Flexural tensile behaviour of alkali-activated slag-based concrete and Portland cement-based concrete incorporating single and multiple hooked-end steel fibres

In this study, three-point bending tests on notched beams according to EN 14651 have been
performed to evaluate the flexural post-cracking behaviour of alkali-activated slag-based concrete
(AASC) and Portland cement-based concrete (PCC) incorporating single (3D) and multiple (4D,
5D) hooked-end steel fibres in different volume fractions up to 0.75 %. According to the exper-
imental results, the post-cracking residual flexural strength increases with the increase in the fibre
volume fraction for each fibre and concrete matrix type. AASC mixes incorporating 3D and 4D
fibres show higher values of residual flexural strength for the same crack opening than PCC mixes
with the same fibre type and dosage. Only for the mixes incorporating 5D fibres, steel fibre-
reinforced PCC (SFRPCC) mixes outperform steel fibre-reinforced AASC (SFRAASC) mixes in
terms of post-cracking behaviour. According to EN 14651, the values of the residual strengths fR1
and fR3, corresponding to a crack mouth opening displacement (CMOD) of 0.5 mm and 2.5 mm,
respectively, and their corresponding characteristic values fR1k and f$_{R3k}$ , respectively, can be
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derived from the experimental load-CMOD curves. Following the fib Model Code 2020, each mix
can then be classified according to the values of fR1k and the fR3k/fR1k ratio. As a result, empirical
models have been developed for SFRPCC to predict the values of f$_{R1}$ and f$_{R3}$ and the applicability
of such models to SFRAASC is evaluated in this study. Once the values of fR1k and f$_{R3k}$ are known,
tensile constitutive models can be derived according to the fib Model Code 2020 and used as input
parameters for finite element modelling. In this study, the accuracy of the code-based constitutive
model to predict the flexural behaviour of SFRAASC and SFRPCC is evaluated using the concrete
damage plasticity (CDP) model available in ABAQUS. The numerical model based on the tensile
stress-strain curve in the fib Model Code 2020 can qualitatively capture the post-cracking
behaviour of SFRAASC and SFRPCC incorporating 3D, 4D and 5D at 0.25 % fibre volume frac-
tion, despite overestimating their tensile strength. For higher fibre volume fractions, the CDP
model, in conjunction with the mode I parameters derived from the fib Model Code 2020, is
unable to adequately describe the post-hardening behaviour exhibited by the composites.