Influence of carbon nanotubes on properties of cement mortars subjected to alkali-silica reaction

This research investigates the impact of carbon nanotubes (CNTs) on the expansion, mechanical properties, and microstructure of cement mortar subjected to alkali-silica reaction (ASR). A total of eight compositions were cast to investigate the influence of CNT surface condition, concentration and aspect ratio, and ultrasonication energy. Two types of CNTs were used as reinforcement: pristine CNTs with an aspect ratio of 800 (Type I) and COOHfunctionalized CNTs with an aspect ratio of 2500 (Type II). CNTs were incorporated at concentrations of 0.1c-wt. % and 0.3c-wt.%. The results indicated that certain combinations of mix proportions could significantly mitigate the ASR-induced damages in the mortar bar test (ASTM C1260). Specimens reinforced with 0.1c-wt.% of Type I CNTs exhibited the highest resistance to alkali-silica reaction. While specimens reinforced with 0.3c-wt.% of Type II CNTs had marginal improvements. More specifically, specimens reinforced with 0.1c-wt.% of Type I CNTs reduced the 14-day ASR expansion by 73% against control, and increased the 28-day compressive strength, flexural strength, static and dynamic elastic moduli by 22%, 36%, 54%, and 22%, respectively. Finally, scanning electron microscopy and X-ray energy-dispersive spectroscopy revealed that CNTs resist ASR with three main chemo-mechanical mechanisms: 1) restrain crack propagation, 2) refine the pore structure of the composite, and 3) reduce the alkalinity of the pore solution by altering the ASR gel compositions.

Automated summary

This research investigates the impact of carbon nanotubes (CNTs) on the expansion, mechanical properties, and microstructure of cement mortar subjected to alkali-silica reaction (ASR). The results show that certain combinations of mix proportions can significantly mitigate the ASR-induced damages in the mortar. Specifically, specimens reinforced with a certain type of CNTs can reduce the ASR expansion and improve the compressive strength, flexural strength, and elastic moduli. Scanning electron microscopy and X-ray energy-dispersive spectroscopy reveal that CNTs resist ASR through three main chemo-mechanical mechanisms.