Open Access

Compressive behavior of metakaolin–fly-ash-based geopolymer fiber-reinforced concrete after exposure to elevated temperatures

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Dec 31, 2024

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Figure 1

Particle size of MK and FA utilized in this investigation.
Particle size of MK and FA utilized in this investigation.

Figure 2

Fiber types: (a) SF and (b) PVA.
Fiber types: (a) SF and (b) PVA.

Figure 3

GPC cylindrical specimens during casting.
GPC cylindrical specimens during casting.

Figure 4

Time–temperature curves of GPC cylinders used in the current study.
Time–temperature curves of GPC cylinders used in the current study.

Figure 5

Test setup used in the current study.
Test setup used in the current study.

Figure 6

Failure modes of representative specimens.
Failure modes of representative specimens.

Figure 7

Compressive strength of all specimens.
Compressive strength of all specimens.

Figure 8

Relative compressive strength: (a) normal strength concrete [36,38,39] and (b) high strength concrete [36,37,40].
Relative compressive strength: (a) normal strength concrete [36,38,39] and (b) high strength concrete [36,37,40].

Figure 9

Stress–strain curves: (a) all specimens, (b) specimens at 25°C, (c) specimens at 300°C, and (d) specimens at 500°C.
Stress–strain curves: (a) all specimens, (b) specimens at 25°C, (c) specimens at 300°C, and (d) specimens at 500°C.

Figure 10

Initial stiffness of all specimens.
Initial stiffness of all specimens.

Figure 11

Initial stiffness of all specimens: (a) the area under the curve until 0.3 peak stress (in the decreased portion) and (b) the area under the curve until peak stress.
Initial stiffness of all specimens: (a) the area under the curve until 0.3 peak stress (in the decreased portion) and (b) the area under the curve until peak stress.

Figure 12

Toughness index of all specimens.
Toughness index of all specimens.

MK’s chemical analysis (% weight)_

Composition SiO2 CaO Fe2O3 Na2O Al2O3 TiO2 SO3 K2O P2O5 MgO Others
Value (%) 50.995 1.287 2.114 0.284 42.631 1.713 0.439 0.337 0.051 0.127 0.022
61.30 0.28 4.39 0.12 24.80 0.80 0.39 1.49 0.45 0.74 5.26

Summary of test results_

Specimens Compressive strength (MPa) Relative difference (%)a Initial stiffness (N/mm) Relative difference (%)a Toughness index (%) Relative difference (%)a
M-25 41.94 19,853.3 2.38
M-300 31.79 24.2 11,560.0 41.8 1.77 25.3
M-500 23.00 45.2 31,88.9 83.9 1.38 41.9
MS-25 45.32 23,696.7 2.91
MS-300 32.85 27.5 7,300.0 69.2 2.25 22.8
MS-500 24.80 45.3 2,387.5 89.9 1.87 35.7
MSP-25 45.10 19,933.7 3.07
MSP-300 34.44 23.6 10,933.3 45.2 2.19 28.5
MSP-500 26.73 40.7 4,096.6 79.4 1.78 41.9

Fiber characteristics_

Properties Fiber
SF PVA
Shape Hooked ends (circular cross section) Straight (circular cross section)
Diameter (mm) 0.75 0.06
Length (mm) 60 12
Aspect ratio 80 200
Tensile strength (MPa) 1,225 1,600
Young’s modulus (MPa) 200,000 35,000
Density (kg/m3) 7,850 1,300

Test matrix utilized in the experimental scheme of the current study_

Mixture ID Specimens ID Temperatures (°C) Fiber volume No. of specimens
SF PVA Total
M0 M-25 25 3
M-300 300 3
M-500 500 3
MS MS-25 25 1% 1% 3
MS-300 300 3
MS-500 500 3
MSP MSP-25 25 0.7% 0.3% 1% 3
MSP-300 300 3
MSP-500 500 3
Total no. of specimens 27

GPC mixture proportions in kg/m3_

Material Weight
MK 277.2
FA 118.8
NaOH solution 92
Na2SiO3 solution 291.3
Fine aggregate Crushed limestone (max size: 4.75 mm) 449.8
White sand (max size: 2 mm) 148.4
Coarse aggregate Crushed limestone, max size: 10 mm) 1365.8