Flyash and coffee silverskin binary blended geopolymer

Exploring alternative precursors other than flyash, slag, metakaolin and palm oil fuel ash for geopolymer synthesis has become very essential owing to the need for reduction in cost and accumulation of solid waste that could contribute to environmental pollution. The use of coffee silverskin (CSS) in binary blending with flyash (FA) in geopolymer synthesis is not yet fully understood, although its performance in ternary blending with silica fume for ordinary Portland cement (OPC) mortar has been established. Thus, binary blended CSS (0–30 %) with FA - such that CSS/(FA+CSS) varied from 0 to 0.3 - was activated by sodium hydroxide (8MNaOH) and sodium silicate (Na2SiO3), and then subsequently cured at 60 °C. Mechanical property, binder morphology, compound product phases and bond characteristics were studied through compressive strength test, scanning electron microscope (SEM/EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIRS), respectively. CSS (CSS/(FA+CSS) = 0.3) significantly contributed to strength loss due to microcracks, carbon content and fiber induced microstructural discontinuity, such that 7-,14-and 28-d strengths recorded were 5.2, 7.8 and 9.7 MPa, respectively. Maximum 28-day strength of 16.5 MPa was recorded in CSS/(FA+CSS) = 0.1. CSS caused the formation of monetite, and disappearance of muscovite and augite in flyash/coffee silverskin based (FACSS) geopolymer. •Coffee silverskin (CSS) and flyash binary geopolymer (AACSS-FA) binder was developed.•Incorporation of CSS in AACSS-FA caused presence of insoluble cellulose fibers in the matrix.•Presence of CSS in AACSS-FA caused microcrack, monetite formation and loss of strength•CSS in AACSS-FA caused formation of monetite and disappearance of muscovite in AACSS-FA.•CSS in AACSS-FA induced hydrogen bond vibration.