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Adding steel or synthetic fibers to concrete at low-volume dosage rates provides benefits not available in conventional concrete.
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If concrete will be exposed to aggressive chemicals in a natural or an industrial environment, what role can admixtures play in improving concrete performance? Admixtures significantly improve performance for some, but not all, exposures.
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By its nature, concrete tends to shrink and ultimately crack as it dries. But a new liquid admixture, introduced to the North American market in March 1996, is the first of its kind available to ready mix producers and contractors for chemically altering the basic mechanism of shrinkage without...
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Some new and updated testing devices measure fresh concrete properties quickly enough to let quality-control personnel rapidly detect changes in the concrete.
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Designed by well-known New York architect Marcel Breuer, St. Francis de Sales Church in Muskegon, Michigan is an inspirational structure that fully demonstrates the architectural potential of cast-in-place concrete construction.
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In the early 1980s, the Michigan Department of Transportation (MDOT) reconstructed several interstate highways using recycled concrete aggregate (RCA). Although most of the RCA pavements performed acceptably, MDOT observed that some of the pavements deteriorated more rapidly than they should have.
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Slab moisture-emission testing is commonly required before contractors can install an impermeable floor topping on concrete slabs on grade.
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Designers often specify the use of distributed steel (welded wire fabric or small-diameter reinforcing bars) in the upper half of concrete floors on ground. It's used to prevent random cracks from widening.
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Slab-on-grade curling can be a big problem, especially when the slab must be covered by wood flooring. That's why curling--not flatness--was the major concern of the wood flooring installer for the new gymnasium at Elmira College.
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The work of most concrete floor designers includes troubleshooting existing floors in distress. Reasons for distress include aging, poor maintenance, and design or construction errors.
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Rent, lease, or own? It's only natural to rely on a combination of all three methods, renting equipment for one-time or short-term jobs, and buying for long-term jobs. Determining just the right mix, however, requires careful evaluation of your business position.
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After nearly nine years of work and the placement of 450,000 cubic yards of concrete, a dedicated construction team completed a much-needed facelift to Arizona's historic Theodore Roosevelt Dam.
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The winners of the 1996 Tilt-Up Achievement Awards provide striking examples of just how adaptable, economical, and beautiful tilt-up structures can be.
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The Design Award competition is held every two years by the Concrete Reinforcing Steel Institute and its co-sponsor, the American Institute of Architects, to honor outstanding cast-in-place reinforced-concrete structures from across the United States.
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By definition, a custom wood form is one that is designed and built for a specific concrete structure. Many contractors find it more economical and efficient to use the prefabricated, modular forming systems now available.
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The American Concrete Institute has recently completed a major revision of its long-standing flagship concrete specification, ACI 301, "Specifications for Structural Concrete for Buildings," last revised in 1989.
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Normal floor placing and finishing practices leave some variations in the finished surface in the form of small bump and dip waves. The location, length, and amplitude of these waves are determined in part by the construction methods and equipment used.
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Proper soil compaction can avoid many pavement problems by increasing load-bearing capacity, decreasing water seepage, and minimizing soil settlement. The goal of compaction is to pack as many soil solids as possible into a given space.
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Successfully maneuvering a large, heavy paver through tight turns, such as those required for parking-lot islands or cul-de-sacs, requires a skilled operator working under ideal jobsite conditions.
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Larry Booth, owner of Advanced Pumping Systems, Puyallup, Wash., created a pumping system that is especially useful for placing granular base material in confined areas.
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The American Concrete Institute defines scaling as "local flaking or peeling away of the near-surface portion of hardened concrete or mortar." Scaling is caused by several factors, with deicing chemicals and severe freeze-thaw cycles being the best known.
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Dallas/Fort Worth International Airport's seventh runway, 8,500 feet long and 150 feet wide, will soon meet demanding construction standards for smoothness.
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Before tackling construction of the 180-foot-span Presumpscot River Bridge in Falmouth, Maine, general contractor Cianbro Corp. realized it couldn't complete the job on schedule using conventional falsework to support forms for the structure's cast-in-place spandrel arch ribs.
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Intersections represent a special challenge in concrete pavement construction. Having to accommodate traffic flow while striving to meet project specifications for drainage, smoothness, and other structural requirements tests a contractor's construction and organizational skills.
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Completed in September 1995, the $194.5 million Calumet Tunnel in south suburban Chicago represents public-works construction at its best.
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Waterstops play a crucial role in concrete construction, preventing seepage of water or other liquids through construction, contraction, and expansion joints.
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Presented here are sample specification excerpts that show contractors and specifiers how F-number requirements are typically addressed in project specifications for random-traffic floors.
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Well before the first winning athlete is acknowledged at the 1996 Summer Olympics in Atlanta, a construction team building a public stadium for the much-anticipated event has put in a performance worthy of a gold medal.
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Dubbed "Concrete Super Bowl 95" by its construction team, an incredible 31-day building effort last summer resulted in the placement of 600,108 square feet of concrete slabs--enough concrete to cover nearly 13 football fields.
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Since its adoption by the American Concrete Institute (ACI) in 1990, the F-number system has become the preferred method for controlling floor surface tolerances on most construction sites.
