Effect of nano-silica on the flexural behavior and mechanical properties of self-compacted high-performance concrete (SCHPC) produced by cement CEM II/A-P (experimental and numerical study)

Abstract

The extensive use of cement exacerbates the greenhouse effect by increasing carbon dioxide (CO₂) emissions. So, many standards recommend using Portland-composite cement in construction as one of the methods for reducing CO₂ emissions, especially cement CEM II/A-P. This paper presents an extensive experimental and numerical study to investigate the effect of micro and nano-silica on the flexural behavior and mechanical properties of Self-Compacted High-Performance Concrete (SCHPC) produced by cement CEM II/A-P. The extensive experimental work consisted of eight mixtures: three with micro-silica (MS), four with nano-silica (NS), and a reference mixture without silica. For both MS and NS, different percentages of adding or replacement content were tested to study their effect on the following: (a) the workability of fresh concrete, (b) concrete compressive strength, (c) splitting tensile strength, (d) flexural behavior including flexural tensile strength, and (e) the optimum percentage of each of the MS and NS to get the maximum structural and economic benefits of using for SCHPC with CEM II/A-P. Also, through a statistical program, these experimental results were used to obtain accurate formulae that could predict both the splitting tensile strength (f_sp) and modulus of rupture (f_ctr ) for SCHPC with adding nano-silica. In addition, the numerical study verified the experimental results based on the finite element program ANSYS. The flexure behavior of SCHPC beams is verified using the Microplane model (recently added to ANSYS). The experimental results showed that adding NS is more effective than replacing or adding MS for SCHPC mixture with CEM II/A-P to increase the concrete compressive strength, splitting tensile strength, and flexural tensile strength, especially for the mixture with adding NS content of 4 %. The numerical results showed the ability of the coupled damage-plasticity microplane model to simulate the flexural behavior of the tested SCHPC beams with MS or NS well. This research confirms nano-silica's structural and economical efficiency in the behavior of SCHPC beams. It was found that the optimum percentage of adding NS is 4 % for SCHPC mixtures with CEM II/A-P.