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2000 green bottles (per m2,) insulating a wall
That glass can have a significant impact on a building's insulation is well known – just ask anyone that has ever sat through a pitch from a double-glazing salesman.
But the material could soon find a surprising new use in 3D-printed buildings after researchers demonstrated that concrete made with ground-up recycled glass has significantly better insulating properties than more traditional concrete mixes.
The researchers found that when they gradually replaced a conventional aggregate traditionally found in concrete with waste glass, the thermal conductivity of the concrete – the rate at which heat transfers through it – correspondingly went down. The results will be particularly exciting for those interested in 3D printing in construction, who are currently in a race to prove the technology with better insulated, more environmentally-friendly buildings.
"Although much of our waste glass can be recycled to produce new glass products, a big quantity is still being sent to landfill," said Dr Seyed Ghaffar, lead of the Additive Manufacturing Technology in Construction Research Group at Brunel University London. "So, to reduce the waste glass that is sent to landfill, different recycling strategies need to be investigated."
Dr Ghaffar believes the construction industry could be one potential destination for the unrecycled glass, a partial substitute for the vast quantities of natural sand that is currently being used to meet the world's insatiable appetite for concrete, at great cost to the environment.
The team estimate that around 2000 recycled beer bottles could be used per square meter, if used in the 3D printing of a building.
Published in the Journal of Building Engineering, the research showed that when used as a substitute for basalt aggregate, a substance that already provides good insulation, glass waste had a thermal conductivity almost a fifth lower.
"To be specific, the samples with 50 percent and 100 percent waste glass volume substitution had lower thermal conductivity by 11 percent and 17 percent, respectively," said Dr Mehdi Chougan, a Marie Curie Research Fellow in Brunel's Department of Civil and Environmental Engineering. "But it's also worth noting that the thermal conductivity of soda-lime glass – the most common type of glass, that you'd find in windows and bottles – is more than three times lower than that of quartz aggregate."
The team also discovered that the addition of 'expanded thermoplastic microspheres' – tiny spheres of polymer filled with gas – provided an additional boost to its thermal properties whist also increasing the viscosity of the poured concrete.
"Simply, they can be explained as a micro 'balloons,' which upon heating exhibit tremendous volume expansion," said co-author Dr Pawel Sikora, an associate professor in civil engineering at Poland's West Pomeranian University of Technology in Szczecin.
"Due to their characteristics and inertness, the material can be introduced to the cementitious composites as a lightweight filler, offering amazing thermal insulating properties."
The researchers will now begin scaling-up the project and 3D printing demonstration walls to get a better understanding of their thermal and mechanical performance.