November 2000 Table of Contents

Features Better from Above

A unique bridge overhang forming system that does not require construction personnel to work from underneath is speeding work, reducing labor hours, boosting safety, and improving concrete quality in the building of a four-level interchange at I-35E and the new President George Bush Turnpike (SH 190) in Carrollton, Texas. This is the first application of the reusable all-steel system, manufactured by Symons Corp., Des Plaines, Ill. Read more

Features Combating Rebar Corrosion

The first line of defense in preventing the corrosion of reinforcing steel in concrete is to use good concreting practices. But designers and contractors can add other corrosion-control weapons to their arsenal including corrosion-resistant rebar; corrosion-reducing additions or admixtures; and concrete membranes, coatings, and sealers that block chloride entry. Here's a summary of the options and their relative costs. Read more

Features Forming the Gates of Time

The morning of April 19, 1995, marked the worst terrorist attack ever experienced in the United States, when a truck bomb destroyed the Edward P. Murrah Federal Building in Oklahoma City, killing 168 men, women, and children. Five years later, to the day, a memorial at the site of the tragedy was dedicated to the memory of those who lost their lives, to their survivors, and to the rescuers who came to the victims' aid. Read more

Features Long Wait for Lightweight

Many building owners and contractors have reported experiencing project delays while waiting for slabs made with lightweight concrete to dry to the moisture-vapor-emission rate typically required by floor-covering manufacturers (3 pounds per 1000 square feet in 24 hours). Though we couldn't find any data regarding the drying time of lightweight concrete, field experience tells us that lightweight concrete takes longer to dry than normal-weight concrete. To help fill this information gap, Concrete Construction devised a testing program to find out how long it takes lightweight concrete to dry. Read more

Features Profiting in a New Market

To increase sales and expand business, some contractors may consider entering a new market niche that requires different equipment, strategies, and procedures. Other contractors may look into offering their current services to a broader geographical area. If you have tried either of these strategies and had no problem selling the work but plenty of trouble realizing profits, it's time to look at the reasons why and consider a few solutions. The answer to greater profits lies not in our ability to obtain more work but rather in our ability to adapt to the needs and demands of a new market. Read more

Features Microwave Water-Content Testing: How Precise Is It?

Many project documents specify a water-cementitious materials ratio (w/cm) for concrete, but it's often difficult to confirm that the specified value has been attained. Verification usually is based on batch records for the amounts of cement and water used. However, the water-content values on these records are sometimes suspect because water content is difficult to estimate precisely due to changes in aggregate moisture content, water left in the truck, and water added at the jobsite. Read more

Features Troubleshooting: Joint Spalls

The direct cause of joint spalling in industrial floors is loading at the joint. The indirect cause is poorly constructed joints that don't adequately support the loads applied to the concrete. Four commonly used joint systems or fillers that can lead to spalling include left-in-place metal keys, plastic crack-inducing strips, elastomeric joint fillers, and high-strength epoxy fillers. When dowels are used to transfer loads across joints, they also must be installed properly. Read more

Concrete Basics Placing Flatwork in Fall

Many concrete contractors dread late fall because temperatures drop and the risk of placing concrete rises. Generally, you should take cold-weather precautions when the temperature is expected to fall below 40° F. But frost damage to concrete isn't the only concern during cold weather. Delays in finishing also can be a problem because the time required for concrete to reach initial set increases dramatically. A drop in concrete temperature from 70° to 40° F more than doubles the time from concrete placement to the end of finishing. Read more

Problem Clinic Differences in Formed-Surface Finishes

What are the differences in appearance and cost for smooth-rubbed, grout-cleaned, and cork-float finishes for formed concrete surfaces? Read more

Problem Clinic Fly Ash in Concrete for Floors

What are the advantages and disadvantages of using fly ash in concrete for industrial floors? I'm interested in properties of both fresh and hardened concrete. Read more

Problem Clinic Date and Number Stamp for Bridge

Where can I buy a brass plate that will allow me to stamp a date and bridge number on a concrete bridge? Read more

Problem Clinic Spray-Paint Removal

While using spray paint on one of our jobs, workers got the paint on a new concrete surface. Is there any way to remove it without leaving a stain? Read more

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