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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.

To my beloved family and friends

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

LIST OF NOMENCLATURES

UPV - Ultrasonic Pulse Velocity

w/c – water cement ratio

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)