混凝土外加劑是什么/What is concrete admixture

混凝土外加劑是指為改善和調節混凝土的性能而摻加的物質。混凝土外加劑在工程中的應用越來越受到重視，外加劑的添加對改善混凝土的性能起到一定的作用，但外加劑的選用、添加方法及適應性將嚴重影響其發展。

混凝土外加劑（英文：concrete admixtures）簡稱外加劑，是指在拌制混凝土拌合前或拌合過程中摻入用以改善混凝土性能的物質。混凝土外加劑的摻量一般不大于水泥質量的5%。混凝土外加劑產品的質量必須符合國家標準《混凝土外加劑》（GB 8076-2008）的規定。

混凝土外加劑按其主要功能分為四類：

1、 改善混凝土拌合物流變性能的外加劑。包括各種減水劑、引氣劑和泵送劑等。

2 、調節混凝土凝結時間、硬化性能的外加劑。包括緩凝劑、早強劑和速凝劑等。

3 、改善混凝土耐久性的外加劑。包括引氣劑、防水劑和阻銹劑等。

4 、改善混凝土其它性能的外加劑。包括加氣劑、膨脹劑、著色劑、防凍劑、防水劑和泵送劑等。

最初使用外加劑，僅僅是為了節約水泥，隨著建筑技術的發展，摻用外加劑已成為改善混凝土性能的主要措施。

由于有了高效減水劑，大流動度混凝土、自密實混凝土、高強混凝土得到應用;由于有了增稠劑，水下混凝土的性能得以改善：由于有了緩凝劑，水泥的凝結時間得以延長，才有可能減少坍落度損失，延長施工操作時間：由于有了防凍劑，溶液冰點得以降低，或者冰晶結構變形不致造成凍害.才可能在負溫下進行施工等。

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Concrete admixtures are substances added to improve and regulate the properties of concrete. The application of concrete admixtures in engineering has been paid more and more attention. The addition of admixtures plays a certain role in improving the performance of concrete, but the selection, adding method and adaptability of admixtures will seriously affect its development.

concrete admixtures (English: concrete admixtures), referred to as admixtures, refers to the mixed concrete before or during the mixing process to improve the performance of concrete substances. The amount of concrete admixture is generally not more than 5% of the cement mass. The quality of concrete admixture products must comply with the provisions of the national standard “Concrete Admixture” (GB 8076-2008).

Concrete admixtures are divided into four categories according to their main functions:

1. Admixtures to improve the variable performance of concrete mixing. Including all kinds of water reducing agents, air entraining agents and pumping agents.

2, adjust the concrete setting time, hardening performance of the admixture. Including retarding agent, early strength agent and accelerating agent.

3, improve the durability of concrete admixtures. Including air entraining agent, water repellent agent and rust inhibitor.

4. Admixtures to improve other properties of concrete. Including aerating agent, expansion agent, coloring agent, antifreeze agent, waterproofing agent and pumping agent.

The initial use of admixtures is only to save cement, with the development of construction technology, the use of admixtures has become the main measure to improve the performance of concrete.

Due to the high efficiency water reducing agent, the high mobility concrete, self-compacting concrete, high strength concrete has been applied; Due to the thickening agent, the performance of underwater concrete can be improved: because of the retarder, the setting time of the cement can be extended, it is possible to reduce the loss of slump and extend the construction operation time: because of the antifreeze, the freezing point of the solution can be reduced, or the deformation of the ice crystal structure will not cause freezing damage. It is possible to carry out construction and so on under negative temperature.