The most urgent need for concrete admixtures is water-reducing admixtures. In actual industry, water-reducing admixtures ensure the fluidity of concrete. Water-reducing admixtures can improve the quality of concrete to a certain extent and adjust the balance and stability of concrete. Workability, etc., improve production quality. Currently, polycarboxylic acid-based water-reducing agents are used on the market. National standards for aliphatic-based water-reducing agents require that they can no longer be used.
Secondly, the commonly used admixtures for concrete include strengthening agents and slump-preserving agents. The main function of strengthening agents is to increase the strength of concrete, which can save part of the production cost of concrete. This is not strictly required and needs to be added based on your needs.
The function of the slump-preserving agent is to maintain the slump of concrete. This is mainly used in summer when the temperature is higher and the slump loss of concrete is faster, because the concrete water-reducing agent contains some The function of slump, so this is not a strictly necessary additive.
Concrete water-reducing agent is essential for ordinary concrete.
The original mix ratio of C30 used per m3 of concrete is 400kg of cement, 200kg of water, 0.5 of water-cement ratio, and 100mm of slump. Now add 0.6% of water-reducing agent to maintain water. Under the same technical conditions of a gray ratio of 0.5 and a slump of 100mm, the water consumption is reduced to 160kg and the cement consumption is reduced to 320kg. Each m3 of concrete can save 80kg of cement and greatly reduce the hydration heat index of concrete.
The development history of concrete admixtures is closely related to the development history of concrete. To a certain extent, in the process of pursuing its own development, concrete admixtures also promote the development of concrete technology. The birth of high-strength concrete, which is generally recognized internationally as the third technological revolution in concrete, is based on a major breakthrough in water-reducing agents.
The role of concrete admixtures
Improve the workability of concrete or mortar mixtures during construction; improve the strength and other physical and mechanical properties of concrete live mortar; save cement or replace special Cement; accelerates the early strength development of concrete or mortar; adjusts the setting and hardening speed of concrete or mortar; adjusts the air content of concrete or mortar; reduces the heat of hydration in the early stages of cement hydration or delays the heat release of hydration; improves the bleeding of the mixture ; Improve the corrosion resistance of concrete or mortar to various aggressive salts; weaken the alkali-aggregate reaction; improve the capillary structure of concrete or mortar; improve the pumpability of concrete; improve the corrosion resistance of steel bars; improve the relationship between aggregate and The bonding force at the mortar interface improves the holding force between steel bars and concrete; improves the bonding force at the interface between new and old concrete; changes the color of mortar and concrete.
Water reducing agent can maintain the slump of concrete, reduce the mixing water consumption, 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, water-reducing agent: powder dosage is 0.75%~1.5%, liquid dosage is 1.5%~2.5%; when using porous aggregate, it is advisable to add water and stir first, then add water-reducing agent; when the slump When it is larger, care should be taken not to vibrate for too long to prevent bleeding and stratification. 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, and when used in combination with other admixtures Concrete compatibility tests should be conducted in advance; slump is highly sensitive to water consumption, and water consumption must be strictly controlled during use; pay attention to concrete surface maintenance.
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