Parking Slab Deterioration
Cracking, spalling, and deterioration of parking garage slabs can result in significant maintenance and repair issues if not addressed in a timely manner.
Slab deterioration is typically related to cracking. Some amount of cracking may occur during the original concrete curing process as shrinkage of the slab occurs. Cracking allows moisture to reach and corrode the slab reinforcing steel. As the steel corrodes it expands placing stresses on the concrete which result in continuing cracking, spalling, and delamination (horizontal cracking). This continued cracking is a cyclical problem and ends with significant concrete and steel deterioration if not treated. Not only is the deterioration unsightly, but problems can range from efflorescence drips damaging vehicles to hazards of falling concrete to structural failures.
In regions where de-icing salts are used, the corrosion of the reinforcing may be greatly accelerated as a result of vehicles carrying in snow and ice that has been treated with de-icing salt.
An annual maintenance program to reduce moisture intrusion and clean the garage may mitigate slab deterioration and extend the life of the structure. As a minimum, a maintenance program should include the following items;
- Wash down the garage annually to remove debris and de-icing salts. This should occur shortly after the winter season.
- Walk the garage annually to look for new or worsening conditions, including cracking.
- If drains are not functioning properly, they should be cleaned or snaked to provide water drainage as needed.
- If areas of ponding are observed away from a drain, manually clearing of the water should occur until a drain can be installed or leveling provided.
- Joints and cracks larger than 1/16 inch should be sealed. We recommend using a sealant rated for exterior use and routing cracks to ensure the sealant is applied to the correct ratio and depth.
- Cracks that have previously been sealed should be resealed as needed. Typically exterior sealants have a lifespan of 5 – 7 years.
For garages with a larger budget, or with concerns about moisture intrusion, penetrating sealants and surficial coatings can be applied to existing slabs to reduce moisture instruction into the slab and reduce the potential for delamination cracking.
If you suspect cracking and moisture intrusion has already resulted in corrosion of the steel and concrete deterioration, a survey and testing can help to determine the severity of the problems. Surveys typically include visual observations and concrete sounding to identify areas of distress. Concrete sounding identifies areas of delaminated concrete which may not be readily apparent. If needed, material testing such as chloride ion content testing or half-cell potential testing may be recommended. Chloride ion content testing can be used to determine if de-icing salts or other chlorides have penetrated the slab to a depth which would affect the reinforcing steel. Half-cell potential testing can help evaluate corrosion activity on the slab reinforcing steel. Using these techniques, probable corrosion areas within large portions of the slab can be identified for evaluation and potentially replacement.
For new parking structures reduced permeability concrete mixes, epoxy or zinc coated reinforcing steel, corrosion inhibiting concrete admixtures, surface-penetrating sealants, and surficial coatings can be used to reduce future maintenance costs. The higher initial cost can be evaluated against the potential maintenance costs over the life of the parking garage
We hope that this “Lessons Learned” has been helpful to you. If you would like to learn more about evaluation of parking garage slab deterioration, delamination detection, and repairs, please contact your nearest ECS office.
ECS Corporate Services, LLC