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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 into veld fires in grassland can now help with scientifically-grounded evidence
2015-04-10

While cattle and game farmers are rejoicing in the recent rains which large areas of the country received in the past growing season, an expert from the University of the Free State’s Department of Animal, Wildlife, and Grassland Sciences, says that much of the highly inflammable material now available could lead to large-scale veld fires this coming winter.

Prof Hennie Snyman, professor and  researcher in the Department of Animal, Wildlife, and Grassland Sciences, warns that cattle and game farmers should be aware, in good time, of this problem which is about to rear its head. He proposes that farmers must burn firebreaks as a precaution.

At present, Prof Snyman focuses his research on the impact of fire and burning on the functioning of the grassland ecosystem, especially in the drier grassland regions.

He says the impact of fire on the functioning of ecosystems in the ‘sour’ grassland areas of Southern Africa (which includes Kwazulu-Natal, Limpopo, Mpumalanga, the Eastern Cape, and the Harrismith environs) is already well established, but less information  is available for ‘sweet’ semi-arid grassland areas. According to Prof Snyman, there is no reason to burn grassland in this semi-arid area. Grazing by animals can be effectively used because of the high quality material without having to burn it off. In the sourer pasturage, fire may well form part of the functioning of the grassland ecosystem in view of the fact that a quality problem might develop after which the grass must rejuvenate by letting it burn.

Prof Snyman, who has already been busy with the research for ten years, says quantified data on the impact of fire on the soil and plants were not available previously for the semi-arid grassland areas. Fires start frequently because of lightning, carelessness, freak accidents, or damaged power lines, and farmers must be recompensed for this damage.

The shortage of proper research on the impact of fires on soil and plants has led to burnt areas not being withdrawn from grazing for long enough. The lack of information has also led to farmers, who have lost grazing to fires, not being compensated fairly or even being over-compensated.

“When above-and below-ground plant production, together with efficient water usage, is taken into account, burnt grassland requires at least two full growing seasons to recover completely.”       

Prof Snyman says farmers frequently make the mistake of allowing animals to graze on burnt grassland as soon as it begins to sprout, causing considerable damage to the plants.

“Plant roots are more sensitive to fire than the above-ground plant material. This is the reason why seasonal above-ground production losses from fire in the first growing season after the fire can amount to half of the unburnt veld. The ecosystem must first recover completely in order to be productive and sustainable again for the long term. The faster burnt veld is grazed again, the longer the ecosystem takes to recover completely, lengthening the problem with fodder shortages further.  

Prof Snyman feels that fire as a management tool in semi-arid grassland is questionable if there is no specific purpose for it, as it can increase ecological and financial risk management in the short term.

Prof Snyman says more research is needed to quantify the impact of runaway fires on both grassland plant productivity and soil properties in terms of different seasonal climatic variations.

“The current information may already serve as valuable guidelines regarding claims arising from unforeseen fires, which often amount to thousands of rand, and are sometimes based on unscientific evidence.”

Prof Snyman’s research findings have been used successfully as guidelines for compensation aspects in several court cases.

 

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