An Investigation of the Ground Walnut Shells’ Addition Effect on the Properties of the Fly Ash-Based Geopolymer

Abstract

The development of geopolymers is in line with the requirements of sustainable development. Creating a new type of material from various industrial and bio-based wastes and by-products can lead to reduced energy consumption, reduced waste generation, reduced global CO2 emissions, as well as reduced resource extraction of natural resources. In this study, geopolymer composites based on class F fly ash with the addition of fine quartz sand and ground walnut shells used as a substitute for sand were examined. The study focused on investigating the effects of different weight percentages of ground walnut shells and quartz sand on the density and strength properties, including compressive and flexural strength, thermal conductivity, efflorescence formation, and water absorption of the fly ash-based geopolymer composites. The microstructure of the studied geopolymers was also analyzed using a scanning electron microscope (SEM). It was observed that the addition of ground walnut shells contributes to the decrease in density and mechanical properties, increase in absorption properties, and decrease in porosity of fly ash-based geopolymers. Furthermore, the addition of ground walnut shells allows for a significant reduction in efflorescence on the surface of the tested geopolymer composites. Moreover, partial or complete replacement of sand by ground walnut shells in geopolymer composites based on fly ash allows for a significant reduction in their thermal conductivity, which makes it possible to use these composites as insulation materials.

Effect of granite flour proportion on the strength properties of geopolymer mortar based on fly ash

“…The highest value equal to 1.7 g/cm 3 was obtained for the sample made from the composition where river sand was completely replaced by granite. The results obtained from the density measurements are close to the values presented in the literature for fly ash-based geopolymers [6,28,29].…”

The Mechanical Properties of Geopolymers from Different Raw Materials and the Effect of Recycled Gypsum

“…In recent years, geopolymers have been a topic of intensive research because of their potential to replace cement in construction. The effect of additives and fillers on shrinking, hardening, final strengths, and other properties of geopolymers has still not been sufficiently elucidated, even though much developmental work has been conducted [44,45]. Therefore, there is good reason to continue basic research on materials in order to achieve their practical applications.…”

“…In recent years, rational environmental management and synthesis of green materials has been directed towards the development of geopolymer-based materials with various bio-based and industrial wastes and by-products. Among organic fillers, for example, palm fiber or ground walnut shells have been tested [44,47]. Inorganic additives, such as limestone [45], nanosilica [48], and gypsum-bearing wastes [49][50][51][52] are extensively studied.…”