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Repair, overlay, replace, and reconstruct: These have become the operative terms for today's paving contractor. Not only are fewer concrete pavements being built on new alignments, the traveling public is demanding fewer construction-related delays.
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When Rockwell Automation Corp., Milwaukee, Wis., set out to build a new conveyor-drive manufacturing facility in Clio, S.C., one of the top demands was a high-performance floor slab with excellent abrasion resistance and minimal cracking and curling.
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Curling at floor joints is a common problem. However, field observations and experimental studies have shown that substantial reductions in curling can be achieved by using proprietary square steel dowels fitted with a clip-on device that puts the sides of the dowel in contact with a compressible...
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One of the most important but often overlooked organizational tasks of a construction supervisor is planning a layout for the project site. Many decisions must be made such as where to place office trailers, where to store onsite materials, and where to keep equipment when not in use. Unfortunately...
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Indispensable tools on any concrete repair jobsite, cut-off saws can be used to make quick, shallow cuts through concrete and steel. Common applications include cutting openings in walls, square cutting patch perimeters, and cutting rebar and post-tensioning tendons.
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When it comes to construction, he who has the plan has the control. Obviously, for any project--especially a large one--contractors should produce detailed plans to identify each phase of a construction project.
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Thanks to a great deal of planning and coordination, winter placement of a massive foundation mat for Columbia Center No. 2, a 14-story office building in Troy, Mich., went without a hitch. The 21,000-square-foot mat was placed in November, at a time of year when Michigan weather is always...
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According to a study funded by the National Cooperative Highway Research Program, initial pavement smoothness significantly affects future pavement smoothness, leading to pavements that remain smoother longer. But what's the best way to get better initial smoothness so that pavements last longer...
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A petrographic report is often used in construction disputes or litigation as evidence of poor workmanship by contractors. Contractors may accept these conclusions because they don't understand the limitations of petrographers' techniques. But because of these limitations, some of the conclusions...
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Longitudinal cracking and low air content due to excessive vibration can cause premature concrete pavement deterioration. Because vibrator frequency is a key controllable factor affecting the consolidation defects that lead to such deterioration, state DOT specifications often require paving...
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Routing and sealing is a common crack-repair method in which the crack is made wider at the surface with a saw or grinder, and the resulting groove is filled with a flexible sealant. This prevents water and debris from entering the crack yet allows the crack to open and close in response to loads...
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Patching of corrosion-damaged concrete is by far the most common concrete repair procedure, comprising a significant portion of the total repair market. In some cases, rebar corrosion has progressed to the point where the concrete member must be replaced. But in most cases, partial-depth patching...
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The U.S. Census Bureau projects the value of construction put in place in 1999 will slightly exceed $700 billion. What share of that number does concrete work command? And what is the size of the different market segments?
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Because corrosion of reinforcement can result in concrete cracking, staining, spalling and costly repairs, corrosion-resistant reinforcement often is the obvious choice for concrete structures exposed to high chloride levels.
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After placing, vibrating, and finishing concrete for a bridge deck, contractors sometimes notice cracks forming directly over the top-mat rebar.
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The next time you buy a drum of cure-and-seal, you may be getting a product quite different from the same brand you've used previously.
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Like colored taffy, strips of the interior concrete floor of Milwaukee's new Midwest Express Convention Center slip under the windows of the building's exterior facade and pass to the outside, where they roll through the gray concrete sidewalk and curl to form flamboyant bus-stop shelters or...
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The most effective way to clean dirt and stains from concrete without damaging its surface is power washing. Most power-washing equipment is simple to use and cleaning procedures are pretty straightforward.
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Miller Park, soon to be the new home of the Milwaukee Brewers, will feature retractable roof sections that unfold, like the petals of a fan, on tracks set atop a 1,050-foot-long curved concrete beam system.
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Form-release agents or form oils cost but a small fraction of the cost of the formwork itself, but they have a big influence on the quality and success of the concrete surface.
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For more than 50 years, concrete finishers have been warned about the dangers of using tools or methods that densify and seal the concrete surface before bleeding has stopped.
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Few contractors would take on a large, elaborate foundation project requiring corner angles of 90, 135, 142, and 153 degrees and wall thicknesses of 8, 10, 12, 14, 16, and 34 inches.
