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DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT

Author’s full name : Oh Teck Yee Date of birth : 09 April 1982 Title : The Effect of Surface Roughness and Curing Condition on The Ultimate Shear Capacity of Composite Slab Academic Session : 2009/2010 I declare that this thesis is classified as : I acknowledged that Universiti Teknologi Malaysia reserves the right as follows:

1. The thesis is the property of Universiti Teknologi Malaysia. 2. The Library of Universiti Teknologi Malaysia has the right to make copies for the purpose

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Date : 04 November 2009 Date :

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(full text)

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820409-05-5212 Dr. Izni Syahrizal Ibrahim

“I declare that I have read through this project report and to my opinion this report is adequate in term of scope and quality for the purpose of awarding the degree of

Master of Engineering (Civil – Structure)”

Signature : _______________________

Name of Supervisor : DR. IZNI SYAHRIZAL IBRAHIM

Date : _______________________

THE EFFECT OF SURFACE ROUGHNESS AND CURING CONDITION ON THE ULTIMATE SHEAR CAPACITY OF COMPOSITE SLAB

OH TECK YEE

A project report submitted in partial fulfillment of the requirement for the award of the degree of Master of Engineering (Civil – Structure)

Faculty of Civil Engineering Universiti Teknologi Malaysia

November, 2009

ii

I declare that this project report entitled “The Effect of Surface Roughness and Curing Condition on The Ultimate Shear Capacity of Composite Slab” is the result of my own research except as cited in the references. The report has not been accepted for any degree and is not concurrently submitted in candidature of any degree.

Signature : _______________________

Name : OH TECK YEE

Date : 04th NOVEMBER 2009

iii

Specially dedicated to my beloved parents and husband.

iv

ACK�OWLEDGEME�T

I have a host of people to thank for their involvement in this major work. The

order in which they are mentioned does not necessarily represent the amount of work

they did.

Major thanks to my supervisor, Dr. Izni Syahrizal Ibrahim, who always there

to provide me guidance and honest feedback on my project. His patience and

immeasurable contribution is the key to generate this project, I would have not

completing my thesis without him.

Huge thanks to Mr. Lee Sid Hwa, Mr. Oh Teck Huat, Mr. Teo, Ms.Teo Mei

Choo, Alex and all the technicians of civil engineering laboratory for their assistance

in the casting and set up of the test frame and instrumentation.

I would also like to express my deepest gratitude to the Universiti of

Teknologi Malaysia (UTM) for providing the necessary experimental facilities and

materials.

Deep appreciation to my dear husband, Kian Wei, my parents and siblings, I

would not get very far without their support and love. They are my QA teams and my

brainstorming teams who always provide inspiring ideas on my work done.

Last, thanks are due to the people that I do not mention their name for their

assistance and encouragement.

v

ABSTRACT

This thesis presents the effect of surface roughness and curing condition on

the horizontal shear capacity of precast slabs with in-situ concrete toppings. When

the composite member is loaded and bent in flexure, they will tend to slide relatively

to each other. In the case where mechanical shear key in the form of reinforcement is

not provided at the interface of the precast units, the texture at the interface becomes

a major parameter to ensure the horizontal shear strength of the contact surfaces is

achieved. Furthermore, the effect of concrete toppings under air cured and water

cured conditions were investigated due to the practical difficulties in achieving even

the minimum specified curing on-site. The experimental results of eight (8) precast

units with different surface roughness (smooth, roughened and exposed aggregates)

under four point bending test is presented. Interface slip was also measured

throughout the test to examine the composite behavior of the composite slabs. Based

on the findings, smooth surface produced the highest ultimate shear capacity in water

cured condition i.e. 19% - 34% higher than the others. However, rough surface in

transverse direction yielded the highest ultimate shear capacity under air cured

condition. The tests had clearly shown the effect of difference surface roughness and

curing condition to the ultimate shear capacity. Large slip of between 1.0 and 1.3 mm

was also observed for the specimen under air cured condition, indicating water cured

produce better interface bond. Furthermore, comparison of the experimental shear

strength with BS 8110 and Eurocode 2 shows that even the as-cast surface can

develop adequate shear resistance. Thus, shear reinforcement is not an essential

requirement and the production of precast slabs can be simplified.

