ISO 15630-1 / ASTM E488 / BS 4449: Testing of concrete-reinforcing steel

Concrete-reinforcing steel turns plain concrete into steel reinforced concrete

Because concrete has high compressive strength but lower tensile strength, it is reinforced with embedded concrete-reinforcing steel. Concrete-reinforcing steel is divided into

• Reinforcing bars (rebars), reinforcing wire rod, reinforcing wire
• Welded mats and lattices

Reinforcing bars are steel products with a circular or nearly circular cross-section that are used for the reinforcement of concrete. Test methods for reinforcing bars, reinforcing wire rod and reinforcing wire are described in the ISO 15630-1 standard.

The smaller diameters are processed into mats or lattices before they are poured with concrete on site. Test methods for these products are described in the ISO 15630-2 standard.

A typical feature of concrete-reinforcing steel are ribs, which are coiled or rolled and serve to improve the bond between concrete and steel.

Determination of physical characteristics in a classic tensile test is still the most common test performed on concrete-reinforcing steel. The tensile test is performed to ISO 6892 -1.

Strain measurement can be performed without making contact (image left + center with videoXtens) or by contact (image right with makroXtens).

Adaptations of ISO 15630-1

• For calculation of the upper yield strength R_eH, the offset yield R_p0,2 and the tensile strength R_m, the nominal cross-sectional area is to be used
• The initial gauge length corresponds to five times the nominal diameter (d), if not otherwise specified in a manufacturer’s standard
• When using an extensometer, the percentage total extension at maximum force A_gt must be > 0.2% of the maximum value before loss of tensile force

The most important characteristic values

• Tensile strength Rm [MPa]
• Yield point Re [MPa]
• Yield point ratio of tensile strength R_m to yield strength R_e
• Ratio of yield strength to nominal yield strength R_{e, actual} / R_{e, nominal}
• Total extension at maximum load A_gt [%]
• The nominal cross-sectional area is to be used for calculation of the strength properties, as long as this is not otherwise defined in the product standard concerned (see ISO 15630).

A test is not valid

• If the gradient of the measuring curve deviates >10% from the theoretical value of the Young’s modulus
• In case of breakage within the specimen grips +20 mm or d (whichever is the higher value) distance to the specimen grips.

Electromechanical testing machines up to 2,500 kN are used for testing on concrete-reinforcing steel.

For tensile tests, both hydraulic grips (up to 2,500 kN) and wedge grips (up to 600 kN) can be used.

For the performance of flexure (bend) tests flexure tables are used, which are fitted with different upper anvils and anvils, and are mounted on the specimen grips via adapter plates.

Strain measurement can be carried out using a contact-type makroXtens extensometer or a non-contact optical videoXtens extensometer. For non-contact strain measurement the surface structure of the reinforcing steel ribs is used as the gauge mark, which is automatically determined by the videoXtens extensometer.

With the re-run procedure it is possible to subsequently determine elongations within the free grip-to-grip separation L_e in tensile tests. This presents the benefit that when a specimen breaks outside of a gauge length L_e, the specimen is not invalid. The elongation can be newly measured within a newly set gauge length. Specimen breaks outside of the L_e measurement range can thus be excluded.