Originally, the science of admixture was the province of a specialist, but with advanced building technology and ever increasing new demands on builder, engineer and architect it is necessary that all involved in building have as much knowledge of admixtures and their effects as of cement, aggregate or the mixing water. Such knowledge permits judicious use of admixtures. The addition of calcium chloride promotes certain desirable properties and affects others but the performance of a concrete containing calcium chloride admixture can reasonably be predicted only when both the short- and long-range effects have been established. Its popularity is due to its ready availability, low cost, predictable performance characteristics, and successful application over several decades.Ĭoncrete has to satisfy many performance requirements. Several chemicals are known to act as accelerators for concrete - calcium formate, aluminum chloride, potassium carbonate, sodium chloride and calcium chloride (among others) - but calcium chloride is most widely used. From the practical point of view this means reduction in the curing period and reduction in the time during which concrete must be protected in cold weather, earlier finishing operations, and earlier availability for public use. In a chemical sense acceleration may mean an over-all increase in the rate of reaction in the physical sense, an increase in the rate of setting in a mechanical sense, an increase in the rate of development df strength.
It does not necessarily accelerate the development of every one of them. Typical examples include water reducers, retarders, water reducing accelerating agents, accelerators, and water-proofers.Īn accelerator, as the term suggests, increases the rate of development of certain characteristic properties of cement and concrete. Most admixtures are known by the function they perform. These are known as admixtures and are added to water, aggregate and hydraulic cement immediately before or during mixing ( CBD 103).
Today, many hundreds of chemicals claimed to possess one or more beneficial effects have been suggested for incorporation in concrete. The Romans used blood, pig's fat and milk as additions to pozzolanic cements to improve their workability and durability. The addition of small amounts of certain materials to concrete to promote desirable properties is as old as the use of cement itself. Home > Publications > Canadian Building Digests > CBD-165.
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