August 1991 Table of Contents

Features Concrete Pumps, Traveling Forms Speed Construction of Twin-Arch Tunnel

The Cassair Connector Project, a 100-million-dollar upgrade from arterial city street to freeway, made use of both precast and site-cast concrete in several different structures. The largest concrete structure in the project is a 2,394-foot-long reinforced concrete twin-arch tunnel. The tunnel has 35 double-barreled segments, each about 68 feet long, 49 feet wide, and 16 feet high. The tunnel's heavily reinforced slabs serve as both structural slabs and finished pavement for the tunnel. Eighteen months were allowed for construction, with only 10 months available for actually pouring the tunnel segments. Read more

Features Consider All Costs When Choosing a Concrete Placing Method

Using a separate placing boom can help you realize a profit by making it easier for you to get a high-rise project done well in the least amount of time possible. Adding a separate crane may fill the obvious gap that allows you to meet your schedule, but it may also have a ripple effect on overtime costs that isn't immediately noticed. Using a placing boom instead allows you to remove time allotted for concrete placement from the crane schedule. The faster placing rates for pump placement also permit a reduced deck cycle. But to make money doing this, the time saved must then be converted to productive work. Read more

Features Concrete Placement for Small Pours

Many contractors find that they don't make money on small pours. But increasing profits on small pours simply requires a little more planning. Don't just take cost into consideration when planning a small pour. Make sure the concrete placement equipment can fit through the openings and can be moved without exceeding weight limitations. Consider using chutes or conveyors to get the concrete to the forms. Read more

Features Underpinning Job Unearths Unexpected Problems

Converting crawl space to usable space in a 70-year-old school building turned into a major headache for the project's engineer and contractor. During excavation of the crawl space, workers discovered that pad footing elevations for two old columns were higher than the new basement floor elevation. With only 3 feet of headroom in the crawl space, workers then had to dig exploratory holes up to 12 feet deep to find the depth of every column footing. They found that footing levels within the crawl space were variable and all were at or above the proposed basement floor level for the new addition. Read more

Features Tilt-Up in Seismically Active Areas

Tilt-ups have historically done well in seismically active areas. Structural engineer High Brooks, author of "The Tilt-up Design and Construction Manual" says "there's not a single known instance of an in-service failure of the estimated 10 million tilt-up panels constructed to date." This excellent record is due to several factors. First, the large monolithic panels inherent to tilt-ups are strong and often capable of surviving seismic forces. Second, the shape and size of typical panels promotes efficient transfer of shear forces and provides good shear resistance. Finally, large panels have few joints or weak areas that are prone to failure. Read more

Features Avoid Joint Deterioration in Concrete Parking Structures

Joints are critical to the performance of concrete parking structures because they allow movement caused by temperature change, drying shrinkage, and creep. Three types of joints are commonly used in concrete parking decks. Control joints, sometimes called contraction joints, are used on parking decks to reduce random cracking. Construction joints occur at the outer edge of each pour sequence. Isolation joints relieve stresses associated with volume change forces caused by shrinkage, thermal cycling, elastic shortening, and creep. They are also used to separate the floor slab from other structural elements of the building. Read more

Features A Contractor's 10 Commandments for Architectural Concrete

Ten Commandments for architectural concrete contractor's. Read more

Features Irish Artist Sculpts with Concrete

Artist Kathy Goodhue, Dublin, Ireland, switched to concrete as a sculpting material after experiencing dissatisfaction with using metal and wood. She found that concrete was less costly and allowed her greater creativity with her color and texture needs. Despite the large scale of most of her concrete sculptures, Goodhue needs only a few simple hand tools to create them. First, she makes a small scale model of the piece in plaster, then she builds a full-scale armature using the model as a guide. Read more

Features Concrete Producers Who Also Pump Concrete

In Calgary, Alberta, most ready mixed concrete producers also run at least two concrete pumps. Yet 160 miles up the road in Edmonton, not one concrete producer runs a pump. All the concrete pumping is done by pumping contractors. U.S. producers pump concrete for several reasons. Meyer Material Co. started pumping concrete in 1968 as a way of improving customer service. Birdsall Sand & Gravel started pumping concrete in 1976 as a way to get trucks unloaded faster and as a potential revenue source. Allen's Ready Mix of Wichita, Kansas, began pumping in 1968 to improve customer service and generate additional revenues. Read more

Problem Clinic Thawing Frozen Subgrades

We do a lot of concrete work in Canada where frozen ground is common. Most specifications prohibit placing concrete on frozen ground. How do concrete contractors in northern climates meet this specification requirement? Read more

Problem Clinic Sources for Georgia Buggies

Where can we buy the hand-pushed, two-wheeled buggies used to place concrete? I believe they're called Georgia buggies. Read more

Problem Clinic Should Whitetopping Have Uniform Thickness?

Your August 1990 article on whitetopping a driveway says that compacted fill was placed in low areas because shrinkage cracks might start at points where the thickness changed. I attended a demonstration by the Michigan Concrete Association where the same Read more

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