An approach for a rapid determination of the aging time of lime putty

A method for determining the effective and long aging time of lime putty, a feature which favors better quality of the corresponding lime mortar, is proposed. Different quicklime precursors were slaked under an excess of water for different times ranging from 3 to 66 months. Each of resulting lime putty was dehydrated by lyophilization and after characterized by thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) analyses, scanning electron microscopy (SEM), and surface area. Taking into account the impurity contents present in the starting quicklime, the mineralogical composition of each lime putty was determined from the weight loss related to the amount of adsorbed water and to the weight losses related to the decomposition of mineral phases present in the lime putty such as brucite, Mg(OH)2, portlandite, Ca(OH)2 and calcite, CaCO3, respectively. The total mineralogical composition of lime putties aged for a time higher than 12 months was close to the expected value of 100%, while such value resulted lower than 100% for lime putties aged for lower times. To justify such result, an incomplete hydration of the quicklime precursor must be considered for lime putties aged for lower times. The delayed hydration can be related to the presence of over burnt of some particles of lime present in the starting quicklime.