A retarder in concrete is an admixture used to slow down the rate at which concrete hardens, specifically by putting off the concrete's initial setting time.
According to the provided reference, concrete retarders are typically used to delay the initial set by up to an hour. Their primary application is in hot weather. High temperatures can cause concrete to harden quickly, which can be problematic. Retarders counteract this effect, preventing the quick hardening caused by high temperatures.
Purpose and Benefits
The main purpose of using a retarder is to provide sufficient time for various crucial processes involving concrete, such as:
- Mixing: Ensuring all components are thoroughly combined.
- Shipping: Transporting the mixed concrete to the job site.
- Placement: Laying and finishing the concrete before it becomes too stiff.
By delaying the set, retarders ensure the concrete remains workable for a longer duration, which is particularly beneficial in challenging conditions like high ambient temperatures or when dealing with complex pours requiring extended placement times.
Related Admixtures
It is also noted in the reference that water reducers are also retarders. This highlights that some admixtures can serve multiple functions, reducing water content while also slightly delaying the set.
In summary, a concrete retarder is an admixture that extends the setting time, primarily used in hot conditions to maintain workability and facilitate mixing, transport, and placement processes.
