fire resistance of corroded structural …fau.digital.flvc.org/islandora/object/fau:30793...vii...

FIRE RESISTANCE OF CORRODED STRUCTURAL CONCRETE

by

Fernando Jose Martinez

A Thesis Submitted to the Faculty of

The College of Engineering and Computer Science

in Partial Fulfillment of the Requirements for the Degree of

Master of Science

Florida Atlantic University

Boca Raton, Florida

December 2014

ii

Copyright by Fernando Jose Martinez 2014

iv

ACKNOWLEDGMENTS

I would like to express my sincere gratitude to my committee chair, Dr. D.V. Reddy, for

his support and advice during the course of this investigation and my graduate studies.

Dr. Reddy came up with the idea for this project, which is a groundbreaking area that has

not been researched before and has major implications worldwide, as corrosion is the

main cause of structural repair worldwide, and these corroded structures are prone to be

subjected to catastrophic fire. Dr. Reddy continually and convincingly conveyed a spirit

of adventure in regard to research and scholarship, and excitement in regard to teaching.

This dissertation would not have been possible without his guidance and persistent help.

I would also like to thank my committee members, Dr. Khaled Sobhan, and Dr. Yan

Yong, for their support and continuous feedback regarding the status of the research.

Thanks are due to Dr. Sobhan for his assistance in obtaining resources for the

experimental program.

Additionally, I would like to thank CEMEX of Pompano Beach, FL, for their kind

donation of the Mix A concrete, used for the Phase I of this research, and Supermix of

Boca Raton, FL, for their donation of Mixes B and C, used for the Phase II of the project.

Also, I would like to express my gratitude to Mr. C. Firlottte of Corrpro Companies in

Medina, Ohio, for his kind donation of a titanium mesh for the accelerated corrosion test,

and Mr. Sailappan and Mr. Monroe, from Quest Engineering, in Pompano Beach, FL, for

lending me their Lab space to conduct the concrete cylinder compressive strength tests.

Furthermore, I would like to thank the Civil Engineering student Mr. Fernando Lascano,

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for his untiring help in fire testing and Mr. John Kielbasa as well as Mr. Hank Van Sant,

from the Ocean and Mechanical and Electrical Engineering Departments, respectively,

for their kind support with electrical equipment. Finally, I want to express my sincere

thanks to my parents for their continued encouragement and support for my education

and personal growth.

vi

ABSTRACT

Author: Fernando Jose Martinez

Title: Fire Resistance of Corroded Structural Concrete

Institution: Florida Atlantic University

Thesis Advisor: Dr. D.V. Reddy

Degree: Master of Science

Year: 2014

One of the major causes of structural repairs worldwide is the corrosion of reinforced

concrete structures, such as residential buildings and piers, which are exposed to harsh

marine environments. This investigation aims to provide experimental evidence of the

fire resistance of corroded high strength reinforced concrete. For this, 14 reinforced

concrete beams of three different concrete mix designs (different strengths) were

prepared along with concrete cylinders for compression strength testing (ASTM C39).

After proper moist curing, all beams were corroded, in two phases, with impressed

current, then „crack scored‟ for corrosion evaluation, after which half were exposed to

fire, also in two phases, following the ASTM E-119-12 time-temperature curve, using a

gas kiln. The fire damage was evaluated and compared between phases by using

Ultrasonic Pulse Velocity technology. Finally, all specimens were tested for

vii

flexural strength by using the third-point loading method (ASTM C78) and the effects of

fire on the corroded beams were analyzed according to the level of corrosion. The loss in

flexural capacity of the corroded beams ranged from 77.7% to 84.4% depending on the

integrity of the corroded beam after the fire exposure, for the Mix A, which had a

compressive strength of 10,142 psi, and an average level of corrosion of 9.3%. This high

loss in flexural capacity resulted from the severe spalling of concrete during both the

corrosion and fire exposure stages. The loss in flexural capacity for the corroded Mix B

(compressive strength of 8,415psi) specimens due to fire, with an average level of

corrosion of 17.59% resulted in an 8.49% loss. For the same Mix B specimens, the loss in

flexural capacity for a corroded beam with an average level of corrosion of 22.8%

resulted in a 31.95% loss after fire exposure. Finally, the loss in flexural capacity for the

corroded Mix C (compressive strength of 6,460psi) specimens due to fire, with an

average level of corrosion of 40.22% resulted in a 27.95% loss. The general trend

observed, from Mix B and Mix C specimens, was that as the corrosion level increased

above 20%, the effect of fire on the flexural strength of the corroded beams increased by

large amount to an average of 30% loss. Additionally, the specimens‟ crack scores

generally demonstrated a linear relationship with the level of corrosion of the steel

reinforcement by mass loss.

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FIRE RESISTANCE OF CORRODED STRUCTURAL CONCRETE

LIST OF TABLES ........................................................................................................................... x

LIST OF FIGURES ....................................................................................................................... xii

CHAPTER 1: INTRODUCTION .................................................................................................... 1

1.1 GENERAL .......................................................................................................................... 1

1.2 RESEARCH OBJECTIVE .................................................................................................. 2

1.3 SCOPE OF WORK ............................................................................................................. 3

CHAPTER 2: LITERATURE REVIEW ......................................................................................... 4

2.1 CORROSION OF STEEL IN CONCRETE ........................................................................ 4

2.1.1 Induced Corrosion using Impressed Current ............................................................. 6

2.1.2 Types of Corrosion in Reinforced Concrete .............................................................. 7

2.2 EFFECT OF FIRE ON CONCRETE STRENGTH ............................................................ 8

2.2 EFFECT OF FIRE ON REINFORCED CONCRETE ELEMENTS .................................. 9

2.3 ULTRASONIC PULSE VELOCITY TEST FOR FIRE DAMAGE ................................ 10

CHAPTER 3: EXPERIMENTAL PROGRAM ............................................................................. 12

3.1 CONCRETE MIX DESIGN ............................................................................................. 12

3.1.1 Phase I, Mix A Design ............................................................................................. 12

3.1.2 Phase II, Mix B Design ............................................................................................ 12

3.1.3 Phase II, Mix C Design ............................................................................................ 13

3.2 SPECIMEN PREPARATION ........................................................................................... 14

3.2.1 Phase I, Mix A, Specimen Preparation .................................................................... 14

3.2.2 Phase II, Mix B, Specimen Preparation ................................................................... 15

ix

3.2.3 Phase II, Mix C, Specimen Preparation ................................................................... 16

3.3 ACCELERATED CORROSION ...................................................................................... 17

3.4 CRACK SCORING ........................................................................................................... 19

3.5 FIRE TESTING ................................................................................................................. 19

3.6 FIRE DAMAGE EVALUATION USING UPV TECHNOLOGY .................................. 22

3.7 FLEXURAL TESTING .................................................................................................... 22

CHAPTER 4: DATA ANALYSIS AND RESULTS .................................................................... 25

4.1 COMPRESSIVE STRENGTH .......................................................................................... 25

4.2 ACCELERATED CORROSION ...................................................................................... 27

4.2.1 Phase I specimens accelerated corrosion ................................................................. 27

4.2.2 Phase II specimens accelerated corrosion ................................................................ 28

4.3 CRACKING AND DEGREE OF CORROSION EVALUATION ................................... 31

4.3.1 Phase I, Mix A Specimens, Cracking and Degree of Corrosion Evaluation ............ 31

4.3.2 Phase II, Mix B Specimens, Cracking and Degree of Corrosion Evaluation ......... 37

4.3.3 Phase II, Mix C Specimens, Cracking and Degree of Corrosion Evaluation ......... 42

4.4 FIRE TESTING ................................................................................................................. 46

4.5 FIRE DAMAGE EVALUATION OF BEAMS USING UPV .......................................... 48

4.5 FLEXURAL TESTING .................................................................................................... 50

4.5.1 Phase I, Mix A, Flexural Testing ............................................................................. 50

4.5.2 Phase II, Mix B, Flexural Testing ............................................................................ 56

4.5.3 Phase II, Mix C, Flexural Testing ............................................................................ 60

4.6 ANALYSIS OF FLEXURAL RESULTS ......................................................................... 65

CHAPTER 7: CONCLUSIONS AND FUTURE WORK ............................................................. 71

APPENDIX A ................................................................................................................................ 74

APPENDIX B ................................................................................................................................ 77

REFERENCES .............................................................................................................................. 79

x

LIST OF TABLES

Table 1: Phase I, Mix A Design ..................................................................................................... 12

Table 2: Phase II, Mix B Design .................................................................................................... 13

Table 3: Phase II, Mix C Design .................................................................................................... 13

Table 4: Phase 1 (Mix A) 28-Day Concrete Compressive Strength .............................................. 25

Table 5: Phase 2 (Mix B) 7-Day Concrete Compressive Strength ................................................ 26

Table 6: Phase 2 (Mix B) 28-Day Concrete Compressive Strength .............................................. 26

Table 7: Phase 2 (Mix C) 7-Day Concrete Compressive Strength ................................................ 26

Table 8: Phase 2 (Mix C) 28-Day Compressive Strength .............................................................. 27

Table 9: Crack Score, Mix A (Phase I), Specimen ID: 1-1............................................................ 31

Table 10: Crack Score, Mix A (Phase I), Specimen ID: 1-2.......................................................... 31





Table 15: Phase I (Mix A) Rebar Mass Loss (DOC) ..................................................................... 34

Table 16: Phase I, Mix A, Rebar Mass Loss Measurements Summary ......................................... 36

Table 17: Crack Score, Mix B (Phase II), Specimen ID: 2-1 ........................................................ 38




Table 21: Phase II (Mix B) Rebar Mass Loss (DOC) .................................................................... 40

xi

Table 22: Phase II, Mix B, Rebar Mass Loss Measurements Summary ........................................ 41

Table 23: Crack Score, Mix C (Phase II), Specimen ID: 2-5 ........................................................ 42




Table 27: Phase II (Mix C) Rebar Mass Loss (DOC) .................................................................... 44

Table 28: Phase II, Mix C, Rebars Mass Loss Measurements Summary ...................................... 45

Table 29 UPV test on Phase I specimens (not exposed to fire) ..................................................... 48

Table 30 UPV test on Phase I specimens (exposed to fire) ........................................................... 48

Table 31: UPV ratio for Phase I specimens ................................................................................... 49

Table 32: UPV test on Phase II specimens (not exposed to fire) ................................................... 49

Table 33: UPV test on Phase II specimens (exposed to fire) ......................................................... 49

Table 34 UPV ratios for Phase II specimens ................................................................................. 50

Table 35: Maximum Moments developed in Phase I Specimens (Mix A) .................................... 51

