The setting time for normal class concrete involves two distinct stages: initial setting and final setting. Based on the reference provided, the initial setting time is around one hour, and the final setting is 24 hours.
Understanding the setting time of concrete is crucial for construction, as it dictates when various operations like finishing can occur and when the structure gains sufficient strength. As per the reference, concrete undergoes two main setting phases.
Initial Setting Time
The initial setting time marks the point at which concrete begins to lose its plasticity and starts to stiffen. It is the time from the addition of water to the cement mix until the paste starts losing its fluidity.
- According to the reference, the initial setting time for normal class concrete is around one hour.
During this initial setting period, activities like placing, vibrating, and initial finishing of the concrete must be completed. Once initial set is reached, the concrete can no longer be easily molded or worked without disrupting the hydration process and potentially compromising strength.
Final Setting Time
The final setting time is when the concrete has achieved significant stiffness and can no longer be considered plastic. It signifies the point where the concrete paste has hardened sufficiently to resist definite indentation by a specific standard test.
- The reference states that the final setting time for normal class concrete is 24 hours.
After the final setting time of 24 hours, the concrete continues to gain strength through a process called hardening. The reference notes that at least 98 percent of the concrete has set (hardened) within 24 hours, although hardening continues at a slower pace thereafter. This final set is an important milestone, indicating the concrete is transitioning from a plastic state to a solid material.
Here's a summary based on the provided reference:
| Setting Phase | Approximate Time | Description |
|---|---|---|
| Initial Setting | Around 1 hour | Concrete begins to lose plasticity. |
| Final Setting | 24 hours | Concrete reaches significant stiffness; ~98% hardened. |
These times are typical for normal concrete mixtures under standard temperature and humidity conditions. Factors such as temperature, humidity, cement type, water-cement ratio, and admixtures can influence the actual setting times.
