August 2000 Table of Contents

FEATURES
Features Contractors to Watch

Successful contractors seldom follow identical paths. Some find a niche market and fill it better than their competitors. Some spend research money--a lot of it--to develop new building methods that solve old problems. Others take risky jobs that their competitors aren't willing to bid on. And still others follow the time-proven formula of doing their work more efficiently than their competitors can. Read more

Features All About Anchors

Soon after your crews complete a large concrete placement, you discover that the required cast-in-place concrete anchors were accidentally left out. No need to panic. Anchors that are bonded or mechanically attached inside drilled holes can serve as substitutes. In fact, these post-installed anchors can be as strong or even stronger than cast-in-place systems. They also can be precisely located and often are less expensive. Read more

Features Bracing for Speed

When Taylor Ball Construction got the contract to pour almost 60,000 lineal feet of riser seating for the new Kansas City International Speedway, it faced a forming dilemma. Because setting the riser forms fast and accurately was the top priority, Taylor Ball originally intended to use a gang-form system moved into position by crane. However, crane access on the job was restricted. Deciding instead to use hand-set forms, the contractor was confronted with another problem--how to meet the high production rates required by the project schedule. Read more

Features Avoid the Hiring Pit

Contractors, both small and large, make poor hiring decisions every day. Falling into the hiring pit is easy to do if you aren't careful. Maybe you're in a hurry to fill a position, or you feel you must grab who you can because the labor market is so tight. We have found that many contractors are poorly prepared to interview candidates no matter what the position--concrete finisher, secretary, or truck driver. Read more

Features What Surface Defects Require Repair?

Concrete specifications often require contractors to repair surface defects immediately after formwork removal. However, surface defects aren't well defined. Nor do specifications give limits on the size or extent of a defect. For instance, section 5.3.7.3 of ACI 301-99, "Specifications for Structural Concrete," instructs the contractor to outline honeycombed or otherwise defective concrete with a 1/2- to 3/4-inch-deep sawcut and remove such concrete down to sound concrete. But ACI doesn't indicate the size and number of voids that will trigger required repairs nor does it define "otherwise defective concrete." Read more

Features Troubleshooting: Efflorescence

Efflorescence results when chemicals in hardened concrete are carried to the surface by moisture. Calcium hydroxide, a product of portland-cement hydration, is the most common source of efflorescence. Calcium hydroxide is a water soluble base, but after appearing on the surface it reacts with carbon dioxide in the air and forms calcium carbonate, which is water insoluble and thus more difficult to remove. Less common sources of efflorescence are sea salts or sulfates that are brought into the concrete on the aggregates or in the mixing water. For efflorescence to occur, water must move through the concrete. This movement may result from hydraulic pressure on the backside of the surface or moisture evaporation from the visible surface of the structure and usually occurs at cracks, joints, or other openings in the concrete. Read more

DECORATIVE CONCRETE
Decorative Concrete Avoiding Surface Crusting

For decorative-concrete contractors who install stamped concrete finishes, surface crusting is one of the most difficult problems to manage in the field. When it occurs, it can lead to large numbers of surface cracks that compromise the appearance of the decorative finish. Read more

PROBLEM CLINIC
Problem Clinic How Long A Wait To Paint?

We placed a concrete slab for an exterior multipurpose game court. How long do we have to wait before painting basketball-court lines? Read more

Problem Clinic Compacting Trench Backfill

We generally use a No. 57 crushed stone (1 inch to No. 4) for backfilling plumbing trenches beneath a concrete slab on grade. Is it acceptable to dump the stone into the trench without compacting it? If not, what's the best method for compaction? Read more

Problem Clinic WWF Through Joints?

We are planning to place a slab on grade containing welded wire fabric. Should the fabric be continuous through sawed contraction joints? Read more

Problem Clinic Definition of "Shingling"

What does the term shingling mean when describing vertical slipformed concrete? Read more

Problem Clinic Dissolving "Hard as Steel" Concrete

We are trying to penetrate a reinforced-concrete bunker built during World War II by the Japanese army. The concrete is literally as hard as steel. I've been told that a product called Ascarlite is a powerful liquid that can eat through concrete with amaz Read more

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