The Application of Spent Coffee Grounds and Tea Wastes as Additives in Alkali-Activated Bricks

The traditional firing process to manufacture building bricks is not sustainable because of the high firing temperature and greenhouse gas emission. Therefore, there is a growing incentive to invest in green technologies with minimal environmental impacts. This study ascertained the potential use of Spent Coffee Grounds (SCG) and Tea Waste (TW) as additives to manufacture unfired clay bricks through alkali-activation. The ambition of this study is to divert SCG and TW from landfills and promote sustainable construction practice. An alkali-activated binder was used in this study by activating mill clay residues (precursor) with a liquid mixture of NaOH and Na2SiO3 solutions at a fixed Na2SiO3/NaOH ratio of 0.7. Small amounts (1, 2.5, 5, 10 and 15 wt%) of SCG and TW were added to the binder and mechanically blended for 2.5 min. Block samples were moulded by compressing the slurry in a steel mould. Once demoulded, the block samples were dried in an oven temperature at 110 °C for 24 h, then cured at ambient temperature. Fabricated samples were subjected to unconfined compressive strength test, moisture absorption test and tested samples were also characterised by Optical and Scanning Electron Microscopy (SEM). SEM micrographs showed the discovery of active fungi in the samples containing high SCG content (5 wt% and above) but not in the samples made with TW. The results showed that the samples with up to 2.5 wt% SCG and 10 wt% TW met the minimum compressive strength requirement (8.6 MPa) for structural applications with satisfactory moisture absorption values, as per ASTM C62.