January 2001 Table of Contents

Features Casting Curved Walls

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 the methods of two contractors who are gaining more work by casting curves. Read more

Features Double Dose?

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 strength faster, allowing finishers to complete their work sooner and decreasing the likelihood of damage caused by early freezing. Read more

Features White Concrete Brightens "Highways of Hope"

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 Monongahela River Valley and western Fayette County to Interstate 68 near Morgantown, W.V. The Southern Beltway will form a 30-mile arc around Pittsburgh between the Mon/Fayette and Beaver Valley expressways, with a radius of about 15 miles measured from Pittsburgh's Golden Triangle. The Pennsylvania Turnpike Commission and the Pennsylvania Department of Transportation have completed the first 18 miles of the Mon/Fayette. Seeking cost-effective ways to enhance the quality and safety of its new route, the commission has specified white concrete for all the mainline bridge parapets on both the Mon/Fayette and the Southern Beltway. The decision to use white parapets came from the recognition that more accidents per mile driven occur at night than during daylight hours. The first white parapets on the Mon/Fayette were constructed in September 1998, and the parapet work continues as the route is extended. A few parapets were cast in place in fixed forms, but on the longer bridges, they are being slipformed. Read more

Features Adding Air to Freezer Floors

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 freezing temperatures? Not necessarily. Read more

Features Upgrading Your Bid Package

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 a checklist of 12 minimum standards that will certainly improve the clarity and professionalism of your bids. But to get top dollar, you must go beyond the minimum. Consider upgrading your bid package by using additional customer-focused strategies. Read more

Features Crack Widths: What's Tolerable?

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 significant amount, even when other report recommendations for limiting crack width are followed. However, the table's values have been used in court cases to imply that the presence of any cracks exceeding the widths listed--at any concrete age--indicates inferior design or construction practices. Read more

Features Troubleshooting: Map Cracking

Map cracking--also called pattern cracking--can be found in almost any type of concrete structure. The most common causes are surface drying shrinkage restrained by underlying concrete that shrinks less, expansion due to alkali-silica reaction (ASR), and restrained thermal contraction, particularly at early ages. Read more

Decorative Concrete Acrylic Sealers for Exterior Flatwork

Applying a sealer to exterior decorative flatwork is the last step before turning a project over to the owner. If the sealer turns cloudy, peels off, blisters, or otherwise mars the appearance of the surface, remedial steps can be costly. A bad sealer application may even require removing and replacing the concrete. So it pays to know what can go wrong, and why. Read more

Problem Clinic Maintaining a High pH

An engineer has requested concrete with a continuously high pH to help protect underground conduit from corrosion due to magnetic-field induction. Read more

Problem Clinic Requirements for ADA Detectable Warnings

When the Americans with Disabilities Act went into effect in 1992, it required detectable warnings on walking surfaces of ramps to help sight-impaired people. The detectable warnings were to consist of closely spaced, raised, truncated domes about an inch Read more

Problem Clinic Gas From Concrete?

We're building a concrete home for an owner who heard that concrete emits gas as it cures. Read more

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