Mechanical properties of metakolin-based geopolymers

Abstract

Geopolymers are similar in behaviour to ordinary Portland cement (OPC) but their chemistry is different. Only a limited amount of work has been reported on detailed mechanical properties of both materials free of aggregates. In this work mechanical properties were determined of four different types of geopolymers, but of the same composition (Na/Al=1, Si/Al=2 molar ratio), made using a combination of precursors. The four types were a) sodium aluminate (NaA102 /NaOH solution), Ludox (colloidal Si02 solution) and metakaolin (MK), (SAGP), b) NaOH, fumed silica and MK (FSGP), c) Ludox, NaOH and MK (LGP) and d) commercial sodium silicate and MK (SGP). The highest crushing strength (CCS) value obtained was for SGP (70 MPa) and the lowest value was for SAGP (16 MPa). The highest modulus of rupture (MOR) value obtained was for LGP (9 MPa) and the lowest value was for SAGP (3 MPa). The fracture toughness (Klc) and Young modulus (E) showed the same trend. The effect of adding sand (40 wt%) on their mechanical properties was also determined. The KIC values increased up to 65% and E values increased up to 80% compared to samples free of sand. However, CCS and MOR values did not change much and gave mixed results. The mechanical properties of geopolymers will be compared with those of OPC.