Steel-fiber reinforced concrete is a composite material that is composed of steel fibers distributed in the matrix of the concrete. The fibers are responsible for improving flexural strength and limiting cracks formation. In addition, the benefits of the steel-fibers in tension cannot be overemphasized. Unfortunately, in compression, little has been researched concerning the effect of fiber content particularly when it comes to fatigue. In fact, for the little that has been researched, there is a scarce variety of compositions and limited number of tests.
A number of studies have been done emphasizing the benefits of fiber in compressive fatigue behavior, but many have not focused on the effect of the amount of fibers on the fatigue life. Some have also not focused on the loading frequency of the tests. However, it is necessary to emphasize that concrete fatigue tests present a great dispersion of results, which may even reach two orders of magnitude for particular stress levels. Therefore, it becomes necessary to resort to a number of tests for which statistical distribution will be pegged to restricted cycles.
Elisa Poveda, Gonzalo Ruiz, Rena C. Yu and Xiaoxin Zhang at Universidad de Castilla-La Mancha in collaboration with Héctor Cifuentes at Universidad de Sevilla in Spain designed a robust self-compacting matrix for low and high fiber amounts while guaranteeing sufficient workability as well as good fiber matrix adherence in all the dosages. This therefore fulfilled the requirements of fresh self-compacting concrete. Their main aim was to establish the optimum fiber content in the low-cycle compressive fatigue and the effect of the dosage on the cyclic creep curve as a parameter that identifies fatigue damage. Their research work is published in International Journal of Fatigue.
The authors analyzed the effect of fiber content in steel-fiber reinforced concrete on the mechanical attributes under low cycle fatigue. The authors therefore prepared five types of self-compacting concrete with varying fiber content, varying from 0 to 0.8% in volume. They maintained the same concrete matrix while guaranteeing the adherence and flowability between fibers and the matrix in all dosages. As opposed to other fatigue studies, this one provided a complete characterization of the materials.
In the static behavior, the authors observed that the fibers did not produce appreciable improvement in compressive strength. However, fibers produced a more gradual softening after the maximum load. Increasing the fiber content enhanced the post peak flexural behavior.
The researchers observed that increasing the amount of steel fibers improved the compressive fatigue behavior. This is because the fatigue life of concrete improves when fibers are added. Concerning the fiber content, in plain concrete, low amount of fiber did not give more improvement in the fatigue attributes. However, intermediary contents led to fatigue life that was five times longer than that of plain concrete. The dosage that resisted a good number of cycle was that of the intermediary content, that of 45kg/m3 followed by that of 30kg/m3. However, increasing the fiber content past the optimum content led to shortening of the fatigue life. This is referenced to the fact that high fiber content distorted that matrix and produced pores as well as imperfections that favored crack initiation.
The authors also verified that the relationship between the secondary strain rate per cycle with the fatigue life was independent of the amount of fibers, and therefore depended on the matrix only. Based on the results obtained, the authors proposed a strain-based fatigue failure criterion entailing mechanical as well as time-dependent deformation.
Elisa Poveda, Gonzalo Ruiz, Héctor Cifuentes, Rena C. Yu, Xiaoxin Zhang. Influence of the fiber content on the compressive low-cycle fatigue behavior of self-compacting SFRC. International Journal of Fatigue, volume 101 (2017), pages 9–17.
Go To International Journal of Fatigue