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Thin-shell concrete dome storage or shop buildings up to 50 feet in diameter can be built quickly and economically using inflatable forms made of high-strength architectural fabric. The forms are reusable and allow the use of about one-third the material required for construction of a conventional...
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The results of a study conducted in the mid-1950s show that it's not high concentrations of deicers that cause the heaviest scaling, but relatively low amounts in the range of 2% to 4%.
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Article profiles the winners and finalists in the eighth annual National Awards Program for Excellence in Concrete Pavement, sponsored by the American Concrete Pavement Association and Concrete Construction. This year's program attracted 85 project nominations. Industry representatives judged each...
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Most manufacturers of floor coverings and adhesives recommend installing an impermeable covering on concrete floors only when moisture flow through the concrete is less than 3 lbs/1,000 sq ft/24 hrs. But problems with loose floor coverings and blistered coatings have increased in the last 10 years...
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Productivity, or rather the lack of it, is the foremost problem confronting many construction firms. Contractors commonly measure their productivity by taking their output (measured in dollars or units) and dividing it by the number of labor hours required to achieve the output. But productivity is...
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Since 1985, Seattle artist Vicki Scuri has worked to enhance the visual environment in urban and public spaces. Concrete has become a significant part of her work because she recognizes its durability, timeliness and cost-effective manufacturing techniques, under both factory-controlled and field...
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Before you unfold the boom of a pump truck on a new jobsite, be sure to check for power lines and other obstructions, excavations, and unstable ground.
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Contractors must take the time and effort to review every contract before signing it, being especially watchful for clauses that make it impossible for them to finish work on time, make a profit or win a contract dispute in court.
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Using float pans, which are attached to the blades of walk-behind or nonoverlapping ride-on power trowels, offers finishers several advantages, including increased productivity, flatter floors, easier transition from wet to dry areas when floating and superior ability to break open the concrete...
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Article discusses what factors contractors should consider before buying a walk-behind or ride-on power trowel, including design features, productivity, power options, drive mechanisms and ease of control.
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Article describes various models of engine-powered vibrating screeds designed to save finishers time, labor and back strain. According to one screed manufacturer, an experienced finisher--with an experienced laborer spreading the concrete--can strike off 20,000 square feet in an eight-hour day when...
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Used widely in commercial construction for years, concrete floor systems have recently blazed trails into the residential market. The main reason is the growing popularity of stay-in-place insulating concrete form homes. A concrete floor works well with ICFs because concrete walls can carry the...
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When high-performance concrete for industrial floors is specified, the concrete must not only perform well in its hardened state, it also must possess certain plastic properties so contractors can properly place and finish it.
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The author, president of a consulting firm that assists in the planning and construction of concrete floors, says that the two most common approaches for judging a floor's surface appearance comparing the final product to a small test panel or evaluating how closely it complies with the project...
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Providing such benefits as easy handling, multiple reuses and smooth surface finishes, GFRP forms are a popular choice for architectural concrete. A combination of about one-third glass fibers and two-thirds polyester resin, GFRP forms are typically used to form columns, beams and slabs (typically...
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Article profiles 11 residential-wall forming systems, ranging from high-density overlaid (HDO) plywood-panel systems to heavy-duty aluminum forms. Special hardware systems for use with plywood panels also are described. The descriptions include panel dimensions and materials, system applications...
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When forming bulkheads, footings, foundation walls and other concrete elements having surfaces that will not be exposed to view, expanded metal stiffened by integrally formed ribs is an effective sheathing material. It remains in place, saving the labor of form stripping, and the rough surface...
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On the calm waters of Lake Erie, against the backdrop of the Rock and Roll Hall of Fame, 25 civil-engineering students across North America raced canoes they crafted out of lightweight concrete and special reinforcing materials. The goal: to win the 1997 ASCE/Master Builders National Concrete Canoe...
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Composite construction is the most common structural system for elevated floors. It consists of concrete placed on metal decking that's supported by structural steel beams and girders. As the concrete hardens, the steel framing and concrete bond together to carry dead and live loads. Until the...
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Is it possible to create exposed-aggregate walkways with enough rock at the surface to make pedestrians think they're walking on gravel paths? Ahal Contracting Co., St. Louis, proved the task can be done when its crews placed 40,000 square feet of exposed-aggregate walkways for the Missouri...
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Available in an endless array of colors and patterns, polymer-modified cementitious resurfacing systems can add beauty to sidewalks, driveways, patios, pool decks and other existing concrete surfaces. The systems can even be used on vertical surfaces, such as walls and step risers. The resurfacing...
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Thanks to the creative talent of artist Vicki Scuri, the colorful concrete flatwork of Play Ray Plaza at Seattle's Key Arena has replaced what was once a dismal asphalt entry resembling a parking lot. In recent years, Scuri's work in concrete has provided the aesthetic concept for this and other...
