1 Introduction
Ref | Type and size of specimens | Concrete type | Parameters | Experiments conducted | Temp. | Main results |
---|---|---|---|---|---|---|
[19] | Cube 100 × 100 × 100 mm | Composite cement pastes | Fly ash 0% to 20% Silica fume 0% to 20% | Compressive strength | 400, 600 | Compressive strength of Composite cement containing fly ash increased by 40% than that containing silica fume |
[5] | Cylinder 75 × 150 mm | Self-compact concrete | 42 kg/m3 SF 1 kg/m3 PPF SF + PPF | Thermal properties, compressive strength, tensile strength, modulus of elasticity | 200°C to 800°C | Addition of SF improve tensile strength and modulus of elasticity While added PP had adverse effect on the mechanical properties |
[26] | Cylinder 100 × 200 mm, cube 150 × 150 × 150 mm | High volume fly ash concrete | Fly ash 40% to 60% | Compressive and tensile strengths | Up to 900°C | The compressive strength and tensile improved by 112% to 136% and 33% to 43%, with increase temperature up to 300 Increase fly ash content led to decrease the concrete strength |
[27] | Cylinder 100 × 200 mm, Cube 150 × 150 × 150 mm | Lightweight concrete | Fly ash 10% to 30% | Compressive and tensile strengths | Up to 800°C | Concrete containing 30%fly ash reported the highest mechanical properties |
[24] | Cube 100 × 100 × 100 mm | HSC | Fly ash 30% to 40% Silica fume 5% to 10% Blast furnace slag 30%, 40% | Compressive strength | 600°C and 800°C | Using fly ash by 30% and Blast furnace slag by 40% give the highest compressive strength of HSC |
[29] | Cube 100 × 100 × 100 mm, Cylinders 100 × 200 mm, Beam100 × 100 × 500 mm | HPC, NSC | 30% Fly ash/blast furnace slag 0.5% SF, PP | Compressive, tensile, flexural strengths | Up to 800°C C | Fly ash and blast furnace slag improve the mechanical properties at high temperature Incorporating SF improve both tensile and flexural strengths |
[31] | Cylinder 100 × 200 mm | HSC | Silica fume 0%, 6%, 10% PPF 0, 1, 2, 3 kg/m3 | Compressive and tensile strengths | Up to 600°C | Addition of 2 kg/m3 PP fibers can significantly promote the residual mechanical properties of HSC during heating |
[37] | Cylinder 150 × 300 mm, Beam 100 × 100 × 400 mm | HSC | SF 30, 60 kg/m3 PPF 0.75, 1.5 kg/m3 | Compressive, tensile, flexural strengths and modulus of elasticity | Up to 750°C | HSC containing 60 kg/m3 SF and 0.75 kg/m3 PP recorded the highest mechanical properties and prevent spalling HSC with 60 kg/m3 showed spalling |
[32] | Cube 100 × 100 × 100 mm, Beam 100 × 100 × 400 mm | Self- compacting HPC | SF 40, 55 kg/m3 PPF 2, 3 kg/m3 | Compressive, flexural strengths | SF improve ultimate load, toughness Combined fiber display better performance than concrete without fiber | |
[8] | RC beam 100 × 150 × 800 mm | Fiber reinforced concrete | 20 kg/m3 SF | Four-point loading | Up to 800°C | The residual bearing capacity was 65% of their initial capacity, where for plain concrete was about 40 |
[10] | RC HSC slab 75 × 700 × 1500 mm Repaired with fiber reinforced-HSC layers 25 mm | Four-point loading | 600°C | Regain in load capacity by 79% to 84% increase in stiffness from 380% to 500% | ||
