Characterization and Comparison of Corrosion Layer Microstructure between Cement Mortar and Alkali-Activated Fly Ash/Slag Mortar Exposed to Sulfuric Acid and Acetic Acid

Abstract

In this study, we investigated the formation and evolution of the corrosion layers in alkali-activated mortar and ordinary Portland cement mortar exposed to sulfuric acid and acetic acid environments with different pH values, and explored the differences in the deterioration mechanisms. The experimental results indicated that ordinary Portland cement (OPC) mortars experienced more severe deterioration in terms of appearance, mass loss, and strength loss as compared with alkali-activated mortars exposed to an acetic acid environment, but their neutralization depths were smaller. Alkali-activated fly ash (AAF) mortar had a the relatively intact appearance but the greatest neutralization depth, which was due to its stable three-dimensional network but highly porous structure. To sum up, alkali-activated fly ash/slag (AFS) mortar had the best resistance to acid attack. In addition, the mortars exposed to acetic acid suffered greater deterioration than those exposed to sulfuric acid with the same pH values, which was mainly due to the highly porous corrosion layer formed in acetic acid, whereas crystallization of gypsum in sulfuric acid had a pore filling effect. However, for alkali-activated slag (AAS) and OPC mortars exposed to a sulfuric acid environment, extensive gypsum resulted in the formation of micro-cracks, and the corrosion layer of OPC mortar was more prone to fall off. OPC mortar also had the greatest resistance difference values of the continuously connected micro-pores before and after acid corrosion, followed by AAS, AAF, and AFS mortars, and these values for all the specimens were smaller in sulfuric acid. Furthermore, the gaps between acetic and sulfuric acid attacks increased with increased calcium content in binders, which were 7%, 13%, 21%, and 29% for AAF, AFS, AAS, and OPC mortars, respectively. Thus, it can be inferred that an appropriate amount of gypsum existed in the corrosion layer which could act as a barrier to some extent ina sulfuric acid environment.

Thermodynamic Modeling and Experimental Validation of Acetic Acid Attack on Hardened Cement Paste: Effect of Silica Fume

“…The solids investigated in this study via XRF represent a similar state as the XRD pattern after ‘161 h, ground’ in Figure 9 a, whereas XRD patterns in other studies [ 1 , 3 , 6 , 19 , 20 , 21 , 22 ] investigated bulk samples, which are more comparable to the example after ‘161 h, washed, ground’ in this figure.…”

“…The intense reddening of the liquid phases for low pH values is probably due to leached iron, which reacts with acetic acid to form red ferric acetate aqueous complex and further hydrolyzes to reddish brown ferric hydroxide colloid, which is very soluble [ 19 ]. The colors of the solids are more difficult to interpret because they may be influenced by colored compounds subsequently precipitated during filtration due to the small amount of water used for washing (see the discussion concerning XRD during drying).…”

“…The main link between chemistry and transport is mostly (over) simplified by using an (apparent) diffusion coefficient that should consider the changes in porosity [ 11 ]. Typically, the acidic acid attack on cement-based materials is investigated by using large samples such as cylinders or cubes [ 1 , 3 , 6 , 19 , 20 , 21 , 22 ]. Therefore, the changes in chemical composition and structural and mechanical properties can be studied.…”

Nano-Modified Vibrocentrifuged Concrete with Granulated Blast Slag: The Relationship between Mechanical Properties and Micro-Structural Analysis

“…The issue of the durability of concretes and mortars based on slag has also received much attention [26,30,[32][33][34][35][36]. At the same time, these characteristics of solutions with the addition of DHS as frost resistance [30] and resistance to chlorides [34], sulfates [33], and various acids [26,32] were studied.…”

“…The issue of the durability of concretes and mortars based on slag has also received much attention [26,30,[32][33][34][35][36]. At the same time, these characteristics of solutions with the addition of DHS as frost resistance [30] and resistance to chlorides [34], sulfates [33], and various acids [26,32] were studied. Moreover, the authors of many works consider the joint effect of GBFS and other additives (ash, limestone, gypsum, nanosilica) on the formation of the micro-and macrostructure of materials based on them and their physical and mechanical characteristics [10,28,30,[35][36][37][38].…”