Table 36: Maximum Moment Developed in Phase II Beam Specimens (Mix B) ......................... 56

Table 37: Maximum Moment Developed in Phase II Specimens (Mix C) .................................... 60

Table 38: Flexural Loss (Phase I specimens, Mix A) .................................................................... 65

Table 39: Cumulative effect of corrosion and fire on uncorroded beams of Mix A ...................... 66

Table 40: Flexural Loss (Phase II specimens, Mix B) ................................................................... 67

Table 41: Cumulative effect of corrosion and fire on uncorroded beams of Mix B ...................... 68

Table 42: Flexural Loss of specimens (Phase II, Mix C). .............................................................. 69

Table 43: Cumulative effect of corrosion and fire on uncorroded beams of Mix C ...................... 70

xii

LIST OF FIGURES

Figure 1: Naturally forming protecting layer around steel rebar in concrete ................................... 4

Figure 2: Corrosion cell in steel reinforcing bar .............................................................................. 6

Figure 3: Phase I, Mix A, beam cross-section ............................................................................... 14

Figure 4: Phase I, Mix A, beam longitudinal view ........................................................................ 14

Figure 5: Phase II, Mix B, beam cross section ............................................................................... 15

Figure 6: Phase II, Mix B, beam longitudinal view ....................................................................... 15

Figure 7: Phase II, Mix C, beam cross section ............................................................................... 16

Figure 8: Phase II, Mix C, beam longitudinal view ....................................................................... 16

Figure 9: Schematic of accelerated corrosion set up ...................................................................... 17

Figure 10: Accelerated corrosion set up for Phase I specimens ..................................................... 18

Figure 11: Accelerated corrosion set up for Phase II specimens ................................................... 18

Figure 12: Crack scoring of Phase I, Mix A, specimen ................................................................. 19

Figure 13: ASTM E-119-12 Temperature Curve ........................................................................... 20

Figure 14: Olympic 2728G Torchbearer gas kiln .......................................................................... 20

Figure 15: Gas kiln used for fire test ............................................................................................. 21

Figure 16: Phase I specimens inside gas kiln ................................................................................. 21

Figure 17: Phase II specimens inside gas kiln ............................................................................... 21

Figure 18 Proceq Pundit Lab UPV device ..................................................................................... 22

Figure 19: Test Schematic for ASTM C 78 Flexural Testing ........................................................ 23

Figure 20: Flexural Strength Testing ............................................................................................. 23

Figure 21: Phase I specimens accelerated corrosion current measurement ................................... 28

xiii

Figure 22: Phase II specimens accelerated corrosion current measurement .................................. 30

Figure 23: Crack Scores of Phase I, Mix A, specimens ................................................................. 34

Figure 24: Phase I, Mix A, Rebar Mass Losses ............................................................................. 35

Figure 25: Partial debonding/desintegration of rebar of specimen 1-4 .......................................... 36

Figure 26: Crack Score vs. DOC for Phase I, Mix A, specimens .................................................. 37

Figure 27: Specimen 2-1 Crack Scoring Marks ............................................................................. 37

Figure 28: Crack Scores of Phase II, Mix B, specimens ................................................................ 40

Figure 29: Phase II, Mix B, Rebar Mass Losses ............................................................................ 41

Figure 30: Crack Score vs. DOC for Phase II, Mix B, specimens ................................................. 42

Figure 31: Crack Scores for Phase II, Mix C, specimens .............................................................. 44

Figure 32: Phase II, Mix C, Rebar Mass Losses ............................................................................ 45

Figure 33: Crack Score vs. DOC for Phase II, Mix C, specimens ................................................. 46

Figure 34: Temperature curve for 15 minutes of fire exposure of Phase I beams ......................... 46

Figure 35: Temperature curve for 15 minutes of fire exposure of Phase II beams ........................ 47

Figure 36: Maximum Moments developed in Phase I Specimens (Mix A) ................................... 52

Figure 37: Specimen 1-3 failure .................................................................................................... 52


Figure 39: Specimen 1-1 Load-Deflection Curve .......................................................................... 53





Figure 44: Maximum Moments developed in Phase II Specimens (Mix B) .................................. 56



Figure 47: Specimen 2-2 after fire exposure .................................................................................. 58

xiv





Figure 52: Maximum Moments developed in Phase II Specimens (Mix C) .................................. 61

Figure 53: Phase II, Mix C, Specimen 2-6 after corrosion ............................................................ 62







Figure 60: Effect of fire on flexural strength of corroded specimens of Mix B ............................ 67

Figure 61: Effects of corrosion and fire on uncorroded specimens of Mix B ................................ 69

1

CHAPTER 1: INTRODUCTION

1.1 GENERAL

In the United States, there are approximately 12,380 miles of ocean coastline, with a

sizeable component in Florida. Lying along the coasts are many reinforced and

prestressed concrete structures, such as high rise residential buildings, bridges, and piers,

which are exposed to a harsh marine and coastal environment. This exposure increases

their susceptibility to the corrosion of the reinforcing steel.

The exposure to fire, either natural or man-induced, can aggravate the structural damage

in already corroded structures. Structural fire safety is one of the main concerns in high-

rise buildings and bridges, where concrete members are often used due to inherent good

fire resistance of concrete materials. Structural members respond to the high temperatures

in a fire with a combination of the following detrimental effects: (1) Deterioration of

material properties, i.e. the loss in mechanical strength, stiffness and durability; (2)

Nonuniform temperatures and stress distributions across the cross sections; (3) Induced

mechanical stresses due to thermal expansion and thermal gradient; and (4) Possible

spalling of concrete, which changes the temperature distribution in the concrete and

reinforcement. This combination can have devastating consequences on structural

stability.

The synergistic combination of these effects of corrosion and fire, forms the basis of this

research.

2

1.2 RESEARCH OBJECTIVE

The objective of this study is to experimentally evaluate the coupled effects of fire and

corrosion in reinforced concrete beams. Reinforced concrete structures near the coastlines

are at very high risk of corrosion due to the high concentration of chloride ions in the

environment. Also, reinforced concrete slabs in roads and bridges that are deiced with

salt products are prone to develop corrosion related problems. Once the chloride ion

concentration has reached a threshold value in the concrete, the natural passive layer

created around the steel rebar will disintegrate and the corrosion rate will accelerate

tremendously. Additionally, these corroded structures could be subjected to elevated

temperatures due to a catastrophic fire, and the coupled effects of both corrosion and fire

further deteriorate the integrity of the structure and cause earlier failure. Corrosion

studies have been carried out at Florida Atlantic University (Edouard 2011), where

corrosion was induced in Portland cement concrete beams following an impressed current

method. This same impressed current method was followed for the acceleration of

corrosion in the specimens in the current research. The main goals of this research were:

To determine and compare the corrosion level of the beam specimens by mass

loss measurements and crack scoring.

To evaluate the effects of corrosion on the concrete specimens and their ability to

maintain concrete cover after corrosion.

To evaluate the effects of fire on the concrete beam specimens by the Ultrasonic

Pulse Velocity test method.

To evaluate the residual strength of the corroded concrete specimens after fire

exposure using the flexural third point load test method.

3

1.3 SCOPE OF WORK

The experimental work involved the fabrication of 14 rectangular beam specimens. All of

the specimens were subjected to accelerated corrosion by using the impressed current

method, crack scored, and then exposed to fire by following the ASTM E119-12

Temperature Curve. The fire damage was evaluated using ultrasonic pulse velocity

technology. After the fire exposure, the flexural strength of the specimens was

determined according to the ASTM C78 “Standard Test Method for Flexural Strength of

Concrete” using an MTS machine. Later, the flexural loss of the corroded specimens due

to fire was investigated and analyzed. This research investigated three different mixes of

concrete: Mix A, Mix B, and Mix C, all with different 28 day compressive strengths. The

experimental program was divided into Phase I and Phase II, because of similar

conditions of accelerated corrosion environment and fire exposure; that is, Phase I

consisted of 6 specimens of Mix A, which were corroded in the same environment and

then exposed to fire together. Similarly, Phase II consisted of 4 specimens of Mix B and 4

specimens of Mix C, which were corroded in the same environment and then exposed to

fire together.

4

CHAPTER 2: LITERATURE REVIEW

2.1 CORROSION OF STEEL IN CONCRETE

Concrete provides natural corrosion protection to the embedded steel with its inner

alkaline environment (pH 12 to 13) (Bentur et al. 1997). At high pH, a thin oxide layer

forms around the steel rebar that prevents metal atoms from dissolving. This thin oxide

layer reduces the rate of corrosion to an insignificant level, which is known as passive

corrosion rate, and is typically 0.1 micrometers per year. Figure 1 shows the protective

layer that is formed around the concrete.

Figure 1: Naturally forming protecting layer around steel rebar in concrete

The destruction of the thin oxide layer, also known as passive layer, increases the

corrosion rate at least 1,000 times the passive corrosion rate (ACI222 2001) due to the

presence of oxygen and moisture at the steel-concrete interface. The passive layer can be

broken or disintegrated when the alkalinity of the concrete is reduced or when the

chloride concentration in the concrete is increased beyond a certain threshold level.

Several studies have indicated that the chloride concentration threshold for initiation of

5

corrosion of bare reinforcing steel in concrete is in the 250-325 ppm range (Spellman and

Strafull 1973; Clear 1976).

The corrosion process involves the progressive removal of atoms of iron (Fe) from the

steel being corroded by an electrochemical reaction and is dissolved in the surrounding

water solution, appearing as ferrous (Fe2+

) ions. For the reinforcing steel, this dissolution

takes place in the limited volume of water solution present in the pores of the concrete

surrounding the steel. As a result of this dissolution process, the steel loses mass, thereby

suffering a reduction in cross sectional area.

The electrochemical process that governs the corrosion of steel in concrete, as its name

suggests, involves electrical and chemical processes. Two electrochemical reactions,

known as „anodic‟ and „cathodic‟ occur at the same time along the steel rebar surface in

areas called „anodes‟ and „cathodes‟:

The steel oxidizes at the anode where corrosion occurs according to the following

chemical reaction:

Fe (metallic atoms at steel surface) Fe2+

(ions dissolved in solution) + 2e-

The released electrons travel through the steel rebar to the local cathode on which they

are used in the oxygen reduction, or cathodic reaction:

O2 (dissolved oxygen molecules) + 2H2O + 4e

- 4OH- (hydroxide ions dissolved in

solution)

These reactions lead to the development of regions of differing electrochemical

potentials, resulting in current flow within the concrete, which is constituted by the flow

of electrons from the anodic area, where they are produced, to the cathodic area, where

they are used in the cathodic reaction, and its counter-current ionic flow in the external

6

concrete pore solution. The loss of metal occurs at the anodic site, where iron atoms are

oxidized to ferrous (Fe2+

) ions as indicated in the anodic reaction. For the continuation of

the corrosion process, the quantity of electrons accepted at the cathode must be equal to

the quantity of electrons released at the anode. Therefore, for every dissolved oxygen

molecule that reacts at the cathode, two iron atoms must be ionized and dissolved at the

anode. The corrosion process will only continue if there is a cathodic reaction that acts as

a sink for the electrons produced at the anodic area. Hence, if water or oxygen is not

available at the cathode, the corrosion process will stop. Figure 2 shows an illustration of

the corrosion process in a reinforcing bar.

