Concrete is one of the most fundamental materials in modern construction, valued for its strength, versatility, and durability. In structural applications, it must consistently withstand the loads and stresses imposed throughout its service life.
To ensure this reliability, a range of on-site and laboratory-based testing methods are used to assess concrete’s performance. These tests help detect potential issues early, minimise the risk of failure, and confirm that the material will perform as expected under real-world conditions.
From verifying mix designs before construction begins to monitoring quality during placement and investigating concerns after completion, concrete testing plays a vital role in supporting the long-term safety, durability, and compliance of structures.
“What Is Concrete Testing?”
Concrete is a composite material made from aggregates, sand, binders (such as cement), and various additives. The quality of these components can vary significantly, directly influencing the strength, durability, and overall performance of the final mix. To manage this variability, precise control over mix design, batching, and mixing is essential.
Concrete testing is a critical process used to confirm that the mix meets required standards across the stages of construction. By evaluating the physical, chemical, and mechanical properties of both fresh and hardened concrete, engineers can ensure that each batch is consistent, fit for purpose, and contributes to the long-term success of the structure.
Why Concrete Testing Matters for Construction Quality
Concrete forms the structural foundation of modern infrastructure, from homes and office buildings to bridges and highways. Its performance directly affects the safety, longevity, and resilience of these structures, making rigorous concrete testing essential.
1. Standardised Procedure
Concrete testing follows strict British Standards, helping manufacturers, suppliers, and contractors improve efficiency, reduce errors, enhance accountability, and meet regulatory requirements for quality and safety.
2. Structural Integrity
Results from concrete testing show that your chosen materials are high-quality, durable, and suitable for their intended application. This is key to ensuring structural integrity and mitigating the risk of harm to the public and the surrounding environment.
3. Project Success
Strong, durable, and correctly applied concrete is key to achieving regulatory compliance and ensuring your projects can proceed without delays related to planning permissions or health and safety concerns.
“How Do You Test Concrete?”
Concrete testing is carried out by UKAS accredited laboratories and qualified on-site technicians to ensure that each mix meets the technical, structural, and regulatory standards required for its intended application. A range of on-site and laboratory-based methods are used to evaluate the physical, mechanical, and chemical properties of both fresh and hardened concrete.
The physical properties of fresh concrete are key indicators of the mechanical performance of its hardened state. Tests usually measure workability, segregation, density, porosity, and temperature behaviour, detecting potential changes in concrete that may affect its long-term performance once in place.
The testing of hardened concrete is typically mechanical, assessing its compressive, tensile, and flexural strength through different test methods. Notably, chemical testing can be performed on both fresh and hardened concrete in a laboratory setting, analysing components such as fibre content, alkali levels, cement composition, and more.
Concrete Testing On Site Methods
Concrete testing on-site is essential for confirming that the fresh concrete mix is suitable for placement and meets immediate performance criteria. Common tests assess consistency, air content, and temperature before or during pouring.
Hardened concrete can also be tested on-site to evaluate surface hardness, strength, penetration resistance, and uniformity. These tests are typically part of compliance checks, routine quality assessments, or failure investigations.
Additionally, both fresh and hardened samples can be collected on-site and transported to a laboratory for more detailed analysis.
How to Test Concrete Strength On Site
Rebound Hammer Test
In this test, a spring-loaded hammer strikes the surface of the in-place concrete, and the rebound distance of the hammer mass is measured. The rebound value, or rebound number, is then correlated with the compressive strength of the concrete using calibration curves.
This is a non-destructive testing method, causing no damage to the structure. It is also quick and easy to perform, providing rapid insights into the surface hardness and uniformity of the concrete. However, results may be affected by surface roughness, moisture, and carbonation.
Penetration Resistance Test
The penetration resistance test, also known as the Windsor Probe Test, is a semi-destructive method used to estimate the compressive strength of in-place concrete by measuring the depth of penetration of a steel probe into the surface.
While this method does leave small holes in the structure, it does not significantly damage it. It can also be performed on both vertical and horizontal surfaces and is effective for concrete aged 3 days and older. However, it is not suitable for very thin or heavily reinforced sections.
Concrete Testing Laboratory Methods
Laboratory-based concrete testing can take place at any stage of the construction process, providing valuable insights into the properties and performance of both fresh and hardened concrete. These tests are carried out in controlled environments, which eliminates the impact of external factors such as weather, ensuring greater accuracy and consistency in results.
During the early phases of construction, fresh concrete samples can be extracted from the site and taken to the concrete testing lab for analysis. These tests may include assessments of fibre content, slump flow, sieve segregation, air content, and alkali levels, among others. Fresh samples can also be cured for mechanical evaluations, such as the compressive strength test.
For completed structures, core samples (hardened concrete cylinders) can be extracted and tested in the lab. These tests help determine key characteristics, such as compressive strength, cement composition, the presence of high-alumina cement (HAC), and chloride content, offering a comprehensive understanding of the concrete’s long-term performance.
How to Test Concrete Strength in the Lab
Concrete Cube Testing
The concrete cube test is a widely used method for determining the compressive strength of cured concrete. To carry out this test, at least four cubes are prepared from each concrete sample by pouring the mix into moulds measuring either 100mm or 150mm.
After curing the samples in a water bath at 20°C for a set duration (this generally being 7, 14, 28 days and/or Spare), the cubes are each tested in a compression machine, where they are subjected to an increasing load until they fail by cracking, crumbling, or collapsing.
Understanding the Concrete Cube Test Lab Report
During the concrete cube test, the maximum load sustained by each cube is recorded and used to calculate its compressive strength based on the cross-sectional area of the cube. This is documented in a concrete cube test lab report.
The results from the concrete cube test will be reported in megapascals (MPa) or newtons per square millimetre (N/mm²), indicating the compressive strength of the concrete specimen. These results are essential for understanding the quality and suitability of the mix.
Common Issues Found in Cube Test Results
The concrete cube test offers valuable insights into the strength of a concrete mix, allowing engineers to predict how the in-place concrete will behave under various load conditions and make informed decisions regarding material use and structural design.
However, some factors may affect the accuracy and validity of the results:
- Improper sample preparation, such as incorrect mould size or poor compaction
- Inconsistent curing temperature or insufficient curing time
- Handling & transport damage, causing cracks or chips in the surface
- Inconsistent mix proportions or poor quality control
- Human error, such as incorrect recording of results or mislabelling of samples
Choosing the Right Concrete Testing Method with CTS
On-site and laboratory-based concrete testing are complementary methods. By strategically combining both, engineers and contractors can ensure that concrete not only performs well during construction but also stands the test of time.
Whether evaluating new mix designs, testing for compliance, assessing the condition of in-situ concrete, or investigating reasons for failure, CTS offers a full range of on-site and off-site UKAS accredited testing. Our continued investment in process and technology means we can offer a rapid turnaround for many of our laboratory tests.
To find out more about our Concrete Testing Services, please get in touch with a member of the CTS team today, and we’ll be more than happy to answer any questions you may have regarding our services and how we can help you.