Effect of Carbon Nanotubes in Metakaolin-based Geopolymer Mortars on fracture toughness parameters and Acoustic Emission Signals

Effect of Carbon Nanotubes in Metakaolin-based Geopolymer Mortars on fracture toughness parameters and Acoustic Emission Signals

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Since geopolymers based on metakaolin are quite brittle materials compared to ordinary cement based materials it reduces the possibility of their application as construction material. Therefore, the objective of this investigation was to improve fracture toughness of geopolymer material by the application of carbon nanotubes, which have excellent tensile properties and can act as reinforcement on the nanoscale level. The effect of carbon nanotubes was evaluated by means of mechanical fracture tests and microscopic observations. The three point bending fracture tests were performed on five sets of beam specimens with initial stress concentrator to quantify the crack resistance of these materials, i.e. obtaining the values of mechanical fracture parameters (e.g. fracture toughness, fracture energy, modulus of elasticity). The material of specimens was different in amount of carbon nanotubes. First mixture was reference without nano-reinforcement, other mixtures contained carbon nanotubes in amount 0.05, 0.10, 0.15 and 0.20%, respectively. Load versus displacement diagrams (P–d diagrams) were recorded during experiments. Subsequently, these outputs were evaluated using an appropriate fracture model. The effective crack extension method and work-of-fracture method were used to evaluate the P–d diagrams in this paper. The acoustic emission measurements were also performed during the fracture experiments.

Since geopolymers based on metakaolin are quite brittle materials compared to ordinary cement based materials it reduces the possibility of their application as construction material. Therefore, the objective of this investigation was to improve fracture toughness of geopolymer material by the application of carbon nanotubes, which have excellent tensile properties and can act as reinforcement on the nanoscale level. The effect of carbon nanotubes was evaluated by means of mechanical fracture tests and microscopic observations. The three point bending fracture tests were performed on five sets of beam specimens with initial stress concentrator to quantify the crack resistance of these materials, i.e. obtaining the values of mechanical fracture parameters (e.g. fracture toughness, fracture energy, modulus of elasticity). The material of specimens was different in amount of carbon nanotubes. First mixture was reference without nano-reinforcement, other mixtures contained carbon nanotubes in amount 0.05, 0.10, 0.15 and 0.20%, respectively. Load versus displacement diagrams (P–d diagrams) were recorded during experiments. Subsequently, these outputs were evaluated using an appropriate fracture model. The effective crack extension method and work-of-fracture method were used to evaluate the P–d diagrams in this paper. The acoustic emission measurements were also performed during the fracture experiments.