Cementitious materials are commonly and extensively used worldwide by construction industry for various types of infrastructures. Despite of their exceptional strength in compression they still possess limited tensile strength and tensile strain capacity. Different types of fibers have been investigated since last fifty decades to reinforce the cementitious matrix against tensile failures and to impart ductility. The size of the reinforcing fillers has diminished from macro to micro and now even to the nano scale with the recent advancements in nanotechnology. Due to exceptional intrinsic properties and large aspect ratio, carbon nanotubes have been successfully investigated as a reinforcing filler to modify the mechanical strength, fracture toughness, electrical and electromagnetic wave absorbing properties of cementitious composites. However the problems associated with its effective dispersion and bonding with the host material limit its widespread applications on large scale. To overcome the aforementioned issues concerning the dispersion and bonding of nano reinforcing materials with the host matrix, graphene nano sheets were explored for the first time as a reinforcing agent for high performance cementitious matrices. Graphene sheets are free form entanglement problems and therefore need comparatively lesser energy for proper dispersion. Due to very high specific surface area and large aspect ratio in comparison with carbon nanotubes they are much capable to develop strong interfacial bond with the host medium. In the commercialization of these nano carbon particles filled cementitious composites, another major concern would be the related expenses. Therefore in parallel, research work was also done to explore the cost effective alternatives for the production of carbon nano particles to be used for modification or improvement in the properties of cement matrices. In recent wok by Prof. Ferro’s research team it has been explored that carbon nano particles produced from coconut shells can be effectively used to improve the mechanical strength and fracture toughness of cementitious composites with limited dispersion issues (G. Ferro et al. 2014, 2015). To continue with the productive research pertaining the cost effective production of carbon nano particles for high performance cementitious composites, bio-waste in the form of bagasse fibers, hazelnut shell and peanut shell was investigated. These particular types of agricultural wastes were selected keeping in view their economic availability as well as the excellent conversion efficiency via pyrolysis. The present work encompasses complete characterization of the investigated materials, detailed study on their dispersion ability in water and the cement matrix, entire mechanical characterization of reinforced cementitious composites at varying proportions as well as their electromagnetic wave absorption properties in 2-10 GHz frequency range. It was determined that graphene nano-platelets can be uniformly dispersed in water as well as in the cementitious matrix without any addition of separate dispersant or surfactant or stabilizing agent. It was found that even at a very low content of addition remarkable improvements in the mechanical strength and fracture toughness were attained. The optimum content of addition for the grade 4 graphene nano-platelets was found as 0.08 wt% providing with a significant increase of 89% and 29% in compressive and flexure strength along with 115% improved fracture toughness. Similarly the carbonized particles produced for bio-waste were found quite effective in modifying the mechanical performance of cementitious composites. Maximum enhancement by 139% and 88% in flexural and compressive strength were achieved on 0.2 wt % addition of nano/micro carbonized particles produced from peanut shell with an increase of 69% in the fracture toughness as well. Microstructural investigations evidenced the proper homogeneous dispersion of GNPs and NMCPs throughout cementitious matrix along with their efficient filling action to refine the pore-structure of the cementitious composite. The phenomena of crack bridging, crack deflections, crack contouring and crack branching were observed via scanning electron microscopy revealing the mechanism behind the remarkable improvements of mechanical properties achieved in the present research. A novel cost effective material in the form of cement composites containing carbonized agricultural residue (comprising CPS and CHS) was proposed for shielding against electromagnetic waves. The investigated material was found much efficient for electromagnetic interference shielding applications, providing the advantage of better dispersion, simple manufacture at a much lower cost (cost saving ˃ 85%) compared to the corresponding carbon nanotubes based cement composite material.

