September 1998 Table of Contents

Features Placing 50,000 Square Feet of Flatwork a Day

To accelerate construction, some building owners will pay contractors a lot more to complete the placement of a concrete floor quickly. But there are many challenges to these fast-track jobs, which may require the placement of as much as 50,000 square feet of flatwork a day. Not only must you hire enough people and buy extra equipment; if you want to make money, you also must carefully select, use and schedule this manpower and equipment. Read more

Features Proposed Tolerances for Sloped Surfaces

No standard tolerance exists for slopes in random-traffic floors and other slab surfaces. But the author -- president of a consulting engineering firm that assists in the planning and construction of slabs on grade and suspended concrete floors -- feels that one is needed. He has developed a proposed specification for sloped random-traffic floors and would like suggestions for improving it. Read more

Features Truss-Type Screeds Save Time and Labor

For the concrete contractor, vibratory screeds provide many benefits -- perhaps the most important being the elimination of labor-intensive manual strike-off of concrete with a conventional straightedge. The screeds also level and consolidate the concrete slab simultaneously, allowing workers to quickly produce smooth, flat surfaces that are ready for subsequent finishing operations. Read more

Features Concrete Chain Saws Cut Deep

Equipped with hard-biting diamond-studded chains, hand-held chain saws specially designed to cut concrete can make some cuts that hand-held rotary power saws simply can't. For example, concrete-cutting chain saws can cut square corners in openings without overcutting the corners. They also can make plunge cuts up to 19 inches deep into a concrete wall, allowing contractors to slice through thick walls in one pass. The chain saws can cut irregular shapes as well, and have even been used by sculptors to carve concrete statues. Read more

Features Avoiding Equipment Breakdowns

Other than bad weather, the primary cause of work shutdowns on the jobsite is undoubtedly equipment failure. Just think of the serious job delays that could result if the equipment you rely on the most were to break down. For many concrete contractors, those indispensable machines are power trowels, internal vibrators and vibrating screeds. Read more

Features Exterior Plazas: Problems and Solutions

Poor construction or design increases the vulnerability of a plaza to temperature changes and precipitation. As a result, many plazas require significant repairs or replacement in 10 to 20 years, much sooner than many other components of a facility. Read more

Problem Clinic Tolerable Shrinkage-Crack Widths

We are a structural engineering firm specializing in the design of residential light-frame housing in Southern California. We specify both conventional and post-tensioned slabs on grade, but the slabs often develop some cracks. In a typical 30x50-foot sla Read more

Problem Clinic Corrosion of Copper in Concrete

Does copper corrode when it's embedded in concrete? I've heard that copper pipes that penetrate concrete floors and copper shower pans in contact with concrete or cement board can corrode. I've also been told to wrap protruding copper pipes with tar paper Read more

Problem Clinic White Splotches on Driveways

When we place driveways, stair stoops and sidewalks during the winter, we cover them with insulating blankets to protect the new concrete from freezing. However, we often find white splotches or stains on the concrete surface when we remove the blankets. Read more

Problem Clinic Liability Concerns When Providing Job References

One of the most troublesome problems that I face is the request for job references for a former worker. Fear of lawsuits makes me hesitant to provide that information. Are there guidelines on what I can and cannot say? Read more

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