Figure 2: Corrosion cell in steel reinforcing bar

2.1.1 Induced Corrosion using Impressed Current

The corrosion process can be artificially accelerated by increasing the chloride ion

concentration in the concrete, therefore breaking the passive layer and allowing the rate

of corrosion to increase exponentially. Andrade (2008) induced corrosion on concrete and

mortar beam specimens with a centrally placed steel bar by immersing the specimens in a

5% NaCl solution and connecting the positive terminal of a Direct Current (DC) power

7

supply to the exposed steel bar as well as the negative terminal to stainless steel plates

placed near the specimens in the solution. The corrosion process was initiated by

applying a constant 30 V anodic potential. Andrade (2008) reported that the current

going to the concrete and mortar specimens increased suddenly whenever the specimen

cracked.

The time that takes for the reinforced concrete specimens to achieve a specific degree of

corrosion (percentage mass loss of the cross sectional area of the rebar) using the

impressed current method, varies with the properties of the mix design, including pH,

porosity, fine content, water/cement ratio, among others. Edouard (2011) performed the

impressed current method on centrally reinforced 6x6x21in concrete beams (at constant

30V) and observed that the current spikes and severe cracking were achieved after

approximately 300 hours of corrosion time.

2.1.2 Types of Corrosion in Reinforced Concrete

Corrosion types in reinforced concrete can be classified according to different criteria,

which include mechanisms of corrosion, final damage appearances, environments that

induce corrosion, etc. Although classification of corrosion types is not absolute, it

provides clues into how to assess the damage for repair purposes. Among the types of

corrosion recognized in the concrete industry are: uniform, galvanic, localized, external

current imposed, and stress corrosion cracking and hydrogen induced embrittlement. The

types of corrosion observed in this experiment include:

2.1.2.1 Uniform Corrosion: In some cases, the distance between anodic and cathodic

areas is too small to be separated from each other. Therefore, anodic and cathodic

8

processes would nearly uniformly occur along the steel surface, and as a result the

dissolution of the steel occurs uniformly along the rebar.

2.1.2.2 Localized Corrosion: For localized, pitting, or crevice corrosion, the anodic area

is much smaller than the cathodic area, but the corrosion penetration rate at the anodic

area is much higher than at the cathode (Broomfield 1997). Therefore, the corrosion cell

consists of a small rapidly corroding anodic area and a large cathodic area surrounding

the anodic area. This feature of extremely high ratio of cathodic to anodic areas make

localized corrosion very dangerous to the steel in concrete.

2.2 EFFECT OF FIRE ON CONCRETE STRENGTH

Reinforced concrete structures are likely to be exposed to elevated temperatures during

their service life due to a catastrophic fire. The mechanical properties of concrete such as

strength, modulus of elasticity and volume stability are significantly reduced during these

exposures. During fire exposure, the chemical composition and physical structure of

concrete change considerably. The dehydration such as the release of chemically bound

water from the calcium silicate hydrate (CSH) becomes significant above about 110 C.

The dehydration of the hydrated calcium silicate and the thermal expansion of the

aggregate increase internal stresses and from 300 C micro-cracks are induced through

the material (Arioz 2007). Calcium hydroxide, an essential component of the cement

paste, dissociates at around 530 C, resulting in the shrinkage of concrete. Arioz (2007)

found that the relative strength of concrete reduces with increase in exposure

temperature.

9

2.2 EFFECT OF FIRE ON REINFORCED CONCRETE ELEMENTS

The exposure of reinforced concrete to fire endangers the structure from three major

perspectives: (1) reduction in the strength of the concrete, (2) possible plastic

deformation of embedded steel, and (3) the loss of bond between reinforcing steel and

concrete (Haddad et al. 2008). The latter endangers mainly the structural integrity of the

reinforced concrete beams as the transfer of tensile stress from concrete to the reinforcing

steel is significantly reduced.

The presence of reinforcement in concrete elements can dissipate the extent of damage at

high temperatures, but may create post-cooling residual stresses that along with possible

loss of bond between reinforcing steel and concrete, may cause unfavorable structural

integrity conditions, even under service loads. It was reported that the loss in bond

strength could reach as high as 60% when reinforced concrete is subjected to

temperatures in excess of 500 °C (Haddad et al. 2008).

Additionally, the steel bars used in reinforced concrete structures are made of hot rolled

steel. The apparent yield strength of the steel tends to increase as its temperature

increases up to approximately 250°C, after which, its actual yield strength will quickly

drop as the temperature continues to increase (Xiao 2004), which will negatively affect

its flexural carrying capacity and cause early failure of the reinforced concrete member.

A beneficial aspect of the exposure to fire of reinforced concrete structures is the internal

axial forces that develop when a reinforced concrete member is subjected to heat at one

point along the member while cooler parts of the same member prevent thermal

expansion of the heated element, phenomenon known as the axial thrust force. The

development of the axial restraint forces (and subsequent moment redistribution) has a

10

positive effect on a reinforced concrete element‟s fire resistance due to the low thermal

conductivity of the concrete, naturally creating a rotational restraint force along the

longitudinal direction of the reinforcement (Bingöl and Gül 2009).

2.3 ULTRASONIC PULSE VELOCITY TEST FOR FIRE DAMAGE

Yang (2008) used ultrasonic pulse velocity technology to quantitatively evaluate the

residual compressive strength of concrete subjected to elevated temperatures. The UPV

ratio was defined as the ratio between the UPV of a fired exposed specimen to the UPV

of same specimen before the fire exposure. The velocity of sound is considered high-

quality thermal-damage indicator, due to its sensitivity to any change of the Young

modulus. As a matter of fact, the evolution of the elastic modulus because of heating is

progressive, with a quasi-linear decrease coming from portlandite decomposition and

CSH gel dehydration, but also from the thermal incompatibility between the aggregates

(which expand) and the cement paste (which at first undergoes shrinkage and later

expands) (Hager 2013).

Additionally, it is well known that the velocity of sound in concrete depends strongly on

its moisture content (Hager 2013). During the heating process, the moisture is

progressively expelled from the material. The order in which the water is removed from

heated concrete depends on the energy that binds the water and the solid fraction. Thus,

free water evaporates first, followed by capillary water, physically-bound water and

chemically-bound water. The process of removing the chemically-bound water (that is a

part of the cement hydrates) is the last to occur. On the whole, water expulsion due to

dehydration and heating strongly affects sound velocity, reducing it to a fraction of the

unheated specimen (Hager 2013).

http://www.sciencedirect.com/science/article/pii/S0379711209000472


11

A relationship between the residual strength ratio and the residual UPV ratio was

developed (Yang 2008) and the following equation proposed for residual compressive

strength prediction:

Where Y is the residual strength ratio and is the residual UPV ratio.

12

CHAPTER 3: EXPERIMENTAL PROGRAM

3.1 CONCRETE MIX DESIGN

High strength concrete was used for all the specimens. The water cement ratios varied

from 0.30 to 0.40.

3.1.1 Phase I, Mix A Design

The Phase I, Mix A design is shown in Table 1.

Table 1: Phase I, Mix A Design

Material Description Specific

Gravity

Weight

(lb/cy)

Cement ASTM C-150…..Type I Cement 3.15 810

Fine Aggregate ASTM C-33…..Sand 2.15 1536

Coarse Aggregate Florida Building Code…..Pearock 3/8” 2.45 1142

Water ASTM C-94 1 308

Admixture 1 W.R. Grace, DCI-S…..Corrosion

Inhibitor (2.5 GALS/CY.)

Admixture 2 W.R. Grace, ASTM C-494,

D…..WRDA60


F…..ADVA 120

The designed water cement ratio was 0.38. Right after mixing, the slump was measured

as 9.5”.

3.1.2 Phase II, Mix B Design

The Phase I, Mix B design is shown in Table 2.

13

Table 2: Phase II, Mix B Design


Gravity

Weight

(lb/cy)



Coarse Aggregate Florida Building

Code…..Pearock 3/8” 2.45 1079



D…..WRDA64


F…..ADVA 120


as 9.0”.

3.1.3 Phase II, Mix C Design

The Phase I, Mix B design is shown in Table 3.

Table 3: Phase II, Mix C Design


Gravity

Weight

(lb/cy)



Coarse Aggregate Florida Building

Code…..Pearock 3/8” 2.45 1079



D…..WRDA64


F…..ADVA 120


as 10.0”.

14

3.2 SPECIMEN PREPARATION

3.2.1 Phase I, Mix A, Specimen Preparation

For Phase I, Mix A, two sets of beam specimens (3 for each set), and one set of cylinder

specimens (3 specimens) were prepared. Cylinders, 6 in.Φ x 12 in., were used to test the

28 day compressive strength of the concrete according to the ASTM C39/C39M,

“Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens”.

The dimensions for all the beam specimens were 152.4 mm x152.4 mm x 533.4mm (6 in

x 6 in x 21in). Also, two No.4, Grade 40, steel rebars were used for reinforcement as

shown in Figure 3 and Figure 4.

Figure 3: Phase I, Mix A, beam cross-section

Figure 4: Phase I, Mix A, beam longitudinal view

Concrete spacers, similar to those used in the field, were used to hold the rebar in place

inside the specimens.

152.4 mm (6 in.)

152.4 mm (6 in.) 133.35 mm (5.25 in.)

533.4 mm (21 in.)

15

3.2.2 Phase II, Mix B, Specimen Preparation

For Phase II, Mix B, two sets of beams (2 for each set), and one set of cylinder specimens

(3 specimens) were prepared. Cylinders, 4 in.Φ x 8 in., were used to test the 28 day

compressive strength of the concrete according to the ASTM C39/C 39M, “Standard Test

Method for Compressive Strength of Cylindrical Concrete Specimens”. The dimensions

for all the beam specimens were 152.4 mm x152.4 mm x 533.4mm (6 in x 6 in x 21in).

Also, two No. 4, Grade 40, steel rebars were used for reinforcement as shown in Figure 5

and Figure 6.

