A Brief Analysis of the Leaching Process in the Backfill Concrete of a Powerhouse

Abstract

The long-term behavior of concrete is an important topic where critical infrastructure projects are concerned. Deterioration of concrete structures subjected to aggressive water is often characterized by the leaching process that occurs gradually in structures in long-term contact with water. Leaching or lime-leaching refers to CaO (in reality Ca2+ and OH–) being removed from the concrete by dissolution in water. Leaching enlarges the pore system of the concrete temporarily increasing the permeability, although dissolved ions may later precipitate inside the pore system, reducing the permeability of the parts involved. Some variables are involved to a greater or lesser degree in such an event, such as hydrostatic pressure or environmental conditions. This study aims to advance research related to the leaching process in the foundation concrete of the Itaipu hydroelectric powerhouse. Previous analysis carried out up to 1993 indicated that there were no risks to the stability of this structure, which could negatively impact the operation of the electromechanical equipment, this being the reason why these analyzes have been partially discontinued since then. Although the instrumentation demonstrates satisfactory behavior of this section, there have been no specific studies regarding the recent characteristics of this section’s concrete. Among drains that exist in this region of the foundation, three of them concentrate the largest flows, currently about 2 l/s, whose chemical analyzes indicate that the concrete leaching still occurs, although the dissolved compound contents are much smaller than those at the beginning of the process. Concrete samples will be extracted to carry out laboratory tests, including compressive strength, to complement chemical tests and establish correlation between them, analyzing the long-term effects of leaching in this section.