Improving Fire Resistance ofFaculty of Engineering ŗŪťƈƌƃŒ ŗƒƄƂ Civil Engineering...
Transcript of Improving Fire Resistance ofFaculty of Engineering ŗŪťƈƌƃŒ ŗƒƄƂ Civil Engineering...
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Islamic University of Gaza ŗƒƆƚŪƗŒ�ŗŶƆœŞƃŒ�ŖŨŹ� ���
Higher Education Deanship�� œƒƄŶƃŒ�ŘœŪŒŧťƃŒ�ŖťœƆŵ� ���
Faculty of Engineering ŗŪťƈƌƃŒ�ŗƒƄƂ� ���
Civil Engineering Department �ƅŪſ�ŗŪťƈƌƃŒŗƒƈťƆƃŒ� ���
Design and Rehabilitation of Structures �¾ƒƋŋř�ƍ�ƅƒƆŮř�ŝƆœƈŧŕŘʼnŬƈƆƃŒ� ���
Improving Fire Resistance of
Reinforced Concrete Columns
ϖϳήΤϠϟ�ΔΤϠδϤϟ�ΔϴϧΎγήΨϟ�ΓΪϤϋϷ�ΔϣϭΎϘϣ�ϦϴδΤΗ��
By
Khaled Mohammed Nassar
Supervised By
Prof. Samir Shihada
A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Civil Engineering Rehabilitation
and Design of Structures
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Dedication
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I would like to dedicate this work to my family specially my mother and
my father who loved and raised me, to my loving wife and daughters and
to my brothers and sisters, for their sacrifice and endless support
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Improving Fire Resistance of Abstract Reinforced Concrete Columns��
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Abstract:����
Fire has become one of the greatest threats to buildings. Concrete is a primary
construction material and its properties of concrete to high temperatures have gained a
great deal of attention. Concrete structures when subjected to fire presented in general
good behavior. The low thermal conductivity of the concrete associated to its great
capacity of thermal insulation of the steel bars is the responsible for this good
behavior. However, there is a fundamental problem caused by high temperatures that
is the separation of concrete masses from the body of the concrete element " spalling
phenomenon ". Spalling of concrete leads to a decrease in the cross section area of
the concrete column and thereby decrease the resistances to axial loads, as well as the
reinforcement steel bars become exposed directly to high temperatures.
With the increase of incidents caused by major fires in buildings; research and
developmental efforts are being carried out in this area and other related disciplines.
This research is to investigate the behavior of the reinforced concrete columns at high
temperatures. Several samples of reinforced concrete columns with Polypropylene
(PP) fibers were used. Three mixes of concrete are prepared using different contents
of Polypropylene ;( 0.0 kg/m³, 0.5 kg/m³ and 0.75 kg/m³). Reinforced concrete
columns dimensions are (100 mm x100 mm x300 mm). The samples are heated for 2,
4 and 6 hours at 400 C°, 600 C° and 800°C and tested for compressive strength.
Also, the behavior of reinforcement steel bars at high temperatures is investigated.
Reinforcement steel bars are embedded into the concrete samples with 2 cm and 3 cm
concrete covers, after heating at 800°C for 6 hours. The reinforcement steel bars are
then extracted and tested for yield stress and maximum elongation ratio.
The analysis of results obtained from the experimental program showed that, the best
amount of PP to be used is 0.75 kg/m³, where the residual compressive strength is 20
% higher than of that when no PP fibers are used at 400 C for 6 hours. Moreover,
a 3 cm of concrete cover is in useful improving fire resistance for concrete structures
and providing a good protection for the reinforcement steel bars, where it is 5 %
higher than the column samples with 2 cm concrete cover at 6 hours and 600 C°.
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Improving Fire Resistance of Abstract Reinforced Concrete Columns��
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)mm300 mm x 100 mm x�������ΔѧѧϔϠΘΨϣ�ΓέήѧѧΣ�ΕΎΟέΪѧѧϟ�νήόΘΘѧѧγ�ϲѧѧΘϟ�ϭ� ,°C 600,C°004
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ACKNOWLEDGMENT
I would like to extend my gratitude and my sincere thanks to my honorable, esteemed
supervisor, Assoc. Prof. Samir M. Shihada, for his exemplary guidance and
encouragement.
Also, I would like extend my sincere appreciation to all who helped me in currying
out this thesis.
I would like to thank all my lecturers in the Islamic University of Gaza from whom I
learned much and developed my skills.
My deepest appreciation and thanks to every one who helped me in the completeness
of this study, especially to the staff of Material & Soil Laboratory in the Islamic
University of Gaza, and the staff of Sharaf factory.
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IV
TABLE OF CONTENTS
ABSTRACT
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ACKNOWLEDGMENT .. III
TABLE OF CONTENTS . IV
LIST OF FIGURES . VII
LIST OF TABLES ... IX
LIST OF APPREVIATIONS . X
CHAPTER 1. INTRODUCTION
1.1 Introduction .................................................................. 1
1.2 Statement of Problem... 2
1.3 Research Objectives . 3
1.4 Research Methodology . 4
1.5 Thesis Organization... 5
CHAPTER 2. LITERATURE REVIEW
2.1 Introduction ............................... 6
2.2 Concrete. 6
2.2.1 Benefits of concrete under fire ................................. 8
2.3 Physical and chemical response to fire . 8
2.4 Spalling . 11
2.4.1 Mechanisms of Spalling .. 12
2.5 Spalling Prevention Measures ... 14
2.5.1 Polypropylene fibers 14
2.5.2 Thermal barriers 15
2.6 Cracking .. 15
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2.7 Effect of Fire on Concrete .. 17
2.8 Performance of reinforcement in fire . 22
2.9 Effect of Fire on Steel Reinforcement ... 22
2.10- Effect of Fire on FRP columns 24
CHAPTER 3. EXPERIMENTAL PROGRAM
3.1 Introduction 25
3.2 Materials and Their Quality Tests .. 25
3.2.1 Aggregate Quality Tests .... 26
3.2.1.1 Unit Weight of Aggregate .. 26
3.2.1.2 Specific Gravity of Aggregate ... 27
3.2.1.3 Moisture content of Aggregate .. 29
3.2.1.4 Resistance to Degradation by Abrasion & Impaction test .. 29
3.2.1.5 Sieve Analysis of Aggregate .. 31
3.2.1.6 Cement 32
3.2.1.7 Water .. 33
3.2.1.8 Polypropylene Fibers (PP) .. 33
3.3 Mix Proportions .. 34
3.4 Sample Categories .. 35
3.5 Mixing, casting and curing procedures .. 38
3.5.1 Mixing procedures 38
3.5.2 Casting procedures 38
3.5.3 Curing procedures . 39
3.6 Heating Process .. 39
3.7 Compressive and Tensile Strength Tests 41
3.8 Reinforcing Steel Tests .. 42
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CHAPTER 4. Results & Discussion
4.1 Introduction... 43
4.2 Effect of polypropylene content. 43
4.2.1 Unheated Columns 43
4.2.2 Heated Columns 44
4.3 Effect of concrete cover . 48
4.3 Effect of high temperature on steel reinforcement . 50
4.3.1 Yield Stress . 50
4.3.2-Elongation .. 51
CHAPTER 5. CONCLUSION & RECOMMENDATIONS
5.1 Introduction 53
5.2 Conclusions 53
5.3 Recommendations. 54
CHAPTER 6. REFERENCES .
