1 Introduction
2 Experimentation
2.1 Materials and Mix Proportions
2.1.1 Cement
Cementitious materials | SiO2 | Al2O3 | Fe2O3 | CaO | MgO |
---|---|---|---|---|---|
Cement | 21.40 | 5.45 | 3.50 | 64.48 | 1.46 |
Silica fume | 94.50 | 0.50 | 0.45 | 0.60 | 0.70 |
Slag | 34.90 | 14.66 | 1.36 | 37.57 | 9.13 |
2.1.2 Silica Fume
2.1.3 Slag
2.1.4 Quartz Sand
2.1.5 Polycarboxylate Superplasticizer
2.1.6 Steel Fiber
2.1.7 Polypropylene Fiber
Constituents | HPRPC | PRPC |
---|---|---|
Ordinary Portland cement (kg/m3) | 815.18 | 816.42 |
Silica fume (kg/m3) | 245.31 | 244.33 |
Slag (kg/m3) | 120.08 | 122.16 |
Quartz coarse sand (kg/m3) | 480.32 | 490.32 |
Quartz fine sand (kg/m3) | 480.32 | 490.32 |
Water reducer (kg/m3) | 35.40 | 35.47 |
PP fiber (kg/m3) | 1.82 (0.2%a) | 2.73 (0.3%a) |
Steel fiber (kg/m3) | 157 (2%a) | – |
Water (kg/m3) | 188.81 | 189.20 |
w/b ratio | 0.16 | 0.16 |
2.2 Specimens Fabrication and Curing
2.3 Testing Approach
2.3.1 Test Equipment
2.3.2 Measurements of Specimen Temperature
2.3.3 Measurements of Specimen Deformation
Temperature ( °C) | Measured in MPa | |||
---|---|---|---|---|
\(f_{c}^{T}\)
| 20% | 40% | 60% | |
120 | 130.8 | 26.2 | 52.3 | 78.5 |
300 | 119.0 | 23.8 | 47.6 | 71.4 |
500 | 99.4 | 19.9 | 39.8 | 59.7 |
700 | 64.2 | 12.8 | 25.7 | 38.5 |
900 | 36.4 | 7.3 | 14.6 | 21.9 |
Temperature ( °C) | Measured in MPa | |||
---|---|---|---|---|
\(f_{c}^{T}\)
| 20% | 40% | 60% | |
120 | 70.4 | 14.1 | 28.2 | 42.3 |
300 | 74.2 | 14.8 | 29.7 | 44.5 |
500 | 64.6 | 12.9 | 25.9 | 38.8 |
700 | 54.8 | 11.0 | 21.9 | 32. |
900 | 29.9 | 6.0 | 12.0 | 18.0 |
2.3.4 Testing Procedure
Strength ratios | Measured in MPa | |
---|---|---|
HRPC | PRPC | |
\(f_{c}\)
| 151.1 | 97.0 |
10% | 15.1 | 9.7 |
20% | 30.2 | 19.4 |
30% | 45.3 | 29.1 |
40% | 60.4 | 38.8 |
50% | 75.5 | 48.5 |
60% | 90.6 | 58.2 |
3 Results and Discussions
3.1 Short-Term Creep
3.2 Comparison of short-term creep of RPC with NSC and HSC
Temp. ( °C) | PRPC (min.) | HRPC (min.) |
---|---|---|
120 | 516.4 | 262.8 |
300 | 102.8 | 23.8 |
500 | 31.7 | 20.2 |
700 | 16.8 | 3.9 |
900 | 5.6 | 1.1 |
Temp. (°C) | Load level (%) | 3 h STC (× 10−3) | 3 h STC/1-year 20 °C Creep | ||
---|---|---|---|---|---|
PRPC | HRPC | PRPC | HRPC | ||
120 | 20 | 0.12 | 0.20 | 0.27 | 0.47 |
300 | 0.29 | 0.51 | 0.66 | 1.17 | |
500 | 0.49 | 0.74 | 1.11 | 1.68 | |
700 | 0.92 | 2.80 | 2.10 | 6.36 | |
900 | 1.82 | 4.42 | 4.14 | 10.05 | |
120 | 40 | 0.25 | 0.36 | 0.57 | 0.82 |
300 | 0.53 | 1.05 | 1.21 | 2.39 | |
500 | 1.06 | 1.47 | 2.40 | 3.35 | |
700 | 1.99 | 6.29 | 4.52 | 14.29 | |
900 | 4.05 | 9.98 | 9.20 | 22.68 | |
120 | 60 | 0.34 | 0.57 | 0.78 | 1.31 |
300 | 0.84 | 1.56 | 1.90 | 3.55 | |
500 | 1.58 | 2.32 | 3.59 | 5.28 | |
700 | 2.88 | 8.82 | 6.54 | 20.04 | |
900 | 5.93 | 14.74 | 13.47 | 33.51 |
3.3 Free Thermal Strain
3.4 Comparison of Free Thermal Strain of RPC with NSC and HSC
3.5 Transient Strain at Constant Loading
3.6 Transient Strain at Variable Loading
3.7 Comparison of Transient Strain of RPC with NSC and HSC
4 Conclusions
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In general, an increase in STC was observed with higher stress levels and rising temperature. The STC originates quickly at the start of the test, and almost half of the total creep developed within 1 h heating. However, its rates ceased down after the first hour. The STC developed below 500 °C, was low for both types of RPC, while above the transition stage of quartz aggregate, the evolution of STC was pronounced. In most severe case 3 h STC reaches up to 33 times of 1 year ambient temperature creep. STC needs to be addressed in fire safety design.
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The STC of HRPC was significantly higher than PRPC. This can be attributed to the presence of steel fibers, which have different thermal expansion coefficient than the RPC matrix at high temperature. Furthermore, steel fibers also start to creep at half of its melting temperature (650 °C). Overall, the thermal incompatibilities increase between the cementitious paste and steel fibers, which damaged the microstructure and a significant increase in strain was obtained. The micro-channels left after melting of PP fiber have no prominent contribution in the STC behavior.
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The STC of HRPC is greater than NSC and HSC. This can be attributed to the high amount of cementitious materials, quartz aggregate and steel fibers being used in HRPC. On the other hand, the STC of PRPC is lower than HSC at high temperature. The STC of PRPC is similar as siliceous aggregate NSC but higher than the carbonaceous aggregate NSC.
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The PRPC has similar evolution of FTS as that of Eurocode siliceous concrete model. However, HRPC observed a steeper gradient due to uneven expansion of steel fibers and RPC matrix.
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The higher stress levels and rising temperature increases TS. The gradient of TS increases prominently when the strength ratio increases. Whereas, by decreasing the strength ratio, there is no obvious increase in the rate of TS. Furthermore, TS of HRPC is higher than PRPC. This can be attributed again due to the uneven expansion between the steel fibers and RPC matrix. Further, TS of RPC is lower than NSC and HSC below 250 °C. However, above 250 °C, both HRPC and PRPC showed higher TS than NSC and HSC. This is due to the siliceous aggregates being used in RPC.
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Constitutive relationships are proposed for creep behavior of HRPC and PRPC, which will be used as input data in numerical models for fire resistance calculations.