Maintenance and Repairs

December 19, 2023 Published by British Columbia Chapter - By Michael Chow, Gary Twomey

Concrete Deterioration In Parkades

From CCI BC Strata Connection Magazine, Volume 01, Fall 2023

Parkades in condominiums are usually designated as strata common property. As such, strata corporations are responsible for repair and maintenance of parkades. If neglected, concrete deterioration in parkades can be disruptive to users and costly to repair. Concrete deterioration can also lead to property damage and pose a risk to public safety. It is helpful to understand how parkades are constructed, how they can deteriorate, and what can be done to prevent deterioration.

What is Reinforced Concrete?

Conventionally, parkades are constructed with reinforced concrete, comprised of the following;

• Concrete (mixture of cement, aggregate, and water)
• Reinforcing steel

Concrete is extremely strong when compressed; however, it does not perform as well under tension. Since concrete generally experiences both compressive and tensile forces, steel bars (i.e., rebar) are embedded as reinforcement, providing the necessary tensile strength.

Common Causes of Concrete Deterioration

Steel corrosion is the most common cause of deterioration in reinforced concrete structures. The steel bars embedded within the concrete can corrode when they are exposed to water and oxygen. The presence of de-icing salts can also make the steel more susceptible to corrosion. When steel corrodes, it increases in volume by 4-6%. This expansion puts pressure and stress on the surrounding concrete and causes it to break apart and fall off (often referred to as “delamination” or “spalling”). Delaminated or spalled concrete can injure building occupants or damage property and may also reduce the strength of the concrete structure.

Another common cause of concrete deterioration is freeze-thaw. Water may enter concrete through cracks or by absorption into concrete pores. If this water freezes, it can expand in volume by about 9-10%, creating high internal pressure and stress in the concrete. This generally happens at a microscopic level (i.e., within the concrete pores). The expanded frozen water can cause the outer concrete surface to break apart, making it easily erodible. This process is referred to as “scaling”. De-icing salts can exacerbate this issue as salt residue can fill up the concrete pores, further reducing the space for freezing water to expand into. Freeze-thaw damage is usually prevented by having small air voids within concrete (also known as “entrained air”), allowing freezing water to expand into these voids, or by protecting the concrete surface with a waterproof coating.

Concrete Cracks

By its nature, concrete will crack, whether it be due to normal drying shrinkage, structure settlement, or seismic events. In many cases, cracked concrete may not present a structural concern. That said, cracks can also be an early indicator of concrete deterioration. The location, size, pattern, and frequency of cracks may help identify the cause and structural significance of the cracks. Cracks can present a concern in parking structures if they are exposed to rainwater, snow melt, or water brought in by vehicles. Cracks can allow water to have direct access to the steel reinforcing bars in the concrete, which can lead to corrosion (see above). Flood tests and acoustic sounding techniques are often used to check whether cracks are presenting a problem.

Concrete delimitation due to corrosion

Concrete scaling due to freeze-thaw

Concrete Cracks

How to Protect Concrete

By protecting reinforced concrete from water and de-icing salts, parkades can be made to last as long as necessary. This protection is typically achieved by using waterproof membranes. The roof slab of the parkade (often referred to as the “podium”) will usually have a membrane applied to the exterior concrete surface, which is then covered by various materials that form the overburden, such as soft landscaping, patios, walkways, or driveways. Within a multi-level parkade, suspended floor slabs will often be protected by an exposed traffic coating membrane.

Over time, waterproof membranes will lose flexibility, crack, and wear down. When this happens, leaks may occur, exposing the reinforced concrete to water and potential de-icing salts. These leaks may be addressed through targeted repairs. Eventually, once the membrane has reached the end of its service life and the problems become systemic, full membrane replacement may be required.

The exterior walls of an underground parkade are referred to as “foundation walls” and are typically protected with a waterproof/dampproof membrane applied on the exterior side. While it may be possible to replace the membrane on foundation walls, there are many limitations that can make replacement difficult or impractical, such as the close proximity to adjacent properties or the structural risk of a deep excavation. Generally, an alternate means of repair is required, and this is normally completed from the interior/negative side of the foundation wall. These methods may include polyurethane/acrylic gel injections or application of cement crystallization products at the locations of wall seepage. The overall purpose is again to reduce moisture contact with the concrete reinforcing steel to prevent corrosion.

Active flood test on podium membrane

Traffic coating membrane

Large concrete slad topside repairs

Conclusion

Concrete deterioration can range from small spalls that are addressed with patch repairs, or large-scale damage that requires extensive repair. The longer repairs are deferred, the more the concrete will deteriorate, resulting in higher costs and greater occupant disruption. With regular inspections, the condition of a parkade can be determined and deterioration can be flagged early. The good news is concrete does not suddenly fail without warning.

When in doubt, we recommend engaging a consultant who specializes in concrete assessment, repair, and renewal. This consultant can identify issues, recommend repair strategies, and help the strata corporation manage a repair or renewal project. As a guide for the appropriate personnel responsible for parkades, the Canadian Standards Association published a standard called CSA S413 – Parking Structures, which provides a recommended maintenance and inspection frequency in Table E.1.

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Michael Chow, P.Eng.
Entuitive

Michael is a senior engineer at Entuitive with over a decade of consulting experience in BC’s strata market, specializing in building envelope and parkade restoration. He has worked closely with strata councils and strata managers on a wide range of projects, including providing expert opinion services, leak investigations, building condition assessments, cand design, tender, contract administration, and site review for restoration projects. Michael also sits on the CCI BC Board of Directors.

Gary Twomey P.Eng.
Entuitive

With 17 years of industry experience, Gary is one of the Restoration team leaders at Entuitive. Gary’s primary role is focused on overseeing the assessment and restoration of existing structures. Drawing from his experience in construction, schooling, and consulting to date, Gary combines his understanding of building systems and material science (wood, brick, stone, concrete, and steel) to accurately diagnose issues often found in existing structures of a l kinds. This knowledge a lows him to adequately develop remedial solutions that lead to improved durability and longevity of the structure.