Investigation of the Properties of Commercially Available Reinforcing Steel Bars

The failure of a structure is attributed to many factors, one factor is the use of substandard construction materials particularly reinforcing steel bars. However, the use of substandard materials can be avoided by conducting some practical test. This study focused on the properties of the reinforcing bars commercially available in the market (rib configuration, wieght/meter, dimensional properties, bend-ability and elongation) and compare them with the existing standards. 


The study aimed to examine the quality of the reinforcing steel bars available in the market today to determine if they conform with the standards set by national Structural Code of the Philippines(NSCP), American Concrete Institute (ACI) code, and American Society of testing of Materials (ASTM). 


Today, steel is one of the most common construction materials in the world and is a major component in buildings, infrastructures, tools, ships, automobiles, machines and appliances. Steel can be classified into different groups or categories depending on the chemical composition, application, shape, production process used, etc. Particular in the construction material formed with a specific shape or cross section such as II, T, L or angle, and C or channel section. Reinforcing bars 'or rebars is a common steel bar used in reinforced concrete and reinforced masonry structures.


Steel is an alloy consisting mostly of an iron mixed with carbon and other alloying elements such as manganese, chromium, vanadium and tungsten. These other elements act as hardening agents. With the right amount, steel can be made harder than iron making it suitable for building various structures.


Concrete is a material that is very strong in compression but relatively without strength in tension. To compensate for this imbalance in the concrete's behavior, rebars are cast into it to carry the tensile loads. While any material with sufficient strength could conceivably be used to a reinforced concrete, steel is still the best choice. This is due to the fact that steel and concrete have similar coefficients of thermal expansion. Thus as a result, a concrete structural member reinforced with steel will experience minimal stress as a result of differential expansions of the two interconnected materials caused by temperature changes.


The samples used in this study were taken from three major suppliers of construction materials within the municipality of Bayombong and Solano, Nueva Vizcaya namely WeldShoppe, Remington and Masagana. Only deformed bars with sizes 10 mm, 12 mm and 16 mm were tested since these are the sizes that are most frequently used for small to medium sized construction.


The results were tested through the following properties of reinforcing steel bars.


A. Identifying Marks


The bars were inspected for any identifying marks stamped  into the surface. These marks were compared to the marks required by ASTM Standards.

The ASTM specifications require that identification marks be rolled into the surface of one side of reinforcing bars to provide information as to the producing mill, the bar size, and the type of the steel. In addition, for Grade 60 or stronger steel, a grade mark is required to indicate the minimum yield point of the steel.


The reinforcing bars purchased from the different suppliers show only the letter "C" and the bar diameter. In one bar, there are no identifying marks at all.


B. Rib Configuration


Visual observation of the bars showed that the rib heights were almost the same for the different bar sizes. The distance center to center of the ribs was observed to be the same for each corresponding bar diameter . For the 16-mm bars, ribs are at 1 cm apart. For the 12-mm bars, the ribs are 0.75 cm apart. For the 10-mm bars, the ribs are 0.67 cm apart. However, the rib configurations differ slightly in height and the angle of inclinations. 


The recommended rib heights is 7% to 8% of the rated diameter of the bar.


C. Standard Weight/Meter


From supplier A, the average weight of the 16-mm bar is 1.503 kg/m, 0.840 kg/m for 12-mm bar and 0.584 kg/m for 10-mm bar.


From supplier B, the average weight of the 16-mm bar is 1.514 kg/m, 0.839 kg/m for 12-mm bar and 0.574 kg/m for 10-mm bar.


From supplier C, the average weight of the 16-mm bar is 1.499 kg/m, 0.840 kg/m for 12-mm bar and 0.599 kg/m for 10-mm bar.


Standard weight per meter of 16-mm bar is 1.568 kg/m, 12-mm bar is 0.941 kg/m and 10-mm bar is 0.589 kg/m


D. Dimension Specifications


Slight differences in the lengths of the bars were observed. The longest bar is at 6.01 m and the shortest of the bars is at 5.983 m. The standard length is 6 m.


As the result of this study, the following summary and conclusions were drawn:


1. The reinforcing steel bars do not contain all the necessary marking as per ASTM standards.


2. the heights of the rib configuration of the bars are above the recommended values. This may increase the bonding between the concrete  and the reinforcing steel bars but it may compromise the weight carrying capacity of the bars.


3. The weight per meter of the bars is generally below the recommended values.


4. On the average, the length of the bars is very slightly shorter that 6 m. Likewise, the nominal diameter measures below the rib configuration is below the rated diameter of the bars. The indicated diameter was observed to be measured outside the ribs.


It is recommended that a thorough study should be made to include other bar diameter. Likewise, the yield strength of the bars must be determined.


Researchers:


Engr. Myrna B. Grospe
Engr. Rodel V. Medestomas
Engr. Rolando Sabado
Engr. Ernesto Padre.
Saint Mary's University, Bayombong, Nueva Vizcaya

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