Section 8: Joint Repair
In PCC pavements, joints are provided to accommodate concrete volume changes due to temperature and moisture variations. In concrete pavement contraction design (CPCD), both transverse and longitudinal joints are used. Only longitudinal joints are used in continuously reinforced concrete pavement (CRCP) except for expansion joints at the bridge approaches and transverse construction joints. These joints relieve stresses in concrete, thereby preventing or minimizing the potential for uncontrolled cracks. The concrete movement at the joints could be substantial, and joint sealants are provided to seal and protect the joints from the infiltration of water and incompressible foreign materials.
Joints are one of the weakest areas in PCC pavement. There is a discontinuity in concrete at saw-cut joints and wheel load is not 100% transferred from one slab to the next, which results in higher wheel load stress. When incompressible materials get into the joints, expansion of concrete slabs due to high temperature will squeeze the incompressible materials and high localized stresses will develop in the concrete. Localized high concrete stresses can cause spalling in the joints. Also, if a good joint seal is not maintained, water can get into the joint and cause rust problems in dowel bars as shown in Figure 10-21.
Figure 10-21. Rusted dowel bar.
At the transverse joints in CPCD, dowel bars are used to improve load transfer efficiency (LTE). The higher the LTE the lower the wheel load stress and the better the pavement performance. For dowel bars to perform as they are intended, their alignment should be parallel to the direction of concrete movement, both horizontally and vertically. If dowel bars are misaligned, high stress concentration and cracking will result in concrete. Figure 10-22 illustrates a misaligned dowel bar.
Figure 10-22. Misaligned dowel bar.Anchor: #i1004205
Pavement Distresses that Require Joint Repairs
In CPCD, any cracking, breaking, or spalling of slab edges on either side of a transverse joints need to be repaired. The repair can be full depth repair (FDR) or partial depth repair (PDR), depending on the extent of the breaking or spalling. If the distress extends through the depth of the slab or hinders the ability of dowel bars to transfer load, FDR is required.
In CRCP, failures in transverse construction joints require joint repairs. Additional longitudinal steel is used at the transverse construction joints to accommodate large concrete stresses, which requires special attention for concrete consolidation under the longitudinal steel. If proper consolidation is not provided at the transverse joints, delamination and distress can result as shown in Figure 10-23. Any repair of the transverse construction joints requires FDR.
Figure 10-23. Construction joint failure.
As for the boundaries of joint repairs in CPCD, if the patch boundary falls within 6 ft. of an existing undoweled transverse joint that does not require repair, extend the patch to the transverse joint. If the boundary falls on an existing doweled transverse joint, and the other side of the joint does not require repair, extend the patch beyond the transverse joint by about 1 ft. to remove the existing dowels.Anchor: #i1004235
Load Transfer Devices
During the joint repair in CPCD, dowels need to be provided at transverse joints and tie bars at longitudinal joints. For CRCP joint repair, tie bars need to be provided as described in Section 2, “Full-Depth Repair.”