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An analogy Construction chemicals and their Implication

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Construction Chemicals
Dr. Siddhartha Sengupta,
Associate Professor, Civil &
Environmental Engineering,
Birla Institute of Technology, Mesra, Ranchi

Construction Chemicals, as the name suggests, are the chemical compounds used in construction/ rehabilitation of different structures. These have always been playing important roles in virtually all sorts of constructions, be it residential or industrial/ commercial building projects. These chemicals are often used in different elements of projects in order to achieve various important qualities such as workability, durability etc. Construction chemicals increase the cost of the project by 2-5% but the benefits are multi-fold. Certain chemical products help in minimizing the quantities of cement and water used in the construction. These compounds impart chemical as well as physical properties in applications such as cross-linking or phase change (from liquid to solid). Construction chemicals are essential for high quality concrete and for promoting the improvement of concrete performance. They also increase the life of construction work and impart additional protection from environmental hazards. Based on end use applications, these compounds can be broadly classified into five categories as shown in Figure 1.

Technical details

  1. a) Concrete admixtures

Cement is a widely used non-metallic material of construction and is mixed with crushed rock, sand and water in specific proportion to produce concrete. For getting better results, better workability, more strength, and finishing, cement or mortar admixtures are used. Chemical admixtures are added to the mix immediately before or during mixing. Admixtures are primarily used

To reduce the cost of concrete construction

To modify the properties of hardened concrete

To ensure the quality of concrete during mixing, transporting, placing, and curing

Admixtures aid in the production of high-strength, durable concrete, used for intricate architectural designs. They allow concrete to flow, thus increasing application time and ease of use and preventing the concrete components from segregating.

Successful use of admixtures depends on the use of appropriate methods of batching and concreting. Most admixtures are supplied in ready-to-use liquid form and are added to the concrete at the plant or at the jobsite.

Normally, admixtures carry less than 0.5% by mass of cement.

It is estimated that 50% of concrete produced in India these days contains one or more types of admixtures.

80% of ready-mixed concrete is produced using fly ash and at least 70% of produced concrete contains a water-reducer admixture.

Concrete admixtures may be broadly classified as mentioned below:

  1. i) Plasticizers: They are also called as water reducing admixtures. They increase the workability of fresh concrete and decrease the consolidating effort.
  2. ii) Super-plasticizers: These are also called high range water-reducing admixtures, and are a class of plasticizers which have fewer deleterious effects when used to significantly increase workability.

iii) Hyper-plasticizers: These are referred as third generation admixtures. They have the capability of ensuring very good flowability at very low water to cement ratios.

  1. iv) Accelerators: They speed up the setting (hydration) time. Sodium and calcium chlorides are basic salts with accelerator properties.
  2. v) Retarders: These slow the hydration of concrete. They are used in large and difficult pours, where partial hydration pouring is undesirable.
  3. vi) Air entrainments: Air entrainments add and distribute tiny air bubbles in the concrete that reduce the damage during freeze-thaw cycles, thereby increasing the durability of concrete.

vii) Corrosion inhibitors: They are used to minimize the corrosion in steel and steel bars in concrete.

 

B) Waterproofing chemicals

Waterproofing caters to various end use applications with products such as polymer modified cementitious composites, elastomeric polyurethane, waterproofing concrete, expanded polyethylene, polysulphide sealants, polyurethane systems, water repellents, and butyl & acrylic sealants, depending on the need or damage to the structure.

Water proofing compounds are available in liquid, solid, slurry and two-component coating forms. These products could be urethane based, modified asphalts, clay based or rubber polymers.

Water proofing compounds are designed to stop water infiltration. These compounds or membranes can be extremely effective when applied on the exterior of a foundation system.

Application of the water proofing compounds can be done by implant treatments i.e. either dipping or spraying or by low-pressure spraying on the surface.

  1. C) Flooring compounds

Flooring compounds are mostly epoxy and polyurethane based.

Industrial flooring compounds are used to meet various industrial needs such as abrasion, load impact, chemical attack, moisture penetration, strengthening of damaged floors, as well as improving the aesthetic appeal of the floor.

They are also used to provide certain special features such as slip resistance, static resistance, fire resistance, antibacterial properties, and so on.

  1. D) Repair and rehabilitation

Rehabilitation /Retrofitting is basically addition of new technology or features to older systems and improving the structures with energy efficiency.

Rehabilitation is reconstruction of the structural components which were damaged.

These products include cementitious repair mortars, concrete floor repairing systems, polyester and epoxy-based resin mortars, moisture insensitive epoxies, structural additives, synthetic adhesives, rust removers and corrosion inhibitors.

The main rehabilitation methods are concrete jacketing, Steel Jacketing and FRP wrapping.

  1. E) Miscellaneous
  2. i) Sealants: are used to seal expansion joints, cracks, joints in concrete roads and to fill gaps between concrete .There are four types of sealants. These are:
  3. a) Polysulphide sealants: These are most commonly used in the construction industry as expansion joints for concrete roads, structural joints and others.
  4. b) Polyurethane sealants: These are used for high-end applications where high flexibility and bonding strength are required.
  5. c) Silicone sealants: These are generally used where good bonding is required between two dissimilar surfaces such as fixing of glass on metal frame.
  6. d) Acrylic sealants: These are generally used for crack or gap filling and for day-today applications such as windows and door gap sealing, etc.
  7. ii) Protective coatings and resins: The protective coatings include high performance waterproof coatings and epoxy resins. These are paints or coatings with more emphasis on protective properties rather than aesthetic properties. They provide excellent bonding, sealing and dust binding characteristics. The most common use of industrial coatings is for corrosion control of steel or concrete.

iii) Grouts: are compounds used for giving extra strength for the foundations of load bearing structures. They are also used for repair and sealing of cracks and gaps. Grouts have different applications as mentioned below:

Epoxy-based liquid grouting compounds are mainly injected into the walls to fill hairline cracks and gaps, thereby improving the strength of the structure.

Cementitious grouts are used for imparting extra strength to machine foundations, base plate or anchor bolts for machines or equipment and others. They are also used for repair of building structures and in heavy industries such as steel, power plants and ports.

Polyester-based grouts are also available, which are used for anchoring to impart strength to foundations that must be achieved in limited available space. Grouts can also be made to have special characteristics such as fast setting, free flow and others by addition of different additives as per the end-user requirement.

iv) Others (Tile adhesives): Tile adhesives are used for fixing tiles on the floors, walls, swimming pools and others. Tile adhesives are based on cement and polymer formulation (mainly acrylic polymer).

Presently, the construction chemicals are being used very commonly. Lots of researches are going on in the subject. New materials and chemicals are being developed. It is expected that with technical advancement as well as with increasing awareness, the field of applications of construction chemicals would become wider.

Sources

  • http://ficci.in/spdocument/20214/Construction-Chemicals-Knowlege-Paper-2013_final.pdf
  • http://www.ardaindia.com/wp-content/uploads/2017/05/ARDA-NSP-3.jpg

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