Abstract
Silica fume is a common mineral admixture used in HSC and HPC, but being its high price and shrinkage in concrete, its usage is under restrictions. As a new mineral admixture, metakaolin gets more and more attention. In order to compare the difference between silica fume and metakaolin, the effects of metakaolin and silica fume on concrete workability, compressive strength, and chloride penetration resistance are studied. It shows that incorporating with fly ash together, silica fume reduces the slump extension, but metakaolin can increases it; silica fume can increases early strength more than metakaolin can, but it isn’t useful for later and long-time strength; metakaolin not only can increase early strength, but also can improve long-time strength. Silica fume and metakaolin can increase the chloride penetration resistance. As a new mineral additive, metakaolin can play a role in concrete which silica fume does, even much better than silica fume.
Highlights
Basing on “activity effect”, “morphology effect” and “micro-aggregate effect”, fly ash is widely used in concrete as a mineral admixture to improve workability and durability, but reduce strength, especial early strength[1].Silica fume is a highly active mineral admixture with high specific surface areas
Metakaolin’s specific surface area and average grain sizes are 2.75m2/g and 2.18μm respectively, and its particle morphology is shown in Fig.[1] which shows that metakaolin is irregular flaky and loose porous particles
The specific surface area and average grain sizes of silica fume are 8.56m2/g and 0.27μm respectively, and its particle morphology is shown in Fig.[1] which shows that silica fume is very small spherical particles
Summary
Basing on “activity effect”, “morphology effect” and “micro-aggregate effect”, fly ash is widely used in concrete as a mineral admixture to improve workability and durability, but reduce strength, especial early strength[1]. Silica fume is a highly active mineral admixture with high specific surface areas. By “filling effect” and “pozzolanic effect”, silica fume can improve the pore structure and interface structure to improve compactness of concrete, and increase concrete strength and durability[2~4]
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