Comparative Experimental Study on Ordinary Portland Cement and Portland Pozzolana Cement in M35 Concrete and Performance Evaluation of Fly Ash-Based Cement Bricks

ABSTRACT The construction sector's rapid growth has significantly increased the demand for sustainable and high-performance building materials. Cement, a primary construction binder, contributes approximately 5–8% of global CO₂ emissions. To address this environmental challenge, this study investigates the mechanical performance and environmental viability of Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC), alongside the fabrication and testing of fly ash-based cement bricks. OPC and PPC concretes were cast with M35 design mix, and their compressive strengths were evaluated after 3, 7, and 28 days of curing. The results showed that OPC exhibited superior early-age strength, achieving a maximum compressive strength of 43.02 N/mm² at 28 days, whereas PPC attained a peak value of 39.02 N/mm², demonstrating competitive long-term performance. With better workability (slump value: 98 mm) and compaction factor (0.98). Additionally, three types of fly ash bricks were cast with increasing fly ash content (20%, 35%, and 50%) by weight, maintaining a fixed cement ratio. These bricks were tested for compressive strength, water absorption, soundness, efflorescence, and structural integrity. The best-performing mix (35% fly ash) achieved a compressive strength of 7.2 N/mm² and water absorption below 12%, meeting IS:3495 standards for non-load-bearing applications. The results confirm that PPC is a more sustainable alternative to OPC in long-term structural applications, and fly ash bricks offer an eco-friendly, cost-effective substitute for traditional clay bricks, supporting the circular use of industrial by-products in civil infrastructure. Keywords: Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC), fly ash bricks, compressive strength, water absorption, sustainable construction materials