Concrete admixtures play a vital role in improving the performance of concrete, and are becoming more and more popular in today’s engineering construction. However, due to the different functions and adaptability of admixtures, it is necessary to select appropriate admixtures based on the properties of the concrete itself and the surrounding environment. The following introduces some commonly used concrete admixtures:
Water reducing agent
Water reducing agent can Under the condition of maintaining the same concrete slump, reduce the mixing water consumption to improve the fluidity of the concrete mixture, or reduce the unit cement consumption to save cement. According to the water-reducing ability of water-reducing agents, they are divided into ordinary water-reducing agents (also called plasticizers, the water-reducing rate is not less than 8%), high-efficiency water-reducing agents (also called superplasticizers, the water-reducing rate is not less than 14%) and High-performance water-reducing agent (water-reducing rate not less than 25%). Among them, high-efficiency water-reducing agent: the powder dosage is 0.75% to 1.5%, and the liquid dosage is 1.5% to 2.5%; when using porous aggregates, it is advisable to add water and stir first, then add the water-reducing agent; when the slump is large, attention should be paid to The vibrating time should not be too long to prevent bleeding and delamination. High-performance water-reducing agent: the common dosage is 0.4% to 1.2%; a concrete trial mix test should be carried out before use to obtain the optimal dosage; it cannot be used in combination with naphthalene series high-efficiency water-reducing agent or other admixtures Concrete compatibility tests should be carried out in advance before use; slump is highly sensitive to water consumption, so water consumption must be strictly controlled during use and attention should be paid to concrete surface maintenance.
Early-strength agent
Concrete early-strength agent can improve the early strength of concrete and improve the later stage. Strength has no significant effect. The main function of early strength agent is to accelerate the hydration rate of cement, and it also has certain water reduction and enhancement functions. Scope of application: The early-strength agent does not contain chloride ions and has no corrosion effect on steel bars. It is suitable for all civil and industrial buildings, prestressed reinforced concrete components, mortars, etc.; the early-strength agent is suitable for construction under low temperature (early winter and early spring) conditions; It is used in Portland cement and has a particularly significant effect on reinforcing and modifying slag cement. Instructions for use: The dosage is generally 3% to 6% of cement; in order to maintain uniform quality of concrete, the mixing time is extended by 1 to 2 minutes; if the early strength agent is damp and agglomerated, it must be crushed or weathered before use, and its performance will not be Change.
Retarder
Retarder works by reducing the hydration rate and water content of cement or gypsum. It uses heat to prolong the hydration and hardening time of cement, so that fresh concrete can maintain its plasticity for a longer period of time, thereby adjusting the setting time of fresh concrete. The dosage is 0.1% to 0.6% of the cement dosage, and is suitable for continuous pouring of concrete, large-volume concrete, ready-mixed concrete and pumped concrete under high temperature conditions.
Air-entraining agent
Air-entraining agent can improve concrete slump, fluidity and Plasticity makes concrete have good bubble structure, small bubble radius, and high frost resistance. It is often used in high-durability concrete structures (such as dams, high-grade highways, ports, etc.). It is also a commonly used admixture to improve the durability of concrete pavement. The dosage of AH-1 is 0.01% ~ 0.03%, which is suitable for general anti-seepage, anti-freeze and durable concrete; the dosage of AH-2 is 0.6% ~ 0.7%, which is suitable for pumping concrete construction.
Expansion agent
Expansion agent is mainly used to compensate for the shrinkage during the hardening process of the material and prevent Concrete cracks. The dosage of concrete expansion agent is 10% to 12% (based on the amount of cement). For concrete that requires higher impermeability and crack resistance, the dosage can be increased through experiments. Before the initial setting of the concrete, the relevant construction regulations should be followed, and the concrete surface should be repeatedly pressed to prevent air drying and avoid cracks caused by settlement. Curing should be started after the final setting, and the curing period should not be less than 12 days. Expanding agents should be tested with local cement before use.
Water reducing agent
Water reducing agent can maintain the condition of constant slump of concrete Under the circumstances, reduce the mixing water consumption to improve the fluidity of the concrete mixture, or reduce the cement consumption per unit to save cement. According to the water-reducing ability of water-reducing agents, they are divided into ordinary water-reducing agents (also called plasticizers, the water-reducing rate is not less than 8%), high-efficiency water-reducing agents (also called superplasticizers, the water-reducing rate is not less than 14%) and High-performance water-reducing agent (water-reducing rate not less than 25%). Among them, high-efficiency water-reducing agent: the powder dosage is 0.75% to 1.5%, and the liquid dosage is 1.5% to 2.5%; when using porous aggregates, it is advisable to add water and stir first, then add the water-reducing agent; when the slump is large, attention should be paid to The vibrating time should not be too long to prevent bleeding and delamination. High-performance water-reducing agent: the common dosage is 0.4% to 1.2%; a concrete trial mix test should be carried out before use to obtain the optimal dosage; it cannot be used in combination with naphthalene series high-efficiency water-reducing agent or other admixtures Concrete compatibility tests should be carried out in advance before use; slump is highly sensitive to water consumption, and water consumption must be strictly controlled during use; pay attention to concrete surface maintenance.
Early-strength agent
Concrete early-strength agent can improve the early strength of concrete and improve the later stage. Strength has no significant effect. The main function of early strength agent is to accelerate the hydration rate of cement, and it also has certain water reduction and enhancement functions. Scope of application: Early strength agent does not contain chloride ions and has no rusting effect on steel bars. It is suitable for all civil and industrial buildings, prestressed reinforced concrete components, and sand.� etc.; early strength agent is suitable for construction under low temperature (early winter and early spring) conditions; it is used in Portland cement, and has a particularly significant effect on strengthening and modifying slag cement. Instructions for use: The dosage is generally 3% to 6% of cement; in order to maintain uniform quality of concrete, the mixing time is extended by 1 to 2 minutes; if the early strength agent is damp and agglomerated, it must be crushed or weathered before use, and its performance will not be Change.
Retarder
Retarder works by reducing the hydration rate and water content of cement or gypsum. It uses heat to prolong the hydration and hardening time of cement, so that fresh concrete can maintain its plasticity for a longer period of time, thereby adjusting the setting time of fresh concrete. The dosage is 0.1% to 0.6% of the cement dosage, and is suitable for continuous pouring of concrete, large-volume concrete, ready-mixed concrete and pumped concrete under high temperature conditions.
Air-entraining agent
Air-entraining agent can improve concrete slump, fluidity and Plasticity makes concrete have good bubble structure, small bubble radius, and high frost resistance. It is often used in high-durability concrete structures (such as dams, high-grade highways, ports, etc.). It is also a commonly used admixture to improve the durability of concrete pavement. The dosage of AH-1 is 0.01% ~ 0.03%, which is suitable for general anti-seepage, anti-freeze and durable concrete; the dosage of AH-2 is 0.6% ~ 0.7%, which is suitable for pumping concrete construction. </p
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