Effect of mixing duration on flexural strength of multi walled carbon nanotubes cementitious composites

- Long mixing durations improve CNT dispersion within the cement paste.
- Effect of CNTs on the flexural strength of cement pastes was investigated.
- Surfactant/superplasticizer overdosing causes a flexural strength reduction in CNT cementitious composites.
- Quantification of CNT dispersion in cement was performed.
- Well dispersed CNTs results in lower voids content in CNT cementitious composites.

This paper investigates the effect of mixing duration on the flexural strength of multi-walled carbon nanotubes (MWCNTs) reinforced cementitious composites. Each batch containing 0.03%, 0.08%, 0.15% or 0.25% MWCNT to cement weight fractions was prepared using mixing durations of 1.5, 15, 30, and 60 min. On the 28th day, the flexural strengths of the specimens prepared from the batches, were obtained using three-point bending tests. The specimen microstructures were investigated using scanning electron microscope (SEM) and image analysis techniques. The purpose of the investigation was to identify potential relationships between strength, dispersion, void ratio, and mixing duration. The results showed that increasing the mixing duration improved the dispersion and strength of most MWCNT reinforced cementitious batches. They also showed a high flexural strength increase for MWCNT reinforced cementitious batches containing a 0.25% CNT to cement weight fraction and mixed for 60 min. Moreover, the results showed that increasing the mixing duration resulted in a reduction of the percent void ratio of MWCNT reinforced cementitious batches. These findings are significant for a wide variety of concrete applications where higher flexural strength and small void are needed.