55
ABBENDIX A : RESEARCH PHOTOS . A
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VII
LIST OF FIGURES
Fig.1.1 Reinforced Concrete Column subjected to Fire "Al Sultan Tower Jabalia..... 2
Fig.2.1 Surface cracking after subjected to high temperatures 7
Fig.2.2 Structural failure.. 7
Fig. 2.3 Concrete in fire physiochemical process.. 9
Fig. 2.4 Spalling in concrete column subjected to fire, Alsultan Tower, Jabalia, North Gaza
Strip 12
Fig. 2.5 The spalling mechanism of concrete cover. 13
Fig. 2.6 Polypropylene fibers provide protection against spalling .. 14
Fig.2.7 Thermal cracks in a concrete column subjected to high temperature 16
F Fig.3.1 Mold of Unit Weight test 27
Fig.3.2 Specific Gravity test equipments 28
Fig. 3.3 Los Angeles Abrasion Machine.. 30
Fig. 3.4 Sieve analysis of aggregate. 32
Fig.3.5 Polypropylene Fibers.. 33
Fig.3.6 Dimension and Reinforcement Details of Samples 35
Fig.3.7 Mechanical mixer .. 38
Fig 3.8 Form of the moulds used for preparing specimens. 38
Fig 3.9 Curing process for hardened concrete 39
Fig 3.10 Electrical Furnace for Burning process... 39
Fig 3.11 Heating process Flow char ............................................. 40
Fig 3.12 Compressive strength Machine .......... 41
Fig 3.13 Tensile strength test for reinforcement steel ...... 42
Fig 4.1 Relationship between axial load capacity and burning periods at 400 C°...... 46
Fig 4.2 Relationship between axial load capacity and burning periods at 600 C°....... 46
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Fig 4. 3 Relationship between axial load capacity and burning periods at 800 C°. 47
Fig 4. 4 Relationship between axial load capacity and heating duration at 600 C°
for different concrete covers. 49
Fig 4.� Relationship between yield stress of steel reinforcement and concrete cover
for 800 C° temperature at 6 hrs.. 50
Fig 4.6 Relationship between elongation of steel reinforcement and concrete cover
for 800 C° at 6 hrs . 51
Fig A.1 Mechanical Mixer .. A-1
Fig A.2 Adding of Polypropylene to the mix .. A-1
Fig A.3 Column samples in water ... A-1
Fig A.4 Column samples in the open air.. A-1
Fig A.5 Electrical Furnace... A-2
Fig A.6 Column samples in the electrical Furnace . A-2
Fig A.7 Cracks and Spalling after heating ... A-2
Fig A.8 Compressive Strength test and column samples after test... A-3
Fig A.9 Yield stress test for the steel reinforcement A-4
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IX
LIST OF TABLES
Table 2.1 Mineralogical Composition of Portland Cement 10
Table 3.1 Capacity of Measures...... 26
Table 3.2 Unit weight test results 27
Table 3.3 Specific gravity of aggregate... 28
Table 3.4 Moisture content values.. 29
Table 3.5 Number of steel spheres for each grade of the test sample..................... 30
Table 3.6 Sieve analysis of aggregate. 31
Table 3.7 Ordinary Portland cement properties "Test Results".. 32
Table 3.8 Properties of Polypropylene fibers.. 33
Table 3.9 mix design of the concrete column samples .. 34
Table 3.10 Concrete without PP and cover 2.0 cm... 36
Table 3.11 Concrete with 0.5 Kg/m³ PP and cover 2.0 cm... 36
Table 3.12 Concrete with 0.75 Kg/m³ PP and cover 2.0 cm.... 37
Table 3.13 Concrete with concrete cover 3.0 cm.. 37
Table 3.14 Concrete without PP 37
Table 4.1 The axial load capacity test results for the columns samples
with polypropylene fibers ..........................
44
Table 4.1 Percentage of reduction in axial load capacity at different % of PP,
and different temperatures................................................................
45
Table 4.3 the axial load capacity test results at 600 Cº for 2 cm and
3 cm concrete cover.
48
Table 4.4 Percentages of reduction in axial load capacity at
600 Cº for 2 cm and 3 cm Concrete cover..
48
Table 4.5 the effect of high temperature on yield stress of
steel reinforcement.. 50
Table 4.6 The effect of heating on the elongation of steel reinforcement... 51
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LIST OF APPREVIATIONS
RC Reinforced Concrete
PP Polypropylene
°C Degree Celsius
fc
' Compressive Strength of concrete cylinders at 28 days
UTM Universal Testing Machine
ASTM American Society for Testing and Materials
ACI American Concrete Institute
Unit Weight
Abs. Absorption
FRP Fiber-Reinforced Polymers
C-S-H Hydrated Calcium Silicate
SSD Saturated Surface Dry
S.G Specific Gravity
BSG Bulk Specific Gravity
Wt Weight
OPC Ordinary Portland Cemen
w/c Water cement ratio
C60 Concrete compressive strength of 60 MPa
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XI
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INTRODUCTION����
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Improving Fire Resistance of CH.1: Introduction Reinforced Concrete Columns��
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Introduction
1.1- Introduction
Fire impacts reinforced concrete (RC) members by raising the temperature of the
concrete mass. This rise in temperature dramatically reduces the mechanical
properties of concrete and steel. Moreover, fire temperatures induce new strains,
thermal, and transient creep .They might also result in explosive spalling of surface
pieces of concrete members. Fire is a global disaster in the sense that it disrupts the
normal human activities and leaves behind its scars for some time to come [1].
Concrete is a good fire-resistant material due to its inherent non-combustibility and
poor thermal conductivity. Concrete is specified in buildings and civil engineering
projects for several reasons, sometimes cost, and sometimes speed of construction or
architectural appearance, but one of concretes major inherent benefits is its
performance in fire, which may be overlooked in the race to consider all the factors
affecting design decisions.
Concrete usually performs well in building fires. However, when its subjected to
prolonged fire exposure or unusually high temperatures, concrete can suffer
significant distress. Because concretes pre-fire compressive strength often exceeds
design requirements, a modest strength reduction can be tolerated. But large
temperatures can reduce the compressive strength of concrete so much that the
material retains no useful structural strength [2].
A study of RC columns is important because these are primary load bearing members,
and a column could be crucial for the stability of the entire structure.
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Improving Fire Resistance of CH.1: Introduction Reinforced Concrete Columns��
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1.2- Statement of Problem
During the recent war in the Gaza Strip, the veil uncovered on the extent of disasters
on constructions. It was noted the large scale of destruction resulting from fires which
were either from direct missile hits, or through flammable materials and burning and
flammable (e.g. gasoline) in the residential, and industrial compounds. The Sultan
Tower, located in Jabalia was damaged by burning of flammable materials.
Concrete structures when subjected to fire showed good behavior in general. The low
thermal conductivity of the concrete associated with its great capacity of thermal
insulation of the steel bars is responsible for this good behavior. However a
phenomenon such as the concrete spalling may compromise the fire behavior of the
elements.
Fig.1.1: Reinforced Concrete Column subjected to Fire "Al Sultan Tower Jabalia"
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Improving Fire Resistance of CH.1: Introduction Reinforced Concrete Columns��
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Spalling of concrete leads to a decrease in the cross section area of the concrete
column and thereby decrease the resistances to axial loads, as well as the
reinforcement steel bars become exposed directly to high temperatures.
