Considerations regarding concrete admixtures

Additives are different products from cement, aggregates and water, which are added to concrete before or during mixing to alter properties such as traceability, curing temperature, setting time, color, among others. Some admixtures have been used for a long time, such as calcium chloride to provide concrete set in cold weather; others are more recent and offer multiple possibilities to increase concrete performance.

Not all additives are inexpensive for a particular project; in addition, some properties of concrete, such as low absorption, can be achieved simply by the continuous use of good concrete pouring practices.

The chemistry of concrete mixes is a complex subject that requires in-depth knowledge and experience. A general mastery of the additives available is necessary for the acquisition of the right product; according to weather conditions and project requirements. 

The more unique details about the aforementioned categories of additives are provided below.

Retardants: they delay the hydration of the cement, prolonging the setting time. Retarders are used beneficially in hot weather conditions, in order to overcome the accelerating effects of elevated temperatures, as well as the effect of large masses of concrete on setting time.

Retardant additives can be made from organic and inorganic agents. Taking into account the specific needs and objectives of the project, the concrete supplier should offer the necessary admixtures as well as the appropriate concrete mixes.

Accelerators: shorten the time for concrete setting, achieving cold weather pouring, early removal of falsework, early surface completion and, in some cases, early application of loads. Care must be taken in choice and proportion. The most commonly used accelerators cause an increase in concrete drying shrinkage.

Superplasticizers: also known as plasticizers, they also include water reducing additives; compared to what is commonly known as a water reducer, or a mid-range water reducer, a superplasticizer is a high-range water reducer. These are additives that allow high water reduction or increased flowability, without substantially reducing set time or increasing included air.

Each type of superplasticizer sodium gluconate Malaysia has defined the limit amounts to be used according to the dosages, as well as the corresponding effects. These can maintain a specific consistency and workability with a considerable reduction in the amount of water. High-strength concretes can also be achieved with them.

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