Structure, composition and properties of geopolymers from mineral wool waste

The waste generated during the mineral wool production makes up to 30 % of the finished product mass. These wastes can be used for producing building materials, in particular as raw materials for the production of geopolymers (alkali-activated binders). The research aim was to determine the influence of the chemical composition of mineral wool production wastes (MWPW) on the phase composition, structure, and physico-mechanical properties of geopolymers. Five types of MWPW with various chemical compositions and specific surfaces were hydrated in the presence of NaOH (from 2 to 4 wt. %). The experimental results were obtained using the methods of X ray differential (XRD), differential thermal (DTA) and thermogravimetric (DTG) analyses. Moreover, scanning electron microscopy (SEM) and physical and mechanical tests were used. The main hydration product of MWPW in the NaOH presence is determined to be calcium hydrosilicates of the C–A–S–H fiber texture type. The largest amount of C–A–S–H was detected in geopolymer samples made of wastes with an acidity modulus between 1.4 and 1.6. The compressive strength of the obtained materials reaches 80 MPa. They are also characterized by high water resistance. The Al₂O₃ content in the waste should be about 10 % in order to obtain geopolymers with stable properties. The obtained results made it possible to define the correlation between the structure, composition, and physic-mechanical properties of geopolymers made of MWPW. The practical effect of the research results lies in the possibility of obtaining higher strength classes concrete.