CIVIL SITE ENGINEERS GUIDE TO TMT QUALITY CONTROL

In any reinforced concrete (RCC) construction, two critical components are TMT Rebar and concrete. The lifespan and safety of such structures heavily rely on the quality of these Rebars and Concrete.

Designers and engineers should only approve TMT Rebars after thorough testing and verification, regardless of the manufacturer’s name.

The first way to check the quality of reinforcement is to check it mechanical properties.

Mechanical testing serves two primary purposes:

1. Providing design data and
2. Ensuring a structure’s ability to withstand specific stress limits without failure.

For instance, the tensile test can determine the yield strength of steel for design calculations or ensure compliance with material standards.

Mechanical property data are collected from a small number of standard tests and usually done by th supplier or by a third-party testing laboratory.

A civil site engineer stationed at a construction site may encounter limitations in conducting comprehensive mechanical testing of reinforcing bars within the on-site laboratory. Consequently, firsthand observation of such testing procedures may not be feasible.

Individuals who have undergone relevant training during their academic pursuits possess a foundational understanding of the mechanics involved in rebar testing.

Nevertheless, there exist alternative means through which a civil site engineer can ascertain the quality of reinforcing bars, before allowing it to use.

These are discussed below.

Storage & Handling:

Typically, reinforcing bars are supplied in 12-meter lengths and bundled together. A site engineer should possess the necessary knowledge to accurately estimate the required quantity of reinforcement for the specific project at hand.

Subsequently, meticulous planning is essential to determine the appropriate procurement quantity, optimal storage locations, and the space allocation for storing the bundles of TMT.

Proper storage and handling of Re-bars at construction sites are crucial.

Due to inadequate storage facilities, damaged steel is often used.

Various operations involve handling TMT Re-bars, including

• unloading,
• hoisting,
• stacking,
• cutting,
• bending,
• fabrication, and
• Efficient handling and storage 

The quality of reinforcement in concrete directly affects a structure’s performance. TMT Re-bars play a vital role in ensuring the safety, integrity, and durability of concrete structures.

Proper storage, handling, cutting, bending, quality checking, welding, and cleaning are essential to maintain their effectiveness.

Stacking & Storing at the Site:

Storing TMT Re-bars correctly at construction sites is crucial to maintain product quality.

Steel is sensitive to water, moisture, and dust. It should be protected from direct contact with these elements using covered sheds and polythene sheets.

Stacking is also critical for quality. Stacking height should be optimized, as excessive stacking can damage the TMT bars’ ribs, reducing tensile and bond strength.

Proper bundling, interlocking, and blocking from all sides are necessary to prevent sliding or collapsing.

Raised platforms should be used to avoid direct contact with the earth, and wooden blocks should separate layers for even weight distribution.

Systematic housekeeping procedures and proper product identification further enhance efficiency and safety.

Bending and Fabrication:

Bending and re-bending TMT Re-bars at construction sites must be done carefully to prevent deformation and breakage. Minimum bend diameters specified in relevant standards should be followed. Sharp bends can weaken the bars and cause cracks.

Re-bending should be avoided whenever possible, but when necessary, pre-heating and suitable equipment should be used.

For consistency and accuracy, cutting, bending, and fabrication should ideally be performed by specialist reinforcement fabricators.

Quality Check and Cleaning:

TMT Re-bars should undergo quality checks, and any loose scale, mud, or oil should be removed.

Mud and dirt can negatively impact bond between concrete and TMT bars.

It’s important to distinguish between light rusting and corrosion, as excessive scaling can reduce the bar’s weight or deformations, making it substandard.

Rust on reinforcement steel isn’t necessarily a negative condition. Many engineers and inspectors still insist on cleaning these materials from the reinforcing bar. However, rust can improve the bond between the bar and the surrounding concrete.

Of course, any loose material should be removed, but firmly attached rust or mill scale is allowed and won’t harm the bond.

Measuring the loss of cross sectional area and nominal mass of a Re-bar because of light rusting, can determine whether the same will be acceptable or not.

To measure the nominal mass of the rusted bar at site, following steps are to be followed:

1. A minimum of 0.5 m long TMT bar is cut.
2. The sample is cleaned, and the loose scales are removed with the help of a brush.
3. The length (L) is measured and recorded in mm.
4. The Weight (W) of the sample is taken with the help of an electronic weighing machine and recorded in kg.
5. The Mass (Kg.) per Meter run is calculated by dividing Weight by Length.
6. The cross-sectional area of the sample is calculated as:

Ae = W/(0.00785 x L) mm2

Where,

Ae = effective cross section area,

W is the weight of the TMT in Kg,

L is the length of the TMT in mm.

Tolerances on Nominal Mass:

Tolerances on nominal mass should align with agreed standards between the manufacturer and purchaser.

Refer the following tables for accepted tolerance limit of TMT bar as per IS-1786.