fullscale jointed plain concrete pavement jpcp with two different dowel bar arrangements, namely, standard and special method, was constructed and evaluated under actual trafficenvironmental condition in florida. For the half of a dowel bar or tie bar placed in hardened concrete, comply with the standard plans and the following. Dowel bar quantities are provided in the contract plans and field measured on an individual basis, regardless of whether they are installed in a basket or drilled into the adjacent slab pay item nos. Crossstitching and slotstitching stitching concrete pavement cracks and joints. Dowelbar retrofit for portland cement concrete pavements. Slot cutting and removal verify that all slots are cut parallel to each other and to the centerline of the roadway within the maximum tolerance permitted by the contract documents, typically. A dowel basket is a simple truss structure used to hold dowel bars at the appropriate height before pcc placement. Properly installed dowel bar retrofits have had an. The steel bars of this assembly are large and, once incorporated into the concrete pavement, transfer the vehicular load from one slab to another, eliminating differential settlement at the joint. Observing the slab behavior of unjointed plain pavements in service for many years can illustrate how joints are used to control.
Jointing for crack control proper jointing is based on controlling cracks that occur from the natural actions of the concrete pavement. Tayabji 1986 identified the following categories of dowel. Dowel bars assemblies must be centered over the existing transverse joint or transverse crack and parallel to the concrete surface. Longitudinal cracking at transverse joints caused by dowel. The alignment of dowel bars is important since significant. Longitudinal cracking at transverse joints caused by dowel bars in jointed concrete pavements vol.
Dowel bar insertion for load transfer at mid panel crack kansas department of. Figure 52 shows the assembled dowel bars, chairs, end caps and foam core boards on a flat bed trailer. The size of dowel bars depends on the thickness of the pavement. Payment for the perimeter saw cut along the shoulder joint for a pavement repair should be provided when the shoulder is. The pavement on this project was originally constructed in 1984 of jointed reinforced concrete, 225 mm 9 in. A properly performed dowel bar retrofit, with a mix comparable to the existing pavement, will result in repair areas that are hardly noticeable to drivers figure 2.
Dbr restores concrete roadways to structurally sound. By linking slabs, the traffic load is shared, preventing differential vertical movement of the slabs at the joints and cracks, thereby eliminating the formation of faults or stepoffs. The bars are placed between two concrete slabs so that loads are transferred between the two slabs and allowing for any horizontal. Repairs of potholes and corner spalls in concrete pavements etc. Concrete pavement crack repair 4 sheets details of cross stitching, slot, and dowel retrofit. There are other methods available, but dbr is the most proven. Jointed reinforced concrete pavement pavement interactive. The natural response causes the concrete pavement to crack at regular intervals. Dowel bars are typically used at transverse joints to assist in load transfer while the reinforcing steelwire mesh assists in load transfer across cracks. Determine distance from longitudinal crack to hole based on slab thickness t and drill angle.
Joints are placed in the pavement to control the crack location and pattern. For the half of a dowel bar or tie bar placed in fresh concrete, comply with the requirements of section 505. Stitching concrete pavement cracks and joints there are two stitching methods used to repair and strengthen cracks or joints in concrete pave ment. Crack surveys, faulting measurements, and falling weight. The sps2 experiment examines the effects of subsurface drainage, warp and curl, dynamic load response, and more. Concrete pavement rehab best practices manual, mn local road research board california section 401, ssp 41. Wcpa annual concrete pavement conference february, 2020 dowel bar installation dowels transfer loads across transverse joints help prevent faulting dowel bar position and alignment are critical dowel misalignment significant effect on pavement performance resulting in cracking. Transverse crack is functioning as the working joint.
There are two stitching methods used to repair and strengthen cracks or joints in concrete pavement. Dowel bar retrofit slots finished and covered with curing compound. The major areas of concrete pavement rehabilitation are partial depth patching, fulldepth patching, slab replacement, jointcrack sealing. The design factors studied include concrete strength, base type, drained versus undrained construction, lane width, shoulder type, and pavement thickness. Details of dowel bar and tie bar placement are also addressed. Dowelcad was created to aid in the optimization of dowel bar design and, by using it, a pavement engineer can determine joint responses to varying dowel sizes or investigate the impact of various alternate dowel bar configurations. Design and construction of joints for concrete streets. The purpose of dowel bars is to transfer loads across a joint without restricting joint movement due to thermal contraction and expansion of the concrete. Dowel bar insertion for load transfer at mid panel crack. Most state agencies specify transverse contraction joints in plain pavement at an. Dowel bar retrofit construction practices pavement interactive. Dbb provides the best in product, service and support for all of your dowel, bar, basket needs. For continuously reinforced concrete pavements, spot check. Stitching concrete pavement concrete paving association.
Joint and crack sealing and repair for concrete pavements. Using the finite element models, transverse stresses along the. The center of the dowel bar should be below the joint. Possible reasons of such cracks are too little or too much vibration of dowel bar inserter unit, stiff concrete mix, shallow depth of dowel bars, and natural. Crossstitching uses deformed tie bars epoxied or grouted into holes drilled at an angle through a crack. Early cracking of concrete pavement causes and repairs. Properly aligned and embedded dowel bars are vital for load transfer in jointed plain concrete pavements. Concrete crack and partialdepth spall repair manual. To develop load transfer across a joint, dowel bars are arranged at specified intervals and at middepth of the pavement thickness. Remove diamond blade slurry and other debris from dowel bar dowel bar slot.