To avoid spalling phenomenon, several studies have been performed worldwide for
the development of concrete compositions of enhanced fire behavior.
Concretes with polypropylene fibers showed good behavior at elevated temperatures
and controlling spalling of concrete [3].
In this research polypropylene fibers (PP) will be used in the concrete mix in order to
improve the resistance of RC columns to compression loads, and also prevent spalling
of concrete in columns at elevated temperatures. The polypropylene fibers (PP) will
be used in the reinforced concrete columns at different contents (0.5 kg/m³ and 0.75
kg/m³).
Also, different concrete covers are to be used in order to study the effect of concrete
cover on elevated temperatures resistance of reinforced concrete columns.
1.3- Research objectives: ��
The main objective of this research is to increase the fire resistance of reinforced
concrete columns by preventing the spalling phenomenon of concrete.
Access to fire-resistant concrete, especially main structural elements such as concrete
columns through the following:
1. Study the effect of concrete cover on enhancing fire resistance of reinforced
concrete columns.
2. Determine the best amount of polypropylene fibers (pp) to be used in the
concrete mix for improving fire resistance of RC columns to compression
loads.
3. Study the effect of elevated temperature and duration on the mechanical
properties and elongation of the reinforcement steel bars and the effect of
concrete covers of 2 cm and 3 cm.
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1.4-Research Methodology: �� 1. Study the available researches related to the subject of the study.
2. Execute a program of tests in laboratories inside and outside the Islamic
University of Gaza.
Testing program will include the following:
Define the properties of constitutive materials of concrete (cement, fine
aggregate, coarse aggregate, steel reinforcement .etc).
Examine the impact of polypropylene fibers (pp) on the reinforced
concrete casting with different contents (0.0 kg/m³, 0.5 kg/m³, and 0.75
kg/m³) of polypropylene fibers.
Heating columns specimens in an electric furnace for different periods
of time (2, 4, and 6 hours), at temperature degrees (400 C°, 600 C° and
800 C°).
3. Tests will be studying the capacity of the reinforced concrete columns under
axial load at materials and soil laboratory in the Islamic University of Gaza.
4. Examination of reinforcement steel bars after exposure to elevated
temperature through the extraction of steel bars from column specimens, then
subjecting those columns to yield stress test and maximum elongation ratio.
5. Test results and data analysis.
6. Conclusions and the recommendations of the research work, based on the
experimental program results and data analysis.
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1.5- Thesis Organization
The thesis contains 6 chapters as follows: Thesis Organization
Chapter 1 (Introduction): This chapter gives some background on fire effect on
concrete structures, especially reinforced concrete columns. Also it gives a description
of the research importance, scope, objectives, and methodology, in addition to the
report organization.
Chapter 2 (Literature Review): This chapter reviews a number of studies and
scientific research on the impact of fire on reinforced concrete columns, and ways to
improve the resistance of concrete columns against fire load.
Chapter 3 (Experimental program): determine the basic properties of materials
consisting of concrete, such as" aggregate, sand, cement" , preparation of concrete
columns samples , heating process , and test of samples after heating.
Chapter 4 (Results & Discussion): This chapter discusses the results of the tests that
were performed on reinforced concrete specimens and reinforcement steel bars
samples.
Chapter 5 (Conclusions and Recommendations): This chapter includes the
concluded remarks, main conclusions and recommendations drawn from the research
work.
Chapter 6 (References).
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LITERATURE REVIEW����
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Literature Review
2.1-Introduction:
Fire remains one of the serious potential risks to most buildings and structures. The
extensive use of concrete as a structural material has led to the need to fully
understand the effect of fire on concrete. Generally concrete is thought to have good
fire resistance. The behavior of reinforced concrete columns under high temperature is
mainly affected by the strength of the concrete, the changes of material property and
explosive spalling.
The hardened concrete is dense, homogeneous and has at least the same engineering
properties and durability as traditional vibrated concrete. However, high temperatures
affect the strength of the concrete by explosive spalling and so affect the integrity of
the concrete structure.
In recent years, many researchers studied the fire behavior of concrete columns. Their
studies included experimental and analytical evaluations for reinforced concrete
columns such as Paulo [3], Shihada [15], Ali [16] and Sideris [22].
This chapter discusses a number of researches and previous studies which were
conducted to study the effect of fire on reinforced concrete columns.
2.2- Concrete
Concrete is a composite material that consists mainly of mineral aggregates bound by
a matrix of hydrated cement paste. The matrix is highly porous and contains a
relatively large amount of free water unless artificially dried. When exposing it to
high temperatures, concrete undergoes changes in its chemical composition, physical
structure and water content. These changes occur primarily in the hardened cement
paste in unsealed conditions. Such changes are reflected by changes in the physical
and the mechanical properties of concrete that are associated with temperature
increase. Deterioration of concrete at high temperatures may appear in two forms:
(1) Local damage (Cracks) in the material itself and Fig (2.1).
(2) Global damage resulting in the failure of the elements Fig (2.2) [4].
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Fig. 2.1: Surface cracking after subjected to high temperatures [4].
Fig.2.2: Structural failure [4].
One of the advantages of concrete over other building materials is its inherent fire
resistive properties; however, concrete structures must still be designed for fire
effects. Structural components still must be able to withstand dead and live loads
without collapse even though the rise in temperature causes a decrease in the strength
and modulus of elasticity for concrete and steel reinforcement. In addition, fully
developed fires cause expansion of structural components and the resulting stresses
and strains must be resisted [5].
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2.2.1- Benefits of concrete under fire [6].
The benefits of concrete under fire include, but not limited to the following
It does not burn or add to fire load.
It has high resistance to fire; preventing it from spreading thus reduces
resulting environmental pollution.
It does not produce any smoke, toxic gases or drip molten particles.
It reduces the risk of structural collapse.
It provides safe means of escape for occupants and access for firefighters
as it is an effective fire shield.
It is not affected by the water used to put out a fire.
It is easy to repair after a fire and thus helps residents and businesses
recover sooner.
It resists extreme fire conditions, making it ideal for storage facilities with
a high fire load.
2.3- Physical and chemical response to fire
Fires are caused by accidents, energy sources or natural means, but the majority of
fires in buildings are caused by human errors. Once a fire starts and the contents
and/or materials in a building are burning, then the fire spreads via radiation,
convection or conduction with flames reaching temperatures of between 600 Cº and
1200 Cº.
Fig (2.3) illustrates the behavior of reinforced concrete during heating and the degree
of effect at each degree of heating after one hour of exposure on three sides, where the
increasing of temperature degree increases the deterioration of concrete member
Harm is caused by a combination of the effects of smoke and gases, which are emitted
from burning materials, and the effects of flames and high air temperatures [6].
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Fig.2.3: concrete in fire physiochemical process for one hour duration [6].
Chemical changes in the structure of concrete can be studied with thermo-
gravimetrical analyses. The following chemical transformations can be observed by
the increase of temperature. At around 100 Cº the weight loss indicates water
evaporation from the micro pores. Dehydration of ettringite
(3CaOAl2O3·3CaSO4·31H2O) occurs between 50 Cº and 110 Cº.The mineralogical
composition of Portland cement shown in Table (2.1).
