Fundamental understanding of the mechanical and post- cracking behaviour of ultra-high performance mortar with recycled steel fibers

The main goal of this paper was to assess the influence of recycled steel fibers sourced from end-life tires on the mechanical performance of self-compacting ultra-high performance mortars. For this purpose, mortars with different amounts of fibers, ranging from 1 to 3%, were prepared. Experimental, analytical and numerical studies were carried out in order to understand the brittle and post-cracking behaviour of the prepared mortar samples. The inspections of the fresh mortars revealed that there was a strong linear relationship between the relative slump flow and the dosage of the fibres. It was observed that mortars keep their self-compatibility when there is an addition of up to 3 % of fibre. In the mortars' hardened state, there was an increase of their mechanical properties i.e. compressive strength and flexural strength, with an increasing content of fibres. Compared to the reference mix, the compressive strength of reinforced mortars increased by 7%, 14% and 32% (7 days) and 7%, 14% and 40% (28 days) when 1%, 2% and 3% of fiber were utilised. Moreover, it was observed that by 1%, 2% and 3% addition of fibres the flexural strength increased by 7%, 14% and 17% (7 days) and 8%, 14% and 21% (28 days).Post-cracking behaviour of mortars was evaluated using residual flexural strengths in service limit state and ultimate limit state. Statistical analysis revealed a linear trend between those strengths and dosage of fibres. Regarding to the post-cracking behaviour, it was obtained that, the mortars with the addition of 1% of fibres did not show any post-cracking responses. However, the behavior of their matrix during failure can change from being brittle to being ductile. It was observed that, the proposed models in RILEM and EN 14651 overestimated the crack mouth opening displacement responses. Accordingly, a new model was proposed in this study. The results of experimental program were validated using finite element simulations. The proposed numerical models allowed the occurrence of cracks, and their propagations, to be detected, and the obtained results were similar to those from the experimental studies.