GROUND GRANULATED BLAST-FURNACE SLAG

Ground granulated blast-furnace slag (GGBFS) makes concrete stronger, more durable, and more workable when used as a replacement for part of the Portland cement in concrete. It also offers significant environmental advantages. GGBFS is a coproduct of the reduction of iron ore into iron in a blast furnace. In addition to high durability and aesthetic value, GGBFS handles much like Portland cement. GGBFS and Portland cement mixtures produce virtually the same binder--calcium silicate hydrate--that is produced when Portland cement reacts with water. Alkali-silica reaction (ASR) occurs when alkalis in Portland cement react with silica minerals in the presence of water. The alkali and silica form a gel, which expands when it comes into contact with water and can cause cracking in concrete. A minimum of 35% GGBFS in a concrete mixture increases ASR resistance. GGBFS is shipped, handled, stored, and batched like Portland cement. It is imperative to follow good concrete finishing and handling practices with both materials.