[20] | RC column 203 × 203 × 3300 mm | HSC, HSC-1 kg/m3 PPF HSC-42 kg/m3 SF, HSC(SF + PPF) | Fire resistance | ASTM E 119 | HSC experience fire-induced spalling Addition of hybrid fibers (PPF and SF) prevent spalling | |
[21] | Slab 120 × 300 × 600 mm | HPC HPC-60 kg/m3 SF HPC-(0.75 kg/m3 PPF + 60 kg/m3 SF) | Spalling | ISO 834 | Plain Concrete and concrete with 60 kg/m3 SF exhibited spalling Added 0.75 PPF to concrete containing 60 kg/m3 allowed to avoid spalling | |
[25] | RC column RC column 203 × 203 × 3300 mm | FAC FAC-2 kg/m3 PPF | Spalling, fire resistance | ASTM E119 | Fly ash concrete exhibit less spalling than HSC Added fly ach and PPF to HSC improve the structure behavior of RC column | |
[9] | RC beam 300 × 500 × 4350 mm strengthened with 40 mm fiber reinforced concrete jacket | Fiber reinforced concrete jacket | Four-point loading FEM | 25°C | An improvement in ultimate load capacity by 215% | |
[11] | RC slab 100 × 300 × 1350 mm strengthened with fiber reinforced concrete | Fiber reinforced concrete | PPF (0.5% to 2%), SF (0.5% to 2%) | Four-point loading | 25°C | Increase volume friction of SF led to improve cracking load While the use of PPF up to 1% can improve it |
[12] | RC slab strengthened with strain hardening cementitious composites | Strain hardening cementitious composites | Four-point loading, FEM | 20°C | The ultimate load enhanced by 25% as compared to un-strengthened slab Steel shear stud prevent desponding the strengthening layer | |
[18] | RC slab 100 × 3300 × 4300 mm | NSC, HSC, FAC, FAC-PPF, FAC-SF | FEM | ISO 834 | RC slab cast with FAC-PPF give the least deflection FAC has lower temperature distribution across slab section | |
[23] | RC beam 80 × 120 × 900 mm | NSC, HSC, HSC with SF | Four-point loading, theoretical study | Up to 800°C | The ultimate load capacity of HSC is higher than that of NSC by 15% to 85% at different temperature Addition of SF improve the ultimate load of HSC by 12% to 100% than NSC Inclusion SF result in ductile failure at high temperature | |
[34] | RC slab 390 × 390 × 120 mm | HSC, HPC with and without PPF | Spalling | 800°C | HSC observed spalling while addition of PPF prevent spalling | |
[35] | RC Beam 120 × 150 × 1260 mm | HSC and fiber reinforced concrete with SF 0, 1% | Four-point flexural test | 20°C to 600°C | Effect of SF appear at high temperature | |
[33] | RC beam 150 × 200 × 2000 mm | Reactive powder concrete | PPF (0.25, 0.75, 1.25%) | Four-point flexural test | ASTM E 119 | Increase % of PPF led to increase the ultimate load up to 25.6% and decrease deflection by 62% |
[38] | Slab 800 × 800 × 100 mm | HPC | 2 kg/m3 PPF 40 kg/m3 SF | Fire test under compression | ISO 834 | Slab cast with HPC or HPC with SF explore fire spalling and addition of PPF prevent spalling |
[39] | Strengthening of RC slabs 120 × 1000 × 2300 mm with RC overlay on the tensile face | Flexural test | 25°C | Shear connector resulted in a performance Gain of 60% to 110% for the shear stress at the interface | ||
[41] | Two-way restrained precast concrete composite slabs | Flexural test | ISO 834 | Bar truss at the interface between the precast and the in-situ concrete layers is sufficient to ensure composite action in fire |
2 Experimental Work
