ArticlePDF Available

Advance Repairing Technique for Enhancement of Stiffness of Post-Heated Concrete Cylinders

DOI:10.1007/s42107-020-00340-1
Authors:
Muhammad Usman at University of Engineering and Technology, Lahore
Muhammad Usman
Dr Muhammad. Yaqub at University of Engineering and Technology, Taxila
Dr Muhammad. Yaqub
Afaq Ahmad at The University of Memphis
Afaq Ahmad
Usman Muhammad at Liaoning ShiHua University
Usman Muhammad
Show all 5 authorsHide
Download full-text PDF
Read full-text
Download citation

Abstract

The present study aims to investigate the effectiveness of epoxy injection on the performance of post-heated concrete cylinders confined with carbon fibre reinforced polymer composites (CFRP). A total of 42 of standard dimensions (diameter of 150 mm x 300 mm) were tested under uni-axial compression. These cylinders were divided in to two groups regarding the heating i.e. un-heated and post-heated. Furthermore, the post-heated concrete specimens were further divided into four specimen groups with respect to various temperatures i.e. 400ºC, 600ºC, 700ºC and 800ºC and then cooled to room temperature. The axial compressive behaviour of un-heated unconfined (UHUC), un-heated CFRP confined (UHC), post-heated unconfined (PHUC), post-heated CFRP confined (PHC) and epoxy injected post-heated CFRP confined concrete cylinders (PHEC) were investigated in terms of axial compressive strength (fc'), stiffness (k), energy dissipation capacity (EDC) and restorability. The test results showed that CFRP confinement can significantly enhance the fc', and EDC of the PHC subjected to the mentioned temperatures. Furthermore, the CFRP confinement effectiveness was increased with increasing the level of fire damage (i.e. at higher temperature). It was found that the fc' of PHEC at 400ºC was restored up to the design value of UHUC. However, the PHEC was unsuccessful for restoring the design value for the temperatures higher than 400ºC.
Content uploaded by Afaq Ahmad
Author content
All content in this area was uploaded by Afaq Ahmad on Oct 29, 2020
Content may be subject to copyright.
1
Advance Repairing Technique for Enhancement of Stiffness of
Post-Heated Concrete Cylinders
Muhammad Usman1, Muhammad Yaqub2, Afaq Ahmad3*, Muhammad Usman Rashid4
1 M.Sc Student, Civil Engineering Department, Univeristy of Engineering & Technology Taxila, Pakistan Email:
m.usman@gamil.com
2 Professor , Civil Engineering Department, Univeristy of Engineering & Technology Taxila, Pakistan Email:
muhammad.yaqub@uettaxila.edu.pk
3 Assistant Professor, Civil Engineering Department, Univeristy of Engineering & Technology Taxila, Pakistan
Email: afaq.ahmad@uettaxila.edu.pk (Corresponding Author)
4 PhD Student, Civil Engineering Department, Univeristy of Engineering & Technology Taxila, Pakistan
Email m.usman@uettaxila.edu.pk)
Abstract
The present study aims to investigate the effectiveness of epoxy injection on the performance of post-heated concrete
cylinders confined with carbon fibre reinforced polymer composites (CFRP). A total of 42 of standard dimensions
(diameter of 150 mm x 300 mm) were tested under uni-axial compression. These cylinders were divided in to two groups
regarding the heating i.e. un-heated and post-heated. Furthermore, the post-heated concrete specimens were further
divided into four specimen groups with respect to various temperatures i.e. 400ºC, 600ºC, 700ºC and 800ºC and then
cooled to room temperature. The axial compressive behaviour of un-heated unconfined (UHUC), un-heated CFRP
confined (UHC), post-heated unconfined (PHUC), post-heated CFRP confined (PHC) and epoxy injected post-heated
CFRP confined concrete cylinders (PHEC) were investigated in terms of axial compressive strength (fc’), stiffness (k),
energy dissipation capacity (EDC) and restorability. The test results showed that CFRP confinement can significantly
enhance the fc’, and EDC of the PHC subjected to the mentioned temperatures. Furthermore, the CFRP confinement
effectiveness was increased with increasing the level of fire damage (i.e. at higher temperature). It was found that the fc’
of PHEC at 400ºC was restored up to the design value of UHUC. However, the PHEC was unsuccessful for restoring the
design value for the temperatures higher than 400ºC.