vi

ABSTRAK

Tesis ini membincangkan kesan kekasaran permukaan dan kaedah

pengawetan terhadap tegasan ricih mengufuk untuk papak pratuang dengan konkrit

tuang di-situ. Secara umumnya, papak rencam bergelangsar sesama sendiri di bawah

lenturan. Kekasaran permukaan unit pratuang memainkan peranan penting untuk

menjayakan tegasan ricih mengufuk di antara permukaan sentuh itu apabila tetulang

ricih tidak dipasangkan. Tambahan pula, kesan konkrit tuang di-situ di bawah

pengawetan basah dan kering juga turut dikaji memandangkan kesukaran untuk

dicapai di tapak bina. Maka, semua faktor-faktor ini akan dikaji dan pengaruh

terhadap tegasan ricih mengufuk papak rencam yang diakibatkan oleh kekasaran

permukaan berserta dengan cara pegawetan dibincangkan dalam tesis ini. Sejumlah

lapan (8) papak rencam dengan kekasaran permukaan yang berlainan (licin, dedahan

batu, kasaran melintang dan kasaran panjang) dan cara pengawetan yang berbeza

(basah dan kering) dibandingkan dalam kajian ini. Gelinciran di antara komponen

turut diukur sepanjang eksperimen dijalankan. Keputusan ujikaji menunjukkan

permukaan licin dengan pengawetan air menghasilkan kekuatan ricih yang paling

tinggi, 19% - 34% lebih tinggi berbanding dengan permukaan kasar. Manakala,

keupayaan permukaan kasar melintang adalah lebih baik berbanding dengan

permukaan licin dalam pengawetan kering. Hasilan ini membuktikan bahawa

kekasaran permukaan dan cara pengawetan yang berlainan akan menghasilkan

kekuatan ricih yang berbeza. Gelinciran di antara 1.0 dan 1.3 mm telah diperolehi

untuk spesimen di bawah pengawetan kering, menunjukkan pengawetan basah

menghasilkan ikatan antara muka yang lebih baik. Tambahan pula, tegasan ricih

mengufuk yang diperolehi dalam ujikaji eksperimen adalah lebih tinggi berbanding

dengan tegasan yang dinyatakan dalam BS 8110 dan Eurocode 2. Dengan itu, dapat

disimpulkan bahawa tetulang ricih bukanlah suatu keperluan dalam pembinaan

papak rencam.

vii

TABLE OF CO�TE�TS

CHAPTER TITLE PAGE

DECLARATIO� ii

DEDICATIO� iii

ACK�OWLEDGEME�T iv

ABSTRACT v

ABSTRAK vi

TABLE OF CO�TE�TS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF �OTATIO�S xv

