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. It is a technique which several U.S. states' departments of transportation have successfully used in repairs to address faulting in older jointed plain concrete pavements. The typical approach is to saw cut and jackhammer out the slots for the dowels. Following dowel placement the slots are then typically backfilled with a non-shrink concrete mixture, and the pavement is diamond-ground to restore smoothness.
As a vehicle travels on jointed concrete roads the weight of the vehicle passes from one concrete panel to the next. As the vehicle traverses the joints its weight is placed on the edge of the panel, where the panel is least able to withstand the deflection force. This can cause cracks as pavement shears off the edge of the panel. On older highways built in the early-to-mid 20th century, dowel bars (steel rods) were placed across the joints to help transfer the load from one panel to the next.
This was discontinued because the dowel bars tended to corrode and required frequent replacement. Stainless steel dowel bars are more resistant to corrosion, but stainless steel is relatively expensive compared to other materials. Instead, for several decades, the cohesion between the panels and the strength of the roadbed was relied upon to collectively distribute the load from one panel to the next, a concept known as aggregate interlock. Over time the joints and roadbed tended to break down under stress, resulting in cracks and displacement of the panels. Most highways in the United States built as part of the Interstate Highway System from the 1950s to the 1980s relied solely upon aggregate interlock and began to show problems in the 1970s and 1980s.
In contemporary highway construction since the mid-1990s, dowel bars are once again placed across joints and at intervals along the pavement. Today, dowel bars are coated with epoxy to prevent the corrosion problems seen in earlier installations.
Many states are retrofitting older highways with epoxy-coated dowel bars. The retrofit begins with cutting of six slots (three in each wheel path) across all transverse joints or cracks. The slots are cut with ganged diamond saws that make six cuts in each wheel path. The concrete between the saw cuts is then removed with lightweight jackhammers (heavy-weight jackhammers tend to damage the concrete around the cuts). The epoxy-coated dowel bars are placed in the slots, then the slots are filled with grout and the joints or cracks are filled with waterproof caulk. The final step is to diamond-grind the joint to remove both excess grout and any displacement of the panels.
The final step often involves diamond-grinding of the entire road surface to remove any bumps or dips. Without the dowel bar retrofit this grinding would have to be repeated every six to eight years, but it is predicted that the retrofit will greatly increase this interval. Dowel Bar Retrofit has been proven to outlast Asphalt Overlay by at least ten years, and significantly improves ride quality.
For dowel bar retrofit, dowels, bond breaker, expansion caps, dowel bar support chairs, foam core insert, caulking filler, non-shrink concrete backfill material and submittals are needed. The dowels need to be smooth, round, epoxy and made of bond breaker coated steel conforming to requirements. The bond breaker is to be applied on all surfaces of the dowel bar. The expansion caps belong at each end of the dowel bar and the dowel bar support chairs are used to firmly hold the dowels centered in the slots during backfill operations. The foam core insert is used to re-establish the joint or crack, which allows the bar within each side of the slot to expand and contract. The caulking filler is used to prevent backfill material from flowing into the joint or crack. Non-shrink concrete backfill material that is tested as rapid set concrete patching materials is recommended for use on DBR projects.
First, make two saw cuts in the pavement to outline the longitudinal sides of each dowel bar slot. Saw to a depth and length that allows the center of the dowel to be placed at mid-depth in the pavement slab. Saw slots parallel to each other and to the center line of the roadway with a maximum tolerance of 1⁄4-inch per 12 inches of dowel bar length. Employ saws equipped with gang-mounted diamond blades capable of cutting three or four slots simultaneously in each wheel path. Skewed joints or cracks may require slots longer than the length specified in the plans. Remove water and paste residue from the pavement surface immediately by means of a vacuum attachment on the sawing machine. For smaller projects, a slot sawing machine might not be feasible. Consider allowing the use of walk-behind saws for slot cutting when the project contains fewer than 100 retrofit bars.
Remove existing concrete from the slots followed by the cleaning out of all debris. Use maximum weight 30 pound jackhammers to remove the concrete remaining between the saw cuts. If the concrete removal operations cause damage to the pavement that is to remain, discontinue concrete removal operations and only resume after taking corrective measures. During concrete removal operations, use a small bush hammer as necessary to produce a flat, level surface within the slot so the backfill flows and consolidates under the dowel bars.
