The Combined Effect of Carbon Fibers and Different Waste Aggregates on the Strength and Modulus of Elasticity of Modified Metakaolin-Based Geopolymer Concrete

Suhad A. Mozan; Wasan I. Khalil

doi:10.2478/cee-2026-0005

Figures & Tables

Waste aggregate (a) Crumbed rubber (b) Mixed plastic

Carbon fiber before and after cutting into a specific length

Compressive Strength Results of GPC mixes

Splitting Tensile Strength Results of GPC mixes

SEM image of GPC specimens with rubber waste aggregate (GR mix)

SEM image of GPC specimens with plastic waste aggregate (GPL mix)

SEM image of GPC specimens with carbon fiber and plastic aggregate (GPL+0.2C mix)

Physical properties of metakaolin

Physical Properties	MK	Requirements of ASTM C 618
Strength activity index at 7 days [%]	113	≥75%
Retained on 45 µm [%]	18.5	≤34%
Specific surface area [m²/kg]	14300	--
Specific gravity	2.64	--
Color	White –pinky powder	--

Properties of Crumbed Rubber Waste after Preparation

Properties	Results	Specifications
Loose bulk density (kg/m³)	--	ASTM C 29-15
Compacted bulk density (kg/m³)	494	ASTM C 29-15
Specific gravity	1.10	ASTM C127-15
Water absorption [%]	4.8	ASTM C 127-15

Chemical properties of metakaolin

Oxide Composition	Weight [%]	Requirements of ASTM C 618
SiO₂	62.410	SiO₂ + Al₂O₃ + Fe₂O₃ = 98.327 ≥70
Al₂O₃	35.026
Fe₂O₃	0.891
K₂O	0.908
TiO₂	0.531
CaO	0.143
SO₃	0.027	≤4%
MnO	0.002
LO I^*	0.71	≤10%

Grading and physical properties of shredded waste plastic aggregate

Sieve size [mm]	Cumulative Passing [%]	Limits of IQS No. 45
20	100	100
14	95	90–100
10	60	50–85
5	3.5	0–10

The typical properties of carbon fiber wrap *

Properties	Description
Fabric length [m]	≥50
Fabric width [mm]	600
Areal weight [g/m³]	230 ± 10
Fabric design thickness [mm]	0.131
Fiber density [g/cm³]	1.76
Tensile strength [N/mm²]	4300
Tensile E-modulus [N/mm²]	234000
Carbon content [%]	99% of the total weight
Elongation at break [%]	1.8

Properties of calcium oxide

	Property	Results
Physical properties	Specific surface area [m²/kg]	16350
	Specific gravity	3.3
	Color	White
Chemical properties	Oxide’s composition	Results [%]
	SiO₂	4.314
	Al₂O₃	--
	Fe₂O₃	0.461
	K₂O	1.667
	TiO₂	--
	CaO	93.40
	SO₃	0.10
	MnO	0.025

Properties of GPC Mixes in this Research

Mix Symbol	Compressive strength at 7 days [MPa]	Tensile strength at 7dayes [MPa]	Modulus of elasticity at 7days [GPa]	Density [kg/m³]
GR	45.40	2.4	18.00	1940
GR+0.15C	50.05	2.8	20.90	2150
GR+0.2C	54.70	3.0	22.50	2170
GPL	39.50	1.7	13.45	2080
GPL+0.15C	43.80	1.9	15.80	2110
GPL+0.2C	48.50	2.7	18.00	2140

Properties of fine aggregate

Sieve Size [mm]	Cumulative Passing [%]	Limits of IQS No. 45 for Zone II
10	100	100
4.75	94	90–100
2.36	82	75–100
1.18	68	55–90
0.6	51	35–59
0.3	27	8–30
0.15	8	0–10
Material passing from sieve 75 µm, [%]	3	≤5%
Sulfate content [%]	0.18	≤0.5%
Fineness modulus	2.71	--
Absorption, [%]	0.4	--
Specific gravity	2.63	--
Bulk density [kg/m³]	1744	--

Details of Geopolymer Concrete Mixes Used in This Study

Mix Symbol	MK^*	SF^*	CaO	CA^*	FA^*	SS^*	SH^*	SP^*	W^*	R^*	PL^*	C^*
[Kg/m³]
GR^#	372	50	50	820	603	192	83	8	58	38	0	0
GR+0.15C^#	372	50	50	820	603	192	83	8	60	38	0	2.8
GR+0.2C^#	372	50	50	820	603	192	83	8	60	38	0	3.8
GPL^#	372	50	50	820	603	192	83	7.5	58	0	38	0
GPL+0.15C^#	372	50	50	820	603	192	83	8	60	0	38	2.8
GPL+0.2C^#	372	50	50	820	603	192	83	8	60	0	38	3.8

Properties of coarse aggregate

Sieve Size [mm]	Cumulative Passing [%]	Limits of IQS No. 45
10	97	85–100
5	12	0–25
2.36	--	0-5
Material passing from sieve 75 µm, (%)	0.3	≥3
Dry density (kg/m³)	1627	--
Specific gravity	2.62	--
Absorption, (%)	0.6	--
Sulfate content (%)	0.059	≤ 0.1

Properties of the high-range water reducer*

Property	Description
Appearance	Dark brown liquids
Specific gravity	1.24–1.26 @20º
Chloride content	Nil
Recommended dosage	1.00–2.00 L/100 kg cementitious

Properties of silica fume

	Property	Results	Requirements of ASTM C1240
Physical properties	State	Amorphous sub-micro powder	--
	Strength activity index with Portland cement at 7 days [%]	122	≥ 105
	Retained on sieve 45 µm max [%]	9	≤ 10
	Specific gravity	2.00 –2.40	--
	Color	Grey to medium grey powder	--
Chemical properties	Oxide’s composition	Results [%]
	SiO₂	88.593	≥85
	Al₂O₃	--	--
	Fe₂O₃	5.564	--
	K₂O	4.777	--
	TiO₂	--	--
	CaO	0.666	--
	SO₃	0.027	--
	MnO	0.27

The Combined Effect of Carbon Fibers and Different Waste Aggregates on the Strength and Modulus of Elasticity of Modified Metakaolin-Based Geopolymer Concrete

Figures & Tables

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Physical properties of metakaolin

Properties of Crumbed Rubber Waste after Preparation

Chemical properties of metakaolin

Grading and physical properties of shredded waste plastic aggregate

The typical properties of carbon fiber wrap *

Properties of calcium oxide

Properties of GPC Mixes in this Research

Properties of fine aggregate

Details of Geopolymer Concrete Mixes Used in This Study

Properties of coarse aggregate

Properties of the high-range water reducer*

Properties of silica fume

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