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29 November 2022 | Story Leonie Bolleurs | Photo Leonie Bolleurs
UFS green concrete
The Department of Engineering Sciences (EnSci) welcomes collaborations with other departments at the UFS. Pictured here are, from the left: Louis Lagrange, Head of EnSci, Prof Kahilu Kajimo-Shakantu, Head of the Department of Quantity Surveying and Construction Management, Dr Abdolhossein Naghizadeh, and Megan Welman-Purchase, analytical scientist in the Department of Geology.

More than 30 million tonnes of fly ash (residue from coal combustion in power plants) are generated in South Africa annually, with 96% of that being disposed of in landfills. There is thus more than enough of this key ingredient to produce green concrete. 

Green concrete, so called due to its environmentally friendly benefits, is an eco-friendly alternative to conventional concrete based on the Portland cement binder. During the production of green concrete, less carbon dioxide is released into the atmosphere than with the production of ordinary Portland cement (OPC). The latter accounts for up to 8% of all global carbon emissions.

Successful tests

In the Green Concrete Lab, established in 2021 within the Department of Engineering Sciences (EnSci) on the Bloemfontein Campus of the University of the Free State (UFS), Dr Abdolhossein Naghizadeh, Senior Lecturer, researcher, and engineer, is working on green cement and concrete projects.

He uses ‘geopolymer’ technology and a mix of waste materials, alkaline solutions, and recycled aggregates to form concrete mixtures that can provide properties similar to conventional concrete.

Besides being a synthesised inorganic material (not a petrochemical product), the geopolymer cement he introduced has the following properties: it is made from a reaction between aluminosilicate materials and strong alkalis (5-7% of the concrete mixture), it uses water and by-products as raw materials, it does not calcinate lime, thus giving it a low carbon emission, and it is also beneficial from a waste management point of view. 

The waste materials used can include waste from industrial and agricultural sources, such as fly ash, rice husk ash, sugar-cane bagasse, or corncob ash, as well as natural materials such as volcanic ash. In South Africa, sufficient amounts of industrial and agricultural waste are available. 

“So far, we have successfully tested various types of green concrete based on different waste materials,” says Dr Naghizadeh. 

Besides researching the green mixture proportions in the lab, Dr Naghizadeh and his students focused their attention on establishing the strength, durability, workability, and production cost of the product. 

They compared green concrete with conventional concrete. Green concrete’s workability is slightly lower (but he believes that with appropriate mix design it can be corrected), and it has a much higher compressive strength (50-90 MPa), a smaller carbon footprint, and comparable production costs to conventional concrete (depending on the mix design). A very high level of resistance against alkali-silica reaction (concrete cancer) is also present, as well as resistance to carbonation, sulphate attack, and acid attack.
So far, we have successfully tested various types of green concrete based on different waste materials.– Dr Naghizadeh. 

He explains, “The superior durability performance of green concrete is related to its chemical compositions and microstructure. For example, the lack of calcium content in the composition provides better resistance to alkali-silica reaction. At the same time, stronger bonds between elements and polymeric microstructure provide better resistance against acids and fire.”

With all the work and research of the past year and a half, Dr Naghizadeh says they are at the stage where they can prescribe green concrete production recipes for the industry parties based on the specified application and the materials they have.

Biggest accomplishments

“We transferred most of the experimental works to the Green Concrete Lab at the beginning of 2022, which improved our productivity tremendously. Since then, nine journal papers and three peer-reviewed conference papers have been published as outputs of the research projects. Currently, there are also multiple publications under review or in the development stages,” says Dr Naghizadeh.

In addition to him, there are three master's students and one research associate working on their own individual projects.

The department is very proud of its research outputs. Dr Naghizadeh was either author or co-author of all 12 research papers. The focus of these papers was mostly on the formulation of green concrete, based on locally available agricultural waste materials, the formulation of one-part geopolymer cement (when aluminosilicate raw material is replaced with pre-activated aluminosilicate material, water can be used instead of alkali solution), and the development of ambient-cured green concrete (replacing the aluminosilicate raw material with a blend of materials).