1 I�TRODUCTIO�

1.1 Background 1

1.2 Problem Statement 2

1.3 Objectives 4

1.4 Scopes of Study 4

1.5 Importance of Study 5

1.6 Thesis Structure 5

2 LITERATURE REVIEW

2.1 Introduction 6

2.2 Shear Capacity of the Interface 6

2.2.1 Surface Roughness 8

2.2.2 Previous Work Related to Surface 9 Roughness

2.2.3 International Codes of Practice on 13 Interface Shear Strength

viii

2.2.4 Previous Work Related to Interface 14 Shear Strength

2.3 Curing Condition versus Shrinkage Problem 17

2.3.1 Previous Work Related to Curing 19 Technique

2.4 Summary 22

3 EXPERIME�TAL METHODOLOGY

3.1 Introduction 23

3.2 Test Specimens 24

3.2.1 Surface Roughness 26

3.3 Specimens Preparation and Casting Procedure 28

3.3.1 Casting of Precast Slab Specimen 28

3.3.2 Casting of Concrete Toppings 30

3.4 Curing Techniques 31

3.4.1 Water Cured 31

3.4.2 Dry Cured 32

3.5 Combined Bending and Shear Test 32

3.5.1 Testing Procedure 34

3.6 Flow Chart of the Research Methodology 34

4 EXPERIME�TAL RESULTS

4.1 Introduction 35

4.2 Concrete Topping Properties and Interface Texture 35

4.3 Test Results 36

4.3.1 Load versus Deflection Relationship 37

4.3.1.1 Water Cured Specimens 37

4.3.1.2 Air Cured Specimens 39

4.3.2 Load versus Interface Slip Relationship 40



4.3.3 Load versus Strain Relationship 47



ix

4.3.4 Cracking Pattern 52

5 A�ALYSIS & DISCUSSIO�

5.1 Introduction 55

5.2 Shear Force and Deflection Relationship 55

5.3 Interface Shear Stress and Interface Slip 58

Relationship

6 CO�CLUSIO� A�D RECOMME�DATIO�

6.1 Conclusion 63

6.2 Recommendation 64

LIST OF REFERE�CES 65

APPE�DIX A – Determination of Pult 67

APPE�DIX B – Calculation of Vu 68

APPE�DIX C – Calculation of Vco 69

APPE�DIX D – Concrete Mix Design 70

APPE�DIX E – Calculation of Shear Strength, �� 72

x

LIST OF TABLES

TABLE �O. TITLE PAGE

2.1 Investigated Test Parameters 11

2.2 Surface Treatment of the Composite Beam 12

2.3

c and � Factors Depending on the Roughness at the Interface

14

3.1 Mix Proportions Design for Specimens 25

3.2 Specimen Details and Test Parameters 27

4.1 Specimen Description and Concrete Properties at Test Day

36

4.2 Water Cured Specimen Shear Test Result 38

4.3 Air Cured Specimen Shear Test Result 40

5.1 Comparisons of Test Results with Vco and Vu 58

5.2 Interface Shear Strength Result 61

xi

LIST OF FIGURES

FIGURE �O. TITLE PAGE

1.1 Interface Shear Stress of Composite Member 2

1.2 Precast Slab with Extruded Shear Key 2

2.1

Measuring Device for Measuring Surface Roughness

8

2.2 Arithmetical Mean Deviation of the Profile, Ra

8

2.3 Specimen Details 10

2.4 Schematic Diagram of Experimental Setup 10

2.5 Test Specimens 12

2.6 Intended Construction Joint 13

2.7 Transformed Uncracked Section 15

2.8 Transformed Cracked Section 15

2.9

Typical Shear Pattern in Test Beams Bent in Flexure

16

2.10 Schematic Diagram of “Push-off” Method 16

2.11 Schematic Diagram of Ideal Curing of Concrete

18

2.12 Concrete Strength with Moisture Present for Curing

18

2.13 Substrate bodies with sandblasted interfaces (S1-S4)

20

2.14 Smooth Interfaces 21

2.15 Notched Interfaces 21

xii

3.1 Dimension of Precast Slabs 24

3.2 BRC Installed in Concrete Topping 25

3.3 Air Hammer Hand Tool 26

3.4 Difference Surface Roughness of the Precast Slab

27

3.5 Concrete Drum Mixer with 0.3m3/cast 29

3.6 Fresh Precast Slab after Casting 29

3.7 Optimum Wet Surface prior to Placement of Topping

30

3.8 Cross Section of the Specimen with Concrete Topping

30

3.9 Specimen Water Cured with Burlap 31

3.10 Combined Bending and Shear Test Setup 32

3.11 Position of Demec Pips attached to Specimens

33

3.12 Demec Gauge 33

3.13 Flow Chart of the Research Methodology 34

4.1 Load vs. Deflection Relationship for Water Cured Specimens

38

4.2 Load vs. Deflection Relationship for Air Cured Specimens

39

4.3(a) Load vs. Interface Slip for Specimen Smooth-A up to 1mm

41

4.3(b) Load vs. Interface Slip for Specimen Exposed-A up to 1 mm

41

4.3(c) Load vs. Interface Slip for Specimen Rough-LD-A up to 1 mm