2.1 Materials
Properties | Cement | GGBFS | FA |
---|---|---|---|
Chemical component% | |||
SiO2 + Al2O3 + Fe2O | 30.1 | 47.4 | 93.86 |
CaO | 62.20 | 42.47 | 2.38 |
Na2O | 0.38 | 0.4 | 0.48 |
MgO | 1.90 | 5.6 | 2.92 |
Loss on ignition | 1.34 | – | – |
Insoluble residue | 0.88 | 0.93 | 1.1 |
Physical properties | |||
Specific gravity | 3.15 | 2.89 | 2.3 |
Specific surface area (cm2/g) | 3500 | 5000 | 4500 |
Properties | Fibers | Steel reinforcement rebar | |
---|---|---|---|
Steel (SF) | Polypropylene (PP) | ||
Length (mm) | 35 | Gradient of 6–18 | – |
Diameter | 0.8 mm | 18 μm | 6 mm |
Specific gravity | 7.85 | 0.91 | 7.85 |
Shape | Hooked end | Fiber mesh | – |
Tensile yield strength (MPa) | ≥ 1000 | 300–400 | 280 |
Elastic modulus (GPa) | 210 | 3.6 | 210 |
Melting point (°C) | – | 160°C | – |
2.2 Mixtures Proportions, Specimens Preparation and Curing
Mix no. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | |
---|---|---|---|---|---|---|---|---|---|
Mix ID | NSC | HSC | FAC | BFSC | FAC-SF | FAC-PPF | FAC-(SF + PPF) | BFSC-SF | |
Concrete type | Normal strength concrete | High strength concrete | Fly ash 30% | Slag 30% | Fly ash 30%, steel fiber (SF) 0.5% | Fly ash 30%, Polypropylene fiber (PPF) 0.5% | Fly ash 30%, steel fiber 0.5% + Polypropylene fiber (PPF) 0.5% | Slag 30%, steel fiber (SF) 0.5% | |
Cement | 350 | 450 | 315 | 315 | 315 | 315 | 315 | 315 | |
FA (kg/m3) | – | – | 135 | – | 135 | 135 | 135 | – | |
GGBFS (kg/m3) | – | – | – | 135 | – | – | – | 135 | |
Sand (kg/m3) | 680 | 694 | 702 | 692.8 | 675.5 | 675.5 | 675.5 | 687.8 | |
CA (kg/m3) | 1020 | 1040 | 1053 | 1039 | 1013 | 1013 | 1013 | 1031 | |
Water (kg/m3) | 200 | 144 | 135 | 144 | 135 | 144 | 144 | 144 | |
W/B | 0.57 | 0.32 | 0.3 | 0.32 | 0.3 | 0.32 | 0.32 | 0.32 | |
HRWR (kg/m3) | – | 7.65 | 4.5 | 12.15 | 6.75 | 6.75 | 12.15 | 12.15 | |
PPF fibers (kg/m3) | – | – | – | – | – | 4.5 | 4.5 | – | |
SF fiber (kg/m3) | – | – | – | – | 39 | – | 39 | 39 | |
Test results of mechanical properties of concrete mixes | |||||||||
Compressive strength (MPa) | |||||||||
28 days | 25°C | 35 | 65 | 60.45 | 60.3 | 58.5 | 59 | 62.2 | 56 |
60 days | 25°C | 40.4 | 68.9 | 64 | 63.9 | 62 | 62.5 | 65.9 | 59 |
600°C | 23.8 | 34 | 40 | 48.8 | 50.3 | 32.9 | 43.66 | 50 | |
Splitting tensile strength (MPa) | |||||||||
28 days | 25°C | 1.8 | 4.82 | 5.5 | 5.68 | 6.5 | 6 | 7 | 6 |
60 days | 25°C | 2.1 | 5.54 | 5.9 | 6.5 | 7.28 | 6.9 | 7.9 | 6.5 |
600°C | 0.94 | 1.9 | 1.77 | 1.47 | 3.79 | 1.29 | 3.36 | 3.81 | |
Flexural strength (MPa) | |||||||||
28 days | 25°C | 2.6 | 4.6 | 4.35 | 5.88 | 3.66 | 4.79 | 4.95 | 5.6 |
60 days | 25°C | 2.9 | 5.3 | 5.4 | 6.1 | 4 | 5.5 | 6.3 | 6 |
600°C | 0.92 | 1.84 | 3.2 | 1.38 | 1.64 | 1.37 | 3.93 | 3.49 |
2.2.1 For Single RC Slabs
2.2.2 For Composite RC Slabs
2.3 Slab Specimens Details
No. | Slab ID | Slab type | Mix ID | HPC/NSC | Side exposed to elevated temperature | Bond connection | ||
---|---|---|---|---|---|---|---|---|
Tension | Compression | Shear stud | Epoxy | |||||
1 | N25 | One unit (control) | NSC | – | – | – | – | – |
2 | N | One unit | NSC | – | √ | – | – | – |
3 | H | One unit | HSC | – | √ | – | – | – |
4 | F | One unit | FAC | – | √ | – | – | – |
