Activation of Blast Furnace Slag with CFB Fly Ash as a Supplementary Binder Material: Hydration Products and Effects of Sulfate Attack
Abstract
:1. Introduction
2. Materials
- Portland cement (OPC):
- Blast furnace slag (BFS):
- CFB fly ash:
3. Experimental Methods
- The same cement-CFB fly ash-BFS mixed binder ratio was used to make mortar specimens to test for compressive strength and to evaluate the quality stability of CFB fly ash material from different sampled batches.
- Different proportions of CFB fly ash were mixed with BFS and used as supplementary binder material to replace Portland cement in making mortar bars for determination of volume change upon sulfate attack.
3.1. Compressive Strength
3.2. Hydration Products Investigation
3.2.1. Thermal Gravimetric (TG) Analysis
3.2.2. X-ray Diffraction (XRD) Analysis
3.2.3. Scanning Electron Microscope (SEM)
3.3. Volume Stability Test (Effects of Sulfate Attack)
4. Results and Discussion
4.1. Compressive Strength Development
4.2. Hydration Products
4.2.1. Thermal Gravimetric (TG) Analysis
4.2.2. XRD Analysis
4.2.3. Scanning Electron Microscope (SEM)
4.3. Volume Stability Test
4.3.1. External Sulfate Attack (ASTM C1012)
4.3.2. Internal Sulfate Attack (ASTM C1038)
5. Conclusions
- CFB fly ash sampled from different production batches was found to have stable quality based on the steady compressive strength development exhibited by mortars made with appropriate proportion of CFB fly ash, BFS, and cement.
- The main hydration products of the CFB fly ash-BFS-cement blends were found to be C-S-H gel, ettringite (AFt), gypsum, and some portlandite (CH). Anhydrite, portlandite, and calcium silicate hydrate can be found within 24 h of hydration.
- The high content of SO3 in CFB fly ash does not cause noticeable expansion of mortars containing various amounts of CFB fly ash upon external sulfate attack. ASTM C1012 test results show all mortar mixtures containing CFB fly ash have expansion much less than 0.1% after 270 days of immersion. The binders consisting of Portland cement, BFS, and CFB fly ash have much-improved resistance to external sulfate attack than OPC.
- Secondary or delayed ettringite formation is likely to occur in mortars containing excessive amount of CFB fly ash. According to the internal sulfate attack (ISA) test result by ASTM C1038, it shows that mixtures containing CFB fly ash release sulfates from high SO3 content in saturated lime solution and react with the large amount of free Ca2+ provided in the solution. Excessive use of CFB fly ash in a binder mixture may lead to the formation of secondary or delayed ettringite and affect the durability of the concrete through rapid expansion behavior. To maintain the dimensional stability of concrete, a suitable amount of CFB fly ash is suggested to be mixed with BFS at a weight ratio of no more than 20%.
Author Contributions
Funding
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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Composition | Binders | ||
---|---|---|---|
Portland Cement | Supplementary Binder Materials | ||
BFS | CFB | ||
SiO2 | 20.42 | 33.97 | 2.96 |
Al2O3 | 4.95 | 14.69 | 0.86 |
Fe2O3 | 3.09 | 0.34 | 0.52 |
CaO | 61.69 | 42.01 | 54.48 |
MgO | 3.29 | 6.26 | 1.36 |
SO3 | 2.40 | 0.41 | 25.17 |
K2O | -- | 0.27 | 0.36 |
Na2O | -- | 0.15 | 0.05 |
Free-CaO | -- | -- | 18.13 |
Portland Cement | Supplementary Binder Materials (SBM) | Ratio of CFB Fly Ash/SBM | W/B | |
---|---|---|---|---|
BFS | CFB Fly Ash | |||
20% | 80% | 0% | 0% | 0.485 |
72% | 8% | 10% | ||
68% | 12% | 15% | ||
64% | 16% | 20% | ||
60% | 20% | 25% | ||
56% | 24% | 30% |
Curing Age (Days) | Strength Range (MPa) | Average (MPa) | SD (σ) (MPa) | Coeff. of Variation (%) |
---|---|---|---|---|
3 | 13.4–27.8 | 19.0 | 3.1 | 16 |
7 | 27.2–34.9 | 31.1 | 2.7 | 9 |
28 | 35.9–44.1 | 40.1 | 2.4 | 6 |
56 | 38.9–48.5 | 44.6 | 2.8 | 6 |
Composition | Temperature Range (°C) | Weight Loss (%) | ||
---|---|---|---|---|
1 Day | 3 Days | 7 Days | ||
Gypsum, Ettringite C-S-H phase, C-A-S-H, C-A-H phase | 80–425 | 4.26 | 6.04 | 7.46 |
Ca(OH)2 | 450–550 | 0.63 | 0.71 | 0.96 |
CaCO3 | 600–750 | 3.31 | 2.96 | 3.64 |
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Chen, G.-Y.; Huang, W.-H. Activation of Blast Furnace Slag with CFB Fly Ash as a Supplementary Binder Material: Hydration Products and Effects of Sulfate Attack. Crystals 2022, 12, 41. https://doi.org/10.3390/cryst12010041
Chen G-Y, Huang W-H. Activation of Blast Furnace Slag with CFB Fly Ash as a Supplementary Binder Material: Hydration Products and Effects of Sulfate Attack. Crystals. 2022; 12(1):41. https://doi.org/10.3390/cryst12010041
Chicago/Turabian StyleChen, Guan-Yu, and Wei-Hsing Huang. 2022. "Activation of Blast Furnace Slag with CFB Fly Ash as a Supplementary Binder Material: Hydration Products and Effects of Sulfate Attack" Crystals 12, no. 1: 41. https://doi.org/10.3390/cryst12010041
APA StyleChen, G. -Y., & Huang, W. -H. (2022). Activation of Blast Furnace Slag with CFB Fly Ash as a Supplementary Binder Material: Hydration Products and Effects of Sulfate Attack. Crystals, 12(1), 41. https://doi.org/10.3390/cryst12010041