42

4.3(d) Load vs. Interface Slip for Specimen Rough-TD-A up to 1 mm

43

4.4(a) Load vs. Interface Slip for Specimen Smooth-B up to 1 mm

44

xiii

4.4(b) Load vs. Interface Slip for Specimen Exposed-B up to 1 mm

44

4.4(c) Load vs. Interface Slip for Specimen Rough-LD-B up to 1 mm

45

4.4(d) Load vs. Interface Slip for Specimen Rough-TD-B up to1 mm

46

4.5(a) Load vs. Strain Relationship for Specimen Smooth-A

47

4.5(b) Load vs. Strain Relationship for Specimen Exposed-A

47

4.5(c) Load vs. Strain Relationship for Specimen Rough-LD-A

48

4.5(d) Load vs. Strain Relationship for Specimen Rough-TD-A

48

4.6(a) Load vs. Strain Relationship for Specimen Smooth-B

49

4.6(b) Load vs. Strain Relationship for Specimen Exposed-B

50

4.6(c) Load vs. Strain Relationship for Specimen Rough-LD-B

50

4.6(d) Load vs. Strain Relationship for Specimen Rough-TD-B

51

4.7(a) Shear Cracking Pattern at Failure for Specimen Smooth-A

52

4.7(b) Shear Cracking Pattern at Failure for Specimen Exposed-A

52

4.7(c) Shear Cracking Pattern at Failure for Specimen Rough-LD-A

52

4.7(d) Shear Cracking Pattern at Failure for Specimen Rough-TD-A

52

4.7(e) Shear Cracking Pattern at Failure for Specimen Smooth-B

53

4.7(f) Shear Cracking Pattern at Failure for Specimen Exposed-B

53

xiv

4.7(g) Shear Cracking Pattern at Failure for Specimen Rough-LD-B

53

4.7(h) Shear Cracking Pattern at Failure for Specimen Rough-TD-B

53

5.1(a) Shear Force vs. Deflection Relationship for Water Cured Specimens

56

5.1(b) Shear Force vs. Deflection Relationship for Air Cured Specimens

57

5.2(a) Interface Shear Stress vs. Interface Slip Relationship for Water Cured Specimens up to 1 mm

59

5.2(b) Interface Shear Stress vs. Interface Slip Relationship for Air Cured Specimens up to 1 mm

60

xv

LIST OF �OTATIO�S

Icomp Second moment are of the composite section

bi Width of the interface

bw , bv Width of the concrete topping

beff Effective width

Scomp First moment of area above and about the centroidal axis

ft Concrete splitting tensile strength

fcp Concrete compressive stress at the centroidal axis due to prestressing

fy Characteristic strength of reinforcement

fck Cylinder compressive strength of concrete = 0.8fcu

fcu , fcc Cube compressive strength of concrete

p Ratio of tensile reinforcement

w Uniform load distribution

d Effective depth of the tension reinforcement

L Effective span length

a Shear span

x Neutral axis

z Lever arm of composite action

yt Distance from the neutral axis of the composite section to half of concrete topping depth

ht Concrete topping depth

ys Distance from the neutral axis of the composite section to the steel centroid

As Area of tension reinforcement

xvi

As’ Area of compression reinforcement

A Compression zone being considered

A’ Effective area under normal compressive stress

Mur Design ultimate bending moment

Vu , Vult Ultimate shear capacity

Vds Transverse shear force

Vco Design ultimate shear capacity of a uncracked flexure section

�� Normal compressive stress

�� Stress per unit area

sn Imposed slip displacement during the cycle

su Shear slip corresponding to maximum mobilized shear stress

�,� Frictional stress response to the nth cycle

�� Design shear stress at the interface

�� Design shear resistance at the interface

�� Experimental shear stress

CHAPTER 1

I�TRODUCTIO�

1.1 Background

Reinforced concrete is concrete in which steel reinforcement bars have been

incorporated to give it extra tensile strength. It can be further classified into cast in-

situ concrete or precast concrete. Precast concrete is cast and cured in a controlled

environment. It is then transported to the construction site and lifted into position. In

contrast, precast concrete is having higher standard compare to cast in-situ concrete.

Apart from the quality, precast concrete system offers faster erection speed when

compared to normal reinforced concrete construction. Erection is carried out with the

aid of lifting equipments.

