Scientists Develop Cement Completely Out of Waste Material
Creating renewable biocement entirely out of waste material
Cement is a binder, a substance utilized while building that hardens, sets, and sticks to other materials to bind them together. When sand and gravel are blended with cement, concrete is made.
Cement is classified as non-hydraulic or hydraulic. Hydraulic cement needs a chemical reaction between water and dry materials, while non-hydraulic cement does not set when water is present.
One of the most widely used materials in the world is cement. Cement usage in the United States was approximated to be 109 million metric heaps in 2021.
Cement production has an effect on the environment at every level of the process. Some instances include airborne pollutants in the form of dust, fumes, noise, and vibration while running equipment, blasting at quarries, and damage to the landscape provoked by quarrying.
At Nanyang Technological University, Singapore (NTU Singapore), scientists have found out a method to generate biocement from waste, choosing traditional cement that is more sustainable and greener.
A sustainable alternative to cement
Biocement is a kind of renewable cement using bacteria to create a hardening reaction binding soil into a solid block.
The Nanyang Technological University scientists have now created biocement from two usual waste materials: industrial carbide sludge and urea (from mammalian urine).
They devised a technique for forming a rigid solid, or precipitate, from the reaction of urea with calcium ions (Ca2+) in industrial carbide sludge. When this reaction takes place in the soil, the precipitate binds soil particles together and fills gaps between them, causing a compact soil mass. This creates a biocement block that is strong, durable, and less permeable.
The study team, led by Professor Chu Jian, Chair of the School of Environmental Engineering and Civil, showed in a proof-of-concept research paper published on February 22, 2022, in the Journal of Environmental Chemical Engineering that their biocement can potentially become a sustainable and affordable approach for soil enhancement, such as strengthening the ground for usage in construction or excavation, controlling beach erosion, building freshwater reservoirs in the desert or on beaches, or lowering wind or dust erosion in the desert.
Different types of biocement
The NTU team’s biocement is created from 2 kinds of waste material: industrial carbide sludge: the waste material from acetylene gas production sourced from Singapore factories, and urea discovered in urine.
First, the team deals with carbide sludge with an acid to create soluble calcium. Urea is then contributed to the soluble calcium to form a cementation solution. To this cementation solution, the team then adds a bacterial culture. To develop carbonate ions, the bacteria from the culture then break down the urea in the solution.
In a process known as microbially induced calcite precipitation (MICP, these ions react with the soluble calcium ions. This reaction creates calcium carbonate: a hard, solid material naturally discovered in chalk, limestone, and marble.
When this reaction occurs in sand or soil, the resulting calcium carbonate creates bonds sand particles or soil together to increase their strength and fills the pores between them to decrease water seepage through the material. The same process can likewise be used on rock joints, which enables statues and the repair of rock carvings.
The soil that has been strengthened with biocement exhibits an unconfined compression strength of up to 1.7 megapascals, surpassing that of the identical soil treated with an equivalent quantity of traditional cement.
This makes the biocement of the team suitable for use in soil enhancement projects such as reducing water seepage or strengthening the ground for usage in construction or excavation, or controlling beach erosion along coastlines.
Waste treatment
Dr. Yang Yang, the lead author of a paper while working as a study associate at NTU’s Centre for Urban Solutions, and who is now a postdoctoral researcher at Chongqing University in China, explained that calcium carbonate precipitation occurring at various levels of cementation can reinforce soil or sand by gradually filling the gaps between particles.
Additionally, biocement can be employed as biogrout to seal fractures in rock and control water infiltration, as well as to repair and maintain monuments such as statues and rock carvings.
According to Prof. Chu, Director of NTU’s Centre for Urban Solutions, “Biocement is a sustainable and renewable alternative to traditional cement and holds great potential for use in ground treatment for building projects.” The researchers’ work employs two waste materials as raw materials for biocement, making it more sustainable and potentially less expensive in the long term by reducing garbage disposal costs.
This study by NTU scientists aligns with the institution’s 2025 strategic plan, which seeks to tackle significant global challenges through sustainable development and research, including mitigating human impacts on the environment.
Urine, bacteria, and calcium: A simple recipe for biocement
Compared to traditional cement manufacturing methods that involve burning raw materials at extremely high temperatures to produce clinkers, the biocement-making process generates fewer carbon emissions and requires less energy. This makes biocement production a more sustainable and environmentally friendly option.
According to Professor Chu, biocement is produced without burning anything, which means it is a greener and less energy-intensive process. In addition, carbide sludge, which is considered a waste material in Singapore, can be used as a raw material for biocement manufacturing.
By extracting calcium from carbide sludge, the production of biocement becomes more sustainable, eliminating the need for materials like limestone, which must be mined from mountains and can deplete natural resources.
Furthermore, limestone is a finite resource that can have a negative impact on the environment and ecosystems when mined. If biocement production is scaled to the level of traditional cement manufacturing, its overall cost could be reduced, making it a more affordable and eco-friendly option for cement production.
Restoring monuments and strengthening shorelines
Another advantage of the NTU team’s approach to developing biocement is that the bacterial culture and cementation solution are both colorless. When applied to soil, rock, or sand, their original color is protected.
This makes it helpful for restoring old rock monuments and artifacts. For example, Dr. Yang has utilized the biocement to repair old Buddha monuments in China. The biocement can be utilized to seal spaces in fractured monuments and has been utilized to bring back broken-off pieces, such as the fingers of a Buddha’s hands. As the solution is colorless, the monuments preserve their original color, keeping the restoration work accurately to the background.
In collaboration with relevant national agencies in Singapore, there is presently trialing their new biocement at East Coast Park, where it is being utilized on the beach to strengthen the sand. A hard crust is formed by spraying the biocement solutions on top of the sand, preventing sand from being washed out to sea.
In Singapore, the team is also exploring further large-scale applications of their biocement, such as road fixing by sealing cracks on roads, sealing gaps in underground tunnels to avoid water infiltration, or even as cultivation grounds for coral reefs as carol larvae like to expand on calcium carbonate.
Read the original article on Tech Xplore.
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