An application of blended fly ash and residual rice husk ash for producing green building bricks

The present study investigates the possibility of using a blended class-F fly ash (FA) and residual rice husk ash (RHA) in the production of green building bricks through the application of densified mixture design algorithm (DMDA) in order to provide a new use for solid waste materials. This study uses unground rice husk ash (URHA) as a partial fine aggregate substitution (10–40%) in the studied cementitious mixtures. Solid bricks of 220 × 105 × 60 mm in size were prepared under forming pressure of 25–35 MPa, a curing temperature of 90 °C, and a relative humidity of 50%, for tests that assessed: compressive strength, flexural strength, bulk density, void volume, and water absorption. The test results showed that all brick samples demonstrated excellent properties. Compressive strength and flexural strength ranged, respectively, between 20.2–33 MPa and 5.4–6.9 MPa. Additionally, up to 30% of URHA content, the values of water absorption and void volume ranged, respectively, between 8.8–15.7% and 1.5–2.1%. All of these values not only conformed well to the requirements of the Vietnamese codes but also demonstrated great potential for using a blended FA–RHA in producing green building bricks.