Evaluation of Atmospheric CO2 Sequestration by 50-Year-Old Concrete Structures Based on 14C and 13C Measurements

Both δ13C and δ14C have been proposed as tracers for CO2 origin in carbonated construction materials.

“Both 𝛿 ¹³C and 𝛿 ¹⁴C have been proposed as tracers f or CO2 origin in carbonated construction materials [33, 34].”

It is not always the case that δ13C values of carbonates formed during carbonation increase; some studies report that the δ13C value of the carbonated material decreases if carbonation occurs in ambient air.

“It is also not always the case that 𝛿 ¹³C values of carbonates formed during carbonation increase as shown in our experiments [38]. Instead, some studies report that the 𝛿 ¹³C value of the carbonated material decreases if the carbonation occurs in ambient air [33, 34, 41].”

During natural carbonation in ambient air and open systems, the heavier 13C isotopes are depleted in the solid phase.

“While accelerated aqueous carbonation at high CO2 concentrations in closed systems leads to an enrichment of the heavier ¹³C isotope in the solid phase, during natural carbonation in ambient air and open systems, the heavier ¹³C isotopes are depleted in the solid phase [33, 34, 41].”

Accelerated aqueous carbonation at high CO2 concentrations in closed systems leads to an enrichment of the heavier 13C isotope in the solid phase.

“While accelerated aqueous carbonation at high CO2 concentrations in closed systems leads to an enrichment of the heavier ¹³C isotope in the solid phase, during natural carbonation in ambient air and open systems, the heavier ¹³C isotopes are depleted in the solid phase [33, 34, 41].”

Isotope methods allow for a fair and transparent assessment of the carbonation degree of recycled concrete when limestone was included as an aggregate or filler.

“In this case, isotope methods allow for a fair and transparent assessment of the carbonation degree of recycled concrete [33, 34].”