How to Optimize Your Flyash Brick Production Line for Maximum Yield
— By Maruti Hydraulics Limited
Practical tips and techniques to optimize flyash brick production for maximum yield and quality.
Flyash bricks are manufactured from fly ash (industrial waste from thermal power plants), lime, gypsum, and water — pressed under high hydraulic pressure without firing. This makes them significantly more sustainable than clay bricks, but consistent quality and high yield require careful attention to raw material specifications, press parameters, and curing conditions.
Raw Material Quality: The Foundation of Brick Quality
Flyash quality is the single most important variable in flyash brick production. Class F fly ash (produced from bituminous coal combustion) is preferred for its high silica and alumina content, which provides better pozzolanic reactivity. Class C fly ash (from lignite combustion) contains more calcium and can cause expansion problems. Before commissioning a flyash brick plant, test your local fly ash supply for: SiO₂ + Al₂O₃ + Fe₂O₃ content (minimum 70% per ASTM C618), loss on ignition (maximum 6%), and fineness (passing 45 micron sieve minimum 66%).
Quicklime (calcium oxide) must have minimum 75–80% CaO content and 85–90% available lime. Low-grade lime with high calcium carbonate content reduces brick strength and increases the lime dosage required, directly cutting profit margins. Always test lime reactivity (Vicat test) at intake.
Mix Design: Getting the Proportions Right
A standard flyash brick mix design is approximately: Fly ash 55–65%, Quicklime 8–12%, Gypsum 1–3%, Water 12–16% by weight. The exact proportions depend on fly ash chemistry, lime quality, and target compressive strength. For IS 12894 Class 2 bricks (minimum 50 kg/cm²), a mix of 60% fly ash, 10% lime, 2% gypsum, and 28% fine aggregate with 14% water typically achieves 60–70 kg/cm² strength after 28 days of water curing.
Over-dosing lime causes expansion cracks in finished bricks. Under-dosing lime reduces strength. The target mix should be confirmed with trial batches and 7-day and 28-day compressive strength tests before full production.
Press Settings and Hydraulic Pressure
Flyash brick strength is directly related to compaction pressure. Most hydraulic press machines operate at 80–150 tonnes of force for a standard 230 × 110 × 75 mm brick. Higher pressure (140–150 tonnes) consistently produces stronger bricks (60–80 kg/cm²) with lower water absorption (8–12%) than lower-pressure production (90–110 tonnes), which yields 40–55 kg/cm² and 14–18% water absorption.
Key press settings to optimise: pressing time (minimum 8–12 seconds per stroke), ejection speed (slow ejection reduces edge cracking), and die clearance (worn dies cause density variation between face and core of the brick).
Curing: Where Most Plants Lose Yield
Water curing is critical for flyash brick strength development. Bricks must be cured under constant water spray or submersion for minimum 14–21 days after pressing. Inadequate curing — the most common cause of field failures — produces bricks that appear strong at 7 days but develop strength below IS specification at 28 days.
Steam curing (at 60–80°C for 8–12 hours) can accelerate strength development to 80–90% of 28-day strength in 24 hours, significantly improving production turnaround. Maruti Hydraulics can advise on steam curing chamber design as an add-on to the flyash brick machine package.
For flyash brick machine specifications and production optimisation consulting, contact Maruti Hydraulics at +91-253-2308131.