Strengthening of Ultra-high Performance Concrete Beams with CFRP Strips

Ali Khalid Ahmed; Mustafa Hameed Al-Allaf

doi:10.2478/cee-2026-0015

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Strengthening of Ultra-high Performance Concrete Beams with CFRP Strips

Civil and Environmental Engineering

Volume 22 (2026): Issue 1 (March 2026)

By: Ali Khalid Ahmed and Mustafa Hameed Al-Allaf

Open Access

|Mar 2026

Figures & Tables

Dimension and reinforcement details of specimens (all dimensions in mm).

(RC-C) control specimen (all dimensions in mm).

(RC-CFRP-U-90-100) (all dimensions in mm).

(RC-CFRP-U-45-100) (all dimensions in mm).

(RC-CFRP-2side-90-600) (all dimensions in mm).

(RC-CFRP-U-90-600) (all dimensions in mm).

(RC-CFRP-full face) (all dimensions in mm).

Linear variable differential transformer (LVDT).

Maximum main steel strain for all beams.

Maximum vertical CFRP strain for all beams.

Maximum diagonal CFRP strain for all beams.

Failure modes_

Sample	CFRP orientation	V_c (kN)	V_f (kN)	*First shear crack V_cr* (kN))**	Percentage gain in shear capacity	Type of failure
RC-C	0	156.615	0	127	0	Pure shear
RC-U-90-100	90°	156.615	70.11	128	44.77%	Depending – shear- flexure
RC-U-45-100	45°	156.615	78.630	127	50.21%	Pure Flexure
RC-2side-90-600	90°	156.615	80.615	132	51.47%	Depending –pure flexure
RC-U-90-600	90°	156.615	95.095	130	60.72%	Depending – flexure - shear
RC-Full-Face	90°	156.615	99.120	/	63.29%	Depending – pure shear

Chemical composition and main compounds of fly ash_

Compounds	Fly ash class F
SiO₂	55
Al₂0₃	26
Fe₂O₃	7
CaO (Lime)	9
MgO	2
SO₃	1

Mix proportions and compressive strength results_

Mixes all in [kg/m³]	Fine sand	Sulphate-resisting Portland cement	Water	Superplastizer	Silica fume	Fly ash	Compressive strength [MPa] 28 days
1	1070	963	204	32	107	0	74.81
2	1070	963	200	32.5	107	192.6	92.9
3	1070	970	184	33.4	107	192.6	126.97

Mechanical characteristics of steel reinforcement bars_

Diameter [mm]	Yield strength [MPa]	Yield strain [με]	Ultimate strength [MPa]	Ultimate strain [με]	Elastic modulus [MPa]
16	582.4	2632	687.9	130000	200000

Observed vs_ estimated shear contributions of CFRP in the strengthened specimens_

Specimens	CFRP contribution determined by the subtraction approach: [kN]	CFRP contribution according to ACI 440.2R-17: [kN]	CFRP contribution according to CNR-DT-215- 2018: [kN]	CFRP contribution according to TR-55 (CS, 2013): [kN]
RC-U-90-100	70.110	73.132	62.218	47.695
RC-U-45-100	80.615	103.698	93.327	67.250
RC-2side-90-600	80.900	109.698	93.327	95.390
RC-U-90-600	95.090	109.698	93.327	95.390
RC-Full-Face	99.120	109.698	93.327	95.390

Chemical analysis of silica fume_

NO.	Components	Silica fume [%]	ASTM C1240 limitations
1	CaO	1.22
	SiO₂	91.05	≥ 85
	Al₂O₃	0.018	--
	Fe₂O₃	0.012	--
	MgO	0.01	--
	SO₃	0.225	--
	Na₂O	0.205	--
	K₂O	0.155	--
	Loss on ignition	2.975	≤ 6
	Moisture content	0.68	≤ 3
2	Activity index with Portland cement at 7 days	132.4	≥ 105
	Percent retained on 45μm (No. 325) sieve, max. [%]	7	≤ 10
	Surface area (Blaine) [m²/kg]	15000	≥ 15000

Physical properties of cement_

Physical properties test		Test results	Limits of Iraqi standard No.5/2019
Surface area (Blaine) [m²/kg]		282	≥250
Setting time (Vicat)	Initial setting, hrs: min.	3:51	≥ 45 min.
Setting time (Vicat)	Final setting, hrs: min.	6:20	≤ 10 hrs.
Compressive strength [MPa]	2 days	23.7	≥20.00
Compressive strength [MPa]	28 days	43	≥42.5
Soundness (Autoclave) [%]		0.13	≤0.8

Total shear capacity, type of failure, and other results_

Sample	Total load [kN]	V_t [kN]	First crack [kN]	Maximum deflection [mm]	CFRP strengthening type at each side	CFRP orientation	V_c [kN]	V_f [kN]
RC-C	313.23	156.615	127	10.11	Without	0	156.615	0
RC-U-90-100	453.45	226.725	128	16.83	U- shape 100 mm width 150 mm spacing c/c	90°	156.615	70.11
RC-U-45-100	470.49	235.245	127	16.53	U- shape 100 mm width 150 mm spacing c/c	45°	156.615	78.630
RC-2side-90-600	474.46	237.230	132	18.63	2-side - shape 600 mm width	90°	156.615	80.615
RC-U-90-600	503.42	251.710	130	17.06	U - shape 600 mm width	90°	156.615	95.095
RC-Full-Face	511.47	255.735	/	12.76	Full face	90°	156.615	99.120

