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  • Metakaolin is the product of calcination of

    2020-08-03

    Metakaolin is the product of calcination of kaolinite rich clay at temperatures between 600 and 850 °C [11], [12] depending on the purity and the crystallinity of the initial clay. The geopolymers from metakaolin as aluminosilicate source have shown promising results in previous works [13], [14], [15] but they have not been considered as effective alternative binders to Portland cement. Less workability and brittleness due to high water demand, shrinkage and cracking during the drying process were pointed as problems affecting the use of metakaolin geopolymers [14], [16]. New methods of elaborating geopolymers using Rice Husk Ash were proposed in the literature. Kusbiantoro et al. [17] studied compressive strength of microwave incinerated RHA and fly ash geopolymer. He et al. [18] characterized red mud/RHA husk ash based geopolymers. In both studies a mixture of sodium silicate and sodium hydroxide was used as alkaline solution. Developments in the fabrication of pure LDN193189 from RHA have shown that sodium silicate can be obtained in the process [19], [20], [21], [22], [23]. RHA has also been shown as a promising Supplementary Cementing Material (SCM) in concrete or as pozzolanic materials with hydrated lime due to its high reactivity [24], [25], [26]. Bouzon et al. [27] observed similarity in strength when they used a suspension of RHA/NaOH heated in a reflux system as an alternative commercial water glass (sodium silicate) for fluid catalytic cracking (FCC) for geopolymer design. Tchakouté et al. [28] and Kamseu et al. [29] recently used RHA to produce geopolymers from metakaolin and RHA, but their focus was to synthetize sodium silicate using RHA. Little attention was given to partial substitution of metakaolin by RHA in the solid mix before reacting it with the sodium hydroxide solution. The objective of the present work is to search for the optimum blend when 12.5–50% metakaolin is substituted by RHA and reacted with 10 M sodium hydroxide solution to produce geopolymers. It was hypothesized that the amorphous silica from RHA will increase the Si/Al ratio of the mix and in situ react with sodium hydroxide to form the silicate gel that will contribute to the polycondensation reaction to improve the performance of the resulting geopolymer. The chemical and mineralogical characteristics and the specific gravity of raw materials were determined. The consistency and setting time of fresh geopolymer pastes were tested. Hardened products underwent tensile strength test based on the standard test method for tensile strength of chemical resistant mortars, grouts and monolithic surfacings, ASTM C 307-03 (2012) [30] for potential use of the elaborated material in non-structural applications in construction like repairs within tension zone and grout works (filling and sealing). Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry (SEM /EDX) and thermo-gravimetric (TG) analyses were also applied on hardened pastes test specimens.