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e sport called crew is an Olympic event. If you have ever witnessed a live crew event, you are immediately impressed with the coordination, leadership, positioning, and skill needed to bring a group of individuals together into a single rhythm. One member of the team who is just a split second...
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For almost 4 decades, the American Concrete Pavement Association's Excellence in Concrete Pavements awards have been presented to agencies, contractors, and engineers whose work represents the best highways, streets, roads, and airports in the United States. The competition for these highly coveted...
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Beginning in the 1950s as a European import, post-tensioned concrete has changed the face of American building construction. Starting from lift slabs with button-headed wires and evolving into flying forms and cast-in-place slabs post-tensioned with strand tendons, post-tensioning has become a...
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Are we ready to accept high-volume fly-ash concrete in cold-weather climates? A number of practitioners in Canada's largest city, Toronto, think so. They are betting that a 50/50 fly-ash-to-portland-cement mix for a four-story 120,000-square-foot computer sciences building on the campus of York...
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The California Department of Transportation (Caltrans) needed a concrete pavement that would deliver a surface ready for traffic in 4 hours. Different admixture manufacturers experimented with various combinations to try to achieve this. Finally, Master Builders came up with what they call "4x4...
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Across the Midwestern states last December, there was a much greater accumulation of snowfall than usual. Ground temperatures, as a result, tended to remain around freezing. With little snow in January and temperatures frequently fluctuating above and below freezing, exterior concrete slabs...
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Perhaps the most visibly distinctive trait of a construction field leader is the ability to keep the "troops" focused on their current and future work. Some practical techniques that you can incorporate immediately are: create a vision, cast the vision, and then recast the vision.
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Emily and the late Joseph Pulitzer Jr. needed a home for their art collection. Introduced to the work of Tadao Ando—Japan's leading architect and a proponent of modernist architecture—they asked him to design the building. Initially they planned to rehabilitate an old building, but Emily Pulitzer...
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Despite 4 years of diverting rush-hour traffic and obstructing Salt Lake City's main freeway with orange barrels and construction equipment, Utah's Department of Transportation boasts a 75% public approval rating. This remarkable accomplishment is a testament to the largest highway design-build...
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During the fall of 2000, radio, TV, and print ads announced the impending openings of Disney's California Adventure theme park, Downtown Disney (an adjacent pedestrian mall), and the adjoining Grand Californian Hotel. Excitement and curiosity were growing among the general public. The concrete...
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How do you build tunnels of interstate highway four lanes wide through poor soil beneath vital railroad tracks without shutting down the rail lines? This was the dilemma faced by the Slattery/ Interbeton/White/Perini Joint Venture, working on a portion of the Central Artery/Tunnel Project—often...
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Finishing concrete has always been about timing: being in the right place at the right time with the right tool. With the now widespread acceptance of the F-number system, good power troweling techniques are essential since floor flatness depends directly on a finisher's ability to run trowel...
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When you are in the military, you don't ask questions. But, when you are working with concrete in hot weather, you had better know the answers. Back in June 1966, my buddy Sammy and I were assigned to pour some concrete near the Danang Air Base to provide a base slab on grade for a military field...
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To prevent thermal cracking, most state departments of transportation cite a maximum temperature differential requirement for mass concrete in bridge piers. This requirement can create headaches for the contractor who hasn't fully considered how to deal with it. We asked Martha VanGeem, principal...
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It started at the very beginning while preparing the ground for the forming crew. Bob had to delay the forming crew by a half day because the job was graded incorrectly. To add insult to injury, the forming crew then placed the forms several inches off the mark in three critical places. Having...
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If you don't remember what formwork was like before plywood, take a look at the exposed concrete in historic structures, and you'll see the marks of hundreds of boards that made up the form faces. The advent of plywood with dependable, waterproof glue was a revolutionary development for form...
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What do an ex-fighter pilot, an engineer, a former Marine, a barn repair specialist, and a surfer have in common? Concrete. On a sunny Friday in May, in Colorado Springs, eight concrete contractors met in a conference room. It's not important how the members came into their professions. What...
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Big contractors and small contractors are different. Or are they? In this issue, Concrete Construction presents its first listing of the top concrete contractors in the United States. We've done our best to get information on the big guys, frankly, just because they are big. And yet, many of our...
