Loss on ignition (LOI) is an important indicator of cement quality and composition. It represents the proportion of volatile material, including moisture, carbon dioxide, and organic substances, released when cement is exposed to elevated temperatures.
This article presents a step-by-step method for determining LOI with a thermogravimetric analyzer, supporting accurate and dependable measurements in accordance with ASTM C150 requirements.
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Obtaining an LOI Measurement from a Thermogravimetric Analyzer
1. Weigh the Empty Crucible
Begin by measuring the mass of a clean, empty crucible and documenting the result. This starting value is necessary to calculate the cement sample mass and to complete subsequent calculations accurately. Precision is important; verify that the balance has been correctly calibrated.
2. Add the Cement Sample
Place approximately 1–10 grams of cement into the crucible. Weigh the crucible and its contents together, then record the combined mass. Subtracting the empty crucible mass from this value gives the initial cement sample mass.
3. Heat the Sample
Transfer the crucible containing the cement to a muffle furnace. Adjust the furnace temperature to between 900 °C and 1000 °C (1650–1830 °F). This range is adequate for driving off the cement’s volatile organic and inorganic constituents.
4. Maintain the Temperature
Keep the sample at the selected temperature for 15 minutes. Holding the temperature for this period promotes the complete release of LOI-related components. Stable and consistent temperature regulation is essential for obtaining dependable results.
5. Cool the Sample
When heating is complete, carefully remove the crucible using suitable heat-resistant equipment. Place the crucible and sample in a desiccator and allow them to reach room temperature. Cooling in a desiccator helps prevent the sample from absorbing moisture from the surrounding air.
6. Weigh the Cooled Sample
After the sample has cooled, measure the mass of the crucible and cement again. The decrease from the pre-heating to the post-heating measurements reflects the volatile substances removed during the process.
7. Calculate the LOI
Use the following equation to determine the LOI:
LOI (%) = (initial sample mass–final sample mass/initial sample mass) × 100
The resulting value expresses the percentage of the original sample mass lost during heating and therefore represents the LOI.
8. Improve Measurement Accuracy
For greater confidence in the result, conduct the LOI procedure on several samples and calculate the mean value. Replicate measurements help reduce the influence of unusual results or inconsistencies affecting individual tests.
The Importance of LOI in Cement Quality
The LOI procedure quantifies volatile constituents in cement, such as moisture, carbon dioxide, and organic compounds. Under ASTM C150 standards, general-use Portland cement has a maximum permitted LOI of 3%. A lower LOI value generally suggests higher cement quality and appropriate storage conditions.
Safety Considerations
The LOI procedure requires exposure to high temperatures and may involve materials that produce hazardous emissions. Therefore, users should wear suitable protective equipment, including heat-resistant gloves and face protection, and the muffle furnace should always be operated in a well-ventilated location to reduce the risk of inhaling fumes released during heating.
Examine LOI with an XRF Scientific Thermogravimetric Analysis Machine
Following the steps described above enables reliable LOI evaluation with a thermogravimetric analyzer and provides information about the overall quality of cement. Applying appropriate safety procedures and testing multiple samples can further improve the dependability of the findings.
For additional guidance on operating thermogravimetric analyzers, consult a beginner’s guide to thermogravimetric analysis. Information about these instruments and their operating principles can provide further explanations and practical advice for achieving accurate and reproducible measurements.
XRF Scientific supplies advanced thermogravimetric analyzers, including the xrTGA 1100. This instrument is suitable for cement LOI measurements and provides high throughput through a 30-sample carousel, an easy-to-use interface, and fast heating and cooling cycles. Using thermogravimetric analyzers of this type can improve the efficiency and accuracy of testing procedures.
This information has been sourced, reviewed, and adapted from materials provided by XRF Scientific.
For more information on this source, please visit XRF Scientific.