Importance Of Admixtures For Concrete Mix

The use of additives is conditioned by obtaining the desired result. The super plasticizing or fluidizing aggregates correspond to a new generation of plasticizing additives, based on melamine or naphthalene products.

These aggregates constitute an evolution of the water-reducing additives, because the absorption and dispersion capacity of cement is much more accentuated.

The main effects derived from the incorporation of a surfactant component are:

-Ionization of the additive filaments, which produces the separation of the cement grains from each other. This leads to effective deflocculation (removing lumps).

On the other hand, the additive molecules are absorbed and are oriented on the surface of the cement grains in a thickness of several molecules. This results in a lubrication of the particles.

To understand how these additives work, it is necessary to remember the behavior of water and cement in the mixing and setting process of concrete.

The first one forms the binder paste product of the lubrication of the cement and aggregate particles, after the absorption of the water. Later, this paste becomes cementitious, a product of the chemical reaction that takes place between cement and water when setting begins.

The first of these stages is when the mixing of the components and the first electrochemical reactions between the water and the cement take place. The characteristics of fresh concrete such as workability, workability or consistency appear.

The harmful effects of flocculation can be counteracted, at least in part, by incorporating certain chemical compounds into the concrete mass such as super-plasticizers, high-range water reducers, or super-fluidizers.

These aggregates act as neutralizers of the electrical charges found on the surface of the cement particles and, consequently, prevent the formation of flocs.

1. Air-inclusive additives

They are from chemical company malaysia those that meet ASTM C260 and C618 requirements, they are mainly used to increase the resistance of concrete to freezing and melting; they provide better resistance to the deterioration action of deicing salts. When concrete freezes, water can leak out of the bubbles, resulting in less cracking than would have occurred without using trapped air.

2. The addition of accelerating additives

The addition of accelerating admixtures such as calcium chloride accelerates the development of its early strength in concrete. The results of such additions (particularly useful in cold climates) are shortened times for concrete curing and protection, as well as prompt removal of the formwork (section 3.6.3 of the ACI code states that due to corrosion problems, the Calcium chloride should not be added to aluminum-drowned concrete, concrete cast on permanent galvanized steel forms, or prestressed concrete.) There are other accelerator additives that can be used, including various soluble salts and other organic compounds.

3. Retardant additives

They are used to retard both the setting of concrete and increases in temperature. They consist of various acids or sugars, or derivatives of sugar. Some concrete truck drivers carry sacks of sugar with them to add to the concrete in case of being delayed by traffic or other circumstances.

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