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    Concrete and Cement

    Compression, flexural, and fibre-reinforced concrete testing

    Compression, flexural, indirect tensile, elastic modulus, and fibre-reinforced concrete tests. Explains how load or displacement control affects results.

    Original conceptual diagram for this guide. Licensed under CC BY 4.0 · Civily

    Conventional failure tests

    • In compression, load increases until the specimen fails. Calculate strength from the maximum load and loaded area in accordance with the applicable method and specimen geometry.
    • Flexural testing measures the response of a supported beam under three-point or four-point loading. The configuration determines the stress distribution and flexural strength calculation.
    • The indirect tensile, or Brazilian, test compresses a cylindrical specimen along two opposite generatrices and estimates tensile strength from the failure load.
    • Elastic modulus testing requires loading and unloading cycles and strain measurements. Specimen centring, alignment, and sensor stability affect the result.

    Load distribution and control

    • Load must be distributed uniformly over the specimen surface. Eccentric or uneven loading can cause premature failure and reduce the recorded load.
    • Applicable standards specify platen and support geometry, alignment, machine verification, and loading rate. The machine must maintain the specified rate during the test.
    • Load control suits conventional tests up to failure. Tests that characterize post-peak response require displacement or crack-opening control.
    Diagram of satisfactory and unsatisfactory concrete specimen failure patterns
    Diagram of satisfactory and unsatisfactory concrete specimen failure patterns

    Fibre-reinforced concrete

    • Fibres limit crack opening and propagation; their contribution is most visible after the first crack.
    • Beam tests measure load against deflection or crack opening. EN 14651 uses a notched beam under centre-point loading; ASTM C1609 uses third-point loading.
    • Panel tests such as EN 14488-5 and ASTM C1550 characterize energy absorption as deformation increases. The support arrangement and control variable affect comparability.
    • To capture post-peak response, control the test by displacement and continuously record load and deformation. Load-only control may become unstable after cracking.
    Illustrative load-deflection curve with post-peak response after the first peak
    Illustrative load-deflection curve with post-peak response after the first peak

    Method selection and reporting

    • Select the method according to the material, specimen geometry, property being assessed, and contractual standard.
    • Record specimen dimensions, preparation and conditioning, loading configuration, rate or control variable, and measured curve.
    • The standards and requirements named in this presentation reflect training material from 2021. Check the current edition and project specification before testing.

    Strength and stiffness calculations

    • Compression: fc = Fmax/A, where Fmax is peak load and A is the specimen’s loaded area.
    • Indirect tensile strength of a cylinder: fct,sp = 2Fmax/(π·L·D), with length L and diameter D. The test creates an indirect stress state and is not equivalent to direct uniaxial tension.
    • Beam flexure: for third-point loading, R = Fmax·L/(b·h²) when fracture occurs in the middle third; for centre-point loading, R = 3Fmax·L/(2b·h²). Check fracture location and the method equation.
    • Secant modulus: E = (σ2 − σ1)/(ε2 − ε1), between the stress levels defined by the procedure. Strain measurement and gauge length must be suitable.
    • Keep units consistent; N/mm² and MPa are numerically equal. Report actual dimensions, failure mode, age, and curing.

    Educational reference guide. Check the current standard, calculation assumptions, and project specification before applying a procedure or acceptance criterion.