Concrete is synonymous with civilization. It gave rise to the cities that have shaped our modern society. It will be evidence of our existence long after we are gone. But as it represents many of the best aspects of civilization it also bears with it much of the cost. Evidence shows production of the material is one of the largest sources of pollution and some scientists have called it the most destructive material on earth. A growing global population needing urban expansion means that it will likely continue to be so. Making an impact on climate change will require expanding cities to curtail concrete jungles. Replacing the ubiquitous material means there won’t be one alternative to concrete, but several. Concrete alternatives will be the new bedrock of cities, infrastructure, and buildings for centuries to come.
The only resource consumed more than concrete on planet Earth is water, making concrete the most widely used man-made material ever created. The backbone of concrete, cement, is responsible for roughly 8 percent of the world’s carbon dioxide emissions. If the cement industry were a nation, it would be the third-largest emitter of greenhouse gases. Concrete production emits CO2 in two ways. First, by requiring extremely high temperatures, using intense amounts of energy to fire kilns. Second, mixing concrete creates calcination, thermally decomposing calcium carbonate for purification, producing lime and CO2.
For centuries concrete has shaped our cities, defined our infrastructure, and been used in our most impressive architectural marvels. Building without concrete will be one of the biggest challenges in the fight against climate change. These materials will give us a fighting chance.
Burning coal produces fly ash, which typically ends up in landfills. Researchers have discovered a way to use molecular engineering to mix fly ash into concrete, replacing the need for heat or cement in the production process while preventing the fly ash from ending up in a landfill. Made from 97 percent recycled materials, AshCrete is roughly twice as strong as Portland cement.
The problem with AshCrete is it will be tough to use at scale. Sourcing fly ash has been an issue in the past. Considering fly ash is a byproduct of burning coal, itself a major source of pollution, in an ideal world, there wouldn’t be much of it. Commercial applications of AshCrete are still being developed, but it looks to be best served as a transition material while we phase out coal and cement.
More a form of paving than a concrete alternative, GrassCrete is a solution for sprawling parking lots and other forms of single slab concrete in outdoor spaces. The process uses less concrete by paving in such a way that allows grass to grow in patterns, reducing the overall need for concrete. Not only does GrassCrete reduce pollution by requiring less cement, it also helps with stormwater by allowing water to pass through for absorption and drainage instead of running off over an impervious concrete surface. Because of this, GrassCrete and other forms of pervious pavement are already taking off in areas inundated by floodings, like Florida and areas along the Gulf Coast.
Rammed earth is one of the oldest building materials in human history. Used for thousands of years, the process is as simple as tightly compacting dirt in a wooden form. The Great Wall of China was built with the technique. Producing rammed earth requires no carbon but the use of machinery to accelerate the process may. Rammed earth also has the added benefit of using local materials, requiring little transport, further limiting carbon emissions.
The downside of rammed earth is it’s not a solution for every climate. Rammed earth works best in areas with high humidity and moderate temperatures. Rammed earth is not a great insulator, so colder or warmer climates need additional insulation. Climates with heavy precipitation need additional protection for rammed earth material. These concerns are well documented with a whole set of building code regulations around them, making rammed earth unfeasible in some areas.
Scientists are just beginning to understand all the uses of fungi aka mushrooms. Filling forms with an organic substrate like straw, sawdust, or corn husks, then introducing mycelium, creates lightweight, durable building material once the fungal digestion has been terminated and dried to create the finished product. Root-like fibers formed by the fungus as it grows and digests the organics give mycelium bricks their firmness and structure. The bricks are super strong, water, mold, and fire-resistant, 100% biodegradable, and lightweight. Mycelium is still in the early stages of development but looks extremely promising. Mycelium can be found all over the planet and grows at a rapid pace, allowing mycelium production to reach an enormous scale. The main downside is in its current state, the lifespan of mycelium isn’t great. Contact with the ground and inclement weather can degrade mycelium bricks rapidly, in the best conditions, mycelium bricks have a roughly 20-year life span. Despite the relative strength to weight, mycelium bricks can only bear a fraction of the psi concrete can withstand. For now, mycelium is comparable to an untreated softwood, best kept indoors, but teams around the world are working to improve the process and finished product.
Ferrock is another material that uses an industrial byproduct, combing steel dust and silica from ground-up glass. The iron in the dust reacts with CO2, forming huge chunks of rust-colored iron carbonate when dried. The two biggest advantages of ferrock is that, unlike concrete, producing ferrock actually absorbs CO2, trapping it while at the same time producing a material five times stronger than Portland cement. Even though it is carbon negative, a huge benefit in today’s regulatory landscape, the challenge of ferrock production will be keeping it cost-effective at scale. Right now, ferrock uses industrial by-products, so any serious level of production will turn byproduct into a valuable commodity, driving up the price, limiting its uses. The chemistry behind ferrock production is less than a decade old, discovered by accident, meaning the potential for the material is just getting started.
Graphene has been dubbed the ‘miracle material’ because of its shocking array of uses. When graphene is separated from graphite, it forms a two-dimensional material one-atom-thick with a tensile strength more than 100 times that of steel. When mixed with concrete, graphene fortifies the material, doubling its strength and making it four times more water-resistant. With the enhanced properties, 50 percent less concrete is needed to meet load specifications for buildings.
The biggest challenge will be sourcing reliable graphene. Measuring the quantity and quality of a material one-atom-thick isn’t easy. Separating graphene and transporting graphene needs to be more environmentally friendly before it can be used at scale. Like many concrete alternatives, uses and production are still in the early stages of development with lots of promise.
Industrial hemp is picking up steam as state and federal lawmakers remove barriers put up to stop the cultivation of cannabis, a relative of hemp. Hemp is fast-growing, making it a rapidly renewable resource. Hemp is also easy to cultivate, meaning it can be grown locally even in places with the short growing seasons, avoiding the need for transportation. Mixing hemp fibers, or to use the technical word hemp hurd, with lime and water creates strong bricks eight times lighter than concrete. Hempcrete is moisture-free, prevents mold, and is avoided by termites, making HempCrete a compelling option for interior use. It also makes excellent insulation, meaning using structural blocks and panels for pre-fab exterior walls reduces the need for additional insulation.
While this may sound intoxicating, HempCrete has 20 times less compressive strength than concrete, making it unsuitable in most load-bearing uses. While it might be a solution for some applications, we won’t be walking on streets or living in buildings made out of hemp any time soon.
These are just a few options for concrete alternatives. It should be said that concrete manufacturing itself is constantly being improved to lower emissions. Materials like sandcrete, timbercrete, papercrete, bamboo, recycled plastics, and more are all being used as an experimental building material in the search for a concrete alternative. At the end of the day, it always comes back to a problem of scale. It’s nearly impossible to fathom how much concrete is used globally every year, how much we’ve already used. Creating a product that can be used as widely and as often as concrete is not easy. While the challenge seems daunting, the incentive to innovate is paramount. Developing a viable concrete alternative is a scientific and economic endeavor second to none.