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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.
Concrete contributing to CO2 has been known for a while - that is why at this point there are a lot of solutions to that problem, including concrete variants that sequester or even absorb CO2.
Notice how old some of the results in that search are...
If CO2 is really a problem, local governments will seek to adopt some of those ideas.
"There is more worth loving than we have strength to love." - Brian Jay Stanley
Not sure how this is suddenly news. It's been called out since the very first IPCC report, and known long before that.
This is part of why nuclear power and hydroelectric power aren't exactly green. Far better than fossil fuels, sure, but much worse than an equivalent solar or wind farms in terms of CO2 release. The amount of concrete used in both nuclear plants and hydroelectric dams is massive. It dwarfs the pads for solar panels and wind turbines.
But like everything, it's complicated. Turns out that over decades, concrete actually absorbs a large amount of CO2. It seems to be close to half that released when making it. If carbon capture could be used during production, over its lifetime, concrete could become carbon negative. And alkali-activated cements seem to be on the horizon, taking industrial CO2 byproducts and making them into concrete-like structures.
Velociraptor = Distiraptor / Timeraptor
Concrete is made with cement and aggregate. Cement is not the same as concrete. The two are not interchangeable.
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
Let's go back to building with wood and replicate the 1906 fire in San Francisco...
Well, instead of wood, we could try sticks and straw.
But then we might get a knock on the door:
"Little pig, little pig, let me come in."
"No, no, by the hair on my chiny chin chin."
"Then I'll huff, and I'll puff, and I'll blow your house in."
Personally, I'll make my house of bricks.
Schroedinger's Brexit: The UK is both in and out of the EU at the same time!
Obviously the solution is to tax cement.
There's another problem. Global concrete production is around 4 Billion tons per year. Every year, we're adding 4 Billion tons to the weight of the earth.
Now, the earth is very heavy -- about 6,000,000,000,000,000,000,000 tons. But still, adding 4 Billion tons every year will eventually cause problems.
Portland cement absorbs CO2 while setting... Just not as much as it takes to make the clinker using fossil fuels. With solar kilns it could be close to neutral
It is far from a given that cement production has to release as much CO2 as it does now. I am in the building world, I will assure you nobody is giving up concrete, but there is a lot of research going into reducing the carbon footprint of cement, along with increasing its strength and decreasing its weight. Most concrete in this world is used to support other concrete, affordably reducing weight would go a long way to reducing demand.
https://en.wikipedia.org/wiki/...
It is what the pyramids were made from, pour-able limestone.
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.
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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.
That last paragraph contained spoilers, so if you don't want spoilers go back and don't have read it.
There are several ways to fix it.
There are ways to replace the portland cement.
There's also ways to SEQUESTER CO2 in concrete as well.
There are also forms of concrete that actually ABSORB CO2.
Chas - The one, the only.
THANK GOD!!!
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.
That last paragraph contained spoilers, so if you don't want spoilers go back and don't have read it.
Because the cement itself is carbon neutral.
Reactions
CaCO3 ==> CaO + CO2
CaO + H2O ==> Ca(OH)2
Ca(OH)2 + CO2 ==> CaCO3 + H2O
So for each molecule of cement you make, you do produce 1 molecule of carbon dioxide. Then to use the cement, you add a molecule of water. And then over time, the result reacts with carbon dioxide (removing the carbon dioxide that was released when the lime was made) and releases a molecule of water.
The only non-neutral production of CO2 from making cement is that from whatever source of energy you use to heat up the calcium carbonate to produce the lime.
Doing a bit of research, it looks like 60% of the carbon dioxide released is from the chemical reaction and 40% from the heat used to drive the reaction. Since the 60% from the reaction will be reabsorbed by the cement, we can ignore it. So the actual amount of CO2 due to cement production isn't the 8% the article mentions, but something closer to 3.2%.
You just contradicted yourself there. That minimum 1,5" / 3" is to protect the passivation layer on the steel (whether you realize that or not). The thicker the layer, the longer that carbonation takes. In ideal conditions, carbonation depth (in mm) progresses at a rate roughly: (-3,59 + 9 * W/B) * sqrt(t) where W/B is the water/binder ratio and t is time. However, a number of factors can significantly accelerate carbonation, so large margins need to be allowed for.
That last paragraph contained spoilers, so if you don't want spoilers go back and don't have read it.