Effect of acidic volcanic perlite rock on physio-mechanical properties and microstructure of natural pozzolan based geopolymers

The paper presents the combined effect of pozzolan, as an alkaline volcanic rock, and perlite, as an acidic volcanic rock, in the synthesis of geopolymers. The perlite proportion varied between 0% and 50% by weight. A mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as an alkaline activator. The effect of perlite on the physio-mechanical properties of the synthesized geopolymers was evaluated by the compressive strength (Rc), P-wave velocity (Vp), bulk density (D), and porosity (P). The microstructural aspects have been explored by X-ray Diffractometry (XRD), Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray spectroscopy (EDS). The results highlight the possibility of obtaining an eco-efficient geopolymer, with compressive strength of up to 50 MPa at 28 days by partially replacing the pozzolan by 40% of the perlite, due to the formation of higher amorphous N-A-S-H type gel. However, the excessive content (more than 40%) of perlite favored the formation of zeolitic phases in the geopolymer matrix, resulting in a heterogeneous structure, which has a negative effect on the development of the compressive strength and microstructure of the pozzolan-based geopolymer. This study confirms the promise of using pozzolan-perlite-based geopolymers as sustainable building materials, which could significantly promote the development of geo-resources and environmental protection in the construction sector.