Customising microstructural and mineralogical characteristics of hydrated lime using biopolymers

The study of lime-based systems is vital to the design of new sustainable building materials. Air lime (calcium hydroxide, Ca (OH)2) is a binder that has attracted considerable attention for its ability to capture CO2 from the atmosphere, its low-cost and low-energy production process. Furthermore, Ca (OH)2 is an important phase of hydrated Portland cements, and lime-based mortars have shown high elasticity and the ability of self-healing. The performance of lime-based building materials can be enhanced by the addition of organic compounds that can modify the mineralogy and microstructure of Ca (OH)2. In this study, the effects of four biopolymers including starch, inulin, pectin, and calcium lignosulfonate, on the microstructure and mineralogy of lime have been investigated. Hydrated lime was produced by slaking quicklime in water. Two sets of hydrated lime batches were produced for each polymer: (i) the polymer was previously dissolved in water and subsequently mixed with lime, and (ii) the polymer was added as a dry powder to the already hydrated lime at the end of the slaking process. Characterisation of the batches was performed using scanning electron microscopy, X-ray diffraction and laser diffraction. Results indicate that biopolymers affect the nucleation and growth of Ca (OH)2 crystals. This influences the microstructure and crystal aggregation of hydrated lime in colloidal suspension, which will have important implications on the use of biopolymers in Portland cement applications and in the use of lime as a binder for mortars.