GGBS + fly ash
(Na2SiO3 + NaOH,
SiO2/Na2O = 1.63,
w/b = 0.55) [22]
- -
Steel: 36 mm × 1.08 mm: 0% to 1.4%.
Ambient curing for 28 days.Addition of 1.4% corrugated steel fiber content increased the toughness factor from 1.32 to 1.82, indicating 1.5 times increase in ductility.Fly ash + 25% rice husk ash +10% GGBS
(Na2SiO3 + NaOH, Na2SiO3/NaOH = 2.5) [70]
- -
Basalt: 6 mm × 13&#;20 µm. Vol. fractions: 1%, 2%, 3%, and 4%.
Cured for 28 days. Values are taken at 3, 7, 28 days.Addition of 2% basalt fiber into alkali-activated concrete increased the tensile strength by 23.98% and flexural strength by 43%. Flexural strength increased from 6 MPa to 7 MPa.70% GGBS + 30% microsilica
(Na2SiO3 + NaOH, Na2SiO3/NaOH = 3.5, w/b = 0.33) [12]
- -
Steel: 15 mm × 0.12 mm: 1% to 2.25%.
- -
Polypropylene: 8 mm × 0.033 mm. Vol. fractions: 0% to 0.25%.
Ambient curing for 28 days.Concrete containing 2.25% steel fibers demonstrated the highest tensile (7.7 MPa) and flexural strength (13.7 MPa) at 28 days. The composite with 2% steel fibers and 0.25% polypropylene fibers exhibited a splitting tensile strength of 8.4 MPa and flexural strength of 13.6 MPa.90% fly ash + 10% GGBS
(Na2SiO3 + NaOH) [66]
- -
Basalt: aspect ratio (AR) of 20: 0% to1%.
- -
Polypropylene: AR = 12: 0% to 2%.
- -
Hooked-end steel: AR = 30: 0% to 2%.
Ambient and oven curing.Addition of 0.2% of basalt fibers increased tensile strength to 2.9 MPa, 0.8% of polypropylene fibers to 2.7 MPa, and 1% of steel hooked-end fibers to 4.5 MPa.
Basalt fiber displays no post-peak response, whereas polypropylene fiber composite showed enhanced behavior when content exceeds 0.6%. Meanwhile, steel fiber exhibits a gradual post-peak response.Fly ash + GGBS
(NaOH + Na2SiO3, Na2SiO3/NaOH = 2.5, w/b = 0.4) [13]
- -
Steel: 6 mm × 0.15 mm: 0.5% to 2.5%.
- -
Polypropylene: 9 mm × 0. mm: 0.5%, 1.0%, 1.5%, 2.0%, and 2.5%.
Ambient curing for 28 days. Values were reported for 7 and 28 days.Incorporating up to 2.5% steel fibers improved the splitting tensile strength by 52% to reach 9 MPa and flexural strength by 57.79% to reach 13 MPa. Concrete with 2% polypropylene fiber had similar tensile strength of 7.5 MPa and flexural strength of 10 MPa. The flexural toughness increased as the fiber content was increased.100% slag
(12 M NaOH + Na2SiO3, Na2SiO3/NaOH = 2.5 and 3) [14]
- -
Steel: 6 mm × 0.75 mm. Vol. fractions: 0% to 2.5%.
- -
Steel: 12 mm × 0.75 mm. Vol. fractions: 0% to 2.5%.
Ambient and heat curing for 28 days.Addition of 2.5% short steel fibers with Na2SiO3/NaOH = 2.5 led to increase in flexural strength reaching 17 MPa, while longer fibers experienced a higher flexural strength of 20 MPa. As subjected to elevated temperatures, the flexural strength of concrete increased with both short and long fibers.100% fly ash
(14 M NaOH + Na2SiO3, Na2SiO3/NaOH = 2.5) [25]
- -
Hooked-end steel: aspect ratio of 65. Vol. fractions: 0% to 0.5%.
Heat cured for 24 h at 65 °C then air cured for 28 days.Addition of 0.5% hooked-end steel fibers to fly ash-based concrete led to an 8% increase in flexural strength and 57% increase in splitting tensile strength. The toughness increased when 0.5% hooked-end steel fibers was added compared to the mix without fibers.100% fly ash
(8 M NaOH + Na2SiO3
NaOH:Na2SiO3 = 0.4:1) [113]
- -
Steel: 10 mm × 0.12 mm: 0%, to 2%.
