Cement is the Source of About 8% of the World's Carbon Dioxide Emissions (bbc.com)

Concrete is the most widely used man-made material in existence. It is second only to water as the most-consumed resource on the planet. But, while cement -- the key ingredient in concrete -- has shaped much of our built environment, it also has a massive carbon footprint. From a report: Cement is the source of about 8% of the world's carbon dioxide (CO2) emissions, according to think tank Chatham House. If the cement industry were a country, it would be the third largest emitter in the world -- behind China and the US. It contributes more CO2 than aviation fuel (2.5%) and is not far behind the global agriculture business (12%). Cement industry leaders were in Poland for the UN's climate change conference -- COP24 -- to discuss ways of meeting the requirements of the Paris Agreement on climate change. To do this, annual emissions from cement will need to fall by at least 16% by 2030.

Comments

That's a trade I'm willing to make.

[olsmeister]

If you're looking to cut CO2 emissions, please look elsewhere. Concrete is pretty much essential to life as we currently know it in the civilized world. Let's go back to building with wood and replicate the 1906 fire in San Francisco...

Re:That's a trade I'm willing to make.

[Rei]

Modern concrete includes the seeds of its own demise - its steel rebar. The steel is protected from corrosion by the highly basic environment of the concrete, but the slowly cement begins being converted back to limestone by absorbing carbon dioxide from the atmosphere. This lowers the pH. When the pH drops too much near the steel, it begins quickly rusting, expands nearly tenfold, and the concrete spalls out. Indeed, minimum wall thicknesses in many places have nothing to do with required compressive strength, and are rather just to protect the steel.

FRP (fibre-reinforced plastic) rebar, by contrast, not only tolerates a more neutral pH, but actually prefers it. It's not a direct drop-in replacement (it bears tensile loads, but is poor (esp. when not using CFRP) at shear and compressive loads). But you can use small amounts of stainless rebar wherever you can't use FRP. Also, while you can bend FRP rebar along gentle curves, it can't handle sharp curves; you order pre-shaped curves for that. On the other hand, it's much easier to work with than steel - it's lightweight and you can cut it with a simple reciprocating saw.

FRP rebar doesn't rust, but its strength does decrease with time. However, most of its strength loss is early on, and the rate of loss slowly declines with time. Among FRP rebar, fibres are generally (from worst to best): GFRP (glass), BFRP (basalt), AFRP (aramid), and CFRP (carbon). CFRP is awesome stuff... suffers almost no degradation in any conditions (even less than its plastic binder)... but it's currently very expensive. IMHO, BFRP is the best balance of price versus mechanical properties. As for binders, epoxy binders are best. Sometimes you see uncoated products (I've even seen a structure entirely reinforced with just bare roving), but that's not ideal for longevity.

Leftists

[Anonymous Coward]

Leftists really do want us living in Mud Huts.

Re:Leftists

[Rei]

I assume that they were talking about wood, which isn't mud. But you can most certainly can reduce the carbon footprint of concrete construction itself. My home uses a pozzolanic mix, with about half of the cement replaced by basalt dust, and most of the steel replaced by basalt fibre rebar.

Pozzolanic concrete is slower to set, but has more long-term durability. Chemically, it harkens partially back to Roman concrete. There are lots of different pozzolans besides basalt dust, including volcanic ash, coal fly ash, activated clays, etc.

Re:carbon capture

[hey!]

Well, there is no end to "cost is no object" solutions to greenhouse gas emissions. The problem is that in the real world, cost *is* an object, and a very important one.

This is why cap and trade is a viable, market oriented solution to greenhouse gas emissions. Normally the 182 kg of CO2 that's emitted when I produce a ton of concrete to sell to you isn't part of our transaction. Under cap-and-trade, CO2 reduction becomes a profit center, because if I can reduce my emissions below some reasonable target (e.g. down to 150 kg), I can sell the surplus to someone who can't meet the target.

The problem is that cap-and-trade is not politically viable, because people invested in technology that can't be upgraded are currently dumping their pollution for free.