In modern concreting, admixtures have become the essential fifth ingredient that offers extra control of many aspects of concrete performance. This article will discuss one group of admixtures the water reducers. In 1932 our company introduced the first water-reducing admixture to the industry. Its main ingredient was calcium lignosulfonate, a by-product of the wood pulp industry. A few years later, a hydroxylated carboxylic acid (HC) was introduced as a base material for water-reducing admixtures. Another type, hydroxylated polymer admixtures, was first used in 1963. The latest development is the high-range water-reducing (HRWR) admixture. It is ordinarily based on a sulfonated melamine (or napthalene) formaldehyde condensate. These four types of admixtures are all currently available. It is important, therefore, that those involved in concrete construction have a basic knowledge of the correct areas of application, benefits to expect, and cautions to observe for each of them.
Small amounts of calcium chloride are most frequently used as the accelerating agent in compounding normal- or accelerated-set water-reducing admixtures. Calcium chloride has a long history of satisfactory use and its actions are extensively documented. In most cases, its use is perfectly satisfactory. However, admixtures containing appreciable amounts of chlorides are not recommended for some applications: prestressed concrete, sulfate-resistant concrete and concrete in contact with galvanized steel. For these applications, water-reducing admixtures with nonchloride accelerators are available. Relative effectiveness is another matter to consider when selecting a water-reducing admixture. Although these admixtures will be discussed in type, different brands of admixtures of the same type can perform differently. Therefore, after selecting a type of water-reducing admixture for a specific application, it will be worth your time to select a brand and be sure that brand is used.