Jun 2017 CONCRETE CURING TECHNIQUES
We delve into concrete curing and the most suitable curing techniques. Curing is a process that is executed immediately after the placement and finishing of the concrete, to ensure that all the ingredients bond fully. This is done by retaining suitable moisture and temperature conditions. Adequately cured concrete will demonstrate the following characteristics:
- Improved strength
- Enhanced volume stability
- Reduced likelihood of cracking
- Resistance to freezing and thawing
- Resistance to wear and abrasion, such as dusting, crazing and scaling
Ultimately, concrete structures that have been properly cured will be more durable in the long term.
The two curing categories
Curing techniques can generally be divided into two groups:
- Those that add moisture
- Those that prevent moisture loss
Each of these methods has advantages and disadvantages that need to be considered before deciding which one is most suitable.
Curing techniques that add moisture
The typical curing methods that add moisture are:
- Sprinkling: This simply involves the continuous sprinkling of the concrete with water at intervals.
- Wet covers: In this technique, the concrete is covered with damp, moisture-retaining materials such as straw, cotton mats or burlap, which is a coarse, hemp-like fibre. Some also use moist earth, but it can be quite messy.
- Ponding: This is done by forming a little wall around the concrete slab normally using sand and by flooding the concrete surface with water.
Both sprinkling and use of wet covers are excellent curing techniques as it also provides cooling through evaporation, which is especially critical in hot weather. When sprinkling, it is just important to keep the intervals frequent enough – so that they concrete will not dry out in between. When using wet covers, it is important to place them as soon as the concrete hardens. Curing techniques that prevent moisture loss
The most common curing method to prevent moisture loss is to seal the surface through the use of the following types of material:
- Plastic sheets: Waterproof plastic film is a lightweight barrier that is easy to apply, regardless of the shape and size of the concrete surface.
- Waterproof paper: The surface needs to be wet with fine water spray before the waterproof paper is placed.
When using waterproof paper, it is imperative to check that it is thick enough, as too thin paper may discolour the hardened concrete
An easy and inexpensive curing method
Curing compounds are membrane-forming substances that are relatively inexpensive in comparison to other curing techniques. It can easily be applied with spray equipment such as hand-operated pressure sprayers. It also allows for long periods of curing even while the concrete is in use. Here are some useful pointers:
- In the case of heavy rains within a few hours of application, the compound must be reapplied.
- Brushes can also be used, but only on formed surfaces; as it could mar smooth surfaces.
- They are also available with dyes in order to see which areas are sprayed and which areas were missed. (The dyes normally degrade after a while and present no discolouration issues).
Adequate curing length
There are several factors that can influence or determine the concrete curing period:
- Ratio of concrete mixture;
- The level of strength required;
- The size and shape of the concrete structure;
- Weather conditions; and
- Future conditions that the concrete will be exposed to.
To determine a suitable length for curing, it is therefore best to consult specialists first. For expert advice on curing techniques, feel free to get in touch with Sephaku Cement.