Mechanical and physical properties of Sikadur®-330 technical data sheet_

Properties	Tensile strength [MPa]	E- modulus [GPa]	Bond strength [N/mm²]	Mixing ratio
Value	30	4500	> 4	A: B = 4: 1 by weight

CFRP reinforcement configurations and strengthening_

Sample	CFRP strengthening type at each side	CFRP orientation
RC-C	Without	0
RC-U-90-100	U-shape,100 mm width,150mm spacing c/c	90°
RC-U-45-100	U-shape,100 mm width,150mm spacing c/c	45°
RC-2side-90-600	2-sided - shape,600 mm width	90°
RC-U-90-600	U-shape,600 mm width	90°
RC-Full-face	Full face	90°

Summary of concrete mechanical characteristics_

Compressive strength [MPa]	Flexural strength [MPa]	Elastic modulus [MPa]	Density of concrete [kg/m³]
126.97	22.756	50619.044	2522

Fine aggregate grading_

Sieve size [mm]	Cumulative passing [%]	Iraqi standard No.45/1984 zone (2)
10	100	100
4.75	91	90 - 100
2.36	86	75 - 100
1.18	72	55 - 90
0.6	51	35 - 59
0.3	26	8 - 30
0.15	9	0 - 10
Fineness modulus	2.68	---

Strain response of tested beams_

Name of beam	Main steel strain [με]	CFRP strain (vertical strain) (με)	CFRP strain (diagonal strain) (με)
RC	4120	/	/
RC-CFRP-U-90-100	3214	8439	4618
RC-CFRP-U-45-100	3157	9954	9954
RC-CFRP-2SIDE-90-600	7211	5609	3812
RC-CFRP-U-90-600	7398	6235	3920
RC-CFRP-FULL FACE	6382	14700	8954

Some properties of fine aggregate_

Physical properties	Test results	Iraqi standard No.45/1984
Specific gravity SSD	2.66	--
Bulk density [kg/m³]	1750	--
Sulphate content [%]	0.16	≤ 0.5 %
Absorption [%]	0.63	--

Chemical composition and main compounds of sulphate-resisting Portland cement_

Oxide composition content	Content [%]	Limits of Iraqi standard No.5/2019
CaO	62.15	---
SiO₂	19.88	---
Al₂O₃	3.5	---
Fe₂O₃	4.7	---
MgO	3.23	<5.00
SO₃	1.84	<2.50
Na₂O	0.26
K₂O	0.51
L.O.I.	1.25	<4.00
Insoluble residue	0.80	<1.5
Lime saturation factor	0.928	0.66-1.02
Main compounds (Bogue's equations)
C₃S	54.51	---
C₂S	18.77	---
C₃A	1.51	<3.50
C₄AF	14.14	---

Mechanical properties of CFRP sheets (strips)

Modulus of elasticity [GPa]	Tensile strength [MPa]	Strain at failure [%]	Thickness [mm]	Width [mm]
230	4000	1.7	0.167	500

References

Authors

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Articles in this issue

DOI: https://doi.org/10.2478/cee-2026-0015 | Journal eISSN: 2199-6512 | Journal ISSN: 1336-5835

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Language: English

Page range: 221 - 244

Submitted on: Jun 24, 2025

Accepted on: Jul 16, 2025

Published on: Mar 24, 2026

Published by: University of Žilina

In partnership with: Paradigm Publishing Services

Publication frequency: 4 issues per year

Keywords:

Ultra-high-performance concrete,

CFRP sheets,

Strengthening,

Beams,

Concrete

Related subjects:

Business and economics,

Political economics,

Economic theory, systems and structures,

Business management,

Industries,

Environmental management

© 2026 Ali Khalid Ahmed, Mustafa Hameed Al-Allaf, published by University of Žilina
This work is licensed under the Creative Commons Attribution 4.0 License.

Volume 22 (2026): Issue 1 (March 2026)

Strengthening of Ultra-high Performance Concrete Beams with CFRP Strips

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Failure modes_

Chemical composition and main compounds of fly ash_

Mix proportions and compressive strength results_

Mechanical characteristics of steel reinforcement bars_

Observed vs_ estimated shear contributions of CFRP in the strengthened specimens_

Chemical analysis of silica fume_

Physical properties of cement_

Total shear capacity, type of failure, and other results_

Mechanical and physical properties of Sikadur®-330 technical data sheet_

CFRP reinforcement configurations and strengthening_

Summary of concrete mechanical characteristics_

Fine aggregate grading_

Strain response of tested beams_

Some properties of fine aggregate_

Chemical composition and main compounds of sulphate-resisting Portland cement_

Mechanical properties of CFRP sheets (strips)