The creation of a durable, corrosion-resistant parking structure with a superior life cycle starts with the formulation of quality concrete as follows:
- Low Water/Cement Ratio: The lower the water/cement ratio the more impermeable the concrete will be, the more strength it will exhibit and the less shrinkage-related cracking it will suffer. Wells Concrete typically fabricates parking ramp double tees with ratios as low as 0.35, whereas 0.38 is considered a low water/cement ratio for cast-in-place concrete and even then is extremely difficult to achieve under field conditions. The concrete water/cement ratio is the dominant factor in reducing chloride permeability.
- Greater Compressive Strength: The greater the concrete strength, the more durable the finished parking structure will be. Wells Concrete’s factory precast prestressed concrete parking deck tees attain minimum concrete strengths of 7,500 psi which is more capable of resisting the forces of deterioration facing parking structures in the Midwest. Site-cast concrete is typically only 4,000 psi.
- Superior Air Entrainment: The addition of microscopic air bubbles to concrete via air entraining agents increases the concrete’s ability to withstand freeze-thaw cycles. While air entrainment can be adversely affected during on-site placing and finishing procedures, our precast prestressed concrete is produced with close control of air entrainment, ensuring a durable driving surface.
- Controlled Curing: Concrete attains strength, durability, and resistance to chemical attack when external humidities are kept at their highest levels. Controlling temperature and climatic conditions of site-cast concrete is nearly an impossible task. In our plant, temperature and humidities for the entire curing period are carefully controlled. Federal Highway Administration tests have shown that heat-cured precast prestressed concrete members absorb thirty to fifty percent less chloride in the first inch of concrete when compared to moist-cured cast-in-place slabs.
- Better Clear Cover: The depth of concrete over reinforcing steel is a critical factor in controlling corrosion. Wells Concrete’s precast pre-stressed deck components have their primary reinforcement well down in the tee webs, away from areas of maximum chloride penetration. Consistent clear cover is almost never achieved in cast-in-place structures.
- Greater Crack Control: Reducing the frequency of cracks is crucial to corrosion control. Weather conditions during on-site concrete placing can have a major impact on the likelihood that shrinkage cracking will occur. Surface cracking of site-cast concrete may also occur due to negative bending of the slab under load near the supports. Wells Concrete’s precast prestressed deck components typically have positive bending moments reducing the likelihood of flexural cracking on the top surface. In addition, our high-strength concrete promotes greater crack resistance.
Advancements made in the last five to ten years to a precast concrete, pre-topped parking structure, in response to the maintenance concerns that the cast-in-place proponents resort to:
- Caulked Horizontal Joints: In the early years urethane was used as it was the best caulking material available at the time. Recently the sealant industry has developed high performance silicone parking structure joint sealants that are ideal for sealing the most demanding dynamically moving joints and horizontal applications.
- Precast Flange-to-Flange Connections: In the early years the typical anchored weld plate from the precast flange of one double tee to the next was simply an embedded galvanized plate that welded with an additional loose galvanized plate that was only 1 inch clear from the top of double tee surface. This anchored weld plate was subject to rusting and deterioration should it be exposed to salts. In response to this the precast parking ramp industry developed a stainless steel anchored weld plate called JVI Vector connectors for shear alignment connections from the precast flange of one double to the next. These connections allow for thermal expansion during field welding, eliminating spalling or cracking. These connections were also positioned 1.5 inches clear from the top of the double tee surface to allow proper room for the backer rod and caulking to bridge the connection.