The Romans had a self-healing concrete lasting for 1 thousand years

Hot mixing: Mechanistic insights into the durability of ancient Roman concrete

Looks like the ancients had a better concrete than us, one that self-heals. But according to the guardian Concrete is the most destructive material on earth But depending on whose criteria you use the results differ considerablky: However even using the worst cae I could find that of 1 metric ton of cement produces 1 metric ton of CO2 doesn’t even bring you to the lowest rung on the ‘Human and Natural sources of CO2 chart’ below, so 6-7% of the world emission is meaning less. What they are quoting alludes to all CO2 sources and this doesn’t even come close. If you smell a rat you would be correct.

Concrete use is a 55 biullion/year industry generating some 4500 metric tons of CO2 world wide.

One shortcoming of most of those estimates is that they report only a part of the cement industry emission, the one related to the calcination process. However, IEA estimates the proportion of the process emission to be two third [8] while Ecofys [9] estimates it at 55%. Data from our GNR database [10] confirms the 2/3. On that basis, total emission from the cement industry can be estimated between 6-7% of world emission.

What s the 6-7% CO2 standard? Likely it’s a fraction of the world total of 4500 tons, in other words, so what?

Assuming 1 metric ton of conrete produces 1 metric ton od CO2  then 4500 metric tons of cement equals 4960 US tons of CO2 so:

4960 US tons x 2000 lb/.ton x 1 / 44 lbs / mole x 359 ft3 / mole (Std conditions) = 8.097 E7 ft3 CO which doesn’t een hit the lowest rung on the Human and natural sources of CO2.chart 

Beware of enviromentalists using percentages to scare you on global warming. The whole of climate change is an elaborate scam to extract billions of dollars out of the gullible.