With challenges and hindrances continuing to plague infrastructure development, the government’s National Infrastructure.. February 2020
Rebars are used in RCC constructions, varying from large infrastructure projects like bridges, ports, airports, urban infrastructure, industrial plants and commercial buildings to small RCC-based individual house construction.
The backbone of civil construction, these are deeply anchored into concrete to bear the loads of buildings, slabs, beams and columns.
Considering their distinct advantages and the crucial role they play in the stability and durability of concrete structures, IRC 122 (Indian Roads Congress Code) specifies the use of TMT bars in the construction of bridges and other RCC structures.
A senior technical executive of PNC Infratech, shares, "TMT rebars have significant advantages in terms of strength, reliability, corrosion-resistance, resilience, resistance to fire and higher ductility."
In fact, all National Highways Authority of India (NHAI) projects include the use of TMT rebars.
RK Pandey, Member-Projects, NHAI, says, "We intend to purchase TMT bars from original manufacturers, for which, we appoint consultants and engineers to appropriately source the material."
TMT rebars are covered under IS 1786:2006 and its amendments for high-strength deformed steel rebars and wires for concrete reinforcement specifications. Mahesh Kumar, Director (Projects), Maharashtra Metro Rail Corporation, elaborates on the advantages of using TMT rebars in segments of viaducts for metro-rail projects, saying, "They have more ductility and ability to bend.
The TMT process gives these rebars anti-corrosive properties and using them increases the longevity of a structure. TMT is resistant to seismic forces owing to its soft core; the structure has more stability during earthquakes. The presence of external ribs running across the entire length of these rebars fosters great bonding strength between the concrete and the rebars, resulting in better structural integrity. And, better ductility and bending ability make TMT bars easy to work with on site."
As TMT rebars are factory-manufactured and processed, 100 per cent quality in conformity to codal requirements and specifications should be ensured during manufacturing by steel producers.
"To ensure quality and soundness, we only procure rebars from the main producers with end-to-end primary integrated steel manufacturing process units,"shares the PNC Infratech executive. "At project sites, we ensure reliability by verifying the manufacturer's symbol and marks on the bars, and regularly send samples to independent third-party testing laboratories to check and confirm their physical and chemical properties in accordance with relevant codal specification and standards, including IS 1786."
Similarly, Arun Sahai, COO, Ahluwalia Contracts, says, "We have our laboratories on site where all physical tests are conducted. While we do not have on-site chemical facilities, random samplings are sent to laboratories to ensure quality. We also ensure that manufacturers send lot-wise test reports, or what we call material test certificates (MTC)."
For his part, Rahul Katyal, Managing Director, Capacit'e Infraprojects, says, "There is a clear-cut guideline on the quality of steel required by IS standards.
As for shortlisting vendors, if the client insists on a primary steel manufacturer, there are three or four companies. But in the case of secondary producers, these are regional players governed by geographical positioning. We select about three in each region based on their track record and competency, and keep buying as and when we require steel on site."Further, the company verifies the test certificates that come from the manufacturer; and chemical and physical tests are conducted on site and results compared.
Pandey refers to standards such as BIS and IRC that exist for any building material. "While NHAI does not have a system of vendor registration, requirement of material and machinery entirely rests with the contractor,"he adds. "However, for all materials, we have specific standards documented in our contract agreement."
Speaking of Maha Metro, Kumar shares, "As soon as the consignment is received at site, its invoice is checked for quantity, grade and date of consignment. Along with verification of the document and consignment, samples are taken for each diameter of rebars and sent for testing. All tests specified in the IS 1786:2006 and its amendments, such as tensile test, elongation percentage test, bend test, rebend test and chemical tests, are done in a reputed third-party laboratory and the manufacture test certificate, containing chemical and physical tests, is verified before use."
Also read: Tata Steel, SAIL, JSW, Tiscon emerge among the key players for TMT rebars
- SHRIYAL SETHUMADHAVAN
To share your views, write in at feedback@ConstructionWorld.in