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EFFECT OF COMPRESSIVE STRESS IN CONCRETE ON
ULTRASONIC PULSE VELOCITY
Chong Chooi Yeng
Bachelor of Engineering with Honours
(Civil Engineering)
2010
THE EFFECT OF COMPRESSIVE STRESS IN
CONCRETE ON ULTRASONICS PULSE
VELOCITY
CHONG CHOOI YENG
Thesis is submitted to
Faculty of Engineering, University Malaysia Sarawak
In Partial Fulfillment of the Requirements
For the Degree of Bachelor of Engineering
With Honors (Civil Engineering)
2010
APPROVAL SHEET
This project report which entitled ―The effect of compressive stress in concrete on ultrasonic
pulse velocity,’’ was prepared by Chong Chooi Yeng (16099) is hereby read and approved
by:
Prof Dr. Ng Chee Khoon Date
Project Supervisor
UNIVERSITI MALAYSIA SARAWAK
R13a
BORANG PENGESAHAN STATUS THESIS
Judul: THE EFFECT OF COMPRESSIVE STRESS IN CONCRETE ON ULTRASONIC PULSE
VELOCITY
SESI PENGAJIAN: 2009/2010
Saya CHONG CHOOI YENG
(HURUF BESAR)
mengaku membenarkan tesis * ini disimpan di Pusat Khidmat Maklumat Akademik, Universiti Malaysia
Sarawak dengan syarat-syarat kegunaan seperti berikut:
1. Tesis adalah hakmilik Universiti Malaysia Sarawak.
2. Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat salinan untuk
tujuan pengajian sahaja.
3. Membuat pendigitan untuk membangunkan Pangkalan Data kandungan Tempatan.
4. Pusat khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat salinan tesis ini
sebagai bahan pertukaran antara institusi pengajian tinggi.
5. ** Sila tandakan ( √ ) di kota yang berkenaan
SULIT (Mengandungi maklumat uang berdarjah keselamatan atau kepentingan
Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972).
TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/ Badan di mana penyelidikan dijalankan).
TIDAK
TERHAD
Disahkan oleh
(TANDATANGAN PENULIS) (TANDATANGAN PENYELIA)
Alamat tetap:
LOT 1298/135, JLN SEROJA 22,, PROF DR. NG CHEE KHOON
TMN TAN CHEE HOE, Nama Penyelia
70450 S’BAN, N.S.DK..
Tarikh: Tarikh:
CATATAN * Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah, Sarjana dan Sarjana Muda.
** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan
menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT dan TERHAD.
Acknowledgement
In preparing this thesis, I wish to express my sincere appreciation to my
supervisor, Professor Dr. Ng Chee Khoon for encouragement, guidance, critics and
friendship. I’m also thankfully to my families especially to my mother and father for
their support and motivation. Without their continued support and interest, this thesis
would not have been the same as presented here.
I’m also indebted to librarians at UNIMAS and Technicians at UNIMAS of
structure laboratory for their assistance in supplying the relevant literature and helping to
conduct the laboratory testing.
And my fellow course mates, who have provided assistance at various occasion.
Their help either directly or indirectly in this project. Their views and tips are useful
indeed.
Abstract
Keywords: Non-destructive testing methods, Ultrasonic pulse velocity method,
Concrete, Strength, Stress
This report presents a study on the effect of incremental compressive stress in concrete
on the measured ultrasonic pulse velocity (UPV). In this study, a total of 60 cube
samples were made from four different grades of mix proportions, which is grades 25,
30, 35 and 40. The cubes test was supposedly to be carried out at age 28 days. Due to the
PUNDIT equipment breakdown, thus the tests were carried out at age 60 days. The
specimens were subjected to monotonic axial loading in stages until failure while UPV
values were recorded. Changes in the amplitude, velocity, and frequency contents of the
pulses were correlated to the increasing levels of stress. Results show that the
dramatically change of UPV values for concrete specimen under incremental loading for
grades 25 and 30 happen at 0.30 stress/strength ratio. Grade 35 concrete shows decrease
in UPV values. Whereas, the grade 40 concrete having a increased of UPV values
throughout the test. The test of stress/strength ratio only can be carried out in 0.35 and
0.30 for grade 35 and 40 respectively. This is due to the limitation of the hydraulic jack.
