How mineralogy is revealing the secrets of Roman concrete

par Murielle Goubard, Tuesday, 13th September 2022

In 2017, researchers at the University of Utah finally answered a rather puzzling question: why is Roman concrete better than ours?

Example of a Roman concrete

Italy’s ancient cities boast many examples of Roman concrete. Often, these are cities on the coast – and the concrete structures are partially submerged in seawater as piers, bridges or breakwaters. Yet these structures have remained standing for millennia, seemingly unaffected by the salt water that would cause modern concrete to crumble away within decades.

Mineralogical secrets

The researchers discovered that these ancient structures actually take advantage of the sea to make themselves stronger! As the saltwater filters through the material, it dissolves the volcanic ash used in the original mixture. This creates an alkaline environment in which other minerals, such as Al-tobermorite and phillipsite, can grow. As they grow, their crystal structures form interlocking plates inside any gaps and make the concrete stronger over time.

In modern concrete structures made with the ingredients of today, this process can’t take place. As small gaps or pores let the sea in, it wears away at the material and causes cracks or other damage.

As Roman concrete relied on volcanic ash to produce this effect, it wouldn’t be very practical for us to copy it exactly – the modern scale of the building materials industry makes it impossible. But what we can do is learn from this example, and find equally innovative ways to increase the strength of our cements and concretes. How? The same way we discovered the volcanic ash secret: mineralogical research.

Learning from the ancients

If we want to learn from the Romans and make sure our cement and concrete are as strong as possible, we need to know exactly what’s in them. The development of new crystalline structures is what gives Roman concrete its unlikely resilience – so understanding the phase composition of our materials, especially clinker, is the key for us today.

Clinker is the binder in cement products, which makes it one of the most important factors in determining how strong those products are. It’s made from a blend of calcareous rocks, such as chalk or limestone, and argillaceous rocks such as clay or shale. Under intense heat treatment, the calcium, silicon, alumina and iron oxides in these materials undergo a series of chemical reactions. Tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) become the main compounds within the mixture. Once cool, the clinker is ground into a powder to be combined with other materials to make cement.

Characterizing these compounds gives insight into how the cement will perform. C3S content affects strength development, while knowing the C3A content helps us understand the fresh properties. Meanwhile, the presence of uncombined or ‘free’ lime can cause expansion issues. Each variable has an important effect.

Mineralogy during cement production

The Bogue calculation is often used to generate phase estimates from chemical analysis. It’s helpful in many ways, but not very accurate. These calculations can only ever give estimates and approximations of the true phase composition of your cement – so if you’re using them to solve specific problems or innovate with precision, you’ll need a clearer picture.

Expert insights

When working with powders such as clinker or cement, one of the most common analytical methods to quantitively determine phase composition is X-ray powder diffraction. Crystal atoms scatter incident X-rays as the rays interact with their electrons, and the resulting array of waves can be analyzed using Bragg’s law to produce an overall diffraction pattern. Modern techniques such as the Rietveld method make this process even more efficient by allowing pre-calibration through the use of control files.

Malvern Panalytical offer a specialized Cement edition of the popular Aeris X-ray diffractometer to support the mineralogical quantification of every typical material in the cement production process. From raw materials, intermediate hotmeal or clinker and final blends of cement, the control files include all common clinker and cement phases, based on industry standards.

But your results are only useful if they can be interpreted easily, which is why our HighScore Plus and RoboRiet software are designed for ease of use as well as in-depth functionality. They provide the accurate data you need to understand and optimize your processes at any stage of production – and they’ll give you output in the format you need to ensure compatibility with your other systems, too.

Supporting innovation for the future

If the cement and concrete industry of today can learn anything from the Romans, it’s that mineralogy is key to performance! And as we all look to a more sustainable future, innovation will remain key to unlocking new materials and better formulations.

At Malvern Panalytical, we’re proud to support this innovation through our range of specialized instruments. That support for our users continues through our range of educational content, and our experts are also always available to give help and advice – so get in touch!

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