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THE EFFECT OF CONCRETE GRADE IN DETECTING INTERNAL DEFECTS OF CONCRETE BY ULTRASONIC
PULSE VELOCITY METHOD
EDDIE CHUNG CHIE JIN
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UNIVERSITI MALAYSIA SARAWAK
TA 2003 403 E21 2003
Universiti Malaysia Sarawak Kota Samarahan
flc
BORANG PENYERAHAN TESTS
Judul: THE EFFECT OF CONCRETE GRADE IN DETECTING INTERNAL DEFECTS OF CONCRETE BY ULTRASONIC PULSE VELOCITY METHOD
SESI PENGAJIAN: 2000 - 2003
Saya EDDIE CHUNG CHIE JIN (HURUF BESAR)
mengaku membenarkan tesis ini disimpan di Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dengan syarat-syarat kegunaan seperti berikut:
I. Hakmilik kertas projek adalah di bawah nama penulis melainkan penulisan sebagai projek bersama dan dibiayai oleh UNIMAS, hakmiliknya adalah kepunyaan UNIMAS.
2. Naskhah salinan di dalam bentuk kertas atau mikro hanya boleh dibuat dengan kebenaran bertulis daripada penulis.
3. Pusat Khidmat Maklumat Akademik, UNIMAS dibenarkan membuat salinan untuk pengajian mereka. 4. Kertas projek hanya boleh diterbitkan dengan kebenaran penulis. Bayaran royalti adalah mengikut kadar
yang dipersetujui kelak. 5. * Saya membenarkan/tidak membenarkan Perpustakaan membuat salinan kertas projek ini sebagai bahan
pertukaran di antara institusi pengajian tinggi. 6. ** Sila tandakan (J)
11
ý
Lu
SULIT (Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972).
TERHAD (Mengandungi makiumat TERHAD yang telah ditentukan oleh organisasi/ badan di mana penyelidikan dijalankan).
TIDAK TERHAD
_s, ý- (TANDATANGAN PENULIS)
Alamat tetap: 6 I, Lorong Jerrwit Barat 3A,
96000 Sibu,
Sarawak. (Nama Penvelia )
Tarikh: 15 March 2003 Tarikh:
CATATAN " Pat. ng yang tklak berkeoaae. Jiks Kerbs Projek b>f SULIT atau TERHAD, aW lampirkao mat daripada pibak berkuasa/ . rgaobad berkeaaao dengan menyertakan sekaü tempab kertas prajek. Jul parka dikek+akaa sebagal SULIT atau TERHAD.
PW200
Disahkan oleh 11
(TANDA^NGAN LIA)
NORSUZAILINA MOHAMED SUTAN
i
Perakuan Penyelia
Laporan Project Tahun Akhir berikut:
Tajuk: THE EFFECT OF CONCRETE GRADE IN DETECTING INTERNAL
DEFECTS OF CONCRETE BY ULTRASONIC PULSE VELOCITY METHOD
Nama penulis: EDDIE CHUNG CHIE JIN
Matrik: 5168
telah dibaca dan disahkan oleh:
F'
ýq. o3"os
Nors Mohamed Sutan Tarikh Penyelia
11
THE EFFECT OF CONCRETE GRADE IN DETECTING INTERNAL DEFECTS OF CONCRETE BY ULTRASONIC PULSE VELOCITY METHOD
P. KNIDMAT MAKLUMAT AKADEMIK UNIMAS
1111111111111111I I 11111111111 0000118374
EDDIE CHUNG CHIE JIN
Tesis Dikemukakan Kepada Fakulti kejuruteraan, Universiti Malaysia Sarawak Sebagai Memenuhi Sebahagian daripada Syarat Penganugerahan Sarjana Muda
Kejuruteraan Dengan Kepujian (Kejuruteraan Sivil) 2003
ACKNOWLEDGEMENT
I would like to extend my deepest gratitude to my supervisor, Puan Norsuzailina
Mohamed Sutan for her guidance and teaching during the duration of this final year project.
My sincere thanks to Mugilan all Meganathan and Joshua Shukor for their help in
carrying out this project.
Many thanks to Mr. Lam from CMS Concrete for their willingless to supply concrete
for the use of this project.
