Chemical corrosion of external stairs – case study

Abstract

On the basis of examinations of the efflorescences formed on the concrete surface, an attempt was made to analyze the sources of concrete corrosion without entering inside the construction. The concrete stairs revealed the symptoms of leaching, as a result of alkali-aggregate reactions developing beneath the surface. As a result of this corrosion process and the carbonation propagating from the concrete surface, the carbonate efflorescences were found. Their phase composition was determined by X-ray diffraction. In order to identify whether the efflorescences were the results of the alkali-silica reaction or alkalicarbonate reaction, the microstructure was investigated using the scanning electron microscope together with energy dispersive spectroscopy.

Condition assessment of selected reinforced concrete structural elements of the bus station in Kielce

“…On their basis, it was found that the aggregate used to make the concrete includes: quartz, calcite and dolomite. In all three concrete samples (two coming from reinforced concrete columns and one of the reinforced concrete slab from the level "-1"), a vaterite was found, which is formed as a transitional product during the carbonation of cement paste [15][16][17][18][19][20].…”

Diagnostics of Concrete and Steel in Elements of an Historic Reinforced Concrete Structure

“…Carbonated cement paste in concrete is characterised by reduced compactness and/or evident absence of portlandite. In this pastes in the place of portlandite various calcium carbonates are formed [ 28 , 66 , 72 , 73 , 74 , 75 ]. As a result of carbonation on the surface of the portlandite, amorphous calcium carbonates are formed, which over time turn into vaterite, from which aragonite can be formed.…”

“…Microstructural studies using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) are often performed as complementary studies to phase analyses [ 22 , 28 , 72 , 74 , 77 ]. By observing the microstructure, changes can be observed on the surfaces of portlandite crystals as a result of the carbonation process [ 71 ] in the form of visible carbonation products ( Figure 1 ).…”

“…Laboratory tests of the concrete samples show that as a result of the carbonation process, the paste underwent significant changes. Three polymorphic forms of calcium carbonate (CaCO 3 ): calcite, aragonite and vaterite are visible in the X-ray diffraction pattern in Figure 8 a [ 28 , 86 ]. Analysis of the used aggregate ( Figure 8 b) reveals the presence of only a trace of calcite.…”

“…On the other hand, in the case of seaside facilities located in the coastal zone (port and tourist buildings), exposed either to the direct influence of sea salt or to the so-called salt mist, as well as road structures (bridges, viaducts, flyovers), concrete surfaces, parking lots and open garages, due to the use of de-icing agents containing NaCl, the cause of degradation is the action of chlorides [ 10 , 21 , 23 , 24 , 25 , 26 , 27 ]. Sulphates that degrade concrete are also dangerous [ 28 , 29 ].…”