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A dilemma sometimes faced by concrete floor contractors and owners is what to do about a recently installed or existing industrial floor that has a weakened surface.
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Proper methods of setting and measuring concrete floor construction tolerances are important to owners, vehicle manufacturers, and designers, as well as to floor contractors. When these groups have a realistic understanding of floor tolerances, they can specify flatness in the most cost-effective...
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To produce successful estimates, many contractors now rely on construction estimating software tailored to their specialties.
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The artistic process of coloring concrete was showcased in Denver in the spring of 1995, as the city installed a unique multicolored concrete intersection to demonstrate the environmental advantages of concrete pavements.
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I've heard the term pinwheel joint used in connection with concrete floors. What is a pinwheel joint?
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We're building an outdoor basketball court that will be flooded in the winter and used as an ice skating rink. What can we do to protect the concrete from damage caused by freezing?
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Building Code Requirements for Structural Concrete (ACI 318-95) prohibits embedding aluminum conduit in structural concrete unless it's effectively coated or covered to prevent aluminum-concrete reaction or electrolytic reaction between aluminum and steel. What coatings are effective and where can...
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We have installed hundreds of thousands of square feet of suspended floor slab on metal decking using lightweight concrete, and we've found it's next to impossible to get a smooth, level floor. All our work is done with power trowels, and when the slab is at its optimum for finishing, the concrete...
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I'm a perfectionist when it comes to concrete finishing. I want to know why discoloration occurs in some instances on recently placed slabs. The discolorations are usually light and dark patches. I know that concrete slabs eventually bleach out with exposure to the sun, but sometimes the building...
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We sometimes have problems with water leakage through construction joints containing polyvinyl-chloride (PVC) waterstops. We believe the leaks are occurring at splices in the waterstop. Is there a good reference on how to splice PVC waterstops so they won't leak?
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Can using hard water as mixing water affect concrete properties?
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We built a slab on grade in a building with rectangular concrete columns. We isolated the columns from the slab by wrapping them with a compressible material. Roughly circular floor cracks developed around some of the columns. Can shrinkage cause this kind of cracking, or is there another more...
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I know that concrete sets due to a chemical reaction between the cement and water. But does water-cement ratio also affect the setting time?
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We're working with a specification that calls for final troweling until the trowel makes a ringing sound as it moves over the surface. This is to be followed by scarifying the surface with a soft-bristled broom. I don't think the broom will scarify a hard-troweled surface, but is there anything in...
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We've got a series of parallel cracks along the joints in our concrete parking lot. An engineer says they're D-cracks. Is this kind of cracking caused by alkali-silica reaction (ASR)?
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I'm the construction coordinator for a city in a freeze-thaw region. Deicer scaling and sheet scaling of city streets are both a concern to us because either form of this distress can affect pavement aesthetics and cause surface roughness.
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How does water that's absorbed by aggregates affect concrete's water-cement ratio?
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When a concrete wall is built on a concrete base slab and both are designed with construction joints that include a waterstop, shouldn't the joints match up?
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What would cause a well-applied, good-quality clear sealer to peel off a concrete slab in thin sheets?
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Do isolation joints need to be cut completely through a slab? For instance, will a 2-inch-deep cut allow vertical movement in a 5-inch-thick slab?
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When a Type I-II cement is specified, does it mean you use one cement that's a compromise between the two types, or does it mean the concrete supplier has the option of using either a Type I or a Type II cement?
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We've read about using chain drags or striking concrete surfaces with a hammer to detect delaminations. Is there a standard procedure for using either of these methods?
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I saw your Problem Clinic regarding too much bond breaker being used on tilt-up panels (January 1996, pp. 76-82). We have this problem on a job. Do you know how to get the bond breaker off the panels so they can be successfully painted?
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What's a reasonable frequency for testing fresh concrete?
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We placed concrete for a basement floor with plastic hoses embedded in it for radiant heating. The concrete was placed directly on expanded-polystyrene insulation laid over plastic sheeting.
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After pouring a cast-in-place wall, we discovered that the top-of-wall elevation doesn't match the elevation shown on the plans. What is an acceptable tolerance for top-of-wall elevation?
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We made a 40-cubic-yard concrete pour for a floor on ground that was to receive a machine-troweled finish. The pour started at 7 a.m., and by 10 a.m. finishers who were edging the slab noticed a fine, white dust coming to the surface.
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Why is air-entrained concrete less permeable than non-air-entrained concrete? Aren't the air voids permeable to water?
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Is there a shelf life for portland cement, or will it last indefinitely?
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We're on a job that requires a fast forming cycle. If we calibrate our rebound hammer for the concrete being used on the job, are the hammer test results accurate enough to determine when forms can be safely stripped?
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What are the pros and cons of using redwood stay-in-place divider strips and bulkheads for flatwork?
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We're having a problem with lignite (coal) in the sand we use to make concrete. There's no cost-effective way to remove it, and it floats to the surface in concrete slabs.
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We're designing a concrete structure in Egypt, and I received test results for the aggregate to be used in the concrete.
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As a materials engineer, I am trying to discover the cause of discoloration.