Abstract
Micro-silica is widely used as an additive to cement in producing high performance concrete. This matter is used to enhance the strength and efficiency of concrete. Recently, due to the development of advanced nano-technology, nano-silica has been produced with particle sizes smaller than micro-silica and higher pozzolanic activity. Studies show that addition of nano-silica into cement-based materials improves their mechanical properties. Considering the unique characteristics of nano-silica, it seems that this material can be used in ultra-high performance concrete (UHPC). Therefore, further studies are needed on how the local bond and bond stress of steel reinforcing bar and UHPC containing nano-silica would be effected. In the present study, after preparing the mix designs and proposed specimens, the effects of various parameters on the local bond of steel reinforcing bars and UHPC containing nano-silica were examined by pullout experiments. In this research, we have numerically investigated the bond strength using numerical methods and calibration of the ABAQUS results in addition to its experimental study of ultra-high performance concrete and steel reinforcement. In numerical analysis, the concrete damage plasticity method was used to simulate the nonlinear behavior of concrete and its strain softness. Comparing between numerical and experimental analysis results shows that numerical analysis with high precision can predict the bond stress, bond load, and concrete specimen fracture mode.
Highlights
The ultra-high performance concrete (UHPC) has many advantages
In specimens R16C1L2, R16C1L3 and R16C1L4 containing ultra-high performance concrete with 6.5% nano-silica, due to the bond length increase, the bond stress decreased by 1.4%, 5.3% and 6.6%, respectively, compared to the specimen R16C1L1
It can be concluded that concrete cover has a significant influence on the bond stress between UHPC and steel reinforcement
Summary
The ultra-high performance concrete (UHPC) has many advantages. Due to its better mechanical properties and low permeability, this type of concrete is gradually replacing conventional concrete. Further research is needed on how to use it in concrete mix designs To this end, the present study used Pullout test to assess the effect of nano-silica on the bond stress between steel reinforcement and ultra-high performance concrete. (2016) conducted an experimental study on the bond stress between ultra-high performance concrete and steel reinforcement. S. et al (2016) conducted an experimental study on the bond stress between ultra-high performance concrete and 10, 13 and 19 mm steel reinforcements [5]. K.H. et al (2010) conducted an experimental study on the bond stress between ultra-high performance concrete and high strength steel reinforcements. The pullout test based on RILEM standards was used in this study [6] These experiments showed that the bond stress of ultra-high performance concrete is 5-10 times higher than conventional concrete. Duchesneau, F., et al (2011) conducted a monolithic and hybrid precast bridge parapets in high and ultra-high performance fiber reinforced concretes [11]
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