1 Introduction
2 Experimental Procedure
2.1 Scoria
Chemical composition (by mass, %) | Materials | ||||
---|---|---|---|---|---|
Scoriaa
| Clinker | Gypsum | Dolomite aggregate | Natural sand | |
SiO2
| 46.52 | 21.30 | 0.90 | 0.42 | 93.39 |
Al2O3
| 13.00 | 4.84 | 0.07 | 0.38 | 0.57 |
Fe2O3
| 11.40 | 3.99 | 0.10 | 0.10 | 0.24 |
CaO | 10.10 | 65.05 | 32.23 | 31.40 | 1.70 |
CaOf
| – | 2.1 | – | – | – |
MgO | 9.11 | 1.81 | 0.20 | 20.46 | 0.20 |
SO3
| 0.27 | 0.25 | 45.29 | 0.18 | 1.15 |
Loss on ignition | 2.58 | – | 21.15 | 46.48 | 2.52 |
Na2O | 2.14 | 0.60 | – | 0.06 | 0.06 |
K2O | 0.77 | 0.28 | – | 0.30 | 0.05 |
Cl−
| <0.1 | 0.05 | – | 0.021 | 0.017 |
Pozzolan activity index [ASTM C 618] | 79 (at 7 days) 85 (at 28 days) |
2.2 Cement Samples
Chemical composition (%) | C1/CEMI | C2/10 % | C3/15 % | C4/20 % | C5/25 % | C6/30 % | C7/35 % | C8/SRPC | |
---|---|---|---|---|---|---|---|---|---|
Chemical properties of plain and blended cements | |||||||||
SiO2
| 20.69 | 21.59 | 22.35 | 23.25 | 24.00 | 24.33 | 24.61 | 20.72 | |
Al2O3
| 5.09 | 5.20 | 5.68 | 5.73 | 6.55 | 6.80 | 7.39 | 4.33 | |
Fe2O3
| 4.23 | 4.75 | 4.79 | 5.15 | 5.43 | 5.47 | 6.31 | 5.79 | |
CaO | 60.62 | 58.21 | 55.18 | 53.05 | 50.30 | 48.00 | 44.84 | 61.69 | |
MgO | 2.46 | 2.66 | 3.23 | 3.39 | 3.87 | 4.11 | 4.63 | 1.21 | |
SO3
| 2.26 | 2.31 | 2.20 | 2.20 | 2.30 | 2.26 | 2.55 | 2.13 | |
Loss on ignition | 1.41 | 1.40 | 1.43 | 1.37 | 1.47 | 1.48 | 1.60 | 2.90 | |
Na2O | 0.60 | 0.71 | 0.83 | 0.94 | 1.07 | 1.16 | 1.31 | 0.21 | |
K2O | 0.35 | 0.39 | 0.43 | 0.46 | 0.50 | 0.53 | 0.57 | 0.19 | |
Cl−
| 0.023 | 0.021 | 0.022 | 0.019 | 0.018 | 0.019 | 0.019 | 0.022 | |
Insoluble residue | 1.03 | 1.58 | 2.09 | 2.51 | 3.48 | 4.08 | 5.33 | 0.36 | |
Main compounds of clinker used in cement specimens (Based on Bogue composition) | |||||||||
C3S | 53.36 | 50.55 | 47.74 | 44.94 | 42.13 | 39.32 | 36.51 | 50.16 | |
C2S | 17.76 | 16.82 | 15.89 | 14.95 | 14.02 | 13.08 | 12.15 | 21.58 | |
C3A | 5.78 | 5.47 | 5.17 | 4.86 | 4.56 | 4.26 | 3.95 | 1.69 | |
C4AF | 11.53 | 10.93 | 10.32 | 9.71 | 9.11 | 8.50 | 7.89 | 17.60 | |
C3S/C2S | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 | 2.32 | |
Physical properties of plain and blended cements | |||||||||
Specific gravity | 3.13 | 3.09 | 3.05 | 3.02 | 2.99 | 2.98 | 2.96 | ||
Initial setting (min) | 151 | 153 | 153 | 153 | 152 | 153 | 158 | ||
Final setting (min) | 178 | 179 | 180 | 180 | 179 | 181 | 188 | ||
Water demand (%) | 25.1 | 25.2 | 25.2 | 25.4 | 25.4 | 25.4 | 25.5 | ||
Soundness (mm) | 0.6 | 0.7 | 0.8 | 0.8 | 0.9 | 1.1 | 0.9 | ||
Residue on 45 µm sieve (%) | 13.6 | 14.3 | 14.8 | 15.2 | 16.1 | 17.0 | 17.9 | ||
Residue on 90 µm sieve (%) | 6.4 | 6.2 | 6.4 | 6.5 | 6.7 | 6.9 | 6.8 | ||
Mechanical properties of plain and blended cement mortars | |||||||||
Strength of mortars at 28 days curing (MPa) | 45.6 | 44.2 | 42.3 | 40.6 | 37.1 | 33.7 | 30.6 |
2.3 Mortar Mixtures
2.4 Concrete Mixes
2.5 Compressive Strength Test of Concrete
2.6 Rapid Chloride Penetrability Test
2.7 Accelerated Corrosion Test
2.8 Acid Attack Test
2.9 Sulfate Attack Test
3 Discussion of Results
3.1 Properties of Scoria and Blended Cements
3.2 Compressive Strength of Concretes
Sample | Compressive strength (MPa)-normalized | ||||
---|---|---|---|---|---|
2 days (%) | 7 days (%) | 28 days (%) | 56 days (%) | 90 days (%) | |
C1/CEM I (control) | 13.6–100 | 24.9–100 | 35.0–100 | 40.6–100 | 42.3–100 |
C2/10 % | 12.8–94 | 24.4–98 | 33.6–96 | 39.8–98 | 41.6–98 |
C3/15 % | 11.8–87 | 21.0–84 | 30.1–86 | 37.0–91 | 39.3–93 |
C4/20 % | 11.0–81 | 20.1–81 | 29.5–84 | 35.1–86 | 38.3–91 |
C5/25 % | 9.9–73 | 17.6–71 | 26.5–76 | 31.8–78 | 36.5–86 |
