Mechanism of rate dependent behaviour of ultra-high performance fibre reinforced concrete containing coarse aggregates under flexural loading

Shaohua Li,Ole Mejlhede Jensen,Qingliang Yu

doi:10.1016/j.conbuildmat.2021.124055

Abstract

Coarse aggregates are often eliminated in ultra-high performance fibre reinforced concrete (UHPFRC) for the sake of homogeneity, however, this causes an impairment on impact resistance. The flexural performance of UHPFRC with coarse aggregates under different loading rates (0.2, 20 and 200 mm/min) is investigated here to clarify the flexure and energy absorption mechanism. The flexural behavior and crack propagation are measured, meanwhile, the fracture of coarse aggregates and the surface morphology of steel fiber are analysed. The results show the energy absorption tends to be more rate dependent than the first crack stress and flexural strength. An increase of crack propagation speed and multiple cracks are observed at higher loading rates. The percentage of fracture across coarse aggregate is 23%, 32% and 58% at loading rates of 0.2, 20 and 200 mm/min, respectively. Further, a rate-dependent model for predicting the fracture of coarse aggregates is proposed. The present results contribute to designing UHPFRC with enhanced flexural performance under different loading rates.

Highlights

With superior mechanical strength, high resistance to cracking and excellent energy absorption capacity, Ultra-high Performance fibre reinforced Concrete (UHPFRC) is considered a very useful material for impact and blast resistant structures [1,2,3], e.g. nuclear power plants, military structures and high risk buildings, which have a potentially high risk of being exposed to loadings with different loading rates
Coarse aggregates are often eliminated in ultra-high performance fibre reinforced concrete (UHPFRC) for the sake of homogeneity, this causes an impairment on impact resistance
The response and post-impact properties of UHPFRC with coarse basalt aggregates under low-velocity impact were measured, and the results showed that coarse aggregates can be successfully introduced into UHPFRC

Summary

Introduction

High resistance to cracking and excellent energy absorption capacity, Ultra-high Performance fibre reinforced Concrete (UHPFRC) is considered a very useful material for impact and blast resistant structures [1,2,3], e.g. nuclear power plants, military structures and high risk buildings, which have a potentially high risk of being exposed to loadings with different loading rates. The excellent mechanical performance of UHPFRC is achieved by optimizing microstructure and improving homogeneity [4,5]. To achieve a good homogeneity, coarse aggregates are eliminated in UHPFRC to decrease the size of microcracks, which is proven to be proportional to the size of. Eliminating coarse aggregates increases the production cost, and increases the autogenous shrinkage [5]. The resistance of UHPFRC structures under projectile impact and blast has been shown to be associated with the size and strength of coarse aggregates [7,8,9]. Without coarse aggregates, impact and blast resistance of UHPFRC structures are impaired

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Conclusion