Correlating the elastic properties of metakaolin-based geopolymer with its composition

Highlights: • Elastic properties of MKG pastes with different AE dosages and Ms levels were measured. • Fracture behaviors of MKG pastes were characterized by axial and lateral stress-stain curves. • AE dosage has a dual effect on Young's and shear moduli characterized by a quadratic double-logarithmic function. • Increasing AE dosage tends to promote Poison ratio and bulk modulus characterized by a sigmoid function. • Ms level has no obvious influences on the elastic properties of MKG pastes. Geopolymer shows great potential as a construction material with low energy consumption and carbon oxide emission. Quantitatively assessment of elastic properties of a geopolymer and understanding the correlations with its composition and microstructure are therefore very important for its rational utilization. In the present investigation, two series of metakaolin-based geopolymer (MKG) were synthesized by controlling, respectively, mass ratio of alkali in activator to powders, namely the alkali equivalent (AE) to the aluminosilicate materials, within a range of 10%–50% and molar ratio of SiO₂ to Na₂O in activator, namely modulus of silicate (Ms), within a range of 1.25–2.25. General elastic mechanical properties (i.e., the Young's, bulk and shear moduli and the Poisson's ratio) of the MKG specimens were evaluated from load–strain curves measured by an integrated measurement and control system and the microstructures were determined by an ESEM–EDS analysis. The experimental results, combined with the analysis of variance method, indicate that, within the test ranges, the AE dosage influences all the characteristic elastic properties of the MKG specimens, whereas the effect of Ms level is insignificant. The morphology observations of the microstructures of the MKG specimens support the mechanical results, although both the AE dosage and Ms level change the chemical composition obviously. The results in the present study may help to tailor MKG material with its composition for further engineering applications.