Mortar properties obtained by dry premixing of cementitious materials and sand in a spout-fluid bed mixer

This study examines the efficacy of a pneumatic, dry premixing process for producing commercially acceptable, ternary-blend mortars, using less cementitious material. Data are presented comparing flowability, compressive and flexural strengths, drying shrinkage, and pore size distribution in the mortars using dry, premixed material with that prepared conventionally in a small-scale, high-shear, rotary mixer. A second generation, spout-fluid bed mixer was developed for dry premixing of sand and cementitious materials which is capable of being scaled to industrial size. This advance provides uniform particle distribution, improves the particle packing density leading to more reproducible mixes, and produces mortars equivalent to those produced with high shear, rotary mixers.Dry premixing allowed the production of commercially acceptable ternary-blend mortars using less cementitious material. At a sand-to-binder ratio of 3.2:1, the compressive strength of the dry premixed mortars was about 10% higher than that of the small-scale, high shear, rotary mixed mortars of the same composition. Other properties of the mortar were also positively affected, including a decrease in the shrinkage, and an increase in the workability.