Figure 5: Phase II, Mix B, beam cross section

Figure 6: Phase II, Mix B, beam longitudinal view

No concrete spacers were used for Mix B specimens, because during casting, the rebars

were allowed to extend beyond the beam ends. After proper curing, these rebar

protrusions were cut and the beam ends sealed with epoxy.

152.4 mm (6 in.)

152.4 mm (6 in.) 133.35 mm (5.25 in.)

533.4 mm (21 in.)

16

3.2.3 Phase II, Mix C, Specimen Preparation

For Phase II, Mix C, two sets of beams (2 for each set), and one set of cylinder specimens

(3 specimens) were prepared. Cylinders, 4 in.Φ x 8 in., were used to test the 28 day

compressive strength of the concrete according to the ASTM C 39/C39M, “Standard Test

Method for Compressive Strength of Cylindrical Concrete Specimens”. The dimensions

for all the beam specimens were 152.4 mm x152.4 mm x 533.4mm (6 in x 6 in x 21in).

Also, No.4, Grade 40, steel rebars were used for reinforcement as shown in Figure 7 and

Figure 8.

Figure 7: Phase II, Mix C, beam cross section

Figure 8: Phase II, Mix C, beam longitudinal view

No concrete spacers were used for Mix C specimens, because during casting, the rebars

were allowed to extend beyond the beam ends. After proper curing, these rebar

protrusions were cut and the beam ends sealed with epoxy.

152.4 mm (6 in.)

152.4 mm (6 in.) 133.35 mm (5.25 in.)

533.4 mm (21 in.)

17

3.3 ACCELERATED CORROSION

An accelerated laboratory electrochemical method was used for the corrosion testing. The

chemical attack was simulated by immersing the test specimens in a saline solution (3%

NaCl), and connecting the steel rebars to the positive terminal of a D/C constant voltage

power supply, while connecting a metal mesh, surrounding (not touching) the beam

specimens, to the negative terminal. The steel rebars acted as the anode, and the metal

mesh as the cathode. The chloride ions (negative) were, therefore, attracted to the anode

(steel rebars), and the concrete chloride ion concentration threshold in the concrete was

exceeded in an accelerated manner to induce corrosion. Current in each rebar was

monitored daily (using a clamp meter) for a constant voltage power supply, until a

sudden increase in current and large (>1mm) cracks were observed in the specimens,

indicative of corrosion. The schematic of the experimental setup is shown in Figure 9.

Figure 9: Schematic of accelerated corrosion set up

The salinity of the water mas measured with a salinity meter, and was kept at 3% for the

corrosion of both the Phase I and Phase II specimens. The specimens of Phase I and

Phase 2 were corroded separately, with the group of beams for each phase corroded

together. Figure 10 shows the specimens of Phase I being subjected to the accelerated

18

corrosion in a 130 gallon plastic tank, and Figure 11 shows the specimens of Phase II

being subjected to the accelerated corrosion procedure in the same 130 gallon plastic

tank.

Figure 10: Accelerated corrosion set up for Phase I specimens

Figure 11: Accelerated corrosion set up for Phase II specimens

19

3.4 CRACK SCORING

Following the completion of the corrosion monitoring phase, the cracking was evaluated

for all specimens with the use of crack scoring criteria. After the number of cracks, their

average lengths, and maximum widths were determined, the total crack score per

specimen, Cs, was calculated as shown in the following equation. Figure 12 shows a

corroded specimen‟s crack scoring marks.

(1)

Figure 12: Crack scoring of Phase I, Mix A, specimen

3.5 FIRE TESTING

Three specimens from Phase I and four from Phase II were exposed to elevated

temperature following the temperature curve of ASTM E-119-12 “Standard Test Methods

for Fire Tests of Building Construction and Materials”, Figure 13, and taking into

account the reduction in time for small scale specimens, based on the test findings of

Young (2006). An Olympic 2827G Torchbearer gas kiln was used for the fire testing of

all the specimens. The 2827G Torchbearer gas kiln is a 5 burner, top loading, stackable

kiln, able to reach a maximum temperature of 1,288 (2,350 ). It‟s inside dimensions

are 717.6 mm (28.25 in.) wide by 685.8 mm (27 in.) deep. The temperature in the kiln

was monitored with thermocouples, and the five burners, as well as the propane gas

pressure, were regulated to achieve the desired temperature profile. The gas kiln used for

20

the fire testing is shown in Figure 14. A photograph of the gas kiln along with the 65lb

propane gas tank used is shown Figure 15.

Figure 13: ASTM E-119-12 Temperature Curve

Figure 14: Olympic 2728G Torchbearer gas kiln

21

Figure 15: Gas kiln used for fire test

Figure 16 shows the corroded Phase I specimens inside the gas kiln.

Figure 16: Phase I specimens inside gas kiln

Figure 17 shows the corroded Phase II specimens inside the gas kiln.

Figure 17: Phase II specimens inside gas kiln

22

3.6 FIRE DAMAGE EVALUATION USING UPV TECHNOLOGY

The effect of the fire on the Phase I and Phase II specimens was explored by determining

the ultrasonic pulse velocity of the corroded beams not exposed to fire and the corroded

ones exposed to fire and then comparing the ratio between the two, for both the Phase I

and Phase II beam specimens, respectively. The Proceq Pundit Lab device was used for

the UPV determination. Figure 18 shows an illustration of the equipment used.

Figure 18 Proceq Pundit Lab UPV device

The type of wave propagated through the specimen was a compressive p-wave with a

frequency of 54 kHz. The distance between the transducers, i.e. the width of the beam,

was set into the device; hence it provided the speed directly, automatically taking into

account adjustment errors.

3.7 FLEXURAL TESTING

The maximum bending load that the corroded as well as corroded and fire-exposed

specimens were able to sustain was determined, using the third-point loading method,

23

according to ASTM C78 -“Standard Test Method for Flexural Strength of Concrete”. The

test schematic is shown in Figure 19 and the actual set up for one beam in Figure 20.

Figure 19: Test Schematic for ASTM C 78 Flexural Testing

Figure 20: Flexural Strength Testing

The loading rate per minute was determined as half of that specified by the ASTM C78

standard due to the very damaged conditions of the beams after corrosion and fire,

especially for the Phase I specimens, which lost large amounts of concrete after corrosion

and fire exposure. The following equation was used to determine the prescribed loading

rate by ASTM C78,

(2)

24

where:

r = loading rate, N/m (lb/min)

S= rate of increase in maximum stress on the tension face, MPa/min (psi/min)

b= average width of the specimen as oriented for testing, mm (in)

d= average depth of the specimen as oriented for testing, mm (in), and

L= span length, mm (in).

Using, S=0.9 Mpa (125 psi) as recommended in the standard, b=152.4 mm (6in.),

d=152.4 mm (6 in.), and L=533.4 mm (21in.), the loading rate r is calculated as 5720

N/min (1286 lb/min). The actual loading rate used was half of the calculated rate, or 2860

N/min (643 lb/min).

25

CHAPTER 4: DATA ANALYSIS AND RESULTS

4.1 COMPRESSIVE STRENGTH

High strength concrete was used for all the concrete beam specimens. For Phase I, 6x12”

cylinders were used for the compressive testing. After 28 days of moist curing, the

compressive strength of the cylinders (Mix A) resulted in the 10,000 psi range, as shown

in Table 4.

Table 4: Phase 1 (Mix A) 28-Day Concrete Compressive Strength

Cylinder # Compressive Strength (psi)

1 10,125

2 10,222

3 10,080

Average 10,142

For the first phase, the concrete was considered high strength, given that the average

compressive strength of 10,142 psi was higher than the threshold of 6,000psi. The

measured slump of the concrete at the time of casting was 9.5 in. Moreover, the

accelerated corrosion process for the Phase I beams was started after they were properly

moist cured for 28 days.

For the second phase of the experiment, 4x8” cylinders were used for the compressive

testing. After 7 days of moist curing, the compressive strength of the cylinders of the Mix

B, was in the 5,000 psi range, as shown in Table 5.

26

Table 5: Phase 2 (Mix B) 7-Day Concrete Compressive Strength


1 5,613

2 5,831

Average 5,722

The four concrete beams corresponding to Mix B were subjected to accelerated

corrosion after 7 days of moist curing. One cylinder of Mix B was allowed to moist

cure for 28 days to verify that the concrete used was high strength. Table 6 shows the

compressive strength of the remaining cylinder of Mix B after 28 days of curing:

Table 6: Phase 2 (Mix B) 28-Day Concrete Compressive Strength


3 8,415

For Mix B, the concrete was considered high strength, given that the average

compressive strength after 28 days of curing was higher (8,415 psi) than the threshold

of 6,000psi. The measured slump of the concrete at the time of casting was 9.0 in.

For Mix C, after 7 days of moist curing, the compressive strength of the cylinders was in

the 4,000 psi range, as shown in Table 7.

Table 7: Phase 2 (Mix C) 7-Day Concrete Compressive Strength


1 4,229

2 4,076

Average 4,153

The four concrete beams corresponding to Mix C were subjected to accelerated

corrosion after 7 days of moist curing. One cylinder of Mix B was allowed to moist

cure for 28 days to verify that the concrete used was high strength. Table 8 shows the

compressive strength of the remaining cylinder of Mix B after 28 days of curing:

27

Table 8: Phase 2 (Mix C) 28-Day Compressive Strength

For Mix C, the concrete was considered high strength, given that the compressive

strength after 28 days of curing was higher (6,460 psi) than the threshold of 6,000psi.

The measured slump of the concrete at the time of casting was 10.0 in.

4.2 ACCELERATED CORROSION

4.2.1 Phase I specimens accelerated corrosion

All the Mix A beam specimens were corroded in the same marine-simulated

environment, that is, a tank filled with 3% NaCl solution. An initial DC voltage of 30V

was applied following the procedure carried out by Andrade (2008). After seen a very

high and sudden increase in current, and a large quantity of corrosion products in the tank

(saline water turned orange), the DC voltage supply was reduced to 5V after 30 hours. At

103 hours, the voltage was increased to 12V because significant current increases were

not observed. The test was ended at 127 hours because of the large quantity of corrosion

products in the water and the severe concrete spalling in the beams. Figure 21 shows the

measured current during the accelerated corrosion procedure for the Phase I specimens.


