1. Cement and Concrete

Continuing with our look at “the four pillars” of modern civilization I want to talk about the numero uno, cement and concrete.

Concrete is the world’s most ubiquitous and most important building material. The Romans were expert concrete engineers. Some of their remarkable constructions are still standing. Things like grouts, stuccos, and mortars have been around since antiquity. The versatility of modern concrete allows it to be used to make roads, bridges, canals, piers, and all types of buildings. It can be poured in place or pre-cast. It can be used for floors, walls, ceilings, counters, roofs, retaining walls, foundations, benches, tables, and too many other things to list. It is lightweight, durable, fireproof, and a good insulator. We make pipes out of the stuff and those pipes bring us fresh water and carry away our wastewater. It can be shaped, molded, colored, and finished in an astonishing variety of ways. There is no modern world without concrete.

Concrete is actually a “greener” choice than other materials because it can be made locally and thus avoid transport costs (both economic and environmental). It’s easy to work with and does not require particularly specialized skills and tools. Homeowners can do amazing stuff with concrete with a modest investment. Obviously there are applications of concrete that demand engineering and construction expertise but that’s true of any building material. Rough-framing a house with 2 x 4s is accessible to many ordinary folks—building a wooden boat less so.

The problem with concrete is cement. Cement is the necessary ingredient. It’s actually only a small part of the mix. The rock, sand, and gravel (“aggregate”) is the biggest part with water taking up the rest. The cement is the binder that holds it all together and thus the most important part. Concrete is formed when the mix of cement, aggregate, and water “cures” and hardens. It doesn’t dry. When the mix loses water too fast the result is brittle. Water molecules are taken up by the cement and help to form the crystalline matrix that results in the final product. Concretes can take many years to fully cure.

Cement is made from limestone, mostly. Silicates and oxides, primarily from clays, are the other components. The problem is that this stuff has to be heated to very high temperatures. Not only does this kilning process use large amounts of fuel it also releases carbon dioxide as part of the process. Limestone is CaCO3 and when it is cooked it forms “lime” or calcium oxide (CaO). You can see that the leftover stuff is CO2! Ain’t chemistry grand?

Cement is made when limestone and the clay minerals are baked together to form lumps called “clinker.” The clinker is then crushed and gypsum (calcium sulfate, CaSO4) and other additives are mixed in. The stuff is ground to a powder much finer than flour. If you’ve ever gotten Portland cement on your hands or clothes you know what that’s like!

Thomas Edison was a big believer in concrete as a building material and he did a lot of work to improve the kilns and the kilning process to make the manufacturing of cement cheaper and more efficient. He also invented the modern rotary crusher that all cement plants use. He was remarkable in that he concerned himself with so many different things. The light bulb was a tiny part of his many accomplishments.


Here’s the rub. Making cement is very energy intensive. The industry is responsible for, as you can see, a large chunk of greenhouse gas emissions.

On the one hand we have a fabulous building material that can be used for almost anything all over the world by almost anyone. On the other hand we have a key ingredient that requires a highly polluting industrial base to create.

This is the dilemma we face as a civilization. So, we have to come up with alternative ingredients that require less energy and we have to come up with better ways to heat the stuff we already use. Many of these technological problems are solvable. Engineers love these kinds of challenges. I’ve no doubt that we will see many innovations in the coming decade that will “decarbonize” the industry. Unfortunately technological innovation is only one part of the puzzle. The economics have to work, too, and the adoption of new techniques and practices will take time. Environmental problems are social and political problems, not just scientific ones.

Climate change is an obvious existential threat. It will take a global effort to work on it. Mostly those efforts will involve education, awareness, and a willingness to take on a personal responsibility for “doing your part.” And it won’t be easy. Our modern, high-energy, high-consumption way of life will have to evolve. We aren’t going to like it, but we don’t like lots of things but do them anyway because they need to get done.

All this to say be suspicious of the techno-optimists and techno-utopians who claim that science will solve all our problems. It won’t. The problems are ours, created by our values and our institutions. We can only change those things by working together to make a better world, by recognizing our limitations and our past mistakes. Humility and empathy are virtues we are all capable of, and those are the things we need going forward. And curious and creative people who like to learn, grow, and tackle tricky things!

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