Performance evaluation of metakaolin clay geopolymers synthesised with bamboo wood ash as an activator

Global concern about substantial CO2 emissions during manufacturing of Portland cement has led to studies on alternative low cost green binders. Geopolymer, an inorganic binder, which is produced from reaction of an alkaline activator and aluminosilicate mineral is receiving attention as an alternative cementitious material. However, one of the drawbacks of geopolymer production is the cost of chemical activators used in its synthesis. Studies are scanty on the use of Bamboo Wood Ash (BWA) as a less expensive alternative biomass ash activator in the synthesis of metakaolin clay geopolymers. Possibility of replacing a part of the alkaline commercial activator with alkaline-rich biomass ash activator was investigated. Metakaolin clay-based geopolymers were synthesised from kaolin clay obtained from Ikere-Ekiti, Ekiti state, Nigeria and calcined at 700°C for 6 hours. Bamboo wood was obtained as a waste from a construction site in Ibadan, ashed and used as alkaline source in place of NaOH. The chemical composition of BWA and calcined clay were characterised by X-ray fluorescence spectroscopy. Geopolymers with BWA to calcined clay ratios of 5:95, 10:90, 20:80, 30:70 and 40:60 were synthesised with sodium silicate solution. Setting time, compressive strength (at 7, 14, 21 and 28 days), water absorption and density of the geopolymers were determined and compared with 100% clay geopolymers synthesised with the reported 8M NaOH/Na2SiO3 activator. The BWA contained 22.9% K2O. Setting time of geopolymers increased with increasing ash/clay ratio, enhancing ease of handling and workability. At 28 days, the compressive strength values of the geopolymers containing less than 30% BWA are higher than the 28.9 MPa of the reference geopolymer. The 10% BWA:-calcined clay geopolymer exhibited the highest compressive strength (45.5 MPa), followed by 20% BWA geopolymer (38.8 MPa). Water absorption capacity values of BWA-metakolin clay geopolymers are lower than that of the reference geopolymer. Increase in the proportion of BWA resulted in increase in geopolymers bulk density. Bamboo wood ash is proposed as an alkali activator in geopolymer synthesis