Effect of multi-walled carbon nanotubes on characteristics of cement paste

Cement has been used as the major construction material for many years in the field of civil engineering. Although cement concrete is known to have high compressive strength, researchers are working on developing even higher strength higher durability concretes, e.g., high performance concrete. Since its development by Iijima in 1991, carbon nanotubes (CNT) have been identified as a noble material in different disciplines like aircraft, sports and other industries. Since, structural integrity has been a key issue in case of civil engineering construction too, it is envisaged that these CNT can actually be an ideal reinforcing agent for cement concrete and other construction materials. With this vision, experimental techniques were designed to mix CNT with cement and test the composites thus prepared.;The major objective of this research was to study different aspects like mechanical behavior, durability against weathering, nano-scale bonding of cement-CNT composites, and effect of CNT on cement setting process. In this research, a control mix along with several CNT-cement composites with different CNT loading were prepared after dispersing CNT by sonication and mixing with just water and cement.;The control mix and cement-CNT composites were tested for 'compressive, splitting tensile and flexural strengths' to investigate mechanical behavior. Similarly, 'rapid freezing and thawing test' was done to check their durability against weathering along with 'scanning electron microscopy' and 'transmission electron microscopy' tests to find out nano-scale bonding of cement-CNT composites. Furthermore, 'A-scan ultrasonic test' was done to figure out the effect of CNT on the cement setting process.;From mechanical strength tests, the performance of cement-CNT composites with 0.5% CNT content was found to be better than that of the control mix. Above 0.5% CNT content, the strengths went down and at a CNT content of 1%; the strengths were much lower than that of the control mix. Cement-CNT composites were found to be inferior to the control mix as far as performance during rapid freezing and thawing test was concerned. The chemical bonding between complex cement compounds and CNT was not identified. However, the physical anchoring of cement compounds with CNT was seen. Moreover, from ultrasonic test, presence of CNT seemed to hinder the cement setting process.;In summary, results of this study indicate that if the bonding property of carbon nanotubes with cement could be enhanced and a suitable technique to disperse nanotubes uniformly is adopted, this may provide opportunities to get more promising results.