Steps to produce a good quality concrete product.
Do I need to compact the subbase?
A Sound subbase is required, compacted, not loose uncompacted fill. Subsidence under driveway slabs is a common cause of cracking.
Why is it necessary to order the correct slump?
You need to specify the requirements for your concrete order, especially the slump (how sloppy concrete is), don’t add water to the mix on site as this will potentially void the concrete supply companies’ warranty. This weakens the mix; the concrete batching plant has set recipes to maintain the strength of concrete and give you the required slump you need.
What can you do about hot weather?
If possible, pour concrete before the heat of the day and consider the use of an evaporation retarder like Aliphatic Alcohol to help prevent surface cracking.
Why is it critical that reinforcement is placed correctly?
Reinforcement is correctly installed when located in the correct location with bar chairs and maintaining the required concrete cover (the distance from the reinforcement to the surface of the concrete).
This is critical for three reasons.
- As the reinforcement needs sufficient concrete around it to achieve the bond required.
- To protect the reinforcement from the elements, prevent corrosion and potential concrete cancer.
- For reinforcement to work correctly as designed by an engineer.
Can you place concrete incorrectly? Yes!
- Place concrete in required location, do not use vibrator to move concrete into place, it causes segregation.
- Concrete needs to be adequately vibrated (compacted) once placed in forms. They say it is hard to over vibrate concrete and most concrete is under vibrated. This increases the concrete density, strength, bond to reinforcement, reduces voids in concrete and reduces permeability.
What is curing concrete? Often overlooked
- What curing does is to keep water in the concrete after the concrete has been finished and set. The reason for this is the chemical process that makes concrete go hard and achieves the required strength, is called hydration, which requires water for this process.
- For concrete to reach its required strength in 28 days it needs to be cured for a minimum period of 7 days. Speak to your concrete supply company regarding their recommended minimum curing period. Not curing concrete may affect your warranty on the concrete product.
- Curing reduces cracking, increases durability.
How to cure concrete?
Apply a curing compound, damp hessian, sand, kept moist, etc.