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While financial statements are critical to managing a profitable company, other key measurements can also shed light on the operational and customer satisfaction improvements your business is making. This article examines one measurement that sheds light on operations, sales, and...
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Deterioration of the nation's concrete bridges and transportation infrastructure has reached alarming levels. Bridge engineers and federal transportation officials have been using and experimenting with new reinforcing materials that provide corrosion protection not provided by traditional black...
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Troweling the surface of a slab while the concrete is still bleeding.
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Polymer-modified concrete is commonly used in many applications. You should know what polymers you are using and their strengths and weaknesses. Making the right choice could determine the success or failure of an installation—and the resultant liabilities.
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Fiber-reinforced polymer (FRP), stainless steel, stainless-clad steel, and MMFX steel bars comprise the new generation of concrete reinforcing materials being used for durable construction. Their service life impressively surpasses traditional materials.
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Cracks in supported concrete slabs are usually the result of normal and expected behavior of a reinforced concrete structure due to shrinkage and deflection.
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This article discusses techniques that contractors find effective to find good workers. It also looks at some more creative avenues, such as Internet postings, local contacts, job fairs, and signing bonuses.
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Ed Finkel of Edward B. Finkel Associates of Berkley Heights, N.J. and Gary Herron, technical services director for Redi-Mix, LP, of Carrollton, Texas, explain how they were able to work together with a stringent specification for aggregate grading and minimum water content.
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Concrete Construction has spoken with five successful concrete contractors and found that successful contractors are, indeed, all alike: they have enthusiasm for the work, they respect their customers and employees, and they aren't worried about sharing the keys to success.
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Commonly called "rod busters" or "ironworkers," workers who place reinforcing steel have one of the most physically demanding jobs in the industry.
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"I felt it would be a lot of fun to design and build a cast-in-place reinforced concrete house, so I sketched out this little bungalow on the brow of a hill," says Harold Ashton, founder and CEO of The Ashton Company, Tucson, Ariz. He took his drawing to Tucson architect Diana Kuhel Osborne, who...
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After 2 years and numerous changes, in January 1999 the final contract was signed for the first phase of artist James Turrell's largest work based on the changing experience of light.
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Insulated concrete forms (ICF) are leading the way as a forming system and a construction technique for above grade homes. Polystyrene forms are held together by form ties and concrete is placed inside these forms. When the concrete cures, the forms remain in place to serve as insulation and...
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Slabjacking has many advantages over slab removal and replacement.
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The Xtender, a new mechanical tension and compression rebar splicing system, finding widespread acceptance in the western United States, has both structural and field installation advantages. Bar end preparation is quick, simple, and economical and can be done either in the shop or in the field...
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A wise construction leader uses production information to determine a crew's efficiency. When properly educated on what performance numbers mean, even an hourly laborer can benefit by recognizing acceptable or nonacceptable work.
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What alternative does the contractor have when concrete test cylinders show strengths are below specification? Is core testing required whenever this happens or are nondestructive tests like the rebound hammer sufficient? Who is responsible when the specified concrete strength is not met?
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While durable concrete can be successfully placed in hot weather, increased rates of hydration and evaporation in fresh concrete and other problems can adversely affect concrete quality.
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Without clear, accurate, and timely information about production, decision-makers have a difficult time making the best decisions. Timely and accurate information in the hands of your leaders and crews can and will make you money.
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Reaction between carbon dioxide and a hydroxide or oxide to form carbonate, especially in cement paste, mortar, or concrete
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Hydrodemolition, faster than a jackhammer, produces a better surface for concrete repair and protective coatings.
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The first step in repairing concrete must always be an objective look at why a repair is needed.
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Major repair projects often exceed budget by up to 500%. You can avoid such a situation if you determine repair requirements and costs systematically and logically, and closely monitor the work.
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The Performance Pyramid is an employee improvement process for coaching any new worker to become a better worker. This entire article is dedicated to training.
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Are we moving toward a recession?
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"It takes a unique kind of person to become a pump operator," says Jack Brundage of Brundage Bone Concrete Pumping, Kent, Wash.