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For optimum performance, repair materials or coatings must form a strong bond with the concrete substrate. But how can you accurately measure this bond strength in the field?
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Surface voids, such as bug holes, form-tie holes, and honeycomb, are a fact of life in cast-in-place concrete construction. Depending on project specifications, they may need to be repaired.
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How do you satisfy a customer who wants an elegant, durable screening wall that's also low-maintenance and reasonable in price?
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With an overall height of 667 feet, the Millennium Tower will usher in the turn of the century as Austria's tallest building.
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What do curved retaining walls and stadium risers have in common? They're just two of the unique applications contractors have found for using slipforming technology.
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When an elevated concrete slab is to be cast on a steel deck, what are the most effective measures architects, engineers, and contractors can take to control cracking? This is an unresolved issue for many builders.
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Prepackaged concrete repair materials come with data sheets listing the material's performance in a variety of lab tests, which presumably attest to the material's quality.
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Contractors who routinely replace driveways, parking lots, or other pavements often say their backhoe loader is indispensable.
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Day in and day out, concrete repair contractors perform the tough task of removing weak or damaged concrete with a very tough tool: the hand-held pneumatic chipping hammer.
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Since its introduction to the construction industry in the 1950s, shotcreting has grown into an important and widely used concrete placement technique, and advances in materials, equipment, and procedures continue to expand its applications.
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How to build and maintain light commercial and residential slabs using single-strand unbonded post-tensioning systems--this is the essential message of Construction and Maintenance Procedures Manual for Post-Tensioned Slabs-on-Ground.
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There are many challenges unique to repairing historic concrete, not the least of which is matching the color, finish, and texture of the existing concrete as closely as possible. Repair of historic concrete should begin with an investigation of the concrete to evaluate the existing condition and...
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In building the underground garage for the new expansion to Milwaukee's art museum, contractor C.G. Schmidt is using some sophisticated forming techniques.
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With the increasing demand for concrete homes, more builders are opting to use insulating concrete forms (ICFs) rather than traditional wood-frame construction.
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At the turn of the century, inventor Thomas Alva Edison developed a clever system of cast-iron molds that would allow a contractor to pour a concrete house in a day.
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Foundations settle for many reasons, including poorly compacted fill, poor drainage, or soil dessication. For residential and light commercial applications, steel underpinning systems are viable solutions for stabilizing and raising sunken foundations.
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The benefits of well-cured concrete don't apply to floors that must reach a low moisture-vapor emission rate before floor coverings are installed.
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Peter Emmons, president of Structural Preservation Systems Inc., talks about the concrete repair market, strategic alliances, sharing leadership, and managing growth.
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When concrete slabs on grade curl, the curling sometimes has little effect on floor performance. If the total curl is less than 1/4 inch or curling occurs primarily in low-traffic areas or under storage racks, the owner can often live with it, provided that cracking isn't excessive. There are...
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Illinois' largest pavement patching company, G.M. Sipes Construction Co., Rushville, Ill., replaces an average of 50,000 to 60,000 tons of pavement annually, leaving the company with a lot of concrete and asphalt rubble to dispose of.
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The Nashville Oilers' new 67,000-seat stadium on the Cumberland River's east bank hosted its first competition long before its fall 1999 opening. You might call it the Nashville Concrete Playoffs because two separate construction teams, both working for the same contractor, squared off to build the...
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When a Missouri River backwater stream near Washington, Mo., in Franklin County, nearly destroyed old Route 100 during floods that struck the St. Louis area in 1993, the water washed out soil to a depth of 16 feet, destroying two lanes of the highway.
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Why is a 10-mile stretch of California's Interstate 10 so special to many contractors and engineers in the concrete pavement industry? Constructed in 1946, this extraordinary section of I-10 is the oldest existing concrete pavement rehabilitation project in the United States.
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Many contractors prefer pumping to crane-and-bucket placement of concrete because it's faster and can reduce labor costs.
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In 1998, when the world's largest pasta maker, Barilla, started to build its first plant in the United States in Ames, Iowa, rapid construction was essential since Barilla was losing more than $1 million in import costs each month.