Lastly, to anyone who had lent a helping hand, either direct or indirectly in this
project. Thank you.
iii
ABSTRACT
Very often internal defects exist in concrete structures, which cannot be detected by
the human eyes. The purpose of this paper is to find out the effectiveness of Ultrasonic Pulse
Velocity Method in detecting internal defects in concrete. Tests were carried out during the
early stages of concrete age, which is during the first 28 days after casting. The approach is
conducted on concrete slabs of two different grades, which are Grade 40 and Grade 25. This
is then compared to see how concrete of different grade influence the accuracy of Ultrasonic
Pulse Velocity in detecting internal defect. The accuracies of UPV obtained foe Grade 25 is
48% to 88% from day 3 to day 28. For Grade 40 concrete, the accuracies of UPV is 66% to
97% from day 3 to day 28.
iv
ABSTRAK
Kerapkali dalam struktur konkrit wujud kecacatan dalaman yang tidak dapat dikesan
oleh mata manusia. Projek tahun akhir ini merangkumi pengesanan kecacatan dalaman
dengan penggunaan Ultrasoni Pulse Velocity. Kejituan pengesanan kecacatan dalaman yang
diperolehi daripada UPV akan dibandingkan dengan kekuatan konkrit dari hari ketiga
sehingga hari keduapuluh lapan. Bagi projek tahun akhir ini, papak konkrit gred 25 dan
konkrit gred 40 telah digunakan dan didapati bahawa kejituan UPV bagi konkrit gred 25
adalah lebih rendah, iaitu dari 48% sehingga 88%. Bagi konkrit gred 40, kejituan UPV ialah
dari 66% sehingga 97%.
V
TABLE OF CONTENTS
Chapter 1 Introduction
1.1 Introduction
1.2 Objective
1
2
Chapter 2 Literature Review
2.1 Concrete Strength 3
2.2 Concrete Grade 4
2.3 Defects in Concrete 5
2.3a Honeycomb 5
2.3b Bleeding 6
2.3c Plastic Settlement 6
2.3d Plastic Shrinkage 7
2.4 Ultrasonic 9
2.4a Nondestructive Testing 10
2.4b Ultrasonic Pulse Velocity Method for Testing Concrete 11
2.4c Usage 21
Chapter 3: Methodology
3.1 Preconcreting
3.2 Concreting
3.3 Post-concreting
22
24
26
vi
3.4 Testing 26
Chapter 4 Results
4.1 Location of X.
4.2 Accuracy of Ultrasonic Pulse Velocity for Each Slabs
4.3 Concrete Cube Test
Chapter 5 Discussion and Conclusion
5.1 Discussion
5.2 Conclusion
30
39
43
44
46
Reference 48
vii
LIST OF TABLES
Table Page
I Pulse Velocity Reading Regarding
to Concrete Quality
2 Design Mix of Concrete
3 UPV Results for Slab 1 Grade 25
4 UPV Results for Slab 2 Grade 25
5 UPV Results for Slab 3 Grade 25
6 UPV Results for Slab 4 Grade 25
7 UPV Results for Slab 1 Grade 40
8 UPV Results for Slab 2 Grade 40
9 UPV Results for Slab 3 Grade 40
10 UPV Results for Slab 4 Grade 40
11 Accuracy of Grade 25 Slabs
12 Accuracy of Grade 40 Slabs
13 Average Accuracy of Grade 25
and Grade 40 Slabs
14 Cube Test Results of Grade 25
and Grade 40 Concrete at 28`h Day
11
24
30
31
32
33
34
35
36
37
39
40
41
43
viii
LIST OF FIGURES
Figure Page
Figure 1 Causes of Honeycomb 5
Figure 2 Cracks in Beam 7
Figure 3 Leakage of Water Due to Crack in Structure 8
Figure 4 Severe Crack in a Bridge Structure 8
Figure 5 Velocity Vs Moisture Content 12
Figure 6 Correlation between Accuracy
and Porosity (GD30) 14
Figure 7 Indirect Method of Determining
the Depth of Defect 16
Figure 8 An easier Indirect Method in
Determining the Depth of Defect 17
Figure 9 Accuracy of UPVM vs Concrete
Age & Correlation with Porosity
for Grade 25, Grade 30 and
Grade 40 18
Figure 10 Types of Materials Used to Prefabricate
Voids in Concrete 20
Figure I1 Attaching styrofoam to a formwork 22
Figure 12 A styrofoam tied to the reinforcement of
the slab 23
ix
Figure13 Illustration of Concrete Slab and its Dimension 23
Figurel4 Casting of Concrete 25
Figure 15 Casting of Concrete Cubes 25
Figure 16 The ELE Portable Unit Nondestructive
Digital Indicating Tester 26
Figure 17 An Indirect Method test was carried
out on a concrete slab 27
Figure 18 Schematic Diagram of Indirectt Method 27
Figure 19 Pulse Velocity Vs Distance 28
Figure 20 Location of Xo for Slab 1 Grade 25 30
Figure 21 Location of X. for Slab 2 Grade 25 31
Figure 22 Location of X. for Slab 3 Grade 25 32
Figure 23 Location of X. for Slab 4 Grade 25 33
Figure 24 Location of X. for Slab I Grade 40 34
Figure 25 Location of X. for Slab 2 Grade 40 35
Figure 26 Location of X. for Slab 3 Grade 40 36
Figure 27 Location of Xo for Slab 4 Grade 40 38
Figure 28 Average Accuracy of UPV for
Grade 40 and Grade 25 Concrete 42
X
LIST OF SYMBOLS
Vd - pulse velocity in the damaged concrete
Vs - pulse velocity in the underlying sound concrete
X. - distance at which the change of slope occurs
Agg - aggregate
xi
CHAPTER 1
INTRODUCTION
1.1 Introduction
The presence of voids in concrete affects the concrete strength and its
durability. Presence of voids increase permeability in the concrete. This is a major
concern if the concrete structure is exposed to sea water and water. This further increase
the degradation in concrete.
