There has always been water content in concrete. In fact, concrete strength and durability is partially defined by the proportion of moisture content to cement. Quarries blast limestone and grind it with clay to create cement, concrete’s binding agent. Manufacturers mix cement powder with water, and the resulting calcium-silicate-hydrate bonds other particulates, like sand or gravel, to make the concrete on which billions of humans tread.
The world’s concrete production volume is an environmental concern. Global consumption of concrete now runs to roughly 30 billion tonnes a year, built on close to 4 billion tonnes of cement. Cement manufacturing alone accounts for approximately 8 percent of global carbon dioxide emissions, according to Carbon Brief, and demand from China and India, the two largest cement producers, continues to drive global output upward.
That’s a lot of carbon dioxide for one building material.
The Composite Truth
Believe it or not, concrete has an environmental upside. Concrete is resistant to temperature fluctuations. It creates thermal mass which can store warmth and cold. Concrete reflects heat and diminishes the urban heat island effect.
Once properly established, concrete foundations retain durability while windows, insulation and plumbing need to be replaced. “Rome wasn’t built in a day,” because the Romans did a thorough job installing their concrete structures. Travelers visit many of them to this day.
Durability and strength make concrete a staple building material for those who expect their structures to endure. The concrete production process has an intense carbon footprint, but the structures it creates last much longer than those made of other more perishable building materials. It’s a trade-off: strength, durability and endurance versus a carbon cost so large that, if the cement industry were a country, it would rank as the world’s third-largest carbon dioxide emitter, behind only China and the United States.
The Ecological Point of View
Hope may lie in human innovation. Several companies have worked to develop low-carbon cements. Novacem developed a cement production process using magnesium oxide, designed to absorb more carbon dioxide than it emitted (known as a negative carbon footprint); the company was liquidated in 2012 and its technology was acquired by Calix. Calera explored filtering carbon dioxide emissions through seawater to create a chalky carbonate, mixing that cement byproduct with aggregate and water to create concrete, a process that sequestered carbon emissions and bypassed the industrial heating step of conventional production. Calera wound down that work in 2015, and former employees later revived the approach at Fortera, which captures carbon dioxide directly from cement kilns. Calix produces cement in a reactor by calcinating dolomitic rock with superheated steam, and the CO2 emissions can be captured by a separate CO2 scrubbing system. Geopolymer cement utilizes waste materials such as fly ash, bottom ash (from the power industry), slag (from the steel industry), and concrete waste to create alkali-activated cements. Each option contains challenges which need to be resolved. However, it would seem that concrete production can include ecological cement mixtures.
Concrete is partially recyclable, too. According to Concretethinker.com, “Most concrete in urban areas is recycled as fill or road base and not placed in landfills.” Driveway replacement at the end of a slab’s service life could generate recyclable materials which could be utilized as recycled aggregates in future road paving projects all over the world.
Concrete materials can also be locally-produced all over the world due to the prevalent availability of its components. This has payoffs both in terms of local economy, and in reducing carbon contributions caused by current shipping practices. If sustainability carries an economic component, one could scarcely argue against the prospect of employing locals to produce local concrete for local use.
And on each and every job site, best installation practices mean that each concrete slab will last to its maximum capacity. Something as simple as Wagner’s Rapid RH® not only protects your reputation as a builder, but also protects the local environment by ensuring each concrete slab and flooring installation can be resistant to moisture-related breakdown through accurate RH testing.
Global Afterthought
Signatories to the United Nations Framework Convention on Climate Change (UNFCCC) are mandated to protect the climate system “… on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities.” The Kyoto Protocol set binding emissions targets for developed nations, but its second and final commitment period closed in 2020, and the Paris Agreement now governs the global response. Rather than assigning targets from the top down, Paris asks each country to set its own nationally determined contribution. The underlying tension remains, because global reductions still depend on participation from both developed nations (such as the United States) and rapidly developing ones (such as China and India), where cement and concrete demand continues to grow.
If humanity reduces its global greenhouse gas emissions, perhaps success begins with the individual. If so, a simple (but profound) change in consumer decisions, such as which type of concrete to install and how to best install the concrete of choice, may drive the developed world into a new concrete era.
