October 2001 Table of Contents

Features Getting the Most from Your Power Trowel

Finishing concrete has always been about timing: being in the right place at the right time with the right tool. With the now widespread acceptance of the F-number system, good power troweling techniques are essential since floor flatness depends directly on a finisher's ability to run trowel machines. Read more

Features U.S. Seebees' Concrete Placement at 115 F

When you are in the military, you don't ask questions. But, when you are working with concrete in hot weather, you had better know the answers. Back in June 1966, my buddy Sammy and I were assigned to pour some concrete near the Danang Air Base to provide a base slab on grade for a military field hospital. Sammy and I were 23-year-old Seabees attached to Mobile Construction Battalion 5 (MCB-5) and were from the same neighborhood in southern Westchester, N.Y. We were both 2nd class petty officers. Sammy had never poured "mud" before, but from doing summer work with my Uncle Joe back home, I did have some experience in placing flatwork. So when we were told by our commanding officer to pour a slab in hot, windy conditions, I was a little skeptical since it was about 115° F—in the shade! We were using a mix with local stone and sand—some of the fines were from the beach. Since I was the only guy with any concrete knowledge, I was the lead man. I had to train our crew as we poured: the epitome of on-the-job-training, courtesy of the U.S. Navy. Read more

Features Are Temperature Requirements in Mass Concrete Specifications Reasonable?

To prevent thermal cracking, most state departments of transportation cite a maximum temperature differential requirement for mass concrete in bridge piers. This requirement can create headaches for the contractor who hasn't fully considered how to deal with it. We asked Martha VanGeem, principal engineer with Construction Technology Laboratories (CTL) in Skokie, Ill., and Ralph Browne, bridge field engineer with the Texas Department of Transportation (TxDOT) Bridge Division in Austin to address this issue. In this discussion they tell us what can be done to provide improved and practical specifications for durable mass concrete construction. Read more

Features CC 100

Big contractors and small contractors are different. Or are they? In this issue, Concrete Construction presents its first listing of the top concrete contractors in the United States. We've done our best to get information on the big guys, frankly, just because they are big. And yet, many of our conclusions about how the top contractors operate apply equally to the smaller contractors. Read more

Features Rework: The Silent Assassin

It started at the very beginning while preparing the ground for the forming crew. Bob had to delay the forming crew by a half day because the job was graded incorrectly. To add insult to injury, the forming crew then placed the forms several inches off the mark in three critical places. Having corrected these two mistakes, Bob thought he was safe until the concrete truck showed up with the wrong mix, causing another delay with additional labor cost. Now Bob could only watch as a once-profitable job was shriveling slowly toward breakeven. Read more

Features New Developments in Forwork Sheathing

If you don't remember what formwork was like before plywood, take a look at the exposed concrete in historic structures, and you'll see the marks of hundreds of boards that made up the form faces. The advent of plywood with dependable, waterproof glue was a revolutionary development for form builders, and today grade B-B plywood, manufactured to established U.S. product standards, is a household word in the industry. Where a smoother finish is needed, high-density and medium-density overlaid (HDO and MDO) plywoods are available, manufactured to the same voluntary product standard (PS 1-95 Construction and Industrial Plywood). Read more

Features Mixing It Up

What do an ex-fighter pilot, an engineer, a former Marine, a barn repair specialist, and a surfer have in common? Concrete. On a sunny Friday in May, in Colorado Springs, eight concrete contractors met in a conference room. It's not important how the members came into their professions. What connects this MIX group now is that all the members have concrete construction companies to run and problems to solve. Read more

Decorative Concrete Efflorescence on Decorative Concrete

The last thing you as a contractor or specifier want to hear when you complete a decorative, colored concrete installation (integral, dry-shake, stamped, textured, stenciled, or trowel finished) is that the owners are unhappy because the color wasn't what they ordered. Then you find yourself in the awkward position of telling them that the color is right, but efflorescence has lightened its appearance. Owners frequently respond to that news by stating they want the color they ordered before they will pay for the job. What to do? Read more

Problem Clinic Can Scaling Be Prevented?

In the past year or so I've had problems with scaling and delaminations while placing and finishing floors. Read more

Problem Clinic Waterproofing a Pond

I am building a 900-gallon concrete fishpond and waterfall, and I am confused as to which type of mortar to use and what I can use as an additive to help waterproof the cement. Read more

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