Cement hydration in 4D: towards a reduction in emissions

Researchers led by the University of Málaga show the Portland cement early age hydration with microscopic detail and high contrast between the components. This knowledge may contribute to more environmentally friendly cements. The results are now published in Nature Communications.

Concrete is a fluid mass that strikingly sets and hardens in hours, even under water. This fabricated rock, which is made of cement, water, sand and gravel, is the basic building block of our civilization. Hence, it is not a surprise that it is the world’s largest manufactured commodity. The enormous production of Portland cement (PC), at 4 billion tonnes per year, results in 2.7 billion tonnes of CO2 emissions per year. If cement production were considered a country, it would be the third CO2 emitter in the world, just after China and USA. Therefore, reducing the CO2 footprint of cement, mortar and concrete is a societal need.

The main drawback of the current proposals for low-carbon cements is the slow hydration kinetics in the first 3 days. “Understanding the processes related to cement hydration as it takes place at its early stages is crucial”, explains Shiva Shirani, first author of the paper and PhD student at the University of Malaga. Despite a century of research, our understanding of cement dissolution and precipitation processes at early ages is very limited. “So we have developed a methodology to get a full picture of the hydration of Portland cement”, she adds.

The team, which is led by the University of Málaga and includes the ESRF, the Paul Scherrer Institute PSI (Switzerland) and the University Grenoble Alpes (France), carried out a tomographic study in the laboratory for an initial characterisation, followed by phase-contrast microtomography experiments with synchrotron radiation to take data very quickly and in large sample volumes, and finally experiments at the nanometric scale, using synchrotron ptychotomography.

Read more on the ESRF website

Image: Scientists followed the hydration process of cement in its early stages

Credit: Shiva Shirani

Building better catalysts to close the carbon dioxide loop

The best way to stave off the worst effects of climate change is to reduce CO2 emissions around the world. And one way to do that, says Zhongwei Chen, a professor in the Department of Chemical Engineering at the University of Waterloo, is to capture the CO2 and convert it into other useful chemicals, such as methanol and methane for fuels. Stopping emissions at the source, and further reducing future ones by replacing CO2-producing fuels with cleaner ones “…is a way to close the circle,” Chen says.

In order to turn CO2 into methanol, you need a catalyst to jump-start the electrochemical reaction. Traditionally, these catalysts have either been made out of precious metals like gold or palladium, or base metals like copper or tin. However, they are expensive and break down easily, hindering large-scale implementation. “Right now we can’t meet industrial requirements,” says Chen, who holds a Canada Research Chair. “So we are trying to design catalysts with better activity, selectivity, and durability.”

Read more on the CLS website

Image: Chithra Karunakaran on the SM beamline at the Canadian Light Source

Credit: David Stobbe