10th U6+ Consortium of African Universities International Conference

The environmental impact associated with the production of Portland cement has intensified interest in sustainable alternatives such as lime-based binders. However, their application is constrained by low early strength and slow hardening. This study evaluates rice husk ash (RHA) and sugarcane bagasse ash (SCBA) as pozzolanic additives to enhance the mechanical performance and durability of lime mortars. Hydrated lime was partially replaced (50%) with RHA or SCBA, and the mortars were air-cured for 28 days. Both ashes satisfied standard pozzolanicity requirements. RHA exhibited a higher amorphous silica content and greater reactivity, whereas SCBA demonstrated slower but sustained pozzolanic activity. The incorporation of these pozzolans significantly improved performance. Compressive strength increased from 0.43 MPa for pure lime to 4.64 MPa and 3.84 MPa for RHA and SCBA mortars, respectively. Flexural strength improved from 0.17 MPa to 2.70 MPa and 0.97 MPa for RHA and SCBA mortars, respectively. Water absorption was substantially reduced in the modified mortars, indicating improved pore structure and durability. RHA provided superior strength development and lower permeability, while SCBA offered moderate strength enhancement with improved flexibility. These characteristics make both materials suitable for non-structural applications, including heritage conservation and restoration. The findings demonstrate that agricultural waste ashes can serve as effective, low-carbon pozzolanic materials for durable lime-based construction.