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At 200 Cº further dehydration takes place which causes small weight loss in case of
various moisture contents. The weight loss was different until the local pore water and
the chemically bound water were gone. Further weight loss was not perceptible at
around 250-300 Cº. During heating the endothermic dehydration of Ca (OH)2 occurs
between 450 Cº and 550 Cº (Ca (OH)2 → CaO + H2O. Dehydration of calcium-
silicate-hydrates was found at the temperature of 700 Cº [4].
Table 2.1: Mineralogical Composition of Portland cement.
Some changes in color may also occur during the exposure for temperatures. Between
300 Cº and 600 Cº color is to be light pink, for temperatures between 600 Cº and 900
Cº color is to be light grey, and for temperatures over 900 Cº color is to be dark Beige
"Creamy".
The alterations produced by high temperatures are more evident when the temperature
surpasses 500Cº. Most changes experienced by concrete at this temperature level are
considered irreversible. C-S-H gel, which is the strength giving compound of cement
paste, decomposes further above 600 Cº. At 800 Cº, concrete is usually crumbled and
above 1150 Cº feldspar melts and the other minerals of the cement paste turn into a
glass phase. As a result, severe micro structural changes are induced and concrete
loses its strength and durability.
Concrete is a composite material produced from aggregate, cement, and water.
Therefore, the type and properties of aggregate also play an important role on the
properties of concrete exposed to elevated temperatures.
Mineralogical composition contribution ratio ( % )
C3S (3 CaO . SiO2) 38.95
C2S (2 CaO . SiO2) 30.55
C3A (3 CaO . Al2O3) 9.91
C4AF (4 CaO . Al2O3 . Fe2O3) 11.98
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The strength degradations of concretes with different aggregates are not same under
high temperatures.
This is attributed to the mineral structure of the aggregates. Quartz in siliceous
aggregates polymorphically changes at 570 Cº with a volume expansion and
consequent damage.
In limestone aggregate concrete, CaCO3 turns into CaO at 800900 Cº, and expands
with temperature. Shrinkage may also start due to the decomposition of CaCO3 into
CO2 and CaO with volume changes causing destructions. Consequently, elevated
temperatures and fire may cause aesthetic and functional deteriorations to the
buildings.
Aesthetic damage is generally easy to repair while functional impairments are more
profound and may require partial or total repair or replacement, depending on their
severity [7].
2.4- Spalling
One of the most complex and hence poorly understood behavioral characteristics in
the reaction of concrete to high temperatures or fire is the phenomenon of spalling.
This process is often assumed to occur only at high temperatures, yet it has also been
observed in the early stages of a fire, and at temperatures as low as 200 Cº. If severe,
spalling can have a deleterious effect on the strength of reinforced concrete structures;
due to enhanced heating of the steel reinforcement see Fig (2.4).
Spalling may significantly reduce or even eliminate the layer of concrete cover to the
reinforcement bars, thereby exposing the reinforcement to high temperatures, leading
to a reduction of strength of the steel and hence a deterioration of the mechanical
properties of the structure as a whole. Another significant impact of spalling upon the
physical strength of structures occurs via reduction of the cross-section of concrete
available to support the imposed loading, increasing the stress on the remaining areas
of concrete. This can be important, as spalling may manifest itself at relatively low
temperatures, before any other negative effects of heating on the strength of concrete
have taken place [8].
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Fig. 2.4. Spalling in concrete column subjected to fire (Alsultan Tower, Jabalia, North Gaza Strip).
2.4.1- Mechanisms of Spalling
Spalling of concrete is generally categorized as: pore pressure induced spalling,
thermal stress induced spalling or a combination of the two.
Spalling of concrete surfaces may have two reasons:
(1) Increased internal vapor pressure (mainly for normal strength concretes) and.
(2) Overloading of concrete compressed zones (mainly for high strength concretes).
The spalling mechanism of concrete cover is visualized in Fig (2.5).
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Fig.2.5.The spalling mechanism of concrete covers [4].
As concrete is heated, the free water vaporizes at�100 Cº and expands; thereby
resulting in increased�pore pressures. Migration of some of this vapor to the�interior of
the concrete member, where it cools and�condenses, will result in an increasingly
wet zone�sometimes referred to as moisture clog. At some�distance from the hot
surface the vapor front�reaches a critical point at which a maximum pore�pressure is
achieved (further movement will result in�a reduction in pressure).
The distance of this point�from the heated surface will depend on other concretes
permeability. Pore pressure spalling occurs if�the maximum pore pressure is greater
than the local�tensile strength of the concrete. However, no pore�pressures have yet
been measured which would exceed the tensile strength of concrete which suggests�
that pore pressure in isolation does not lead to the�occurrence of spalling.
Strong thermal gradients develop in concrete as it is�heated, due to its low thermal
conductivity and high�specific heat. These thermal gradients induce compressive
stresses close to the surface due to restrained thermal expansion and tensile stresses in
the�cooler interior regions [9]�
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It is most likely that spalling occurs due to the combination of tensile stresses induced
by thermal expansion and increased pore pressure. Much debate�still surrounds the
identification of the key mechanism (pore pressure or thermal stress). However, it is
noted that the key�mechanism may change depending upon the section�size, material
and moisture content [5].
2.5- Spalling Prevention Measures:
There are some principal methods by which the incidence of spalling can be reduced.
2.5.1- Polypropylene fibers
One well-known method is the addition of polypropylene (pp) fibers to the concrete
mix. This approach works on the basis that, as the concrete is heated by fire, the
Polypropylene fibers melt at about 160 Cº - 170 Cº thus creating channels for vapor to
escape and thereby release pore pressures. The influence of compressive load during
heating is important Fig (2.6).
Fig.2.6 Polypropylene fibers provide protection against spalling [10].
Tests have indicated that, for unloaded concrete, 1kg of fibers per m³ of concrete may
be sufficient to eliminate spalling. For a load of 3 N/mm² the fiber content needs to be
increased to 1.5-2 kg/m³ and for a load of 6 N/mm² a further increase to 3 k/m³ may
be required to combat explosive spalling. Although concrete segments are lightly
stressed under normal conditions, it should be pointed out that a circumferential
compressive hoop stress will develop in the concrete during heating which is a
function of the thermal expansion of the aggregate [10].
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2.5.2- Thermal barriers
Another anti-spalling measure is to place thermal barrier over the concrete surface a
method sometimes used in tunnel construction. Thermal barriers reduce the rate of
heating (and peak temperatures) within the concrete and thus reduce the risk of
explosive spalling as well as loss of mechanical strength. They are therefore the most
effective method (pp fibers do not reduce temperatures). However, there are two
potential drawbacks: (a) the cost of the insulation is likely to be more than that of the
fibers and (b) with some of the manufacturers there has been a problem with
delaminating during normal service conditions.
The design criteria normally are to apply a sufficient thickness of coating so as to
reduce the maximum temperature at the surface of the concrete to below about 300 Cº
and the maximum temperature at the steel rebar to about 250 Cº within 2- hours of the
fire. It should be noted that experience indicates that while 25 mm of coating may be
adequate for concrete strength up to about C60 a coating thickness of 35mm may be
required for high strength concrete to avoid explosive spalling.