C6/30 % | 8.9–65 | 16.5–66 | 24.6–70 | 29.6–73 | 33.1–78 |
C7/35 % | 8.5–63 | 16.0–64 | 23.4–67 | 28.0–69 | 30.9–73 |
3.3 Rapid Chloride Penetrability
3.4 Corrosion Resistance
3.5 Corrosion Initiation Time Versus Chloride Penetrability of Concrete
3.6 Acid Attack
Cement type | Number of days to register 10 % weight loss | |||||||
---|---|---|---|---|---|---|---|---|
5 % H2SO4
| 10 % HCl | 5 % HNO3
| 10 % CH3COOH | |||||
28 days curing | 90 days curing | 28 days curing | 90 days curing | 28 days curing | 90 days curing | 28 days curing | 90 days curing | |
C1/CEMI | 3.5 | 3.5 | 3.7 | 3.2 | 22.5 | 25.9 | NR | NR |
C2/10 % | 3.7 | 3.7 | 3.7 | 3.1 | 25.4 | 22.8 | NR | NR |
C3/15 % | 3.8 | 3.8 | 3.8 | 3.6 | 55.5 | 48.9 | NR | NR |
C4/20 % | 4.0 | 4.1 | 3.9 | 3.7 | 79.1 | 97.3 | NR | NR |
C5/25 % | 4.7 | 5.1 | 4.1 | 4.3 | NR | NR | NR | NR |
C6/30 % | 5.2 | 5.8 | 4.4 | 4.9 | NR | NR | NR | NR |
C7/35 % | 6.2 | 6.7 | 4.6 | 5.2 | NR | NR | NR | NR |
C8/SRPC | 3.0 | 3.0 | 3.2 | 2.9 | 20.1 | 18.8 | NR | NR |
3.7 Sulfate Attack
4 Conclusion
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The studied scoria is a suitable material for use as a natural pozzolan. It satisfied the ASTM & EN requirements for such a material. The physical properties of binders containing scoria are also in conformity with the standards requirements.
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The compressive strength of concrete containing scoria-based binders was lower than that of plain cement concrete at all ages of concrete in this study. At early ages, the concrete containing CEM II/B-P binder types had compressive strengths much lower than that of plain cement concrete. However, at 90 days curing, the compressive strengths of blended cement concretes are comparable to those of plain cement concrete.
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The chloride penetrability of scoria-based concrete mixes is much lower than that of plain concrete, especially at high replacement levels of scoria.
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According to the results of accelerated corrosion test, concretes produced with scoria-based binders decelerated rebar corrosion. Particularly, CEM II/B-P binder types with 25, 30 and 35 % scoria content were found to delay corrosion significantly. Use of scoria at 30 % cement replacement level delayed significantly initial corrosion times under chloride-bearing environments.
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Based on the results, blending CEM I of 6 % C3A content, with 25 % scoria content or more resulted in a performance similar to that of SRPC and an enhanced acid resistance, as well.
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Adding scoria as cement replacement reduced the expansion of the mortar bars exposed to sodium sulfate solution. More reduction occurs with increasing the replacement level.
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Blended cement concretes have lower compressive strengths, but greater resistance to chloride penetration, longer corrosion initiation times, greater resistance to acid attack and lower expansion in sodium sulfate solution compared with plain cement concretes after 28 and 90 days curing. So, it would be erroneous to predict durability based on strength.
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Based on the results obtained, it is suggested that scoria can be used up to 30 % as a partial substitute for PC in production of blended cements. This addition ratio can reduce the quantity of CO2 released by Syrian cement plants, and the consumed energy. So, production of a green concrete could be promoted.