ABSTRACT
The exploration of the potentiality of Acha (Digitaria Exilis) husk (AH) as an alternative pore-former in insulating bricks was investigated. X-ray florescence (XRF) analysis was conducted for both beneficiated and un-beneficiated kaolin sample. Fourier Transform Infra-Red (FTIR) and XRF analysis was conducted for five AH samples sourced from different locations. The beneficiated kaolin was calcined at 1280oC and milled into six different grain sizes, which were further collapsed into two coarse: fine grog ratios. Batch formulation of the dried AH, grog ratios and beneficiated kaolin was made using Andreason‟s Parameter. Two variables were investigated. AH wt% varied between 1-10% in each five Coarse: fine grog ratio that is, 70:30, 66:34, 60:40, 55:45 and 50:50. Insulating bricks were produced by semi-dry mixing and hydraulic press. Samples were dried and fired in a kerosene fueled Kiln at 1280oC. The results showed that, sinterability of the beneficiated kaolin for drying and firing shrinkage were 6% and 7.4% respectively. Atterberg plasticity index (API) result was 18%classified as intermediate plasticity. Particle size distribution (PSD) result showed that, more than 71% of the kaolin sample passed through mesh 200 (75μm). XRF analysis results of kaolin sample showed that, 31.60% Al2O3, 54.80% SiO2and 0.87% Fe2O3 were within tolerable limits required for refractory materials while the AH results showed, 6.67% Al2O3in addition to other oxides, a major advantage because it enhances the refractoriness of the bricks. FTIR analysis showed high percentage of organic materials in the AH, which are highly combustible, enhancing their insulating properties. Results obtained from the property tests of insulating bricks showed that, total shrinkage increased with increased in AH contents. Coarse: fine grog ratios 50:50 and 60:40 results ranged from1.0% - 2.1% compared with Indian Standard Testing Methods (ISTM, 2014),which ranged from 0.5% - 1.5%. Apparent porosity test results ranged between 20% - 75% for Coarse: fine ratios 50:50 and 60:40, meeting the acceptable range of international standard 20 – 80% and ISTM ranged between 45 – 70%.Bulk density generally decreased with increase in AH. It ranged between -0.9g/cm3- 1.58g/cm3for grog ratios 50:50, 55:45 and 60:40 compared with ISTM 0.65g/cm3-1.60g/cm3. Thermal conductivity decreased with increased AH content and values obtained ranged between 0.005 – 0.32 W/m.k , the minimum is outside ISTM values 0.23 – 0.70 W/m.k. the maximum is within. Cold Crushing Strength (CCS) results showed that higher the coarse grog size, lower the CCS while high fine grog size resulted to high CCS. Also as AH admixture increased, CCS reduced. Thermal shock resistance results of the ten samples showed no crack or warpage after passing through 30 cycles and rated excellent thermal shock. It was concluded that, insulating bricks with good physical, mechanical and thermal properties were noted in Coarse: fine grog ratios, 66:34, 55:45 and 50:50, maximum AH content 6%.Bricks No 10, 11, 12, 14 and 19 gave optimal results. From these products, AH produced uniformly distributed micro-porosity in the solid bricks. The AH is of circular morphology and fine enough to allow better binding and relatively high bulk density. This conferred structural strength to the insulating bricks which can be used where compressive strength is required. Further investigation of potential properties of AH to ascertain its thermal integrity is recommended.
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