There are many different types of precast concrete forming systems

including slabs, walls, beams, columns, foundations, etc. However, main focus is

given to floor systems as this is the key to creating optimal building structures.

Difference in floor systems may have significant impact on construction schedule

and materials cost. Precast concrete flooring offers an economic and multitalented

solution to ground and suspended floors in any types of building construction. In

order to enhance the structural performance, cast in-situ toppings are added to the

precast slab. This composite member is designed to act monolithically. Hence,

understanding the behavior of monolithic action of composite member has become a

topic of particular challenge to researchers throughout the world recently.

1.2 Problem Statement

The principle of composite construction can be demonstrated by comparing

the action of two joists placed one on top of the other. When the precast

concrete toppings is bent in flexure, the composite members tend to slide to e

other as shown in Figure 1.1.

Figure 1.1: Interface Shear Stress of Composite Member

If these composite

key, the bending strength and stiffness will be significantly improved. Nevertheless,

reliance has to be made on the shear strength and bond between the contact surfaces

without any mechanical

Figure

Problem Statement


the action of two joists placed one on top of the other. When the precast

bent in flexure, the composite members tend to slide to e

Figure 1.1.

: Interface Shear Stress of Composite Member

these composite members are physically connected using mechanical shear


made on the shear strength and bond between the contact surfaces

shear key.

Figure 1.2: Precast Slab with Extruded Shear Key

2


the action of two joists placed one on top of the other. When the precast unit with

bent in flexure, the composite members tend to slide to each

: Interface Shear Stress of Composite Member

mechanical shear


made on the shear strength and bond between the contact surfaces

3

Normally, the need for reinforcement across the interface will depend upon several

factors: type of surface texture, the loading or geometry of the construction [6]. In the

case where joint surface area is having the same area as the topping, it is referred as

low shear area at the interface, where the force can be transmitted without shear key

as long as adequate interlocking effects are available.

In designing the interface to ensure composite action, several Codes of

Practice [2,5,6] have considered surface roughness as the major factor contributing to

limiting stresses for different roughness categories. Some attempts to enumerate

surface texture are given in the FIP document [6]. The general types of surface texture

are smooth and rough. Within the FIP Commission itself, they believe smooth

interfaces have better bonding effects compared to the roughened. The design

guidance is still lack of congruency especially at the serviceability limit state.

Other than surface texture, surface preparations may cause problems and

affect the monolithic behaviour of the composite member. According to the research

work carried out by Walraven [16], the precast slab surface preparation will affect the

capacity of the interface shear strength. This includes reductions to the interface

shear strength and lead to occurrence of interface slip.

The other common problem associated with concrete industry is cracking

problem. The most common causes of cracks in concrete are: stress due to applied

loads or stress due to drying shrinkage or temperature changes. Stress cracks can be

easily eliminated by having proper concrete design for the load. However, drying

shrinkage is an inescapable and inherent property of the concrete. To minimize these

cracks, proper curing to hold the moisture is obligatory. As long as the moisture in

concrete is trapped for certain period, and that adequate tensile strength is allowed to

gain in concrete for this particular period, the concrete is unlikely to shrink [1].

Two major parameters will be focused in this study i.e. surface texture of the

precast slab and the curing technique applied for the concrete topping. The effect of

these parameters on the interface shear strength shall be examined.

4

1.3 Objectives

The objectives of this study are as follows:

(i) To study the structural performance of composite slab with different surface roughness

(ii) To evaluate the interface shear strength of the composite slab for different curing condition

(iii) To compare the experimental shear stress result with the minimum horizontal shear stress provided in BS 8110 and Eurocode 2

1.4 Scopes of Study

The endeavor of this project is to study the interface shear strength between

the 100 mm thickness precast solid slab and 75 mm thickness concrete toppings with

different surface roughness and curing conditions. A total number of eight precast

units will be prepared in this study. The performance of these specimens will be

assessed through the shear capacity and load-deflection relationships of the

composite slabs under the combined bending and shear test.

Since the precast concrete slab surface is not provided with any shear

mechanical key, the texture of the interface of the precast units becomes the key

parameter for determining the interface shear strength of the composite members. It

is vital to study what kind of surface can produce better bond at the interface.

