Case 3 – Shrinkage Cracks
- Introduction
- Causes of Defects
- Good Practices
- Standards
- Maintenance and Diagnostics
- Remedial
- Similar Cases
- References
Good Practices
Concrete
Material
Ensure that the concrete mix is appropriate for construction. If the concrete is ready mix, it shall comply with SS 289.
Potential excessive shrinkage may be reduced by using cement with the following properties such as:
- as low a water content as possible. Add only enough water to obtain an even and workable mix.
- maximising coarse aggregates content
- use of aggregates and cement with low shrinkage characteristics
- use of a suitable admixture, so that shrinkage can be controlled
Construction
To control the occurrence of concrete cracks caused by drying shrinkage, the following steps are recommended:
Concreting should be started early in the day or night to minimize excessive drying due to hot weather. In addition, ensure that there are sufficient able-bodied helpers to assist in placing, compacting, and finishing the concrete until entire job is complete.
Ensure the provision of correct placement of steel reinforcement to control cracks resulting from shrinkage and thermal movement. Spacers can be used to place the re-bars in correct positions.
Place the concrete carefully. If concrete is placed directly from a truck or concrete pump, place concrete vertically into position. Do not allow the concrete to fall from a height of more than 1 to 1.5 metres.
Ensure thorough compaction of the concrete during placement. The concrete should be properly cured.
Quality Control
- Check for quality of concrete before placing [9]. e.g. water cement ratio, slump test, etc.
- Avoid the followings during concreting in order to minimize cracks:
- Avoid excessive manipulation of the surface, which can depress the coarse aggregate, increase the cement paste at the surface, or increase the water-cement ratio at the surface.
- Do not finish the concrete before it has completed bleeding.
- Do not dust any cement onto the surface to absorb bleed water.
- Do not sprinkle water on the surface while finishing.
Construction Joint
Design
Sufficient movement joints should be provided at a suitable distance to accommodate movements.
