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Using finite element parametric analysis, the engineers have managed to model the fire-resistance of twelve solid, cavity and composite panel configurations. Since finding that wall density is key to averting incendiary outbreaks, the team have proposed that Rockwool should be used as insulation in the next-generation of inhabitable 3D printed homes, to make them as flame-proof as possible.
Fire safety in 3D printed homes
Leveraging concrete 3D printing, it’s now possible to fabricate complex buildings in free-form designs, without the use of disposable supports. In fact, by recycling additive manufactured formwork such as that developed by BigRep and BASF subsidiary Forward AM, it’s estimated that construction firms could cut their related waste by up to 60%.
Compared to conventional construction, concrete 3D printing also yields substantial cost and lead time benefits, thus the technology is increasingly being used to build commercial properties as well. The PERI Group, for instance, is 3D printing a three-floor apartment in Germany, while ICON recently listed an additive manufactured home on the Austin housing market.
However, concrete 3D printing may be starting to fulfill its construction potential, but little research has been published on the fire performance of resulting structures. Given the trend towards habitable accommodation, and the fact that thousands die in fires within the U.S. each year, the team have now developed a model for holding 3D printed housing to the same safety standards as normal properties.
Standardizing flame-retardancy testing
According to the researchers, the flame-resistance of 3D printed walls depends on numerous factors, including material composition, density and panel thickness, as well as their configuration and insulation, but in the past, assessing these factors has involved destructive testing via costly and time-consuming trials by fire.
Instead, in their study, the engineers sought to investigate the flame retardancy of 3D printed concrete walls numerically, based on the outcomes of testing at Stellenbosch University last year. At Stellenbosch, a team of researchers heated eight different rectangular samples to 300 °C, finding that the porosity of additive manufactured concrete made it less vulnerable to breakage than conventionally-cast equivalents.
In order to turn this heat-transfer data into firm conclusions, the UK-led team used ABAQUS software to create 2D and 3D Finite Element (FE) models, and once validated against the original study’s results, deployed them to determine fire-resistance of non-load-bearing panels in five different densities, four wall thickness, and three configurations, including prototypes with integrated Rockwool insulation.
Interestingly, the team’s FE model revealed that wall density rather than thickness is key to achieving the highest possible insulation fire rating, while using Rockwool to pack the cavities of unfilled panels was found to improve their flame retardancy significantly, allowing them to last for up to five hours at high temperatures and retain up to 45% of their mass.
“[Our] novel composite 3D printed concrete wall configuration demonstrated a significant enhancement of insulation fire rating with a negligible increment on total weight,” concluded the team in their paper. “Therefore, novel composite non-load bearing wall configurations are proposed to be employed in construction, to achieve superior insulation fire ratings with substantial material savings.”
Concrete’s AM applications
While concrete 3D printing is often deployed for house-building purposes, the technology’s flexibility has also made it useful within other large-scale construction applications. Using COBOD’s concrete-based technology, GE Renewable Energy and LafargeHolcim have announced their intention to build record-tall wind turbine towers.
ICON, meanwhile, has lent its proprietary technology to student members of NASA’s Artemis Generation program, who in turn, have used it to 3D print an experimental lunar landing pad for future space missions. The novel device features an internal geometry that’s designed to direct lunar dust outward, reducing its susceptibility to turbulent cosmic dust storms.
More conventionally, concrete AM is used as a means of building sustainable infrastructure, such as the record-breaking pedestrian bridge being constructed by BAM and Weber Beamix in the Netherlands. Once finished, the structure will measure nearly 97 foot in length, beating Tsinghua University’s 86-foot bridge in Shanghai, reportedly making it the largest of its kind in the world.
The researchers’ findings are detailed in their paper titled “Fire performance of innovative 3D printed concrete composite wall panels – A Numerical Study.” The study was co-authored by Thadshajini Suntharalingam, Perampalam Gatheeshgar, Irindu Upasiri, Keerthan Poologanathan, Brabha Nagaratnam, Marco Corradi and Dilini Nuwanthika.
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Featured image shows a 3D printing construction site. Image via the Case Studies in Construction Materials journal.