What are Admixtures?
Introduction The freshly-mixed and hardened properties of concrete may be changed by adding liquid (chemical) or mineral admixtures to the concrete, during batching. Admixtures are commonly used to (1) intentionally entrain air, (2) reduce water demand, (3) increase workability, (4) adjust setting time or hardening, and (5) adjust other concrete properties, such as strength. Common chemical admixtures include water reducers, set retarders and accelerators, air entraining, and super-plasticizers. Common finely-divided mineral admixtures are usually classified as either cementitious materials (i.e. ground-granulated blast furnace slag and lime), or pozzolans (i.e. fly ash and silica fume). Admixtures that affect the workability of a concrete mixture will also affect the slump, which is a test of the consistency of the mix. The slump of a mix with the same aggregate, cement and water can vary significantly by adding an admixture such as a high-range water-reducing admixture (super-plastic
Admixtures are chemicals or minerals added to concrete to change or improve its properties, either while it is still fresh or after it has hardened. Chemical admixtures include water reducers, set accelerators, set retarders, air entrainers, shrinkage reducers, corrosion inhibitors and defoaming agents. Mineral admixtures generally refer to pozzolans, such as fly ash, silica fume, metakaolin and slag, but can also include nonreactive materials, such as pigments. To explain each one of these admixtures and its use in concrete countertops would be a very long article. I will answer specific questions about specific admixtures in subsequent blog entries. In the meantime, for lots of good, readily understandable information about admixtures, visit The Concrete Network’s section on admixtures. Or read the Portland Cement Association publication Design and Control of Concrete Mixtures, a widely used textbook for engineers. Chapter 6 is all about admixtures. You can also refer to ASTM C494, w
Admixtures are substances that are added to concrete in order to enhance the quality of the concrete in some manner. Often, the role of admixtures is to expedite the curing process for the concrete, making it possible for the mixture to set and dry quickly. At other times, an admixture may be used to help slow down the setting and drying process, making it possible to work with the concrete for longer periods of time. Generally, admixtures are divided into two specific categories: mineral and chemical. It is important to recognize that admixtures are different from aggregates. While it is true that aggregates also impact the final quality of the concrete, they are more concerned with texture and color. By contrast, admixtures are more focused on enhancing the workability of the concrete in some manner, as well as making it possible for the concrete to set and dry under various types of temperature conditions. Most commercially produced concrete mixes sold today include at least one adm
Admixtures are natural or manufactured chemicals which are added to the concrete before or during mixing. The most often used admixtures are air-entraining agents, water reducers, retarders and accelerators. Why Use Admixtures? Admixtures are used to give special properties to fresh or hardened concrete. Admixtures may enhance the durability, workability or strength characteristics of a given concrete mixture. Admixtures are used to overcome difficult construction situations such as hot or cold weather placements, pumping requirements, early strength requirements or very low water-cement ratio specifications.
