Conco knows that the need for quality concrete doesn’t end with any one season, and we employ proven techniques during cold-weather concreting to prevent scaling and other issues.
The National Ready Mixed Concrete Association (NRMCA) defines scaling as local flaking or peeling of a finished surface of hardened concrete as a result of exposure to freezing and thawing. Scaling will normally begin as a small area, but can expand to affect large areas. Although it is unlikely that scaling will ever be completely eliminated due to the many contributing variables, following guidelines to help minimize scaling have been developed by the experts in our industry:
- Use an air-entrained, low water/cement ratio (0.45 or less w/c, as delivered), moderate slump concrete (not exceeding five inches) with a 28-day compressive strength potential of at least 4000 psi. Except when absolutely necessary, do not retemper concrete before placement.
- Avoid finishing practices that reduce or eliminate the air-entrained voids in the wearing surface layer, or that result relative to the bulk concrete at lower depths. Do not perform any finishing operations with water present on the slab surface. Delay finishing until all bleed water has risen to, and disappeared from, the surface.
- Avoid late season concrete placement, where concrete can experience freezing conditions and/or exposure to deicing salts before (a) the concrete has reached 4000 psi, and/or (b) the slab has had at least 30 days of air drying.
- Protect first year concrete from the harsh winter environment. Prevent newly placed concrete from becoming saturated with water prior to freeze and thaw cycles during the winter months by applying a silane or siloxane-based breathable concrete sealer (do follow the manufacturer’s application recommendations). Do not use deicing salts in the first year after placing the concrete. Use clean sand for traction. When conditions permit, hose off salt accumulations deposited by vehicles on newly placed drivways, approaches, and garage slabs. Never use ammonium sulfate or ammonium nitrate as a deicer; these are chemically aggressive and destroy concrete surfaces.
- Provide adequate curing to develop of strength, water-tightness and durability in hardened concrete. It is very important to provide and maintain satisfactory moisture and temperature conditions immediately after concrete placement and finishing, and for as long as practical. As a general rule, the length of the curing period for concrete flatwork in temperatures above 40 degrees F should be a minimum of seven days, or the time necessary for the concrete to reach 70% of its specified compressive strength. The later in the season it gets, the longer it will take to reach these points.
- Ensure proper drainage. Poor drainage permits water or de-icer/water mixes to stay on the concrete surface for extended periods, which increases the severity of exposure of the concrete and promotes scaling, especially in driveway, sidewalk, and curb and gutter applications.
For your next Fall or Winter project, call Conco Companies to ensure that the cold weather doesn’t affect your timeline or the final product.