Also, there are some methods as:
1- Spray coating of finished concrete with a substance that slows down the rate of
heat transfer from fire. It is the rate of temperature change in the concrete that has
been proven to be at least as important a cause of spalling as the ongoing exposure
to high temperature itself.
2- The relatively new concept to counter the spalling threat is to provide vents in the
concrete to alleviate pore pressure [9]. �
2.6- Cracking
The processes leading to cracking are generally believed to be similar to those which
generate spalling. Thermal expansion and dehydration of the concrete due to heating
may lead to the formation of fissures in the concrete rather than, or in addition to,
explosive spalling. These fissures may provide pathways for direct heating of the
reinforcement bars, possibly bringing about more thermal stress and further cracking.
Under certain circum stances the cracks may provide path ways for fire to spread
between adjoining compartments Fig (2.7).
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The penetration depth of the crack is related to the temperature of the fire, and that
generally the cracks extended quite deep into the concrete member. Major damage
was confined to the surface near to the fire origin, but the nature of cracking and
discoloration of the concrete pointed to the concrete around the reinforcement
reaching 700 °C. Cracks which extended more than 30 mm into the depth of the
structure were attributed to a short heating/cooling cycle due to the fire being
extinguished [11].
The importance of the stress conditions in the concrete should be noted. Compressive
loads which may arise from thermal expansion can be very beneficial in compact the
material and suppressing the formation of cracks; this results in much smaller
degradation of compressive strength and elastic modulus than in specimens bearing
reduced loading [12].
Fig.2.7. Thermal cracks in a concrete column subjected to high temperature [13].
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2.7- Effect of Fire on Concrete
Concrete is arguably the most important building material, playing a part in all
building structures. Its virtue is its versatility, i.e. its ability to be molded to take up
the shapes required for the various structural forms. It is also very durable and fire
resistant when specification and construction procedures are correct. Concrete can be
used for all standard buildings both single storey and multistory and for containment
and retaining structures and bridges.
Under normal conditions, most concrete structures are subjected to a range of
temperatures no more severe than that imposed by ambient environmental conditions.
However, there are important cases where these structures may be exposed to much
higher temperatures (e.g., building fires, chemical and metallurgical industrial
applications in which the concrete is in close proximity to furnaces, some nuclear
power-related postulated accident conditions, and buildings that subjected to bombing
and arson).
Concretes thermal properties are more complex than for most materials because not
only is the concrete a composite material whose constituents have different properties,
but its properties also depending on moisture and porosity. Exposure of concrete to
elevated temperature affects its mechanical and physical properties. Elements could
distort and displace, and, under certain conditions, the concrete surfaces could spall
due to the buildup of steam pressure. Because thermally induced dimensional
changes, loss of structural integrity, and release of moisture and gases resulting from
the migration of free water could adversely affect plant operations and safety, a
complete understanding of the behavior of concrete under long-term elevated-
temperature exposure as well as both during and after a thermal excursion resulting
from a postulated design-basis accident condition is essential for reliable design
evaluations and assessments. Because the properties of concrete change with respect
to time and the environment to which it is exposed, an assessment of the effects of
concrete aging is also important in performing safety evaluations. [14]
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Paulo et al. [3] presented the results of a research program on the behavior of fiber
reinforced concrete columns under fire. Polypropylene fibers were included in the
concrete in order to enhance the fire behavior of the columns and avoid concrete
spalling. Polypropylene fibers under elevated temperatures will create a network of
micro-channels for the escape of the water vapor and the use of polypropylene in
concrete improves the behavior of the columns in fire. Thus, the use of polypropylene
fibers can control the spalling.
Shihada. [15] Investigated the effect of Polypropylene fibers on fire resistance of
concrete. In order to achieve this, three concrete mixtures are prepared using different
percentages of Polypropylene; 0 %, 0.5 % and 1%, by volume. Out of these mixes,
cubes (100 × 100 × 100 mm) in dimension were cast and cured for 28 days. The cubes
were then burned at 200 C°, 400 C° and 600 C°, for 2, 4 and 6 hours for each of the
three temperatures, and tested for compressive strength. Based on the results of the
experimental program, it is concluded when Polypropylene fibers are used in certain
amounts they improve fire resistance of concrete. Furthermore, it is observed that
concrete mixes prepared using 0.5 %, by volume reserve more than 84 % of the initial
compressive strength when burned at 600 C° for 6 hours. On the other hand, samples
prepared using 0 % Polypropylene reserve about 50 % of their initial strength under
the same temperature and duration.
Ali et al. [16] presented the results of a major research executed on high and normal
strength concrete elements. The parametric study investigated the effect of restraint
degree, loading level and heating rates on the performance of concrete columns
subjected to elevated temperatures with a special attention directed to explosive
spalling. The study included a useful comparison between the performance of high
and normal strength concrete columns in fire.
Using polypropylene fibers in the concrete (3 kg/mᶟ) reduced the degree of spalling
from 22% to less than 1% .Also the study illustrated a method of preventing explosive
spalling using polypropylene fibers in the concrete.
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Hodhod et al. [17] investigated the effect of different coating types and thicknesses on
the residual load capacities of reinforced concrete loaded columns when subjected to
symmetrical temperature rise up to 650 C° for 30 minutes. Seventeen RC column
specimens with concrete cover of 1.0 cm and a specimen dimensions (100 mm x150
mm x700 mm) were cast and reinforced with 4Ö6 mm longitudinal reinforcement
bars and 7 Ö 3.5 mm stirrups equally distributed along the length.
Five different types of coating were used in this study; namely traditional-cement
plaster, perlite-cement, vermiculite-cement, LECA-cement and perlitegypsum. Three
different thicknesses of 1.5, 2.5 and 3.5 cm were used.
Every column specimen was equipped with eight thermocouples to measure the
temperature distributions in side the specimen at mid height. An electric furnace has
been used in this work. Every specimen was exposed to the simultaneous effect of the
axial service load and temperature of 650 Cº for 30-minutes period. The readings of
applied loads and thermocouples were recorded at 5-minuts interval. Testing the
columns after cooling to obtain their residual axial load capacity showed that, perlite
proves to be the most effective plaster in increasing the loaded columns resistance to
elevated temperature. Specimens coated with vermiculite cement came in the second
place. Specimens coated with LECA-cement came in the third place. Finally,
specimens coated with traditional-cement came in the last place.
Hertz and Sørensen. [18] discussed a new material test method for determining
whether or not an actual concrete may suffer from explosive spalling at a specified
moisture level. The method takes into account the effect of stresses from hindered
thermal expansion at the fire-exposed surface. Cylinders are used for testing the
compressive strength. Consequently, the method is quick, cheap and easy to use in
comparison to the alternative of testing full-scale or semi full-scale structures with
correct humidity, load and boundary conditions. A number of concretes have been
studied using this method, and it is concluded that sufficient quantities of
polypropylene fibers of suitable characteristics may prevent spalling of a concrete
even when thermal expansion is restrained.
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Jau and Huang. [19] investigated the behavior of corner columns under axial loading,
biaxial bending and a symmetric fire loading. They concluded that, under a
longitudinal stress ratio of 0.10 f`c the residual strength ratios of the columns after fire
loading show:
(a) The 2 and 4 hours fire loadings resulted in residual strength ratios of 67% and
57%, respectively. Compared with unheated columns a 10% reduction on residual
strength results as the duration changes from 2 to 4 hours;
(b) Increasing the thickness of concrete cover caused lower residual strength ratios.
