X-ray absorption studies of drying of cementitious tile adhesive mortars

X-ray absorption measurements have been applied to studying film formation at the exposed surface during the drying of cementitious tile adhesive mortars as a function of ingredients and mixture proportions. Preliminary observations suggested that in addition to a drying front, concurrently, a densification front is observed proceeding from the exterior of the specimens inward. Due to the extremely high viscosity of the pore “solution” in these mortars, an analysis based on Stokes equation actually suggests that some of the smaller cement particles will be “carried” along with the drying pore solution to the top surface of the specimen where they are sequentially deposited. To verify this hypothesis, further experiments were conducted using either a coarse cement or a fine limestone as a total replacement for the commonly used cement. The X-ray absorption results are further supported by concurrent mass loss measurements on equivalent specimens for each experiment and by particle size distribution analysis of the final dried limestone/silica sand system as a function of depth.