Portland cement composites with carbon nanotubes (CNT) addition: Properties in freshly state and compressive strength

Currently there are some studies on the addition of carbon nanotubes (CNTs) in cement composites. These studies indicate enhancements in the mechanical properties, such as increase in compressive strength, tensile strength and durability, and porosity decrease. Based on these possible improvements, this research was conducted to analyze the influence of CNTs on the compressive strength of mortar for rehabilitation of concrete structures, as well as in their consistency. Compressive strength, squeeze flow, flow table, marsh funnel and mini-slump tests were carried. A control mortar and paste were used (without carbon nanotubes added), which was replicated with the same mix proportioning and the incorporation of 5 levels of CNTs related to the cement mass: 0.1%, 0.2%, 0.3%, 0.4% to 0.5%. These concentrations were chosen to cover the commonly range used in researches about Portland cement composites with CNTs addition. Regarding the tests for measuring the fluidity of mortars and pastes, it was found that the higher the percentage of CNT, more consistent the cement Portland composite became, with evidence that smaller or equal to 0.3% levels of NTCs are more adequate to maintain the fluidity of the Portland cement composite. Results indicate that the addition of 0.40% of carbon nanotubes increases the compressive strength by 27%. On the other hand, addition of 0.5% of CNT became the Portland cement composite very consistent, making difficult the molding process, so that the increase in compressive strength was zero compared to the control mortar.