Flexural strength of low-strength RC beams using CFRP composite

Mand Kamal Askar; Yaman Sami Shareef Al-Kamaki

doi:10.2478/msp-2025-0041

.blurhash-client-img { display: none !important; }

Flexural strength of low-strength RC beams using CFRP composite

Materials Science-Poland

Volume 43 (2025): Issue 4 (December 2025)

By: Mand Kamal Askar and Yaman Sami Shareef Al-Kamaki

Open Access

|Dec 2025

Figures & Tables

Table 1

Mechanical properties of LSC.

	() MPa	(f _t) MPa	(f _r) MPa	(E) GPa	Poisson’s ratio	Slump test (mm)	Velocity based on UPV test mm/μ _s	Density (kg/m³)
LSC	17.3	2.38	3.59	21.36	0.172	65	4.25	2,246

CFRP coupon testing: (a) universal machine test; (b) coupon under testing; (c) laminate CFRP coupons failure; and (d) fabric CFRP coupons failure.

Table 2

Material properties of CFRP fabric and CFRP laminate provided by the manufacturer.

Characteristics	Manufacturer data
Characteristics	CFRP fabric	CFRP laminate
Ultimate tensile strength (MPa)	4,000	3,100
Fiber modulus (GPa)	230	170
Ultimate tensile elongation (%)	1.7	1.8
Thickness (mm)	0.167	1.4
Fiber density (g/cm³)	1.82	1.6

Table 3

Details of strengthened RC beams.

Label	Beam symbol	FRP material	Scheme	Notes
F1	BF-L			Flexural control beam
F2	BF-L-LB	CFRP strip	1-layer 100 mm	Bottom soffit
F3	BF-L-SB-2	CFRP sheet	2-layer 100 mm	Bottom soffit
F4	BF-L-LB-UE	CFRP strip/sheet	1-layer 100 mm/1-layer 100 mm at both ends	Bottom soffit/U-wrapped only ends
F5	BF-L-LB-UE5	CFRP strip/sheet	1-layer 100 mm/1-layer 500 mm at both ends	Bottom soffit/U-wrapped only ends
F6	BF-L-SB-UE	CFRP sheet/sheet	1-layer 100 mm/1-layer 100 mm at both ends	Bottom soffit/U-wrapped only ends
F7	BF-L-SB-UE2	CFRP sheet/sheet	2-layer 100 mm/1-layer 100 mm at both ends	Bottom soffit/U-wrapped only ends
F8	BF-L-LBT-UE	CFRP sheet/strip	1-layer 100 mm/1-layer 100 mm/1 layer at both ends	Bottom soffit/top soffit center compression/U-wrapped only ends

Table 4

CFRP composite material properties.

Coupon	Ave. width (mm)	Ave. thick. (mm)^a	Max load (kN)	Max tensile stress (MPa)	Max tensile strain	Modulus of elasticity (GPa)	Poisson’s ratio
	CFRP sheet (0.167 mm/ply)
1	50.1	0.71	21	2,560	0.0122	209.8	—
2	50.3	0.73	21	2,530	0.0121	209.1	—
3	50.5	0.78	23	2,700	0.0131	206.1	—
4	50.0	0.82	22	2,606	0.0125	208.5	0.28
5	50.8	0.88	23	2,690	0.0127	211.8	—
6	50.1	0.90	22	2,620	0.0126	207.9	—
Average	50.3	0.80	22	2,618	0.0125	208.9
	CFRP laminate (1.4 mm plate thickness)
1	50	1.4	133	1,897	0.0114	166.4	—
2	50	1.4	131	1,872	0.0105	178.3	—
3	50	1.4	127	1,808	0.0093	194.4	0.26
4	50	1.4	134	1,908	0.0114	167.4	—
5	50	1.4	130	1,863	0.0103	180.9	—
6	50	1.4	131	1,871	0.0105	178.2	—
Average	50	1.4	131	1,870	0.0106	177.6	—

^aAverage thickness of epoxy + CFRP.

Table 5

Results of RC beams critical in flexural (F1–F11).

Beam ID	P _cr (kN)	M _cr (kN m)	V _cr (kN)	Δ _cr (mm)	P _y (kN)	M _y (kN m)	V _y (kN)	Δ _y (mm)	P _u (kN)	P _u/P _u.control	M _u (kN m)	V _u (kN)	Δ _u (mm)	Failure mode
F1	9	3.0	4.5	0.76	48.4	16.1	24.2	6.7	51	—	17.0	25.5	16	Flexural tension failure
F2	22	7.3	11.0	2.06	58.2	19.4	29.1	7	73.4	43.9%	24.5	36.7	10.8	Concrete cover separation and flexural tension failure
F3	14	4.7	7.0	1.33	46	15.3	23.0	5.9	73.4	43.9%	24.5	36.7	20.1	CFRP plate debonding and concrete cover separation and flexural tension failure
F4	12.5	12.6	4.2	0.91	67.2	67.2	22.4	6.4	76.4	62.7%	27.7	41.5	17.6	CFRP plate debonding and flexural tension failure
F5	23	7.7	11.5	1.9	104	34.7	52.0	7.2	111.8	119.2%	37.3	55.9	18.6	CFRP plate debonding and flexural tension failure
F6	16.5	5.5	8.2	1.91	60.8	20.3	30.4	11.1	71.6	40.4%	23.9	35.8	30.2	CFRP plate debonding and flexural tension failure
F7	22	7.6	11.4	2.69	67	22.3	33.5	10.7	78.2	53.3%	26.1	39.1	22.8	CFRP plate debonding and flexural tension failure
F8	24	8.1	12.1	2.38	60.6	20.2	30.3	6.1	72.8	42.7%	24.3	36.4	11.3	CFRP plate debonding and flexural tension failure and flexural compression failure

Crack pattern and associated modes of failure.

