TRMA Dispels Rebars Myths
Congratulations on the formation of Thermex Rebar Manufacturers' Association (TRMA). Please brief us on TRMA and its function. What prompted Thermex® rebar manufacturers to come together to form this body?
There are almost 150 Thermex® installations in the Indian region. This region comprises India, Pakistan, Nepal, Sri Lanka, and Bhutan. With such a large number of Thermex® licensed producers, the need for a cohesive association was felt, and thus TRMA was born.
As one united group, TRMA aims to uplift the quality of steel rebars used in India's civil construction by spreading awareness of desirable properties in rebars amongst the civil engineering fraternity. Towards this objective, we will travel to many cities to deliver a factual and comprehensive talk on various aspects of steel rebars. We hope our exposé of the myths and realities of steel reinforcement will clear the confusion and doubts that exist.
Since TRMA's prime focus is on steel reinforcement, we have confined the association's membership to persons that are somehow related to this subject. That is why TRMA includes structural engineers, quality control auditors, and senior members of engineering bodies as its members; besides of course Thermex® rebar manufacturers.
TRMA is headquartered in Mumbai with representation from the various zones of India.
The Chennai meeting of TRMA was an important milestone during which the association launched its campaign for proper 'Steel Reinforcement' and dispelled various myths confronting the industry. What were these myths addressed at the meeting?
Here I need to correct you as our campaign for proper steel reinforcement actually started in Mumbai on 5th March 2011. At this inaugural event, we decided to take our crusade to many Indian cities. So after Mumbai came the Chennai campaign. At each of these events, we highlighted the myths and realities of steel reinforcement so as to present the actual position to the structural engineers.
For example, it is a common myth that rebars made by secondary mills are not good because they use scrap as raw material. Civil engineers are unaware that secondary mills use steel scrap for melting into liquid steel and converting into billets or ingots. This is done globally. Steel scrap is refined steel unlike iron ore where only 60-65% is iron content. Thus use of steel scrap saves energy as compared to making steel from iron ore. Today, builders get platinum rating for their projects that employ rebars where steel scrap is the starting raw material.
Secondly, you have some companies claiming to manufacture earthquake resistant bars. It is important for people to know that the amount of energy released and the focal depth are key factors in the destructiveness of an earthquake. Shallow quakes at depths of less than 20-30km can cause great destruction. No one can predict when, where, and how shallow an earthquake will be. So one questions the effectiveness of these so called earthquake resistant bars. The recent New Zealand Christchurch quake is a prime example because they have the strictest rebar codes.
At best, we can improve the quality of rebars that are used in high-seismic hazardous areas. High-strength, high-ductility rebars drastically reduce the risks of total building collapse thereby increasing the opportunity for residents to escape instead of being crushed to death by a building collapse. This requires that, irrespective of the Yield Strength, the bars should have excellent ductility (high stress ratio and elongation). Thermex® rebars fulfill this requirement.
Are the Indian rebar manufacturers following any standard to produce rebars of desirable quality? Is there an urgent need to revise the IS code to keep pace with global standards?
We, at TRMA, feel that the code should be made simpler and easy to implement at the ground level. One specific change is with regard to Elongation - the Indian code still specifies elongation values at fracture and this includes the localised elongation in the 'necking' area which has no structural importance. Globally uniform elongation is specified i.e. total elongation at maximum force. The Indian code gives this as an option for 3 out of 7 grades only (415D, 500D, 550D) and only if demanded by purchaser. Here too, the 5 percent value specified is shockingly low for earthquake prone areas.
At present, India has nearly 130 rolling mills where Thermex® systems are installed. How do you ensure consistency in quality at all these mills?
In the Indian sub-continent, Thermex® systems are supplied, installed and commissioned by H&K India, the exclusive and perpetual collaborator of HSE Germany. To ensure consistency in the quality of Thermex® rebars produced by such a large number of manufacturers, H&K India spends close to Rs.1 crore annually in third-party quality audit. Thermex® rebars from each licensee are audited once every quarter to ensure that besides meeting the IS Code, they also a) exhibit uniform peripheral tempered martensite and b) meet the strict Thermex® standards of tensile properties and ductility according to global norms.
H&K India has appointed STRUCTWEL, a NBAL accredited laboratory, to send their inspectors to each licensee for a surprise audit. The auditors conduct rebar tests on site as well as separately at the STRUCTWEL laboratory. Here it is important to note that auditors are changed regularly to avoid a manufacturer-auditor nexus. The exhaustive system of quality control also requires each licensee to main- tain a register of daily quality tests which are shared with H&K India.
The Indian civil engineering industry, where CTD bars have had a stronghold for the past 2 to 3 decades, is now turning its attention towards the THERMEX® Quenching and self-tempering (QST) technology. Kindly elaborate on the technology and its benefits.
The Thermex® QST technology enables production of desired high-strength steel rebars that meet all requirements of civil construction - yield strength ranging from 500MPa or more, toughness, ductility, weldability and excellent bend properties. The Thermex® process has two major steps:
Quenching
A short, intensive but very precise in-line cooling of the rolled bar is imparted through proprietary equipment, and this treatment results in a hardened periphery without any major effect on the core.
Tempering
The bars are allowed to cool naturally on leaving the proprietary quenching pipes. At this stage, a thermal exchange (THERMEX®) occurs between the hot inner core and the quenched martensite surface whereby the resultant bar structure is a distinct tempered martensite at periphery and a fine grained ferrite-pearlite structure in the central zone.
The Thermex® bar produced as above has unique qualities of high strength, toughness and ductility with A5 elongation values of 18 to 26%.
What was happening in the case of CTD bars was that cold twisting of deformed (CTD) bars raised yield strength, but at the cost of ductility. Further, the process of cold twisting introduced surface stresses on the bars and such bars had a very high rate of surface corrosion. CTD bars lying at the project site rusted at a rapid rate. Additionally, these CTD rebars were, on account of poor ductility, unsuitable for use in seismic areas. As a result, their usage is declining. Unfortunately, some Indian builders continue to use CTD bars even today.
You may be surprised to know that Europe stopped usage of CTD rebars in the early 1970s.
In India's infrastructure development, steel plays a pivotal role. What is the current status of Thermex® Quenching and Self-tempering technology in the country?
Today, approximately 60-65% of the rebars produced in our country are manufactured by using the Thermex® quenching system and technology. That is, you would agree, extremely impressive.
But this was not the case in 1992 when the first Thermex® system was installed in the Durgapur Steel Plant of SAIL. Since then a lot has been done to educate the engineering fraternity about the advantages of Thermex® rebars. There have been technical seminars, a sustained advertising campaign in steel and civil engineering publications for over 20 years, sponsorship of infrastructure-related conferences etc. But most importantly, the technology speaks for itself. Word-of-mouth apprecia- tion by satisfied mill owners has created positive publicity and endorsement for the technology within the industry. It is no wonder that Thermex® enjoys front-runner status in the world for 'quenching and self-tempering' technology.
NBMCW August 2011
