Towards understanding the behavior of fiber-reinforced concrete in aggressive environments: Acid attacks and leaching

Abstract

This article intends to study the influence of metal fibers on the behavior of concrete exposed to aggressive media. The main contribution of the experimental work proposed here lies in the detailed monitoring of the concrete degradation process as a function of fiber deterioration.To do this, fiber-reinforced and non-fiber-reinforced concretes were immersed respectively in concentrated solutions of 5 % hydrochloric acid (HCl), sulfuric acid (H2SO4) and acetic acid (CH3COOH), over a period of 135 days. At the same time, the leaching phenomenon was studied for the same formulations by exposing the concretes under study to a concentrated solution of 6 mol/l of ammonium nitrate NH4NO3, for a period of 462 days. Afterwards, fiber-reinforced concretes were tested and compared with non-fiber-reinforced concrete in terms of ultrasonic pulse velocity (UPV), porosity, mechanical properties, microstructure using the scanning electron microscopy (SEM) and the X-ray diffractometry (XRD), mass loss, degradation thickness, electrical conductivity and diffusion of calcium ions.The experimental results showed that the incorporation of metal fibers reduces the porosity by 14% and consequently improves the mechanical performance of concrete in a healthy environment. In acidic environments, fiber-reinforced concretes begin to lose their efficiency after only a few weeks as a result of the corrosion of the metallic fibers, thus engendering compressive strength drops between 10% and 19% and flexural strengths drops from 14% to 48%, depending on the nature of the acid used. On the other hand, fiber-reinforced concretes are more resistant to ammonium nitrate (NH4NO3) because the diffusion phenomenon of calcium ions is slower. In addition, the microstructural study revealed that the interfacial transition zone (ITZ) of fiber-reinforced concretes, exposed to HCl, increases by 10 times compared to the ITZ of concretes preserved in a healthy environment, and by 6 to 7 times for fiber-reinforced concretes immersed in other aggressive solutions.