Steel reinforcing bars or rebar is used in concrete construction to provide tensile strength, complementing concrete's excellent compressive properties. Rebar also helps maintain structural integrity as concrete cracks from expansion and contraction cycles. The tensile strength of rebar steel and the tensile rebar-concrete bond strength are extremely important properties of rebar. Tensile testing of rebar is relatively straightforward. No modifications to the material geometry are necessary as lengths of the actual rebar used are necessary to determine the strength and elongation of the rebar. Typically a gage length and intermediate gage marks are marked using a punch, so efforts must be taken to create light marks that will not affect test results. Testing the concrete-rebar bond strength is a more involved process as reinforced concrete samples must be poured and cured, ensuring a consistent bond length between samples. 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

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