Carbonation of high-calcium lime mortars containing cactus mucilage as additive: a spectroscopic approach

Lime mortar is one of the oldest building materials. In Mexico, ingredients added to it to enhance its properties may include cactus mucilage, among others. We have evaluated the effect of adding, at two different concentrations, mucilage from Opuntia ficus-indica (prickly pear), Acanthocereous tetragonus (fairy castle cactus), and Hylocereus undatus (pitahaya or dragon fruit) in the accelerated carbonation of hydrated lime. The carbonation kinetics were followed by spectroscopic techniques such as Fourier transform mid-infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, energy-dispersive X-ray (EDX) spectroscopy, and scanning electron microscopy (SEM). The results showed that mucilage promoted carbonation, functioning as a positive catalyst. Analysis of the infrared (IR) absorption corresponding to the in-plane asymmetric stretching $${v}₃$$ of the $${\text{C}}{\text{O}}₃^2-$$ anion indicated that the carbonation rate increased with the percentage of mucilage, being directly dependent on the concentration of Opuntia and Acanthocereous mucilage at both concentration levels tested. SEM observations confirmed that the inclusion of mucilage promoted the creation of the aragonite polymorph of calcium carbonate (CaCO3).