Study of the Dispersion, Working, and Mechanical Properties of Carbon Nanotubes in Ultrahigh-Performance Concrete

The dispersibility of carbon nanotubes (CNTs) in ultrahigh-performance concrete (UHPC) under different preparation processes was investigated. The dispersion stability, dispersion degree of CNT aggregates, and absorbance of CNT dispersions were measured by static observation, microscope observation, and ultraviolet spectrophotometer. The results showed that compared with adding polycarboxylic acid superplasticizer (SP) after ultrasound, adding SP at the same time as ultrasonic CNT solution obtained a better dispersion of the CNT solution. When the mass ratio of SP to CNT was 1∶1, the dispersion of CNT suspension was the best under 400-W ultrasonic power for 30 min. The flow properties, setting time, and compressive strength of CNT-modified UHPC also were studied. The experimental results show that the flow performance of CNT-UHPC decreases with the increase of CNT content. The condensation time of CNT-UHPC decreases with the increase of CNT content. The addition of 0.1% by weight CNT can improve the compressive strength of UHPC and refine the microstructure of UHPC. In conclusion, the study results can help to improve the dispersion and stability of carbon nanotubes in UHPC and effectively enhance the strength of UHPC adding carbon nanotubes in terms of working performance, mechanical strength, and microscopic morphology.