Pozzolanic activity of Hwangtoh clay

Hwangtoh is a clay that has long been used as a traditional Korean building material. In these days, Hwangtoh is often used for plastering and flooring in newly constructed buildings to minimize sick building syndrome. In such applications, it is useful to determine whether the clay has pozzolanic properties. In this research, the pozzolanic activity of Hwangtoh clay was indicated by a reduction in calcium hydroxide and an increase in compressive strength in mortars, in which 20% of the Portland cement was replaced by the clay. The thermally activated Hwangtoh clay showed clear pozzolanic activity at 14 and 28 days, and the as-received clay showed some evidence of pozzolanic activity as well. The compressive strength provided by the activated clay was less than that provided by a synthetic mixture of metakaolin and quartzite, but still greater than that provided by the as-received Hwangtoh. The strength development may be improved further by removing the quartzite from the Hwangtoh clay.