Therefore, eight composite slabs with four different types of surface roughness

(smooth as-cast, roughened in both the longitudinal and transverse direction, and

surface with exposed aggregate) were prepared.

It is obvious that curing method affect significantly the performance expected

from specified water/cement ratio and cement content. In reality, it is always difficult

to cure concrete satisfactorily due to some practical problems especially when the

surface area is large. Hence, the concrete toppings of these eight specimens shall be

5

further categorized into two curing conditions i.e. air cured and water cured. Air

cured represents the actual poor curing practice at construction site and the effect on

the shear strength in lieu to this condition will be studied. Meanwhile, all the precast

slab units will be water cured as practiced by the manufacturer.

In the combined bending and shear test, a pair of point loads was applied at

1.5H from the support at both ends, where H is the overall depth of the composite

slab. The interface slip of the longitudinal joints will be monitored throughout test.

1.5 Importance of Study

The study is intended to determine the most suitable casting method

according to different surface characteristic and curing conditions. Appropriate

casting method may reduce the remedial work due to delamination, loss of

serviceability or curvature problem associated with concrete toppings. By improving

the composite performance, the overall construction cost and maintenance cost can

be reduced.

1.6 Thesis Structure

The structure of this thesis is as shown below: (a) Chapter 2 describes a review of the literature on the subject of this project

(b) Chapter 3 presents the preparation work for the specimens and the experimental

setup for combined bending and shear test

(c) Chapter 4 interpret the experimental results

(d) Chapter 5 presents the analysis and discussion of the results

(e) Chapter 6 presents the conclusions and the recommendations for further

investigation

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

For full composite action of the precast slab with concrete topping, the shear

and bond strength of the interface between the two elements are critical. Various

international codes of practice recommend different allowable interface shear

strengths depending on the surface characteristics. Whereas, the relationship between

shear, surface roughness and bond strengths of interfaces in different composite

concrete structures have been investigated by many researchers in the previous

studies. The results and findings shall be discussed in detail in the following sections.

2.2 Shear Capacity of the Interface

To retain the continuity and efficiency of monolithic construction, composite

construction is the most cost-effective way of combining precast and cast in-situ

concrete. The monolithic behavior is possible only if the horizontal shear is

effectively transferred between the topping and precast slab at their interface. When

the composite member is bent in flexure, they tend to slide with each other

respectively. For ensuring the horizontal strength is achieved, shear connector is

provided at the interface to transfer the force and act as an interlocking device. In the

case where no mechanical key is provided, reliance has to be made on the bond and

shear strength between the contact surfaces.

7

In 1991, Ueda and Stitmannaithum [15] conducted an experimental program to

investigate the shear-carrying capacity of precast prestressed hollow core slabs

(HCU) with concrete topping. Ten specimens were prepared and the study parameter

includes pre-stressing force, tension reinforcement ratio, shear span-to-effective-

depth ratio and the concrete topping depth. In their experimental investigation, two

types of shear cracking were observed; web shear cracking and flexural shear

cracking. In the prediction of ultimate shear capacity, reference was made to the

formula proposed by Niwa [11] for ordinary reinforced concrete beams (a/d < 2.5) and

the modified formula proposed by Okamura et. al. [12] for ordinary reinforced

concrete slender beams (a/d > 2.5) without shear reinforcement. These formulas are

given as:

�� = 0.244��1 + !" #1 + 3.33 %

� & ''(#)

*&� +%, if (a/d < 2.5) (2.1)

�� = 0.20��-�(100!)

-�(1000/,)

-1(0.75 + '.4

)*

)+%, if (a/d > 2.5) (2.2)

They observed in their tests complete composite action although only rough

surface finishing was provided. Small slips were measured between the precast and

topping concrete elements, and there was no evidence that the interface was an

initiator of ultimate failure. For both the thick and thin concrete topping, web shear

cracking always took place in the precast element at the level of the hollow where the

narrowest web width was found. Because of the circular hollow, the highest principle

tensile stress – resulting from the combination of shear stress and flexural stress due

to the external applied load, as well as the compressive stress due to the effective

prestressing force – can be found at the narrowest web instead of that of the

centroidal axis depth. The comparison between the calculated and experimental

results shows good agreement. Ueda [15] suggested that the equations used to

calculate the ultimate shear capacity for ordinary reinforced concrete beams without

shear reinforcement can also be applied to the HCU with concrete toppings by using

the strength of the concrete toppings and its width in the prediction.

