As one of the most widely used materials in construction, concrete demands strict quality control to ensure its strength and long-term performance.
The strength will depend on many factors, including water-cement ratio, quality of materials and quality control during the production of concrete.
Below are three common concrete tests that help to ensure it meets the required standards and design specifications for its use.
1. Slump Test
A concrete slump test is conducted in-field on fresh concrete mix. It helps to determine if the, soon to be poured, concrete will meet its specified standard. It is a simple test that can confirm, over multiple batches, that the concrete is consistent – providing a chance to amend the mix before it is poured on site.
By measuring the overall ‘slump’ of the concrete, you can tell whether the water-cement ratio is too high, and whether a mix will have high workability or not.
How it works
A cone is placed firmly on a flat, smooth surface. In three layers, the cone is filled with the fresh concrete sample in a uniform manner. Each layer is tamped with a steel rod to compact the concrete. Once filled, any overflow is removed, and the concrete is levelled.
The cone is then slowly and steadily lifted and placed upside down beside the slump. The slump is then measured against the upturned cone. The concrete should largely retain its cone shape, demonstrating that the mix is cohesive, and its workability isn’t too high.
2. Compressive strength test
The compressive strength of concrete a common performance measure used by engineers to design building and other structures. Compressive strength is defined as the ability of the concrete to withstand specific compressive forces. The test will help to determine whether the concrete performs to the appropriate standards.
In a laboratory, you can measure the compressive strength of the concrete using highly controlled cylindrical moulds.
How it works
Concrete samples are placed into the cylinders measuring 200mm high and 100mm in diameter (AS 1012.9) on-site. Once dried, say the next day, they are then transported to the laboratory, de-moulded and placed into a curing tank. At test intervals (7, 14 and 28 days) the samples are placed between compression plates under an increasing force at a set pace rate. The force applied for the sample to fail (crack/break) is recorded. Further calculations are performed to ascertain the strength compression and whether it has passed or failed the test.
3. Drying shrinkage test
Drying shrinkage occurs when the concrete structure contracts due to moisture/water loss. This can adversely impact the durability, aesthetics, and serviceability of concrete structures.
The drying shrinkage can be determined in a laboratory setting.
How it works
Samples are cast into moulds and stored in a humid environment until hardened. The concrete samples are then de-moulded and placed in lime saturated water baths and then a drying chamber for the duration of the test. The initial reading is measured at 7 days from time of casting. The samples are then stored in a controlled environment with the length measured and recorded up to 90 days. The accuracy of the measurement readings are very precise, 0.001mm
The drying shrinkage is calculated as the difference between the original wet measurement and the dry measurement expressed as a percentage of dry length. Generally, the specification requires conformance at 21 and or 56 days.
Contact Douglas Partners
Douglas Partners can provide concrete testing for various applications, including pavements, bridges, drainage culverts and headwalls, industrial, commercial, and residential buildings, precast walls, retaining walls and driveways.
Contact your local Douglas Partners team here.