3 6,460

28

Figure 21: Phase I specimens accelerated corrosion current measurement

4.2.2 Phase II specimens accelerated corrosion

The Mix B and C beam specimens were corroded in the same marine-simulated

environment, that is, a tank filled with 3% NaCl solution. The constant DC voltage of

12V was applied to all the beam specimens (total of 8, including the Mix B and C

specimens), and the current was measured daily using a current clamp meter until a

sudden increase in current or visible cracks were observed in the specimen. Figure 22

shows the measured current during the accelerated corrosion procedure for the Phase II

specimens. Most of the beams were corroded for about 300 hours, with specimen 2-6

being removed earlier (after 194 hours) because both rebars showed a spike in the current

readings. Some specimens did show an early spike for one of the two rebars and therefore

were allowed to remain in the corrosion tank until both rebars showed a spike in the

29

current going through them. Specimens 2-1, 2-3, 2-5, 2-7, and 2-8 were removed at 313

hours because most rebars had showed a considerable increase in current and cracks were

observed in the specimens. Specimens 2-2 and 2-4, however, were allowed to remain in

the tank for 24 more hours, for a total of 337 hours, because the current readings did not

show a significant increase and cracks were not observed in the specimens.

30

Figure 22: Phase II specimens accelerated corrosion current measurement

31

4.3 CRACKING AND DEGREE OF CORROSION EVALUATION

4.3.1 Phase I, Mix A Specimens, Cracking and Degree of Corrosion Evaluation

The first phase beams lost a lot of concrete during the accelerated corrosion procedure

(due to partial debonding of corroded reinforcement) and much more during the fire part

of the experiment, given the already weak state (rebar debonding) after the accelerated

corrosion process. The crack scores for the Phase I beam specimens are summarized from

Table 9 to Table 14.

Table 9: Crack Score, Mix A (Phase I), Specimen ID: 1-1

Crack #

Max. Width

(mm) Length (mm)

1 1.20 335.00

2 1.47 120.00

3 2.72 533.40

4 1.89 57.00

5 0.48 74.00

6 0.93 210.00

7 1.76 490.00

Average 1.49 259.91

Crack Score 2,716.10 mm^2 (4.21 in^2)


Crack #

Max. Width

(mm) Length (mm)

1 1.59 533.40

2 0.52 200.00

3 1.70 250.00

4 1.50 235.00

5 1.36 505.00

6 1.55 300.00

7 1.10 220.00

Average 1.33 320.49

Crack Score 2,986.93 mm^2 (4.63 in^2)

32


Crack #

Max. Width

(mm) Length (mm)

1 0.56 65.00

2 0.97 240.00

3 1.01 155.00

4 1.35 355.00

5 0.66 125.00

6 0.44 170.00

7 1.26 533.40

8 0.56 80.00

Average 0.85 215.43

Crack Score 1,467.04 mm^2 (2.2739 in^2)


Crack #

Max. Width

(mm)

Length

(mm)

1 2.24 533.40

2 0.76 129.00

3 1.23 123.00

4 0.99 121.00

5 1.41 213.00

6 0.46 90.00

7 1.75 365.00

8 0.60 85.00

9 1.10 215.00

10 0.62 108.00

11 0.10 80.00

Average 1.02 187.49

Crack Score 2,111.15 mm^2 (3.27 in^2)

33


Crack #

Max. Width

(mm)

Length

(mm)

1 1.00 166

2 2.20 378

3 0.50 388

4 0.79 155

5 1.40 104

6 0.68 53

7 0.45 97

8 1.23 285

9 0.05 125

10 0.35 62

11 0.24 32

12 0.34 51

Average 0.7692 157.9583

Crack Score 1,457.96 mm^2 (2.26 in^2)


Crack #

Max. Width

(mm) Length (mm)

1 1.22 533.40

2 0.20 45.00

3 0.68 79.00

4 0.60 67.00

5 1.00 382.00

6 0.37 30.00

7 0.64 80.00

8 1.47 278.50

9 1.07 73.00

Average 0.81 174.21

Crack Score 1,263.03 mm^2 (1.96 in^2)

Figure 23 presents a histogram with the crack score for each specimen of Mix B, for ease

of comparison.

34

Figure 23: Crack Scores of Phase I, Mix A, specimens

The mass losses of the reinforcing bars of the specimens of Phase I, Mix A, were

measured and correlated with the crack scores of their corresponding beams, as

summarized in Table 15.

Table 15: Phase I (Mix A) Rebar Mass Loss (DOC)

Specimen

ID Rebar

Initial

Mass (g)

Final Mass

(g) % Loss

Avg. %

Loss, DOC

1-1

Most Corroded 588 520 11.56

6.97 Less Corroded 588 574 2.38

1-2


13.10 Less Corroded 588 544 7.48

1-3


4.08 Less Corroded 588 562 4.42

1-4


17.35 Less Corroded 588 572 2.72

1-5


4.93 Less Corroded 588 560 4.76

1-6


4.17

Less Corroded 588 572 2.72

The average mass losses of the Phase I specimens, Mix A, are presented in histogram

form for ease of comparison in Figure 24.

0

500

1000

1500

2000

2500

3000

3500

1-1 1-2 1-3 1-4 1-5 1-6

Cra

ck S

core

(m

m^2

)

Specimen ID

35

Figure 24: Phase I, Mix A, Rebar Mass Losses

As can be seen in the Figure 24, some specimens experienced very high levels of

corrosion, as measured with mass loss, compared to other specimens subjected to the

same corrosion environment. This was due to localized corrosion, which occurred in

some specimens and caused premature spalling of the concrete, leading to extreme loss of

cross-sectional area of the reinforcement, due to direct exposure to the corrosion

environment of the steel rebars. Table 16 records the observations of whether corrosion-

induced segmental debonding or uniform corrosion occurred in the specimens. It can be

seen that the specimens that suffered the highest mass losses, experienced corrosion-

induced segmental debonding as well as uniform corrosion.

0

2

4

6

8

10

12

14

16

18

20

1-1 1-2 1-3 1-4 1-5 1-6

Avg

. M

ass

Loss

(%

), D

OC

.

Specimen ID

36

Table 16: Phase I, Mix A, Rebar Mass Loss Measurements Summary

Specimen

ID

DOC (%) Note

1-1 6.97 Corrosion-induced segmental

debonding/Uniform corrosion



1-3 4.08 Uniform corrosion





Figure 25 shows the corrosion-induced segmental debonding of a rebar in Specimen 4.

Figure 25: Partial debonding/desintegration of rebar of specimen 1-4

Most specimens of Phase I, Mix A, experienced a corrosion mass loss of less than 7%,

with only two specimens presenting corrosion mass loss above 10%, due to localized

corrosion of the rebars.

The crack scores related to the steel reinforcement mass loss measurements, for most of

the specimens. The three least corroded specimens (3,5,6) had the three corresponding

lowest crack scores. However, due to some corrosion-induced segmental debonding,

occurring at the end of the specimens, higher crack scores were observed for specimens

1, 2, and 4. Figure 26 shows a plot of the relation between the crack scores and DOC for

the Phase I, Mix A, specimens.

37

Figure 26: Crack Score vs. DOC for Phase I, Mix A, specimens

4.3.2 Phase II, Mix B Specimens, Cracking and Degree of Corrosion Evaluation

The crack scores for the Phase II specimens, Mix B, are summarized from Table 17 to

Table 20. Figure 27 show the crack scoring marks for specimen 2-1.

Figure 27: Specimen 2-1 Crack Scoring Marks

y = 77.931x + 1343.2 R² = 0.3542

0

500

1000

1500

2000

2500

3000

3500

0 5 10 15 20

Cra

ck S

core

(m

m^2

)

DOC (%)

38

Table 17: Crack Score, Mix B (Phase II), Specimen ID: 2-1

Crack #

Max. Width

(mm)

Length

(mm)

1 2.88 410

2 2.3 400

3 1.5 150

4 0.94 45

5 0.2 20

6 0.15 65

7 0.3 50

8 0.15 60

9 0.25 55

10 0.4 80

11 0.25 85

12 0.5 160

13 0.6 60

14 0.3 60

15 0.4 50

Average 0.74 116.67

Crack Score 1,297.33 mm^2 (2.01 in^2)


Crack #

Max. Width

(mm)

Length

(mm)

1 0.54 185

2 1.15 160

3 0.26 90

4 0.74 295

5 0.12 30

6 0.15 90

7 0.88 375

8 0.78 65

Average 0.58 161.25

Crack Score 744.98 mm^2 (1.15 in^2)

39


Crack #

Max. Width

(mm)

Length

(mm)

1 0.33 45

2 0.18 130

3 0.24 135

4 0.38 115

5 0.52 215

6 0.14 70

7 0.25 30

8 0.64 20

9 0.35 10

10 0.27 25

11 0.58 40

12 0.54 20

13 0.8 150

14 1.37 155

15 2.08 155

Average 0.578 87.67



Crack #

Max. Width

(mm)

Length

(mm)

1 1.92 135

2 1.10 190

3 0.80 100

4 1.29 55

5 0.10 185

6 0.12 135

7 0.31 80

8 0.15 150

Average 0.72 128.75


Figure 28 presents a histogram with the crack score for each specimen of Mix B, for ease

of comparison.

40

Figure 28: Crack Scores of Phase II, Mix B, specimens

The mass losses of the reinforcing bars of Phase II, Mix B specimens, were measured as


Table 21: Phase II (Mix B) Rebar Mass Loss (DOC)

Specimen

ID Rebar

Initial

Mass (g)

Final Mass

(g)

%

Loss,

DOC

Avg. %

Loss, DOC

2-1


26.08 Less Corroded 568 479 15.67

2-2


17.25 Less Corroded 571 480 15.94

2-3


19.51 Less Corroded 567 484 14.64

2-4


17.93 Less Corroded 566 472 16.61

The average mass losses of the Phase II specimens, Mix B, are presented in histogram


0

200

400

600

800

1000

1200

1400

2-1 2-2 2-3 2-4

Cra

ck S

core

(m

m^2

)

Specimen ID

41

Figure 29: Phase II, Mix B, Rebar Mass Losses

As can be seen in Figure 29, most specimens in Phase II, Mix B, experienced uniform

corrosion below 20% DOC. However, some specimens like 2-1 suffered high levels of

corrosion due to corrosion-induced segmental debonding. Table 22 records the

observations of whether corrosion-induced segmental debonding or uniform corrosion

occurred in the specimens.

Table 22: Phase II, Mix B, Rebar Mass Loss Measurements Summary

Specimen

ID DOC (%) Note

2-1 26.08

Corrosion-induced segmental



2-3 19.51




The crack scores correlated with the DOC for all of the specimens of Mix B. The higher

the crack score corresponded to a higher DOC. Figure 30 shows a plot of the relation

between the crack scores and DOC for the Phase II Mix B specimens.

0

5

10

15

20

25

30

2-1 2-2 2-3 2-4

Avg

. M

ass

Loss

(%

), D

OC

.

