Concrete Foundation Walls - Structural Deterioration And Damage
Problem: Cracks and spalling from poor construction practices - 3.
Cause: Improper curing of concrete.
Concrete will only reach its full design strength if it is allowed to cure properly in conditions that minimize the loss of the original water from the mixture. Where forms are stripped early, backfilling of the wall could prove disastrous if the concrete has not become strong enough.
Solutions: Moist-cure concrete for as long as possible.
- Keep concrete continuously moist unless formwork is left in place for a minimum of 24 hours. Improved performance will result from leaving formwork on for a minimum of two days, and it is recommended that slabs be moist-cured for a minimum of three days.
- Curing of foundation walls can be improved by;
- fogging or sprinkling them,
- covering them with wet burlap or waterproof paper or material,
- covering the exterior surfaces with curing compounds (following the manufacturers' recommendations),
- covering both the exterior and interior sides of the walls as soon as you remove the forms.
The combined effects of over watering and improper curing can result in very weak concrete. For example, if you start with a design mix of 2,175 psi (15 MPa), add 4 gallons (18 L) of water per cubic yard on site and strip the forms within 18 hours, the resulting concrete will have a 28 day design strength of as low as 725 psi (5 MPa). Where proper curing practices are not followed, 4,350 psi (30 MPa) concrete should be used.