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One of the most effective tax-saving tools, a like-kind tax-deferred exchange, is finally gaining widespread attention in the construction industry. Construction equipment is largely, if not entirely, depreciated by the time you replace it. But since the equipment retains significant market value...
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Among the top building types -- pre-engineered metal, masonry, precast concrete and tilt-up concrete -- what is the best option for today's consumer, who demands products that are cheaper, faster and better? Recent studies show that the building industry is gravitating toward tilt-up construction...
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Implementing a bulletproof plan is critical to the success of a tilt-up project, especially on a large, fast-track job. The author, president of a successful tilt-up contracting firm in North Carolina, presents five essential steps to developing an effective plan. They include reviewing the...
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Topped out in May 1997, the $97 million Charles Evans Whittaker U.S. Courthouse in Kansas City, Mo., is already being called one of the city's most impressive landmarks. The 587,000-square-foot C-shaped concrete-frame building was built using 20-inch-deep by 66-inch-wide pan forms, with joists and...
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Many design professionals choose not to use welded wire fabric in slabs or pavements because they believe the amount of cover can't be controlled. To address these concerns, research was conducted in 1996 to determine if WWF was at its correct location in a completed slab or pavement in which...
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After a highly successful first run, the Post-Tensioning Institute's Design and Construction of Post-Tensioned Slabs-on-Ground has been extensively revised. Since the book's initial publication in 1980, it has been used by engineers and contractors to successfully design and construct hundreds of...
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We're going to be placing concrete slabs on grade in an area where the water soluble sulfate content of the soil is 0.4% (severe exposure). Is the use of Type V cement mandatory for this exposure?
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An early start on concrete curing can provide many benefits, especially for hot-weather placements. It can help to prevent stickiness, sponginess and surface crusting conditions that can cause finishing problems. It can also eliminate plastic shrinkage cracking and reduce drying shrinkage cracking...
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If you're a concrete contractor, it's important that you maintain adequate clear cover in vertical concrete structures. With proper cover, reinforced-concrete structures are likely to exhibit improved structural integrity and finished appearance as well as greater resistance to fire and corrosion...
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Because federally funded construction projects are now required to be designed in metric units and built with metric materials, mills are reducing and will eventually eliminate their output of inch-pound bars and produce soft metric bars instead. Fortunately, the use of soft metric rebar will not...
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From the street, it appears that the glass facade of the new Rio Suites Hotel, Las Vegas, wraps around the curved building like smooth cellophane. But the "curved" edge of each floor slab actually is segmented to fit the flat panes of glass. Had just one of these segments on a single floor been...
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Because a concrete boom pump can be a $300,000 to $1 million equipment investment, you need to weigh your options carefully before you buy. Should you buy a pump to improve your efficiency and get more work? Should you consider starting a separate pumping division to hedge your bet by creating a...
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Thanks to two high-speed cranes, design-build contractor Marnell Corrao Associates was able to erect one floor of Las Vegas' Rio Suites Hotel every four days. The last bucket of concrete was placed in November 1996, a year after Marnell Corrao broke ground.
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Article presents three case studies to illustrate how conveyors--used alone or in combination with other placement methods--can be profitable because they place concrete continuously and are able to transport materials other than concrete. The projects involved:
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With the right attachment, a skid-steer loader can perform excavation work, an excavator can demolish concrete, and backhoe-loaders and forklifts can do many things in between. The attachments featured in this roundup should be particularly useful to concrete contractors. They include a funneling...
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Are your company's tool-replacement costs getting out of hand? Then consider tracking your tools' whereabouts using a computerized bar-coding system. A tracking system manufactured by ToolWatch Corp., Denver, has only five standard components and is simple to use. After tagging each item in your...
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Both pour lines and cold joints are common in concrete construction, but cold joints have more serious consequences. Using case histories, the authors discuss several testing methods that can be used to evaluate whether a visible pour line found on an exposed concrete surface is just a noncritical...
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Limited data are available on the relationship between the strengths of test cylinders and cores taken from in-place high-strength concrete. Because high-strength concrete structures may be heavily reinforced, it can be difficult to obtain cores with the same aspect ratio (core length divided by...
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Vibrator trails are streaks of high-paste-content, low-air-content concrete found in the vibrator paths of some slipformed pavements. They are caused by excessive vibration of concrete and are prone to longitudinal cracking. In 1995, a field research project was initiated in Iowa to evaluate the...
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Problems occur when the surface of concrete flatwork crusts over and looks like it's ready to finish while the underlying concrete is still soft, like jelly. If finishers get on the crusted surface with a power trowel, the soft underlying concrete may bulge beneath the trowel, creating a wavy or...
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Many designers of concrete structural elements know that concrete shrinks when it dries, but they often fail to consider this in their designs. Article describes the possible consequences of drying shrinkage, including failures at filled joints, slab curling, and excessive cracking.
