 Under ideal conditions, a PCC pavement might last forever. You probably would too if you lived under ideal conditions. But just as time and nature take their toll on people, they also can wear down even the best built pavement. Thousands of miles of PCC pavement were constructed in the 1950s and 60s, which means many of these roads are pushing 40 years old. Cracks form the wrinkles on their weathered faces, and a constant diet of heavy loads have caused faulted slabs to bulge above what was once a long flat line. Not only is this unsightly, but it can prove annoying and possibly even dangerous in bad weather. I've been on roads where I could have sworn I was driving on square tires. That constant thump-thump-thump caused by uneven joints just about drove me nuts. You might say I was fit to be died. Which, coincidentally, is the title of this program. Of course, we're not talking about me or other frustrated motorists. We're talking about deteriorating PCC pavements, which have become a series of uneven slabs. Slabs that are fit to be tied. Obviously, these deteriorated PCC pavements need to be rehabilitated. This rehabilitation can be as extreme as removal and replacement. However, it may be as simple as retrofitting the joint with dowel bars and then grinding the surface. Grinding is a proven process. Retrofitting, on the other hand, may be new to you. That's the reason for this videotape. To introduce the procedure for retrofitting, plain jointed Portland cement concrete with dowel bars. Washington State has selected this process as a life-cycle cost-effective method to rehabilitate many of their concrete pavements. The details of this tape refer to this project, which is one of the first in the country to do large-scale retrofitting of dowel bars. Obviously, subsequent projects, or projects in different geographical areas, may need modifications to the procedure. So it is important to thoroughly review the conditions of existing plain jointed PCC pavements prior to selecting this rehabilitation procedure. In this tape, we'll cover the reason for retrofitting dowel bars and their installation. We've already mentioned the need for retrofitting. Age and heavy traffic have caused cracking and faulting at joints and resulting in tolerable, rough concrete pavements. To understand how this happened, let's review some basic facts about PCC pavements. First, concrete cracks as it cures. You can't prevent it, but you can control it. This is done by saw cutting or placement of joint forming tape in the new PCC, which causes the concrete to crack at these joint locations. Washington State does this at 12 to 15-foot intervals. It should be noted that this procedure is for unreinforced plain jointed PCC pavements and not for continuously reinforced PCC pavements. So in essence, the PCC pavement in this video is not one long continuous pavement. Instead, it is a series of individual slabs or panels. One of the main concerns with this jointed pavement is how vehicle weight shifts from one slab to the next. This is referred to as load transfer. Inadequate load transfer leads to faulting of joints. Think of each slab as a seesaw, a heavy load, in this case an 18-wheeler, is placed on one end of the slab. The weight pushes down on the end of the slab causing it to deflect. As the load moves across the joint, the adjacent slab end is deflected while the previously deflected slab is returning to its original position. This action across the joint leads to movement of fine material beneath the slab, wearing of the PCC surfaces of the crack and in this case, lifting of one slab above the other or faulting. The problem worsens over time because now the weight is falling from one slab to the other as the fault increases. Dowel bar retrofitting and grinding help correct these problems. The dowel bars provide for weight transfer from one slab to the next, minimizing end slab deflection. Grinding removes the fault and together with dowel bar retrofitting dramatically reduces the effects of the faulting mechanism. Today, many jointed PCC pavements are constructed with dowel bars. Assemblies called load transfer units are placed on the base prior to paving or the bars may be placed automatically during the paving operation. On older pavements, however, dowels may not have been used or their design life loading has been exceeded. The result has been faulting. To remedy this problem, dowel bars are placed or retrofitted into the pavement. How well do they work? Preliminary results indicate success on this project. The existing road was heavily faulted. The average fault was three eighths of an inch with some faults as bad as three quarters of an inch. The average load transfer was only 33%. In other words, only about a third of each vehicle's weight was distributed evenly between panels. The rest of the weight caused excessive deflections of these slab units. After retrofit dowel bar placement and surface grinding, the fault was removed and load transfer exceeded 80%. So future faulting is unlikely. Not only is the process considered successful, but comparable or cheaper than other rehabilitation procedures. Other possible rehabilitation procedures of removal and replacement or overlaying with ACP or PCC were considered. Removal and replacement or overlaying with PCC pavement far exceeded the cost of this procedure. Overlaying with ACP, although comparable in cost, does not address the problem of reflective cracking and pavement rutting. This procedure provides for extension of the pavement life from 10 to 15 years at a low yearly cost, yet not eliminating other rehabilitation options that could be used at a later date. That is, as long as the bars are properly installed. Research shows that in order for the dowel bars to function properly, certain criteria have to be met regarding the type and size of bar used, bar spacing along each joint, bar position in the concrete, and allowance for concrete expansion and contraction. Let's begin with bar type and size. On this project, a one and one half inch diameter, 18 inch long smooth dowel bar is used. It's epoxy coated to prevent rusting, which locks up the bar, not allowing it to move. It's smooth, so it does not bond to the concrete. The one and a half inch diameter was chosen to