16 - Batching and Dispensing of Admixtures

Abstract

This chapter presents information on the operational aspects pertaining to the use of admixtures in the field. It offers guidance in the selection, use and control of uniformity of the product. Most of the issues apply equally to the three major fields of concrete construction— namely, site batched and placed concrete, ready-mixed concrete, and precast concrete. The quantity of an admixture used is small relative to other constituents of the mix but its effect, depending on the amount used, may be quite potent. Therefore, the method used to prepare the admixture is important. Most proprietary admixtures are ready to use liquids which require no further preparation at the location of use. Indeed, site preparation with these products is strongly discouraged by the manufacturer. Manufacture may involve making standard solutions or dilution to provide the manufacturer's recommended dosage to facilitate accurate dispersion. Admixtures are supplied in various forms of packaging, depending on the amount contained and the ease of use required. Most proprietary admixtures are neutral or slightly alkaline solutions that are supplied in different containers, according to the volume of concrete intended to be mixed. Since admixtures are potent modifiers of the concrete's characteristics, it is imperative to minimize potential mistakes. Thus, it is important that all containers in which admixtures are delivered or stored should be clearly labeled and marked in such a way that the information cannot be altered.