The Journey of Development in Bangladesh
Bangladesh has been making significant strides in development. Over the past decade, political stability and the ambitious goals of the ruling government have played a pivotal role in transforming the nation’s infrastructure. A key component of this infrastructure revolution is rebar (commonly known as rods). However, there are numerous disagreements about rebar.
Currently, the combined production capacity of all companies in Bangladesh is approximately 9 million metric tons, while the demand stands at around 5.5 million metric tons. In 2021, total rebar sales reached nearly 5.56 million metric tons. During the COVID-19 pandemic in 2020, rebar supply was about 10% lower than in 2019. In November 2021, the supply was approximately 5.57 million metric tons, and surveys indicate that supply could surpass 6 million metric tons in 2022
The market for rebar in Bangladesh is worth around 54,000 crore BDT annually, a fact unknown to many. With 8 years of experience in the construction materials market, I have observed numerous misconceptions among engineers and the general public. These misconceptions are not only frustrating but also embarrassing as a professional engineer. Below, I aim to address some of these misconceptions.
The Disagreements About Rebar Are Highlighted Below
Disagreements About Rebar Disagreements About Rebar
Rebar plays a significant role in construction projects, but several disagreements and misconceptions exist regarding its use and quality. Below are some common misunderstandings about rebar:
1.Sixty Grade vs. Five Hundred Grade
Many people confuse Sixty Grade (60 Grade) with Five Hundred Grade (72.5 Grade). These are two completely different grades of rebar. Good quality manufacturers produce two types of 60 Grade rebar (ASTM 615 and ASTM 706) and two types of 72.5 Grade rebar (B500C WR and B500D WR).
2.Shiny Rebar Means High Quality
The quality of rebar depends on its mechanical properties (e.g., yield strength, tensile strength, ductility, elongation, bendability) and chemical properties (e.g., carbon, silicon, manganese, phosphorus, sulfur, and carbon equivalent). The external color (black, red, or coppery) has no direct connection to the quality of the rebar.
3. Reddish Color Means Poor Quality
This is perhaps the most common misconception in Bangladesh regarding rebar.In a previously published article explained this in detail.
“Reddish Does Not Mean Rust, and Rust Does Not Mean Poor Quality Rebar“
Engr. Md. Golam Hossain Farhan
In summary:
Rebar naturally develops a reddish hue when exposed to air, but this is not rust. This reddish layer does not alter the fundamental properties or characteristics of the rebar. Research shows that rebar left outdoors for up to 18–24 months exhibits no significant changes in its mechanical or chemical properties.
If rust adheres tightly to the bar, it can enhance the bond between the rebar and concrete. There is no need to remove this rust. However, any oily substances on the rebar must be wiped off before use.
In a January 2004 ASTM study, it was found that rust affecting up to 2% of a rebar’s external surface can actually improve its bonding characteristics with concrete. According to the Concrete Reinforcing Steel Institute (CRSI), brushing off this light rust is unnecessary. Loose debris will fall off naturally during handling.
4: High Carbon Content Causes Rebar to Break
The carbon content in rebar is usually around 0.3%. If the carbon percentage exceeds this level, the material no longer qualifies as mild steel but becomes medium-carbon steel. Reputable manufacturers strictly adhere to international standards, such as ISO or ASTM, which specify a maximum carbon content of 0.3%.
Rebar often breaks or cracks during bending due to improper use of a mandrel. The mandrel diameter should be at least four times the rebar diameter for rebars up to 16mm and at least seven times the diameter for larger rebars.
Another common mistake is bending rebar 90° and then trying to straighten it again. International standards allow rebars to be bent at 90° and then straightened to a maximum of 135° at specified temperatures. Exceeding this limit damages the internal properties of the rebar.
5: Which Rebar Is Better – Sixty, Five Hundred, Five Fifty, or Six Hundred?
This decision should be left entirely to your construction engineer. Each grade of rebar has unique mechanical and chemical properties. The best and most cost-effective grade depends on the structure type and concrete mix design.
Never rely on masons to make this decision.
6: Is 500CWR Better Than 500DWR?
Both rebars are good and have different properties. However, 500DWR is often marketed as superior due to its higher ductility. But its higher carbon content reduces bendability, posing challenges for many construction projects.
If skilled labor and mandrel machines are available on-site, 500DWR can be a good choice. Otherwise, 500CWR may be more practical.
7: Which Technology Produces the Best Rebar?
Modern technology is essential for refining raw materials, maintaining the proper chemical composition, and achieving desired physical properties.
The most advanced technology in Bangladesh today is Quantum Electric Arc Furnace Technology, which is fully automated and state-of-the-art. Other technologies like Electric Arc Furnace, Thermex, and Pomini are also noteworthy. Advanced technology increases the likelihood of producing high-quality rebar.
Weight Disputes: A Common Issue
Buyers frequently accuse manufacturers of supplying underweight rebar. However, I firmly believe that the top-tier manufacturers in Bangladesh, such as BSRM, AKS, GPH Ispat, and KSRM, as well as second-tier manufacturers like Rahim Steel, Anwar Ispat, SCRM, and Akij Steel, do not engage in such practices.
These companies have factory weighbridges calibrated regularly by BSTI (Bangladesh Standards and Testing Institution).
Where Do Disagreements Arise?
According to the International Organization of Legal Metrology and the National Institute of Standards and Technology in the USA, a weight difference of up to 20 kg in a 10-ton load between two calibrated weighbridges is acceptable. However, most weighbridges used by customers for verification are either not calibrated or calibrated long ago.
Similarly, smaller scales used by dealers or retailers are often uncalibrated and cannot measure 10 tons at once. In such cases, rebar is weighed in smaller batches, leading to slight variations during each measurement. When these variations are added together, they can sometimes result in significant discrepancies, creating doubt among buyers.
Counting Individual Rebars: A Scientific Approach
In the absence of a calibrated weighbridge, a scientific method to verify weight is to calculate the weight of individual rebars.
You can determine the weight of a single rebar using the formula:
Weight=({162.2/Diameter2}x2)×12
Multiply this by the total number of rebars to find the theoretical total weight.Since the diameter of rebar may slightly vary, international standards allow for a variation of 4% to 8%.
Resolving Weight Disputes
To eliminate weight-related disagreements:
- Use a calibrated weighbridge where the maximum permissible discrepancy is 20 kg per 10 tons.
- Alternatively, count individual rebars and accept a 4% to 8% difference between theoretical and actual weight.
Conclusion
Many misconceptions about rebar exist in Bangladesh. However, the above points are among the most significant. As an engineer, I’ve tried to clear up some of the confusion surrounding rebar used in construction.
This article was first published on December 20, 2022, in Bangla Daily 24 under the title “রড নিয়ে যত মতভেদ“. It was later republished on January 1, 2023, in Jago News 24 and Daily Jagrat Bangla under the title “রড নিয়ে যত ভুল ধারণা“.