Binary Blended Plantain Stalk Ash-Metakaolin as Source Materials for Sustainable Geopolymer Concrete

R. B. Oyeleke, J. H. POGU

Abstract: Concrete is one of the most extensively used construction material in the world. The research aims at examining the potential use of bio-ash derived from plantain stalks biomass as sustainable material in the production of geopolymer concrete. Large quantity of the first source material was collected from the dump site of a segment of the Kaduna Central market designated for sales of all kinds of fruits. At the onset, biomass was collected and transported to the Civil Engineering Laboratory, Kaduna Polytechnic, thereafter, sundried and burnt into ashes in a fabricated steel rotary kiln. The burnt ash was then pulverised with a ball milling machine. A second source material used was metakaolin derived from is industrial kaolin subjected to elevated temperature of 750 oC in a furnace and at retention time of 1 hr. For material characterisation, series of physicochemical tests were performed on several aliquots obtained from both materials. Tests performed include, visual inspection, particle density, LOI, scanned particle morphology, types and quantity of metal oxide via X-Ray Fluorescence, mineral composition via X-Ray diffractometer, FTIR and determination of pH. Geological mineral aggregates used include oven dried mass of fine river sand, quarry dust and gravels as coarse aggregate are combined either in fine-to-coarse ratio of 1: 1 (1000 g: 1000 g) or river sand - to-quarry dust-to-coarse grave ratio of 1: 1: 2 (500 g: 500 g: 1000 g). For production of the geopolymer concrete, alkaline liquid prepared from a combination of NaOH and Na2SiO3 at a concentration of 12 M. Also, ratio of the activator solution-to-(PPSA + MK) by dry mass was maintained at 0.4 throughout the research. The designed aggregates were mixed with the prepared geopolymer binder; the aggregates formed about 75% of the entire mixture by mass, which was adapted for the research. In its fresh state, the mixture was poured into the 5 fabricated steel moulds (70 mm x 70 mm x 70 mm), vibrated on vibrator table, air cured for 24 hrs under transparent low density polythene, then steam cured at varying steam temperature of 60 oC or 90oC. Finally, series of crushing strength tests were carried out on all the 110 test cubes on completion of the recommended 28 day air-cured. Test trend obtained from the three experimental hypotheses put forward indicate that, as the mixing duration increases from 2 to 10 day (stepwise of 2), the average compressive strength increase from 15.45 N/mm2 to 22.15 N/mm2, when steam-cured at 60 oC, as against 19.78 N/mm2 to 28.21 N/mm2, steam9cured at 90 oC. The effect of variation in the duration steam-cure at varying temperature showed average compressive strength of 9.10 N/mm2 (for the control cubes) to 35.81 N/mm2 steam-cured at 60 oC. Whereas, average compressive strength of 9.53 N/mm2 was obtained for control specimen. This later increased to 38.81 N/mm2 at 5 day subjected to 90 oC steam-curing temperature. The proposed blended kaolin-PPSA source material has been proven to be a promising alternative matrix in the production of sustainable geopolymer concrete.

Keywords: Geopolymer binder, Plantain Stalk, Metakaolin, Physicochemical tests