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There are many causes of water leakage into building foundations. By using this checklist, contractors can eliminate as many of these causes as possible and increase the odds that a basement will stay dry throughout its service life.
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For newly formed concrete structures, the responsibility for ensuring that coatings are applied properly typically rests on the shoulders of the concrete or general contractor. It's necessary to develop detailed coating procedures, monitor the coating contractor's work, and understand what tests...
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Most tilt-up contractors don't seal tilt-up panel joints themselves. But how can they ensure that subcontractors do the job right? Article offers the following 10 tips, based on the advice of experienced caulking contractors:
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Looking for a new way to dress up plain concrete? Tired of fussing with repeating patterns? If so, it's time to try a new concrete texturing tool: Brickform Shasta Seamless Texture Skins.
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An innovative anchor-bolt template system manufactured by Las Vegas-based Precision Concrete Anchor-Setting Systems Inc. (PCAS) helps to ensure accurate and plumb bolt placement in concrete. The system uses rigid but fully adjustable clamps to hold the anchor bolts in an open steel framework. It...
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Do expansion joints between parking-deck slabs allow for differential vertical slab movement when one slab carries much greater loads--due to more vehicles--than the other slab?
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I'm looking for information about drilling holes into concrete. A number of tool manufacturers have alluded to a geological map of the United States that shows the varying hardness of concrete across the country.
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Do expansion joints between parking-deck slabs allow for differential vertical slab movement when one slab carries much greater loads -- due to more vehicles -- than the other slab?
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We snapped a chalkline in the wrong place on a concrete driveway before sawing joints.
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To get a paving job done on time, we're planning to have our crews work six 10-hour days per week. However, I'm concerned about the cumulative effect of long hours on worker productivity. Is there any data on productivity and overtime specific to the construction industry?
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For corrosion protection, ACI 318-95, Building Code Requirements for Structural Concrete, specifies maximum water-soluble chloride ion in concrete as percent by weight of cement. What are acceptable levels when measuring chloride-ion content in existing concrete—specifically, by weight of the...
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We've got a dispute on a poured wall placement regarding acceptable bug hole size. ACI 116R-90, Cement and Concrete Terminology, defines bug holes as small regular or irregular cavities usually not exceeding 15 mm (0.60 inch) in diameter.
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On a hot day in August, we poured 40 lineal feet of concrete foundation wall for a house addition.
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I was called in to advise on problems with a parking structure. The owner is unhappy with the finishing work on all four slab levels.
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We've got a concrete paving contract in a mountainous region where the only water source is a lake with some algae growth. We've read that water containing algae is unsuitable for making concrete, because the algae reduces strength by interfering with cement hydration or by producing high air...
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A client of our New Jersey architectural firm wants to use a rock-salt texture for the concrete deck of her swimming pool. We're not familiar with this process and wondered how the effect is achieved.
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Safety inspectors told us that the Occupational Safety and Health Administration now prohibits the use of plastic mushroom caps for protecting workers from impalement on projecting rebar.s?
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Three different strengths of concrete were specified for one of our jobs in the Midwest: 3000 psi for foundations, 4000 psi for flatwork and 5000 psi for structural members above grade. Specifications give the same maximum water-cement ratio for all three concretes 0.44. Working with our concrete...
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What precautions are needed regarding the crane and its rigging?
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In the May 1990, issue of Concrete Construction (page 464) you showed magnets being used to anchor blockouts to metal forms. Is this a new idea? And where can people get the magnets?
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We're considering grooving a slippery concrete floor in our manufacturing plant to reduce the danger of accidents. However, I'm concerned about the effect of such grooving on the floor's structural strength and abrasion resistance. Is this a valid concern?
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Is a granular base needed beneath city streets or parking lots that will be paved with concrete? Some specifications require a subbase and some don't. If one is needed, how thick should it be?
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I'm a remodeling contractor who builds a lot of additions, usually at the rear of an existing house. We pour our own footings, foundations, and flatwork, but often the 10-cubic-yard ready mixed concrete trucks are too heavy or too big to get to the home's backyard without damaging the lawn and...
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We accidentally added 6% calcium chloride by weight of cement to a truckload of concrete that went into a residential driveway placed during cold weather. Though the contractor had no trouble placing and finishing the concrete, he is concerned about low concrete strength. He heard that using more...
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I've read about false curl, which results when concrete settles in the middle of a strip pour, making the fresh concrete surface lower than the side forms.
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We're placing massive concrete walls using forms that have expanded polystyrene form liners. The wall sections are 25 feet high, 32 feet long and 12 to 24 inches thick.
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While we were getting ready to build some slabs that required protection against moisture intrusion, we searched for all the information we could find on vapor barriers. Looking through the American Concrete Institute booklet Slabs on Grade (2nd ed.), we noticed slip sheets mentioned in the same...
