Owing to a dense microstructure, reduced pore space and different fiber inclusions, ultra-high performance concrete (UHPC) has demonstrated a much higher compressive and tensile strength, lower permeability, increased durability and ductility than normal and high performance concretes (HPC). In addition, more than two decades of research on the correlation between the microstructure of ultra-high performance concrete (UHPC) and its mechanical properties demonstrated that by removing coarse aggregates from the concrete mix, thereby eliminating the interfacial transition zone (ITZ) from the microstructure, its mechanical properties can be significantly improved. However, recent experimental works suggest, eliminating the coarse aggregate completely, relinquishes its benefits such as reducing the autogenous shrinkage and lowering the cost of UHPC as it reduces the volume of the relatively expensive binder content.
The primary focus of this study is to apply a multi-level micromechanics based homogenization to investigate the elastic mechanical properties of UHPC. As UHPC is a multi-level composite whose properties are highly influenced by constituents existing at different length scales, a combined analysis of different modeling strategies is required to fully capture and understand its final effective property. Taking this into account, this study combines the tools of molecular dynamics (MD) and different micromechanical tools to parametrically investigate the effects of the different constituents.
Based on the multi-level homogenization and experimental investigation to validate the model’s predictions, the study was able to quantitatively prove the importance of CSH–gel constituents, the unreacted clinker reinforcing effect and the modulus reducing effects of gel and capillary porosity. In addition, the study also indicated the importance of fiber type and orientation. Moreover, it demonstrated the critical ranges for fiber aspect ratio and the significance of fiber interface effect on the final elastic property. Last but not least, the study quantitatively demonstrated the reducing effects of coarse aggregate on the effective property of UHPC.