This paper investigates the potential of corn straw ash as a supplementary cementitious material (SCM), focusing on its contribution to sustainable civil construction. The ash was characterized using X-ray diffraction (XRD) and X-ray fluorescence (XRF) to analyze its chemical and mineralogical composition, as well as its pozzolanic potential. Mortars incorporating 35% replacement of cement by corn straw ash were compared to reference mortars, with compressive strength and microstructural analyses performed at 28 and 56 days to evaluate the progressive pozzolanic reaction. The results demonstrated that corn straw ash enhances the mechanical performance of mortars, attributed to its role in improving microstructural densification over time. This approach aligns with the principles of the circular economy by repurposing agro-industrial residues, reducing Portland cement usage, and mitigating environmental impacts. The findings highlight the practicality of integrating agricultural waste into cement matrices, supporting more sustainable and efficient construction practices. Beyond mechanical improvements, the research emphasizes the broader significance of using alternative materials to address key challenges in resource efficiency, waste management, and carbon emission reduction within the construction industry. By showcasing the technical and environmental benefits of corn straw ash, this preliminary study advances the development of innovative, sustainable strategies for transforming agricultural waste into valuable resources, offering practical insights into its application potential.