Complete installation of retrofit dowels, with dowel bars and backfill placed prior to reopening the lane to public traffic. Place silicone at all joints and cracks followed by the dowel bar assemblies in each slot. Following that, place patching material and then consolidate and finish patching material. Finally, diamond-grind the pavement surface within 30 working days of dowel bar retrofit placement. [1] [2]
Dowel bar retrofits, if done badly, can cause serious problems. These problems are usually due to poor workmanship and can be avoided by careful following of specifications and close supervision of workers. Use of heavy jackhammers (heavier than 14 kg class) tends to cause cracking of the concrete all around the slots. Lack of caulk or voids in the caulk put in the joints or cracks leads to cracks around the joints. Voids in the grout (especially below the dowel bar) can cause failure of the grout.
The completion of the dowel bar retrofit process usually leaves marks on the concrete pavements which consist of short parallel lines in two groups, left and right, 18 inches (46 cm) inward the traveling lane from the lane markings. Each group has 3 or 4 slots that are parallel to the traffic flows. Each rectangular slot has the width of about 2.5 inches (6.4 cm) and the length of about 2 feet (61 cm) or more. [3] The backfilled slots may sometime give an impression that the highway pavements have been milled into grooves especially after the wear of patching material caused by studded tires. [4]
The visible marks may appear to be a symmetrical pattern of dash marks on the roadway, as if there were an associated meaning to the pattern. [5] When there are many of them along the roadway, motorists on the interstate highways may interpret the grind marks as an unknown form of mechanical markers, such as ground-in strips, or strange road surface markings. [6] [7] In some cases, these marks are confusing for motorists. When roads are under construction and lanes are laterally shifted, such marks may interfere with temporary lane markings. As the marks from the dowel bar retrofit are not intended to be any form of road surface markings, the responsible agencies try to make these marks smooth and hope to make them less visible to the motorists. [8]
A road is a thoroughfare for the conveyance of traffic that mostly has an improved surface for use by vehicles and pedestrians. Unlike streets, whose primary function is to serve as public spaces, the main function of roads is transportation.
A chisel is a tool with a characteristically shaped cutting edge of blade on its end; for carving or cutting a hard material such as wood, stone, or metal by hand, struck with a mallet, or mechanical power. The handle and blade of some types of chisel are made of metal or wood with a sharp edge in it.
Highway engineering is a professional engineering discipline branching from the civil engineering subdiscipline of transportation engineering that involves the planning, design, construction, operation, and maintenance of roads, highways, streets, bridges, and tunnels to ensure safe and effective transportation of people and goods. Highway engineering became prominent towards the latter half of the 20th century after World War II. Standards of highway engineering are continuously being improved. Highway engineers must take into account future traffic flows, design of highway intersections/interchanges, geometric alignment and design, highway pavement materials and design, structural design of pavement thickness, and pavement maintenance.
Terrazzo is a composite material, poured in place or precast, which is used for floor and wall treatments. It consists of chips of marble, quartz, granite, glass, or other suitable material, poured with a cementitious binder, polymeric, or a combination of both. Metal strips often divide sections, or changes in color or material in a pattern. Additional chips may be sprinkled atop the mix before it sets. After it is cured it is ground and polished smooth or otherwise finished to produce a uniformly textured surface. "Terrazzo" is also often used to describe any pattern similar to the original terrazzo floors.
A road surface or pavement is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, macadam, hoggin, cobblestone and granite setts were extensively used, but these have mostly been replaced by asphalt or concrete laid on a compacted base course. Asphalt mixtures have been used in pavement construction since the beginning of the 20th century and are of two types: metalled (hard-surfaced) and unmetalled roads. Metalled roadways are made to sustain vehicular load and so are usually made on frequently used roads. Unmetalled roads, also known as gravel roads, are rough and can sustain less weight. Road surfaces are frequently marked to guide traffic.
Asphalt concrete is a composite material commonly used to surface roads, parking lots, airports, and the core of embankment dams. Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century. It consists of mineral aggregate bound together with bitumen, laid in layers, and compacted.
Grout is a dense fluid that hardens used to fill gaps or as reinforcement in existing structures. Grout is generally a mixture of water, cement, and sand, and is employed in pressure grouting, embedding rebar in masonry walls, connecting sections of precast concrete, filling voids, and sealing joints such as those between tiles. Common uses for grout in the household include filling in tiles of shower floors and kitchen tiles. It is often color tinted when it has to be kept visible and sometimes includes fine gravel when being used to fill large spaces. Unlike other structural pastes such as plaster or joint compound, correctly mixed and applied grout forms a water-resistant seal.
