February 2001 Table of Contents

Features The Case for Early-Entry Saws

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 documents from the American Concrete Institute, Portland Cement Association, and American Concrete Pavement Association still recommend using these joint-cut depths. However, deep cuts made many hours after concrete placement often are less effective in controlling random cracking than shallow cuts made earlier. This article discusses the differences between these two approaches to sawcutting joints and presents research on the factors affecting the ability of the sawcut to control random cracking. Read more

Features Justice Center for All

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 to the high-rise building at each floor. One of the most unique features of the building, however, is a 350-foot-long, 60-foot-high concrete wall that starts outside the building at one property line, passes through the center of the building--forming the backdrop for a public atrium, and then goes outside again to the opposite property line. Called the "Universal Justice Wall," it will be faced with native sandstone to reflect the local environment. Laser-cut into the stone will be phrases representing the concept of justice throughout history. Read more

Features Pumps for Wet-Mix Shotcreting

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? The answer depends mainly on the volume of concrete to be placed. Read more

Features Going Hybrid

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 range of solutions to construction problems. Read more

Features Connecting the Dots

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 foundation concrete for the $22 million Rancho Del Rey Middle School in Chula Vista, Calif. Spread over 26 acres, the school includes 18 distinct buildings of various shapes and sizes housing 120,000 square feet of classrooms, administration offices, an auditorium, and physical-education facilities. Because of the enormous number of layout points and amount of survey data that had to be calculated and input, Taylor Ball used a handheld graphing calculator along with data-collection and field-computation software for surveyors. By combining this data-collection system with an electronic total station, the layout crew was able to save time and minimize worker uncertainty and errors on this complex job. Read more

Features Testing a Petrographer's Conclusions

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 than the surrounding concrete, the appearance of the broomed finish wasn't uniform and "soft surface conditions" were reportedly exhibited. The parking lot owner questioned the quality of the concrete, and had cores sent to a test lab. The petrographic report stated that the coarse aggregates were generally sound but the entrained-air content in the top 1/4 inch of the two samples was inadequate to resist freeze/thaw damage. The petrographer further concluded that freeze/thaw damage was expected to be a problem for the concrete slab. Read more

Features Removable Forms for Concrete Homes

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 rotting wood, and even in the center of a noisy city, the living space is quiet. Read more

Problem Clinic When to Wash Decorative Concrete

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. Read more

Problem Clinic Pumping Without Consolidating

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 Read more

Problem Clinic Rolling Stones

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. Durin Read more

Problem Clinic Cracks at the Ends of Sawed Joints

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 Read more

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