Specimen ID

42

Figure 30: Crack Score vs. DOC for Phase II, Mix B, specimens

4.3.3 Phase II, Mix C Specimens, Cracking and Degree of Corrosion Evaluation

The crack scores for the Phase II specimens, Mix C, are summarized from Table 23 to

Table 26.

Table 23: Crack Score, Mix C (Phase II), Specimen ID: 2-5

Crack #

Max. Width

(mm)

Length

(mm)

1 1.89 170

2 0.06 30

3 0.27 275

4 0.51 285

5 0.48 260

6 0.68 90

Average 0.65 185


y = 66.262x - 451.03 R² = 0.9557

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25 30

Cra

ck S

core

(m

m^2

)

DOC (%)

43


Crack #

Max. Width

(mm)

Length

(mm)

1 1.56 533.4

2 0.2 90

3 0.3 275

4 0.66 130

5 1.02 135

6 0.4 110

7 1.05 331

Average 0.74 229.2

Crack Score 1,189.55 mm^2 ( 1.84 in^2)


Crack #

Max. Width

(mm)

Length

(mm)

1 2.23 360

2 0.89 340

3 0.43 140

4 0.65 315

5 0.12 95

6 0.14 15

7 1.36 90

8 0.54 175

Average 0.80 191.25

Crack Score 1,216.35 mm^2 (1.88 in^2)


Crack #

Max. Width

(mm) Length (mm)

1 1.08 533.4

2 2 480

3 1.5 533.4

4 1.01 330

Average 1.3975 469.2

Crack Score 2,622.83 mm^2 (4.06 in^2)

44

Figure 31 presents a histogram with the crack score for each specimen of Mix C, for ease

of comparison.

Figure 31: Crack Scores for Phase II, Mix C, specimens

The mass losses of the reinforcing bars of Phase II, Mix C specimens, were measured as


Table 27: Phase II (Mix C) Rebar Mass Loss (DOC)

Specimen

ID Rebar Initial Mass (g) Final Mass (g) % Loss

Avg. %

Loss

2-5


17.43 Less Corroded 566 469 17.14

2-6


23.78 Less Corroded 569 465 18.28

2-7


38.61 Less Corroded 570 462 18.95

2-8


43.82 Less Corroded 561 468 16.58

The average mass losses of the Phase II specimens, Mix C, are presented in histogram


0

500

1000

1500

2000

2500

3000

2-5 2-6 2-7 2-8

Cra

ck S

core

(m

m^2

)

Specimen ID

45

Figure 32: Phase II, Mix C, Rebar Mass Losses

As can be seen in Figure 32, most specimens in Phase II, Mix C, experienced corrosion-

induced segmental debonding and uniform corrosion. This might be due to the higher

porosity of the concrete that permitted localized corrosion cells to develop faster than for

Mix B. Table 28 records the observations of whether corrosion-induced segmental

debonding or uniform corrosion occurred in the specimens.

Table 28: Phase II, Mix C, Rebars Mass Loss Measurements Summary

Specimen

ID DOC (%) Note


2-6 23.78



2-7 38.61



2-8 43.82



The crack scores correlated with the DOC for all of the specimens of Mix C. The higher

the crack score corresponded to a higher DOC. Figure 33 shows a plot of the relation

between the crack scores and DOC for the Phase II Mix B specimens.

0

5

10

15

20

25

30

35

40

45

50

2-5 2-6 2-7 2-8

Avg

. M

ass

Loss

(%

), D

OC

.

Specimen ID

46

Figure 33: Crack Score vs. DOC for Phase II, Mix C, specimens

4.4 FIRE TESTING

For the first phase of the experimental program, the temperature reached in the kiln for 15

minutes of exposure, as measured using thermocouples, followed closely the ASTM E-

119-12 temperature curve, as shown in Figure 34.

Figure 34: Temperature curve for 15 minutes of fire exposure of Phase I beams

y = 54.622x - 251.26 R² = 0.6736

0

500

1000

1500

2000

2500

3000

0 10 20 30 40 50

Cra

ck S

core

(m

m^2

)

DOC (%)

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12 14 16

Tem

pe

ratu

re (

°C)

Time (min)

47

For the second phase of the experimental program, the temperature reached in the kiln for

the 15 minutes of exposure (Figure 35), as measured using thermocouples, followed the

ASTM E-119-12 temperature curve closely, until around the seventh minute, after which

the temperature was about 13% below the target prescribed by the ASTM E-119 curve.

This was not considered a very significant error, and may have been caused by the

difference in thermodynamics inside the gas kiln for the second stage of the experiment,

given that four beams specimens were burned at the same time, as compared with three in

the first stage of the experiment.

Figure 35: Temperature curve for 15 minutes of fire exposure of Phase II beams

Ultrasonic pulse velocity (UPV) technology was used to compare the fire damage

between the first and second phases of the experiment, as the UPV of the fire damaged

specimens is expected to be reduced after the exposure of the concrete beams to fire.

0

100

200

300

400

500

600

700

0 2 4 6 8 10 12 14 16

Tem

pe

ratu

re (

°C)

Time (min)

48

4.5 FIRE DAMAGE EVALUATION OF BEAMS USING UPV

Ultrasonic Pulse Velocity tests were conducted on all the beams specimens to compare

the fire damage between the first and second phase specimens. Table 29 shows the

ultrasonic pulse velocities found for the Phase I specimens, corroded but not exposed to

fire, made with Mix A. Additionally, Table 30 shows the ultrasonic pulse velocities found

for Phase I specimens, corroded and exposed to fire, made with Mix A.

Table 29 UPV test on Phase I specimens (not exposed to fire)

Mix A

Specimen

ID UPV (m/s)

1-1 3,990 (13,089 ft/s)

1-2 3,801 (12,469 ft/s)

1-3 3,791 (12,438 ft/s_

Average 3,860 (12,665 ft/s)

Table 30 UPV test on Phase I specimens (exposed to fire)

Mix A

Specimen

ID UPV (m/s)

1-4 3,073 (10,081 ft/s)

1-5 2,791 (9,157 ft/s)

1-6 3,153 (10,344 ft/s)

Average 3,006 (9,861 ft/s)

The UPV ratios, UPV of the corroded specimens exposed to fire divided by the UPV of

the corroded specimens not exposed to fire, for Mix A of the Phase I specimens are

shown in Table 31.

49

Table 31: UPV ratio for Phase I specimens

Mix A

Avg. UPV (corroded, not exposed to fire) 3,860 m/s (12,665 ft/s)

Avg. UPV (corroded, exposed to fire) 3,006 m/s (9,861 ft/s)

UPV ratio (exposed to fire/not exposed) 0.779

Table 32 shows the ultrasonic pulse velocities found for the Phase II specimens, corroded

but not exposed to fire, made with Mix B and C, respectively. Additionally, Table 33

shows the ultrasonic pulse velocities found for the phase 2 specimens, corroded and

exposed to fire, made with Mix B and C, respectively.

Table 32: UPV test on Phase II specimens (not exposed to fire)

Mix B

Specimen

ID UPV (m/s)

2-1 3,663 (12,019 ft/s)

2-4 3,663 (12,019 ft/s)

Average 3,663 (12,019 ft/s)

Mix C

Specimen

ID UPV (m/s)

2-6 3,569 (11,710 ft/s)

2-8 3,552 (11,655 ft/s)

Average 3,561 (11,683 ft/s)

Table 33: UPV test on Phase II specimens (exposed to fire)

Mix B

Specimen

# UPV (m/s)

2 3,335 (10,941 ft/s)

3 3,073 (10,081 ft/s)

Average 3,204 (10,511 ft/s)

Mix C

Specimen

# UPV (m/s)

5 3,149 (10,331 ft/s)

7 3,306 (10,846 ft/s)

Average 3,228 (10,589 ft/s)

50

The UPV ratios, UPV of the corroded specimens exposed to fire divided by the UPV of

the corroded specimens not exposed to fire, for mixes B and C of the phase 2 specimens

are shown in Table 34.

Table 34 UPV ratios for Phase II specimens

Mix B




Mix C




The UPV ratio of the first phase specimens, 0.779, was smaller than the average one for

the second phase specimens, 0.891, due to the higher temperature developed in the Phase

I fire exposure, which represents 12.57% more damage due to fire for the first test

specimens, if the UPV ratio is used as the fire damage indicator.

4.5 FLEXURAL TESTING

The maximum bending load that the corroded and fire-exposed as well as the corroded

and non fire-exposed specimens were able to sustain, according to ASTM C78-

“Standard Test Method for Flexural Strength of Concrete”, were determined using an

MTS machine.

4.5.1 Phase I, Mix A, Flexural Testing

Table 35 shows the maximum moments developed in Phase I specimens, Mix A.

51

Table 35: Maximum Moments developed in Phase I Specimens (Mix A)

Specimen

ID

Fire

Exposure

Av. degree

of

Corrosion,

DOC (%)

Maximum

Third Point

Load (N)

Maximum

Moment

Developed

(N-m)

Notes

1-1 Non-fired

6.97%

13,291.29

(2,988.00 lb)

2,025.59

(17,927.98

lb.in)

--

1-2 Non-fired

13.10%

17,543.79

(3,944.00 lb)

2,673.67

(23,663.97

lb.in)

--

1-3 Non-fired

4.08%

11,347.41

(2,551.00 lb)

1,729.35

(15,306.04

lb.in)

--

1-4 Fired

17.35%

3,122.65

(702.00 lb)

475.89

(4,211.98

lb.in)

Both rebars

retained bond to

concrete after fire

1-5 Fired

4.93%

2,192.97

(493.00 lb)

334.21

(2,958.01

lb.in)

One rebar

retained bond

to concrete after

fire

1-6 Fired

4.17%

155.69

(35.00 lb)

23.73

(210.03

lb.in)

Both rebars

debonded

from the concrete

after fire

Figure 36 shows the maximum moments developed in each specimen of Mix A in

histogram form.

52

Figure 36: Maximum Moments developed in Phase I Specimens (Mix A)

All of the not fire-exposed beams of Phase I failed by typical flexure failure (Figure 37).

Due to the severe corrosion-induced segmental debonding of the Phase I specimens, and

the spalling of cross sectional concrete, the fire exposed beams showed reinforcement

debonding as a prominent cause of failure (Figure 38).

Figure 37: Specimen 1-3 failure

0.00

500.00

1,000.00

1,500.00

2,000.00

2,500.00

3,000.00

1-16.97 DOC

1-213.10 DOC

1-34.08 DOC

1-417.35 DOC

Fired

1-54.93 DOC

Fired

1-64.17 DOC

Fired

Max

. Mo

me

nt

De

velo

pe

d (

N-m

)

Specimen ID

53


Figure 39 to Figure 43 shows the third point load vs. deflection curves for each specimen

of the Phase I, Mix A, beams.

