Mechanical Strength Evaluation of Unburnt Bricks Incorporating Fly Ash and Bone Ash as Sustainable Binders

Abstract

The production of conventional fired clay bricks consumes significant energy and contributes to environmental degradation. This study investigates the feasibility of producing unburnt clay bricks by incorporating fly ash and bone ash as partial replacements of clay to enhance mechanical performance and sustainability. Six brick mixes were prepared using 0%, 5%, 10%, 15%, 20%, and 25% replacement levels of fly ash and bone ash by weight of clay. The prepared bricks were cured under ambient conditions and evaluated for plasticity, bulk density, and compressive strength in accordance with relevant British and ASTM standards. The results demonstrated that the inclusion of fly ash and bone ash significantly influenced brick properties. Bulk density increased from 1.58 g/cm³ for the control mix to a maximum of 1.71 g/cm³ at 20% replacement, indicating improved matrix densification. Similarly, compressive strength increased from 9.2 MPa for 100% clay bricks to a peak value of 12.5 MPa at 20% fly ash and bone ash, representing an improvement of approximately 36%. A slight reduction in both density and strength was observed at 25% replacement due to excessive non-plastic material content.