Concrete Foundation Walls - Structural Deterioration And Damage
Problem: Cracks and spalling from poor construction practices - 1.
Cause: Poor placement and finishing techniques.
Improper placement and finishing techniques can result in a segregation of the fines and aggregates in the concrete mix.
Solutions: Proper preparation and placement.
- Dampen the earth, and moisten or lubricate the forms to prevent the drawing of water from the concrete into the forms. Lubricate the forms before you erect them to prevent the lubricant from forming puddles on top of the footings.
- Place concrete within two hours of batching in cool weather and within one hour in hot weather.
- Use a vibrator to consolidate each lift, especially around openings , corners and form ties.
- To prevent horizontal cold joints in walls, roughen the top of the previous pour and vibrate the next pour as shown in Figure 5.
Figure 5 - Horizontal Construction Joint
- To prevent cold joints in floor slabs, blend new concrete with previously placed concrete on the interface.
- Minimize concrete drops to prevent the segregation of aggregate. Excessive segregation will result in a loss of strength and the increased potential for water leakage. A maximum drop of 5 feet (1.5 m) is recommended where reinforcing rod is used as shown in Figure 6.
Figure 6 - Concrete Drops
- Use chutes or buckets or pumped concrete to get concrete as close as possible to its final destination. Do not move concrete with a rake or vibrator as segregation will result.
- Do not finish concrete when bleed water is present. Soak up the excess water with burlap or remove with a squeegee. Over toweling of the finished surface will result in the removal of air entrainment and further segregation of the fines, reducing the concrete's durability.