best transfer a load across the joint. The 18 inch length ensures enough of the bar will be in each slab to transfer the load. Spacing is carefully planned to provide load transfer across the joint. Here, six bars are placed along the transverse joint of each slab. The bars are divided into two groups of three. The bars are 12 inches apart in each group. One group begins two feet from the centerline joint and the other begins one foot from the shoulder joint. This places each group under the areas that most effectively provide for load transfer. Now for positioning inside the concrete, the bar should be centered across the joint. Vertical placement should be approximately mid depth or at the slab neutral axis. The bar must also be parallel to both the surface and centerline. A skewed bar would interfere with concrete expansion and contraction and possibly cause failure of the dowel bar retrofit. Not only must the bars be parallel to allow for expansion and contraction, but also the grout cannot be allowed to bind to the bar. If concrete's allowed to adhere to the bar, the concrete would crack and spall when the concrete expands and contracts. So as already mentioned, the bars are smooth to prevent adhesion. In addition, each bar is coated with a bond breaker which further prevents bonding. Also, caps are placed on the end of each bar. There is a quarter inch cap inside each cap to allow for bar movement during concrete expansion and contraction. Okay, if those requirements are met, the dowel bar should function properly. It's designed to anyway. Of course, even the best laid plans must be followed through. So let's examine the installation procedure used on this project, starting with an overview of the construction steps. First, joints to receive retrofit dowel bars are identified and marked. Second, slots are cut across the transverse joint. Third, concrete inside each slot is broken out with a light jack hammer. Fourth, the slot is cleaned. Fifth, cracks in the slot are filled with an approved caulk. Six, a foam core board is placed over the dowel bar which has been pre-coated with parting compound. Seventh, caps are placed on the end of the dowel bar. Eight, two chairs are placed on the bar. Ninth, the dowel is placed in the slot so it rests on both chairs. Tenth, grout is placed in the slot. Eleventh, the grout is saw cut. Twelfth, the pavement is ground to the proper texture and surface smoothness. And finally, 13th, the transverse joints are sealed. Let's go back and look at each of those steps in more detail. The first step is to determine if a slab is suitable for retrofitting. If there's minimal cracking along the joint, retrofitting will work. However, if there's severe or multiple cracking within a panel or another type of major distress, the pavement is beyond the help retrofitting can provide. In these cases, slab removal and replacement is the more viable option. This rehabilitation project combined both retrofitting and replacement. Another thing to look for are transverse cracks that are actually acting as joints. For some reason, the concrete may not have cracked at the design joint. So it cracked elsewhere in the slab. Or the panel may have cracked naturally in the middle of the slab to relieve pressure. Faulting at a transverse crack is a good indication that it's a working crack and it's serving the same purpose as the design joint. On this project, some transverse cracks are marked to receive retrofit dowel bars as well. All transverse cracks with poor load transfer and faulting should be retrofitted. Next, the slot ser cut, either with concrete saws or with a specially designed piece of equipment. Here, the slot machine cuts all the slots at the same time. Slot locations are preset on the machine. In any case, it's a good idea to ensure the cuts are in the proper location. Two feet from the center line, one foot from the edge line with one foot spacing between bars in each group. The dimensions of the cut must also be correct to assure that the bar is placed within a quarter inch tolerance vertically and horizontally. Proper dimensions are important. The length and width provide adequate clearance to ensure the bar can be properly positioned and backfilled. The depth is necessary to ensure that the bar is placed approximately in the middle of the slab and parallel with the surface of the roadway. Next, any concrete remaining in the slot should be chipped away with a jackhammer weighing 30 pounds or less. Anything heavier may cause spalling on the sides or bottom of the slot or cracking of the surrounding concrete. The walls of the slot will be smooth because of the saw cuts. The bottom of the slot, however, will be in a semi-ruffened condition. It can't be too rough though. The bar has to be set level with the required clearance below. The next step is cleaning, which consists of removing debris, sandblasting, and one or more passes with an air blast. First, broken up concrete is removed and properly disposed of. Next, all exposed walls of the slot should be sandblasted. This allows for better bonding. Of course, any residue left in the slot following sandblasting will also prevent bonding, so it should be removed by air blasting. During cleaning, see the precautions are taken to safeguard workers and motorists. The proper gear should be worn and screens should be set up to protect passing cars. The next step is crack filling. The crack in the wall or bottom of the slot must be filled to prevent intrusion of the grout into the crack, which would interfere with concrete expansion and contraction. An approved caulking filler should be used. In this case, silicone was used. After the slot has been cut and cleaned and with the cracks caulked, a slot is ready for the dowel bar. The bar must be properly prepared, however, before being placed in the slot. Each bar should be coated with an approved liquid membrane-forming bond breaker. Here, it's already been applied. The entire bar should be lightly coated and prevented from bonding to the grout. Care should be taken during coating and later during bar placement that none of the bond breaker comes in contact with the slot surface. You don't want to prevent bonding there. So if any bond breaker drips onto the walls or bottom of the