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W.A. Jennings, founder of form manufacturer EFCO, said more than 64 years ago: "It's not the initial cost of equipment that counts, but the initial cost plus the cost of using." That statement underlies the methods EFCO has developed for comparing the cost-effectiveness of various forming systems.
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Forming footings with lumber and installing a drainage system are time-consuming chores for foundation contractors.
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By nature, construction is a risky business. An economic downturn, labor difficulties, material shortages, equipment problems, and a host of other problems can cause a contractor's business to fail—leaving projects at a standstill. That's why an increasing number of owners are requiring surety...
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Over the past 15 years, manufacturers have developed numerous high-solids, fast-curing coating systems they claim will resist sulfuric acid in sewers and wastewater treatment plants.
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This is an article defining concrete for the new worker.
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Within the last few years, major U.S. admixture suppliers have introduced a new category of chemical admixtures—shrinkage-reducing admixtures (SRAs).
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A first-time exhibitor at World of Concrete, Doka Formwork Technology is a full-line formwork supplier with principal factories in Austria and Germany, and other facilities in more than 16 countries around the world.
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Will using a thin sand layer under floor slabs reduce subgrade or subbase support, causing cracking and poor joint performance, especially under repeated loadings such as forklift traffic? To gather data to help answer this question, The Aberdeen Group performed California Bearing Ratio tests on...
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Convinced there had to be an easier way to form concrete footings, builder Richard Fearn invented and patented two fabric forming systems that overcome many of the disadvantages of using lumber.
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When Whiteman Industries, a division of Multiquip Inc., Carson, Calif., built a new 134,000-square-foot manufacturing facility in Boise, Idaho, in 1998, it hired Concrete Northwest of Idaho to do all the concrete work. Whiteman also gave CNI a unique opportunity: the chance to test drive the latest...
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Years ago, many bridges had unsealed joints. A simple gap in the deck accommodated small movements, and finger-plate joints or similar systems accommodated larger movements.
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For more than 20 years, builders of parking structures have predominantly used all-steel forming systems, which are mechanically set, stripped and moved.
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Until the summer of 1997, the two-story attached parking garage of Park Place Tower, a residential high-rise in Chicago, contained only 600 parking stalls for the residents of the tower's 900 deluxe apartments.
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Non-air-entrained concrete with a moisture content near saturation is susceptible to surface scaling caused by freeze-thaw cycles.
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Due to the high cost of litigation and its tendency to drag on, contractors are showing an increased interest in using arbitration to resolve disputes, especially those involving smaller settlements.
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Imagine trying to build a large concrete structure without the use of modern equipment and skilled labor. This is exactly the situation that confronts contractors in the West Indies every day, says the author, who describes his experiences overseeing the construction of a large reinforced-concrete...
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In the fall of 1997, officials at the airfield at Ft. Campbell, KY., faced a problem concerning the disposal of water contaminated with jet fuel.
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More than 1.5 billion square feet of unbonded post-tensioned structures have been built in the United States since the mid-1960s.
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Imagine you were suddenly unable to retrieve your accounts-receivable records, or your project-management software lost track of all activities scheduled for completion early next year.
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Everybody and everything that represents your business creates an image and promotes an identity. It's up to you to decide if this company image turns out to be positive or negative, says the author, the president of a successful concrete construction company located in a Chicago suburb.
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Before erecting tilt-up concrete panels, you must allow them to gain enough strength to withstand lifting stresses.
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Because a construction site is a hazardous place, your business can be hit hard with the many direct and indirect costs of nonfatal accidents and injuries including medical expenses, lost productivity, delays and disruptions to work, and administrative costs.
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Narrow-strip concrete placements are the industry standard for narrow-aisle, defined-traffic warehouse slabs. To meet the tight flatness tolerances, usually Fmin 50 to 100, contractors perform narrow-strip construction by setting edge forms 14 to 20 feet apart and striking off the concrete with a...
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"To stay on schedule, especially for fast-track projects, general contractors may be tempted to have floor coverings installed on concrete slabs regardless of the water-vapor emission rate of the slab. But before assuming responsibility for floor-covering performance, they should assess the...
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Composed of cement, water and small, discrete air cells, cellular concrete is a lightweight material that solves many heavy-duty construction problems. Used beneath roadways, bridge ramps, buildings and other structures, it reduces soil loading while adding compressive and shear strength...
