Concrete is a building material made of portland cement or a blended binder, water, fine and coarse aggregates, and often chemical admixtures, which hardens through a chemical reaction called hydration.
Most parking structures are concrete, whether precast, cast-in-place post-tensioned or conventionally reinforced. A garage is one of the harshest environments concrete faces: wet, salted, driven on and exposed to freezing and thawing. The mix and how it is placed and cured largely decide whether the structure lasts 20 years or 60.
Mix choices that matter in a garage
- Low water-cementitious ratio. Less water makes denser, less permeable concrete; codes cap it, commonly at 0.40, for concrete exposed to chlorides.
- Air entrainment. Tiny air bubbles let water expand when it freezes without cracking the concrete.
- Supplementary cementitious materials. Fly ash, slag and silica fume reduce permeability and replace some cement, which also lowers embodied carbon.
- Corrosion inhibitors for exposed decks in severe climates.
Placing and curing
- Proper curing, keeping the concrete moist for days, is as important as the mix.
- Adequate cover over reinforcing steel.
- Industry guidance specific to parking structures is published by the American Concrete Institute.
The Parkonomics view
The durability of a garage is decided in the first week of its life, in the mix and the cure. Paying for better concrete then is far cheaper than paying for repairs later.
Related terms: Cement, Chloride-Ion Contamination, American Concrete Institute, Embodied Carbon, Conventionally Reinforced Concrete, Spalled, Subgrade Material