Abstrak
Projek ini adalah bertujuan untuk mengaji kesan daripada tegasan mampatan terhadap
konkrit dengan menggunakan teknik ultrasonic pulse velocity (UPV). Dalam pengkajian
ini, sebanyak 60 biji kiub konkrit sampel telah diacuan dengan gred yang berlainan, iaitu
gred 25, 30 35 dan 40. Sepatutnya, sampel konkrit kiub ujian dijalankan pada hari ke-28
dari masa konkrit diacuan. Disebabkan, mesin UPV tidak berfungsi terpaksalah kiub
ujian ini ditundakan pada hari ke- 60. Data UPV dicatatkan selepas specimen menjalani
transformasi monotoni beban paksi sehingga kiubnya mencapai kegagalan. Perubahan
amplitud, halaju dan frekuensi pulse adalah berkolerasi dengan penambahan tekanan.
Hasil daripada graf menunjukkan UPV mengalami perubahan mendadak bagi specimen
kiub konkrit gred 25 dan 30 pada 0.30 stress/strength ratio.Penurunan UPV dicatatkan
bagi konkrit gred 35. Manakala, konkrit gred 40 mencatatkan penambahan UPV
sepanjang kiub ujian dijalankan. Ujian stress/strength ratio hanya dapat dilaksanakan
pada 0.35 dan 0.30 bagi gred 35 and 40 masing-masing. Ini adalah disebabkan had limit
pada hydraulic jack.
TABLE OF CONTENTS
Page
DEDICATION i
ACKNOWLEDGEMENTS ii
ABSTRAK iii
ABSTRACT iv
CONTENTS v
LIST OF TABLES vii
LIST OF FIGURES ix
LIST OF ABBREVIATIONS AND NOTATIONS xi
CHAPTER 1 INTRODUCTION
1.1 General 1
1.2 Aim and objective 2
CHAPTER 2 LITERATURE REVIEW
2.1 Ultrasonic pulse velocity in concrete under
compressive stress
3
2.2 Factor affecting the ultrasonic pulse velocity in
stress free concrete
10
CHAPTER 3 METHODOLOGY
3.1 Instruments
3.1.1 Ultrasonic’s Pulse Velocity Test
Equipment
12
3.1.2 Test Frame 15
3.2 Test Method
3.2.1 Test program 17
3.2.2 Testing Procedure 18
3.3 Schedule 19
CHAPTER 4 RESULTS, ANALYSIS AND DISCUSSION
4.1 UPV values of stress-free concrete 21
4.2 Effect of compressive stress on UPV values 22
CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS
5.1 Review of work done 32
5.2 Major Finding 33
5.3 Recommendations 34
Appendix A
Table A-1 : Detail results for grade 25 concrete
35
Table A-2 : Detail results for grade 30 concrete 36
Table A-3 : Detail results for grade 35 concrete 37
Table A-4 : Detail results for grade 40 concrete 38
References 39
LIST OF TABLES
Table Title Page
2.1 Relation of ultrasonic pulse velocity to concrete
quality
10
3.1 Concrete mix 18
4.1 Average measured concrete strength and
measured UPV of test cubes under stress-free
condition
22
A-1 Detail results for grade 25 concrete 35
A-2 Detail results for grade 30 concrete 36
A-3 Detail results for grade 35 concrete 37
A-4 Detail results for grade 40 concrete
38
LIST OF FIGURES
Figure Title Page
2.1 Reduction in transverse wave velocity with
increase in stress
6
2.2 Effect of compressive stress on the ultrasonic pulse
velocity of concrete cubes at 28 days
7
2.3 Typical compressive stresses against transverse
ultrasonic pulse velocity relationship for a
concrete. The dashed line shows the conceived
relationship represented by the experimental data
(points); the solid line is a computer approximation
9
2.4 Variation of strength and pulse velocity with age of
concrete
11
3.1 PUNDIT 14
3.2 Test set up for transducers 14
3.3 Test Frame 15
3.4 Hydraulic jacks 16
3.5 Test set up 16
3.6 Project Schedule 20
4.1 Strength Vs UPV at 60 days for grade 25 concrete 27
4.2 Strength Vs UPV at 60 days for grade 30 concrete 28
4.3 Strength Vs UPV at 60 days for grade 35 concrete 29
4.4 Strength Vs UPV at 60 days for grade 40 concrete 30
4.5 Strength Vs Average UPV at 60 days for grades
25, 30, 35 and 40 concrete
31
Chapter 1
Introduction
1.1 General