Defects in concrete are something that cannot be taken lightly. Strength of a
structure is in question when defects occur in concrete. In a more serious case, it is
going weaken the structure, and the structure might collapse. This is a serious case
especially in bridges, high rise building, flyover and etc. Defects in concrete are usually
due to poor workmanship. This means defect often happens at the early stages of
concreting.
Ultrasonic Pulse Velocity Method (UPVM) is used to detect defects in concrete.
Although UPVM is used for a lot of other purposes, such as determining the strength of
concrete, it can be used to detect the presence of a defect or cavity in concrete and
determining the depth of the defects in the concrete.
I
1.2 Objective
The objective of this final year project is to detect cavity in concrete slabs of
Grade 40 and Grade 25 by using Portable Ultrasonic Non-Destructive Digital Indicating
Tester (PUNDIT). The test is conducted during an interval time of 28 days after casting.
A void is fabricated in concrete slab. Once the slab is casted, PUNDIT is used to
detect the fabricated void in the concrete at day 3,7,14 and 28 days.
The results produced by PUNDIT will then be compare with the grade of the
concrete. It is then determine how concrete grade influences the accuracy of defect
detection in concrete.
2
CHAPTER 2
LITERATURE REVIEW
2.1 Concrete Strength
According to J. M Illston (1994) strength is probably the most important
parameter of concrete. It is usually taken as the highest stress value in a loading test.
For this project, the desired strength is Compressive Strength, which is normally
obtained by cube test. Compressive strength varies between concrete grades. A lower
grade of concrete gives a lower compressive strength, thus a higher grade of concrete
gives a higher compressive strength. A grade 25 concrete has a compressive strength of
25N/mm2 upon 28 days.
The main factor that influences the strength of concrete is porosity. Strength
depends mainly on porosity. The strength of concrete is indirectly proportionate to the
capillary porosity. When concrete hardens, hydration of cement take place, and when
cement hydrates, it expands in volume, thus cover more space. 1 cm3 of cement occupies
about 2cm3 of space when hydrated. This explains the decrease in porosity when
concrete matures with time. When porosity decreases, concrete strength increases.
There are other factors that affect the strength of concrete. There are
water/cement ratio, time, and materials such as cement and aggregates. Of all factors,
water/cement ratio is of great importance regarding concrete strength. Normally, the
3
desired water/cement ratio is 0.4 -0.7. The higher the water cement ratio, the weaker
the concrete.
The influence of time means the age of the concrete. As concrete ages, the
compressive strength increases. This is due to the continuation of hydration of cement.
2.2 Concrete Grade
Concrete grade is usually taken as the crushing strength N/mm2 at 28 days.
Grade 25 concrete means the concrete has crushing strength of 25 N/mm2 at 28 days.
For this final year project, the concrete grade chosen are Grade 25 and Grade 40.
Grade 25 concrete is usually used as reinforced concrete for building structures. Grade
40 concrete is usually used for pretensioned concrete.
The reason those 2 concrete grades are chosen is to compare the accuracy of
Ultrasonic Pulse Velocity between the two grades and to see the significant in the
accuracy.
4
2.3 Defects in Concrete
I
Causes of Honeycomb
III Poor Workmanship Ineflec6He vibration Grout Leakage
while concreting
Figure 1: Causes of Honeycomb
2.3a Honeycomb
Honeycomb is a type of defect usually occurs due to poor workmanship. It
occurs when voids in between aggregates are not filled up by grout. This caused voids
around the aggregates and as the name implies, the void structure looks like
honeycomb.
Causes of honeycomb defects
1. Poor workmanship.
" Main cause of honeycomb is due to poor workmanship during casting of
concrete. Concrete that is not properly vibrated and gaps on formwork is
the common errors occur at the site, which can be easily rectified if care
is taken during concreting. Sometimes reinforcement is too dense to
allow proper vibration.
