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Tuesday, 20 August 2019
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Raw materials & technologies, Applications, Industrial coatings

Eco-friendly cement is strong and durable

Friday, 20 September 2013

Researchers at the University of Copenhagen demonstrate that cement manufactured with waste ash from sugar production is stronger than conventional cement.

In the research project, cement was made with waste ash from sugar production

Source: Ingo Bartussek - Fotolia.com

In the research project, cement was made with waste ash from sugar production

Source: Ingo Bartussek - Fotolia.com

New research from the Niels Bohr Institute at the University of Copenhagen shows that cement made with waste ash from sugar production is stronger than ordinary cement. The research demonstrates that the ash helps to bind water in the cement so that it is stronger, can withstand higher pressure and crumbles less. At the same time, energy is saved and pollution from cement production is reduced.

Cement is comprised of chalk and clay, which are mixed together and heated at high temperatures in a cement kiln. The mixture is then crushed into a powder. When the cement powder is mixed with water, a chemical process takes place, causing the cement mixture to harden.

In some countries where sugar cane is grown, agricultural waste product from sugar production has been added to the cement mixture for many years. Once the sugar has been extracted from the sugar cane, a lot of fibre waste is left, which is used as fuel for energy production. From the energy production a lot of ash remains, which needs to be disposed of. In some countries, like Cuba and Brazil, the ash is added into cement mixtures.

Property investigation on a nano-scale

"I have been studying cement using quasi-elastic neutron scattering for several years and researchers from Brazil asked whether I wanted to analyse samples of cement mixed with waste products in the form of sugar cane ash. I decided to say yes to the project, which aimed to investigate the properties on a nano-scale and map the mobility of water in the cement. The quality and strength of cement is directly related to how much of the water is chemically bonded. The more the water can move around, the worse it is for the strength and durability,” explains Heloisa Bordallo, who does research in nanophysics at the Niels Bohr Institute.

Heloisa Bordallo was sent a number of cement samples from Brazil. The samples contained varying amounts of ash from sugar cane production. Their innermost dynamics were then examined. The samples were placed in an instrument where they were bombarded by neutrons.

"Using neutron scattering, we can see how the water inside the sample moves. Neutrons are shot into the sample and when neutrons hit the water’s hydrogen atoms, they interact and the neutrons scatter and are picked up by the detectors. We repeat this for several hours and by analysing the data we can determine how the water inside the sample is moving and also determine its local environment,” explains Johan Jacobsen (Niels Bohr Institute).

Good properties: cement mixed with 20 % ash

The experiments showed that the cement mixed with approx. 20 % ash had good properties. The water in the cement pores was bound to the ash and moved around less. This explains why the ash cement is stronger, can withstand higher pressure and will crumble less.

Cement typically takes a week to solidify. After one month, 70 % of the process has been completed, but the process continues for many years. Ordinary cement is generally stronger during the first few months than the ash cement, but after a year the ash cement is stronger than the ordinary cement.

Cement is a porous material. In fresh cement paste the largest pores will be filled with water and as the cement gradually ages this water will move from the largest pores to the smaller pores and become increasingly bound to the cement. After 28 days the larger pores are completely empty of water.

Great potential

"The cement industry is huge and if they are to adopt a new idea, they need to have proof that it works. Using quasi-elastic neutron scattering we have now studied cement mixed with ash and shown what is happening and why it is stronger. Cement production uses a lot of energy and emits large amounts of CO2, because it needs to be heated up to very high temperatures. Cement production accounts for 5 percent of global CO2 emissions. If you replace 20 % of the content with ash, you are saving both CO2 emissions and raw materials, as you use 20 % less by utilising a waste product like ash,” says Heloisa Bordallo.

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