Making buildings more energy efficient is a key part of a lower carbon future. According to the International Energy Agency, the production of cement and concrete represents 30% of world energy consumption. And the United Nations Environment Program says that instead of declining in recent years, this proportion continues to grow. The design of the outer shell of a building and the materials used to construct it have a great impact on the final energy consumption of the building.
The walls, floors, ceilings, windows, stairs, doors, elevator shafts, and roof all combine to dictate the thermal performance of the overall structure. That, in turn, defines the cost of maintaining comfortable interior temperatures once the building is occupied. And improving thermal performance usually means increase the thickness of your insulation. Generally since this is where aerogels come in.
Aerogels were developed more than six decades ago and are among the lightest solid materials ever known. While they can be made from a variety of chemical compounds, the most common are those based on silica. It is enough to combine silicon dioxide with a solvent, producing a moist and porous gel structurally similar to gelatin (of course it is not edible). It is then put through a process called supercritical drying, whereby the gel is pressurized and heated in the presence of a fluid (for example, carbon dioxide). When done correctly, it removes the liquid from the gel and replaces it with air, without damaging the structure. The solid but extremely low-density framework of the gel disappears, giving you gives aerogels the ghostly appearance that characterizes them since for the most part, up to 99.8%, they are air. This not only makes them super light, it also means they can be effective thermal insulators.
More insulating and economical
Aerogels were first used in construction projects more than twenty years ago. The most common approach then was to combine the material with glass, mineral or carbon fibers to create ultra-insulating blankets that can be installed behind walls and ceilings. These airgel panels can now be found in schools, museums, sports venues, churches, hospitals, stadiums, and airports around the world. What makes them so useful is their unique combination of properties: thanks to their transparency they allow daylight to pass through, but their low thermal conductivity means they minimize heat loss.
Now a new study, published in the Journal of Building Engineering, adds another property to aerogels: structural resistance. Scientists at the Swiss Federal Laboratory of Science and Technology have designed a novel silica airgel-filled glass brick that has the performance of highest isolation known to date. Also, its bricks are many times stronger than standard clay insulating blocks.
Aerobricks, or aero bricks, have three main components: standard float glass, epoxy, and airgel. Glass makes up the majority of the structure: its best-performing prototype uses four pieces of glass. The scientists measured the thermal performance of the new brick (and a simulated wall of six rows of bricks) using a full-scale hot plate. They also did a simulation of the brick using thermal analysis software. The results showed fairly close agreement: the measured thermal conductivity was 53.0 mW/(m·K) and the simulated value was 50.5 mW/(m·K). This makes them more insulating than “anything known or available on the market.”
To understand how strong each brick was, they put one in a compression machine that applies large amounts of force to a material, gradually increasing it until the material breaks. This test showed that the bricks had a compressive strength of almost 45 MPasuggesting that, unlike polycarbonate panels, they would be suitable for use in load-bearing structures.
Researchers have presented a patent request for their invention and they say their hoverbricks are the most suitable to replace the perimeter walls. The authors point out in the study that this technology “…opens up the potential to create an outer shell with a translucent façade…. which not only insulates well, but also brings natural light into the building”.