April 1991 Table of Contents

Features Backfilling Basics

Backfilling is all too often the beginning of basement destruction. But the problems associated with improper backfilling can be avoided by taking a few simple precautions.The four key elements to backfilling are: Read more

Underpinning Systems for Settled Foundations Features Underpinning Systems for Settled Foundations

Settlement of building foundations can often be arrested and the building restored to near its original condition by using proprietary underpinning systems. The systems increase foundation load-bearing capacity with steel piers that are pushed or screwed into the ground beneath the footings or floor slab. Jacking against the piers raises the foundation back to its original elevation, and the increased bearing capacity from the piers provides permanent support. It's smart business sense for owners to repair settlement damage to ensure the structure's resale market value. Read more

Features Overlaying Concrete Bridge Decks with Polymer Concrete

An increasing number of highway engineers are choosing polymer concrete for concrete bridge deck rehabilitation, finding that its advantages as an overlay material justify its high cost. A polymer concrete overlay not only improves the abrasion and skid resistance of the deck surface, it also protects against corrosion of steel reinforcement. Containing no portland cement, polymer concrete is impermeable to water, deicing salts, and chemicals that can accelerate corrosion. A polymer concrete overlay also minimizes traffic disruption. It's generally applied at a total thickness of only one-half to three-quarter inch and cures in as little as 2 hours. In some cases, workers can place the overlay at night then open it to traffic the next day. Read more

Features New Saw Blade Permits One-Pass Joint Sawing

Specifications often require a two-step procedure for sawing contraction joints in concrete pavements. The first cut, called a green cut, is made with a one-eighth-inch-thick blade that cuts through one-quarter the slab thickness. Green cutting is done as soon as possible to induce cracking through the remainder of the slab thickness and to prevent random cracks between joints. A second cut made 1 to 3 days later enlarges the top of the green cut to form a sealant reservoir with the proper shape factor. Now there is a more efficient way to saw joints by using a patented step-cut blade that performs both the functions at the same time. Read more

Features Power Screed on Skis Speeds Concrete Paving Job

Ray Heid Construction Ltd., St. Clements, Ontario, Canada, finished a 65,000-square-foot concrete driveway and parking lot in just 3 days using a power screed mounted on skis. The skis enabled workers to control screed elevations without the need for rails, forms, or other screed guides. The concrete driveway and parking lot, built for the Nova Steel Ltd. plant in Cambridge, Ontario, is 7 inches thick. Because of its size and thickness, the pavement required 1,390 cubic yards of concrete. The job was done in three pours, each taking a day to complete. The largest pour was 537 cubic yards. Read more

Concrete Screed Rails Used for Concrete Placed on Metal Decks Features Concrete Screed Rails Used for Concrete Placed on Metal Decks

Leave-in-place concrete screed rails have been used most commonly in slab-on-grade work, but now the rails are being used for elevated slabs on metal decks. Instead of using wet screeds for elevation control, contractors fasten high-strength concrete screed rails to the deck. This permits the use of vibrating truss-type screeds for concrete consolidation without requiring form stripping. Read more

Features Short-Span, Rigid-Frame Bridge

Construction time and cost were reduced by using precast concrete to create an elegantly proportioned and detailed entrance bridge for an upscale Florida subdivision. Read more

Features Self-Propelled Aerial Work Platforms Solve Overhead Access Problems

On construction jobs requiring overhead access, a self-propelled aerial work platform can be a cost-effective, efficient way to transport workers and tools to the work area. Of the four major types of aerial work platforms, telescopic booms and telescopic articulated booms are the most effective for construction site use. They have excellent vertical and horizontal reach capabilities and often can get to overhead areas that other means of access can't reach. Read more

Problem Clinic How a Half Cell Detects Corrosion

From time to time I see references to "half cell" readings as a measure of corrosion activity in concrete. Often there is computerized equipment for recording and analyzing the data, and it looks like a "black box" to me. How does this system really work? Read more

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