Cast-in-Place vs. Precast Concrete: Parking Structure Maintenance Considerations

From concrete to steel parking structures, no matter how a garage is built, it is susceptible to deterioration. But the type, location and extent of this deterioration can vary greatly, depending on how the garage was constructed. For concrete garages, it’s important to understand the design differences between precast concrete and cast-in-place garages. By understanding these differences and how they affect the potential for damage, you can develop a maintenance approach that best serves your structure.

Cast-in-place vs. precast concrete parking garages

The construction of a precast parking garage is much like that of a LEGO® set. Individual components, like beams, walls and columns, are built off-site, typically in a climate-controlled manufacturing facility, and then shipped and assembled on-site. Once constructed, the connections are then welded, bolted and sealed.

Because precast parking structures are constructed in a controlled plant environment, it’s easier for the precast producer to monitor the concrete quality and other design criteria, such as the accuracy of reinforcing placement. Also, precast fabrication requires the use of high-performance materials, due to all of the handling requirements This type of construction can also reduce the costs associated with building a new parking garage because the job is often completed more quickly.

A cast-in-place parking garage is constructed on-site by pouring concrete into forms that will later be removed. This type of garage is traditionally reinforced with mild steel or post-tensioning.

Cast-in-place structures can be highly durable, with fewer joints and mechanical connections than a precast garage. Fewer joints means a smoother ride for visitors and less opportunity for deterioration caused by leakage. With this type of garage, owners also get more design flexibility, and customization options.

Maintenance considerations by parking structure type

Now that we understand the difference between cast-in-place and precast parking structures, it’s time to talk about how these differences affect maintenance and repair needs. From an engineering perspective, the way a concrete garage was built will influence how it performs and how it needs to be inspected. Likewise, the main problems that occur — structural or otherwise — often stem from how the garage was originally constructed.

Areas of concern in precast parking garages

Top Concerns

• Waterproofing methods at the joints
• Failure points at mechanical connections
• Precast component interfaces and bearing conditions 

The areas that need the most attention in precast parking structure construction are often the joints. Usually, the joints, the most vulnerable parts of the structure, pose the most deterioration risk. Joint sealants can be used to waterproof these areas, but without continued upkeep, it’s easy for water to seep in at these connection points, especially as the joint sealants break down over time due to exposure to the elements. Thus, regularly inspecting and maintaining waterproofing methods should be on everyone’s preventive maintenance list for precast parking structures.

When considering structural issues, the joints are a common culprit again. The interfaces and connections between the individual components can be subject to wear and deterioration. Thermal expansion and contraction, dynamic loading from excessive vehicle speeds, and exposure from failed sealants can cause significant damage to embedded connections. These problems can be identified during a routine inspection. For structural repairs, engineers and contractors must work closely together to identify the root cause and then design and implement an engineering solution.

Areas of concern in cast-in-place parking garages

Top Concerns

• Corrosion of exposed steel 
• Shallow concrete cover
• weather exposure during construction

The construction of a cast-in-place structure has fewer joints, so the areas of concern for these garages tend to be the internal steel reinforcement and the concrete itself. Here, water plays a different role in deterioration than it does in precast structures. Because the internal reinforcing is susceptible to corrosion, waterproofing is necessary to ensure the reinforcing remains protected. Although you can’t always observe this damage externally, there can be a lot going on beneath the surface that routine inspections and testing will catch. Engineers can use technology like ground-penetrating radar (GPR) and acoustic sounding to help them identify damage under the surface. In any case, waterproofing systems, like sealants, sealers, and coatings, should always be replaced once they’ve reached their recommended service life.

The concrete used in cast-in-place construction may be more susceptible to cracking and wear because design requirements do not dictate the use of higher-performance materials like in precast construction. This may allow water to penetrate its surface and cause corrosion more readily. Lack of needed repairs, overloading, and chemical damage can all exacerbate this issue. Another construction flaw that may be present in cast-in-place garages is shallow concrete cover — the result of reinforcing steel being placed too close to the concrete surface. This allows water to penetrate through the shallow concrete cover and reach the steel reinforcing, where it can lead to corrosion.

Whether you have a precast parking structure or a cast in place structure, it can be difficult to recognize the signs of deterioration, especially when many issues begin below the surface. But routine inspections and assessments of your concrete garage by an experienced parking structure engineering team often catch these problems before major repairs are necessary. For any cast-in-place or precast concrete parking structure, you’ll want to continue preventive maintenance activities by monitoring for cracks, leaks, rust and other structural issues throughout your garage’s service life.