Analyzing the Composition of Cement - XRF Sample Prep

Shutterstock | Banana Republic images

Shutterstock | Banana Republic images

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 best preparation method, using Specac’s Fusion Fluxer, for the XRF analysis of cement.

Cement is a versatile and important material that is used for infrastructure, roads, and houses. Hence, it is only expected that cement is 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 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

Elemental analysis of cement 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.

Formerly, pressed powder pellets were used to perform XRF analysis of cement samples. However, thanks to the development of new methods of sample preparation combined with the use of alternative raw materials and additives in cement, pressed powder pellets are not the best choice for XRF sample preparation of cement samples anymore.

Fused Disc Preparation for Cement XRF

Producing fused discs from cement samples for XRF analysis can be advantageous over pressed powder pellets for many reasons. Forming cement samples into fused discs involves mixing the sample with a flux (typically a lithium tetraborate or tetraborate/metaborate mixture) and melting the mixture in a platinum crucible at a very high temperature (900-1200 °C). The molten mixture can be subsequently formed into a disc using a mold.

Preparing fused discs from cement samples poses certain challenges. Identifying the right preparation strategy usually involves trial and error to find the best fusion parameters, ratios, and additives. To achieve accurate XRF analysis, the fused disc samples must be prepared accurately, and the method must also be reliable and repeatable. It is mandatory to validate preparation methods, and XRF measurements should also be calibrated using reference materials with known elemental compositions prepared in the same manner as the cement samples.

Using a sample preparation instrument such as Specac’s Fusion Fluxer can help in developing a suitable XRF sample preparation method, thereby practically ensuring accurate XRF results and reliable preparation. Specac supplies Fusion Fluxers that are extremely customizable, and therefore suitable preparation parameters are always within reach. After determining a suitable preparation method, Specac’s Fusion Fluxers provide reliable and repeatable preparation with extreme efficiency, automation, and high-throughput. The Fusion Fluxers supplied by Specac are also user-friendly and economical.

Conclusions

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 a cement for a given application. With Fusion Fluxer from Specac, reliable, repeatable preparation of cement samples for XRF analysis is made easy.

References and Further Reading

  1. ‘The global cement industry: Ready-mixed fortunes’ https://www.economist.com/news/business/21579844-worlds-cement-giants-look-set-recoverybut-will-it-be-durable-ready-mixed-fortunes
  2. ‘Cement Materials Analysis’ http://www.claisse.com/en/medias/fichiers/nouvelles/claisse_cement_materials_analysis_accurate_total_solution_worldcement_xrf__35.pdf
  3. ‘Analysis of Chemical Composition of Portland Cement in Ghana: A Key to Understand the Behavior of Cement’ M. Bediako, E. Opoku Amankwah, Advances in Materials Science and Engineering, 2015.
  4. ‘Mineral and oxide composition of portland cement’ http://iti.northwestern.edu/cement/monograph/Monograph3_6.html
  5. ‘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’ F. Bosch Reig, V. Peris Martinez, J. V. Gimeno Adelantado, S. Sánchez Ramos, D. J. Yusá Marco, F. Bosch Mossi, Journal of Analytic Atomic Spectrometry, 1998.
  6. ‘XRF Fusion Beads | Electric & Gas Fusion Fluxers’ https://www.specac.com/en/products/sample-preparation/xrf/xrf-automatic-fusion-bead- machine

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This information has been sourced, reviewed and adapted from materials provided by Specac.

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