Reinforced concrete: Why XRF analysis holds the key to the perfect mixture

by Murielle Goubard, Thursday, 26th May 2022

The ability to accurately analyze chlorine and sulfur levels is a gamechanger for this most timeless of composite materials.

analysis of chlorine and sulfur in cement

France, 1858. As dawn breaks, the engineer Joseph Lambot anxiously launches his odd-looking boat into the water. Unlike most other vessels of the time, the boat is made not of wood, but of iron encased in cement. Not only is the non-wood boat resistant to humidity, but amazingly, it also floats.

While few saw the appeal of Lambot’s invention (concrete boats remain unpopular to this day), his idea to merge steel and cement went on to revolutionize the field of construction, offering the world one of the very first composite materials.

Chlorine and sulfur in cement: How much is enough?

The art of concrete reinforcement has continued to evolve over the intervening period, with various other materials being added to the mix over the past two centuries. One such ingredient is soluble chlorine, typically calcium chloride, which works as an accelerating agent for faster strength development or shorter setting times. Another, sulfur, is often included in mixtures to improve drying rates and strength and to enable cement to dry underwater.

However, these additives only serve a purpose if applied in the correct quantities. An overload of chlorine in reinforced concrete, for example, can cause the steel reinforcing material to corrode, potentially causing premature structural damage. Achieving the optimal sulfur oxidation state in concrete is essential to limit corrosion.

XRF: For when accuracy really matters

Monitoring and controlling chlorine and sulfur levels in reinforced concrete is a sensitive and delicate process, and it requires a high level of precision. Enter X-ray fluorescence spectrometry (XRF): an advanced analytical technique used to accurately determine the chemical composition of a wide variety of sample types including solids, liquids, slurries, and loose powders.

Like other atomic emission methods, XRF enables practitioners to accurately gauge the wavelength and intensity of ‘light’ emitted by energized atoms in a sample. By providing clear visibility over which elements are present in a mixture – and in what quantity – the technique delivers vital qualitative and quantitative information. What’s more, the ability to combine these two potential data sets in a single assessment also opens the door to rapid screening (semi-quantitative) analysis.

XRF can be used for analyzing chlorine and sulfur content, but careful attention (and experience overseeing the process) is needed to achieve quality results. For example, in sample preparation for chlorine, a fused-glass disk preparation can offer up to 10 times greater accuracy during the quantification of elements than with a pressed powder approach.

This method of preparation involves removing mineralogical and particle size effects (especially useful when the raw materials are of varying quality) – a tricky process with a volatile element like chloride, but one that the XRF can handle.In the case of sulfur, too, good XRF spectrometer resolution and a specific analytical program are needed to achieve accurate and reproducible results in the case of specific ions such as SO₄^2- and S^2-.

Putting our experience – and technology – to good use

At Malvern Panalytical, we have extensive experience in helping our customers undertake these kinds of specific, intricate analyses. And we have the technology to match: our Zetium XRF spectrometer offers high stability and excellent reproducibility, providing the accuracy to separate sulfide and sulfate signals, leading to both SO₄^2- and S^2- concentrations.

When using Zetium for sulfur analysis, step one is to set up the right calibration using nine standards with varying concentrations of sulfate and sulfide. The two sulfur compounds can be distinguished because the energy of the sulfur k-alpha line is influenced by the chemical state of the sulfur compound, resulting in two effective lines for sulfur. By applying a line overlap correction, the two compounds can be determined from pressed powder samples of cement. All with one easy-to-use instrument!

While Zetium is no concrete boat, we like to think we’re offering a solution that Monsieur Lambot himself could be proud of.

To find out more about our modern XRF solutions, or any of our other solutions for building materials, please visit our dedicated webpages, or contact us.

Chlorine and sulfur in cement: How much is enough?

XRF: For when accuracy really matters

Putting our experience – and technology – to good use

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