Companies conduct compressive tests on concrete samples using compression machines. These machines are “expected” to be accurate since many important decisions are made based on their results. These machines can go “out of tolerance” and thereby not conform to the relevant British and/or American Standards.
To ensure that the machines’ results are accurate, companies and/or their clients may require that the machine be calibrated at regular intervals and a “Certificate of Calibration” be issued as evidence of the accuracy of the unit.
Using a “Load Column” that is pre-calibrated and traceable, SCL (Trinidad) Limited can conduct a “Verification” of the unit in question, and quantify its degree of accuracy. If the unit is out of calibration/ tolerance, SCL can then conduct a calibration to bring the accuracy back “within tolerance”.
Most companies conduct this exercise based on the volume of testing done, on an annual basis or if the unit is suspected to be “out of tolerance”.
Compression Testing of Cubes and Cylinders
Most construction requires that the quality of concrete supplied to the site be verified. For acceptance by the purchaser, generally, the concrete strength can be used as a good indicator of quality.
Samples of the fresh concrete are used to make specimens in the shape of cubes or cylinders. These are allowed to harden for a number of days and they are then subjected to a compressive load until they fail. The load required to crush the specimen is considered the strength of the concrete. Many important decisions are made using these results.
Compressive Strength Testing
SCL has three Compression Testing Machines capable of stresses up to 1100kN and 2000kN respectively and capable of testing cubes, blocks and cylinders (typically from 2 inch to 6inch).
The machines used are calibrated semi-annually and calibration records are available to customers. The laboratory is also equipped with storage facilities to maintain customer samples until testing has been completed. Results are provided within two working days after testing.
Schmidt Hammer Test
If concrete is placed in a structure and no cubes or cylinders were tested to verify the strength of the concrete, and more so, if there is reason to question the quality of the concrete, a Schmidt Hammer Test can be done to estimate the strength. It is a non-destructive test that does not leave the structure blemished and it can be done within an hour, depending on the size of the structure.
This test is done for the same reasons as the Schmidt Hammer test, except that this involves cutting a core out of the suspect concrete, that is, it is a destructive test. Special equipment is used for extracting the core(s) and then they are tested for strength like a cylinder. Cores can be used for checking the properties of the concrete other than strength, such as aggregate distribution, maximum size aggregate etc.
A sieve analysis is the test that is done on sand and gravel to determine the distribution of the different particle sizes that make up the material. It is done by passing a dried sample of the material through a series of sieves (screens) of varying sizes; the material that is retained on each sieve is weighed and calculated as a percentage of the total weight. This information can be cross-referenced with ASTM or other standards and is useful when doing mix designs for concrete and asphalt.
There are a number of tests that can be done on cement, however, at SCL, the cement test offered to its customers only covers the check for setting time and strength. These are two properties of cement that can affect the average construction site and knowing their values can help the concrete producer.
This is the process of determining the quantity of each ingredient required to produce a concrete that has certain properties in its fresh and hardened states. It uses information from a sieve analysis etc. and the properties of the other raw materials to inform the process.
This is the process of actually batching and mixing the materials together as derived from the mix design process. This is done to verify the mix design and to confirm that the design meets the requirements.
Consultancy services are available for the supervision or pours, the pre-pour planning and troubleshooting of problems in concrete.
Training & Development
SCL also offers training services to its customers in the concrete field such as training of batchers, technicians and sales staff.