Ultrasonic pulse velocity test is known as a non-destructive test method for
measuring the total time taken for longitudinal waves of pulse travel from one
transmitting transducer to another receiving transducer. There was a need for the present
research to develop a testing method for evaluating the properties of concrete in
structure, in relation to the in situ concrete under compressive stress.
1.2 Aim and Objectives
The main aim of the test was to examine the effect of compressive stress in
concrete on ultrasonic pulse velocity. The test was carried out to examine the effect of
compressive stress in lateral direction only. The aim of the test is to proved that the
increase in compressive stress has significant effect on the ultrasonic pulse velocity
value due to the progressive cracking during the compression test, where micro cracks
start to propagate in the concrete at stress as low as about 25% of the concrete strength,
which reduced the measurement of pulse velocity .
In order to achieve the main aim, the following objectives are defined:
i) Determine the design mix for different types of concrete used in the test.
ii) Determine the effect of concrete grade on ultrasonic pulse velocity of stress
free
concrete.
iii) Determine the ultrasonic pulse velocity in concrete with incremental compressive
stress.
Chapter 2
Literature Review
2.1 Ultrasonic pulse velocity in concrete under compressive stress
Based on the report by Hsu and Slate (1963), very fine cracks at the interface
between coarse aggregate and cement paste exist prior to application of load on the
concrete.These micro cracks were stable up to the state of stress of 0.30 stress/strength
ratio after which they begin to increase in length, width and number (Slate and Hover,
1984).
The presence of stresses in the concrete would reduce the ultrasonic pulse in it, at
least under initial loading. For the fact that micro cracks start to propagate in the
concrete at loading as low as 25% of the ultimate load, and this may reduce the
ultrasonic pulse velocity (Brandtzaeg, 1927,Hsu et al ,1963, Propovics,1969). However,
the ultrasonic pulse velocity does not change significantly if the internal compressive
stress is within 40% of the ultimate compressive strength of concrete
(Vivithkeyoonvong, 1992). Randomness of crack propagation in concrete under load
was not a factor in the non-responsiveness of pulse velocity to stress in concrete
(Popovics, 1990).
From the experimental results the pulse velocity of test concrete specimen (100mm
x 200mm) cylinder was independent of the stress level to a surprisingly large extent of
about 70% of the stress strength ratio. In this test, the ultrasonic pulse velocity was
tested in lateral direction (Popovics, 1991). Hence, this indicates that when pulse
velocity data were used for the evaluation of the quality of concrete, the stress in the
concrete of a structure do not have to be taken into account. Beside that, during the
loading the apparent modulus of elasticity of the concrete was reduced and micro cracks
were developed too. However, the ultrasonic pulse velocity cannot be affected directly
because it is too narrow for the pulse to produce any effect.
The axial pulse was found to increase slightly at the beginning of load application,
apparently because of better transducer contact and the closure of crack or voids due to
the applied compressive stress. Only a marginal decrease in the axial velocity at the peak
stress was observed. This can be expected, as crack growth would predominantly be
parallel to the axis of the specimen.
