Researchers at the Royal Melbourne Institute of Technology (RMIT) in Australia have developed special “energy-smart bricks” that can be made by mixing clay with glass waste and coal ash. These bricks can help mitigate the negative effects of traditional brick manufacturing, an energy-intensive process that requires large-scale clay mining, contributes heavily to CO₂ emissions, and generates a lot of air pollution.

According to the RMIT researchers, “Brick kilns worldwide consume 375 million tonnes (~340 million metric tons) of coal in combustion annually, which is equivalent to 675 million tonnes of CO₂ emission (~612 million metric tons).” This exceeds the combined annual carbon dioxide emissions of 130 million passenger vehicles in the US.

The energy-smart bricks rely on a material called RCF waste. It mostly contains fine pieces of glass (92 percent) left over from the recycling process, along with ceramic materials, plastic, paper, and ash. Most of this waste material generally ends up in landfills, where it can cause soil and water degradation. However, the study authors note, “The utilization of RCF waste in fired-clay bricks offers a potential solution to the increasing global waste crisis and reduces the burden on landfills."

What makes the bricks “energy-smart”

Compared to traditional bricks, the newly developed energy-smart bricks have lower thermal conductivity: They retain heat longer and undergo more uniform heating. This means they can be manufactured at lower firing temperatures. For instance, while regular clay bricks are fired (a process during which bricks are baked in a kiln, so they become hard and durable) at 1,050° C, energy-smart bricks can achieve the required hardness at 950° C, saving 20 percent of the energy needed for traditional brickmaking.

Some of the waste material that ends up part of these bricks. Credit: Seamus Daniel, RMIT University

Based on bricks produced in their lab, they estimated that “each firing cycle led to a potential value of up to $158,460 through a reduction of 417 tonnes of CO₂, resulting from a 9.5 percent reduction in firing temperature.” So basically, if a manufacturer switches from regular clay bricks to energy-smart bricks, it will end up saving thousands of dollars on its power bill, and its kilns will release less CO₂ into Earth’s atmosphere. Scaled up to the estimated 1.4 trillion bricks made each year, the savings are substantial.

But brick manufacturers aren’t the only ones who benefit. “Bricks characterized by low thermal conductivity contribute to efficient heat storage and absorption, creating a cooler environment during summer and a warmer comfort during winter. This advantage translates into energy savings for air conditioning, benefiting the occupants of the house or building,” the study authors explained.

Tests conducted by the researchers suggest that the residents of a single-story house built using energy-smart bricks will save up to 5 percent on their energy bills compared to those living in a house made with regular clay bricks.

Making and testing energy-smart bricks

Regular bricks are made of clay, water, and sand. However, energy-smart bricks use 20 percent coal ash and 15 percent fine glass waste. This RCF waste is mixed with crushed clay particles and then oven-dried. Water is then added to the dried mixture, resulting in the production of green-colored bricks that are air-dried for 48 hours.

Next, the bricks are placed in a furnace where they are fired at 950°C, eventually turning into the desired energy-smart bricks. “We can also produce light-weight bricks in a range of colors from white to a dark red by changing our formulations,” Dilan Robert, one of the researchers and an associate professor at RMIT, said .

The team tested the strength and durability of the bricks, comparing them to regular clay bricks. When they measured the compressive strength of the latter, the bricks withstood 23.1 Megapascal (MPa) before failing. However, for bricks with 15 percent glass waste, it was 31.6 MPa, indicating higher durability and strength.

“Over 100 bricks were manufactured under different firing temperatures and tested in this study to ensure comprehensive compliance against construction standards. All bricks manufactured and fired at 950°C using RCF waste exceeded the industry's compliance and standards, demonstrating their suitability in construction,” the study authors note.

The energy-smart brick manufacturing process also meets the key compliance requirement of fired clay bricks set by Standards Australia. Moreover, “the use of RCF wastes in brick production offers potential for reducing greenhouse gas emissions, with a 7 percent reduction compared to control bricks,” the study authors added.

Time for mass production?

It took RMIT researchers four years to arrive at the perfect energy-smart brick formulation; they had started working on energy-smart bricks in 2020. To arrange the RCF waste for their experiments, they collaborated with Visy, an Australia-based company that specializes in recycling rejected glass waste into new glass packaging.

Visy was struggling to find a way to use glass pieces smaller than 3 millimeters in size. It was not possible to make new glass products using these pieces, and most of them ended up in landfills. So when the RMIT team approached them with the idea of energy-smart bricks, “the company was thrilled to find a solution for material that cannot be recycled into food and beverage packaging,” Paul Andrich, a Visy representative, said in a press release.

Energy-smart bricks are now ready for use, but there are still some challenges left for the researchers. For instance, they have only produced a limited number of bricks in the lab. Whether mass-produced bricks are as energy-efficient, eco-friendly, and commercially viable as the lab samples will be a critical question.

“We are focusing on scaling up the production process to facilitate the commercialization of our innovative bricks in collaboration with brick manufacturers in Melbourne,” Robert said.

According to arstechnica.com