Fairy tales on CO2 cement reabsorption

I want you to react to some biased arguments that are often opposed to the development of Geopolymer Concrete. In a recent blog published by the WORLDBANK, go to

one can read the following comment to the article that favored Geopolymer concrete:

“Not really all that amazing.
The CO2 emissions from cement production (from calcination, ie, not from the fuel used) are all reabsorbed by the cement over the decades that it stands there as a building.”

This is a fairy tale. I posted following comment:

“Tim Worstall is wrong for at least three reasons.
1) Yes, it is known that Portland cement concrete reabsorbs CO2, but this phenomena occurs only on the surface of the concrete blocks (maximum 1-2 centimeters deep).
2) This CO2 absorption happens very slowly and it would take centuries to recarbonate concrete blocks. There are historical remains of lime-based concrete that still contain uncarbonated lime after more than 1000 years. This means that the kinetic of CO2 emission during Portland manufacture is 1000 times faster than its reabsorption.
3) Concrete specialists avoid CO2 absorption because it is deleterious to Portland cement concrete. Indeed, Carbonation lowers the pH of the concrete and by so doing weakens the steel bars that become susceptible to rust (main cause of concrete degradation).”

Can you post your own comments also?

Prof. Joseph Davidovits