Influence of Silicate Modulus and Eggshell Powder on the Expansion, Mechanical Properties, and Thermal Conductivity of Lightweight Geopolymer Foam Concrete.

To address the demands of the low-carbon era, this study proposed a solution by using eggshell powder (ESP), fly ash, and ground granulated blast furnace slag together with alkaline solution in the preparation of lightweight geopolymer foam concrete (LWGFC). The aim of this study is to investigate the influence of replacing precursor materials with 5-20% ESP on the expansion behavior, physical, mechanical characteristics, and thermal conductivity of LWGFC. Additionally, the study examines the effect of varying the silicate modulus (SiO/NaO ratios of 1.0, 1.25, and 1.5) on the properties of LWGFC. Incorporating ESP from 5% to 20% with a constant SiO/NaO ratio reduced the initial setting time, while a high SiO/NaO ratio controlled the setting time and expansion volume. The high SiO/NaO ratio decreased the porosity and enhanced the compressive strength of the LWGFC but increased the thermal conductivity. The inclusion of more than 10% ESP content negatively affected compressive strength; however, a high SiO/NaO ratio can mitigate this detrimental effect. The thermal conductivity of optimal-content ESP mixtures with a SiO/NaO ratio of 1.0 was about 0.84 W/m·K, which is 2.1% lower than mixtures with a ratio of 1.25 and 18.6% lower than those with a ratio of 1.5. High-content ESP mixtures had a density of 1707 kg/m, 0.97 W/m·K, and a compressive strength of 18.9 MPa at a low SiO/NaO ratio. Finally, the inclusion of ESP in the LWGFC, along with the use of an appropriate silicate modulus, resulted in improved strength development while decreasing porosity.