Table 5.

Complex hybrid R-FRC containing recycled metallic materials and recycled plastics.

Cement Type	Fiber 1- (Dimensions: L, W, T or d)—Doses (in Volume Fraction)	Fiber 2 (Dimensions: L, W, T or d)—Doses (in Volume Fraction)	Recycling Source	Effect on Mechanical Properties	Other Effects	Application	Ref.
Hybrid FRC Beams: - PPC 53 Grade (IS1489) - w/c = 0.4 - Sand IS 4.75 - Crushed granite stones 10-20 mm - Superplasticiser	Scrim bled steel (Non-recycled) (L = 50 mm, d = 1 mm)—0.38%, 0.25% and 0.12%	Recycled PET (L = 38 mm, d = 0.02 mm)—0.38%, 0.25% and 0.12% PP (Non recycled) (L = 38 mm, d = 0.1 mm) —0.38%, 0.25% and 0.12%	-	ΔCS = 22% *, ΔTS = 17% * ΔFS = 19% *, ΔTS = 2% ** (0.38% steel fibers + 0.12% PET) ΔCS = 7.5% **, ΔTS = 12% **, ΔFS = 15% ** (0.38% steel fibers + 0.12% PP) 28 days curing	Increase in shear performance. First crack load increased 7% *	Structural applications	[145]
FRC: - C30/37 grade concrete -C55/67 grade concrete	Recycled steel (L = 25 mm)—4% (w/v)	PP (Non-recycled) (L = 54 mm)—0.45% (w/v)	Automotive industry waste steel fibers	ΔCS = −6% ** (for Concrete of 60 MPa) ΔCS = −11% ** (for concrete of 80 MPa)	Blast performance was kept	Protection of transport infrastructure against blast loading	[146]
Concrete: - OP ASTM type I - Crushed limestone 16 mm - Sand - Superplasticiser	Recycled metallic fibers (L = 30–60 mm)—1–3%	Recycled PP fibers (L = 30, 50, 60 mm)—0.5–1%	Metal—Locally available metal lathe workshop; PP—Storage bags	ΔCS = −20% *; ΔFS = 12% * 0.75% steel 60mm + 0.75% PP 60 mm	Improved post cracking behaviour	Normal concrete applications	[97]
FRC: - CEM I 42.5R - Sand - Coarse aggregate (river stones) - Rubber aggregate	Recycled steel and plastic fibers partially coated with rubber—8.5–42% (in weight/volume) replacing rubber aggregates. (L= 10–45 mm; d = 75% of them lower than 25 µm)		Waste tires	ΔCS = −36% *; ΔEM = −35% *, ΔFS = −7.3% *; ΔIEA1 = 100% *, ΔIEAU = 600% *;ΔCS = 9% ***; ΔEM = −3% ***; ΔFS = 15% *** (8.5% complex fibers) ΔIEA1 = 4500% * (33.5% complex fibers)	Bulk density increased 7% keeping similar thermal conductivity *** (8.5% complex fibers)	Conventional rubberized concrete for thermal rehabilitation of buildings	[51,52]
FRC: - CEM II/A-LL 42.5N w/c = 0.35 - Coarse aggregate - Fine aggregate - Sand - Superplasticiser	Metallic powders (mean size = 12 mm) – ~1%	Recycled PA fibers (L = 8 mm, d = 0.038 mm)—0.5%	PA – Textile carpet waste Rail steel	ΔCS = 18% *	Thermal conductivity increased due to steel 120–170% *	Thermal storage units for solar plants	[70]
	Recycled metallic shavings (L = 10–20 mm)—1%			ACS = −10% *
SCC: - CEM I 42.5R - w/c = 0.6–0.64 - Fly ash - Silica fume - Superplasticiser	Micro-steel (L = 6 mm, d = 0.16 mm)—0.82% (w/v)	HDPE (L = 3–10 mm, d = 0.1 mm)—0.82% (w/v)	Municipal wastes	ACS = −30% * ACS = 0% ** AFS = −10% * AFS = 0% **	Drying shrinkage reduction: 11% * Flowing diameter reduction: 10% *	-	[79]