slot, it must be removed by sandblasting. Now, because the existing joint was removed during slot cutting, a filler is needed to maintain the transverse joint during grout placement. The filler remains in the permanent joint to allow for concrete expansion. Here, a half-inch foam core board is used, which can be obtained from most office supply stores. Other thicknesses may be used with one quarter-inch considered to be the minimum. The board is cut to the proper dimensions. To stand on its own, it must be slightly wider than the slot. On this project, it's two and a half inches wide. The board's length may vary. The important thing to remember is that the combination of the saw cut and board provide a continuous zone allowing for expansion and contraction of the concrete. A hole with the same diameter as the dowel bar is cut a half-inch from the bottom of the board. Then the board has slid halfway down the bar. Next, plastic caps are fitted on both ends of the bar. Remember, there must be a gap inside each end to allow for bar movement. Here, quarter-inch-long nubs inside the cap prevent the bar from sliding all the way to the end. There's one more step before bar placement, two non-metallic or epoxy-coated chairs are placed on the bottom of the slot or are attached directly to the bar. They will support the bar and give it the required clearance from the sides, bottom, and ends of the slot. Now the board and bar can be placed into the slot. The bar should be approximately mid-depth in the concrete, in the middle of the slot. It should be equal distance from the sides and ends of the slot. The foam board should fit tightly in the slot. The bottom of the board resting on the bottom of the slot. The top of the board at the location where the transverse joint will be saw cut. So in this case, because the saw cut will be an inch and a half deep, the top of the board was placed an inch and a half below the surface. With the board and bar securely in place, the slot is almost ready for grout. But first, it's cleaned one final time by air blasting. In this case, it's then sprayed with water. Some grouts may require a wet surface and some may not. In either case, grout placements should be done according to the manufacturer's recommendations or as tested for use. Now the slot's ready for grout. The type used must be an approved low shrink material. Foss Rock Patch Rock 1060 is being used on this project. The grout should be mixed according to the manufacturer's recommendations. The proper type and amounts of ingredients should be thoroughly mixed. In this case, the Foss Rock material is extended 100% with quarter inch minus P gravel. Because the grout sets quickly, it should be placed soon after it's mixed. But that doesn't mean the pour itself should be done hurriedly. The grout must be placed with care. The board and bar cannot move during placement. Remember, exact positioning is critical for performance. So any movement is cause for rejection. The slot should be filled until it's even with the pavement surface. The grout should be vibrated to ensure consolidation around the dowel bar. Excess grout should be struck off and the surface given a smooth, even finish. The grout should be protected while it cures according to the manufacturer's instructions. No traffic should be allowed over the slots until a minimal strength as designed has been obtained. The grout is green-cut as quickly as possible to allow for concrete expansion. In this case, within 24 hours. Okay, that's the basic retrofitting procedure. With the dowel bars in place, further faulting and cracking is minimized. However, the existing faults still must be corrected by grinding. Although this video concentrates on retrofitting dowel bars, let's briefly review the grinding procedure as well. Self-propelled machines dedicated only to smoothing and texturing PCC pavements should be used. In this case, diamond-tipped saw blades are used to do the cutting. Care should be taken to ensure the equipment does not cause excessive ravelling, aggregate fractures, spalls, or any other damage to the joints or underlying pavement. Any damage caused must be corrected and the problem solved before grinding proceeds. The grinding residue should be continuously removed so it does not drain across traffic lanes or onto the shoulder. The residue should be disposed of properly. Here it's placed on the slopes, which is acceptable as long as the runoff doesn't enter a waterway. Of course, the main concern with grinding is the finished result. The two key factors are texture and profile. First, texture. This is what the completed surface should look like. This texture provides the best possible traction and skid resistance. The width of the grooves in the area between them must be within the tolerances of the contract documents. This is achieved by the width of the diamond blades and spacers. The height of the ridges may vary depending on the hardness of the aggregate in the concrete pavement. If the specified texture is not being produced, the blade spacing should be adjusted. The other surface concerns are the profile and cross slope. There are two ways to check the profile. One method is to use a straight edge placed parallel to the center line. The more exact method of checking the surface profile is to use a profile graph. The profile graph must be an approved type, meeting agency specifications for design and operation. In order for the surface to be considered smooth enough for acceptance, the profile index must be within specification ranges. The method to check the cross slope, assuring that wheel rutting is removed, is to use a straight edge placed perpendicular to the center line. And that's grinding. The last step of the operation is joint sealing, which is performed basically the same way as a typical joint sealing or resealing operation. So there is no need to cover that procedure here, which brings us to the end of this program. Remember the old surface? Quite a face lift, huh? And one that should last for a long time because retrofitting dowel bars has greatly increased load transfer between slabs. There should be far less cracking and falling. It's as if deteriorating PCC pavements have found a new life, a second wind, possibly even a fountain of youth.