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The all-terrain forklift (ATF), or material handler, is truly a versatile machine. While a backhoe is designed specifically for trenching and a loader for moving dirt, an ATF can adapt to any material-handling job.
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As the coach of a construction team, you should continually observe your "players"—at all skill levels and then do everything possible to motivate them. This article considers some coaching strategies.
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Daily reports help superintendents and project managers track job progress and subcontractor performance. If you are a subcontractor, daily reports can document interferences by the general contractor or other subcontractors. Estimators can use daily reports to price future similar projects. Daily...
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In the Denver area, most claims against home builders are due to foundation problems. Contractors across the country face a similar dilemma.
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With most available modular wall forming systems offering pressure ratings no higher than 1650 psf, EFCO made news at World of Concrete 2001 when it introduced a new modular form system designed to handle 2400 psf lateral pressure.
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Soon after Harbor Towers in Boston was built in 1972, residents complained about water leaking into their units. Over the next several years, saltwater from winds coming off the sea penetrated the porous concrete and corroded the steel reinforcement. Carbonization reduced the alkalinity of the...
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Although we don't actually want concrete to crack, we certainly expect it to, and all good designs plan for it. Indeed, the reinforcement in concrete doesn't even begin to work until it cracks. We even put in lines of weakness and beg the cracks to follow, which of course they sometimes don't.
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Low compressive strength test results can be due to one of three things. This article discusses the three causes of low results and how to prevent these problems.
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Imagine living in a house that is fireproof, can safely protect you and your family from tornadoes and hurricanes, and is earthquake resistant. Your costs for heating and air conditioning are greatly reduced (at a time when energy costs could double), you have no need to worry about termites and...
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There's an ongoing debate about the minimum sawcut joint depth needed to minimize random cracking in pavements. For many years, specifiers have required a minimum depth one-third or one-fourth the slab thickness, with the deeper cuts being used for longitudinal joints in highway pavements. Many...
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When the Las Vegas Justice Center is complete in February 2002, it will comprise 710,000 square feet of space. The main structural elements of the concrete-frame building include an 18-story high-rise tower, a 5-story low-rise building, and an independent elevator tower with footbridges connecting...
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The number of construction projects using wet-mix instead of dry-mix shotcrete continues to grow, primarily because wet-mix shotcreting can achieve a higher production rate. Contractors using this concrete placing method have a number of pump options. But what's the best pump type to own or rent...
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How can designers improve the quality, efficiency, and safety of construction operations? In the United Kingdom, greater use of hybrid structures may be the answer. By combining a variety of appropriate structural elements in one building, architects and designers can offer their clients a wide...
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Connect the dots, color between the lines, and share. These lessons we learned in kindergarten can be applied throughout our lives and even on the jobsite. Taylor Ball, San Diego, recently applied the first lesson by taking a simple connect-the-dots approach to the layout of footing excavations and...
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During the summer of 1999, a concrete contractor placed an exterior parking lot for a commercial building in the Midwest. The concrete was air entrained and received a broomed finish, followed by 3 days of moist curing with plastic-coated burlap. Because some of the concrete set at a different rate...
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Some design-build contractors whose building types include tilt-up concrete now offer their clients a curved-wall option that enhances a structure's architectural appeal. This also enables the contractors to create a niche market--separating themselves from other tilt-up builders. Here we describe...
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In structures for which rebar corrosion isn't an issue, calcium chloride is the most economical and effective accelerating admixture. It's widely used in a liquid solution in unreinforced pavements, residential foundation walls, and floors placed in cold weather. It helps concrete set and gain...
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Two expressways with a total price tag of $3 billion and a construction schedule that could span 15 years have been referred to as "highways of hope" for the region around Pittsburgh in western Pennsylvania. The Mon/Fayette Expressway will extend about 70 miles south from Pittsburgh through the...
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Typically, air-entraining admixtures are added to exterior concrete to increase the concrete's durability. When you think of exterior conditions, you think of freezing temperatures. Thus, shouldn't air be added to concrete for a freezer floor slab as well, since the concrete will be exposed to...
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Is your bid getting fair consideration? Does it stand out from the rest of the crowd? More important, do customers understand your proposals and are they leading to sales? For concrete contractors to be profitable in today's competitive marketplace, addressing these questions is essential. Here is...
