Construction materials are the source of a huge chunk of a building’s embodied carbon (GHG emissions from processing, transporting and using the material). Carbon-negative construction materials can offset these emissions.
These new materials can be a powerful tool in the quest to achieve carbon neutrality. These carbon-neutral or carbon-storing construction materials are gaining traction as the market demands more green alternatives to concrete, steel and aluminium.
Radiata Pine
Pines are a versatile and carbon-negative material that can be used in a variety of ways. They can be incorporated into walls and roofs, and they can also be used as decorative accents. In addition, they can help reduce air pollution and improve the quality of indoor air. They also provide a number of benefits to the environment, including providing shelter for wildlife and absorbing carbon dioxide.
Pinus radiata, or radiate pine, is an evergreen conifer tree native to only three limited areas of the United States: a narrow strip on the central coast of California and two islands off the Mexican coast (Point Lobos). The species is widely cultivated as plantation timber worldwide but is now in danger of extinction in its natural range because of the widespread occurrence of pine pitch canker, a fungal disease that causes trees to die.
This fungus is particularly problematic for agroforestry systems dependent upon radiate pine, such as New Zealand. The disease is spread through wounds in the trees and can be transmitted by bark beetles. The infection can also cause the trees to degrade, attracting beetles and accelerating tree loss and disease spread.
Despite this, radiate pine is an extremely valuable wood for construction and furniture making. Its rapid growth rate makes it a great alternative to hardwoods, and it is highly sustainable. Its only drawback is that it must be grown on a plantation to maintain its market value. It is also a sensitive material that requires preservatives. In addition, working with the wood can cause allergies in some people.
Mycelium Insulation
Mycelium—the stringy main body of fungi—is a great alternative to traditional building materials because it is biodegradable, low-cost and carbon-neutral. It can be grown in sheets and shaped to fit the design of a structure, and it uses less energy to make than petrochemical or plastic-based products. And because it is a natural material, it’s also safer and healthier for the building’s occupants.
Mycologists—people who study fungi—are experimenting with growing mycelium composites from agricultural waste. They mix a raw form of the fungi with sawdust, agricultural waste or plant stalks and husks—and then add water. The mycelium grows and binds the materials together, and within weeks they can have a solid material ready to use.
For example, a team led by RMIT engineering professor Everson Kandare developed a system of slender knitted mycelium that can be used to insulate and fireproof buildings and sequester carbon. They’ve already constructed a 1.8m-high, self-supporting freestanding pavilion out of the biomaterial.
Its insulating properties are comparable to expanded polystyrene foam, but the mycelium has the added advantage of being flame retardant and able to resist heat transfer. And pound for pound, it’s stronger than concrete. The mycelium can be molded to produce furniture, insulating panels and bricks with enhanced thermal and acoustic properties. And, best of all, it’s made from waste agricultural products that would otherwise be discarded and it has a lower carbon footprint than most petrochemical-based construction materials.
Carbon-Neutral Concrete
With concrete accounting for up to 8% of construction industry emissions, researchers are hard at work slashing the material’s carbon footprint. One such innovation is a 3D printed concrete alternative that eliminates the need for traditional cement. It’s also cured with captured CO2 from factory flues, making the entire process carbon neutral. Montreal-based Carbicrete is one of many companies using this technology.
Another approach to reducing the embodied carbon in concrete is a mix design that cuts out some of the cement by replacing it with mineral compounds like fly ash, blast-furnace slag, or calcined clays. These materials can reduce the embodied carbon of concrete by up to 30%.
In an even more innovative approach, a team of researchers at the University of Colorado Boulder is working on a concrete that can be used as carbon-neutral or even carbon-negative. Popular Mechanics profiles the algae-based concrete, which uses limestone crafted from algae grown through photosynthesis, to create a cement that’s net negative in embodied carbon footprint — it releases less carbon dioxide into the atmosphere than it draws down during growth.
Meanwhile, the Spanish cement manufacturer CEMEX is accelerating the commercialization of low-carbon concrete with its Vertua range. The brand offers a number of bespoke mix designs, including the Vertua ultra zero option that achieves a 70% reduction in embodied carbon emissions through the use of an innovative concrete chemistry and by partnering with Natural Capital Partners to offset any remaining unavoidable emissions.
Mineral Carbonation
A number of commercial approaches to mineral carbonation are already employed on a small scale. The construction materials market is one of the largest in the world and offers opportunities to significantly increase penetration of these low-carbon building products.
Cementing systems based on mineral carbonation can be manipulated to exhibit much longer workability windows than conventional concrete, allowing for the fabrication of structures with a superior strength-to-weight ratio and optimized topology. These systems can also be used to fabricate complex shapes that would not be possible through traditional casting or molding methods.
Additionally, these systems can be designed to produce aggregates and binding agents for use in a wide variety of construction applications. This can allow these products to displace natural and existing synthetic sources of these key construction materials components.
Mineral carbonation can also be used to sequester atmospheric CO2 in the form of mineral carbonates. These processes can be engineered to utilize dilute sources such as flue gases, bypassing the energy-intensive solvent capture steps of conventional geo-CCS.
However, the high cost of these processes makes it difficult to achieve a significant reduction in net life-cycle energy required to carbonate a tonne of CO2. This can be overcome by developing better mineral carbonation chemistries and process engineering that reduce the amount of net external energy needed.