The tensile strength of rebar steel and the tensile rebar-concrete bond strength are important to consider when measuring rebar quality. Steel reinforcing bars or rebar are used in concrete construction to provide reinforcement, complementing the exceptional compressive properties of concrete. Rebar also helps maintain structural integrity as concrete cracks from expansion and contraction cycles. Tensile testing of rebar is relatively straightforward. Lengths of the actual rebar are used to measure the strength and elongation of the material, so modifications to the material geometry are not necessary. Typically a gage length and intermediate gage marks are created using a punch, so efforts must be taken to generate light marks that will not affect test results. Testing the concrete-rebar bond strength is a more delicate process as reinforced concrete samples must be poured and cured, ensuring a consistent bond length between each sample. The concrete specimens are then secured and a tensile load applied by clamping and pulling on the exposed rebar end, using a test machine. ASTM and other industry standards organizations have specified standard test methods to test the tensile properties of steel reinforcing bars. Along with characterizing the properties of the plain rebar, these methods attempt to simulate the use of rebar in construction and measure the strength in these conditions. Popular test standards are ASTM A370 for steel products and ASTM A944 for the bond strength of steel rebar and concrete. Machines and tensile grips for tensile testing of steel reinforcing bars must be capable of applying very high loads. Based on ASTM specifications for the ultimate strength of various grades rebar, breaking forces can range from 11 kip (50 kN) for #3 rebar to loads up to 135,000 lb (600 kN) and more.
Applicable Testing Standards
- ASTM A370 Tensile Bend Strength Steel Test Equipment
- ASTM A944 Bond Strength Steel Reinforcement Rebar Test Machine
- ASTM A1034 Steel Reinforcing Bars Rebar Test Machine
Recommended Test Machine
Force range of 5 kN to 600 kN (1,125 lbf to 135,000 lbf)
Adjustable test space
The most popular choice for static tension and compression tests
These dual column testers are available in both tabletop and floor standing models
Recommended Testing Accessories
Load ratings from 100 kN to 500 kN (22,500 lbf to 112,500 lbf)
Best for higher force requirements
Gage lengths from 50 mm (2.0 in) to 250 mm (10 in)
Measuring ranges up to 100 mm (4.0 in)