A close friend of mine from my days at the University of Waterloo’s Civil Engineering program is now completing his Master’s degree, with a focus on concrete. Jeffrey Ianni, P.Eng, describes a way to reduce carbon emissions in concrete production by up to 15%:
Concrete is the most used building material in the world. In the face of rising CO2 emissions due to human development and increasing global populations, any effort to find material efficiency can contribute to the solution for attaining global sustainability as a species.
In 2007, CO2 emissions from cement production represented 4.5% (377 million metric tons) of the global CO2 releases. Current concrete supply practice typically uses only two grades of aggregate: fine and coarse, causing “gap graded” or “poorly graded” concrete pours.
“Well graded” aggregates can save up to 15% of cement paste required. Therefore, aggregate selection can potentially reduce 15%*4.5% = 0.675% of global CO2 emissions.
Poor or gap graded aggregate requires more cement to fill in the gaps, and therefore requires more carbon in production. Credit Civil Engineer’s Forum
Gap Graded Aggregate
Well Graded Aggregate, credit Portland Cement Association
The above image represents what “well graded” aggregate looks like: a perfect amount of every size of stone from sand to pebble. Well graded aggregate can reduce porosity, permeability, and shrinkage, which improves performance and durability. It also makes for a more consistent finish, which I hear architects love. Furthermore, A reduction in cement content can lower crack vulnerability, making concrete less susceptible to corrosive damage and future repairs, which reduces the life-cycle CO2 costs of concrete and litigation costs due to failed concrete.
If you are an Architect on a project and you can’t get around using concrete, you can require your contractor to provide this kind of aggregate to reduce on emissions. Concrete with exposed aggregate finishes illustrate whether or not the pour was “well graded”; I would love to have included a photo of what “well graded” concrete looks like, but its use in the field is exceedingly rare due to the aggregate industry primarily supplying mostly two sizes of stone to contractors. This could conceivably be addressed by changing our energy codes.
Interesting, thanks!
A friend of mine has been working for many years on a technology to inject CO2 into concrete, essentially using it to make a better concrete. It’s been hitting some key milestones recently and it’s now being used on projects around the world.
http://carboncure.com/
Recent research has suggested that most concrete sequesters a large portion of the CO2 generated during its manufacture. The ongoing curing process creates carbonates.
http://arstechnica.com/science/2016/11/the-crumbling-cement-around-you-is-soaking-up-carbon-dioxide/
Grout mixtures were shown to sequester most of the CO2, which I’d imagine is somewhat related surface area and exposure.
I read about that as well, which goes to show that the issue is not black and white.
One of our favourite materials.
As with anything of interest it is good to have some perspective. Are CO2 emissions from concrete production important? Perhaps. Should we expend energy on this? Maybe.
Do we consider the usage of concrete in China important?
Do people generally realise that between 2011 and 2013 China used more concrete in those three years than the United States used in the ENTIRE 20th Century.?
It is worth thinking about.
https://www.washingtonpost.com/news/wonk/wp/2015/03/24/how-china-used-more-cement-in-3-years-than-the-u-s-did-in-the-entire-20th-century/?utm_term=.fedbc7620ae6
https://img.washingtonpost.com/wp-apps/imrs.php?src=https://img.washingtonpost.com/blogs/wonkblog/files/2015/03/cement.png&w=1484
What makes EcoSmart concrete different from conventional concrete is that it uses an optimum percentage of supplementary cementing materials to replace cement in the mix. Depending on the application and the SCM used up to 80 % of cement can be replaced with supplementary cementing materials. These materials are industrial by-products, so EcoSmart concrete is generally cheaper and can lower construction costs. In laboratory tests and field applications, EcoSmart concrete often outperforms conventional concrete in strength development and durability. It also offers significant environmental benefits, since each tonne of cement replaced by a supplementary cementing material reduces CO2 emissions by approximately one tonne.
http://ecosmartconcrete.com/?page_id=214
Simply put, displacing a portion of the Portland cement in concrete with waste products like fly ash will reduce the CO2 signature dramatically. This concrete takes longer to set in cold weather because the curing process produces less heat than standard concrete mixes. But its performance is often better.
One would think that Canadian engineers could figure out a way to go the extra km and displace the calcination heating fuel (sometimes they even burn old tires) with electric induction kilns using clean renewable energy, then patent the process. But of course we’re Canadian and prefer to sell off our raw resources and ignore R&D and innovation.