Title:
Hardening and Shrinkage Kinetics of Geopolymers
Author(s):
Hugo Thuilliez, Christophe Lanos, Annabelle Phelipot-Mardelé, Gérard Mauvoisin
Publication:
Symposium Paper
Volume:
362
Issue:
Appears on pages(s):
487-498
Keywords:
3D scanner, alkali activated binder, alternative material, drying shrinkage, geopolymer, macroindentation, shrinkage
DOI:
10.14359/51741005
Date:
6/14/2024
Abstract:
Geopolymers are amorphous mineral materials manufactured from aluminosilicates and a strongly basic alkaline solution. One of their advantages is a lower carbon footprint than conventional cementitious binders. However, they are subject to significant drying shrinkage. In this study, geopolymer samples are produced from metakaolin, silica fume, and a potash solution. The mixture proportions are selected to reach the molar ration Si/Al=1.8, K/Al=1.15, and H2O/K=5.3 leading to satisfactory rheology while mixing. Cylindrical samples (70 mm diameter, 40 mm height) are exposed to various curing conditions (temperature and relative humidity). A protocol including 3D scanning and instrumented macroindentation is used to monitor the drying shrinkage and hardening kinetics. Sample volume change and hardness are measured periodically until sample mass stabilization. It appears that the hardest samples are also the most cracked. Covering the sample for 5 days at 23°C or 24 hours at 40°C limits the shrinkage to ~1% but leads to a large decrease of the hardness compared to the hardest samples. An optimal geopolymerization requires a minimal amount of water which decreases with the progress of the reaction. Optimal curing conditions are identified. Thus, covering the sample for 3 days at 23°C allows to limit the shrinkage to 3% without cracking while reaching satisfactory mechanical properties.