Grading of Steel Rebar’s used in Cement Concrete Based on Compression Test

Abstract

Compressive strength test is the most common test carried out on concrete and is considered good enough for design and decision making for concrete and reinforced concrete works. Meanwhile the quality of steel used for reinforcement works is determined by its tensile strength, yield strength, weight and elongation. In addition, the chemical composition content which affects the quality is also determined. However, it is difficult to know all these things for a common man and so a simple test called bend test conducted on site is usually carried out to assess the quality of steel. When bent to make an angle of 90 to 135 degrees and then bent back straight, there should be no cracks on the rebar and its original shape retained once it is straightened, one can be assured that it is of best quality. Even at this the strength of the rebar which informs its Grade cannot be known. Since the compression strength test is universally acceptable for concrete grading, it should be equally universally acceptable for rebars. This informed the authors decision to work and recommend appropriate ratio of height to diameter as 2 for yield stress for circular rebars. Fourteen and twenty four Samples of supposed mild steel rebars and high yield steel rebars where tested in compression. Half of this was tested for height to diameter ratio of 1 and the other half tested for a ratio of 2. The result revealed for a ratio of 2 that the high yield steel where of grade 60 or grade 420  since the average of the stresses for this ratio was 460.01N/mm² meanwhile the supposed mild steel was actually medium tensile steel and not mild steel as was reported in the purchase certificate. The result of this study support the grading in ASTM A 615, BS4449, Euro Standard(DIN 488) and  Indian Standard (IS: 1786) and compares favorably with recent works.

Key Words: Rebar, Steel, Grade, yield, Strength, Concrete