High Performance Self-Compacting Cementitious Materials Using Nano/Micro Carbonaceous Inerts / Khushnood, RAO ARSALAN. - (2015). [10.6092/polito/porto/2604995]

High Performance Self-Compacting Cementitious Materials Using Nano/Micro Carbonaceous Inerts

KHUSHNOOD, RAO ARSALAN
2015

Abstract

Cementitious materials are commonly and extensively used worldwide by construction industry for various types of infrastructures. Despite of their exceptional strength in compression they still possess limited tensile strength and tensile strain capacity. Different types of fibers have been investigated since last fifty decades to reinforce the cementitious matrix against tensile failures and to impart ductility. The size of the reinforcing fillers has diminished from macro to micro and now even to the nano scale with the recent advancements in nanotechnology. Due to exceptional intrinsic properties and large aspect ratio, carbon nanotubes have been successfully investigated as a reinforcing filler to modify the mechanical strength, fracture toughness, electrical and electromagnetic wave absorbing properties of cementitious composites. However the problems associated with its effective dispersion and bonding with the host material limit its widespread applications on large scale. To overcome the aforementioned issues concerning the dispersion and bonding of nano reinforcing materials with the host matrix, graphene nano sheets were explored for the first time as a reinforcing agent for high performance cementitious matrices. Graphene sheets are free form entanglement problems and therefore need comparatively lesser energy for proper dispersion. Due to very high specific surface area and large aspect ratio in comparison with carbon nanotubes they are much capable to develop strong interfacial bond with the host medium. In the commercialization of these nano carbon particles filled cementitious composites, another major concern would be the related expenses. Therefore in parallel, research work was also done to explore the cost effective alternatives for the production of carbon nano particles to be used for modification or improvement in the properties of cement matrices. In recent wok by Prof. Ferro’s research team it has been explored that carbon nano particles produced from coconut shells can be effectively used to improve the mechanical strength and fracture toughness of cementitious composites with limited dispersion issues (G. Ferro et al. 2014, 2015). To continue with the productive research pertaining the cost effective production of carbon nano particles for high performance cementitious composites, bio-waste in the form of bagasse fibers, hazelnut shell and peanut shell was investigated. These particular types of agricultural wastes were selected keeping in view their economic availability as well as the excellent conversion efficiency via pyrolysis. The present work encompasses complete characterization of the investigated materials, detailed study on their dispersion ability in water and the cement matrix, entire mechanical characterization of reinforced cementitious composites at varying proportions as well as their electromagnetic wave absorption properties in 2-10 GHz frequency range. It was determined that graphene nano-platelets can be uniformly dispersed in water as well as in the cementitious matrix without any addition of separate dispersant or surfactant or stabilizing agent. It was found that even at a very low content of addition remarkable improvements in the mechanical strength and fracture toughness were attained. The optimum content of addition for the grade 4 graphene nano-platelets was found as 0.08 wt% providing with a significant increase of 89% and 29% in compressive and flexure strength along with 115% improved fracture toughness. Similarly the carbonized particles produced for bio-waste were found quite effective in modifying the mechanical performance of cementitious composites. Maximum enhancement by 139% and 88% in flexural and compressive strength were achieved on 0.2 wt % addition of nano/micro carbonized particles produced from peanut shell with an increase of 69% in the fracture toughness as well. Microstructural investigations evidenced the proper homogeneous dispersion of GNPs and NMCPs throughout cementitious matrix along with their efficient filling action to refine the pore-structure of the cementitious composite. The phenomena of crack bridging, crack deflections, crack contouring and crack branching were observed via scanning electron microscopy revealing the mechanism behind the remarkable improvements of mechanical properties achieved in the present research. A novel cost effective material in the form of cement composites containing carbonized agricultural residue (comprising CPS and CHS) was proposed for shielding against electromagnetic waves. The investigated material was found much efficient for electromagnetic interference shielding applications, providing the advantage of better dispersion, simple manufacture at a much lower cost (cost saving ˃ 85%) compared to the corresponding carbon nanotubes based cement composite material.
2015
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2604995
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