May 1998 Table of Contents

Features Where to Place the Vapor Retarder

The location of a vapor retarder is often a compromise between minimizing water vapor movement through the slab and providing the desired short- and long-term concrete properties. Some specifiers require concrete to be placed directly on the vapor retarder, and others require a granular blotter layer that's placed between the concrete and the vapor retarder. Advocates of each option argue that their preference results in a better concrete slab. Read more

Features Bonded Overlay Beefs Up Freezer Floor

When a major Midwestern food processor wanted to increase the thickness of an existing 4-inch-thick freezer-warehouse floor to at least 5 inches to carry additional storage loads, the concrete contractor opted to use a bonded overlay rather than full-depth floor replacement. The overlay was faster to install and provided the durable, long-term performance that was required at a lower cost. Read more

Features Roundup of Early-Cut Concrete Saws

Increasingly, contractors are using early-cut saws to make cuts in concrete slabs within a few hours after final finishing. Not only do early-cut saws allow workers to cut joints sooner, the saws also reduce the depth of cut required because the cuts are made before stresses build up in the concrete. Read more

Features Controlling Boom Bounce

Boom-bounce problems aren't confined to deck pours where the pump boom's reach is extended with slick line. When the boom is extended horizontally for placing slabs on grade, it moves down on the forward piston stroke of the pump and up on the return stroke. The bouncing motion makes the discharge hose flail about, which can cause injury to nearby workers. Read more

Features Fine-Grading with Tractor Loaders

A tractor loader equipped with a laser-guided grader box can improve production, material yields and the overall quality of concrete slabs on grade. That's because with a laser-control system, the grader box can precisely cut and fill the subgrade to a predetermined level. Read more

Features Shoring With Shotcrete

Using an innovative method combining earth anchors and shotcrete, foundation contractor Schnabel Foundation Co., Cary, Ill., temporarily shored a deep roadside excavation. Earth on one side of a quarter-mile stretch of the roadbed was about 25 feet above the proposed grade. Normally, excavating such a hill down to grade would require the use of sheet piling or soldier piles and lagging to shore the embankment until a permanent retaining wall could be built. But Schnabel determined that it could do the job more cost effectively by using earth anchors and shotcrete -- a method the contractor had used successfully on other projects. Read more

Problem Clinic Aluminum Tremie Pipe

The contractor on one of our jobs is placing concrete underwater through 10- to 12-inch-diameter tremie pipes 90 to 120 feet long. He has proposed using aluminum instead of steel pipes. I know that alkalies in concrete can attack aluminum. Can the concret Read more

Problem Clinic Admixture to Protect Concrete From Ammonium Nitrate Attack

Is there a concrete admixture that will prevent ammonium nitrate fertilizer from attacking the portland cement in concrete? Read more

Problem Clinic Yellow Spots in Vinyl Flooring

What chemicals in ready-mixed concrete will cause vinyl flooring to develop yellow spots after the flooring has been in place for several months? I've had this happen several times in residential applications and want to understand the cause so I can prev Read more

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