One of Australia’s most invasive weeds could hold the key to eliminating carbon emissions from the cementation process.
Production of cement and concrete is one of the world’s biggest polluters, according to the World Economic Forum.
The sector generates eight percent of global carbon dioxide emissions, more than aviation and shipping combined. One kilogram of cement produces one kilogram of carbon dioxide.
UniSA geotechnical engineer Professor Mizanur Rahman MIEAust has discovered that one of Australia’s most invasive weeds could hold the key to eliminating carbon emissions from the cementation process.
Stabilising the soil
Rahman screened 50 native plants and weeds in a quest to find a cheaper and more environmentally friendly source for bulk producing of urease enzymes to strengthen soil.
He remembered a colleague mentioning paddy melons and asked for a bag of them.
“We tested the [melons] in the lab and we’re really surprised: they were really [effective],” Rahman told create. “They have a very high concentration of enzymes. So we started collecting them.”
While soybean protein has existed as an eco-friendly enzyme source for cementation for a while, it is expensive and used primarily for food.
Paddy melons, on the other hand, are weeds; Rahman collects them from the side of the road in South Australia.
Paddy melon seeds are rich in urease enzymes that are capable of combining carbonate ions with calcium ions in interparticle spaces within the soil. This induces precipitation of calcium carbonate that binds particles and stabilises the soil.
One of the benefits of this process is there is no need to disrupt the soil that needs to be stabilised; the liquid can simply be sprayed on and percolated through.
This can work, for example, as a thin crust across the top of tailings dams to prevent contaminated sludge from escaping; as a way to reduce soil erosion; to fix cracks in concrete; and to stabilise soil before road construction.
“Using this technique, we cut down the cementation time from one week to six hours,” Rahman explained. “With the enzyme kinetics and through a mathematical model, we can control the precipitation time and the amount.
“If we want the desired amount of calcium carbonate precipitation in six hours, we can do so by controlling enzyme and substrate concentration.”
A generous yield
Crude enzyme solutions can degrade over time, which makes it hard to produce and store it for large-scale applications.
Rahman’s method involves crushing the seeds and extracting enzymes in a liquid form, which is then freeze-dried to create a powdered, high-concentration cementation agent. It is hoped this will offset any degradation problems.
Individual plants can yield 50 or more paddy melons, each containing up to 200 viable seeds. Taking into consideration the time taken to harvest, extract the seeds and turn them into a powder, the UniSA researchers estimate a 75 per cent saving compared to lab-grade enzyme production costs.
“Compared to the production of commercial enzymes, paddy melon enzymes are cheaper, more sustainable and more efficient than other enzymes used to cement and stabilise soils,” Rahman said, adding that the relatively high density of seeds adds to the solution’s scalability.
Eliminating concrete-related emissions is only one of the benefits of this research. The paddy melon weed is estimated to cost Australia’s agricultural industry around $100 million each year in lost grain yields, cattle deaths and control measures.
Harvesting the weeds reduces the availability of seeds for spreading and helps to preserve biodiversity.
It can also be used as a weed suppressant, replacing herbicides.
“Not only is herbicide harmful to the environment, but weeds often develop a resistance to these chemicals,” Rahman explained. “Spraying paddy melon enzyme solution around the trees would create a thin crust, preventing weed emergence completely. In essence, we are using a weed to control a weed.
“I’m [also] working with some Aboriginal groups to find some correlation between harvesting the paddy melons and helping them to protect native lands.”
A win for everyone
Abu Rabbi CPEng, Senior Geotechnical Engineer at ENGEO, said he is looking forward to having the paddy melon cement available commercially.
He gave an example of a riverbank protection project where he found the base wasn’t strong enough to sustain the proposed retaining wall, so the team had to design soil stabilisation using traditional cement.
“In the future, I can see it would be great to have [a] natural cementing agent that we could use to stabilise the subsoil,” he said.
Rabbi also sees potential to use the agent to both improve the base of roads and also fix cracks in existing roads as a short-term solution.
“Initially people were using microbially-induced cementing agents which are normally developed in the lab from bacteria,” he explained.
Not only does it save money to use the natural material, it’s also environmentally friendly and helps the agriculture industry.
“It’s a win-win solution for everyone.”