Effects of fly ash microsphere on rheology, adhesiveness and strength of mortar

This paper presents a study on the effects of fly ash microsphere (FAM), a superfine spherical-shaped fly ash that can fill into the interstitial voids in cement, on the fresh and hardened properties of mortar. Using a wet packing method to measure the packing density of the solid particles in mortar, it was found that the addition of FAM could effectively increase the packing density and decrease the voids volume. This would, at the same water content, increase the amount of excess water for forming water films coating the solid particles to improve flowability, or at the same flowability requirement, allow the water/cementitious materials ratio to be lowered to increase strength. Furthermore, the water film thickness was found to play an important role in the rheology, adhesiveness and strength of mortar, and is therefore a key parameter to be considered in the design of mortar and concrete mixes.

► Addition of fly ash microsphere to fill voids between cement grains can increase packing density and water film thickness.
► The increase in packing density would allow the W/CM ratio to be lowered to increase strength.
► The increase in water film thickness would improve flowability and rheology.
► Using a new test method, it was found that the addition of fly ash microsphere can increase adhesiveness.