DIC frame illustrates crack initiating at different stages; (a) sample F1 (BF-L); and (b) sample F2 (BF-L-LB).

Comparison in ultimate deflection between experimental and DIC test for samples F1 (BF-L) and F2 (BF-L-LB).

Increase in ultimate moment capacity according to different CFRP schemes.

Comparison between F2 (BF-L-LB) and F3 (BF-L-SB-2) in moment and shear vs deflection.

Comparison between F6 (BF-L-SB-UE) and F7 (BF-L-SB-UE2) in moment and shear vs deflection.

Increase in ultimate load capacity according to different CFRP schemes.

Table 6

Ductility index.

Beam symbol	Beam ID	P _y (kN)	Δ _y (mm)	P _u (kN)	Δ _u (mm)	μ ε _u (steel-tension)	P _u /Δ _u	Ductility index Δ _u /Δ _y (μd)	Increase in μd %	Area under curve (kN mm)	Increase in area under curve %
BF-L	F1	48.4	6.7	51	16	2,364	3.2	2.39	—	138	—
BF-L-LB	F2	58.2	7	73.4	10.8	3,398	6.8	1.54	−36%	192	39%
BF-L-SB-2	F3	46	5.9	73.4	20.1	2,871	3.7	3.41	43%	413	199%
BF-L-LB-UE	F4	67.2	6.4	76.4	17.6	2,942	4.7	2.75	15%	411	198%
BF-L-LB-UE5	F5	104	7.2	111.8	18.6	3,580	6.0	2.58	8%	510	270%
BF-L-SB-UE	F6	60.8	11.1	71.6	30.2	2,900	2.4	2.72	14%	696	404%
BF-L-SB-UE2	F7	67	10.7	78.2	22.8	—	3.4	2.13	−11%	547	296%
BF-L-LBT-UE	F8	60.6	6.1	72.8	11.3	2,872	6.4	1.85	−23%	195	41%

Table 7

Number of cracks at ultimate load.

Beam symbol	Beam ID	Number of shear cracks diagonal	Number of flexural cracks	Crack width at failure-mid span (mm)	Failure mode
BF-L	F1	0	13	2.2	Diagonal tension failure
BF-L-LB	F2	1	16	1.0	Flexural compression failure
BF-L-SB-2	F3	2	17	1.0	Flexural compression failure
BF-L-LB-UE	F4	2	15	1.0	Flexural tension failure and flexural compression failure
BF-L-LB-UE5	F5	0	17	1.5	Flexural compression failure
BF-L-SB-UE	F6	2	19	2.0	Flexural tension failure and flexural compression failure
BF-L-SB-UE2	F7	1	19	1.0	Flexural tension failure
BF-L-LBT-UE	F8	0	15	1.0	Flexural compression failure

Section force distribution without CFRP.

Load–deflection comparison between experimental, analytical, and GiD results for sample F1 (BF-L).

Load–deflection comparison between experimental, analytical, and GiD results for sample F2 (BF-L-LB).

Load–deflection comparison between experimental, analytical, and GiD results for sample F5 (BF-L-LB-UE5).

Crack pattern comparison between experimental and GiD.

Table 8

Comparison between experimental, numerical, and analytical analysis.

	Exp.				GiD				Analy.				Evaluation
Beam ID	P _u (kN)	M _u (kN m)	V _u (kN)	Δ _u (mm)	P _u (kN)	M _u (kN m)	V _u (kN)	Δ _u (mm)	P _u (kN)	M _u (kN m)	V _u (kN)	Δ _u (mm)	P _u.Exp./P _u.GiD	P _u.Exp./P _u.Analy.	Δ _u.Exp./Δ _u.GiD	Δ _u.Exp./Δ _u.Analy.
F1	51	17.0	25.5	13	49.8	17	25.5	12	54.2	15.4	—	9.4	1.024	0.941	1.08	1.38
F2	61.4	20.5	30.7	10.8	67.5	22.5	33.8	7.5	64	21.4	—	10.1	0.909	0.959	1.44	1.07
F5	111.8	37.3	55.9	18.5	100.5	33.5	50.3	18	—	—	—	—	1.112	—	1.03	—

References

Authors

Metrics

Articles in this issue

DOI: https://doi.org/10.2478/msp-2025-0041 | Journal eISSN: 2083-134X (formerly 2083-124X) | Journal ISSN: 2083-1331

Journal RSS Feed

Language: English

Page range: 38 - 58

Submitted on: Oct 8, 2025

Accepted on: Dec 2, 2025

Published on: Dec 31, 2025

Published by: Wroclaw University of Science and Technology

In partnership with: Paradigm Publishing Services

Keywords:

CFRP,

Strengthening,

Flexural,

RC beams,

Low-strength concrete

Related subjects:

Materials sciences,

Materials sciences, other,

Nanomaterials,

Functional and smart materials,

Materials characterization and properties

© 2025 Mand Kamal Askar, Yaman Sami Shareef Al-Kamaki, published by Wroclaw University of Science and Technology
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Volume 43 (2025): Issue 4 (December 2025)

Flexural strength of low-strength RC beams using CFRP composite

Figures & Tables

Table 1

Figure 1

Figure 2

Table 2

Figure 3

Table 3

Figure 4

Table 4

Figure 5

Table 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Table 6

Figure 15

Table 7

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Table 8

Paradigm

My account