Keywords: Temperature; Epoxy Injection; CFRP; Strength, Post-heated Concrete
Abbreviations and Symbols
CFRP = Carbon Fibre Reinforced Polymer
EDC= Energy Dissipation Capacity
LD = Load Displacement
UHUC = Un-Heated Un-Confined
UHC = Un-Heated CFRP Confined
Manuscript Click here to access/download;Manuscript;PAPER-2020-06-
06.docx
Click here to view linked References
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
  • A preview of this full-text is provided by Springer Nature.
  • Learn more
Preview content only
Content available from Asian Journal of Civil Engineering
This content is subject to copyright. Terms and conditions apply.
... Consequently, repairs and retrofitting are urgently required. Several repair techniques for heated columns were investigated, such as concrete jackets [3,4], ferrocement jackets [5,6], lap-spliced textile-reinforced mortar jackets [7], steel jackets [8,9], fiber-reinforced polymer (FRP) [10][11][12], and Ultra-High Performance concrete [13][14][15]. ...
Retrofitting of post-heated R.C. columns using steel fiber reinforced self-compacting concrete jackets
Article
This work aims to examine the effectiveness of using steel fiber-reinforced self-compacting concrete (SFRSCC) jackets in retrofitting RC columns subjected to high temperatures. In order to do that, eleven RC columns were cast and tested under axial loading. One column served as an unheated control column, and ten columns were heated to 400 ◦C and 600 ◦C for two hours. Subsequently, eight columns were retrofitted using SFRSCC jackets. The volume fraction of steel fibers and the thickness of the SFRSCC jackets were the main parameters considered for the retrofitting technique. According to the experimental findings, SFRSCC jackets can significantly enhance the structural performance of post-heated columns as evaluated by failure load, stiffness, and toughness. The percentage increase in the failure load, stiffness, and toughness of retrofitted post-heated columns is greatly impacted by the thickness of the SFRSCC jackets. The retrofitted columns with 25 mm and 50 mm SFRSCC jackets increased their failure load by 63.9% and 211.8%, respectively, relative to that of the heated control column at 600 ◦C. It is obvious that the failure load of the retrofitted columns was not significantly impacted by increasing the volume fraction of steel fiber in the SFRSCC jackets. Finally, a proposed design equation was suggested to predict the failure load of retrofitted post-heated columns with SFRSCC jackets.
View
Finite Element Modeling and Statistical Analysis of Fire-Damaged Reinforced Concrete Columns Repaired Using Smart Materials and FRP Confinement
Chapter
  • Jan 2022
Practical testing for observing the failure modes is expensive, time consuming and often limits the pace of research progress. Moreover, because of the limitations of equipment, the existing structures cannot be tested at ultimate failure and scale effect is not observed on large scale experimentally. Thus, numerical modeling and statistical analysis is required for prediction of the behavior of fire damaged and fire-damaged repaired structures. This Paper explores the regression models and Finite element studies to predict the load-deformation response of bolstered concrete columns, damaged through exposure to heat at 300 °C, 500 °C and 900 °C, strengthened using smart materials and confined by carbon fiber reinforced polymers. Using software ABAQUS, a numerical model was developed, capable of predicting the axial load-deformation performance of undamaged, fire damaged and fire-damaged reinforced columns repaired by employing various confinement techniques. SPSS Software was used for Regression modeling (Linear, multiple, and Quadratic). The obtained results showed that regression equations and numerical modeling offered a better alternative to the experimental methods. High correlation coefficient r and coefficient of determination r², more than 90%, for all developed equations, confirmed it as an excellent fit statistical model for prediction of axial load capacity and axial deformation. Similarly, the response predicted by numerical modeling showed minor difference i-e less than 10% with that of experimental. Thus, it can be concluded that, the numerical modeling and prediction formulae agree quite with the experimental results and can be used as alternatives for prediction of loads and deformations.
View
FRP Confinement of Heat-Damaged Circular RC Columns
Article
Full-text available
To investigate the effectiveness of using fiber reinforced polymer (FRP) sheets in confining heat-damaged columns, 15 circular RC column specimens were tested under axial compression. The effects of heating duration, stiffness and thickness of the FRP wrapping sheets were examined. Two specimen groups, six each, were subjected to elevated temperatures of 500 �C for 2 and 3 h, respectively. Eight of the heat-damaged specimens were wrapped with unidirectional carbon and glass FRP sheets. Test results confirmed that elevated temperatures adversely affect the axial load resistance and stiffness of the columns while increasing their ductility and toughness. Full wrapping with FRP sheets increased the axial load capacity and toughness of the damaged columns. A single layer of the carbon sheets managed to restore the original axial resistance of the columns heated for 2 h yet, two layers were needed to restore the axial resistance of columns heated for 3 h. Glass FRP sheets were found to be less effective; using two layers of glass sheets managed to restore the axial load carrying capacity of columns heated for 2 h only. Confining the heat-damaged columns with FRP circumferential wraps failed in recovering the original axial stiffness of the columns. Test results confirmed that FRP-confining models adopted by international design guidelines should address the increased confinement efficiency in heat-damaged circular RC columns.
