A 20% Rice-Husk Ash, 6% Alkali Formulation for Fly-Ash Geopolymer Wall Blocks: A Formulation Search Priced in Strength, Cost and Carbon per Square Metre of Wall

A formulation search (SIMULATED, NOT MEASURED; nothing built or load-tested) over 240 combinations of rice-husk ash share (0-40%), activator dose (4-10% Na2O equivalent), curing temperature (23-80 C) and curing time (12-48 h) for an alkali-activated fly-ash wall block, scored in strength, cost and embodied carbon per square metre of 150 mm hollow-block wall. The recommended robust formulation - 20% rice-husk ash, 6% dose, cured 60 C for 24 h - reaches 8.02 MPa at US$17.30 and 24.28 kg CO2e per m2; the activator is 39.3% of cost and 76.7% of carbon, a 100-house programme needs 194.4 tonnes of activator bought in, and doses above 8% are excluded by a stated high-alkali handling limit.