Sponsored by Specac LtdReviewed by Maria OsipovaFeb 8 2023
The chemical composition of cement influences its performance. Through elemental analysis, the quality of cement can be determined; it also indicates which applications it is most suitable for. XRF is the most preferred elemental analysis method in the cement industry. This article describes the pellet preparation method, using Specac’s APEX 400 Press, for the XRF analysis of cement.
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Cement is a versatile and important material that is used for infrastructure, roads, and houses. Hence, it is only expected that cement will be a large-scale business — with global cement makers making revenues of $250 billion every year.
The Composition of Cement Determines its Performance
Cement is produced by heating various materials, including chalk or marl, shells, and limestone, combined with clay, shale, blast furnace slag, slate, iron ore, and silica sand. The outcome is a powder that mainly contains oxides of silicon, calcium, magnesium, iron, aluminum and other trace elements, including potassium and sodium.
Cement is valuable as it acts as a binder. When cement is mixed with rocks or gravel and water is added, the mixture subsequently hardens and forms concrete. Upon adding water to cement, SiO2, CaO, Fe2O3, and Al2O3 are hydrated to form aluminoferrite hydrate and calcium aluminosilicates, resulting in the hardening of the cement.
The performance of cement depends on its mineral composition and its exact chemical composition. For instance, elevated levels of MgO can lead to weakness in the hardened cement. The nature of the raw materials used to produce cement can result in considerable variations in the chemical composition of the final cement.
Hence, chemical analysis of cement can be used to find out the quality of cement as well as to identify the exact applications a specific cement type may be suited to.
Chemical analysis is regularly used in cement manufacturing for cement quality control, to test quarry sites, and assess intermediate products. Those in construction and manufacturing may consider analyzing their cement to make sure that it is suitable for the preferred application and prevent costly repairs afterward.
Elemental Analysis of Cement
Cement elemental analysis can estimate the proportion of each element present in the sample. While the mineral composition of cement can be more important in establishing the properties and quality of cement, it can be challenging to measure.
Elemental analysis is much easier to carry out than mineral analysis, and the elemental ratios acquired can be converted into weight fractions of each oxide present in the sample. The mineral composition of the cement can then be estimated from the ratios of oxides present in the sample.
An extensive range of elemental analysis methods are available, including atomic spectroscopy, gravimetry, X-Ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry. However, several methods of elemental analysis need complex methods and expensive instrumentation. X-Ray fluorescence (XRF) analysis offers versatile elemental analysis with simple procedures and relatively inexpensive equipment.
Research has demonstrated that with suitable calibration and by using a reliable sample preparation method, XRF analysis can attain the accuracy level of other elemental analysis methods, such as X-Ray photoelectron spectroscopy. Therefore, XRF is extensively used in the cement industry for elemental analysis.
XRF is Widely Used for Cement Analysis
As a versatile characterization technique, XRF has become the most preferred method for cement analysis. XRF entails exposing a sample of cement to X-Ray light, which excites the elements present in the sample. The elements emit light as they return back to their ground state.
The light emitted as the elements relax is distinctive to the particular elements present in the sample, and measuring the fluorescence makes it possible to calculate the exact chemical composition of the sample. While XRF analysis is non-destructive, quick, and simple to perform, correct sample preparation is required to realize accurate results.
Both the fusion method of producing glass discs and pressed powder pellets are used to perform XRF analysis of cement samples. Pressed pellets are generally a faster method of preparation, especially when using an automatic press, and therefore they allow for more rapid feedback on the cement-making process.
Pressed Pellet Preparation for Cement XRF
Cement’s chemical composition can vary extensively, and this can considerably influence performance. Elemental analysis of cement using XRF can provide peace of mind concerning the quality and suitability of cement for a given application. With the APEX 400 Press from Specac, reliable, repeatable preparation of cement samples for XRF analysis is made easy.
The advantages of preparing samples for XRF analysis are increased sensitivity to lighter elements and the removal of noise from the spectra, which might interfere with the quantitation of the elements in the sample. When calculating composition using the standardless ‘fundamental parameters’ technique, small underestimations in one element can lead to over estimation in another.
Samples are prepared for pressing by grinding the specimen to a fine powder and then mixing the resulting powder with a binding agent. The binding agent is typically boric acid or a cellulose mixture, both of which are composed of lightweight elements that cannot be detected by the XRF and thus do not interfere with measurements. It helps the powder particles to bind together into a solid pellet when pressed in the pellet die.
Once ready, the powders are put in a mold (called a ‘die’) with a 32 mm or 40 mm cylindrical bore and compressed under a load of around 20 tons using a hydraulic press. The final pellet is then sent for analysis on the XRF spectrometer.
References and Further Reading
- The global cement industry: Ready-mixed fortunes. Available at: https://www.economist.com/news/business/21579844-worlds-cement-giants-look-set-recoverybut-will-it-be-durable-ready-mixed-fortunes
- M. Bediako, E. Opoku Amankwah, (2015) Analysis of Chemical Composition of Portland Cement in Ghana: A Key to Understand the Behavior of Cement. Advances in Materials Science and Engineering.
- F. Bosch Reig, V. Peris Martinez, J. V. Gimeno Adelantado, S. Sánchez Ramos, D. J. Yusá Marco, F. Bosch Mossi, (1998) X-ray fluorescence analysis of iron(III), potassium and sulfur oxides in cements with a hyperbolic addition-dilution model and using a single multicomponent standard. Journal of Analytic Atomic Spectrometry.
- APEX 400 Press for XRF. Available at: https://specac.com/product/apex-400-press
This information has been sourced, reviewed and adapted from materials provided by Specac.
For more information on this source, please visit Specac.