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I've heard that it's not a good idea to use a steel-trowel finish for air-entrained exterior flatwork. However, I can't find any references that specifically recommend avoiding this practice.
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What's the required mixing time and drum speed when an accelerator is added to ready-mixed concrete at the jobsite?
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I live in Louisiana. Many times my garage and shop floors become very wet and slippery during the winter, when the air temperature changes quickly from cold to warm. What can be done to concrete floors to prevent this from happening? I'm also installing a new shop floor and would like to know what...
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While inspecting reinforcing bars that were to be used on a project, I found several bundles designated N for type of steel. I know that the designations S, I, A and W indicate billet, rail, axle and low-alloy steels, respectively. But I can't find any ASTM reference to Type N. What kind of steel...
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I want to use diammonium citrate to remove discoloration from newly placed concrete. I've called chemical-supply houses and pharmacies, but no one seems to recognize the term. How do I find this material, and how much is it likely to cost?
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We used an early-cut saw to joint a concrete floor immediately after finishing. The floor is 6 inches thick and the sawcut depth is 3/4 inch. Although the floor has no random cracks, the engineer says we now have to chase the joints with a conventional saw so the cuts are 1 1/2 inches deep...
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I run a pressure-washing business in Georgia. To remove the red clay that stains many driveways, I wet the driveway, then use a low-pressure hand sprayer to apply a dilute solution of muriatic acid (one part commercial-grade muriatic acid to three parts water). After that, I immediately rinse the...
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Questions such as the one in the March 1997 Problem Clinic (p. 313), where a reader asks if there is a published thickness tolerance for residential driveways, bring out the importance of placing important construction parameters in easily accessible formats. There are recommended tolerances for...
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What is the difference between cast stone and precast concrete? Or is there a difference?
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We need to replace two arch bridges in a local park. One is a three-span structure with a 70-foot center span flanked by two 56-foot spans. The smaller bridge is a single 35-foot span.
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We delivered concrete to a poured wall contractor building residential foundations in a subdivision.
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Does limestone aggregate give better fire resistance than other aggregates?
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We see many references recommending dilution ratios for muriatic acid that's used for efflorescence removal, acid etching, and other surface preparation applications. The references imply that there's a standard muriatic-acid solution, but our constructio
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I attended a seminar at which a speaker said that concrete doesn't expand. I told him I've always read that concrete expands when the temperature rises or when the moisture content increases. The speaker held his ground, however, and said that concrete doesn't expand. Is my literature outdated?
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I'm a pattern-stamping contractor in Louisiana and last winter I had a problem with slow setting and excessive bleeding of a concrete slab. The weather was unusually cold here, with air temperatures around 45 F. The cementitious material was 20% fly ash, and the concrete also contained a water...
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Our company does commercial work that often requires us to construct bollards, which are simply 4- or 6-inch-diameter steel pipes filled with concrete.
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I've heard that it's possible to use concrete in making kitchen and bathroom counter tops. Do you know where I can get information on how they're built?
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We placed a 6-inch-thick, 16x40-foot air-entrained concrete slab during cold weather. The 12-cubic-yard load of 3000-psi concrete was made with hot water and contained an accelerator that permits placement at temperatures down to 20 F. Concrete arrived at 9:30 a.m. with a 4-inch slump, and we added...
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Do you know of any data describing which curing methods produce the best results?
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We do everything possible to prevent cracking of the concrete driveways and patios that we place. We promptly cut joints to the correct depth and space them no more than 12 feet apart. We also use medium-slump concrete and start curing it as soon as we can without marring the surface. However, we...
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Where can we get some pure white and pure black pebbles for a special concrete mix? Our exposed aggregate renovation job calls for matching some existing concrete, and it looks like black and white were both used.
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The contractor who plans to build the foundation walls for our house makes a practice of using concrete with a slump of 6 ± 1 inch.
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Experience shows that repairs have been made at disturbingly frequent intervals on a bridge deck that bears heavy traffic.
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We are considering purchasing concrete from a plant that uses recycled aggregate. This job will continue for some time, so we are concerned about whether the plant will be able to deliver the same quality of concrete throughout the job.
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Is there a published thickness tolerance for residential driveways? I'm a concrete consultant, and one of my clients is a homeowner who had a concrete driveway built. The contract specified a 5-inch thickness. After the concrete had cured, the owner cored it and found that the thickness was only...
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For sidewalks placed directly on the subgrade soil, is a sheet-plastic vapor retarder useful or harmful?
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I need to place concrete in four 30-inch-diameter, 37-foot-long steel-shell piles that are driven at the bent lines of a river bridge. River depth varies, but is 5 feet in the deepest spot. After the steel shell is driven, the water level is about 1 foot below the top of the pile. The water moves...