Scientists replaced 40 percent of cement with rice husk cinder, limestone crushing waste, and silica sand, giving concrete a rubber-like quality, six to nine times more crack-resistant than regular concrete. It self-seals, replaces cement with plentiful waste products, and should be cheaper to use.

[u/mvea]

https://newatlas.com/materials/rubbery-crack-resistant-cement/

[u/uslashuname]

It captures 43% of the CO2 created during conversion per https://www.sciencedaily.com/releases/2016/11/161121130957.htm

[u/ahfoo → u/uslashuname]

Depends on the time frame. Concrete is a carbon sink, it densifies as it ages by absorbing CO2 from the atmosphere. The number you will arrive at will depend on how long you are assuming the concrete will be in place. It's not a fixed number.

"What most people do not realize is that the release of carbon dioxide from calcination in the manufacture of portland cement may also be part of a cyclic process and is partially carbon neutral in smaller timeframes such as decades and may be fully carbon neutral in longer timeframes."

https://www.cement.org/for-concrete-books-learning/concrete-technology/concrete-design-production/concrete-as-a-carbon-sink

Furthermore, concrete has a very low embodied energy score mostly because it is commonly sourced very near the location it is used. Transportation costs are part of the embodied energy calculation used to compare building materials and concrete is one of the lowest scores with locally sourced wood being the only construction material with less embodied energy. Most timber is not locally sourced by a long shot. Typically it is shipped thousands of miles before use and this is part of the calculation of embodied energy. Only locally sourced and milled wood has a lower embodied energy score than concrete --again, only locally sourced wood, not wood in general but only and exclusively locally sourced wood. Locally sourced wood is rare.

[u/mercury1491 → u/ahfoo]

PCA literally exists to promote concrete use. It isn't the most unbiased source.

[u/ahfoo → u/mercury1491]

Okay, go on. How about the embodied energy score? Is that a product of the PCA?

Also. . . here is another independent Danish researcher emphasizing the point made by PCA.

"The existing models for calculating carbonation do not take into account that the concrete is crushed and recycled after use. Consequently, the contribution of the cement and concrete industry to net CO2 emissions is strongly overestimated. This overestimation has a significant influence on CO2 policy; on the criteria for environmental labelling; and on the selection of materials based on principles of environmentally correct design. A comparison of the environmental impacts from different building materials (e.g. concrete versus wood and steel) is at present unfair because of the lack of documentation of the CO2 uptake in concrete."

http://www.dti.dk/_root/media/21043_769417_Task%201_final%20report_CBI_Bjorn%20Lagerblad.pdf