It was also found that the temperature distribution across the cross-section was not
affected by concrete cover thickness. The residual strengths can be used for future
evaluation, repair and strengthening.
Chen et al. [20] investigated the compressive and splitting tensile strengths of
concretes cured for different periods and exposed to high temperatures. The effects of
the duration of curing, maximum temperature and the type of cooling on the strengths
of concrete were also investigated. Experimental results indicated that after exposure
to high temperatures up to 800 C°, early-age concrete that was cured for a certain
period can regain 80% of the compressive strength of the control sample of concrete.
The 3-day-cured early-age concrete was observed to recover the most strength. The
type of cooling also affected the level of recovery of compressive and splitting tensile
strength. For early-age affected concrete, the relative recovered strengths of
specimens cooled by sprayed water were higher than those of specimens cooled in air
when exposed to temperatures below 800 C°, while the changes for 28-day concrete
were the converse. When the maximum temperature exceeded 800 C°, the relative
strength values of all specimens cooled by water spray were lower than those of
specimens cooled in air.
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Chen et al. [2] they studied an experimental research on the effect of fire exposure
time on the post-fire behavior of reinforced concrete columns. Nine reinforced
concrete columns (45 mm x 30 mm x 300 mm) with two longitudinal reinforcement
ratios (1.4% and 2.3%) were exposed to fire for 2 and 4 hours with a constant preload.
One month after cooling, the specimens were tested under axial load combined with
uniaxial or biaxial bending. The test results showed that the residual load-bearing
capacity decreased with increasing fire exposure time. This deterioration in strength
which is followed by an increase in fire exposure time can be slowed down by the
strength recovery of hot rolled reinforcing bars after cooling. In addition, the
reduction in residual stiffness was higher than that in ultimate load; consequently,
much attention should be given to the deformation and stress redistribution of the
reinforced concrete buildings subject to earthquakes after afire.
Komonen and Penttala. [21] investigated the effect of high temperature on the
residual properties of plain and polypropylene fiber reinforced Portland cement paste.
Plain Portland cement paste having water/cement ratio of 0.32 was exposed to the
temperatures of 20, 50, 75, 100, 120, 150, 200, 300, 400, 440, 520, 600, 700, 800, and
1000 C°. Paste with polypropylene fibers was exposed to the temperature of 20, 120,
150, 200, 300, 440, 520, and 700 C°. Residual compressive and flexural strengths
were measured. The gradual heating coarsened the pore structure. At 600 C°, the
residual compressive capacity (fc600 C°/fc20 C°) was still over 50% of the original.
Strength loss due to the increase of temperature was not linear. Polypropylene fibers
produced a finer residual capillary pore structure, decreased compressive strengths,
and improved residual flexural strengths at low temperatures. According to the tests, it
seems that exposure temperatures from 50 C° to 120 C° can be as dangerous as
exposure temperatures 400500 C° to the residual strength of cement paste produced
by a low water cement ratio.
Sideris et al. [22 ] studied the mechanical characteristics of Fiber Reinforced Concrete
subjected to high temperatures . Fiber reinforced concrete is produced by addition of
Polypropylene fibers in the mixtures at dosages of 5 kg/m³. At the age of 120 days,
specimens are heated to maximum temperatures of 100, 300, 500 and 700 C°.
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Specimens are then allowed to cool in the furnace and tested for compressive strength.
Residual strength is reduced almost linearly up to 700 C°. The study recommended
the use polypropylene fibers as part of a total spalling protection design method in
combination with other materials such as external thermal barriers. Otherwise the
overall thickness of the concrete members should be increased to provide a sacrificial
layer who will be removed after fire in order to efficiently repair the structure
2.8-Performance of reinforcement in fire The performance of steel during a fire is understood to a higher degree than the
performance of concrete, and the strength of steel at a given temperature can be
predicted with reasonable confidence. It is generally held that steel reinforcement bars
need to be protected from exposure to temperatures in excess of 250-300 Cº. This is
due to the fact that steels with low carbon contents are known to exhibit blue
brittleness between 200 and 300 Cº. Concrete and steel exhibit similar thermal
expansion at temperatures up to 400 Cº; however, higher temperatures will result in
significant expansion of the steel com pared to the concrete and, if temperatures of the
order of 700 Cº are attained, the load-bearing capacity of the steel reinforcement will
be reduced to about 20% of its de sign value. Bond failure may be important at high
temperatures, as discussed in section Physical and chemical response to fire.
Reinforcement can also have a significant effect on the transport of water within a
heated concrete member, creating impermeable regions where moisture may become
trapped. This forces the water to flow around the bars, increasing the pore pressure in
some areas of the concrete and therefore potentially enhancing the risk of spalling. On
the other hand, these areas of trapped water also alter the heat flow near the
reinforcement, tending to reduce the temperatures of the internal concrete [8].
2.9- Effect of Fire on Steel Reinforcement
Ünlüoðlu et al. [23] investigated the mechanical properties of steel reinforcement bars
after the exposure to high temperatures. Plain steel, reinforcing steel bars embedded
into mortar and plain mortar specimens were prepared and exposed to 20 C°, 100 C°,
200 C°, 300 C°, 500 C°, 800 C° and 950 C° temperatures for 3 hours individually. A
concrete cover of 25 mm provides protection against high temperatures up to 400 C°.
The high temperature exposed plain steel and the steel with 25-mm cover has the
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same characteristics when the reinforcing steel is exposed to a temperature 250 C°
above the exposure temperature of plain steel.
Mamillapalli.[6] investigated the impact of the elevated temperatures on
reinforcement steel bars by heating the bars to 100° C°, 300 C°, 600 C°, 900 C°. The
heated samples were rapidly cooled by quenching in water and normally by air
cooling. The changes in the mechanical properties are studied using universal testing
machine (UTM). The impact of elevated temperature above 900 C° on the
reinforcement bars was observed.
There was significant reduction in ductility when rapidly cooled by quenching. In the
same case when cooled in normal atmospheric conditions the impact of temperature
on ductility was not high.
Topҫu and IºIkdag. [24] investigated the mechanical properties of reinforcement
steel bars after exposure of elevated temperatures. The mortar was prepared with
CEM I 42.5N cement and fired clay. The S 420a, B16 mm ribbed steel bars were used
to prepare (56 x 56 x 290) mm, (76 x 76 x 310) mm, (96 x 96 x 330) mm and (116 x
116 x 350) mm specimens with concrete covers of (20, 30, 40 and 50) mm against
elevated temperatures up to 800 Cº. The reinforcement steel bars were embedded in
mortars, and then specimens were exposed to 20, 100, 200, 300, 500 and 800 Cº
temperatures for 3 hours, individually. After the cooling process, the specimens were
cured for 28 days. The mechanical tests were conducted on cooled specimens, and the
ultimate tensile strength, yield strength and elongation of mortar specimens at various
temperatures were also determined at the end of the experiments. It is observed that a
cover of 20, 30, 40 and 50 mm thickness provides a protection to rebar in exposure of
high temperatures. The cover reduces the losses in yield and tensile strengths of rebar
and ensures 15% higher strength compared to rebar without cover. For temperatures
up to 300 C°, rebar with cover had the same yield and tensile strengths with that of
the rebar without cover in exposure to elevated temperatures. However, when the
temperature increases up to 800 C°, the rebar without cover loses an average of 80%
of its strength capacities compared with a 20% loss for the rebars with cover. It was
observed that 20, 30, 40 and 50 mm cover thickness was not sufficient to protect the
mechanical properties of rebars in exposure of temperatures above 500 C°.
