Sustainable alkali-activated foam concrete with pumice aggregate: Effects of clinoptilolite zeolite and fly ash on strength, durability, and thermal performance

Abstract

The utilization of natural clinoptilolite zeolite (CZ) as a precursor in geopolymers represents a promising approach to enhancing both the performance and sustainability of alkali-activated composites. This study investigates the development of sustainable alkali-activated foam concrete (AAFC) by employing 100 % pumice aggregate as a lightweight aggregate and partially replacing ground blast furnace slag (GBFS) with fly ash (FA) and CZ. The objective is to assess the combined effects of FA and CZ on the mechanical, thermal, and durability properties of AAFC under varying curing conditions, including exposure to extreme temperatures and freeze-thaw cycles. The results indicate that flowability of the fresh mixtures increased with the incorporation of FA and CZ. Compressive strengths ranging between 2 and 5 MPa were achieved over a curing period of 7–120 days with unit weights below 723 kg/m³ through the combined use of FA and CZ as GBFS substitute. The thermal conductivity values ranged from 0.155 to 0.229 W/mK, with the lowest value observed in the mixture containing 20 % FA and 20 % CZ. This indicates excellent thermal insulation performance, making the material highly suitable for energy-efficient construction applications. The combination of FA and CZ contributes to the creation of a highly insulating material, further enhancing the material's potential for use in applications where thermal resistance is crucial, such as in building walls, roofs, and other energy-efficient structures. At 900°C, mixtures with 10 % FA and 5–20 % CZ demonstrated strength gains, while mixtures with 20 % FA and 5–20 % CZ showed minimal strength losses of only 3–6 %, highlighting the material's excellent high-temperature resistance. This performance is crucial for applications requiring structural integrity under extreme thermal conditions, such as fire-resistant construction and industrial insulation. After 30 F-T cycles, all mixtures exhibited strength gains, while after 75 F-T cycles, strength losses ranged between 29 % and 33 %. The lowest strength loss, 29.2 %, was observed in the mixture containing 20 % FA and 20 % CZ, which is considered a favorable result for pumice-based foam concrete. These findings demonstrate the material's good durability under freeze-thaw conditions, with the mixture containing FA and CZ showing relatively better resistance to strength degradation.