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The combined effects of traffic loading and the environment will cause every pavement, no matter how well-designed/constructed to deteriorate over time. Repair and rehabilitation are done to slow down or reset this deterioration process. 

The causes and types of failure of pavements, particularly of rigid pavements needs to be understood in order to initiate proper repair and rehabilitation programme to increase their service life. The repair and restoration of rigid pavement depends on the type of distress. Cracking is the most common feature of the rigid pavement. Pumping, faulting, spalling, shrinkage, polished aggregates, punch out, deterioration of joint load transfer system, corner break, alkali-aggregate reaction, pop-outs and blow-ups are some the other causes of failure of rigid pavements.

Crack filling, Crack sealing, Stitching, Diamond grinding, Dowel bar retrofitting, Joint repair, Partial-depth repair and Full-depth repairs are the most common techniques used for restoration of rigid pavements.

It is the process of filling crack filler into 'non-working cracks' to substantially reduce the intrusion of incompressible material and the infiltration of moisture in the pavement. Usually cracks less than 2 mm and are 'non-working' require crack filling. Low viscosity epoxy and polymer- modified asphalt are used as crack filler.

Placement of a specialized material into 'working cracks' using unique configurations to reduce the intrusion of incompressible material and the infiltration of moisture in the pavement is known as crack sealing. Working crack is a crack in the pavement that undergoes significant deflection as well as thermal opening and closing movements greater than 2 mm. These cracks are oriented transverse of the pavement centreline. All unsound material near the crack should be chiseled out to form a trapezoidal notch of 30 to 40 mm deep with width at the bottom of the notch slightly more than at top for better interlocking. After thoroughly cleaning, the notch is given a tack coat and then sealed using epoxy resin mortar.

Stitching 

It is a repair technique to maintain aggregate interlock at the point of cracking and to provide added reinforcement and strength to the pavement. Stitching is carried out for strengthening longitudinal cracks in slabs. Stitching is also adopted to alleviate the problems of omission of tie bars during construction, to tie roadway lanes and centreline longitudinal joints of pavements. There are three types of stitching used; cross-stitching, slot-stitching, and U-bar stitching. Cross-stitching is the most widely used method. 

Cross-stitching is used to repair longitudinal cracks that are in a fair condition. It increases load transfer at the crack by adding steel reinforcement to restrict widening of the crack. It is not an alternative for cracks that are severely deteriorated or functioning as a joint. In cross-stitching, holes are drilled at an angle so that they intersect the longitudinal cracks or joints at about mid-depth of the slab. Dusts are removed by compressed air and epoxy is injected into the holes. Tie bars are inserted and excess epoxy is removed.

For wider cracks/lane separations, slot-stitching should be used. Slot-stitching is the most economical repair method for restoring load transfer, preventing separations, and improving performance of longitudinal joints and wide cracks. In slot-stitching, slots with lengths no shorter than 25 in. are cut approximately perpendicular to the longitudinal joints or cracks using a slot cutting machine or walk-behind saw. Slots are prepared by removing the concrete and cleaning the slot. Deformed bars are placed and a repair mortar is applied, finished, and cured. In slot-stitching, the concrete slabs are held together by the shear stress of deformed bars. It is important to provide high strength repair mortar with good bond and to have good consolidation around the bars.

In U-bar stitching, slots are cut using a slot-cutting machine, and concrete is broken and removed by pneumatic hammer. In this method, anchoring action by the U-bars provides most of the restraining force. Use of proper repair materials and consolidating around the ends of the U-bars is important.

Partial-depth repairs correct surface distress and joint/crack deterioration in the upper third of a concrete slab. When the deterioration is greater in depth or reaches embedded steel, a full-depth repair must be used instead. It involves removing the deteriorated concrete, cleaning the patch area, placing new concrete, and reforming the joint system.

Full-depth repairs fix cracked slabs and joint deterioration by removing at least a portion of the existing slab and replacing it with new concrete. This maintains the structural integrity of the existing slab and pavement. Full-depth repair is also appropriate for shattered slabs, corner breaks, punchouts in CRCP, and some low-severity durability problems. It involves marking the distressed concrete, saw cutting around the perimeter, removing the old concrete, providing load transfer, and placing new concrete. Each repair must be large enough to resist rocking under traffic, yet small enough to minimize the amount of patching material.

Dowel-bar retrofit increases the load transfer efficiency at transverse cracks and joints in PCP and JRCP pavements by linking the slabs together so that the load is distributed evenly across the joint. Improving the load transfer increases the pavement's structural capacity and reduces the potential for faulting.

Slots of required size are cut using diamond saw slot cutters. Dowel bars are then placed in the prepared slots and then the slots are back filled. Backfill materials should have similar thermal properties to the concrete, provide strong bond to the existing concrete, be fast setting, have little shrinkage, and develop enough strength to allow traffic in a short time. High early strength concrete is used for this purpose. Aggregates in the mix should be small enough to allow the concrete to flow around the bar and consolidate properly. Consolidation of backfill material is done with a small spud vibrator. Once the backfill material is applied, the surface is finished flush with the surrounding surface.

Diamond grinding improves a pavement ride by creating a smooth, uniform profile by removing faulting, slab warping, studded tyre wear, and patching unevenness. It is also used for removing bumps in the newly placed concrete pavement, especially at the transverse construction joints. This extends the pavement's service life by reducing impact loadings, which can accelerate cracking and pumping.

Diamond grinding removes a thin layer at the surface of hardened concrete pavement using closely spaced diamond blades. The level surface is achieved by running the blade assembly at a predetermined level across the pavement surface, which produces saw-cut grooves. The uncut concrete between each saw-cut breaks off more or less at a constant level above the saw-cut grooves, leaving a level surface with longitudinal texture