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2.10- Effect of Fire on Fiber Reinforced Polymers (FRP) columns
Kodur et al. [25] presented the results of a full-scale fire resistance experiments on
three insulated FRP-strengthened reinforced concrete reinforced concrete columns. A
comparison was made between the fire performances of FRP-strengthened RC
columns and conventional unstrengthened reinforced concrete columns.
Data obtained during the experiments is used to show that the fire behavior of FRP-
wrapped concrete columns incorporating appropriate fire protection systems was as
good as that of unstrengthened RC columns. Thus, satisfactory fire resistance ratings
for FRP-wrapped concrete columns could be obtained by properly incorporating
appropriate fire protection measures into the overall FRP-strengthened structural
systems. Fire endurance criteria and preliminary design recommendations for fire
safety of FRP-strengthened RC columns were also briefly discussed. The performance
of protected FRP-strengthened square RC columns at high temperatures can be
similar to, or better than, that of conventional RC columns.
Chowdhurya et al. [26] demonstrated that fiber-reinforced polymers (FRPs) could be
used efficiently and safely in strengthening and rehabilitation of reinforced concrete
structures. In there study they were presented the recent results of an experimental
study of the fire performance of FRP-wrapped reinforced concrete circular columns.
The results of fire tests on two columns were presented, one of which was tested
without supplemental fire protection, and one of which was protected by a
supplemental fire protection system applied to the exterior of the FRP-strengthening
system. The primary objective of these tests was to compare fire behavior of the two
FRP-wrapped columns and to investigate the effectiveness of the supplemental
insulation systems.
The thermal and structural behaviors of the two columns were discussed. The results
show that, although FRP systems are sensitive to high temperatures, satisfactory fire
endurance ratings could be achieved for reinforced concrete columns that were
strengthened with FRP systems by providing adequate supplemental fire protection.
In particular, the insulated FRP-strengthened column was able to resist elevated
temperatures during the fire tests for at least 90 minutes longer than the equivalent
uninsulated FRP-strengthened column.
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EXPIRIMINTAL PROGRAM����
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Experimental Program����
3.1- Introduction
The experimental program consists of fire endurance tests. These tests will examine
the effect of high temperatures on reinforced concrete columns and testing their
compressive strength. The program consist of 3 types of small scale reinforced
concrete columns (100 mm x 100 mm x 300 mm) ,one type of specimens is free from
polypropylene and the other two types contain 0.5 kg/m³ and 0.75 kg/m³ of
polypropylene fibers , samples of this group have the same concrete cover (2.0 cm).
The samples will be tested at (ambient temperature, 400 C°, 600 C° and 800 C°) at
(0, 2, 4 and 6 hours) exposure. The other groups have a concrete cover of 3.0 cm and
will be tested at 600 C° for 6 hours to determine the behavior of RC column with
deferent concrete covers at high temperatures.
In addition, the behavior of steel reinforcement under high temperature 800 C°, with
different concrete covers (0 cm, 2 cm, and 3 cm) is tested.
3.2-Materials and Their Quality Tests:
It is very important to know the properties and characteristics of constituent materials
of concrete, as we know, concrete is a composite material made up of several different
materials such as aggregate, sand, water, cement and admixture. These materials have
properties and different characteristics such as "Unit weight, Specific gravity, size
gradation and water content ... etc". .
We must therefore work out necessary tests on these components, and that to know
the unique characteristics and their impact on the strength of concrete.
The necessary tests are conducted in the laboratory of materials and soil in the Islamic
University and in accordance with ASTM "American Society for Testing and
Materials".
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3.2.1-Aggregate Quality Tests.��
3.2.1.1- Unit Weight of Aggregate:��
Unit weight ( ) can be defined as the weight of a given volume of graded aggregate.
It is thus a measurement and is also known as bulk density, but this alternative term is
similar to bulk specific gravity, which is quite a different quantity, and perhaps is not
a good choice. The unit weight effectively measures the volume that the graded
aggregate will occupy in concrete and includes both the solid aggregate particles and
the voids between them. The unit weight is simply measured by filling a container of
known volume and weighting it based on ASTM C 566 [27].
However, the degree of compaction will change the amount of void space and hence
the value of the unit weight.
Table.3.1: Capacity of Measures
Capacity of
Measure (Liter)
Max.Aggregate��
Size (mm)
2.8 12.5��
9.3 25��
14��37.5��
28 75
The sample shall be in oven dry condition and the capacity of measures are shown in
Table (3.1), the molds of unit weight test for coarse and fine aggregate are shown in
Fig (3.1).
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Fig.3.1: Mold of Unit Weight test [IUG-Lab]
The unite weights of coarse and dine aggregate are shown in Table (3.2).
Table 3.2: Unit weight test results��
Dry unit weight 1444.00 kg/ m3���Coarse aggregate
SSD unit weight 1460.4 kg / m3���
Dry unit weight 1440.00 kg/ m3���Fine aggregate sand
SSD unit weight 1445.40 kg / m3�
3.2.1.2- Specific Gravity of Aggregate:
The density of the aggregates is required in mix proportioning to establish weight -
volume relationships. The density is expressed as the specific gravity. Specific gravity
is defined as the ratio of the weight of a unit volume of aggregate to the weight of an
equal volume of water. Specific gravity expresses the density of the solid fraction of
the aggregate in concrete mixes as well as to determine the volume of pores in the
mix.
Specific Gravity (S.G) = (density of solid) / (density of water)
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Since densities are determined by displacement in water, specific gravities are
naturally and easily calculated and can be used with any system of units. The specific
gravity tested for coarse and fine aggregate are shown in Fig (3.2).
The specific gravity of aggregate is to determine the volume of aggregates in a
concrete mix as well as to determine the volume of pores in the mix based on ASTM
C127 and ASTM C128 [28,29].
Fig.3.2: Specific Gravity test equipments [IUG-Lab].
The specific gravity of coarse and fine aggregate is shown in Table (3.3).
Table.3.3: Specific gravity of aggregate
Bulk (Gs) SSD 2.63��
Bulk (Gs) dry 2.55 Coarse aggregate
Apparent Bulk (Gs) 2.632
Bulk (Gs) SSD 2.16
Bulk (Gs) dry 2.15 Fine aggregate sand
Apparent Bulk (Gs) 2.17
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3.2.1.3- Moisture content of Aggregate: ��
Since aggregates are porous (to some extent), they can absorb moisture. However, this
is a concern for Portland cement concrete because aggregate is generally not dry and
therefore the aggregate moisture content will affect the water content and thus the
water-cement ratio also of the produced Portland cement concrete and the water
content also affects aggregate proportioning (because it contributes to aggregate
weight), based on ASTM C127 and ASTM C128 [28,29].
The moisture content values of coarse and fine aggregate are shown in Table (3.4).
