Polymer-Concrete Composites with CO2 Curing

The untreated
(PET and PVC) and treated (TPET and TPVC) plastic waste specimens
were used as fillers for the dicalcium silicate cement base to prepare
the proposed polymer–concrete composites. Different weight
ratios, ranging from 0 to 10 wt %, were individually formulated through
the mechanical mixing of fillers in the cement base. Then, specimens
of the obtained composites and blank cement were poured into molds
for curing. The curing process was performed in the carbonation chamber
where the pressurized CO₂ gas inlet at about 0.3 MPa was
purged into the cabin at 65 °C and 60% RH for 24 h. The blank
dicalcium silicate reference sample and polymer–cement composites
were cured using the carbonation process. It is proposed that CO₂ reacts with the prepared dicalcium silicate through converting
the gas-phase CO₂ into carbonate (CaCO₃). Such
conditions are able to precipitate the hard carbonate which is the
source of improved mechanical properties, in addition to preventing
the further release of CO₂ gas in air and reducing the
carbon footprint. With the warm and humid environment inside the used
chamber, CO₂ gas is first converted into aqueous phase
through dissolution to carbonic acid (H₂CO₃),
which is ionized to bicarbonate (HCO₃^–) and then to carbonate anions (CO₃^2–) and protons (H⁺) reaching neutralization. The prepared
dicalcium silicate (Ca₂SiO₄) is simultaneously
dissociated, giving calcium cations (Ca²⁺) and solid silica
gel (SiO₂). The curing output is precipitated through the
reaction between Ca²⁺ and CO₃^2–, yielding the hard calcium carbonate, as shown in eqs 2–5; the overall reaction is represented in eq 6.^{52 (link)−54 (link)}