Compressive strength and microstructural properties of spent coffee grounds-bagasse ash based geopolymers with slag supplements

Spent coffee grounds (CG) is a beverage waste derived from the drinking coffee. Bagasse ash (BA) is the residue obtained from the burning of sugarcane for electricity. This paper aims to create and assess the feasibility of a recycled construction material formed by binding CG with a BA geopolymer, through the alkaline activation of BA using sodium hydroxide (NaOH). Slag (S), an industrial waste, was used to supplement CG+BA mixes. The mass ratios of the granular solids used were 70CG:30BA, 70CG:10BA:20S, 70CG:20BA:10S, and 70CG:30S. Strength development was assessed using the Unconfined Compressive Strength (UCS) test. Microstructural analyses were done by scanning electron microscopy (SEM). Specimens were cured at 21 degrees C and 50 degrees C, for durations of 7, 28, 60, and 90 days. This study found that 50 degrees C curing was necessary to adequately strengthen the mixes and inhibit organic content growth at long curing durations. Conclusively, this CG+BA geopolymer requires extended curing periods to achieve high UCS. The maximum recorded UCS in this study was 1482 kPa, achieved by 70CG:20BA:10S cured at 50 degrees C for 90 days. 70CG:20BA:10S provided the optimum aluminosilicate-to-alkali ratio for geopolymerization. Under optimum curing conditions, the geopolymer mixes were found to meet the minimum specified UCS requirements for subgrade materials in various countries. (C) 2017 Elsevier Ltd. All rights reserved.