5 | G | One unit | BFSC | – | √ | – | – | – |
6 | FS | One unit | FAC-SF | – | √ | – | – | – |
7 | FP | One unit | FAC-PPF | – | √ | – | – | – |
8 | FSP | One unit | FAC-(SF + PPF) | – | √ | – | – | – |
9 | GS | One unit | BFSC-SF | – | √ | – | – | – |
10 | H-N | Composite | HSC/NC | T | √ | – | √ | – |
11 | F-N | Composite | FAC/NC | T | √ | – | √ | – |
12 | G-N | Composite | BFSC/NC | T | √ | – | √ | – |
13 | FS-N | Composite | FAC-SF/NC | T | √ | – | √ | – |
14 | FS-NE | Composite | FAC-SF/NC | T | √ | – | √ | |
15 | FP-N | Composite | FAC-PPF/NC | T | √ | – | √ | – |
16 | FP-NC | Composite | FAC-PPF/NC | T | √ | √ | – | |
17 | FSP-N | Composite | FAC-(SF + PPF)/NC | T | √ | – | √ | – |
18 | GS-N | Composite | BFSC-SF/NC | T | √ | – | √ | – |
19 | GS-NR | Composite | NC/BFSC-SF | T | √ | – | √ | – |
20 | N-FSP | Composite | FAC-(SF + PPF) | C | √ | – | √ | – |
21 | N-FSPE | Composite | FAC-(SF + PPF) | C | √ | – | – | √ |
2.4 Heating of RC Slab
2.5 Slab Specimens Test Method
3 Test Results and Discussion
3.1 Thermal Behavior
3.2 Structural Behavior of RC Slab Specimens After Exposure to Elevated Temperature
Slab | PCr (kN) | Pu (kN) | \({\Delta }_{{\varvec{f}}} (mm)\) | \({\Delta }_{{\varvec{y}}}(mm)\) | Ductility index \(\left(\frac{{\Delta }_{{\varvec{f}}}}{{\Delta }_{{\varvec{y}}}}\right)\) | Stiffness (kN/mm) | Toughness (kN mm) |
---|---|---|---|---|---|---|---|
N25 | 18 | 32.5 | 25.4 | 5 | 4.45 | 4.2 | 625 |
N | 12.4 | 14.78 | 15.89 | 4.3 | 3.67 | 3.11 | 162.5 |
H | 22.16 | 26.14 | 18.6 | 4.3 | 4.32 | 5.76 | 396.36 |
F | 25 | 29.76 | 28 | 6 | 4.67 | 3.84 | 635.7 |
G | 25 | 29 | 30 | 5 | 6 | 4.53 | 739.3 |
FS | 26 | 28.4 | 30 | 4.7 | 6.38 | 5 | 679 |
FP | 27 | 30.1 | 28.64 | 4.3 | 6.66 | 6.4 | 714.39 |
FSP | 25 | 30.49 | 30 | 5 | 6 | 4.7 | 680.55 |
GS | 27.3 | 33 | 30 | 4.3 | 6.97 | 6.1 | 806.5 |
H-N | 15 | 19.75 | 25 | 5.3 | 4.71 | 3.36 | 340 |
F-N | 22 | 23.84 | 25 | 4 | 6.25 | 5.46 | 355.8 |
G-N | 12 | 13.83 | 25 | 4.3 | 5.81 | 3.3 | 255.7 |
FS-N | 18 | 24.26 | 25 | 3.66 | 6.83 | 5.44 | 499.45 |
FS-NE | 6.65 | 9.6 | 25 | 5 | 5 | 2.1 | 191.4 |
FP-N | 21.7 | 26.48 | 25 | 4.5 | 5.55 | 6.11 | 409 |
FP-NC | 18.5 | 22.4 | 25 | 5.5 | 4.54 | 3.83 | 345.4 |
FSP-N | 27 | 31.94 | 25 | 3.64 | 6.86 | 8 | 708 |
GS-N | 16 | 18.11 | 25 | 5 | 4.93 | 3.7 | 387 |
GS-NR | 6 | 6.97 | 12.5 | 3.5 | 3.57 | 2.32 | 48 |
N-FSP | 22 | 26.86 | 25 | 5.5 | 4.5 | 5.96 | 565 |
N-FSPE | 11 | 12 | 25 | 4 | 6.25 | 3 | 133.6 |
3.2.1 Load–Deflection Behavior
3.2.1.1 Single-Concrete Slabs
3.2.1.2 Composite Slabs
3.2.2 Ductility Index, Stiffness and Toughness
3.2.2.1 Single-Concrete Slabs
3.2.2.2 Composite Slabs
3.3 Prediction of the Ultimate Limit Capacity of RC Slab Specimens
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Plain section before bending remain plane after bending.
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Prefect bond between reinforcement and concrete, concrete substrate and concrete overlay.
-
Temperature in reinforcement is equal to the temperature of surround concrete.
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Concrete in tension zone is neglected except concrete containing steel fiber.
