Abstract
Nowadays, the sulfate attack on concrete structures is one of the serious problems in the Middle East region. On the other hand, rate of C3A and C4AF in cement clinker has increased, related with the increase of amount of industrial-by-product. Therefore, the purpose of this research is to evaluate the sulfate resistance of specimens mixed with C4AF and gypsum after autoclave curing. The influence of C4AF and gypsum on the formation mechanisms of tobermorite also have been examined by X-ray diffraction analysis and FT-IR. As the result of sulfate immersion test, the results of length change ratios of specimens with autoclave curing were much better than specimens with water curing. At low additional ratio of C4AF, tobermorite peak was detected by X-ray diffraction analysis. On the other hand, tobermorite peak was not detected at high additional of C4AF, and the frequency of 980cm-1 and 1,050cm-1 was confirmed by FT-IR. Therefore, improvement of sulfate resistance for the specimens with autoclave curing is due to the generation of tobermorite at low additional ratios of C4AF and the generations of Si structures like tobermorite at high additional ratios. Also, the formation of tobermorite was increased by the addition of gypsum, and the generation of hydroxyl-ellestadite that is intermediate during autoclave curing of tobermorite was suggested at specimens mixed with gypsum.
