Abstract:
This research is aimed to study the effect of biochar on compressive strength, setting time and surface characteristics of geopolymers. Biochar is obtained by burning eucalyptus wood using by pyrolysis method at 400 °C. Fly ash is used as a starting material for the synthesis of geopolymers. Biochar was substituted for fly ash at 0, 1, 2, 4 and 6 by weight of the binder. The sodium hydroxide solutions concentrations were various of 4, 6, 8, 10 and 12 molars, and sodium silicate solution was used. The ratio of sodium hydroxide to sodium silicate was kept at 1:1 by weight. Compressive strength was investigated at 7, 14, 28 and 60 days. Setting time of geopolymer pastes was studied. The effect of using ultrasonic pulses was also determined. The surface characteristics of geopolymers were characterized using SEM-EDS and the mapping technique.
The results found that geopolymer with 2% by weight biochar and sodium hydroxide at a concentration of 10 molars provided the highest compressive strength. Geopolymers with biochar as a binder has reduced initial and final setting times. The relationship between the ultrasonic pulse waves and the compressive strength found that the compressive strength was increased, and the speed of the ultrasonic pulse decreased. In addition, a study of the surface characteristics of biochar-containing geopolymer revealed that the geopolymer pastes tends to enter the biochar gap, resulting in a dense surface. There is a reduced gap.