- -
Polyvinyl alcohol: 8 mm × 0.04 mm. Vol. fractions: 0%, 1%, 2%.
Steam cured at 60 °C after casting for 24 h then stored in lab.Addition of up to 2% of steel fibers to fly ash-based concrete enhanced the modulus of rupture (MOR) compared to PVA fibers but resulted in decreased deflection capacity due to its high modulus. The addition of up to 2% PVA fibers in fly ash-based concrete enhanced deflection capacity compared to steel fibers.100% slag
(Na2SiO3, SiO2/Na2O = 1.18, w/b = 0.56) [55]
- -
AR-glass: 12 mm × 14&#;20 µm. Vol. fractions: 0.11%, 0.22%, 1.1%.
Air curing for 28 days.The flexural strength of both Ordinary Portland cement and sodium silicate-activated slag mortars were not affected by the addition of glass fibers of volume fractions of 0.11%, 0.22%, and 1.1%.100% fly ash
(12 M and 16 M NaOH) [56]
- -
Glass: aspect ratio of 600. Vol. fractions: 0.1%,0.2%,0.3%,0.4%, and 0.5%.
Normal and thermal curing for 7 and 28 days.The addition of 0.3% glass fiber content in thermally cured fly ash-based concrete activated with 16 M of sodium hydroxide resulted in an increased splitting tensile strength and flexural strength to 1.6 MPa and 6 MPa, respectively.OPC+ metakaolin + fly ash
(K2SiO3 + KOH
w/b = 0.4 and 0.5) [101]
- -
Short carbon: 6 mm × 7 µm. Vol. fractions: 0%, 0.2%.
Ambient curing for 28 days.
Thermal curing for 28 days.Addition of 0.2% short carbon increased the flexural strength of concretes cured at room and elevated temperatures. Initial strength increases at 100 °C; however, subsequent exposure within the 100 °C to 800 °C range led to some strength degradation, particularly noticeable in alkali-activated concrete in comparison with OPC.Ladle slag + metakaolin
(8 M NaOH + Na2SiO3
SiO2/Na2O = 1.99) [109]
- -
Carbon HT: 7 ± 1 mm × 10 µm.
- -
E-glass fiber: 7 ± 1 mm × 10 µm.: 0%, 1%.
- -
PVA fiber: 7 ± 1 mm × 10 µm: 0% to 1%.
- -
PVC fiber: 7 ± 1 mm × 10 µm.
Ambient curing.
Values are taken at 28 days.Addition of 1% carbon fiber, glass fiber, PVA, or PVC into alkali-activated concrete led to increase in flexural strength for all the fiber-reinforced samples. The strength improvement ranged from 30% to 70% in comparison to the alkali-activated concrete without fibers.
Carbon fibers had the highest increase in flexural strength and post-cracking behavior, resulting in high fracture toughness and increased ductility.100% fly ash
(NaOH + Na2SiO3, SiO2/Na2O = 3.2, w/b = 0.4) [37]
- -
Basalt: 3 mm, 6 mm, 12 mm, 18 mm in length. Vol. fractions: 0%, 0.1%.
Heat curing for 16 h.The addition of 0.1% volume fraction of 6 mm basalt fibers in fly ash-based concrete led to the highest achieved splitting tensile strength of 4.84 MPa.70% fly ash + 30% slag
(NaOH + Na2SiO3, SiO2/Na2O = 1.5, w/b = 0.4) [26]
- -
Polypropylene fiber: 12 mm × 18&#;30 µm. Content: 0.1% to 0.5%
- -
Basalt: 12 mm × 7&#;30 µm. Content: 0.1% to 0.5%.
- -
Steel: 13 mm × 0.2 mm. Content: 0.1% to 0.5%.
Curing for 24 h and demold until 28 days.The optimum values of fibers to enhance flexural strength were 0.2% polypropylene, 0.4% basalt, and 0.5% steel, which increased the flexural strength by 7.7%, 12.3%, and 21.5%, respectively.60% fly ash + 40% slag
(NaOH + Na2SiO3, NaOH:Na2SiO3 = 1:2.5) [41]
- -
Polypropylene: 12 mm × 40 µm: 0% to 5%.
