What are Admixtures?
According to ACI 212, admixture are defined as materials other than the normal compounds of concrete (such as water, aggregates, cement, fibers) that is added to the mixture to modify its freshly mixed, setting, or hardened properties and that is added to the batch before or during its mixing”.
Thus, admixture either improves an existing feature to cement paste or add a feature that does not exist.
What are Water-reducing Admixtures?
What are Accelerators?
Accelerators are often sold under other names such as hardeners, anti-freezes, or frost-proofers. The use of an accelerator does not eliminate the necessity to insulate the concrete once it has been poured in order to keep it warm and protect it from the cold.
So, what does accelerating admixtures do?
As the name implies, the addition of an accelerator speeds the setting time and hardening process of whatever it is added to. This is crucial in locations where early strength development is required such as in repair works and concreting in cold weather.
Accelerators or accelerating admixtures increases the speed of the hydration reactions (hydration: chemical reactions between the cement and water), which in turn increase the early strength development.
An important note here is that later-age strength (strength at 28 days) is not affected by accelerators; only the early age strength.
It should be emphasised that accelerators are not as effective in mortars as concrete since any heat produced by the quicker reaction is soon lost due to the thickness of mortar, whether in a joint or on a rendering.
Accelerating Water-reducing Admixtures
Water Reducers Can Also Acts as Accelerators for Concrete
This kind of admixture possesses dual functions: water-reducing feature and accelerator feature.
The accelerating water-reducing admixtures have an accelerating function in addition to the same water-reducing capabilities as the “regular” water reducer. Faster setting times and greater strengths during the early hydration phase are provided by this accelerating feature, which enables finishing operations to be completed on schedule, especially at lower temperatures.
The formulation of this kind of product includes high amounts of accelerators (chloride or non-chloride), frequently a non-ionic surfactant, and water-reducing ingredients with little set-retarding impact, such as low-sugar processed lignosulfonates or blends of lignosulfonates with superplasticizers. In order to increase workability or water reduction without significantly prolonging set times, the mid-range water reducing additive can be used at higher dosages.
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