چكيده به لاتين
In the last two decades, the appearance of graphene oxide has attracted a lot of attention and many researches have been conducted on the reinforcing effects of graphene oxide in cement composites. But regardless of the favorable effects of graphene oxide, the thing that has turned its use into a serious challenge is the uniform and stable dispersion of these nanosheets in cement composites. Until today, many efforts have been made to improve the dispersion of graphene oxide, which are either not adequate and sufficient, or may cause harmful side effects on the structure of graphene oxide, or are not compatible with cement hydration products; However, one method that has been suggested is the use of polycarboxylate ether along with pozzolanic materials. In this research, the effect of fly ash pozzolan on the dispersion and stability of graphene oxide nanosheets in water and alkaline cement medium was studied in order to find the optimal ratio between them. In this study, hypotheses for the performance mechanisms of fly ash in an alkaline cement environment, including the spatial obstruction mechanism and pozzolanic activity, were considered. In the spatial obstruction mechanism, it was assumed that fly ash particles can physically separate the nanographene oxide sheets and reduce their agglomeration in the cement matrix. Another hypothesis was based on the fact that fly ash particles can react with calcium hydroxide through their pozzolanic activity and produce a secondary hydrated calcium silicate gel, thus leading to a decrease in the concentration of calcium ions around the graphene oxide nanosheets and thus reducing the possibility of interaction between the nanosheets with polyvalent calcium ions and subsequent reduction of graphene oxide agglomeration. In this research, the effect of fly ash on the dispersion of graphene oxide was investigated first. then the mechanical properties of the cement paste containing both materials were examined. The results of pH measurement, ultraviolet-visible spectroscopy, visual examination, zeta potential, and scanning electron microscope imaging showed an increase in graphene oxide agglomeration with an increasing amount of fly ash in both aqueous and alkaline cement environments, but with the addition of polycarboxylate ether to the samples, dispersion of GO increased significantly, which became more stable in the presence of fly ash. Also, the results of mechanical tests on cement paste samples containing fly ash-graphene oxide show an improvement in compressive strength, bending strength, bending modulus of elasticity, and bending toughness by 27, 13, 58, and 25%, respectively, compared to the control sample at the age of 28 days. It was effective.
