Quantitative microstructural characterisation of Portland cement‑carbon nanotube composites using electron and x-ray microscopy

Durability Characterisation of Portland Cement–Carbon Nanotube Nanocomposites

“…This effect is illustrated in the C-S-H formations surrounding dispersed CNTs shown in Figure 7 . This finding is supported by microstructural characterisation conducted on the same material reported in a separate study [ 16 ].…”

“…In contrast to the lower dosage mixes, specimen C 25 , with 0.25 wt.% CNTs, exhibited only a 1% (within the estimated uncertainty for the experiment) lower mean resistance to chloride diffusion compared to the reference mix. With the higher CNT dosage loading within the nanocomposite, it is hypothesised, and supported by previous research quantitatively characterising the size and spatial distribution of porosity (and CNTs) within the material [ 16 ], that there was a greater prevalence of randomly distributed small, localised CNT agglomerations, as well as closer average spacing of CNTs throughout the nanocomposite microstructure, thereby leading to additional diffusive pathways for chloride ions to transport through the material.…”

“…However, at 28 days, although the expected ongoing hydration reactions in the reference specimen R 0 resulted in a small decrease in the sorptivity coefficient, the nanocomposite N 10 exhibited a dramatic reduction in the sorptivity (32% smaller than for the reference at the same age), indicative of a significant refinement to the connected capillary pore network within the nanocomposite specimen compared to the unmodified reference paste. A companion study [ 16 ] on the effects of CNTs upon the microstructural development of the OPC–CNT nanocomposite demonstrated quantitatively that, as the nanocomposite aged, specimen N 10 showed an increase in the relative proportion of hydration products including C-S-H. This resulted in a further refinement of the pore network—compared to that observed in specimen R 0 —and led to the 45% reduction in the rate of initial water absorption from the 7-day specimen.…”

“…Reference specimens R 1 and R 0 with and without the addition of the cement superplasticiser, respectively, were also prepared for the purpose of comparison with the OPC–CNT specimens. For all OPC–CNT specimens incorporating a superplasticiser, a fixed superplasticiser-to-CNT ratio of 4 was used, following prior studies [ 16 , 34 ] with demonstrated CNT dispersion. A total water (including the superplasticiser)-to-binder ratio (w:b) of 0.4 was used for all mixes.…”

“…The examination and subsequent segmentation of the microstructure of specimens for fluid flow simulations was performed according to a process detailed in a companion study previously reported by the authors [ 16 ]. Cropped 500 µm × 500 µm × 500 µm volumes (resolution of 0.9–1.3 µm) were produced from the X-ray computed microtomography (XR-µCT) experimental datasets investigated in this study.…”