Title: Effects of Si/Al Molar Ratio on the Structure and Properties of Metakaolin-Based Alkali Activated Binders

Author(s): Jessica Lohmann and Frank Schmidt-Döhl

Publication: Symposium Paper

Volume: 362

Issue:

Appears on pages(s): 268-282

Keywords: geopolymer, metakaolin, alkali activated binder, Si/Al molar ratio

DOI: 10.14359/51740888

Date: 6/6/2024

Abstract:
The reaction of metakaolin with alkaline activators produces an X-ray amorphous, aluminosilicate gel matrix, as well as sodium or calcium aluminate-silicate hydrate phases in varying proportions. The degree of crosslinking depends on the Si/Al ratio of the starting products. This study investigates fundamental relationships between the Si/Al ratio of alkali-activated metakaolins and their mechanical properties. In particular, porosity, compressive strength, and thermoanalytical properties were considered. The crystallinity was determined by X-ray diffraction. The precondition for the formation of an amorphous microstructure is the solution of the reactive starting materials. The sodium cations contained in the solution serve to balance the charge in the network. It was found that a Si/Al ratio of 2 resulted in the highest strength. A higher ratio was associated with a higher pore volume and lower bulk density. Thermogravimetric investigations showed that at lower molar ratios, more water was incorporated into the structure. In addition, as the ratio increases, the dehydration temperature decreases, indicating weaker bonds in the network.