Ambient curing.The addition of 5% polypropylene fiber content into alkali-activated concrete containing 60% fly ash and 40% slag led to the highest increase in flexural strength (7.03 MPa).60% fly ash + 40% slag
(NaOH + Na2SiO3, SiO2/Na2O = 1.2, w/b = 0.28) [39]
- -
PVA: 8 mm × 40 µm: 0% to 2%.
- -
PVA: 12 mm × 100 µm: 0.5% to 2%.
Standard curing. Values reported for 28 days.The addition of 2% short PVA fiber content (8 mm in length) increased the flexural strength from 4.81 MPa to 13.45 MPa. Meanwhile, the addition of 2% long PVA fiber content increased the flexural strength to 18.19 MPa.80% metakaolin and
20% class F fly ash
(14 M NaOH + Na2SiO3, Na2SiO3/NaOH = 2) [31]
- -
Industrial steel: 10 mm in length. Tensile strength: MPa.
- -
Waste tire steel fibers (WTSF): 10&#;60 mm × 0.3 mm.
Ambient curing.Alkali-activated concrete incorporating both rubber particles and steel fibers exhibited higher flexural strength compared to the concrete reinforced solely with steel fibers, exhibiting enhanced post-peak energy absorption, owing to synergistic effects at the interfaces that allow for greater deformations.100% slag
(12 M NaOH + Na2SiO3,
Na2SiO3/NaOH = 2.5) [90]
- -
Hooked-end steel: 50 mm × 0.8 mm.
- -
Polypropylene: 48 mm × 0.85 mm: 0% to 1.5%.
Ambient curing for 28 days.Addition of 2% polypropylene fibers increased the tensile strength from 3 MPa to 4.5 MPa. Meanwhile, the addition of 2% steel fibers increased the tensile strength to 4.3 MPa.100% slag
(8 M, 10 M NaOH + Na2SiO3) [114]
- -
AR-glass: 12 mm × 10&#;17 µm.
- -
Basalt: 12 mm × 13&#;20 µm.
- -
Polypropylene: 10&#;60 mm × 0.3 mm.
Air curing for 90 days after curing at a temperature of 60 °C.Addition of 3 kg/m3 polypropylene, basalt, and glass fibers independently led to improvements in the fracture energy of slag-based concrete. Slag (w/b = 0.45)
fly ash (w/b = 0.27)
fly ash + silica fume
(w/b = 0.35)
NaOH + Na2SiO3 [30]
- -
Hooked-end short steel: 12.5 mm × 0.4 mm: 0.3%, 0.6%.
- -
Straight long steel: 50 mm × 1 mm: 0.3%, 0.6%.
- -
Macro-polypropylene fibers: 54 mm × 0.8 mm: 0.3%, 0.6%.
Ambient cured at 20 °C.Addition of 0.6% blended long and short steel fibers and macro polypropylene fibers in alkali-activated concretes did not improve splitting tensile strength, possibly due to the relatively low fiber content. However, slight improvements in flexural strength were observed, with steel fibers in alkali-activated concretes and macro polypropylene fibers. 100% slag
(Ca(OH)2 + Na2SO4, w/b = 0.26, 0.3, 0.34, and 0.38) [93]
- -
Polyethylene: 18 mm × 12 µm. Vol. fractions: 0%, 1.75%.
Ambient curing for 28 days.Addition of 1.75% of polyethylene fiber in slag-based concrete exhibited a tensile strength of 13.06 MPa and a tensile strain capacity of 7.50%. The composite with the lowest water-to-binder ratio of 0.26 exhibits higher toughness.Slag + 10% cement + 10% sodium silicate
(Na2SiO3, w/b = 0.4) [47]
- -
Steel: 10 mm × 0.03 mm: 0%, 0.5%, 1%.
- -
Polypropylene: 10 mm × 0.012 mm: 0%, 0.5%, 1%.
- -
PVA: 8 mm × 0.04 mm: 0%, 0.5%, 1%.
Sealed and water bath-cured specimens.Water-cured concretes reinforced with 1% PVA or steel fibers experienced higher flexural strength than those sealed. This water curing enhanced the polymerization process and reduced porosity.100% slag
(Na2SiO3 + Ca(OH)2
w/b = 0.34, 0.38, and 0.44) [98]
- -
PVA: 12 mm × 39 µm. Volume fractions: 0%, 2%.
