Mineralogical investigation of microbially corroded concrete. (2). Microbial corrosin on mortar bar.:(2) Microbial Corrosin on Mortar Bar

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Mortar bars are exposed to H<SUB>2</SUB>S gas (25-300ppm) for 10 months at 12-30C°. Sulfate-generated deteriorations in the mortar bars include expansion, cracking and disintegration. The heavily corroded mortar bar produced gypsum, calcite and secondary ettringite with a trace amount of barite. The secondary ettringite shows the same chemistry as the primary ettringite, but the morphology is quite different from the primary one. Ettringite crystals with sharp point, 10-20μm long, are primary formed during the hydration of mortar bar, whereas small lath-shaped crystals, about 3μm long as observed by SEM are high concentration of hydroxyl ions. Gypsum, calcite and the secondary ettringite are formed step by step under acidic condition. The iron oxides layer is presented significantly between corroded and un-corroded zones which is the same process of deterioration on portland cement concrete.
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