This page is a list of construction topics.
Road surface marking is any kind of device or material that is used on a road surface in order to convey official information; they are commonly placed with road marking machines. They can also be applied in other facilities used by vehicles to mark parking spaces or designate areas for other uses. In some countries and areas, road markings are conceived as horizontal traffic signs, as opposed to vertical traffic signs placed on posts.
Botts' dots are round non-reflective raised pavement markers. In many parts of the US, Botts' dots are used, along with reflective raised pavement markers, to mark lanes on highways and arterial roads. They provide tactile and auditory feedback to drivers when moving across designated travel lanes, and are analogous to rumble strips.
A butt joint is a wood joint in which the end of a piece of material is simply placed against another piece. The butt joint is the simplest joint. An unreinforced butt joint is also the weakest joint, as it provides a limited surface area for gluing and lacks any mechanical interlocking to resist external forces.
This glossary of woodworking lists a number of specialized terms and concepts used in woodworking, carpentry, and related disciplines.
In civil engineering, concrete leveling is a procedure that attempts to correct an uneven concrete surface by altering the foundation that the surface sits upon. It is a cheaper alternative to having replacement concrete poured and is commonly performed at small businesses and private homes as well as at factories, warehouses, airports and on roads, highways and other infrastructure.
A snowmelt system prevents the build-up of snow and ice on cycleways, walkways, patios and roadways, or more economically, only a portion of the area such as a pair of 2-foot (0.61 m)-wide tire tracks on a driveway or a 3-foot (0.91 m) center portion of a sidewalk, etc. It is also used to keep entire driveways and patios snow free in snow prone climates. The "snow melt" system is designed to function during a storm to improve safety and eliminate winter maintenance labor including shoveling, plowing snow and spreading de-icing salt or traction grit (sand). A snowmelt system may extend the life of the concrete, asphalt or under pavers by eliminating the use of salts or other de-icing chemicals, and physical damage from winter service vehicles. Many systems are fully automatic and require no human input to maintain a snow/ice-free horizontal surface.
Maintenance of today's bridge infrastructure presents many challenges. Transportation engineering and maintenance personnel must maintain around the clock service to millions of people each year while maintaining millions of cubic meters of concrete distributed throughout their facilities. This infrastructure includes bridges. Presently only a limited number of accurate and economical techniques exist to test these structures for integrity and safety as well as insure that they meet original design specifications.
Polished concrete is a multi-step process where a concrete floor is mechanically ground, honed and polished with bonded abrasives in order to cut a concrete floor's surface. It is then refined with each cut in order to achieve a specified level of appearance.
Concrete pavement restoration (CPR) together with concrete pavement preservation (CPP) is a group of various techniques used to maintain concrete roadways.
Diamond grinding is a pavement preservation technique that corrects a variety of surface imperfections on both concrete and asphalt concrete pavements. Most often utilized on concrete pavement, diamond grinding is typically performed in conjunction with other concrete pavement preservation (CPP) techniques such as road slab stabilization, full- and partial-depth repair, dowel bar retrofit, cross stitching longitudinal cracks or joints and joint and crack resealing. Diamond grinding restores rideability by removing surface irregularities caused during construction or through repeated traffic loading over time. The immediate effect of diamond grinding is a significant improvement in the smoothness of a pavement. Another important effect of diamond grinding is the considerable increase in surface macrotexture and consequent improvement in skid resistance, noise reduction and safety.
Pavement milling is the process of removing at least part of the surface of a paved area such as a road, bridge, or parking lot. Milling removes anywhere from just enough thickness to level and smooth the surface to a full depth removal. There are a number of different reasons for milling a paved area instead of simply repaving over the existing surface.
Bluegrass Companies is a non-explosive demolition company headquartered in Greenville, Alabama. It was founded in 1979 by CEO and owner Nicholas Jenkins. The business comprises the sub-companies: Demolition Technologies, The Machine Shop, Bluegrass Concrete Cutting Inc., and Bluegrassbit. Bluegrass Company has always been headquartered in Greenville, Alabama, though now incorporated in Wyoming. The company is known for the advancement of diamond wire sawing as a technique for non-explosive demolition, later for the creation and patenting of an underwater diamond wire saw, and for assisting the U.S. Department of Energy with various tests as well as nuclear decommissioning.
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