Analysis of the compressive creep strain of the concretes with steel fibers: A holistic view in micro and macro scale

The aim of this paper is to evaluate the behavior of steel fiber reinforced concrete (SFRC), compared to concrete without fiber at the strength classes of 30 MPa and 50 MPa and subjected to compression creep. The volumetric contents of steel fibers were 0.38, 0.50, 0.64 and 0.77%. Test were carried out on concrete specimens at the age of 28 days, subjected to compressive strength from 30 to 40% of the estimated ultimate compressive strength, in controlled conditions of temperature and relative humidity. The duration of loads was 84 days. Thus, elastic deformation (ED) and specific creep (SC) values were measured. In addition, the theoretical SC was calculated based on Brazilian standards and compared to the experimental SC. As a result, no specimen failed under constant loads during the study time. The ED was higher for C30 concretes (about 35 x 10-6/MPa) than for C50 concretes (nearly 23 x 10-6/MPa), independent of the volume of fibers. Besides that, C30 concretes showed values of specific creep ranging of from 3.4 to 5.6 x 10-6/MPa and from 2.4 to 3.9 x 10-6/MPa for C50. This performance was justified by the microstructural differences in the cement matrices and their hydrated products, cracks, and porosity, among others. Moreover, there was a difference between the experimental and theo-retical specific creep values. For the C30 series, these differences were 50% and for C50 were 20%. The volumetric fraction of steel fibers of 0.38% and 0.50% produced minors creep strain for C50 and C30, respectively. This reduction corresponded to 24.4% and 41.7% in comparison to reference concrete. On a macroscopic and mesoscopic scale, this optimum fiber content can be important for controlling of crack open, crack widths, crack propagation, and durability of concrete harsh environments. Finally, the positive impact on concrete durability properties was discussed in terms of scientific arguments.