There is growing interest within the reinforced concrete industry in using higher strength reinforcing steel for certain applications. This interest is driven primarily by relief of congestion, particularly in buildings assigned a high seismic design category (e.g., West Coast moment frame buildings).
Intersections represent a special challenge in concrete pavement construction. Having to accommodate traffic flow while striving to meet project specifications for drainage, smoothness, and other structural requirements tests a contractor's construction and organizational skills.
Cooperation and excellence are key to achieving outstanding results in concrete paving, as demonstrated by the 1995 winners and runners-up in the sixth annual National Awards Program for Excellence in Concrete Pavement. The winners in each category are:
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.
If construction speed is a priority when you build a tall concrete structure, slipforming may be the answer. Slipforming differs from conventional concrete forming because the forming panels move semicontinuously in relation to the concrete surface being formed and form ties are not used.