Performance Characteristics of Concrete Incorporating A Natural Amorphous Silica

A natural amorphous silica with a purity of approximately 90 percent is mined from an extensive geothermal deposit near Rotorua, New Zealand. After refining and processing to remove impurities, the 'Microsilica 600tm' has properties which comply with Australian Standard AS 3582 Part 3 'Silica Fume' as a supplementary cementitious material for use with portland cement. The performance characteristics of concrete incorporating the 'Microsilica 600' were evaluated at two cement levels of 320 and 400 kg/cubic meter and two silica addition levels of 7 and 10 percent. Properties evaluated were compressive strength, tensile strength, concrete shrinkage, sulfate resistance, resistance against chemical attack, abrasion resistance, and chloride permeability. Performance improvement compared favorably with published data on concretes incorporating processed 'conventional' silica fume.