The Advantages of Prestressed Concrete

Article excerpt

The Advantages of Prestressed Concrete There has been much bad press about the extent of corrosion problems in concrete parking structures. Closer examination will reveal that the expensive work is done to correct problems of concrete deterioration caused by intrusion of water and chloride through the surface to the reinforcement steel.

Premature deterioration of parking structures takes one or more familiar forms--surface scaling or chloride-induced corrosion that results in surface spalling, cracking, and faulty expansion joint systems. In these cases, the deterioration can be seen as leakage, leaching, deterioration of the surface, or structural damage. The problems are pervasive in northern climates where road salt usage is common and many freeze-thaw cycles occur in the course of a year.

Every owner of a parking structure knows that these problems exist. Traffic-bearing membranes, epoxy coating reinforcement, specialty concrete and asphalt toppings, and cathodic protection are all measures once considered uneconomical that are being employed today to prevent problems from occurring. Each approach represents a significant increase in the price of a new structure but is money wisely spent in light of huge restoration bills.

The three main structural types of precast, prestressed concrete construction--double tees with topping, untopping double tees, and hollow-core slabs with topping--are highly resistant to chloride-induced deterioration. That is not to say these types of structures do not have problems. They do, especially related to cracking, expansion joints, bearings, connections, and drainage. But the corrosion of reinforcement steel is not one of the problems.

Why precast/prestressed concrete?

* Low cost. The use of precast/prestressed concrete offers a more economical approach for new structures. High quality concrete and predictable structural behavior are key reasons precast/prestressed concrete resists deterioration.

Due to the inherent cost savings associated with mass production, the precast/prestressed concrete components can mean significant savings in both materials and interim financing costs. Further savings can be realized through the use of smaller, more efficient erection crews that offer lower insurance rates and minimal maintenance costs. Components can be erected from the truck to the structure in almost every instance, making it ideal for projects with limited site access.

* Quality controlled factory manufacturing. Precast, prestressed concrete components are uniformly mass produced under strictly controlled, inplant manufacturing conditions for reliable consistency, assured quality, and prompt, on-schedule delivery. With this standardized approach, components fit together and are readily positioned into place.

* Low maintenance. Because precast/prestressed concrete is highly resistant to abrasion, impact, corrosion, vandalism, and the ravages of time, it is an ideal solution for the demanding use experienced by a parking structure. And because painting and other exterior care is minimized, maintenance is reduced considerably for substantial, long-term savings.

* Clear spans. Traffic engineers and parking consultants generally agree that large, clear spans are the most important criterion for successful multilevel parking facilities. Thoughtful design planning, in conjunction with the expertise offered by a prestressed concrete producer, can result in clear spans of 60 feet or more to permit two-way traffic, wider aisles, easier parking and maneuvering, less congestion, faster parking turnover, easier interior maintenance, and increased parking capacity and revenues.

* Limited access advantages. Precast/prestressed concrete is ideal for limited access locations. Pretensioned parking structures have been erected sandwiched between buildings in a busy urban setting or over a main thoroughfare--without the need to block off the job-site area. …