1 Introduction
2 Refractory Concrete
3 Significance of Study
4 Experimental Study
4.1 Materials
Component | Cement | Silica fume (SF) |
---|---|---|
CaO | 40–36 | 1.5 |
SiO2 | 8–3 | 90–95 |
C | – | 0.8–3 |
Al2O3 | 42–36 | 1 |
Fe2O3 | 2–3.5 | 2 |
MgO | 1 | 2 |
K2O | – | 0.2–0.5 |
SO3 | – | – |
H2O | 0.01–0.4 | |
TiO2 | < 0.5 | |
Total alkali | – | – |
Specific surface area (m2/kg) | – | 15,000–30,000 |
Unit volume weight (kg/m2) | - | 310–350 |
Sieve No. | Sieve size (mm) | silica sand (T60) | Granite Waste |
---|---|---|---|
30 | 0.6 | 100 | 100 |
40 | 0.42 | 89.5 | 94.1 |
50 | 0.3 | 53.5 | 88.3 |
70 | 0.21 | 18.6 | 77.4 |
100 | 0.15 | 4.1 | 50.1 |
170 | 0.09 | 0 | 29.5 |
200 | 0.075 | 0 | 9.6 |
400 | 0.038 | 0 | 0 |
Component | Standard sand (ASTM C146, 2004) | Used silica sand | Used granite waste (GW) |
---|---|---|---|
SiO2 | 96–98.1 | 97–99 | 91.18 |
Fe2O3 | 0.2–0.7 | 0.2–0.6 | 1.9 |
Al2O3 | 0.51–1.63 | 0.4–1.7 | 0.22 |
CaO | 0.4–0.7 | 0.07–0.2 | 0.53 |
Na2O | 0.03–0.8 | 0–0.1 | 0.08 |
K2O | 0.02–0.08 | 0.02–0.06 | 1.13 |
MgO | – | – | 1.82 |
TiO2 | – | – | 0.05 |
P2O5 | – | – | 0.04 |
MnO | – | – | 0.11 |
SO3 | – | – | 0.37 |
Cl | – | – | 0.05 < |
LOI | – | 0.01–0.35 | 2.72 |
4.2 Mix Designs
Mixture No | SF/B | W/B | Amount of ingredients (kg/m3) | ||||
---|---|---|---|---|---|---|---|
C | SF | B | W | Agg | |||
M1 | 0.15 | 0.17 | 1190 | 210 | 1400 | 243 | 685 |
M2 | 0.15 | 0.2 | 1190 | 210 | 1400 | 284 | 606 |
M3 | 0.2 | 0.17 | 1120 | 280 | 1400 | 243 | 694 |
M4 | 0.2 | 0.2 | 1120 | 280 | 1400 | 284 | 581 |
M5 | 0.15 | 0.17 | 1020 | 240 | 1200 | 211 | 999 |
M6 | 0.15 | 0.2 | 1020 | 240 | 1200 | 246 | 901 |
M7 | 0.2 | 0.17 | 960 | 210 | 1200 | 211 | 977 |
M8 | 0.2 | 0.2 | 960 | 210 | 1200 | 246 | 879 |
4.3 Preparing the Specimens
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Dry mixing of cement, silica fume, aggregates, and GW at 120 rpm for 3 min;
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Adding half the measurements of water and superplasticizer and further mixing at 120 rpm for 5 min;
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Adding the remainder of water and superplasticizer and proceeding to mix at 360 rpm for 5 min.
5 Results
5.1 Effects of Granite Waste on Compressive Strength before Heating
5.2 Effects of Key Parameters on mechanical properties of Refractory concrete mixes without GW
5.2.1 Effects of binder content
5.2.2 Effects of silica-fume-to-binder ratio on mechanical properties
5.2.3 Effects of water-to-binder ratio on mechanical properties
5.3 Effects of GW on compressive and flexural strength loss after heating
5.4 Effects of Using GW on the Required Amount of Plasticizer
6 Summary and Conclusion
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Increasing the binder content in mixes with and without GW improved their compressive and flexural strengths before heating. Furthermore, the higher compaction of the concrete containing more binder increased the vapor pressure due to the dehydration of crystals, reducing the strengths after heating by developing more micro-cracks.
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Adding more silica fume to the HAC concrete mixes with and without GW enhanced the compressive strength of the specimens before heating by forming stronger crystals. Given the lower melting point of these crystals compared to those of the concrete without silica fume, increasing SF/B led to a reduction in compressive strength due to heating.
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The higher W/B lowered the compressive and flexural strengths before heating by increasing porosity in mixes with and without GW. Moreover, after heating by increasing W/B of mixes, mechanical properties decrease due to the increased vapor pressure.
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Substituting silica aggregates with GW in concrete mixes with B = 1400 kg/m3 increased the compressive and flexural strengths before heating by 3–15% and 4–25%, respectively, due to formation of more dense crystals, whereas in concrete mixes with B = 1200 kg/m3, this replacement reduced the strengths by 0% and 12%, respectively, due to the lack of sufficient aggregate coverage.
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In HAC concrete with B = 1200 kg/m3, replacing silica aggregates with GW enhanced the strengths of the specimen after being exposed to 1200 0C temperature by 20–78% and 15–60%, respectively, due to sintering. In contrast, using GW in the concrete specimen with B = 1400 kg/m3 exacerbated the loss in the compressive strength due to heating
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As GW is finer than silica sand, it has a larger surface area. Therefore, using GW in the concrete required more superplasticizer to maintain the same level of fluidity.
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Powder high-strength refractory concrete can be used to make high-strength refractory components. Each cubic meter of the studied concrete mixes use 400–1000 kg of aggregates. Accordingly, at a 50% replacement ratio of the aggregates by GW in the high-strength refractory concrete, 200–500 kg GW is used up, which supports sustainable development and helps protect the environment.