Sustainable mortar production using volcanic ash and crushed laterite as partial cement replacements

Cement is a critical construction material globally and particularly in Ethiopia, where its production is energy-intensive, costly, and a major source of greenhouse gas emissions. This study explores the partial replacement of Portland cement with volcanic ash and crushed laterite powder in cement mortar as a sustainable and cost-effective alternative. Preliminary mix designs were prepared with varying proportions of volcanic ash and laterite powder to determine optimal combinations which is equal percentage of volcanic ash and laterite powder as selected based the compressive strength result. Subsequent experimental mixes replaced cement with equal proportion of volcanic ash and laterite soil at 0%, 5%, 10%, 15%, 20%, 25%, and 30% by weight, following ASTM C109 standards. The study assessed characterization, mechanical (compressive strength and ultrasonic pulse velocity), durability (sulfate resistance, porosity, and water absorption), and microstructural properties using Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), and differential thermal analysis (DTA) analyses. Characterization results showed that volcanic ash and crushed laterite are finer than cement and are predominantly pozzolanic. Bernauer-Emmett-Teller (BET) analysis confirmed their fine particle sizes, contributing to the dense packing of the mortar. At 10% of replacement of cement by equal amount of volcanic ash and laterite soil, the highest compressive strength was recorded 33.1 MPa at 28 days and 46.2 MPa at 56 days. Water absorption decreased with increasing the replacement percentage up to 15%, indicating improved durability. Microstructural analysis revealed a denser morphology due to secondary C-S-H formation and filler effects. Overall, volcanic ash and laterite powder improved both mechanical and durability properties of mortar up to 15% replacement, with optimal performance at 10%. This shows the potential of those pozzolanic as a viable partial cement substitute, promoting sustainable construction practices in Ethiopia.