Slab | \({P}_{\text{Exp}}\) (kN) | \({\text{P}}_{\text{th}}\) (kN) | \(\frac{{P}_{\text{Exp}}}{{\text{P}}_{\text{th}}}\) | Slab | \({P}_{\text{Exp}}\) (kN) | \({\text{P}}_{\text{th}}\) (kN) | \(\frac{{P}_{\text{Exp}}}{{\text{P}}_{\text{th}}}\) |
---|---|---|---|---|---|---|---|
N25 | 32.5 | 24.85 | 1.31 | G-N | 13.83 | 24.69 | 0.56 |
N | 14.78 | 24.60 | 0.60 | FS-N | 24.26 | 29.70 | 0.82 |
H | 26.14 | 25.00 | 1.04 | FS-NE | 9.60 | 29.70 | 0.32 |
F | 29.76 | 25.19 | 1.18 | FP-N | 26.48 | 24.66 | 1.07 |
G | 29.00 | 25.03 | 1.16 | FP-NC | 22.4 | 24.48 | 0.92 |
FS | 28.4 | 30.61 | 0.93 | FSP-N | 31.94 | 30.10 | 1.06 |
FP | 30.1 | 25.25 | 1.19 | GS-N | 18.11 | 29.4 | 0.61 |
FSP | 30.49 | 31.55 | 0.97 | GS-NR | 6.97 | 5.80 | 1.20 |
GS | 33 | 31.70 | 1.04 | N-FSP | 26.86 | 25.79 | 1.04 |
H-N | 19.75 | 24.20 | 0.82 | N-FSPE | 12.00 | 26.40 | 0.45 |
F-N | 23.84 | 24.70 | 1.17 |
3.4 Crack Patterns and Mode of Failure
3.4.1 Pre-loading After Heating and Cooling Phase
3.4.2 Post-loading
4 Conclusions
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No spalling in either single slabs or composite slabs. In addition, the temperature distribution in HPC single slabs and composite slabs is lower than the temperature distribution in single slab cast with NSC.
-
The use of polypropylene fibers plays an important role in the temperature distribution of composite slabs. Composite slab cast with fly ash and polypropylene fiber displayed a higher temperature variation between the reinforcing steel and the inner parts compared to composite slab cast with steel fiber or hybrid fibers.
-
Single slab cast with NSC showed more deterioration after exposure to elevated temperature, as the cracking load, ultimate load, ductility, stiffness, and toughness decreased by 31.11%, 54.52%, 17.53%, 26%, and 74% compared to NSC at 25°C, respectively.
-
Generally, strengthening the RC slab in tension or compression with HPC significantly improved slab performance after exposure to elevated temperature compared to a single slab cast with NSC, with relative increases in cracking laod, ultimate load, ductility, stiffness, and toughness of (21% to 117%), (22.5% to 116%), (23.7% to 86.9%), (8% to 157%), and (17% to 335.6%), respectively.
-
The highest cracking load, ultimate load capacity, stiffness, toughness, and ductility index was recoded for composite slab cast with fly ash concrete and using hybrid fibers in tension side (slab FSP-N) compared to a single slab specimen cast with NSC with increasing ratios of 92.8%, 116%, 157%, 335, and 86.9%, respectively.
-
Composite slab without steel reinforcement showed the least performance as compared to slab with steel reinforcement.
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The direction of the fire clearly affects the flexural behvior of composite slab, as the composite slab cast with fly ash concrete and polypropylene fibers in the tension side proves its efficiency in case of exposure to elevated temperature from the tension side more than from the compression side.
-
Shear studs efficiently contribute to enhancing the flexural behavior of the composite slab after exposure to an elevated temperature, while the use of epoxy resin is not suitable in the case of elevated temperature.
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All composite RC slabs showed a decrease in flexural properties after exposure to elevated temperature compared to the single slab cast with the same types of HPC, except the slab specimen cast with hybrid fibers, which showed a significant improvement.
-
The theoretical models used appear to be qualified for predicting the flexural properties with reasonable accuracy for slab specimens cast with HPC. Modelling revealed that HPC incorporating fibers and fly ash in addition to being cost-effective can be effective for expansion in a certain direction serving some environmentally friendly construction applications, which is attributed to the remarkable improvement in the flexural properties of RC composite slabs when subjected to fire.
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Additional parameters, such as fiber content, HPC thickness, and geometry of RC members, should also be evaluated to comprehensively explore the potential of HPC material for composite RC members exposed to fire.