Tensile response of UHPFRC under very low strain rates and low temperatures

Abstract

This paper addresses the uniaxial tensile response of Strain Hardening Ultra High-Performance Fiber Reinforced Concretes (SH-UHPFRC) subjected to very low strain rates and low temperatures. The influence of four different strain rates; 1 × 10 −5 , 1 × 10 −7 , 1 × 10 −8 and 5 × 10 −9 1/s on the tensile properties like elastic limit, elastic modulus, tensile strength and the strain at tensile strength, was studied for two types of SH-UHPFRC mixes; Mix I with type I cement and silica fume, and Mix II with silica fume and 50% mass replacement of type I cement with limestone filler, at three curing temperatures; 20°C, 10°C and 5°C. The tests at strain rates lesser than 1 × 10 −6 1/s are the first of their kind for UHPFRC materials and the results show a considerable impact on the elastic limit of the mixes. Acoustic Emission tests were also carried out for validation of test results of the elastic limit.

Performance Comparison between Densified and Undensified Silica Fume in Ultra-High Performance Fiber-Reinforced Concrete

“…Along with compressive strength and durability, excellent crack resistance performance is one of the main features of UHPFRC, which can contribute to the construction of innovative and sustainable concrete structures [ 70 ]. This is the reason that the strength under flexural or tensile loading is an important property of this concrete [ 71 ]. Regarding this, one notable result was that, unlike the compressive strength, which increased due to the promoted pozzolanic reaction, there was no noticeable change in flexural tensile strength despite the increase in temperature (60 to 90 °C) and duration (up to 4 days) during heat treatment [ 72 ].…”

Modelling of the tensile behavior of SH-UHPFRC at low and high stress levels, under very low loading rates

“…The influence of very low strain rates on the tensile properties of the mixes in the present study was discussed in detail in [10]. The elastic limit is the point that separates the activation of M1 and M2, and therefore it is very important to include the effect of strain rates on the elastic limit in the model.…”

“…Moreover, [5] showed that the viscoelastic response of UHPFRC of type CM22_TKK was much higher at an age of 2 days when compared to that at 7 days, and attributed this behavior to an ''early age hydration induced" non-linearity. The influence of time dependent phenomena on the strength and deformability of cementitious materials was shown by [6][7][8][9] for normal concrete and more recently for SH-UHPFRC under tension by [10], with the general conclusion that the strength properties increase with an increase in the rate of loading. However, the trend of effect of strain/stress rate on the strain at tensile strength (deformability) is not fully understood.…”

“…However, the trend of effect of strain/stress rate on the strain at tensile strength (deformability) is not fully understood. [11][12][13][14][15][16] reported an increase in the strain at tensile strength with an increase in the strain rate whereas [6,10,17] reported a decrease. Furthermore, at higher stress levels, the non-linear viscoelasticity is influenced by damage [18][19][20][21][22], thereby exhibiting a much higher relaxation response along the failure envelope (non-linear) when compared to that at lower stress levels.…”

Tensile response of Ultra High Performance PE Fiber Reinforced Concretes (PE-UHPFRC) under imposed shrinkage deformations

“…8, the S-UHPFRC (I) entered the hardening domain when the eigenstresses in this specimen reached the elastic limit at 10 MPa which is lower than 12.3 MPa that stated in Table 2. The differences between these two values can be explained considering the fact that in this case, the specimen was loaded under very low loading rate of imposed shrinkage deformations, and the decrease in the strain rate considerably decreases the elastic limit of the UHPFRC [46]. This highlights the importance of considering eigenstresses in designing UHPFRC layers for rehabilitation.…”