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Putting cement to the test

Adeel Hassan Product Manager at ELE International, explains how the latest cement testing technology is enabling manufacturers to implement efficient quality control procedures simply and cost-effectively.

In virtually every construction project the safety and durability of the finished structure are critical to its success. Essential to achieving this is the implementation of effective quality control procedures in the production of building materials such as cement. While traditionally quality control has often translated into additional resource requirements and costs for cement manufacturers, a new generation of testing technology is enabling procedures to be carried out quickly, accurately and simply, with minimal resource and budget.

Test methods

Many of the test methods used to determine the properties of cement have been in practice for some time, although the technology used has been continually developed and refined to offer more accurate results and simplified operation.

For example, flame photometers can now determine the chemical properties of a cement sample with digital accuracy. Chemical analysis plays an important role in the categorisation of cements, allowing manufacturers to predict the way that the material will react to its environment when mixed. Alkali content, for instance, can be effectively tested using flame photometry equipment. 

Likewise, testing to determine the setting time and soundness of cement is now made simpler and more accurate using the latest technology. A process known as the Vicat method has been proven to determine effectively the water content required to produce the desired consistency in cement. Automatic Vicat apparatus is now available to automate the process, again saving time, resources and money while offering greater accuracy and repeatability. The latest devices feature an integrated memory able to hold up to 50 tests, which can then be printed or downloaded for analysis.

With cement a crucial ingredient in mortar and concrete supplied to the construction industry, both the air content and density need to be measured in order to ensure that the strength and durability of the material will meet the required specifications. Clients often specify minimum levels of air content and density, requiring manufacturers to be able to determine accurately the properties of the cement supplied. Air entrainment meters have been developed for this purpose, incorporating a pressure gauge giving readings of air content as a measure of pressure. 

Preparing samples

While relatively simple but proven testing processes for determining the chemical properties, fineness, workability and flow, and density of cement are still providing manufacturers with an effective means of controlling the quality of cement produced, more advanced equipment has been developed to collect and analyse data from hardened cement mortar samples. 

For hardened cement mortar to be tested, samples must first be prepared, through mixing, moulding and curing. The correct mixing sequence and homogeneity of mix is crucial if consistent, repeatable test results are to be obtained. A mixer should be powerful enough to ensure that the speed of its motor is not affected by the mix constituents, but not so powerful that the mixer action and blade break down individual sand particles. Additionally, many mixing apparatus now provide automatic mixing cycles, for significantly more efficient operation.

For example, the Mortar Mixer from ELE can be used in either manual or automatic mode for more flexible operation. When in manual mode, the mixing speed can be changed at the flick of a switch while the motor is running. In automatic mode, any one of the pre-set mixing programmes can be selected for fast and simple use. The mixer is specially designed to mix mortars and cement pastes to the required standard, incorporating a mixing paddle with a planetary motion, which is driven by a motor with a microprocessor based speed and programme controller.

Likewise, the successful moulding of prisms, cubes and briquettes (depending on the relevant standards being adhered to) is essential for subsequent strength testing to be meaningful. Moulds need to be robust enough to retain their form through heavy usage. Equipment is now available that has been specifically designed for this purpose, including jolting tables and vibrating machinery, to compact samples using purpose made moulds.

Additionally, prior to testing, EN196, one of the most widely used and recognised standards for determining the strength of cement, requires samples to be cured for at least 24 hours at 20 ±1ºC, 90% RH minimum. The samples must then be removed from the moulds and stored under water for the remaining curing time, which can range from 48 hours to 28 days.

For the early curing of mortar samples prior to storing under water, samples can be placed in a humidity cabinet. These units, incorporating a circular chart recorder to record temperature and humidity, are able to offer relative humidity levels of up to 98% RH. Using a humidity cabinet for curing samples helps to ensure that the results from hardened cement mortar tests are as accurate and consistent as possible.   

