The Pozzolanic Activity of Calcined Clay - Silica Gel Composites

The effect of silica gel additive on pozzolanic activity of burned clays was investigated on this study. It was determined that calcined (600 degrees C - 730 degrees C) clay of Saltiskiai quarry has very low pozzolanic activity (104 mg - 55 mg CaO/g). It was observed that during calcination process the fluorine ions from silica gel were not combined to another compounds but directly passed to atmosphere. Moreover, silica gel additive significantly increases the mentioned clay activity, which depends on the quantity of the used additive. It was determined that 10 % of silica gel additive increases the pozzolanic activity of composite with clay of Saltiskiai quarry up to 109 mg CaO/g, meanwhile the 80 % - unto 257 mg CaO/g. The same effect of silica gel additive was observed in the samples with Dukstyna quarry clay. It was found that the pozzolanic activity of Dukstyna clay-silica gel composite with 10 % of silica gel additive, burned at 600 degrees C for 1h, was 7 % higher (168 mgCaO) than the activity of the clay samples (157 mgCaO/g), whereas 229 mgCaO/g pozzolanic activity was reached than 80 % additive of silica gel was used. Despite this fact, the pozzolanic activity decreases when the calcination at 700 degrees C - 860 degrees C temperature was carried out.