Technology : Construction Chemicals

 

Concrete is a construction material that consists of cement (Ordinary Portland cement or Portland Slag Cement or Portland Pozzulana Cement), Cement Additives (FlyAsh or GGBS Slag or Micro-silica), Aggregates (generally Gravel and Sand), Water and Admixtures.

Concrete solidifies and hardens after mixing and placement due to a chemical process known as hydration. Free water, present in concrete, reacts with the cement, which bonds the other components together, eventually creating a stone-like material.

Concrete is used to make pavements, architectural structures, foundations, motorways / roads, overpasses, parking structures, brick / block walls and footings for gates, fences and poles etc.

 

Regular Concrete

Regular concrete is the lay term describing concrete that is produced by following the mixing instructions that are commonly published on packets of cement, typically using sand or other common material as the aggregate, and often mixed in improvised containers. This concrete can be produced to yield a varying strength from about 10 MPa to about 20 MPa, depending on the purpose, ranging from blinding to structural concrete etc. Many types of pre-mixed concrete are available which include powdered cement mixed with an aggregate, needing only water.

 

High Strength Concrete : Use of Plasticizers and Super-plasticizers

Plasticizers are additives that soften the materials (usually a plastic or a concrete mix) to which they are added. Although the same compounds are often used for both plastics and concrete, the desired effect is slightly different. The plasticizers for plastics soften the final product increasing its flexibility. Plasticizers for concrete soften the mix before it hardens, increasing its workability , and are usually not intended to affect the properties of the final product, after it hardens.

Superplasticizers are chemical admixtures that can be added to concrete mixtures to improve workability and strength of concrete.

Strength of concrete is inversely proportional to the amount of water added or water-cement (w/c) ratio. In order to produce stronger concrete, less water is to be added, which makes the concrete mixture very unworkable and difficult to mix.

This difficulty is overcome by using plasticizers and superplasticizers. These admixtures increase workability of concrete at lower water-cement ratio. Although, plasticizers and superplasticizers do not directly affect the strength of concrete, their action of reducing the water-cement ratio results in concrete of increased compressive strength.

Use of Plasticizers in concrete usually results in higher compressive strengths in the range of 20 to 40 MPa. Use of Superplasticizers results in strengths upto 60 Mpa (Previous Generation) and upto 120 Mpa (New Generation : Polycarboxylate Ethers)

Plasticizers are commonly manufactured from lignosulfonates , a by-product from the paper industry. Superplasticizers have generally been manufactured from sulfonated naphthalene formaldehyde or sulfonated melamine formaldehyde , although new generation products, based on polycarboxylate ethers, are now available.

Polycarboxylate Ethers (PCE), the new generation of superplasticisers are not only chemically different from the older sulphonated melamine and naphthalene based products but their action mechanism is also different, giving cement dispersion by steric stabilization , instead of electrostatic repulsion. This form of dispersion is more powerful in its effect and gives improved workability retention to the cementitious mix. Furthermore, the chemical structure of PCE allows for a greater degree of chemical modification than the older generation products, offering a range of performance that can be tailored to meet specific needs.

 

HISTORY

 

Concrete Curing Compound

Concrete Curing Compounds when sprayed or brushed on newly laid concrete surface forms a tough and elastic membrane thereby reducing the loss of water from concrete during early-hardening period. The concrete gets adequately hydrated by matrix water since evaporation of water from the surfaces is minimized by the film barrier of resin. The concrete achieves maximum beneficial properties including increase of mechanical strength.