Abstract
Carbonic anhydrase (CA) catalyzes the hydration of CO
2
to HCO
3
−
at rates that could enhance the carbonation of the calcium hydroxide reservoir in cement-based binders. In practice the reported magnitude of this enhancement varies considerably among the few studies that have examined it, and the procedures for translating raw thermogravimetric (TG) mass-loss measurements into reported “equivalent CaCO
3
” contents are rarely stated explicitly. Here we report a preliminary TG-based comparison between portland cement pastes hydrated for 3-7 days with: (i) no enzyme, (ii) CA, and (iii) cross-linked enzyme aggregates of CA (CLEA-CA), at CO
2
concentrations from 0.04% to 1.0%. Equivalent-CaCO
3
content is computed by an explicit tangent-line construction on the TG curve that excludes the C-S-H bound-water background; this method gives roughly half the values of an endpoint-difference method that omits baseline subtraction. We find that CA does not enhance CaCO
3
formation in cement paste at any of the CO
2
levels studied, while CLEA-CA produces a clear enhancement (+20% over the enzyme-free control) at the highest CO
2
concentration (1.0%); the enhancement at lower CO
2
is weaker and non-monotonic. The data are consistent with the hypothesis that CLEA-CA are more stable and enable measurable product formation in the high-pH, mass-transfer-limited cement matrix. The result motivates additional engineered-CA work to extend this enhancement to atmospheric-CO
2
curing conditions.