Abstract

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.

Highlights

  • Nanotechnology has gained much attention for research in the development of materials with unique properties

  • This work investigated the effect of the Carbon nanotubes (CNTs) aspect ratio on the rheology, thermal conductivity and mechanical properties of Portland cement paste

  • Based on the results presented, the following conclusions were drawn: (i) Squeeze flow test showed that the increase in CNT content progressively increased the yield stress and viscosity of the paste, by up to 119% in comparison with plain cement paste

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Summary

INTRODUCTION

Nanotechnology has gained much attention for research in the development of materials with unique properties. Carbon nanotubes (CNTs) are potential candidates for use as nano reinforcements in Portland cement-based materials [5] It exhibits extraordinary strength (tensile strength in the range of GPa) and modulus of elasticity in the order of TPa, in addition to having unique electronic and chemical properties [1]. The very high specific surface area of CNTs and their trend for clustering tend to reduce the flowability of cement paste when CNTs are added [27] Such flowability loss may be overcome with the incorporation of superplasticizer as confirmed by Skripkiunas et al [28]. This work investigated the effect of CNTs aspect ratio on the thermal conductivity and rheological properties of cement paste (through the squeeze flow test), in addition to mechanical performance characterization

Materials and mixes
Sample preparation
Testing methods
Rheological behavior
Mechanical tests
CONCLUSIONS
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