Question

How to measure specific gravity lab test for silica fume?

Answer 1

The American Concrete Institute (ACI) defines silica fume as “very fine non-

crystalline silica produced in electric arc furnaces as a by-product of the production

of elemental silicon or alloys containing silicon” (ACI 116R). It is usually a gray

colored powder, somewhat similar to portland cement or some fly ashes. Figure

1.1 shows a typical silica fume as it appears after being collected from a furnace.

FIGURE 1.1.

As-produced silica

fume. This is what the

material looks like

after it is collected.

Silica fume is usually categorized as a supplementary cementitious material. This

term refers to materials that are used in concrete in addition to portland cement.

These materials can exhibit the following properties:

■ Pozzolanic — will not gain strength when mixed with water. Examples

include silica fume meeting the requirements of ASTM C 1240,

Standard Specification for Silica Fume Used in Cementitious Mixtures,

and low-calcium fly ash meeting the requirements of ASTM C 618,

Standard Specification for Coal Ash and Raw or Calcined Natural Pozzolan for

Use in Concrete, Class F.