Concrete testing is a key part of the concrete quality assurance process. It involves assessing concrete for its:

• Workability
• Strength
• Setting time
• Air content
• Permeability

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How concrete is tested depends on the quality it’s being tested for.

• Air content is measured by pouring wet concrete into a container with a known volume, with the pressure set to the percentage of air that was already in the container. When concrete is poured into the container and fills it, the only air remaining inside is the air contained in the concrete.
• Temperature, which impacts the speed and efficiency of curing concrete, is measured by surrounding a thermometer in at least 100mm of concrete and measuring how temperature increases. This happens within the transporting equipment and after pouring.
• Strength is tested by concrete compression testing, which requires placing a hardened concrete sample in a compression machine and applying weight at a specified rate until the concrete can no longer withstand the pressure.
• Permeability, or the concrete’s ability to absorb liquids and gases, is also measured using a compression machine. This time, water pressure is applied to the machine and the depth of water penetration to the cured samples is measured.
• Shrinkage (the contraction of concrete in response to moisture loss) is measured by placing hardened concrete samples in water baths and then drying chambers for long periods.
• Workability is measured by a slump test in which a cone is filled with concrete in uniform layers and then turned upside down. Testers then measure the height difference between the cone and the cone-shaped concrete as it slumps. Higher workability concrete is tested by flow or slump-flow tests as appropriate.

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Concrete testing is essential for many reasons, including:

• Insight into problem causes and solutions
• Achieving structural integrity
• Access to superior and improved concrete
• Compliance with national regulations
• Production of more aesthetically pleasing concrete structures
• Reducing amount of upkeep and repair work required in future
• Upholding safety

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At Heidelberg Materials, we uphold British Standards in our concrete testing, including:

• BS EN 12350-2 for slump testing
• BS 8500, BS 5075-2 and BS EN 12350-7 for air content
• BS EN 206 and BS 8500 for the minimum and maximum temperatures of concrete respectively
• BS EN 12390‑16 for shrinkage
• BS 8500 for concrete strength

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There are multiple ways to test concrete on existing structures. Some are non-destructive techniques, meaning the testing will not significantly damage the concrete. Others are destructive but offer more definitive results.

Non-destructive concrete testing techniques 

• Rebound hammer testing measures the rebound of a spring driven hammer mass after its impact with concrete to test strength, although surface condition and other factors such as whether your concrete has a rebar can affect results here.
• Ultrasonic Pulse Velocity detects damages by measuring the travel time of acoustic waves in a medium and correlating them to the density and elastic properties of the material to gather an impression of the internal conditions.
• Carbonation depth testing measures how much CO2 has reduced concrete pH using a phenolphthalein indicator solution. This is key, as alkaline concrete will not protect steel from corrosion.

Destructive concrete testing techniques 

• Concrete coring, widely regarded as the most definitive method, involves extracting a concrete core and then taking this back to the lab for analysis, such as concrete compression testing.
• The pull test requires a piece of equipment to be attached to the concrete fixing and pulled to a designated stress load level.

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