6 SPECIAL MATERIALS USED IN CONCRETE CONSTRUCTION

Special Materials in Concrete Industry

1. Ferrocement

Ferrocement is a type of reinforced concrete composed of concrete with small aggregate (or coarse cement mortar), 12 to 30 mm thick, reinforced with a minimum of two layers of small diameter, orthogonally woven wire mesh separated by 3 to 6 mm diameter galvanized spacer wires or weld mesh. The cement mortar is made with plasticizers and polymers to make it dense without pores. Due to the closely spaced wire mesh, shrinkage cracks are absent in this work.

This method can be used to provide protective reinforced membrane for rehabilitation of distress RCC members. A number of constructions like making a small non-load bearing partitions or even a small water tank can also be made with cement mortar laid on a layer of weld mesh and chicken mesh by an experienced worker without solid formwork.

2. Fibre Reinforced Concrete (FRC)

Different forms of fibres
Different forms of fibres

Fiber reinforced concrete is the Portland cement concrete mixed with uniformly dispersed short length fibres. These fibres can be natural fibres like coir or man-made fibres like steel, carbon, polymer etc. we generally use the second type of fibres, the most common type being steel fibres. They are available in different forms.

They are commonly used for the construction of industrial floors and road pavements. Today, many types of fibres have been developed to be used with concrete for many purposes. Both steel and polypropylene fibres are used for placing of concrete by shotcreting (or guniting). Fibres reinforced concrete not only prevents early shrinkage cracks but also improves strength and ductility of the reinforced sections.

3. Fibre Reinforced Polymer (FRP)

This is one important modern development in the repair of RC members. We have polymers as one of the concrete chemicals. We have also different types of strong fibres like carbon, glass or aramid (a synthetic or organic fibre). These two are joined together for the manufacture of modern FRP product. Many such products are available. Some are strong only in one direction – along the length. Others are strong in both directions – along the length and the breadth.

The FRP is very strong and hence, it can be used as reinforcement. It can be bonded to the concrete by using a high strength epoxy resin as an adhesive. We can also stretch the fibre along its length and then bond it to the concrete member so that it acts as a prestressing device. The RC member is ten under prestress. Thus, it can be used both as reinforcement and a prestressing device.

4. Cementcrete (Microconcrete)

In most of the repair works, we use concrete with the coarse aggregate of size 6 mm to 8 mm (mostly below 10 mm). This concrete with small-sized coarse aggregate is called cementcrete or microconcrete. Microconcrete with chicken mesh can be used in places in repair works.

5. Geopolymer Concrete (Concrete without Portland cement)

An alkaline liquid is made to react with silicon and of geologic origin or produced as an industrial byproduct. This produces concrete without Portland cement. As the chemical reaction that occurs to produce binders is a polymerization process, such concrete is termed as polymer concrete. Our conventional concrete is Portland cement concrete or simply cement concrete. Geopolymer concrete can be produced from ground granulated blast furnace slag (GGBS) and alkaline liquids. Water is added to this concrete only for workability and easiness in placing the concrete. On the other hand, in Portland cement, concrete water is necessary for the hydration of cement.

6. Silica Fume Concrete

Silica fume concrete is the concrete wherein silica fume (very finely divided pozzolanic material) is used to produce high strength Portland cement concrete. The addition of silica fume is to be not more than 10% by weight of cement. Superplasticisers are also needed to produce the necessary workability. If the depth of repair is less than 150 mm, then an epoxy bonding agent should be used to bond fresh silica fumes concrete to the old concrete.

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