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Table 4.1 in ACI 224R-90, "Control of Cracking in Concrete Structures," lists tolerable crack widths for reinforced concrete under various exposure conditions. Section 4.4 of ACI 224R-90 indicates that a portion of the cracks in a structure should be expected to exceed the values in Table 4.1 by a...
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We have a problem with a concrete stain product. It appears that the stain did not truly penetrate. We are told that the use of liquid curing compounds created a barrier to the stain even though the contractor applied a paint stripper first. These areas need to be re-done, but we would like to know...
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I recently poured a 30x50-foot pad that has cracked very badly. The pad had no rebar and no expansion joints.
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In the past year or so I've had problems with scaling and delaminations while placing and finishing floors.
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I am building a 900-gallon concrete fishpond and waterfall, and I am confused as to which type of mortar to use and what I can use as an additive to help waterproof the cement.
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Our garage floor has several popouts, some as large as a hand and 1/2 to 3/4 inch in depth. What causes them, and what is the best way to repair them? We live in Minnesota and thought the salt in the winter time was the culprit. Any information would be appreciated.
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We recently placed a concrete floor with a laser screed. The floor had an FF requirement of 35 and an FL of 30.
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I had a new concrete driveway poured in September of 2000. In January of 2001, I noticed that the very thin top layer is chipping and flaking.
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Before we purchased our home, part of the foundation under the house dropped approximately 4 inches. At that time the owner hired a contractor to fix the problem. By digging down alongside and putting jacks under the foundation, the contractor raised the level of the home to its proper elevation...
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Do you have any information about concrete mixes for better soundproofing? The contractor wants to use the smallest amount of concrete between building floors but wants to achieve maximum soundproofing benefits.
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We have been lining manure pits with concrete on slopes of 2H:1V for some years and have always specified (per ACI recommendations) the use of long chutes or pumps to place the concrete as near to its final position as possible.
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Do you know of any equipment that uses vibration or ultrasonic waves to pulverize concrete? We have a bridge demolition project in Rock Island, Ill., that requires removing existing concrete-filled grating from the structure. Conventional means of removal is impractical due to a tight schedule, so...
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In the February 2001 issue of Concrete Construction, a reader asked, "Is there any way to saw joints all the way to a wall?"
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I would like to comment on a question in the December 2000 Problem Clinic. The problem was blistering of epoxy-terrazzo applied to a concrete slab with a 4-inch layer of granular fill over the vapor retarder. The question was if a vacuum pump could be us
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Our home is 2.5 years old, and the basement slab is constantly wet. Water is moving from the subgrade through the concrete. We did a pH test on the moisture, and it has a considerable acid content. The carpet, which was glued to the concrete, has come loose. What can we do about this problem?
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In the February issue, Concrete Construction's editors requested reader feedback on the subject of rolling stones. Here are their responses:
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ASTM C 42-99, Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete, requires measuring the length of the capped specimen to the nearest 0.1 inch (2 mm) and using this length to compute the length-to-diameter ratio prior
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I'm in a concrete apprenticeship-training program and would like any information you could send me about concrete construction.
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The specification for the floor of a maintenance building called for a 6-inch slab thickness and concrete with a design compressive strength of 3000 psi. The actual average cylinder strength for the floor concrete was 3630 psi. Four months after the floor
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A large number of 2- and 3-foot diameter, 18-foot-high concrete columns were placed on caissons without the required reinforcing steel that connects the caissons and columns. To repair this, the contractor had to drill holes in the caisson outside each co
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We supplied concrete for a large floor, which the concrete contractor placed using a laser-guided self-propelled screed and riding power trowels. He initially floated the surface with pans and then used combo blades for later floating and troweling. During the late troweling stages, the blades were...
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When we saw contraction joints for slabs placed when walls are already in place, we have to end the cut 2 to 4 inches from each wall, depending on the saw-blade diameter. The crack that forms at the end--as a continuation of the cut--is never straight. Is there any way to saw joints all the way to...
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We've just started doing decorative concrete work and want to know how soon to power-wash and seal a colored surface after concrete placement.