Impact of the slaking method on the mineralogy of natural hydraulic limes and its effects on mortar mechanical properties

The influence of slaking on the properties of natural hydraulic limes (NHL) has been little studied so far. Laboratory-manufactured limes have been produced to investigate the mineralogical changes that occur during the slaking process. Two different hydration methods have been compared: conventional slaking, by adding water in a 1:1 water:CaO ratio, and passive slaking, by exposure of the quicklimes to a relative humidity of 60 ± 5 % and 80 ± 5 % RH. The mineralogical evolution of limes was monitored under different slaking conditions using the X-ray diffraction Quantitative Phase Analysis. The resulting NHLs have been used to produce mortars, to assess the influence of the slaking conditions on their mechanical strength. The results show that passive slaking at relative humidities higher than 60 % ensures complete transformation of CaO into Ca(OH) 2 , and gives place to natural hydraulic limes with comparable, or even slightly improved properties to those conventionally slaked. • Faster conversion of CaO into crystalline portlandite under conventional slaking • Conventional slaking generates up to 10% of calcium aluminate hydrates • Exposure of NHL quicklime to 80% RH ensures total though slower hydration of CaO • Passive slaking at 60% reduces pre-hydration of hydraulic phases • Mortars made with NHL slaked under 60% RH display higher mechanical strengths