Enhancement of Mechanical Properties of Unfired Clay Bricks Using Rice Husk Ash and Fibre Reinforcement

Abstract

This study investigates the production of unfired clay bricks incorporating cement and rice husk ash (RHA) as a binder, with rice husk (RH) serving as fiber reinforcement. The need for eco-friendly building materials is critical, as cement production contributes 7-8% of global CO₂ emissions, and while fired clay bricks are stronger, their high production cost due to significant energy requirements makes them less sustainable. Providing lower-cost building materials can reduce rural-to-urban migration and make housing more affordable for low-income earners. RH fibers were added in varying volumes (0, 5, 10, 15, 20, and 25 vol%) while maintaining a constant RHA and cement content of 10 vol.%. The mixed clay bricks were dried for seven days and cured at room temperature (22°C to 28°C) for 21 days, totalling 28 days of curing. Mechanical properties, including compressive strength, flexural strength, and fracture toughness, were evaluated alongside the chemical composition and textural characteristics of the clay and RHA. Particle size distribution (PSD) analysis classified the clay as sandy clay with higher sand content, determined using sieve analysis and the hydrometer method. X-ray fluorescence (XRF) confirmed that the RHA met NIS/ASTM standards, with a minimum of 70% combined SiO₂, Al₂O₃, and Fe₂O₃, qualifying it as a pozzolanic material. Optimal mechanical performance was observed at 5% RH fiber content, with fibers 2-4 mm in length, achieving compressive strength of 7 MPa, flexural strength of 2.1 MPa, and fracture toughness of 2.15 MPa√m, while fiber content beyond 5% resulted in gradual declines, particularly significant after 20%. The study concludes that RH fiber-reinforced composites are suitable for lightweight, durable building materials, promoting environmental sustainability and improved performance