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Ambient curing for 28 days.Addition of 2% PVA fiber in slag-based concrete with the lowest water-to-binder ratio of 0.34 achieved the highest tensile strain capacity of 4.48%, first-cracking strength of 3.87 MPa, and tensile strength of 4.69 MPa at 28 days. The tensile strain-hardening behavior increased up to 4.5% ductility.100% fly ash
(NaOH + Na2SiO3, w/b = 0.4) [97]
- -
PVA: 18 mm × 12 µm. Vol. fractions: 0%, 2%.
Heat curing for 28 days.Addition of 2% of PVA fibers in fly ash-based concrete cured at a temperature of 60 °C for 8 h resulted in the highest increase in tensile strength, reaching a value of 3.4 MPa.100% slag
(Na2SiO3 + Ca(OH)2) [100]
- -
PVA: 18 mm × 12 µm. Vol. fractions: 0%, 0.02%.
Air cured.
Values are taken at 28 days.Addition of 0.02% of PVA fiber in slag-based concrete increased the tensile strength to 4.7 MPa and tensile ductility to 4.3%.100% fly ash
(NaOH + KOH) [115]
- -
Carbon fiber: 0.24 mm in diameter. Vol. fraction: 39.47 ± 0.5%.
- -
E-glass: 0.38 mm in diameter. Vol. fraction: 41.17 ± 0.3%.
- -
Basalt: 0.16 mm in diameter.
Air cured at 70 °C for 24 h.Carbon fibers outperformed E-fiber and basalt fiber in fly ash-based concrete in terms of increase in flexural strength and thermal conductivity at elevated temperatures. Carbon fibers exhibited strong adhesion to the geopolymer matrix, reducing pull-out. E-fiber showed volatilization and pull-out tendencies, and basalt fiber induced chemical reactions causing agglomeration.100% fly ash
(12 M NaOH + Na2SiO3) [33]
- -
Polypropylene: 12 mm × 0. mm. Vol. fractions: 0%, 0.4%, 0.8%, 1.2%.
- -
PVA: 8 mm × 0.04 mm: 0%, 0.4%, 0.8%, 1.2%.
Heat cured with 80 °C for 24 h. Values were taken at 7 and 28 days.Addition of 1.2% polypropylene, steel, and polyvinyl alcohol fibers increased the flexural strength by 14.6%, 31.45%, and 39.84%, respectively.100% fly ash,
(8 M NaOH + Na2SiO3
Na2SiO3/NaOH= 2.5) [68]
- -
High-strength steel: 13 mm × 200 micron.
- -
Polyvinyl alcohol (PVA): 8 mm × 40 micron.
- -
Polypropylene: 12 mm × 50 micron.
- -
Polyester fiber (PET): 6 mm × 30&#;40 micron.
- -
Carbon: 10 mm × 15 micron.
Ambient curing for 28 days.Increasing fiber volume fractions up to 1%, which was found to be the optimum level in the study, led to enhanced flexural strength and toughness in high-strength steel (HSS) and PVA-reinforced mortars. However, this enhancement was not significant in the case of CR, PET, and PP-reinforced geopolymer mortars.80% OPC + 20% fly ash [116]
- -
Glass: 6&#;18 mm × 14 µm: 0%, 0.5% recycled coarse aggregates.
Ambient curing for 24 h.The combined influence of glass fibers and fly ash in concrete has a more pronounced impact on its mechanical strength than their individual effects combined.100% fly ash
(Na2SiO3 + NaOH) [58]Cellulose fiber.Heat curing for 24 h.Incorporating cellulosic fibers in geopolymers results in improved toughness, ductility, flexural capacity, and crack resistance compared to cement-based composites without fibers.Fly ash + 20% slag
(8 M, 12 M NaOH + Na2SiO3, NaOH/Na2SiO3 = 1, w/b = 0.4, 0.45) [17]
- -
Hooked-end steel: 35 mm × 0.55 mm. Vol. fractions: 0%, 0.5%, 1%, 1.5%.
