Hydration characteristics of silicafume - fly ash composite cement pastes

Abstract EN

Composite cement is composed of Portland cement and two or more inorganic materials that take part in the hydration reaction.

Composite concretes have properties such as slower and decreased total heat evolution in massive structures, improved durability with microsilica, strengths above the normal range.

The objective of this work is to study the properties of silica fume-fly ash composite cement pastes up to 90 days.

The substitution of silica fume (SF) by fly ash (FA) decreases the water of consistency and accelerates the setting.

Partial substitution of silica fume by 5-15 % FA shortened the setting time and decreased total porosity, increased bulk density and compressive strength of the cement pastes.

The addition of 20 % FA retards the initial setting due to its low hydraulic properties in comparison with SF.

Mixes with 15 and 20 % FA show a high compressive strength at later ages.

The IR and DTA of 20 % fly ash cement pastes show that the free lime and combined water contents increase with curing time up to 28 days and then decrease at 90 days.

On the other side, the free lime increases and the combined water decreases with FA content due to the high pozzolanic activity of silica fume in comparison with FA .