FAQ

Can I drive on new Concrete??

We recommend waiting 7- 14 days of cure time after new concrete is placed before vehicles are allowed to drive on it. Concrete will crack otherwise

Can you prevent cracks?

Koncept Concreting Pty Ltd offers no guarantee for lineal shrinkage / cosmetic cracking, although every measure is taken to prevent cracking in accordance with the material that we specify which is of the highest standard. This includes the proper sub grade preparation to cutting the control joints in the correct locations

How thick is standard Concrete?

Our standard slab is a minimum of 4 inches (100mm) thick with the supplied reinforced steel (Please note that whilst strict attention is given to concrete thickness, Koncept will always guarantee above the minimum)

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Some situations will require us to pour 6 inches of concrete and this would be discussed before the project takes place.

How are exposed-aggregate concrete finishes produced?

There are three ways of obtaining exposed-aggregate finishes on concrete slabs: seeding a select aggregate into the concrete surface, the monolithic technique where a select aggregate, usually gap-graded, is mixed throughout the batch of concrete, and exposing gap-graded aggregates in a special topping course. The process for producing monolithic exposed-aggregate finishes is as follows:

20121120_121121-150x1501) Place the concrete containing the chosen aggregate in a normal manner in which you fill the forms.

20121121_101928-150x150 2) Spray the surface with retarder. Retarder does typically contain sugars but the formulations that are designed for use with concrete are strongly recommended for a more consistent performance. The retarder will slow the set characteristics of the discrete surface layer allowing the interior to harden while the exterior remains soft.

20121121_153146-150x1503) The third phase is the difficult part. When the concrete has become hard enough to carry your weight without displacing the aggregate the surface is washed with a hose and scrub brush to remove the top layer of cement paste. Care must be taken not to displace the aggregate and not to expose the aggregate too deeply (this can cause the aggregate to lose bond and/or be displaced).

Caution: A too long delay in this part of the process can create extreme difficulty in the removal of the top paste layer. The retarder slows the set of the top surface but does not stop it completely. After the desired surface has been achieved with a final acid wash, the slab should be sealed with a clear sealer and curing compound.

 

What causes random concrete cracks and can they be avoided?

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Random cracks in new concrete slabs are a common complaint from owners. What causes random cracks; what are the best strategies to avoid the occurrence of random cracks; what are reasonable expectations; and do all random cracks in slabs constitute a failure of the concrete? Random cracks in concrete slabs are most frequently caused one of the following mechanisms:

  • Settlement of the soils supporting the concrete slab
  • Restraint of horizontal movement due to fixed foundation elements
  • Overloading, applying a load larger than the slab was designed to support
  • Restrained drying shrinkage of the slab

Settlement cracking takes place when the soils or fill beneath the slab have not been adequately compacted to provide a consistent level of support for the slab to limit the bending stresses which crack the concrete. Settlement can be controlled with consistent preparation (compaction) of the base supporting the slab.

Slabs placed against fixed foundation elements (frost foundations, light standards, etc.) produce cracks caused by bending forces as the slab moves on the surface while the fixed foundation does not. This mechanism is controlled by placing isolation joint material between the slab and the fixed foundation to allow the elements to move independently, thus limits the bending stresses and subsequent cracking.

Overload cracking is easily controlled with proper thickness design of the slab considering the largest load that may be applied to its surface.