Dr Naghizadeh is also the project leader of a group of scientists from local and international universities who are researching sustainable construction materials. These institutions include the Universities of Johannesburg, KwaZulu-Natal, Yaoundé in Cameroon, Erzurum Technical University in Turkey, as well as Nelson Mandela University and the Central University of Technology, which recently came on board. 

 


 


News Archive

Research by experts published in Nature
2011-06-02

 
The members of the research group are, from the left, front: Christelle van Rooyen, Mariana Erasmus, Prof. Esta van Heerden; back: Armand Bester and Prof. Derek Litthauer.
Photo: Gerhard Louw

A  research article on the work by a team of experts at our university, under the leadership of Prof. Esta van Heerden, and counterparts in Belgium and the USA has been published in the distinguished academic journal Nature today (Thursday, 2 June 2011).

The article – Nematoda from the terrestrial deep subsurface of South Africa – sheds more light on life in the form of a small worm living under extreme conditions in deep hot mines. It was discovered 1,3 km under the surface of the earth in the Beatrix Goldmine close to Welkom and is the first multi-cellular organism that was found so far beneath the surface of the earth. The worm (nematode) was found in between a rock face that is between 3 000 and 12 000 years old.

The research can shed some new light on the possibility of life on other planets, previously considered impossible under extreme conditions. It also expands the possibilities into new areas where new organisms may be found.

These small invertebrates live in terrestrial soil subjected to stress almost for 24 hours They live through sunshine, rain, scorching temperatures and freezing conditions. Through time they developed a means to cope with harsh conditions. Terrestrial nematodes (roundworms, not to be confused or related to earthworms) are among those very tough small invertebrates that deal with those conditions everywhere. After insects they are the most dominant multi-cellular (metazoan) species on the planet having a general size of 0,5 to 1 mm and are among the oldest metazoans on the planet, Nature says in a statement on the article.

They inhabit nearly every imaginable habitat form the deep seas to the acid in pitcher . Some nematodes simply eat bacteria and these are the ones we study here. Terrestrial nematodes have developed a survival stage that can take them through hard times (absence of food, extreme temperatures, too little oxygen, crowding, and more).

At the head of the research was Prof. Gaetan Borgonie of the Ghent University in Belgium and a world leader in the discipline of nematode research. He was brought into contact with the South African research leader, Prof. Esta van Heerden, who set up a cooperation agreement with the University of Ghent and Prof. Borgonie. Prof. Van Heerden manages the Extreme Biochemistry group at the UFS and the research was funded by several research grants.

The search for worms began in earnest in 2007, but it was soon clear that the sampling strategy was insufficient. A massive sampling campaign in 2008-2009 in several mines led to the discovery of several nematodes and the new nematode species Halicephalobus mephisto. It is named after the legend of Faust where the devil, also known as the lord of the underworld is called Mephistopheles.

Nature says special filters had to be designed and installed on various boreholes. Unfortunately, there is no easy way of finding a magic formula and designs had to be adapted by trial and error; improving existing designs all the time. The work of the UFS Mechanical Workshop, which manufactured, adapted and helped design it, was crucial in this respect. Filters were left on the holes for varying periods, sometimes for a few hours and sometimes for months. Prof. Derek Litthauer from the UFS played a big role in sampling, filter designs and coming up with ideas for names for the new nematode with Prof. Borgonie.

Research showed that the nematodes can live in the deep for up to 12 000 years. Three students – Armand Bester, Mariana Erasmus and Christelle van Rooyen from the UFS – did the work on this.

The importance of multi-cellular animals living in the ultra-deep subsurface is twofold: The nematodes graze on the existing bacterial population and influence their turnover. Secondly, if more complex multi-cellular organisms can survive in the deep subsurface on earth, this may be good news when looking for life on other planets where the surface is considered too inhospitable (e.g. Mars). Complex life forms can be found in ecosystems previously thought to be uninhabitable. Nature says this expands the possibilities into new areas where new organisms may be discovered.

Future research will focus on selective boreholes to look for more metazoans, so that a better idea of the complexity of the ecosystems there can be obtained. It will also look for metazoans in the deep subsurface on other continents to determine similarities and differences.

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