Concrete, both non-reinforced and reinforced, is often used for footings, foundation walls, basement floor slabs and garage slabs-on-grade. Concrete for columns, fireplaces, chimneys and foundation walls must have a minimum strength of 15 MPa (2,200 psi). Basement floors must have a minimum strength of 20 MPa (3,000 psi).
Garage and carport floors, exterior steps and driveways must have a minimum strength of 32 MPa (4,600 psi), and air-entrained concrete must be used for exterior applications. Air entrainment is required to reduce degradation caused by de-icing salts and exposure to freezing temperatures. The tiny air bubbles also make concrete more workable and easier to place than plain concrete. Air entrainment for exterior applications must be between 5 and 8 per cent.
In areas where soils are sulphate reactive, cement types 20, 40, 50 or equivalent must be used to protect the concrete. Aggregates used in the manufacturing of concrete should not contain sulphides such as pyrite, pyrrhotit and marcasite as these compounds may oxidize and hydrate, leading to volume increases within the concrets material causing the concrete to crack and spall, or the release of sulphate which produces sulphate attack upon the cement paste.
Whether concrete is delivered from a plant or mixed on site, additional water should not be added at the construction site to make concrete easier to place. Additional water will lower strength, increase permeability and decrease freeze-thaw resistance. If more workability is required, the concrete supplier should be asked to adjust the mix, possibly by adding a plasticizer or other concrete admixture to improve workability and placement, while conforming to the appropriate concrete standards.
Source : Canada Mortgage and Housing Corporation (CMHC)