Thermal treatment of geopolymers and cement

Abstract

This paper explores the effect of heating geopolymers to 1000C and compares the change in physical properties with those of similarly treated calcium aluminate marine grade cement, which is used to immobilise low level nuclear waste.

Laser dilatometry and thermogravimetry were carried out simultaneously on Na:Al:Si ratio geopolymers, fabricated using sodium silicate solution (PQ Australia Pty. Ltd.) and metakaolinite (Metamax, USA). For these tests, 40mm diameter x 100g samples were prepared by casting a mixed paste of the reagents into 40mm Perspex moulds, followed by curing at 60C for 24 hours.

A laser dilatometer was used to simultaneously monitor the diameter of two samples during heating, using a He:Ne laser measurement system (Z-Mike, USA), which scanned across the sample 150 times each second. Changes in temperature, diameter and weight were logged using an in-house generated Labview program.

For the thermogravimetry studies, the weight change of the sample was measured using a loadcell located beneath the heat treatment furnace. Measurements showed that dehydration of the geopolymer was more rapid than that of the cement sample, with dehydration complete by 300C. The cement sample, on the other hand, had to be heated to temperatures in excess of 70.