FRC: - CEM I 42.5R - Sand - Coarse aggregate - Rubber aggregate	Steel and textile fibers coated with rubber and rubber dust (7.7%—38.4% v/v) (replacing coarse aggregates 20—100%)		Waste from recycling rubber from waste tires	ΔCS = 9% *** (7.7% complex fiber with rubber)(28d)	Shrinkage 62% *** (7.7% complex fiber with rubber) Bulk density decreased	-	[52]
SCC: - OP 42.5R - w/c = 0.76 - Fly ash - Aggregate - Superplasticizer	Recycled steel fiber (L = 50 mm, d = 0.15 ± 0.5 mm) 0.5%, 0.75% and 1%	PP (Non-recycled) (aspect ratio = 461) 0.5%, 0.75% and 1%	Recycled steel: waste tires	ΔCS = 30% *; ΔCS = −12% ** ΔFS = 20% *; ΔFS = −10% ** (0.5%PP + 1% recycled steel)	Impact energy absorption increased 1800% * (0.5%PP + 1% recycled steel)	-	[108]
- OP IS 12269 - w/c= 0.4 - Sand IS 4.75 - Crushed granite stones 10–20 mm - Silica fume - Superplasticiser	Recycled steel fibers (L = 10–15 mm)	Recycled nylon fibers (L = 40 mm)	Steel lathe waste Nylon waste from local industries	Best performance: total fiber = 2% ΔCS = 12% *; ΔTS = 54% * (steel/nylon ratio = 2) ΔMOR = 50% * ΔIE1 = 238% *; ΔIEU = 205% *; ΔFE = 197% * (steel/nylon ratio = 1)	Air content increased up 75%	-	[147,148]
	Total fiber fraction 0.5%, 1.0%, 1.5% and 2.0% Steel/nylon ratios: 1/2, 1, 2 Superplasticiser at demand to get desired workability
SCC: - CEM I 42.5 R -w/c = 0.38 - Fine aggregates -superplasticiser	Recycled steel fiber (L = 50 mm, d = 0.15 mm)—0.35%, 0.7% and 1.05% (in volume fraction)	PP (Non-recycled) (L = 12 mm, d = 0.018 mm)—0.35% and 0.7% (in volume fraction)	Recycled steel: waste tires	Best performance: ΔCS = 39% *; ΔFS = 31% * ΔCS = 11% **; ΔFS = 10% ** (1.05% steel + 0.7% PP) ΔIE1 = 27% * (0.7% steel + 0.7% PP)	Slump flow diameter decreased linearly with fiber fraction ΔSlump = −19% * (1.05% steel + 0.7% PP)	-	[144]
FRC: - CEM I 52.5N - w/c = 0.4 - Sand - Crushed granites - Superplasticiser	Recycled steel fiber (L = 23 mm, d = 0.22 mm)—0.5–0.9%	PP (Non-recycled) (L = 12 mm, d = 0.05 mm)—0.1–0.5%	Recycled steel: waste tires	Best performance: ΔCS = −5% *; ΔFS = −1% * ΔCS = −10% **; ΔFS = −14% ** ΔTS = 40% *; ΔTS = −34% ** (0.9% steel + 0.1% PP)	Increase chemical resistance in chlorine environments Decrease shrinkage 5% **–35% ** (0.4%PP + 0.6% steel)	-	[89]
- CEM II 52.5 - w/c = 0.56 - Coarse aggregate - Fine aggregate - Superplasticizer	Recycled steel fibers (L = 19–21 mm, d= 0.11–0.19 mm) 40 kg/m3	Recycled polymer fibers (L = 4–30 mm, d= 0.02–0.03 mm) 2 kg/m3 and 5 kg/m3	Waste tires	ΔCS = −1% * (40 kg/m3 steel + 5 kg/m3 polymer)	Prevention of fire spalling	FRC-lined tunnels	[149]

Nomenclature: CS: Compressive Strength; d: diameter; EM. Elastic Modulus; FRC: Fiber Reinforced Composite; FS: Flexural Strength; HDPE: High Density Polyethylene; L: Length; OP: Ordinary Portland cement; PPC: Portland Pozzolana cement; SCC: Self-Consolidating Concrete; T: Thickness; TS: Tensile Strength; W: Width; IEA1: Impact Energy Absorption at first crack; IEAU: Impact Energy Absorption at ultimate stage. * compared to plain cement (without fibers); ** compared to single recycled fiber cement-based composite, *** compared to the equivalent rubberized concrete (with high quality recycled rubber) without fibers.