Boosting Concrete Efficiency: The Power of Admixture Synergy
In concrete, various admixtures can be used together, but certain principles must be followed. Below are some common combinations of admixtures that can be used together:
1. Water-Reducing Agent and Air-Entraining Agent
- Principle of Action
- Water-reducing agents primarily work by adsorbing onto the surface of cement particles, reducing the attractive forces between cement particles, thereby releasing the water encapsulated around the cement particles to achieve the goal of reducing water usage. Air-entraining agents introduce a large number of tiny bubbles during the concrete mixing process.
- When used together, while the water-reducing agent reduces water usage, the bubbles introduced by the air-entraining agent can further improve the workability of the concrete, making it easier to vibrate and finish. For example, in some hydraulic concretes, both a water-reducing agent to enhance concrete strength and an air-entraining agent to improve freeze-thaw resistance are needed.
- Precautions
- When used together, it is important to pay attention to the compatibility between the two. Some water-reducing agents and air-entraining agents may interact with each other, affecting their respective effects. It is necessary to determine the appropriate dosage through testing, with an air content generally controlled between 3% - 6% being more appropriate.
2. Retarder and Water-Reducing Agent
- Principle of Action
- Retarders delay the setting time of concrete, and Water-reducing agents reduce water usage to enhance concrete strength. In mass concrete projects, they are often used together. Retarders slow down the rate of heat release from hydration, reducing the peak internal temperature of the concrete and reducing the formation of temperature cracks. Water-reducing agents ensure sufficient concrete strength without increasing water usage.
- Precautions
- The dosage of the retarder should be determined based on specific project requirements and environmental temperatures. If too much retarder is added, it may lead to an excessively long setting time, affecting the progress of the project. At the same time, attention should be paid to the chemical compatibility between the retarder and the water-reducing agent to avoid adverse reactions.
3. Accelerator and Water-Reducing Agent
- Principle of Action
- Accelerators can speed up early-age strength development in concrete, and Water-reducing agents reduce water usage to increase concrete strength. In concrete projects that require rapid demolding or early use (such as in a precast component factory), they are often used together. Accelerators promote rapid cement hydration, and water-reducing agents optimize the pore structure and distribution of hydration products, jointly enhancing the early-age strength of concrete.
- Precautions
- There are many types of accelerators, such as calcium chloride-based accelerators containing chloride ions, which should be used with caution in reinforced concrete structures because chloride ions can corrode reinforcement. The appropriate type of accelerator should be selected based on the structural type and corrosion protection requirements of the reinforcement, and the optimal dosage in combination with the water-reducing agent should be determined.
4. Pumping Aid (Usually a composite of various admixtures) and Other Admixtures
- Principle of Action
- Pumping aids generally comprise a composite of water-reducing agents, retarders, air-entraining agents, etc. Suppose a project has additional special requirements beyond pumping, such as pumping concrete in high-temperature environments. In that case, it may be necessary to add an appropriate amount of retarder based on the pumping aid to further extend the setting time of the concrete and ensure smooth pumping and construction.
- Precautions
- When adding other admixtures, consider the interaction with the existing components in the pumping aid. For example, if the pumping aid already contains a certain amount of air-entraining agent, additional air-entraining agent should be added with caution to prevent an excess of air-entraining agent, which could affect concrete strength.
