Mechanical Strength Analysis of Silt-Filled, NaOH-KOH Activated Metakaolin-Based Geopolymers

The present study reports the variation of the mechanical properties of engineered metakaolin-based geopolymers synthetized using NaOH-KOH alkali activators and sodium disilicate, investigated after 7 and 28 days of aging by means of unconfined compression tests for mechanical strength analysis. The geopolymers were synthetized by mixing KOH and NaOH in different proportions in the alkaline activating solution, from 0% to 100% of KOH addition, fixing the Si/Al ratio and water content. The binders were synthetized with different curing temperatures. A novel composition using quarry-derived materials (silt from sedimentation lakes) was developed to realize an innovative composite. The materials were characterized by XRD, ESEM-EDS and unconfined compression tests. The mechanical results underlined that the addition of the filler tends to preserve the mechanical properties of the composite. Generally, curing at 40 °C followed by a 28-day aging period for the mixed Na-K geopolymers demonstrated the highest mechanical strength of all the synthesized products, with a maximum strength of 21 MPa. Mixed NaOH-KOH composites generally exhibited lower performances compared to sample consisting solely of 100% NaOH when cured at a temperature of 85 °C. Nonetheless, the synthetized composites reported in this study can have diverse applications across various technological fields requiring low-strength materials.