Effect of Carbon Nanostructures on Thermal Properties of Cementitious Materials

  • Fatima Bardan

Student thesis: Master's Thesis

Abstract

Cement used in constructing concrete structures is one of the most used synthetic materials in the world. The importance of thermal properties of cementitious materials is justified by many practical needs such as mitigating early-age cracking of concrete structures, enhancing the cooling and heating energy consumption of buildings, and improved thermal energy storage capabilities. Therefore, enhancing the thermal properties of cement-based materials like thermal conductivity and specific heat enable to enhance the thermal properties of concrete. Recently, a various range of additives at the micro and nano scales have been used to enhance mechanical properties of cementitious materials like carbon nanofibers (CNFs) and multi-walled carbon nanotubes (MWCNTs) with much less emphasis on thermal properties. This work investigates the effect of adding carbon nanostructures on thermal properties of cementitious materials by using a new and cost-effective carbon nanostructures (CNS) that have been developed by the well-known defense company Lockheed Martin Corporation and compare it with commercially-available MWCNTs. Experiments for obtaining thermal conductivity and specific heat for different percentages of CNS and MWCNTs with cement at various temperatures are presented. Additionally, the effect of surfactant, which is used in dispersing nano-filaments in aqueous solutions, on the thermal properties of the cement paste nanocomposite is studied. The results show a significant increase of thermal conductivity and specific heat of small concentrations of CNS and MWCNTs, and that the hydration of cement paste has a significant impact on the thermal properties of samples at high temperatures (above 100 °C). It is shown that the degradation in thermal properties of the nanocomposite cement is significantly mitigated with the addition of CNS and MWCNTs. The specific heat and thermal conductivity of 1% CNS (by weight of cement) with cement paste samples in present of surfactant show the best performance over the temperature range studied in this work (20 to 150 ° C). The results show reduction in thermal properties at high concentrations of CNS due to the agglomeration of CNS in cement paste that leads to increasing the air void content in the samples. On the other hand, the samples of 0.1% MWCNTs with cement show high specific heat at higher temperatures, and have the highest thermal conductivity and lower air void content. Based on the results, one of the targeted applications where the material with high specific heat could be potentially used is in thermal energy storage. While the material with high thermal conductivity could be used in reducing early-age thermal stresses in concrete structures, accelerating ice and snow melting on roads and bridges, and heating/cooling energy efficiency in buildings.
Date of AwardMay 2017
Original languageAmerican English

Keywords

  • Carbon Nanostructures;Thermal Properties; Cementitious Materials; Multi-Walled Carbon Nanotubes (MWCNTs); Thermal Energy Storage; United Arab Emirates.

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