2. Concrete was not thoroughly vibrated.
5
" Concrete was vibrated during casting to expulse air and to uniformly
distribute the concrete in the formwork. If the concrete is not well
vibrated, segregation of aggregates may occur. When this happens,
segregation of concrete may prevent concrete from filling up all the
space in the formwork, and thus causes honeycomb.
3. Grout leaks from gaps on formwork.
" When there are gaps in formwork, grout leaks out from the gaps, leaving
insufficient grout to fill up the formwork, and thus leaving a substantial
amount of air voids.
Other Defects
Other defects in concrete include bleeding, plastic shrinkage, plastic settlement
and chemical attack.
2.3 Bleeding
" occurs when water in concrete moves upward to the top layer of concrete,
causing a weak structure at the top layer of the concrete.
2.3c Plastic settlement
" movement in fresh concrete causes cracks on the top layer of the concrete.
Cracks may penetrate up to any local restraint such as reinforcement bars.
6
2.3d Plastic Shrinkage
" loss of water at a fast rate causes the top layer of concrete to shrink, this
leaving the top layer in tensile stress zone. This causes cracking at the
surface of the concrete.
Figure 2,3, and 4 shows some of the defects found in structural members.
Figure 2: Crack in a beam (Source: http: //www. mint. gov. my/)
7
Figure 3: Leakage of water due to cracks in structure (Source: http: //www. mint. gov. my)
Figure 4: Severe cracks in a bridge structure (Source: http: /iwww. mint. gov. my)
8
2.4 Ultrasonic
Ultrasonic is vibrating waves at frequencies above the hearing of an average
person. According to Einsminger (1988), the normal hearing frequencies for an average
person is 16 kHz.
Ultrasonic were first developed during World War I, but only in World War II it
gained much interest and was further studied and developed. The best example use of
ultrasonic is in submarine.
To say that ultrasonic were developed during the 20th century will be unfair as
history has shown that the earlier usage of ultrasonic dated back to the 6th century BC
when Pythagoras discovered pitch of strings differs from the length of the strings.
Ultrasonics are used by some animals such as bats, dolphins, birds, dogs and
moths.
Ultrasonic waves are stress waves and because of this, it can only be transmitted
through a medium. They are transmitted from one mass to another mass by close
contact.
Ultrasonic is divided into two groups, low intensity and high intensity. Low
intensity applications are used for nondestructive testing of materials, measurement
of elastic properties of materials, medical diagnosis and livestock judging. High
intensity application is to produce an effect on a material in which the wave is
transmitted. Such applications include medical therapy, atomization of liquids and etc.
9
2.4a Nondestructive Testing
According to Einsminger (1998), Nondestructive testing is the most widely used
ultrasonic method. It is the most used method for low intensity ultrasonic energy. There
are three types of nondestructive testing. There are:
1. Resonance Method
2. Pulse Methods
3. Acoustic emission methods
Pulse method is widely use in terms of nondestructive testing. There are three
types of pulse method. There are:
1. Pulse Echo
" This method uses transducers to emit ultrasonic pulses and then detect the
echo from defects or interfaces
2. Pitch-Catch
" This method operates by using two piezoelectric elements, one emit
ultrasonic pulses, and the other receive the reflected pulse
3. Through Transmission
" This method operates by using two transducers located near each other. The
first transducer emit ultrasonic pulses into a medium until it reaches the
receiving transducer. If there is a defect, there will be a lost of energy, and
this can be represented by a drop in the velocity. This is the method that is
going to be used in this project.
10
2.4b) UPVM for testing Concrete
The measurement of velocity of Ultrasonic Pulse Velocity Method is usually
used to determine the quality of concrete. Based on past research, UPVM is widely use
to monitor the strength of concrete. The frequency usually used for concrete testing is
35 to 100kHz. As concrete cures with time, the velocity increases until it reaches a
constant value.
Some researchers used ultrasonic to determine the quality of concrete.
According to Mikhailov and Radin (1956), the higher the velocity, the better the quality
of the concrete. The results are tabulated at the Table 1 below.
Pulse Velocity (m/s) Concrete Quality
Over 4500 m/s Excellent
4000 to 4500m/s Good
2300 to 4000m/s Acceptable
Less than 2300m/s Very Poor
Table I Pulse Velocity Readings Regarding to Concrete Quality (Source: Mikhailov,
Radin)
A research done by Jones (1956) used ultrasonic to determine the thickness of
the slab and to determine cracks in concrete. The severity of defects in concrete can be
determined as well.
11