The elastic properties of the concrete started to degrade significantly, at
approximately 75% of the concrete strength. This shows that the stress level has reached
the nonlinear portion of the stress-strain curve. At peak, the measurement of pulse
velocity was difficult. This is due to the great reduction of the signal amplitude.
Although, formation of micro cracks was started at low stress levels (less than 0.30
stress strength ratio), but the degradation of the elastic properties of concrete started at a
later stage when macroscopically the material departs from its linear range. Due to the
sharp increase in the curvature of the stress-strain diagram—between 0.75 and 0.9 stress
strength ratios, the linear range has been characterized. The acute increase in that range
of axial load is shown in the lateral strain as shown Figure 2.1 (Carnot and Kaspar 2001)
Figure 2.1: Reduction in transverse wave velocity with increase in stress (Carnot and
Kaspar 2001)
In a separate investigation by Ng and Ngu (2009), ultrasonic pulse velocity dropped
dramatically after 0.25 of the stress-strength ratio as shown in Figure 2.2. It can be
assumed that at stress/strength ratio of more than 0.25, the compressive stress in
concrete has significant effect on the measured ultrasonic pulse velocity.
Therefore, due to the increment of compressive stress, it is expected that the micro
cracking propagation and the ultrasonic pulse velocity would gradually decrease with
increasing compressive stress. It is expected that due to the closing of some of the
cracking with unloading, the ultrasonic pulse velocity in the unloaded state would be
greater than the loaded state. Hence, studied need to be carried out to make clear for
these effects (Ng and Ngu 2009).
Figure 2.2: Effect of compressive stress on the ultrasonic pulse velocity of concrete
cubes at 28 days (Ng and Ngu 2009).
Observation for compressive, tensile and other loading need to be further studied.
In order, confirm with the gradual development of micro cracking in concrete under
compression, further investigation need to be carried out. For cubes in compression, the
ultrasonic pulse velocity in the direction of loading remains constant as the load is
increased to failure. In the transverse direction, the pulse velocity decreases as the load
3.0
3.5
4.0
4.5
5.0
0 10 20 30 40 50
Stress-strength ratio (%)
Ultra
sonic
puls
e v
elo
city,
UP
V (
km
/s)
a
Grade 25
Grade 30
Grade 35
Grade 40
is less than the ultimate and further decreases in the velocity will occur as the load is
increased to failure (Figure 2.3). Based on the contradiction and observation to concrete,
the volume change of hardened cement paste under load was related to the presence of
aggregate particles. The micro crack in concrete between the interface of coarse
aggregate and mortar exist before they are subjected to any external load. These bond
crack seem chiefly to be a result of differential volume changes of matrix and aggregates
during hydration and drying as well of bleeding and segregation. The weakening effect
of the interface has been proved directly, at least in normal-strength concrete where the
hardened paste is weaker than the aggregates. The bond cracks begin to increase in
length, width and in number with increasing strain at above about 30% of the ultimate
compressive load, while the crack in the mortar remain negligible. Generally, the bond
cracks begin to develop in the larger aggregate particles. This implies that with increases
in maximum particle sizes, by the same time the strength of the comparable concrete
should be decreased. At around 70 % to 90 % of the ultimate load, crack through the
mortar or aggregate particles begin to increase and continuous crack pattern by bridging
the near by bond crack can be noticed (Popovic, 1998).
Pu
lse
velo
city
(in
/µ s
ec)
Stress (psi)
Figure 2.3: Typical compressive stresses against transverse ultrasonic pulse
velocity relationship for a concrete. The dashed line shows the conceived
relationship represented by the experimental data (points); the solid line is a
computer approximation .1 ksi = 6.9 MPa, 1 in. /µsec = 25,400 m/s (Popovics
and Popovics, 1991)