This is a commonly asked question within our industry and happens often, cracking will occur it’s just a matter of when. Your concrete professional should have all the answers in place to suit most conditions, ensuring your concrete meets its anticipated design life.
Basically there are two types of cracks:
- Surface cracking – non-structural, this does not affect the strength of the substrate, rather leaving a spider web aesthetic on the surface. This can be easily hidden with a concrete sealer.
- The two main causes for surface cracking are 1. Extreme Heat and 2. Excess Water added to the mix, or a combination of both which in turn causes shrinkage as the concrete dries.
- Structural cracking, which is typically diagnosed by the gap being >1mm in thickness. Causes for this will vary but are not limited to the list below
- Poor substrate preparation
- Inadequate compaction
- Poor material, for example contaminated materials with deleterious mater (vegetation)
- Disturbed clayey types of material (which will not re-compact without heavy machinery)
- Concrete that is out of specification
- All concrete has a mix design; this is basically a formula for the batch plant to follow which includes measured quantities of cement, sand, aggregate (stone) and water. For example if you add additional water to what is specified, ultimately this will reduce the compressive strength. Just like adding water to cordial, it’s weaker.
- Cooked load – the load has begun curing in the truck; this can be determined by feeling the agitator barrel and it is warm to hot. If your concrete has to travel a long distance it would be wise to ask your contractor to assess this and also consider peak hour traffic. Best practice is to pour early in the warmer months.
- Inadequate steel reinforcement or no reinforcement
- Steel reinforcement does not stop cracking, but it does add tensile strength to the substrate, when a crack occurs, it assists in stopping differential settlement and the crack widening.
o Choosing the correct reinforcement is important; your concrete professional should know the correct standards and for structural concrete, this needs to be engineered.
There are remedies for structural cracking and generally water proofing contractors are quite adequate to undertake this, but it isn’t cheap. Do it right in the first place and check that your contractor has enough experience. If the quote is cheap, this generally means corners are cut, hence problems down the track.
Our aim at Walker Civil Construction is to carry out all works to best industry practice by our suppliers and also the appropriate “Australian Standards”. Please feel free to contact us www.walkercivil.com.au for more information.