July 2000 Table of Contents

Features The Art of Acid-Etch Staining

Picture a concrete coloring material that produces a unique look whenever it's applied. No two floors or walls look the same after being treated with this material. That's the magic of the acid-etch chemical staining process--an infinite number of possible results limited only by the creativity of the installer. Read more

Features Finishing-Tool Primer

Although power trowels often are used for their speed and efficiency to finish large slab areas, hand tools are still required for slab edges, steps, and other tight areas where power trowels can't maneuver. And hand tools are still the best way to finish smaller slabs, such as residential flatwork. But in order for these tools to work their magic, finishers must choose the right tool for the job, know how to use it properly, and understand the importance of timing. Here are tips for using the basic finishing tools needed by most flatwork contractors: bull floats and darbies, edgers, groovers, hand floats, and steel trowels. Read more

Features Examining Puncture Resistance

When constructing a floor, concrete contractors often unroll a sheet of plastic vapor retarder over the subbase and cover it with a blotter layer of compacted granular fill before placing concrete on the fill. But how effectively do vapor retarders resist punctures during construction operations? Read more

Features Recruiting Workers When Labor is Scarce

The outlook for finding good workers in the construction industry appears to be dismal, according to statistics released by the Construction Industry Institute predicting a 75% shortage of people entering the construction workforce. It's no wonder, then, that finding and hiring workers has fast become the No. 1 problem for many contractors. Clearly, these desperate times require rigorous recruitment strategies. To track down your next new hires, you must be willing to use a variety of recruiting techniques, even if your efforts require extra time and money. Here are some good strategies to try. Read more

Features Curing Cylinders in Hot Weather

When the weather gets hot, low concrete test-cylinder breaks are more likely. These low breaks can slow job progress by delaying acceptance of the concrete until further testing confirms adequate strength. Too often, though, low strength-test results occur due to improper concrete-cylinder storage and curing at the jobsite during the critical first 2 days after the cylinders are made. Although test-lab personnel usually make and test the cylinders, the contractor often is responsible for safe storage and proper initial curing of cylinders at the jobsite. Read more

Features Can a Petrographer Determine Slump?

By examining hardened concrete cores, petrographers can provide information regarding the concrete's composition and serviceability. ASTM C 856, "Standard Practice for Petrographic Examination of Hardened Concrete," outlines procedures for the petrographic examination of hardened concrete samples. But sometimes petrographers report information that's not specifically covered by the ASTM standard procedures, such as an estimate of the slump of the concrete when it was plastic. Read more

Features Troubleshooting Exposed Reinforcing Steel

Exposed reinforcing steel can result when detailing or construction problems reduce the depth of concrete cover. These problems include rebar not fabricated to exact nominal dimensions or placed at the exact location given in contract documents, workers stepping on rebar before or during concrete placement, and failure to secure rebar adequately enough to keep it in position during concrete placement and vibration. Read more

Problem Clinic Finishing Low-Slump Concrete

With 1-inch slump concrete topping mixes, it's hard to close the top surface with a bull float. Sprinkling the surface with water helps to close it but also can cause craze cracks. What's a better way to close the surface? Read more

Problem Clinic Does Concrete Absorb Adhesive Moisture?

We're the general contractor for a commercial building in which the concrete floor will receive a moisture-sensitive covering. The floor-covering manufacturer requires a maximum water-vapor emission rate of 3 pounds/1,000 square feet/24 hours. Before appl Read more

Problem Clinic Fly Ash and Bleeding

Does fly ash affect concrete bleeding? Read more

Problem Clinic Volcanic Eruptions on Concrete Surface

What would cause tiny craters to form on the surface of parking decks made with concrete containing a calcium-nitrite corrosion inhibitor? The craters are about 1 inch in diameter and 1/4 inch high. They primarily occur over deep beams, and sometimes crac Read more

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