Recycling used coffee grounds as fine aggregate in alkali-activated lightweight non-load-bearing composites

Coffee is one of the most consumed drinks, which releases large amounts of used coffee grounds (UCG), causing environmental problems. Thus, UCG was re-used in combination with bottom ash (BA) as fine aggregates in making alkali-activated non-load-bearing lightweight composites (ANLC) in this study. To evaluate the effect of UCG on the properties of ANLC, seven ANLC mixtures with UCG/BA ratios of 0/100, 5/95, 10/90, 15/85, 20/80, 25/75, and 30/70 were prepared. Results showed that the properties of ANLC were influenced significantly by UCG contents. Indeed, an increase in UCG content led to a decrease in dry density, strength, and drying shrinkage while increasing the ANLC’s water absorption, except for the specimen with 5% UCG incorporation. Correlations among properties of ANLC were established and the potential applications of ANLC in real practice were also suggested, proving that the ANLC could be applied to non-load-bearing elements. Among the mixtures, the 28-day ANLC specimen containing 5% UCG exhibited the highest flexural and compressive strengths of 7.12 MPa and 39.4 MPa, respectively, and the lowest water absorption of 10.29% with the relatively low dry density of 1671 kg/m3­, indicating the feasibility of using UCG as fine aggregate in the production and application of ANLC.