The potential of applying geopolymerization to a wide range of solid industrial waste and by-products is of great interest. In this research, the physical and mechanical properties of fly ash (FA)-based geopolymer concrete (GC), compared to those of cement concrete (CC), were studied. Three GCs with different content of FA and three appropriate CCs were designed, prepared, tested and evaluated. The results were compared with the requirements of Standards EN 206-1 and EN 1992-1-1. It was shown that in some cases minor adjustments of the regulations are needed, while in other cases complete revision is required. GC indicated competitive compressive strength compared to CC, tensile strength within the limits specified by Eurocode 2 for CC and modulus of elasticity about 50% less than that of CC. The ratio of binder (FA) to aggregates seems to have a significant effect on the properties of GC. The concrete with 750 kg/m³ FA seems to be the best choice taking into consideration both engineering and environmental criteria.

One of the areas of priority in a circular economy, regarding waste management, regards the valorization of construction and demolition wastes (CDW). This study suggests the synthesis of geopolymeric binders based almost entirely on construction and demolition wastes. Ceramic waste was used as the aluminosilicate precursor of the geopolymer synthesis, while glass waste was applied in the preparation of the activation solution. A fractional experimental design defined the optimum synthesis parameters, based on compressive strength values. The final products were characterized by means of X-Ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The glass waste was appropriately processed in order to prepare the activation solution for the geopolymerization of brick waste. In this work, CDW-based geopolymers were produced with a compressive strength in the range 10–44 MPa. The developed products contained 80–90 wt.% CDWs, depending on the method of activator preparation.

In this study, the use of expanded polystyrene and expanded perlite as lightweight aggregates for the preparation of lightweight geopolymers is tested. The geopolymers’ performance was evaluated through physical, mechanical and thermal testing. Polypropylene fibers were used as reinforcement agents, while the long-term durability was assessed though repeated wet–dry and freeze–thaw cycles and sorptivity tests. The results showed that the introduction of lightweight aggregates in the geopolymer mixes decreased the compressive and flexural strength of the specimens by 77% and 35%, respectively. However, the density and thermal conductivity were substantially improved because of the addition of low-density aggregates. The fiber reinforcement of lightweight samples led to a drastic increase in flexural strength by 65%, leaving unaffected the compressive strength and density of the specimens. The freeze–thaw and sorptivity tests were also improved after the introduction of both aggregates and fibers. Lightweight geopolymer composites exhibiting density in the range of 1.0–1.6 g/cm³, compressive strength of 10–33 MPa, flexural strength of 1.8–6.3 MPa, thermal conductivity of 0.29–0.42 W/mK, and sorptivity of 0.031–0.056 mm/min^0.5 were prepared.