November 1995 Table of Contents

Features Using Concrete Pumps for Shotcreting

In wet shotcreting, a concrete pump delivers ready mixed concrete with a predetermined water-cement ratio to the shooting nozzle at a rate of approximately 3 feet per second. Compressed air traveling at 150 to 200 feet per second is then introduced at the nozzle, a precise dose of fluid accelerator is usually injected into the propellant air. The mix of air and accelerating agent breaks up the concrete flow inside the nozzle, intensely mixing the concrete with the set accelerator. The propellant air drives the concrete out of the mixing nozzle at the ejection velocity required for compaction (typically 150 to 200 feet per second), and then guides it through the shooting hose to the surface. The plastic concrete begins to set a few seconds after impact with the base surface. The nozzle operator can vary the amount of air introduced, but has no direct control over the concrete's properties. Read more

Features Shotcreting Underground

The use of shotcrete to build new concrete structures as well as to restore and repair existing structures is well-known and documented. Although this versatile method of placing concrete is widely accepted by the construction industry, shotcrete for ground support in tunnel and mine operations is perhaps less known in the general construction community. Underground shotcreting, however, consumes the largest volume of concrete of all pneumatic applications. Today, nearly all tunnels under construction in North America will use shotcrete as part of their support system. And rather than cast-in-place concrete lining, a shotcreted final tunnel lining, installed after the ground support system is in place, is also practical and gaining acceptance. Read more

Features Protecting Construction Equipment from Vandalism and Theft

Though many concrete contractors rely on general contractors to protect jobsite equipment - especially equipment left overnight such as forming systems, paving machines, and cranes - improved jobsite security should be everyone's concern. Moreover, say many administrators of anti-theft and anti-vandalism programs, high-tech security systems are rarely needed and are generally much too expensive. The most effective crime prevention activities, they say, are often the simplest and least expensive: writing a security plan, establishing worker responsibility at the jobsite, and giving the crews the resources needed to implement security measures. Read more

Features Roads of the Roman Empire

The Romans built nearly 53,000 miles of roads linking the capital to their far-flung empire. To put this amazing feat in context, consider that the United States, to date, has built 42,000 miles of interstate highways. Roman roads were remarkable for preserving a straight line from point to point, regardless of obstacles. They traversed marshes, lakes, ravines, and mountains. Read more

Features Keep Your Cool When Cold-Weather Concreting

Concrete is a temperature-sensitive material and is most susceptible to frost damage in the first hours or days after casting. The problem of cold-weather concreting is further complicated by two conflicting needs: To protect the concrete surface from drying due to highly evaporative winter conditions; and to make sure the surface is dry when exposed to freezing temperatures. Read more

Features Concrete Home Won't Blow Down

To prove that hurricane-proof homes can be built Mel Adler, president of Mel Adler & Associates Inc., Miami, recently erected a prototype all-concrete house in Homestead, Fla., that is designed to stand up to 600-mph winds as well as wind-blown debris. At the home's grand opening celebration last April, sponsored by the Florida Concrete & Products Association, Adler demonstrated his confidence in the home's indestructibility by crane-lifting a 3-ton pickup truck onto the steel-reinforced concrete roof. The home recently earned the 1995 Gold Prism Award for concrete structure design from the Gold Coast Builders Association of Southeast Florida. Read more

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