Figure 39: Specimen 1-1 Load-Deflection Curve

The deflection at the maximum load of Specimen 1-1 was 7.51 mm.

54





55




The deflection at the maximum load of Specimen 1-5 was 5.41 mm. The load-deflection

curve of specimen 1-6 was not possible to obtain because the unreinforced specimen

failed with a 69 lb load of the rollers that transmit the load from an MTS machine, and

therefore no machine loading, or deflection, was recorded.

56

4.5.2 Phase II, Mix B, Flexural Testing

Table 36 shows the maximum moment developed in Phase II specimens, Mix B.

Table 36: Maximum Moment Developed in Phase II Beam Specimens (Mix B)

Specimen

ID

Fire

Exposure

Avg. degree

of

Corrosion

(%)

Maximum

Third Point

Load (N)

Maximum

Moment

Developed

(N.m) Notes

2-1 Non-fired 26.08

22,502.51

(5,058.77 lb)

3,429.38

(30,352.59

lb.in) --

2-2 Fired 17.25

23,032.72

(5,177.96 lb)

3,510.19

(31,067.76

lb.in)

Both rebars

retained bond

to concrete after

fire

2-3 Fired 19.51

15,313.96

(3,442.72 lb)

2,333.85

(20,656.29

lb.in)

Both rebars

retained bond

to concrete after

fire

2-4 Non-fired 17.93

25,171.04

(5,658.68 lb)

3,836.07

(33,952.05

lb.in) --

Figure 44 shows the maximum moments developed in each specimen of Mix B in

histogram form.

Figure 44: Maximum Moments developed in Phase II Specimens (Mix B)

0.00

500.00

1,000.00

1,500.00

2,000.00

2,500.00

3,000.00

3,500.00

4,000.00

4,500.00

2-126.08 DOC

2-217.25 DOC

Fired

2-319.51 DOC

Fired

2-417.93 DOC

Max

. Mo

me

nt

De

velo

pe

d (

N-m

)

Specimen ID

57

Figure 45 shows a typical flexural failure for specimen 2-1 of Phase II, Mix B.


Some specimens experienced combined flexural/shear failure (2-2, 2-3, 2-4), which is

attributed to the loss of rebar (and therefore concrete spalling) at the beam ends, where

corrosion is more severe, reducing the strength of the beam in shear. Figure 46 shows the

combined flexural/shear failure of specimen 2-2. Concrete spalling can also occur due to

fire exposure, as shown in Figure 47, which can contribute to the failure mode.


58

Figure 47: Specimen 2-2 after fire exposure


of the Phase I, Mix B, beams.


The deflection at the maximum third point load for specimen 2-1 was 7.95mm.

-5000

0

5000

10000

15000

20000

25000

0 2 4 6 8 10

Load

, N.

Deflection, mm.

59


The deflection at the maximum third point load for specimen 2-2 was 8.23 mm.



60



4.5.3 Phase II, Mix C, Flexural Testing

Table 37 shows the maximum moment developed in Phase II specimens, Mix C.

Table 37: Maximum Moment Developed in Phase II Specimens (Mix C)

Specimen

ID

Fire

Exposure

Degree of

Corrosion

Maximum

Third Point

Load (N)

Maximum

Moment

Developed

(N.m) Notes

2-5 Fired 17.72

17,259.08

(3,880.00

lb.in)

2,630.28

(23,279.97

lb.in)

Both rebars

retained bond

to concrete after

fire

2-6 Non-fired 23.78

13,165.54

(2,959.73

lb.in)

2,006.43

(17,758.38

lb.in) --

2-7 Fired 38.61

11,187.48

(2,515.05

lb.in)

1,704.97

(15,090.27

lb.in)

Both rebars

retained bond

to concrete after

fire

2-8 Non-fired 43.82

15,527.81

(3,490.79

lb.in)

2,366.4

(20,944.74

lb.in) --

61

Figure 52 shows the maximum moments developed in each specimen of Mix C in

histogram form.

Figure 52: Maximum Moments developed in Phase II Specimens (Mix C)

As can be seen in Figure 52, the maximum moment of the beam specimen 2-6, corroded,

and exposed to fire, with an average degree of corrosion of 23.78%, was 2,006.43 N-m

(226.70 lb.in), which is less than the maximum moment developed in the beam specimen

2-5, corroded (avg. DOC of 17.72%) and not exposed to fire, of 2,630.28 N-m (297.18

lb.in). The lower strength of beam 2-6 might be due to the fact that it had a higher degree

of corrosion and the reinforcement partially debonded during the accelerated corrosion

procedure, leaving parts of the concrete beam essentially without the contribution of the

steel to the moment capacity of the beam, which precipitated a failure at a lower strength.

Figure 53 shows the loss of concrete and partial debonding of the reinforcement due to

corrosion for specimen 2-6.

0.00

500.00

1,000.00

1,500.00

2,000.00

2,500.00

3,000.00

2-517.72 DOC

Fired

2-623.78 DOC

2-738.61 DOC

Fired

2-843.82 DOC

Max

. Mo

me

nt

De

velo

pe

d (

N-m

)

Specimen ID

62

Figure 53: Phase II, Mix C, Specimen 2-6 after corrosion

For Phase II, Mix C, most specimens experienced pure flexural failure (Figure 54), with

only specimen 2-5 showing signs of combined flexural/shear failure, which include

flexural and shear cracks. Figure 55 shows specimen 2-5 failure.


63



of the Phase I, Mix C, beams.



64





65



4.6 ANALYSIS OF FLEXURAL RESULTS

The effect of fire on the flexural capacity of the beams for the Phase I specimens, Mix A,

is shown in Table 38.

Table 38: Flexural Loss (Phase I specimens, Mix A)

Specimens Avg. Maximum

Moment

Developed

(N.m)

% Flexural

Moment

Loss

Notes

Fire-Exposed Full Integrity

Maintained (Specimen 1-4)

475.89

(4,211.98 lb.in)

77.79% Both rebars

retained bond to

concrete after fire

Fire-Exposed (debonded

rebar)

(Specimen 1-5)

334.21

(2,958.01 lb.in)

84.82% One rebar retained

bond to concrete

after fire

With an average degree of corrosion of 9.3% for all the specimens of Phase I combined, a

flexural loss of 77.79% to 84.82% is very significant. The high loss in flexural strength,

in part, is attributed to the severe spalling of concrete from the specimens of Phase I, not

only on the flexural cover, but on the sides, which significantly reduced cross section,

66

and therefore the moment capacity. The theoretical maximum moment developed for an

uncorroded and not exposed to fire beams of Mix A, using a concrete compressive

strength of 10,142 psi and the procedure outlined in ACI 318-11, Building Code

Requirements for Structural Concrete, was calculated as 9,047.37 N-m (80,076 lb.in).

Taking this moment strength value as the control strength for an uncorroded beam of Mix

A, the percentage loss in flexural strength due to only corrosion, and the cumulative loss

due to corrosion and fire was calculated. Table 39 shows the loss in flexural strength for

the Mix A specimens due to only corrosion, and the cumulative loss due to corrosion and

fire (for the specimen that retained bond to both rebars after fire exposure).

Table 39: Cumulative effect of corrosion and fire on uncorroded beams of Mix A

Mix A. Avg. 9.3 DOC

Flexural Moment loss (%)

due to corrosion 76.315


due to corrosion and fire 94.74

The effect of fire on the flexural capacity of the corroded beams of Phase II, Mix B, was

calculated according to the level of corrosion of the beams. For this, corroded specimens

not exposed to fire were paired with corroded ones exposed to fire that had a similar or

close corrosion level (DOC).

Table 40 summarizes the flexural moment loss of the corroded beams due to fire for Mix

B.

67

Table 40: Flexural Loss (Phase II specimens, Mix B)

Mix B Pair 1 - Avg. 17.59 DOC

Specimen ID

Avg.

DOC

Max. Moment Developed

(N-m)

2-2 (fired) 17.25 3,510.19 (31,067.76 lb.in)

2-4 (non-fired) 17.93 3,836.07 (33,952.05 lb.in)

Corroded Specimen


due to fire 8.49

Mix B Pair 2 – Avg. 22.80 DOC

Specimen ID

Avg.

DOC

Max. Moment Developed (N-

m)

2-1 (non-fired) 26.08 3,429.38 (30,352.59 lb.in)

2-3 (fired) 19.51 2,333.85 (20,656.29 lb.in)

Corroded Specimen


due to fire 31.95

The average corrosion level (DOC) for each pair of specimens of Mix B were plotted

against the loss in flexural strength of the corroded beams due to fire in Figure 60

Figure 60: Effect of fire on flexural strength of corroded specimens of Mix B

The theoretical maximum moment developed for an uncorroded and not exposed to fire

beam of Mix B, using a concrete compressive strength of 8,415 psi and the procedure

y = 1.1677x - 2.239 R² = 0.7107

-5

0

5

10

15

20

25

30

35

0 5 10 15 20 25

Loss

in F

lexu

ral S

tre

ngt

h in

co

rro

de

d

be

am d

ue

to

fir

e (

%)

Degree of Corrosion (% loss of cross sectional area)

68

outlined in ACI 318-11, Building Code Requirements for Structural Concrete, was

calculated as 8,993.14 N-m (79,596 lb.in). Taking this moment strength value as the

control strength for an uncorroded beam of Mix B, the percentage loss in flexural

strength due to only corrosion, and the cumulative loss due to corrosion and fire was

calculated. Table 41 shows the loss in flexural strength for the Mix B specimens due to

only corrosion, and the cumulative loss due to corrosion and fire, according to their

average DOC level.

Table 41: Cumulative effect of corrosion and fire on uncorroded beams of Mix B

Mix B Pair 1 - Avg. 17.59 DOC





Mix B Pair 2- Avg. 22.80 DOC





Figure 61 shows the graphed relation, along with its corresponding trend line for the

compounding effects of corrosion and fire on the Mix B specimens.

69

Figure 61: Effects of corrosion and fire on uncorroded specimens of Mix B

The effect of fire on the flexural capacity of the beams was compared according to the

level of corrosion for the Phase II beam specimens, Mix C, as shown in Table 42.

Table 42: Flexural Loss of specimens (Phase II, Mix C).

Mix C Pair 1 – Avg. 20.75 DOC

Specimen ID

Avg.

