12th Jan 2023
Concrete retarders are used to slow down the setting time of concrete. They are typically used in hot weather or when long transportation times are expected, to prevent the ready-mix concrete from setting too quickly before it can be properly placed and finished. They can also be used to extend the working time of the concrete, which can be useful when pouring large or complex structures.
Additionally, some retarders may be used to create specific surface finishes or to enhance the workability of the concrete. In general, it is recommended to use concrete retarders when the ambient temperature exceeds 25 degrees Celsius or when the concrete will be placed in a location that is difficult to access.
Some Popular Concrete Retarders Commonly Used
Some popular concrete retarders commonly used include:
- Calcium lignosulfonate: derived from wood pulping process and is one of the most widely used retarders.
- Sodium gluconate: derived from fermentation of glucose and is a popular choice due to its low toxicity and biodegradability
- Sodium carboxymethyl cellulose (CMC): derived from natural cellulose and is a popular choice for high-performance concrete.
- Chlorinated paraffin: it is a liquid and often used in precast concrete.
- Hydroxpropyl methyl cellulose (HPMC): derived from natural cellulose and is a popular choice for high-performance concrete.
- Synthetic polymers: they are often used in high-performance concrete and can be customized to meet specific needs.
It is important to note that the type of retarder used will depend on the specific application and the desired outcome. It is always best to consult with a concrete supplier before choosing a retarder for a specific project.
Advantages of Using Concrete Retarders
There are several advantages of using ready mix concrete retarders:
- Prolonged working time: Concrete retarders can extend the working time of the concrete, allowing for more time to place and finish the concrete.
- Improved workability: Retarders can improve the workability of the concrete, making it easier to place and finish.
- Reduced cracking: Concrete retarders can reduce the risk of cracking due to the slower setting time of the concrete.
- Enhanced surface finishes: Some retarders can be used to create specific surface finishes, such as a smoother surface or a more exposed aggregate finish.
- Improved strength: Retarders can improve the final strength of the concrete by allowing the concrete to cure more slowly and evenly.
- Cost-effective: Retarders can be used to reduce costs by extending the working time of the concrete and reducing the risk of cracking.
- Better control of setting time: Retarders can be used to better control the setting time of the concrete, which can be especially useful in hot weather or when long transportation times are expected.
- Better control of concrete temperature: Concrete retarders can help to control the temperature of the concrete, which can help to prevent thermal cracking
It is important to note that the use of the retarder may cause some limitations like colour variation and surface pop-outs, so the use of retarder should be balanced with the requirements of the project and the conditions of the job site.
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