Table.3.4: Moisture content values��
Coarse aggregate 2.8 %
Fine aggregate Sand 0.994 %
3.2.1.4-Resistance to Degradation by Abrasion & Impaction test. ��
The Los Angeles test is a measure of aggregate resulting from a combination of
actions including abrasion, impact, and grinding in a rotating steel drum containing a
specified number of steel spheres. The Los Angeles test has a wide use as an indicator
of aggregate quality, shown in Fig (3.3), based on ASTM C131 [30].
The charge shall consist of steel spheres averaging approximately 46.8 mm in
diameter and each weighing between 390 and 445 g, details are shown in Table (3.5).
Abrasion Loss shall be not more than 50%.
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Fig.3.3: Los Angeles test (Abrasion) Machine. [30]
The charge, depending on the grading of the test sample, shall be as follows:
Table.3.5: Number of steel spheres for each grade of the test sample
Grading Number of Spheres Weight of Charge, g
A 12 5000 +/- 25
B 11 4584 +/- 25
C 8 3330 +/- 20
D 6 2500 +/- 15
A 12 5000 +/- 25
% Abrasion Loss = ( Woriginal Wfinal ) / Woriginal * 100
Original weight = 5000 gm
Final weight = 3977.8 gm
Abrasion = (5000 - 3977.8 / 5000) * 100 = 20.44 % < 50 % OK.
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3.2.1.5-Sieve Analysis of Aggregate:
The size of aggregate particles differs from aggregate to another, and for the same
aggregate the size is different. So in this test we will determine the particle size
distribution of fine and coarse aggregate by sieving. This method is used to determine
the compliance of the aggregate gradation with specific requirements, ASTM C136
[31].
Table (3.6) and Fig (3.4) illustrate the results of sieve analysis test for coarse and fine
aggregate.
Table 3.6 : sieve analysis of aggregate
SIEVE SIZE Wt. % Retained % Passing
NO. size ( mm ) Retained,(gm)
1.5" 37.5 0 0.00 100.00
1" 25 350 4.71 95.29
3/4" 19 2092.5 28.18 71.82
1/2" 12.5 3122.5 42.05 57.95
3/8" 9.5 3727.5 50.20 49.80
# 4 4.75 4797.5 64.61 35.39
# 10 2 192.3 27.32 27.55
# 16 1.18 293.5 41.69 22.11
# 30 0.6 390.1 55.41 16.90
# 40 0.425 456.9 64.90 13.31
# 50 0.3 492.9 70.01 11.37
# 100 0.125 562.4 79.89 7.63
# 200 0.075 638.5 90.70 3.53
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��- ASTM C136 maximum and minimum limits for aggregate size distribution .
Sieve 1.5" 1" 3/4" # 4 # 200
Passing 100% 75 - 100 60 - 90 30 - 65 5.0 - 10
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��Sieve Analysis Curve��
0
10
20
30
40
50
60
70
80
90
100
0.01 0.1 1 10 100 Dia. (mm)
% P
assi
ng
Test Sample
ASTM Min Limit
ASTM Max Limit
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Fig 3.4 : Sieve Analysis of Aggregate
3.2.1.6-Cement: ��
The cement type which was used for this research is Portland Cement EN 197-1
CEM I 42,5 R & EN 197-1 CEM I 42,5 N " produced in Turkey , and the properties
of cement met the requirement of ASTM C 150 specifications. Table (3.7)
summarizes the properties of this cement [32].
Table.3.7: Ordinary Portland cement properties "Test Results"
No. Description Sample Results Specification ASTM C-150
1- Normal Consistency 27 %
2-
Setting Time
1-Initial Setting (min)
2-Finial Setting (min)
100
165
>45
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3.2.1.7-Water: Drinking water was used in all concrete mixtures and in the curing all of the test
samples.
3.2.1.8-Polypropylene Fibers (PP):
Polypropylene is a plastic polymer that was developed in the middle of the 20th
century. Over the years, polypropylene has been used in a number of applications,
most notably as fiber for carpeting and upholstery for furniture and car seats.
Polypropylene has also make an industrial revolution with the plastics industry,
providing an inexpensive material that can be used to create all sorts of plastic
products for the home and office, recently become widely used in the construction
industry, in order to enhance fire resistance concrete. Table (3.8) shows the property
of polypropylene fibers used in this research work, and Fig (3.8) shows the shape of
the used sample.
Table 3.8: Properties of Polypropylene fibers
Fig. 3.5:Polypropylene Fibers
Property Polypropylene Unit weight (kg/m³) 0.9 0.91 Tensile strength (MPa) 400 Fiber Length(mm) 3 - 19 Melting point (Cº) 170-160 Thermal conductivity (w/m/k) 0.12 Density: ( kg/m³) 0.91 kg/m3
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3.3- Mix Proportions��
Concrete consists of different ingredients. The ingredients have their different
individual properties. Strength, workability and durability of the concrete depend
heavily on the concrete mix ration of the individual ingredients. Since the process of
concrete formation is a unidirectional chemical reaction, concrete gets its different
properties all together. In this research work, three mixes for different contents of PP
(0 kg/m³, 0.5 kg/m³ and 0.75 kg/m³) were used.
Design Requirements�
1- Characteristic cube concrete strength (cube) fc' 300 kg/cm²
2- Max water cement ratio (w/c) 0.56
3- Minimum cement content 350 kg/m³
4- Max Aggregate Size 3/4" (20mm) crushed limestone aggregate
The following tables (Table 3.9) illustrate the mix design of the column samples.
Table.3.9: mix design of the concrete column samples
��
Weight per one cubic meter kg/m3
Materials Mix 1 Mix 2 Mix 3
Cement 350�� 350 350
Water 196 196 196
Coarse aggregate 1092�� 1092 1092��
Fine aggregate sand 728 728�� 728
Polypropylene PP�� 0.00 0.5 0.75
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3.4-Sample Categories:
All columns samples were fabricated to satisfy the requirements of ACI 211.1 code;
the samples are 100 mm x 100 mm, and 300 mm in dimensions. The main
reinforcement steel bars are 4Ô10 mm, 25 cm in length, and 3 stirrups Ô 6 mm in
diameter Fig (3.6).
The total number of reinforced concrete samples will be 123 samples.
30 c
m
10 cm
Y10 mm
main reinforcement
Y6 mm
For stirrups
Fig.3.6: Dimension and Reinforcement Details of Samples.
The total number of concrete columns samples was 123 samples, and the samples
were categorized and distributed according to the following factors:
1- A mount of polypropylene fibers PP (0 kg/m³, 0.5 kg/m³ and 0.75 kg/m³).
2- According to concrete cover thickness ( 2 cm , 3cm )
3- According to time of heating (0, 2, 4 and 6 hours).
4- According to degree of temperature (0, 400, 600 and 800 Cº).
The following tables (Table.3.10, Table.3.11, Table.3.12, Table.3.13, and Table.3.14)
illustrate the samples categories:
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RC Concrete Samples Category
Table.3.10: Concrete without PP and cover 2.0 cm
������������
��Temperature Time (hrs) Total��Room Tempt 400 C°��600 C° 800 C°
3 3��0 0 0 0
9 0 3 3 3 2
9 0 3 3 3 4
9 0 3 3 3 6
������������
Total No. of samples = 30 ������
Table.3.11: Concrete with 0.5 Kg/m³ PP and cover 2.0 cm
������������
��Temperature Time (hrs) Total��Room Tempt 400 C°��600 C° 800 C°
3��3��
0