Thiele Kaolin Company's KAOROCK™
KAOROCK™ is a metakaolin pozzolan that enhances the properties of concrete and cement-based products. It is an ultra-fine material that is white in color produced from kaolin, an aluminum silicate mineral mined in middle-Georgia.
Because KAOROCK™ is not a by-product as other pozzolans such as silica fume and fly ash, product quality and specifications can be strictly controlled.
Metakaolin differs from other supplementary cementitious materials like fly ash, slag or silica fume, in that it is a not a by-product of an industrial process; it is manufactured for specific purpose under controlled conditions.
Metakaolin is produced by heating kaolin, a natural clay that is in abundance in middle-Georgia, to temperatures between 1200-1750°F (650-900°C). This treatment, called calcination, radically modifies the particle structure making it a highly reactive, amorphous pozzolan.
During the cement hydration process, water reacts with Portland cement to form calcium-silicate-hydrate (CSH). A by-product of this reaction is the formation of calcium hydroxide, or lime. This lime is the weak link in concrete, and it reduces the effect of the CSH. When KAOROCK™ is present in the hydration process, it reacts with the free lime to form additional CSH material, thereby making the concrete stronger and more durable (see equations below).
Portland Cement + Water = Cementitious Materials + Lime
Lime + KAOROCK™ = Additional Cementitous Materials
A recent, independent laboratory study of mortar pastes demonstrates the ability for KAOROCK™ to react with the free lime at early stages in the curing process (See Figure ‘a’ below). For the control, pastes were made without any pozzolanic material, and then KAOROCK™ and silica fume replaced a portion of the Portland cement (8% and 15%). The pastes containing KAOROCK™ showed higher heats of evolution than the control mix or silica fume.
Silica fume reduced both the rate of heat evolution and the total heat evolved, likely due to the removal of cement from the system. Further, silica fume rate curves follow the same general profile as the control, with the first peak, corresponding to the CSH hydration, reaching higher than the second peak (C3A). This reflects dilution of the cement hydration and indicates that there is little secondary reaction occurring at these early ages.