Testing hardened cement mortar

The latest generation of testing equipment, such as the ADR-Auto 250 series cement compression machine from ELE International, enables hardened cement mortar samples to be tested simply and quickly. The machinery automates the testing process, incorporating microprocessor control to provide consistently accurate results.

This advanced testing equipment has been developed to satisfy the requirements for high throughput strength testing of cement mortar samples as specified in various testing standards, including EN196, EN 1105 and ASTM C109. After being mixed, moulded and cured, samples of various sizes and shapes are subjected to compressive loads up to a maximum of 250kN. 

By automating processes that have previously been carried out manually, the machines are able to reduce the time, cost and resource required for testing cement. The technology makes testing as simple as possible for operators, incorporating pre-programmed test routines reducing variability of testing. Integrated memory enables up to 500 test results, each with a unique reference ID, to be stored in the system, and then downloaded to a laptop or PC using the built in serial port for streamlined results analysis and distribution, which is particularly useful in high throughput environments. 

Unlike conventional automated compression testing technology using valve systems, which can be prone to high oil temperatures, requiring additional oil coolers, the latest equipment features variable output hydraulic pump technology, which provides an automatic loading cycle controlled by a closed loop microprocessor hydraulic system. This ensures far more efficient performance and consistent results, with the closed loop control enabling the applied force required to be continually monitored and adjusted, for far greater accuracy than is possible with manual testing.

Delivering results

As an example of the application of this latest technology, ELE International has supplied the equipment to a major supplier of dry mortar in the UK and Ireland, enabling the company to take greater control of its testing processes and ensure the high quality of its materials.

The company’s Technical Manager explained, “With our customers relying on us for their mortar, ensuring that our materials are of a consistently high quality is essential to our success. Prior to integrating the new equipment at our sites across the country, we were reliant on external labs for testing our product. Outsourcing in this way meant that we had very little control in the processes that were carried out as well as having the ongoing expenditure.” 

By comparison, following the installation of the cement testing machines at its sites across the UK, the company has been able, cost-effectively, to manage the testing of its mortar samples in-house. This has been made possible as the microprocessor-controlled equipment significantly reduces the time, cost and resource required, compared to manually testing samples, replacing conventional processes with a significantly more efficient automated system, enabling hardened mortar samples to be tested simply and quickly. 

The technology has enabled the mortar supplier to test samples of varying sizes as set by European Standards up to a maximum load of 250kN for the most demanding testing. The company also chose to incorporate the optional 25kN load frame for low strength compression and flexural testing for even more comprehensive quality control.  

The company’s Technical Manager has been impressed by the results, “The compression testing machines have not only removed the ongoing costs of outsourcing our mortar testing; they have also given us access to far more information than we were previously aware of. The new technology has allowed us to tighten our quality control even further, and offer our customers not only the most convenient, but also the highest quality supply of dry mortar on the market.”

Conclusion

Many of the largest cement and concrete producers in the world are seeing the benefits of investing in the latest testing technology to ensure the quality of their products across the globe. It is crucial to these companies that the cement they deliver to their customers meets the companies’ own internal standards, the relevant testing standards and also the individual specifications of their clients. Using the latest automated testing technology is contributing considerably to standardise quality control procedures globally, with more accurate testing enabling these major producers to offer customers the high level of service they require.

With the latest cement testing technology now able to offer manufacturers and suppliers a simple and fast means of achieving accurate analysis of the properties of the materials being supplied, effective quality control procedures can be implemented extremely cost effectively. The result is correctly specified cement delivered consistently, maintaining successful client relationships and ultimately benefiting a company’s bottom line.

For further information contact Adeel Hassan, Product Manager, ELE International, Chartmoor Road, Chartwell Business Park, LEIGHTON BUZZARD, Bedfordshire, LU7 4WG.  Tel: 01525 249 240. Fax: 01525 249 249.  Email: ele@eleint.co.uk.  Web: www.ele.com.  

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