Guide for the Use of Silica Fume in Concrete

Description

Silica fume, a by-product of the ferrosilicon industry, is ahighly pozzolanic material that is used to enhance mechanicaland durability properties of concrete. It may be added directlyto concrete as an individual ingredient or in a blend of portlandcement and silica fume. ACI Committee 234 estimates thatat least 120,000 metric tons (130,000 tons) of silica fume areused in concrete worldwide annually. Using this figure, morethan 6 million cubic meters (nearly 8 million cubic yards) ofsilica-fume concrete are placed globally each year.

Interest in the use of silica fume resulted from the strictenforcement of air-pollution measures designed to stoprelease of the material into the atmosphere. Initial use ofsilica 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) allowednew possibilities for the use of silica fume to produce highlevels of performance.

This document provides basic information on using silicafume in concrete. The document is organized as follows:•

Chapter 1 provides general information on silica fume;•

Chapter 2 describes the physical properties and chemicalcomposition of silica fume;•

Chapter 3 describes the mechanisms by which silicafume modifies cement paste, mortar, and concrete;•

Chapter 4 describes the effects of silica fume on freshconcrete;•

Chapter 5 describes the effects of silica fume onhardened concrete;•

Chapter 6 shows how silica fume has been used onactual projects. This chapter covers only a very smallnumber of applications because ACI Committee 234 iscurrently developing an additional document that willprovide detailed case histories of many more projects;•

Chapter 7 discusses specifications for silica fume andsilica-fume concrete;•

Chapter 8 presents a step-by-step methodology for propor-tioning silica-fume concrete for specific applications;•

Chapter 9 presents recommendations for working withsilica fume in field concrete;•

Chapter 10 summarizes research needs for using silicafume in concrete; and•

Chapter 11 presents all of the references from the other chapters