The Impact of Chloride and Sulphate Aggressiveness on the Microstructure and Phase Composition of Fly Ash-Slag Mortar
2. Materials and Methods
2.1. CFBC Fly Ash
2.2. Ground Granulated Blast Furnace Slag
2.3. Specimen Preparation
2.4. Test Methods
- The chloride and sulphate ion contents were assessed as per standard . The test procedure set out in the standard defines transient state diffusion, since the stream of diffusing aggressive ions changes over time. As the changes can be induced by the binding of ions in the material, fragments of previously cut mortar slices were ground separately in a porcelain mortar, and the wet chemical analysis was applied . Then the content of chloride ions (for 6 slices) and sulphate ions (for 4 slices) for each of the mortar slices exposed to the action of NaCl and Na2SO4 was determined. It was noted that the analysis results were related to the binder content in the mortars, taking into account the natural moisture of the specimens.
- The sulphate content results were then converted into SO42− content. Furthermore, water extraction as per  was executed for each of the slices (6) of each specimen, after previously grinding and sieving the material through a 1.0 mm mesh-sized filter. Water extracts were used as a mortar pore liquid model, where the pH was determined.
3. Results and Analysis
3.1. Flexural and Compressive Strength
3.2. Chloride and Sulphate Ion Content
3.3. Phase Composition Qualitative Tests
- The action of a NaCl and Na2SO4 solution caused a reduction of flexural strength of bars in comparison to the strength of specimens stored in tap water, probably due to the microcracks which were observed in the specimens.
- The impact of chloride and sulphate ion diffusion on the compressive strength of mortars is minor and within measurement uncertainty limits. The compressive strength of the specimens exposed to chloride aggressiveness is lower than the strength of specimens exposed to sulphate aggressiveness.
- Chloride action had a slight (adverse) influence on the pH of the pore liquid. However, no impact of sulphate action of the pore liquid pH was noted—this outcome may be due to its formation in a NaOH solution.
- Chloride and sulphate concentration in the specimen decreased with increasing specimen depth.
- Based on the tests, it can be concluded that the content of chlorides and sulphates in the specimen was lower than the limit concentration at a distance of less than 60 mm from the specimen’s plane of contact with the aggressive medium.
- The qualitative tests of phase composition using the XRD method revealed minor amounts of Friedel’s salt in the specimen exposed to the action of chloride ions.
- The diffraction patterns for all studied specimens exhibit the clear presence of quartz, calcite, calcium aluminosilicates, and ettringite. The presence of a small amount of Friedel’s salt was recorded in specimens subjected to diffusion with chloride ions.
- SEM-EDS microstructure tests indicated that there were more microcracks on the surface of specimens subjected to ion diffusion than the surface of other specimens. Moreover, sodium chloride in the form of regular crystals was evident. In addition, chlorine ions were incorporated into the hydrated calcium aluminosilicates.
- The local presence of ettringite crystals in the form of pseudo-hexagonal columns were identified in the microstructure of specimens exposed to sulphate ion diffusion.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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|No.||Ingredient||Ingredient Content [g]|
|3||CFBC fly ash||135|
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Falaciński, P.; Machowska, A.; Szarek, Ł. The Impact of Chloride and Sulphate Aggressiveness on the Microstructure and Phase Composition of Fly Ash-Slag Mortar. Materials 2021, 14, 4430. https://doi.org/10.3390/ma14164430
Falaciński P, Machowska A, Szarek Ł. The Impact of Chloride and Sulphate Aggressiveness on the Microstructure and Phase Composition of Fly Ash-Slag Mortar. Materials. 2021; 14(16):4430. https://doi.org/10.3390/ma14164430Chicago/Turabian Style
Falaciński, Paweł, Agnieszka Machowska, and Łukasz Szarek. 2021. "The Impact of Chloride and Sulphate Aggressiveness on the Microstructure and Phase Composition of Fly Ash-Slag Mortar" Materials 14, no. 16: 4430. https://doi.org/10.3390/ma14164430