Effect of Carbon Nanotubes (CNTs) aspect ratio on the rheology, thermal conductivity and mechanical performance of Portland cement paste

Abstract

Carbon nanotubes (CNTs) are potential candidates to enhance the heat balance of concrete, reducing internal stresses caused by differential heating in massive concrete elements. The higher the aspect ratio (AR) and content of CNTs, the greater the expected thermal conductivity (TC). However, high AR may impair the proper dispersion of CNTs in cementitious matrix, potentially harming the workability and mechanical strength of the composite. This work evaluated the effect of the AR (35, 250, 900, and 3500) and content (0.05% and 0.10%) of CNTs on the TC, rheology (squeeze flow), and mechanical strength of cement paste. Results showed that 0.05% CNT increased the TC of paste by up to 15% for AR of 250, but further increasing AR progressively reduced the TC of the composite. In turn, 0.10% CNT incorporation did not result in significant TC gains. The yield stress and viscosity of the mixes progressively increased as CNTs content and AR increased, by up to 119% compared with plain cement paste. No significant differences were observed in 28-day compressive strength with 0.05% CNT incorporation, while 0.10% CNT led to slight strength reductions for some mixes. Regarding flexural strength, 0.05% incorporation of either CNT decreased the strength of the mixes while 0.10% incorporation generally compensated this reduction, except for the lowest aspect ratio. Overall, CNTs with intermediate AR (around 250) was effective in improving the thermal conductivity of cement paste, increasing it by 15% with relatively low content (0.05%) while did not significantly impair the fresh and mechanical performance of the composite.

Utilization of Thermally Treated SiC Nanowhiskers and Superplasticizer for Cementitious Composite Production

“…These results agree with those reported by Du et al [20], who observed increases in the thermal conductivity of geopolymer-SiC composites and this was expected since SiC whiskers are excellent heat conductors [20,42]. Similar results were also reported for the cementitious matrix reinforced with carbon nanotubes [43]. The higher increases in thermal conductivity with the addition of 500-NWs compared with NT-NWs are probably due to the higher surface area of the former.…”

Why Carbon Nanotubes Improve Aqueous Nanofluid Thermal Conductivity: A Qualitative Model

“…Longer CNT particles are more uniformly aligned in the fluid and create continuous pathways for heat conduction [81]. However, in some literature, the effect of aspect ratio on thermal conductivity is not guaranteed [82].…”

Mechanical Strength and Conductivity of Cementitious Composites with Multiwalled Carbon Nanotubes: To Functionalize or Not?

“…Fewer studies of composites were found for electrical conductivity, and none were found for thermal conductivity, using the criterion of a pristine MWCNT control sample. It is known that the thermal conductivity of cementitious composites improves with the addition of nanotubes [ 12 , 81 , 87 ] for both pristine and functionalized MWCNTs.…”

“…Thermal conductivity of cementitious composites improves on the addition of nanotubes [ 12 , 81 , 87 ]. To the authors’ knowledge, there are no studies where the thermal conductivity of cementitious composites was compared for bare and functionalized MWCNTs.…”