Nonlinear finite element study on element size effects in alkali-activated fly ash based reinforced geopolymer concrete beam

The practical application of geopolymer concrete structure is getting attention due to its environmentally friendly characteristics. This paper presents non-linear Finite Element Analysis (FEA) on the element size effect in reinforced geopolymer concrete beam. Element size significantly influences the failure mechanism of structure especially in ductile fracture of reinforced concrete. The critical failure strain, crack patterns and orientations are mesh sensitive in finite element analysis for reinforced concrete structure. The impact of the element size on behavioral aspects of reinforced geopolymer concrete beam such as the crack pattern, ultimate load capacity and load-displacement behavior studies discussed along with a formerly conducted experimental data. Further validation of FEA is carried out using the theoretical flexural strength of the beam according to Euro code 2. Results show that element size has a significant effect in capturing the cracking pattern of reinforced geopolymer concrete beam. FEA result from the positive principal strain contour confirms that the fine mesh size captured the tension, the diagonal shear and compression cracks, even the band of surrounding cracks around the bottom reinforcement, precisely as compared to coarse meshes. It has been observed that the utilization of fine mesh with 10 mm element size predicts the experimental and theoretical ultimate load by 99.46% and 96.11%, respectively. Coarse mesh having 25 mm element size shows slightly higher variation in predicting the experimental and theoretical ultimate load by 93.75% and 90.42%, respectively. In addition, fine mesh confirms the experimental mid-span vertical deflection by 99.44% however the coarse mesh predicts in significant deviation by estimating 48.04% of the experimental mid-span vertical deflection. Furthermore, the ductile failure of the beam was accurately traced by the fine mesh.