These percentage are based on what is produce during the year while existing cement things that are picking up CO~2~ were fabricated in the span of many decades.

trivial example to illustrate what i am saying here

...
supposed we are making each year one new building for 100 years in a row.
After that time, we have 100 buildings picking up CO~2~ from the air but in that year we create only one new building.
Now, we calculate total amount of CO~2~ picked up by 100 building divided by CO~2~ emitted to build this new single building.

This is how misleading this calculation is.

in fact if we were to make new buildings at a steady pace for long enough, we would eventually reach "kinetic equilibrium" in which the rate of CO~2~ picked up is equal to the rate of CO~2~ emitted : so we would reach 100% of annual CO2 production. (equilibrium)