Ambient curing for 28 days.The flexural strength of the mortar increased with higher NaOH molarity and steel fiber content. The mixture containing 1.5% polypropylene fibers in 12 M NaOH-activated fly ash/slag concrete with a water-to-binder ratio of 0.4 achieved the highest flexural strength, reaching 9.8 MPa.Slag + silica fume
(8 M NaOH + Na2SiO3) [117]
- -
Cotton: 8 mm × 0.04 mm: 0%, 0.3%, 0.5%, 0.7%, 1%.
Ambient curing.
Values taken at 28 days.Addition of 0.5% cotton fibers improved the flexural strength, modulus, and toughness. However, exceeding 0.5% results in reduced flexural strength due to workability issues.Metakaolin + fly ash
(K2SiO3, SiO2/K2O molar ratios of 1.0) [101]
- -
Cotton: 6 mm × 7 µm. Vol. fractions: 2%.
Room temperature curing.Addition of 2% cotton fiber increased the flexural strength. This increase happens slightly after exposure to 100 °C. It decreases in the range of 100&#;800 °C due to thermal deformations.100% fly ash
(10 M NaOH + Na2SiO3) [60]
- -
Sisal fiber: 35&#;40 mm × 179 µm: 0% to 1.0%.
- -
Coconut: 35&#;40 mm × 117 µm: 0% to 1.0%.
- -
Glass: 12 mm × 20 µm.
Heat cured.Addition of sisal increased flexural strengths ranging from 5.3 to 6.6 MPa, outperforming the control mix. In addition, mortars reinforced with sisal fibers achieved splitting strengths between 2.2 and 3.3 MPa, outperforming the control mix.100% fly ash
(Na2SiO3 + NaOH) [76]
- -
Polyethylene: 12 mm × 20 µm. Vol. fractions: 0%, 1.5%, 2%.
Room curing followed by oven curing.The incorporation of 1.5% polyethylene fiber increased the tensile strain capacity to 13.7% tensile strain capacity and tensile strength to 6.8 MPa after 28 days of testing.GGBS + fly ash
(8 M, 10 M NaOH +Na2SiO3, Na2SiO3/NaOH = 2.5) [18]
- -
Basalt: 12 mm × 13 µm.: Vol. fractions: 0.1% to 0.35%.
- -
Crimped steel: 25 mm × 0.5 mm. Vol. fractions: 0.4% to 0.6%.
- -
Polypropylene: 12 mm × 0.038 mm. Vol. fractions: 0.05% to 0.25%.
Ambient curing. Values were recorded for 7 and 28 days.At both 7 and 28 days of curing with 8 M and 10 M NaOH concentrations, the inclusion of 0.55% steel fibers, 0.3% basalt fibers, and 0.1% polypropylene fibers independently led to the highest tensile and flexural strengths, with steel fibers showing the most reduction.Cement + microsilica [32]
- -
Carbon fiber: 10 mm in length. Vol. fractions: 0.2%, 0.4%, 0.6%, 0.8%, 1%.
Values were recorded for 28 days of curing.Addition of 0.6% carbon fiber content increased the tensile strength to 6.86 MPa. However, increasing the carbon fiber beyond 0.6% decreased the tensile strength.100% OPC and OPC + 25% GGBS [102]
- -
Jute: 10 mm in length. Vol. fractions: 0.2%, 0.4%, 0.6%, 0.8%, 1%.
Water curing for 28 days. Then conditioned indoors for 7 days.Addition of 0.5% jute fiber and superplasticizer increased the flexural strength by 24.3% and splitting tensile strength by 21%. When 0.5% jute fiber was combined with 25% GGBS and superplasticizer, it resulted in a 33% enhancement in flexural strength.Metakaolin + fly ash
(NaOH + Na2SiO3, Na2SiO3/NaOH = 6.27, w/b = 0.65) [40]
- -
PVA: 12 mm × 40 μm. Vol. fractions: 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, and 1.2%.
Curing at 25 °C and 200 °C.The inclusion of 1.2% PVA fibers led to a 58% and 66.3% increase in flexural strength at temperatures of 25 °C and 200 °C, respectively. As temperature exceeded 200 °C, significant decline in mortar flexural strengths was observed.Metakaolin concrete
(NaOH or KOH) [118]
- -
PVA: 12 mm × 40 μm: 0% and 2%.
- -
Polyethylene: 12 mm × 20 μm: 0% and 2%.
