Researchers transform sugarcane by-product into slabs and bricks

Sugarcane is the world’s largest crop by production and bagasse is what is left when sugar juice is extracted from it.

According to international science journal Industrial Crops and Products, 513M.t of this dry fibrous material is created globally every year.

In countries such as India, bagasse is being converted into biofuel for low-carbon electricity, but its potential to contribute to global decarbonisation could soon extend to the construction sector.

Academics at the University of East London (UEL) are involved in an extremely promising project to create slabs and bricks made from bagasse combined with mineral binders. The product is called Sugarcrete and early test results have already led to pilot projects in sugarcane producing countries including India, Costa Rica and Tanzania.

Following the juice extraction from the sugarcane, the bagasse fibres are a tangled mass and binders are poured onto them to hold them together before they are compressed and moulded to form blocks.

Project origin

The project started in the architecture department of UEL, which has a strong environmental and social agenda.

In 2021, UEL senior lecturer in architecture Armor Gutierrez Rivas challenged his MSc students to develop a materials research project with circularity and sustainability at its heart. Their work was to be based on what could be found in the vicinity of the campus at the Royal Docks. This led the students to investigate the nearby Tate & Lyle sugar refinery.

“We approached them and asked about the byproducts they generate and that was the first time we heard of bagasse,” Rivas says. From there, the students started to examine how this could be turned into a construction material.

UEL Sustainability Research Institute (SRI) co-director Alan Chandler is a co-creator of Sugarcrete and has collaborated with the university’s architecture department since 2003. The two departments have a mutual interest in applying the results of sustainability research and the synergies that the Sugarcrete research has created have taken this activity to a new level. The expertise of Sugarcrete’s third co-creator, SRI senior research fellow Bamdad Ayati, has guided the materials science.

The slab

The university was approached by architects Grimshaw which had been researching the interlocking geometries of building components that could create self-supporting assemblies. It was looking for biomaterials to test them out on.

This led to a project where the brief was to create a 3m by 3m structurally viable slab from Sugarcrete.

Engineering consultancy AKT II also became involved to help test the compressive strength of different Sugarcrete recipes, based around the ratio of bagasse to binder. The binders can be adjusted depending on where the Sugarcrete is being made, but initial forms used mineral-based and silica-based binders.

Supported by AKT II associate Nicolo Bencini, the team started casting cubes with 100mm sides using different Sugarcrete recipes. They left them to cure for two to three weeks before testing the compressive strengths. The team found that the length of the tangled bagasse fibres meant they became more interlocked during the mixing process and this was enhanced during compression.

Bencini says: “The initial tests [produced compressive strengths that] were close to 1kN/m², which was fine, but once we achieved 5kN/m² we were getting close to low grade concrete so we could talk about slabs.”

This mixture was then used for the slab project, where the UEL Digital Fabrication Lab used a 3D cutting robot to produce Sugarcrete moulds for 200mm long and 200mm tall trapezoidal blocks. This shape was chosen for its interlocking geometry, allowing the blocks to transfer loads from one to the other when bound in formation at right angles to form a slab. These were assembled into a five by five interlocking grid that was restrained using post tensioned perimeter ties.

Publication of the video showing the results immediately sparked interest around the world. Indian company Chemical Systems Technologies, whose subsidiary Ecoware is using bagasse to make plates, saw that UEL’s work was aligned with its own and immediately got in touch.

“They said they had the funding and they wanted to start using Sugarcrete,” Rivas says. This marked the start of a pilot project to build a classroom from Sugarcrete bricks in the state of Uttar Pradesh, one of the largest sugarcane producing areas in India. This project is just getting underway.

Before taking Sugarcrete to market, the team knew that the product would have to comply with ISO certification standards. As it is a biomaterial, fire safety is always one of the first considerations. Five different Sugarcrete ratios were tested.

“We’ve got the highest value, A1, which means you can install it in cladding everywhere in London,” Rivas says. “We also got A2 and B1, which means we got the highest three values you can get.

“This means, depending on the application, you could use one or another – or you could even combine them. Something we developed is that you could have one ratio as a core and then coat it with another that provides better protection.”

The brick

While the slab was a good test of the material’s viability, Rivas saw that Sugarcrete bricks could have an impact on global carbon emissions. Making Sugarcrete bricks requires no heating, the material is merely mixed and cured, meaning their carbon footprint is extremely low.

Making each brick produces around 400g of CO₂e – roughly six times less embodied carbon than a standard brick. But each brick also contains and thus sequesters roughly 848g of CO₂. Assuming it is produced close to a sugar plantation, this makes it potentially a carbon negative material.

“I did some quick numbers and realised that even if only 30% of the annual production of bagasse is used to make Sugarcrete bricks, it would be enough to replace the whole clay brick industry, which generates 3% of CO₂ globally,” Rivas says.

In countries like India, Sugarcrete bricks are also easier to make than the trapezoidal blocks used in slabs, as there is an enormous number of brick production lines but few 3D cutting robots. The country’s brick factories only need minor modifications to start making Sugarcrete bricks and the first production line to be created can manufacture 400 a day, says Rivas.

As with the slab components, there is a geometric element to the bricks. They have ridges on the top side and a corresponding groove on the underside so they interlock vertically.

“If there is seismic movement, they will react better,” Rivas says. “And it helps with storage – you are able to stack them to around 20 units.”

There are also different bricks for different parts of a building. The standard brick that UEL is working on is 230mm by 230mm by 75mm, while bricks that go in the corner are slightly longer, at 305mm, to provide extra strength.

Despite being around twice the size of a standard brick, they are not much heavier, with different recipes weighing between 2.9kg and 3.3kg.

The recipe for the bricks varies depending on locality. “[In India] we are using binders that are available locally and cheaply,” Rivas explains.

“By adding pressure with a hydraulic press, we are getting the properties that we were getting with more expensive binders.”

India has a monsoon season, where floodwater can remain on the ground for several days or weeks. Weather testing has shown that Sugarcrete softens when submerged for a long period, so UEL is advising that the Sugarcrete bricks are only used from 300mm above ground level.

The future

UEL is not patenting Sugarcrete because the mix of binder and bagasse is not standard and depends on locality and use. Importantly too, its creators want the material to be accessible to all.

UEL architectural research assistant Oluchukwu Okonkwo is studying the properties of different mixtures for her PhD.

“Our aim is to end up with a gigantic library of different ratios of Sugarcrete that you can apply based on your geographic location, what you’re trying to build and how tall it’s going to be,” she explains.

“We’re currently testing different ratios in the climate chamber and it’s performing really well.”

“There is no magic ratio,” Rivas says. “It’s a project that disseminates knowledge and adapts to the local conditions.”

Despite the encouraging results and investment in further research, the team acknowledges that there will be challenges to the wider adoption of Sugarcrete.

Rivas believes that the first challenge is simply getting over misconceptions.

“Even with all the drawbacks of concrete, it is what has been used historically and it’s what’s socially accepted,” he says.

“High carbon materials are almost like a proof of status.”

This is less the case in rural areas and many of those who have approached UEL about the bricks think that they would work well for buildings in plantation communities.

The next challenge is to establish green production processes and implement a business model that can be presented as a business opportunity.

Once the classroom project in India is complete, UEL will test it, learn from it and look into replicating it. This could be through either a centralised or decentralised model, Rivas explains.

“It could be a centralised model where we fabricate the bricks in one location and ship them to where there might be a market, or it could be a decentralised model where we transfer the machinery and know-how to particular areas that are interested,” he says.

“I think both ways can work, but for us the interest is to decentralise it as much as possible, to maximise the impact and the carbon sequestration opportunities.” 

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