Silica Fume in High Quality Concret - A review of Mechanism and Performance.

The influence of silica fume (SF) on performance of cementitious systems like concrete is due to physical (i.e. improved particle packing) and chemical i.e. pozzolanic reaction) effects. Since silica fume particles are much smaller than cement grains they will pack in the voids between cement grains. In this way the system is densified already at the time of setting. SF is an active pozzolana that leads to strength increase. When SF is not used to obtain equal strength at higher w/cm than reference, but to obtain high performance concrete with lower w/cm including plasticizers, no durability problems should occur unless adequate precautions are not taken to prevent cracking from autogenous shrinkage and high heat of hydration. In general, the use of SF in concrete mixtures reduces the permeability to waterborne aggressive ions (e.g. alkalis, chlorides, sulfates), thus mitigating the potential for sulfate attack, alkali-aggregate reactions, and corrosion of reinforcing steel in concrete.