The effects of lightweight aggregates on the properti̇es of geopolymer mortars

Lightweight geopolymer concretes are attracting attention due to their superior durability, low environmental impact and sustainable properties and offer unique solutions to reduce dead loads and increase the geopolymer concrete (GP) coverage of a structure using cementless concrete materials. GPs are products obtained by mixing low specific gravity natural/artificial aggregates with aluminosilicate binders and alkaline solutions. This study aims to develop innovative geopolymer materials that support environmental sustainability, reduce carbon emissions, and minimize cement consumption. In the experimental program, pumice and expanded vermiculite (EV) were used as lightweight aggregates, while fly ash (FA) and CEM II/B-S 42.5 R cement served as binders. Sodium silicate (SS) and sodium hydroxide (SH) were employed as alkaline activators. The quantities of binders and activators were kept constant across all mixture series, with EV replacing pumice at rates of 25%, 50%, 75%, and 100%. Mortar prisms with 40x40x160 mm dimensions were produced, the samples were removed from the mold after one day and kept in the curing room during the test period, 7 and 28 day flexural and compressive strengths, 30 and 60 day sulphate, acid durability tests, 300 and 400°C high temperature tests were performed and thermal conductivity coefficients were determined. As the EV content increased, both the fresh and unit weight of the mixtures decreased. However, EV was observed to reduce flexural and compressive strengths. The 28-day flexural strength ranged from 1.20 to 1.94 MPa, while the compressive strength varied between 13.5 and 21.3 MPa.