154132Silica Fume

Silica fume has been widely used in HPC for structural purposes and for surface application, and as repair materials in situations where abrasion resistance and low permeability are advantageous. When silica fume is used, the following specifications are to be considered carefully. SO3 content should be controlled below 4.0%. SiO2 content directly determines the reactive ability of silica fume, so its content should be controlled over 70% for ensuring the development of high performance of HPC with silica fume added. The loss of ignite of silica fume is closely related to the water demand for HPC, thus the less the content, the better. According to ATSTM C 618, loss of ignite must be no more than 10.0%. In addition, pozzolanic activity indicator of silica fume has a great impact on its reactive properties. At least 75% should be ensured.

The use of silica fume to produce HPC increased dramatically in the 1990s. Both laboratory and field experiences indicate that concrete incorporating silica fume has an increased tendency to develop plastic shrinkage cracks. Thus, it is necessary to quickly cover the surfaces of freshly placed silica fume concrete to prevent rapid water evaporation.

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