Fig. 1.
The fibers utilized in this study: (a) crimped polypropylene and (b) Hooked-steel.
Table 1.
Physical and mechanical properties of fibers
| Properties | Fiber Type | |
|---|---|---|
| Polypropylene (PP) | Steel (SF) | |
| Shape | Crimped | Hooked ends |
| Length (mm) | 50 | 60 |
| Section dimensions (mm) | 1.0 × 0.6 (Rectangular) | 0.75 (Circular) |
| Specific gravity | 0.90 | 7.85 |
| Modulus of elasticity (GPa) | 4.0 | 200 |
| Tensile strength (MPa) | 550 | 1225 |
Table 2.
Mix proportions used for concrete in kg/m3
| Material | Weight |
|---|---|
| Cement | 378 |
| Crush sand | 294 |
| Silica sand | 489 |
| Coarse aggregate (dagg.= 20 mm) | 675 |
| Coarse aggregate (dagg. = 10 mm) | 320 |
| Water | 190.5 |
| Super-plasticizer | 1.0 Liters |
Table 3.
Test matrix
| Concrete mix | Specimens ID | Percentage of fiber by volume | Temperatures | Strengthening | No. of specimens | ||
|---|---|---|---|---|---|---|---|
| Polypropylene (PP) | Steel (SF) | Total | |||||
| M-C0 | C0-RT | – | – | – | 26°C | – | 3 |
| C0-600 | 600° C | 3 | |||||
| C0-RT-S | 26°C | WWM | 3 | ||||
| C0-600-S | 600°C | 3 | |||||
| M-SF | SF-RT | – | 0.6 | 0.6 | 26°C | – | 3 |
| SF-600 | 600°C | 3 | |||||
| SF-RT-S | 26°C | WWM | 3 | ||||
| SF-600-S | 600°C | 3 | |||||
| M-PPF | PPF-RT | 0.2 | 0 | 0.2 | 26°C | – | 3 |
| PPF-600 | 600°C | 3 | |||||
| PPF-RT-S | 26°C | WWM | 3 | ||||
| PPF-600-S | 600°C | 3 | |||||
| M-SF+PPF | SF+PPF-RT | 0.2 | 0.6 | 0.8 | 26°C | – | 3 |
| SF+PPF-600 | 600°C | 3 | |||||
| SF+PPF-RT-S | 26°C | WWM | 3 | ||||
| SF+PPF-600-S | 600°C | 3 | |||||
| Total No. of specimens | 48 | ||||||
Fig. 2.
Concrete cylinders during casting
Fig. 3.
Heated cylinders after (a) sandblasting procedure, (b) WWM jacketing, (c) mortar layer, and (d) final appearance
Table 4.
WWM and mortar properties
| Material | Unit | Values | |
|---|---|---|---|
| WWM | Thickness per layer | mm | 0.6 |
| Elastic modulus | MPa | 108 | |
| Yield stress | MPa | 382 | |
| Ultimate stress | MPa | 544 | |
| Mortar for WWM composite | Compressive strength-28 day | MPa | 45 |
| Tensile strength-28 day | MPa | 3.8 | |
| Bond strength | MPa | 0.79 |
Fig. 4.
Specimens inside the electrical oven prepared for heating
Fig. 5.
The time-temperature curves employed in this research
Fig. 6.
Test setup used in this research
Fig. 7.
Representative typical failure mode for control and strengthened specimens
Fig. 8.
Effectiveness of WWM strengthening for unheated and heated specimens: (a) room temperature and (b) heated at 600°C
Fig. 9.
Stress-strain curves for unheated and heated specimens: (a) room temperature and (b) heated at 600°C
Fig. 10.
Effect of fiber types on compressive strength of unheated and heated specimens
Table 5.
Summary of test results
| Specimen ID | Compressive strength | Initial stiffness | ||
|---|---|---|---|---|
| (MPa) | Relative Variation* | (N/mm) | Relative Variation* | |
| C0-RT | 30.2 | – | 20133.3 | – |
| C0-600 | 14.1 | −53.3% | 2169.2 | −89.2% |
| C0-RT-S | 50.6 | +67.5% | 25948.7 | 28.9% |
| C0-600-S | 29.9 | −1.0% | 8542.9 | −57.6% |
| SF-RT | 40.7 | – | 26688.5 | – |
| SF-600 | 28.5 | −29.9% | 4560.0 | −82.9% |
| SF-RT-S | 71.0 | +74.4% | 47333.3 | 77.4% |
| SF-600-S | 56.5 | +38.8% | 19316.2 | −27.6% |
| PPF-RT | 32.9 | – | 43866.7 | – |
| PPF-600 | 18.0 | −45.3% | 3600.0 | −85.0% |
| PPF-RT-S | 60.1 | +82.7% | 25849.5 | 8.0% |
| PPF-600-S | 34.5 | +4.9% | 11311.5 | −52.7% |
| SF+PPF-RT | 40.5 | – | 27000.0 | – |
| SF+PPF-600 | 30.9 | −23.7% | 4414.3 | −83.7% |
| SF+PPF-RT-S | 66.1 | +63.2% | 46386.0 | 71.8% |
| SF+PPF-600-S | 44.3 | +9.4% | 14644.6 | −45.8% |