Accelerator

Definition

An accelerator is a substance added to concrete, mortar, or grout that increases the rate of hydration of the hydraulic cement. This accelerates the setting time and enhances the rate of hardening or strength development, thereby speeding up the overall curing process.

Purpose

The primary purpose of accelerators in concrete and mortar is to shorten the setting time and increase the early strength development. This is especially useful in cold weather conditions where the setting process is naturally slower, or in construction projects requiring fast-track schedules. Accelerators help in achieving desired structural strength quickly, allowing for faster progress in construction timelines.

Examples of Use

1. Cold Weather Concreting: In low temperatures, accelerators are used to counteract the slow hydration process, ensuring that the concrete sets and hardens properly.
2. Rapid Repairs: For emergency repairs or quick maintenance work on infrastructure like roads, bridges, and airport runways, accelerators enable the concrete to set and gain strength rapidly.
3. Precast Concrete: In the production of precast concrete elements, accelerators help in achieving the necessary strength quickly, facilitating faster turnover and production cycles.
4. Tunnel Construction: Accelerators are often used in tunnel lining systems to expedite the setting process, allowing for continuous progress in tunnel boring and construction.
5. Winter Construction Projects: During winter construction, accelerators ensure that concrete can be poured and set effectively despite the cold conditions, maintaining project schedules.

Related Terms

1. Retarder: A substance that slows down the setting and hardening process of concrete, opposite in function to an accelerator, used when prolonged working time is needed.
2. Admixture: General term for substances added to concrete to modify its properties, including accelerators, retarders, plasticizers, and air-entraining agents.
3. Hydration: The chemical reaction between cement and water that causes concrete to set and harden, accelerated by the use of accelerators.
4. Curing: The process of maintaining adequate moisture, temperature, and time to allow concrete to achieve its desired properties, influenced by the use of accelerators.
5. Set Time: The period required for concrete or mortar to transition from a plastic state to a solid state, reduced by accelerators.

Notes

1. Common accelerators include calcium chloride, though non-chloride accelerators are often used to avoid corrosion in reinforced concrete.
2. The use of accelerators should be carefully controlled and monitored to ensure they do not adversely affect the long-term durability and strength of the concrete.
3. Accelerators are particularly beneficial in fast-track construction projects where early load-bearing capacity is required.
4. Compatibility of accelerators with other admixtures and the specific cement used should be verified to ensure optimal performance.
5. Environmental conditions, such as temperature and humidity, play a significant role in determining the effectiveness and necessity of using accelerators in concrete.