Properties and Mechanism on Flexural Fatigue of Polypropylene Fiber Reinforced Concrete Containing Slag

Properties and mechanism were investigated on flexural fatigue of concrete containing polypropylene fibers and ground granulated blast furnace slag（GGBFS）.Four polypropylene fibers’volume fractions and five slag proportions were considered.An experiment was conducted to obtain the fatigue lives at three stress levels in 20 Hz frequency and at a constant stress level of 0.59 in four frequency respectively.Mechanism and evaluation were investigated based on the experimental data.Fatigue life span models were established.The results show that the addition of polypropylene fibers improves the flexural fatigue cumulative strength and fatigue life span.It is proposed that the slag particles and hydrated products improve Interfacial Transition Zone（ITZ）structure and benefit flexural fatigue performance.A composite reinforce effect is found with the incorporation of slag and polypropylene fibers.The optimum mixture contents 55%slag with 0.6%polypropylene fiber for the cumulative fatigue stress.Fatigue properties are decreased as the stress level increasing,the higher frequency reduces the fatigue strength more than lower frequency at a constant stress level.

Flexural Fatigue Behavior of Polypropylene Fiber Reinforced Segment Concrete

The influence of polypropylene fiber on the flexural fatigue performance of high-strength concrete (HSC), which could be used as cover of reinforcement of segment, was investigate by three-point load bending tests. Also, the flexural fatigue equations of high-strength concrete with and without polypropylene fiber were established through test analysis. The experimental results indicate that the addition of polypropylene fiber can improve the static bending strength of segment concrete, and the important is that it can markedly increase the flexural fatigue performance of the HSC subjected to cyclic bending load. Especially when with 1.37 kg/m3 addition of the fiber was corporate with silica fume and slag powder, the fatigue life of the HSC can be increased by 43.4% compared to that of the segment concrete without fiber, silica fume and slag.

Damage and Fatigue Failure of Conventional and Bulk-Filled Resin Composites

Objectives: Resin-based composites are the most widely used dental restorative materials. Bulk-fill resin composites are of rising interest as they can be clinically applied in thicker increments compared to conventional composites. The purpose of the study was to evaluate the flexural fatigue strength of a conventional and bulk-filled resin composite placed incrementally or non-incrementally. Methods: Resin composite specimens were fabricated using either a conventional (Brilliant EverGlow?) or a bulk-fill (Fill-Up!TM) resin composite by either non-incremental filling (2 × 2 × 25 mm3) or in increments of (1 × 2 × 25 mm3). Specimens were stored in distilled water for 24 h or thermocycled for 5000 cycles. The static flexural strength (σ), flexural fatigue limit (FFL) after 105 cycles and post-fatigue flexural strength (PFσ) were measured. Data were analyzed using ANOVA, with a post-hoc Tukey’s test to compare mean FFL (p σ and PFσ compared to conventional composites regardless of incremental cure or thermocycling (p σ and FFL for conventional composites but not bulk-filled composites. There was no significant difference in PFσ compared to σ after 24 h storage, but a significant increase in PFσ after thermocycling (p < 0.05). Conclusions: The type of composite rather than incremental placement had a greater effect on flexural strength, suggesting that operator placement technique had less influence than material selection. Thermocycling in combination with cyclic loading caused a strengthening effect in the composites, likely due to the absorption and dissipation of stresses, thereby enhancing resistance to fracture.