View
Effects of Increased Slenderness in Short Heat-Damaged RC Columns Confined with FRP Composites
Article
Full-text available
  • Feb 2017
Twenty-six circular RC columns were tested under axial compression to explore the confinement effects of fiber reinforced polymer (FRP) sheets on the performance of heat-damaged short columns. The effects of increased column slenderness, level of heat-induced damage and stiffness of the FRP wrapping system were examined. Columns with l/r ratios of 12.5 and 18.75 were subjected to 500 °C for 1, 2 and 3 h. Eighteen heat-damaged columns were wrapped using unidirectional carbon and glass FRP sheets over their full heights. Test results showed that FRP wrapping significantly enhanced the axial resistance, toughness, ductility and deformation capacity of the heat-damaged columns but failed to restore their axial stiffness. Increasing the stiffness of the FRP jacket resulted in further enhancements in axial resistance, stiffness and toughness of the heat-damaged columns while adversely affecting their ductility. Carbon fiber reinforced polymer jackets with a confinement modulus of 0.65 GPa managed to reinstate, and even exceed, the original strength of heat-damaged columns. The effectiveness of FRP confinement of heat-damaged columns increased significantly with increasing damage level and decreasing column slenderness. The heat- and confinement-induced increases in column slenderness had no tangible effects on buckling stability of the test columns that were originally of low slenderness.
View
Rectangular RC Columns Strengthened with: CFRP Sheets Using CSB Method
Article
The objective of current study is to investigate the effect of the recently developed corner strip-batten (CSB) technique on rectangular columns strengthened with carbon fiber reinforced polymer (CFRP) sheets. In this technique, FRP battens do not experience any curvature in confining the section but are stretched as completely flat strips similar to flat coupons. For this purposes, 12 rectangular reinforced concrete (RC) columns, each with a cross section of 110 × 160 mm (4.33 × 6.30 in.) and a height of 500 mm (19.69 in.), were subjected to load eccentricities of zero, 30, 90, and 120 mm (zero, 1.18, 3.54 and 4.72 in.). Results showed that the CSB technique improved the performance of rectangular specimens in terms of both axial strength and ductility. However, comparison of the results obtained in the authors’ previous experimental study on square RC columns revealed that the improvement (i.e., load carrying capacity and ductility enhancement) gained with rectangular specimens was not as prominent as that obtained with square ones. Finally, comparison of the experimental axial load–bending moment (P–M) interaction diagrams for the strengthened columns and those obtained from the expressions suggested in such different codes as ACI 440.2R, fib Bulletin 14, and CNR-DT 200 R1, showed that the estimates of the codes were conservative when compared to experimental results. Keywords: CFRP composites; Rectangular RC column; Corner strip; Batten; Load eccentricity; P–M interaction diagram.
View
View
Behavior of Eccentrically Loaded High Strength Concrete Columns Jacketed with FRP Laminates
Article
This study is an experimental investigation into the performance of high strength concrete columns subjected to uniaxial eccentricity and strengthened by glass fiber reinforced polymer fabrics (FRP). The study aims to evaluate the potential enhancement in the structural performance of seven 200 × 200 × 1050 mm columns subjected to single eccentricity strengthened by external FRP fabrics, and to investigate the effect of arrangement and amount of FRP laminates to achieve optimal enhancement. The test parameters considered are the number and arrangement of fabric layers and the value of load eccentricity. The laminates are applied in single or double layers; in partial or full wrapping in small eccentricity loading. Longitudinal laminates are provided along tension side of specimens under large eccentricity loading then overlaid by transverse FRP wraps applied partially in single layer. In the present work, test results of seven large-scale concrete columns are presented and discussed. The study has experimentally proven the efficiency of FRP laminates in enhancing the strength of uniaxially loaded HSC columns through increasing flexural capacity (by up to 23% and 59% for small and large eccentricity loaded specimens, respectively). The ductility capacity of small eccentricity loaded columns was not objectively assessed due to early termination of small eccentricity tests for safety concerns; however, a significant ductility enhancement was achieved in large eccentricity specimens strengthened by fiber reinforced polymers.