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Proper design and execution can make compaction grouting a reliable method for densifying loose soils and raising settled structures.
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When using a fog spray to prevent plastic shrinkage cracking during a concrete flatwork placement, aren't you taking a chance that the water-cement ratio at the surface will increase, reducing concrete quality?
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What's the difference between hydrophilic and hydrophobic polyurethane grouts? Whenever I ask anyone, they say that hydrophilic grouts "love water" and hydrophobic grouts "hate water," but this means nothing to me when I'm trying to select a grout for a certain application. When should each be used?
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I'm a distributor of concrete repair materials that are often used in steel manufacturing plants.
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We just had our first experience with slab curling. What causes it and what can be done to avoid it?
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If reinforcing bars have been stored outside and have a coating of rust, how much rust is acceptable?
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Where should we place rebar in a floor that's a slab on grade? I've heard it needs to be near the top. But to increase tensile strength, shouldn't it be near the bottom?
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We have a job calling for shrinkage-compensating concrete.
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I am required to monitor the differences between interior and exterior concrete temperatures on a mass concrete placement. How many thermometers, or thermocouples, are needed to get a reliable measure of the internal temperatures?
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When rebar have been bent but then aren't used, is it permissible to straighten them in the field for use as straight bars in reinforced concrete?
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Specifications for entrained-air content always include a minimum and maximum limit. I know that too little air reduces concrete's resistance to damage caused by freeze-thaw cycles and deicers. But if the air content exceeds the maximum by a percent or two, how does that affect the concrete?
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How do you calculate form pressures if the rate of placement for walls will exceed 10 feet per hour or the lift height for columns will exceed 18 feet?
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In ACI 117-90, "Standard Specifications for Tolerances for Concrete Construction and Materials," what are the tolerances for deflections of concrete slabs placed on metal decking supported by structural steel frames? My client has a problem with excessive deflection.
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We're considering using steel fibers instead of rebar to reinforce a concrete slab on grade. However, we're concerned about the effects of these fibers on floating, restraightening and troweling operations, and on floor flatness. What floor flatnesses are achievable when steel fibers are used in...
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We build a lot of forms for square cross-section columns with 24-inch sides. Depending on the forming details, at least half of the 48-inch-wide sheathing panels have to be cut 24 3/4 inches wide to allow for overlap at the corners. That leaves us with a lot of leftover plywood 23 1/4 inches wide...
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We're working on a project that requires building a secondary containment structure using concrete made with Type K expansive cement. The design compressive strength is 4000 psi, which makes us concerned about the low strength-test results we've been gett
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We know that overlaid plywood forming panels have greater dimensional stability and smoother, more durable forming surfaces than nonoverlaid panels. But what factors should we consider when choosing between medium-density overlaid (MDO) and high-density overlaid (HDO) panels?
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We are a small residential contractor in southern Arkansas, building slab-on-grade monolithic foundations reinforced with steel and welded wire fabric. During the past couple of years we started having trouble with slab settlement and cracks in the concrete, so we started pouring wider and deeper...
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We are placing a 4-inch-thick concrete floor for a 93,000-square-foot department store, but the architect has limited the size of each pour to 2,160 square feet to prevent premature shrinkage cracks. This limitation will severely cut our productivity and increase our costs. How can we convince the...
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What is the rate of expansion and contraction for a concrete slab on grade due to temperature changes, and how much movement can be expected because of temperature change?
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We're placing a concrete slab on metal decking, and the plans require welded wire fabric to be supported by chairs. Because the chairs are likely to be dislodged by workers during placement, we're trying to convince the designer that we can pull the fabric into the correct position with hooks. Does...
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We want to embed rigid polyvinyl-chloride pipe in concrete to allow drainage under a golf-cart path. The engineer won't allow this because chemicals in the concrete might attack the PVC. I know PVC has been widely used in this sort of application, but I'm
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We build the concrete floor for a building occupied by a tenant who requires tight control of temperature and relative humidity in the work area. The tenant must maintain a relative humidity of 30% to 50% at a temperature of 68° F. But even though HVAC equipment was installed, the relative humidity...