27-12-2012, 03:30 PM
Guide for the Use of Silica Fume in Concrete
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ABSTRACT
This report describes the physical and chemical properties of silica fume;
how silica fume interacts with portland cement; the effects of silica fume on
the properties of fresh and hardened concrete; recent typical applications
of silica-fume concrete; how silica-fume concrete is proportioned, specified,
and handled in the field; and areas where additional research is needed.
INTRODUCTION
General
Silica fume, a by-product of the ferrosilicon industry, is a
highly pozzolanic material that is used to enhance mechanical
and durability properties of concrete. It may be added directly
to concrete as an individual ingredient or in a blend of portland
cement and silica fume. ACI Committee 234 estimates that
at least 120,000 metric tons (130,000 tons) of silica fume are
used in concrete worldwide annually. Using this figure, more
than 6 million cubic meters (nearly 8 million cubic yards) of
silica-fume concrete are placed globally each year.
Interest in the use of silica fume resulted from the strict
enforcement of air-pollution measures designed to stop
release of the material into the atmosphere. Initial use of
silica fume in concrete was mostly for cement replacement,
along with water-reducing admixtures (WRAs). Eventually,
the availability of high-range water-reducing admixtures
(HRWRAs, often referred to as superplasticizers) allowed
new possibilities for the use of silica fume to produce high
levels of performance.