Curing in dry plastic bags for two weeks.The flexural strengths of NaOH-activated metakaolin concrete and potassium-based metakaolin concrete were measured at 19.7 MPa and 13.7 Mpa, respectively, while composites containing polyethylene fibers exhibited even higher flexural strengths. Cement + GGBFS + fly ash + microsilica [19]
- -
Hooked-end steel: 35 mm × 0.55 mm: 0.5% down to 0.1%.
- -
Microsteel: 10 mm × 0.12 mm.
Moist cured for 7, 14, and 28 days.The combination of hooked steel and microsteel fibers with volume fractions of 0.4% and 0.1% led to 79.65% to 87.12% increase in compressive strength depending on concrete grade. There are similar improvements in flexural strength.100% fly ash
(NaOH + Na2SiO3) [35]
- -
Polypropylene: 12 mm × 34 µm. Vol. fraction: 0%, 0.05%, 0.1%, 0.2%.
Curing at 80 °C for 24 h.The addition of 0.05% polypropylene microfibers enhanced the flexural strength by 17%. The toughness of geopolymer binders decreased with elevated temperatures exceeding 200 °C, particularly in fiber-reinforced specimens.Slag + fly ash + silica fume
(Na2SiO3 + NaOH, w/b = 0.32) [20]
- -
Corrugated steel: 13 mm × 0.12 mm.
- -
Hooked-end steel: 13 mm × 0.12 mm: 0% to 3%.
- -
Straight steel: 13 mm × 0.12 mm.
Standard curing at 20 °C.Inclusion of steel fiber improves splitting tensile strength. Increasing steel fiber content to 3% leads to a substantial increase of 42.1% in splitting tensile strength.Slag + fly ash + silica fume
(Na2SiO3 + NaOH, w/b = 0.32) [20]
- -
Corrugated steel: 13 mm × 0.12 mm.
- -
Hooked-end steel: 13 mm × 0.12 mm.
- -
Straight steel: 13 mm × 0.12 mm.
Standard curing at 20 °C.Increasing steel fiber content from 1% to 3% increased deflection corresponding to first crack, increased flexural strength, and decreased peak deflection.Fly ash + slag + basalt
powder [54]
(Na2SiO3 + 12 M NaOH)
- -
Basalt: 12 mm × 0.02 mm. Vol. fractions: 0.4%, 0.8%, and 1.2%.
Cured at 60 °C for 24 h.Addition of 1.2% basalt fibers led to a 34.15% increase in flexural strength. Even at 800 °C, the inclusion of basalt fibers led to improvements in flexural strength ranging from 11.61% to 44.69% when basalt volume fractions ranged from 0.4% to 1.2% compared to mortar without basalt.Geopolymeric cement [10]
- -
Basalt: 45 mm and 9 µm. Vol. fractions: 0%, 0.5%, 1%.
Ambient curing for 1 day then water curing for 27 days. Addition of 1.0% basalt fibers increased splitting tensile and flexural strengths in geopolymeric cement. Geopolymeric cement demonstrated superior load capacity and fracture toughness.80% fly ash + 20% slag
50% fly ash 50% slag
(Na2SiO3 + NaOH, Na2SiO3/NaOH = 2.5) [62]
- -
Fibers: coir, ramie, hemp, jute, and bamboo: 1% and 2% of the volume of fine aggregates: natural sand; lead smelter slag; and waste glass sand.
Ambient curing.
Values taken at 7, 14, and 28 days.Addition of 1% natural fibers enhances the tensile strengths of geopolymers. However, when coir, sisal, and jute fibers are added at the same percentage, there is a slight decrease in strength compared to unreinforced geopolymers. Geopolymers reinforced with 1% ramie fiber displayed the highest tensile strength.100% slag
(Na2SiO3 + NaOH, SiO2/Na2O molar ratio: 2.1) [119]
- -
AR-glass: 12 mm in length: 0% to 0.5%.
- -
E-glass: 12 mm long.
- -
Basalt: 12 mm long.
- -
Carbon: 12 mm long.
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Ambient curing at 20 °C.Short fibers, particularly carbon fibers (content up to 0.5%), led to a substantial increase in flexural strength. This effect was observed both in the short term and over a longer duration of 28 days, resulting in 30% improvement in tensile strength.