Cement Your Knowledge

One of the most famous and beloved films of 1985, Back to the Future, ends with the line, "Where we're going, we don't need roads." Well, it's the last week of 2020 now, and we still need roads. Most of us know that roads consist mainly of concrete, but I bet that most of us probably don't know much about concrete itself—how old it is, how it makes us feel, or some of its side effects.
         Concrete may seem an odd topic to discuss, but it is just so ubiquitous we should all think about it more. "Like language, concrete is a universal medium."1

         We use so much concrete today that we might think it's a twentieth-century innovation. It isn't. Let's go back to ancient Greece and Rome, an ancient world of times gone by.

Antiquity
The Mycenaeans didn't use cement, the active ingredient in concrete, first, but they did use it early. They built a palace at Tiryns, in modern Greece, with a concrete floor for their ruler in 1400–1200 BCE.2 In 2011, Greek archaeologist Angeliki Kottaridi discovered weapons from Alexander the Great's time at this site.3 It's therefore very possible that the Romans, often credited with discovering cement, learned about it most proximately from Greeks, their near neighbour.
         The Romans did take concrete to a new level. The Pantheon, built in the first century CE, has a 43.4-metre-wide freestanding concrete dome, still the largest of its kind in the world. At its best, Roman concrete was remarkably like Portland concrete, the stuff we use today. "Romans made the architectural mortars by calcining limestone at ~900 degrees Celsius to produce quicklime (CaO), hydrating the quicklime to form portlandite ((Ca(OH)₂), a trigonal calcium hydroxide) putty, and laboriously incorporating granular Pozzolane Rosse ash."4 Roman architect Vitruvius recommended using one part of lime and 15 to 20 per cent water by volume as the bonding agent for four types of concrete.5 Volcanic ash and rock were widely used: 18,000- to 36,000-year-old "fractals" of Roman concrete have been found in stone at the Campi Flegrei Caldera near Mt. Vesuvius, which famously buried Pompeii.6
         But after the fall of the Roman empire, Europeans did not resume using concrete until after the Renaissance. I'm going to talk about a possible reason why that might have been.

Artifice versus Nature
Forty also discusses the difference between artifice and nature. He calls concrete an apparently "trans-natural" material, more so than wood, hewn stone, or even brick.7 Yet, as he points out, this is a fallacy because every building material does come from nature and is substantially altered to be made into building material. Perhaps the fact that concrete is reinforced with steel has something to do with it. The compressive strength of concrete (ability to withstand pressure pushing in) is 17 to 70 MPa;8 steel reinforcement is what gives it tensile strength (ability to withstand stretching).
         It's also noteworthy that the German Autobahn was designed with concrete to take, in the words of architect Walter Ostvald, "the most noble connection between two points."9 It's sobering to think how similar the Nazis were to the Romans and to us, given that we often try "to overcome the contradiction between nature and technology."10 Of course, the Nazis were horribly wrong about how to do it, but we are, too—just in a different way. Forty points out that the phrase "to concrete over nature" has extremely strong negative connotations to many people. This goes right into one of the biggest issues relevant to concrete, and indeed, most things today: the environment.

Brown Grey Stuff
Concrete is an environmental travesty in general, but I'm only going to talk about two big drawbacks. First, there's the climate. The cement industry is the third greatest source of greenhouse gas emissions on earth, after only transportation and land use changes. It generated an estimated 1.51 GtCO₂e, or 5 per cent of all that was emitted globally, in 2016.11
         Second, there's the water use. Concrete is a very thirsty material. Water is used at every stage of the manufacturing process to make supplementary cementitious materials, admixtures, and cement itself, to quarry and crush rock, and for mixing and batching. Globally, concrete production involved 16.6 billion litres of water in 2012.12
         These concerns are probably not uppermost in most people's minds. We still use roads and more people will use them more as the lockdown eases. But I hope I've given you some food for thought.

Conclusion
Concrete is ubiquitous but little thought about. It's been in our buildings even longer than it has been in our roads.
         Most of us probably don't think about how the Romans used something very close to what we walk on to build the Pantheon and the Colosseum. That thought probably adds to the air of seeming unreality that surrounds it; if you get close to it, you may wonder how something so weird could be so pedestrian otherwise.
         But for something so little thought about and so necessary, it is an environmental travesty. It's a quiet climate change contributor and water thief.
         Not all of us regularly leave our residences, but many of us do. But it bears close thinking consider that the roads themselves changed the global environment.

Footnotes
1  Adrian Forty, 2012. Concrete and Culture: A Material History. London: Reaktion Books. Page 7.
2  Amelia Carolina Sparavigna, 24 October 2011. “Ancient concrete works.” arXiv:1110.5230. Retrieved 26 May 2020.
3  Malcolm Brabant, 12 April 2011. “Macedonians created cement three centuries before the Romans.” BBC News Online. Retrieved from https://www.bbc.com/news/av/world-europe-13046299/macedonians-created-cement-thr... 26 May 2020.
4  Marie D. Jackson, Eric N. Landis, Philip F. Brune, Massimo Vitti, Heng Chen, Qinfei Li, Martin Kunz, Hans-Rudolf Wenk, Paulo J. M. Monteiro, and Anthony R. Ingraffea, 30 December 2014. “Mechanical resilience and cementitious processes in Imperial Roman architectural mortar.” Proceedings of the National Academy of Sciences, 111(52): 18484–18489, at pp. 18484–5. DOI: 10.1073/pnas.1417456111.
5  Cited in Norbert J. Delatte, July 2001. “Lessons from Roman Cement and Concrete.” Journal of Professional Issues in Engineering Education and Practice, 127(3): 109–115, at p. 113.
6  Tiziana Vanorio and Waruntorn Kanitpanyacharoen, 7 August 2015. “Rock physics of fibrous rocks akin to Ro-man concrete explains uplifts at Campi Flegrei Caldera.” Science, 349(6248): 617–621.
7  Forty, supra, p. 39.
8  National Ready Mixed Concrete Association, 2003, 2014. Concrete in Practice Paper 35. Retrieved from https://www.nrmca.org/aboutconcrete/cips/35pr.pdf, 1 June 2020.
9  Quoted in Forty, supra, p. 63.
10  Ibid., p. 64.
11  Robbie M. Andrew, 26 January 2018. “Global CO₂ emissions from cement production.” Earth System Science Data, 10(1): 195–217. DOI: 10.5194/essd-10-195-2018. Johanna Lehne and Felix Preston (13 June 2018. Making Concrete Change: Innovation in Low-Carbon Cement and Concrete. London: Chatham House. Retrieved from https://www.chathamhouse.org/sites/default/files/publications/2018-06-13-making-... 1 June 2020) add International Energy Agency estimates bumping the total up to 8 per cent.
12  Sabbie A. Miller, Arpad Horvath, and Paulo J.M. Monteiro. January 2018. “Impacts of booming concrete production on water resources worldwide.” Nature Sustainability, 1(1): 69–76. DOI: 10.1038/s41893-017-0009-5.