Geopolymer is a novel cementitious material that was first developed by Davidovits in 1978. It serves as a good alternative for ordinary Portland cement (OPC). Geopolymers are a class of inorganic polymeric amorphous materials that can be synthesized at low temperature. The synthesis of geopolymer involves the mixing of an aluminosilicate source with amorphous silica which is dissolved in highly caustic alkaline solutions. The structure of geopolymer consists a network of cross-linked tetrahedral aluminosilicate which is charge balanced by alkali metal cations such as sodium and potassium. The carbon footprint of the synthesis of geopolymer is very low and hence it is cheaper and more environmental friendly than conventional OPC. Geopolymer also has the advantage of higher compressive strength, better durability and faster curing. Geopolymer has been applied in many industries such as structural and mechanical engineering. There has been extensive experimental study on the properties, chemistry and synthesis of geopolymer at macroscopic scale. However, not much research has been done at the molecular scale for geopolymer. Therefore, in this study, the objective is to investigate the mechanical and fracture properties of geopolymer at nano-scale using atomistic scale simulation. Classical molecular dynamics (MD) is used as the computation method for this study. Large-scale atomic/molecular massively parallel simulator (LAMMPS) is used for the MD simulation. The structure of the geopolymer in the simulation is generated by placing the basic building block of sialate, sialate-siloxo or sialate-disiloxo units in the simulation box with metal cations and water molecules. The building block of sialate, sialate-siloxo and sialate-disiloxo corresponds to Si:Al ratio of 1,2 and 3. The metal cations used in the simulation are Na+ and K+. The structure is heated to 4000 Kelvin and equilibrated, followed by a rapid quenching to room temperature to obtain the amorphous structure of geopolymer. The Young’s modulus, strength and fracture properties are investigated for different Si:Al ratio and different metal cations. Uniaxial tensile test is simulated to generate the stress-strain curve of the geopolymer binder. Compact tension test with an initial crack is simulated to calculate the Mode I fracture toughness. The results provide both qualitative and quantitative insights about the mechanical and fracture properties of geopolymer binder. The final goal of this study is to provide a systematic framework to investigate the composition-mechanical property relation for geopolymer design.
|Published - Jun 26 2017