DOC

Max. Moment

Developed (N-m)

2-5 (fired) 17.72

2,630.28

(23,279.97 lb.in)

2-6 (non-fired) 23.78

2,006.43

(17,758.38 lb.in)

Corroded Specimen


due to fire N/A due to error in specimen 6

Mix C Pair 2 – 41.22 DOC

Specimen #

Avg.

DOC

Max. Moment

Developed (N-m)

2-7 (fired) 38.61

1,704.97

(15,090.27 lb.in)

2-8 (non-fired) 43.82

2,366.4

(20,944.74 lb.in)

Corroded Specimen


due to fire 27.95

y = 2.8236x + 1.4263 R² = 0.9725

0

10

20

30

40

50

60

70

0 5 10 15 20 25

Loss

of

Fle

xura

l Str

en

gth

du

e t

o t

he

co

mb

ine

d e

ffe

cts

of

corr

osi

on

an

d f

ire

(%)

Degree of Corrosion (% loss of cross sectional area)

70

The theoretical maximum moment developed for an uncorroded and not exposed to fire

beam of Mix B, using a concrete compressive strength of 6,460 psi and the procedure

outlined in ACI 318-11, Building Code Requirements for Structural Concrete, was

calculated as 8,894.17 N-m (78,720 lb.in). Taking this moment strength value as the

control strength for an uncorroded beam of Mix C, the percentage loss in flexural

strength due to only corrosion, and the cumulative loss due to corrosion and fire was

calculated. Table 43 shows the loss in flexural strength for the Mix C specimens due to

only corrosion, and the cumulative loss due to corrosion and fire, according to their

average DOC level.

Table 43: Cumulative effect of corrosion and fire on uncorroded beams of Mix C

Mix C Pair 1 - Avg. 20.75 DOC




due to corrosion and fire

N/A due to error

in specimen 6

Mix C Pair 2- Avg. 41.22 DOC





The general trend observed, from Mix B and Mix C specimens, was that as the corrosion

level increased above 20%, the effect of fire on the flexural strength of the corroded beam

suddenly increased by large amount to an average of 30% loss.

71

CHAPTER 7: CONCLUSIONS AND FUTURE WORK

The accelerated corrosion procedure was carried out in Phases I and II. Phase I specimens

experienced lower levels of mass loss but more partial debonding of the reinforcement

due to direct exposure of the rebar to the corrosion environment as a consequence of the

severe concrete spalling. In general, it was found that the higher the crack score, the

higher the corresponding mass loss, unless some partial debonding of the reinforcement

had occurred. Crack scores seemed to follow linear relationships with the corresponding

degrees of corrosion (mass loss), for all the specimens.

The most detrimental observed consequence of the compounding effects of fire and

corrosion was the premature debonding of the reinforcement from the concrete (before

flexural testing). After fire exposure of Phase I beams, one specimen experienced

complete debonding from the rebars, another lost the bond of only one rebar, and only

one retained its structural integrity, with both rebars bonded to the concrete after the fire

exposure. However, Phase II specimens presented less overall fire damage (as measured

using UPV), not only because the temperature achieved inside the kiln was slightly lower

than that for the Phase I, but because the corrosion damage was more uniform and

controlled and therefore large pieces of concrete did not spall from the specimens in the

same proportions as in Phase I.

For Phase I, Mix A Specimens, with an average 9.30% corrosion level:

72

The residual flexural moment for the corroded fire exposed beam that maintained

its full integrity by retaining both rebars bonded to concrete after the fire

exposure, showed a significant loss of approximately 77.8%, compared to the

average flexural moment for the corroded beams not exposed to fire.

Residual flexural moment for the corroded fire exposed beam that retained only

one rebar bonded to the concrete after fire exposure, showed a significant loss of

approximately 84.4%, compared to the average flexural moment for the corroded

beams not exposed to fire.

For Phase II, Mix B Specimens:

The residual flexural moment for the corroded fired exposed beam, at the 17.59%

corrosion level, showed a loss of approximately 8.49% when compared to the

flexural moment for the corroded beam not exposed to fire.




For Phase II, Mix C Specimens:




Mix A, Mix B, and Mix C had different concrete compressive strengths, 10,142 psi,

8,415 psi, and 6,460 psi, respectively. Given the fact that concrete compressive

strength is negatively affected by the sustained temperature rise typical of a fire, the

higher the temperature the concrete is exposed to, the highest the reduction it will

73

experience in its compressive strength (Arioz, 2007). This coupled with the fact that

the loss in bond strength could reach as high as 60% when reinforced concrete is

subjected to temperatures in excess of 500 °C (Haddad et al. 2008), and the

characteristic mass loss and cracking to which a reinforced concrete member is

exposed under corrosion, it is safe to assume that as the concrete compressive

strength decreases, a fired exposed corroded reinforced concrete member will

experience a higher flexural moment loss when compared to a corroded member not

exposed to fire. However, future experimental work is recommended, on the coupled

effects of fire and corrosion across a wide w/c spectrum, which plays a key role in

high strength concrete‟s resistance to fire, because low w/c ratios might cause

concrete spalling during fire exposure. This will benefit the industry by providing

insights into the appropriate mix design that should be used in the coastal

infrastructure, which is more prone to corrosion due to its proximity to saline

environments.

74

APPENDIX A

Table A 1: Current Readings for Phase I, Mix A, Specimens 1-3.

Time (h) Specimen 1-1 Specimen 1-2 Specimen 1-3

Current for each

rebar (mA)

Current for each

rebar (mA)

Current for each

rebar (mA)

0 609 672 920 755 757 744

30 98 78 728 70 106 76

55 95 71 844 80 100 86

79 103 93 1046 102 119 92

103 288 234 2877 293 310 275

127 793 555 2418 330 952 416

Max. 793 672 2877 755 952 744

Table A 2: Current Readings for Phase I, Mix A, Specimens 4-6.

Time (h) Specimen 1-4 Specimen 1-5 Specimen 1-6

Current for each

rebar (mA)

Current for each

rebar (mA)

Current for each

rebar (mA)

0 665 0.718 655 709 988 905

30 34 94 74 136 237 328

55 25 93 86 105 196 580

79 52 64 80 104 360 923

103 393 326 313 857 642 910

127 798 1080 308 934 2368 1357

Max. 798 1080 655 934 2368 1357

s

75

Table A 3: Current Readings for Phase II, Mix B, Specimens.

Time (h) Specimen 2-1 Specimen 2-2 Specimen 2-3 Specimen 2-4

Current for each

rebar (mA)

Current for each

rebar (mA)

Current for each

rebar (mA)

Current for each

rebar (mA)

0 483 474 452 457 460 450 472 500

0.5 448 434 426 407 443 398 416 462

1.5 422 420 405 382 411 377 419 430

3.5 398 396 405 376 407 392 420 465

7.5 380 383 388 362 383 370 412 428

22.17 364 375 371 350 347 366 374 380

32.5 375 397 353 349 350 350 372 407

44 390 398 376 370 345 381 398 444

56 390 414 404 393 335 354 405 408

71.7 404 447 431 421 380 404 489 467

80.17 404 462 428 462 382 372 468 502

92.4 408 467 431 460 406 381 465 460

104.3 418 499 420 444 403 410 481 519

116.17 402 498 412 434 435 393 464 638

128.73 409 485 412 450 436 436 476 558

144.83 419 503 408 422 432 440 482 577

152.58 426 499 417 425 431 453 453 619

165 446 528 418 437 440 547 447 636

189.87 458 608 424 428 481 974 429 611

194.32 474 621 437 441 524 950 431 586

195.53 470 644 434 448 500 928 446 588

212 470 1133 428 436 469 879 434 565

223 501 1258 461 463 467 881 464 619

236 440 1261 479 443 459 876 408 615

247 441 1255 433 430 463 705 405 486

260 488 1179 449 480 457 796 464 534

275 511 1735 442 443 459 771 481 557

286 542 1802 414 425 420 720 423 460

298 534 1625 429 350 336 703 414 485

313 571 1617 453 472 472 712 533 631

325

503 488

628 623

337

533 512

615 733

Max. 571 1802 533 512 524 974 628 733

76

Table A 4: Current Readings for Phase II, Mix C, Specimens.

Time (h) Specimen 2-5 Specimen 2-6 Specimen 2-7 Specimen 2-8

Current for each

rebar (mA)

Current for each

rebar (mA)

Current for each

rebar (mA)

Current for each

rebar (mA)

0 543 522 568 557 499 570 571 557

0.5 532 508 554 531 499 555 524 505

1.5 472 448 485 488 443 481 472 437

3.5 432 426 478 462 390 435 440 401

7.5 402 395 453 443 397 444 405 392

22.17 390 374 398 389 325 376 373 359

32.5 348 331 405 394 334 373 380 381

44 368 348 407 403 333 398 389 380

56 394 364 424 424 366 458 426 384

71.7 437 409 441 458 375 470 439 381

80.17 449 424 461 460 406 928 490 418

92.4 403 435 514 540 424 1513 781 404

104.3 445 443 575 731 417 1847 2094 428

116.17 457 421 462 1168 423 2057 3019 411

128.73 441 431 671 1227 403 1949 4039 434

144.83 459 438 1039 1108 416 1840 3725 454

152.58 447 428 1623 1055 435 1673 3397 431

165 452 423 2183 1020 415 1820 3161 423

189.87 425 419 2720 634 406 2034 2466 444

194.32 435 407 2469 628 417 2047 2509 451

195.53 448 432

408 2117 2449 462

212 423 419

430 1756 1333 450

223 403 420

412 787 854 430

236 410 550

433 674 803 402

247 351 392

396 407 568 404

260 425 410

404 347 667 448

275 417 441

432 374 407 526

286 428 492

402 344 418 464

298 360 535

355 311 330 468

313 402 445

383 306 349 574

325

337

Max. 543 550 2720 1227 499 2117 4039 574

w

77

APPENDIX B

Table B 1: Temperature inside gas kiln for Phase I, Mix A, Specimens.

Time

(min.)

Temperature

(ºC)

Temperature

(ºF)

0 27 80

1 582 1079

2 571 1060

3 653 1208

4 666 1231

5 662 1223

6 668 1234

7 692 1277

8 673 1244

9 689 1273

10 697 1287

11 699 1290

12 704 1299

13 715 1319

14 726 1338

15 747 1377

t

78

Table B 2: Temperature inside gas kiln for Phase II, Mixes B and C, Specimens.

y

Time

(min.)

Temperature

(ºC)

Temperature

(ºF)

0 25 76.9

1 529 985

2 555 1031

3 577 1071

4 582 1080

5 609 1129

6 592 1097

7 597 1107

8 594 1101

9 607 1125

10 609 1129

11 621 1150

12 621 1150

13 604 1120

14 642 1187

15 636 1177

79

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