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    Technical reference

    Concrete and cement testing

    Aggregates, cement and mortar, concrete, non-destructive testing, and steel.

    5 learning resources
    Discipline

    Concrete and cement

    05 resources
    GUIDEConcrete and cement

    Aggregate characterization

    Grading, shape, cleanliness, wear resistance, and aggregate durability.

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    Aggregates as the skeleton

    • Aggregates occupy much of the volume in concrete and road layers; size, shape, texture, and strength affect workability and performance.
    • A suitable combined grading helps control voids and the amount of paste required, but must fit the application and specification.

    Sampling and grading

    • Obtain a representative sample and reduce it with a suitable splitter; poor sampling invalidates an otherwise precise grading test.
    • Sieve analysis separates fractions by aperture and calculates retained or passing percentages to build a grading curve.
    • Shape indices and sand-equivalent or methylene-blue tests help identify unfavourable particles and clay-rich fines.

    Strength and durability

    • Abrasion or fragmentation tests compare aggregate resistance to wear and impact.
    • Moisture, salt, freeze-thaw, and weathering cycles explore environmental stability; density and absorption help describe porosity.
    • For pavements, polishing and friction tests provide information about texture evolution and skid resistance.

    Reporting

    • Record source, lot, preparation, mass, sieves, and moisture condition; report the standard and fractions tested.
    • Compare results with current contractual limits. No single test replaces an overall aggregate assessment.
    GUIDEConcrete and cement

    Cement and mortar testing

    Sampling, fineness, soundness, consistency, setting, and cement strength.

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    Hydration and properties

    • Hydraulic cement reacts with water to form a paste that hardens and binds aggregates. Fineness and composition affect hydration rate and strength development.
    • Heat of hydration matters particularly in massive elements, where limited heat dissipation can create thermal gradients and stresses.

    Physical tests

    • Fineness can be estimated by measuring air flow through a compacted cement bed or by sieving, among other methods.
    • Paste consistency is determined by penetration; initial and final setting times are defined by penetration under controlled conditions.
    • Soundness testing looks for delayed expansion; methods such as Le Chatelier or autoclave accelerate detection of expansion tendencies.

    Mortar strength

    • Mix mortar using defined proportions and sequence, mould specimens, and compact them as required by the standard.
    • Maintain controlled curing, temperature, and humidity; specimens may be tested in flexure and then compression as specified.

    Comparability

    • Take increments from several bags or points in a lot and prepare a representative composite sample.
    • Dimensions, penetration thresholds, compaction, and curing differ between standards. Follow the contractual edition and method without mixing requirements.
    GUIDEConcrete and cement

    Fresh and hardened concrete

    Fresh-state workability and uniformity; hardened-state preparation, curing, and durability.

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    Fresh concrete

    • Workability describes how easily concrete can be transported, placed, and compacted without excessive segregation or bleeding.
    • Slump, flow-table, and Vebe tests assess consistency over different ranges; none alone captures every rheological property.
    • Air content, density, segregation, and bleeding may also be assessed. For self-compacting concrete, filling ability and segregation resistance are important.

    Specimen preparation

    • Take a representative sample, mix uniformly, and record time, temperature, and transport conditions.
    • Fill moulds of specified dimensions and compact using the appropriate method to avoid voids or excessive vibration.
    • Identify every specimen and protect it during initial curing to prevent moisture loss or temperature changes.

    Hardened concrete

    • Standardized curing enables comparison of compressive, flexural, and other properties between batches.
    • Loading faces must be flat and parallel; prepare them by grinding or an approved capping method.
    • Density and water-penetration tests provide complementary indicators of porosity and durability.

    Interpretation

    • Relate each result to specimen age, geometry, curing, moisture, and failure mode.
    • Use the current standard to select the test and acceptance criteria; fresh-concrete tests do not replace hardened-strength control.
    GUIDEConcrete and cement

    Non-destructive concrete assessment

    Ultrasonics, rebound hammer, reinforcement location, durability, and monitoring methods.

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    What NDT can and cannot tell you

    • Non-destructive tests help locate anomalies, compare uniformity, and plan investigations on existing structures.
    • An indirect reading rarely gives exact strength by itself; interpret it in light of material, moisture, geometry, and calibration.

    Quality and strength methods

    • Ultrasonic pulse velocity depends on density and elastic properties; voids, cracks, moisture, reinforcement, and transducer contact can affect it.
    • A rebound hammer measures surface hardness. It can compare areas, but conversion to strength requires a suitable correlation, ideally using cores from the structure.
    • Combining ultrasound and rebound can broaden an assessment, but correlations still require validation for the concrete being investigated.

    Durability and monitoring

    • A covermeter estimates reinforcement location and cover before drilling or intervention.
    • Chloride, half-cell potential, and carbonation tests investigate mechanisms that can compromise steel protection.
    • Mechanical gauges, crack gauges, and flat jacks can monitor deformation, crack width, or stress in masonry.

    Inspection planning

    • Divide the structure into zones, take several readings per area, and record location, orientation, and environmental conditions.
    • If strength is needed, calibrate correlations against representative direct tests and document uncertainty; NDT is a diagnostic tool, not a standalone verdict.
    GUIDEConcrete and cement

    Tensile testing of reinforcing steel

    Stress-strain response, yield strength, ultimate strength, and ductility.

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    Why test reinforcing steel

    • Concrete performs well in compression, while reinforcing steel supplies tensile and flexural capacity.
    • Tensile testing verifies steel mechanical properties and supports comparison of batches with the applicable specification.

    Stress-strain response

    • In the elastic region, deformation is approximately reversible; its slope represents elastic modulus.
    • At yield, plastic deformation begins. Strain hardening, maximum load, localized necking, and fracture may follow.
    • Tensile strength and final elongation describe different properties: maximum resistance and deformation capacity.

    Test procedure

    • Measure and mark the gauge length, check diameter or section, and grip the specimen with compatible jaws.
    • Apply axial load under control and measure force and strain using the extensometry method required.
    • Record fracture mode and location; a break at the grip or outside the valid region may invalidate a result.

    Reporting and safety

    • Report yield strength or specified proof strength, maximum tensile strength, elongation, and the control method used.
    • Steel can fragment at failure. Use guards and follow the current standard for rate, extensometer, and specimen validity.

    Learning guides based on technical presentations, written to make civil engineering materials and test methods easier to understand.