Recycling of Olive Pomace Bottom Ash (by-Product of the Clay Brick Industry) for Manufacturing Sustainable Fired Clay Bricks

The present work investigates the effect of using olive pomace bottom ash, the by-product of the clay brick industry, as an additive in the manufacture of fired clay bricks. Furthermore, it aims to improve the properties of clay bricks by using naturally available materials and also to develop an innovative way of recycling the waste resulting from the brick firing process. Olive pomace bottom ash was added to clay with multiple proportions (0%, 5%, 10%, 15%, and 20%) by weight. Bricks were molded by compression at 6.5 MPa, using a hydraulic brick press machine, and fired in an industrial scale furnace. The physicochemical, mineral, and geotechnical properties of raw materials were identified to study raw materials’ effect on the final fired products’ performance. The quality of fired specimens was determined by bulk density, linear shrinkage, water absorption, porosity, compressive strength, and thermal conductivity. In fact, samples with 5% olive pomace ash represent the highest compressive strength level, 11.5 MPa, compared to 9.65 MPa of reference samples. On the other hand, additions up to 20% increase the brick sample’s porosity from 18.28% to 34% for the reference mixture and the brick incorporated with 20% of additive, respectively, and decrease the brick’s bulk density from 1522 kg/m3 to 1431 kg/m3 for the reference mixture and the brick incorporated with 20% of additive, respectively. The incorporation of ash also improves the thermal conductivity of brick specimens. Expressly, thermal conductivity went from 0.41 W/m.K to 0.33 W/m.K for the reference mixture and the brick incorporated with 20% of additive, respectively, showing 37% of gain in thermal insulating properties of brick. Unfortunately, the capillary water absorption coefficient increases to 28% when 20% of additive is incorporated, which is not desired in the properties of construction materials. ASTMC67-07a standards: 2003, recommend water absorption level less than 17% for bricks with moderate weathering resistance. It was concluded that the addition of olive pomace bottom ash should not exceed 10% since it can be helpful in fired clay brick production based on standards requirements, leading to remarkable ecological gains without a loss of brick’s performances.