An AFM-SEM investigation of the effect of silica fume and fly ash on cement paste microstructure

Atomic force microscopy (AFM) was used to observe particle shape and surfac e texture details of normal portland cement and supplementary cementing mat erials (silica fume, low-calcium fly ash, and high-calcium fly ash). The la tter materials mixed with cement were examined after prolonged hydration. S ignificant innovative information on particle shape and hydrated paste micr ostructure was obtained. Conventional microscopy techniques, such as scanni ng electron microscopy (SEM), cannot provide such detailed images and surfa ce texture characteristics of the fine materials (especially silica fume) a nd of the product microstructure. AFM showed, for the first time, that sili ca fume particles are primarily composed of two complimentary parts (hemisp heres or semicylinders). Nano-size particles were found in all materials. A relatively smooth product surface was observed in the hydrated cement past e. The hydrated surface of the addition-cement pastes presented small spher oid bulges, giving an additional roughness as was measured by AFM. A suffic ient correlation of this microscopical quantitative information with macros copical engineering and durability properties of cement products is also pr esented. (C) 1999 Kluwer Academic Publishers.