View
View
View
Repair of Damaged Prestressed Concrete Girders with FRP and FRCM Composites
Article
  • Nov 2016
Traditional methods used to repair prestressed concrete (PC) girders subjected to impact damage due to overheight vehicles include strand splicing and external posttensioning. These methods have proven to be partially satisfactory in restoring the damaged girder’s ultimate strength. The use of composite materials in the strengthening, rehabilitation, and repair industry has been gaining popularity due to their excellent material behavior and ease of application. Composites such as fiber-reinforced polymer (FRP) and fabric-reinforced cementitious matrix (FRCM) systems are presently available alternatives for restoring the integrity of a damaged girder that eliminate the need for girder replacement. The use of externally bonded carbon FRP (CFRP) materials for the repair of damaged bridge components has been successfully deployed and has been shown to reduce repair costs and traffic closure time. FRCM composites represent an alternative material to FRP for structural retrofit/rehabilitation. However, the use of FRCMs is rather new and technical literature is limited in the United States and does not include design provisions for the repair of PC structures. The objective of this study is to evaluate both experimentally and analytically the effectiveness of FRP and FRCM as repair systems to impact-damaged precast PC girders. The specimens consisted of three PC girders retrieved from a bridge after 55 years of service. One specimen was load tested undamaged and used as a benchmark. The other two were damaged (four cut strands) and repaired with FRP and FRCM prior to being load tested. A cross-sectional analysis was performed to predict strength and behavior of all specimens using provisions of current design specifications and guides. Theoretical values were compared to experimental values and the effectiveness of the strengthening methods and respective design approaches were evaluated.
View
Axial Compression Behavior of Fire-Damaged Concrete Cylinders Confined with CFRP Sheets
Article
  • Mar 2016
This paper presents the axial compression behavior of standard ∅150×300 mm concrete cylinders after exposure to elevated temperatures of 300, 500, and 700°C for heating periods of 2 h (for all temperatures) and 3 h (only for 700°C). A total of 192 specimens were tested in static compression to investigate the stress-strain relationships and failure modes of fire-damaged concrete before and after strengthening with carbon fiber–reinforced polymer (CFRP) wraps. The test results showed that the exposure temperature and duration, unconfined concrete strength, and cooling method (air or water cooling) influence the postfire compressive strength, strain at compressive strength, and modulus of elasticity of concrete. Low-strength concrete is more susceptible to the loss in residual properties caused by fire than high-strength concrete. The CFRP wrapping can significantly enhance both strength and ductility of concrete after exposure to elevated temperatures. The level of strength enhancement by CFRP confinement for fire-damaged concrete is higher than undamaged concrete. The confinement effectiveness increases with an exposure temperature, especially for the lowest-strength (20-MPa) water-cooled concrete. In contrast, the level of ductility enhancement on fire-damaged concrete is lower than undamaged concrete. The application of an equation to predict the compressive strength of CFRP-confined fire-damaged concrete is also discussed. It was found that the equation conservatively predicts the ultimate strength of CFRP-confined fire-damaged concrete. However, the prediction becomes less accurate as exposure temperature increases.
View
Confinement strengthening of heat-damaged reinforced concrete columns
Article
  • Mar 2016
The effectiveness of different strengthening techniques in restoring heat-damaged concrete short columns was evaluated experimentally. Four confinement strengthening systems were employed: high-strength fibre-reinforced concrete (HSFRC), ferrocement (FC), glass-fibre-reinforced polymer (GFRP) and steel plate (SP) jacketing. Fifty-one reinforced concrete prisms of size 150 x 150 x 450mm were first subjected to different elevated temperatures. Heated specimens were strengthened using one of the chosen techniques. Thereafter, all specimens were tested under monotonic loading to determine the axial ultimate strength, stiffness, ductility, energy absorption and peak stress-strain behaviour. It was observed that the GFRP jacketing was effective in restoring the compressive strength and energy dissipation, but was not capable of restoring the stiffness. However, FC and HSFRC jacketing were effective mainly in restoring the stiffness of heat-damaged concrete. SP jacketing was not effective in improving the strength or the stiffness properties. GFRP jacketing was found to be the most effective method for strengthening of fire-or heat-damaged concrete structures.
View