2.2.1 Surface Roughness

In the FIP Guide to Good Practice (FIP 1982)

surface roughness in which a precast unit may have prior to

concrete toppings. They were categorized based on the end production and there is

no clear guidance to differentiate between

Nevertheless, FIP Commission it

better overall bonding than rough surfaces. According to Swedish Standard

measuring device as shown in Figure 2.1 is use

a member. The measuring device shall be

and the gauge is read. The measurement procedure is based on procedure given in

BS1134 [3]. The roughness amplitude represented by

deviation of the profile, taking the average value of t

Figure 2.2.

Figure 2.1: Measuring Device for Measuring Surface Roughness

Figure 2.2: Arithmetical Mean Deviation of the Profile,

Surface Roughness

In the FIP Guide to Good Practice (FIP 1982) [6], there are ten categories of

in which a precast unit may have prior to the casting of the


no clear guidance to differentiate between the rough and smooth surface.

Nevertheless, FIP Commission itself believes that smooth interface always provide

better overall bonding than rough surfaces. According to Swedish Standard

measuring device as shown in Figure 2.1 is used to measure the surface roughness of

a member. The measuring device shall be placed along one measured


. The roughness amplitude represented by Ra is the arithmetical mean

deviation of the profile, taking the average value of the surface profile shown in


: Arithmetical Mean Deviation of the Profile, R

8

, there are ten categories of

the casting of the in-situ


rough and smooth surface.

self believes that smooth interface always provide

better overall bonding than rough surfaces. According to Swedish Standard [13], a

to measure the surface roughness of

line at a time


is the arithmetical mean

he surface profile shown in


Ra

9

The departure of the profile is represented by y1 to yn, where n is the number of

profile departures. The equation of Ra given by:

56 = '7 8 9:(;)<,;7

= (2.3) or approximately,

56 ≈ '� ∑ (:@

�@A' )

(2.4) In practice, the values of Ra are determined within the evaluation length which

covers several sampling lengths, l, i.e. equal to the cut-off point. In the work by

Mitchell Gohnert [7], similar roughness measurement was used to determine the

roughness for smooth and rough surfaces. The work shall be further discussed in the

following section.

2.2.2 Previous Work Related to Surface Roughness

In 1987, Theodossius & Elisabeth [14] studied the mechanism of load

transferred along unreinforced concrete interfaces by means of friction for several

surface roughnesses. The behavior of both smooth and rough interfaces of plain

concrete subjected to monotonically or cyclically impose shear displacements was

investigated through several series of tests. Unreinforced concrete blocks of 0.90 m

long x 0.30 m height x 0.15 m wide were cast in metal molds. During concreting,

two grooves with 15 mm deep and 300 mm long were provided at each face of the

specimen. Before testing, the specimens were cracked by splitting. Thus, between

adjacent concrete sub-blocks, two interfaces were formed as shown in Figure 2.3.

The three concrete sub

steel rods, 30 mm in diameter. Schematic

shown in Figure 2.4. The tests were displacement

branch of the shear stress versus shear displacement diagram is obtained. Shear

displacement was imposed by means of mechanical jacks and the re

specimen was measured by using load

experimentally investigated are summarized in Table 2.

Figure 2.4: Schematic Diagram of Experimental Setup

Figure 2.3: Specimen Details

The three concrete sub-blocks were held together by means of four external

steel rods, 30 mm in diameter. Schematic diagram of the experimental setup is as

shown in Figure 2.4. The tests were displacement-controlled so that the falling


displacement was imposed by means of mechanical jacks and the re

specimen was measured by using load-cells. Test parameters

experimentally investigated are summarized in Table 2.1.


10

blocks were held together by means of four external

experimental setup is as

controlled so that the falling


displacement was imposed by means of mechanical jacks and the response of the

which were


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