a study on quality control and assurance measures …

A STUDY ON QUALITY CONTROL AND ASSURANCE MEASURES IN USING ASPHALT

by K.W. MAYAKADLMA

DEPARTMENT OF CIVIL ENGINEERING UNIVERSITY OF MORATUWA MORATUWA, SRILANKA.

A STUDY ON QUALITY CONTROL AND ASSURANCE MEASURES IN USING ASPHALT

CONCRETE

by

KEERTHI WIJAYA MAYAKADUWA BSc Eng(Hons), CEng, MIE(SL)

A PROJECT REPORT SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING IN

CONSTRUCTION MANAGEMENT

November 1997

Supervised by Dr. N. D. Gunawardana

6 2 5 . 7 5 2 .

DEPARTMENT OF CIVIL ENGINEERING FACULTY OF ENGINEERING UNIVERSITY OF MORATUWA ^ & %

ABSTRACT

D u r i n g t h e p a s t two d e c a d e s , S r i L a n k a a c h i e v e d r a p i d

i n d u s t r i a l a n d e c o n o m i c d e v e l o p m e n t . The i n c r e a s e d d e v e l o p m e n t

a c t i v i t i e s h a v e c r e a t e d s u d d e n s u r g e on t r a f f i c v o l u m e on r o a d s .

H e n c e , t h e g o v e r n m e n t h a s g i v e n p r i o r i t y t o r o a d d e v e l o p m e n t

p r o g r a m m e s i n w h i c h m o r e t h a n 75% o f t h e r o a d s a r e g o i n g t o b e o v e r

l a i d b y a s p h a l t c o n c r e t e .

I t w a s - o b s e r v e d t h a t , t h e r e c e n t l y l a i d a s p h a l t c o n c r e t e s u r f a c e s r e c e n t l y l a i d by v a r i o u s c o n t r a c t o r s h a v e f a i l e d w i t h i n 5 y e a r s a f t e r c o n s t r u c t i o n . The f a i l u r e o f a b o v e a s p h a l t s u r f a c e s may b e d u e t o v a r i o u s p r o b l e m s a s s o c i a t e d w i t h d e s i g n i n g , m i x i n g , l a y i n g a n d e n v i r o n m e n t a l f a c t o r s d u r i n g s e r v i c e .

T h i s r e s e a r c h w a s c a r r i e d o u t t o i d e n t i f y t h e p r o b l e m s a s s o c i a t e d w i t h a s p h a l t c o n c r e t e s u r f a c e s , t o i n v e s t i g a t e t h e p o s s i b l e c a u s e s o f t h e m a n d t o s u g g e s t b e t t e r q u a l i t y c o n t r o l a n d a s s u r a n c e m e a s u r e s t o e l i m i n a t e t h e a b o v e p r o b l e m s .

U s i n g t h e i n f o r m a t i o n c o l l e c t e d f r o m s i t e i n v e s t i g a t i o n s , p a s t r e s e a r c h p a p e r s , d i s c u s s i o n s , t e x t b o o k s e t c , t h e -main c a u s e s f o r a s p h a l t c o n c r e t e d e f o r m a t i o n s w e r e i d e n t i f i e d a n d c a u s e a n d e f f e c t d i a g r a m w a s d r a w n . The c a u s e s w e r e a n a l y z e d i n m o r e d e t a i l i n r e l a t i o n t o c a u s e a n d e f f e c t d i a g r a m t o make c o n c l u s i o n s a n d r e c o m m e n d a t i o n s .

R e c o m m e n d a t i o n s w e r e made i n r e l a t i o n t o t h e m e t h o d s o f m i x d e s i g n , t y p e a n d q u a n t i t y o f b i t u m e n u s e d f o r p r o d u c t i o n o f a s p h a l t a n d r e m e d i a l m e a s u r e s t o b e t a k e n d u r i n g p r o d u c t i o n a n d l a y i n g a s p h a l t c o n c r e t e .

ACKNOWLEDGEMENTS

I express my deepest gratitude to Dr N.D. Gunawardana who supervised my work, for his guidance, availability throughout, kindness and support.

I wish to express my thanks to all lecturers and batch mates of construction management course for their valuable advices and discussions.

I am grateful to the staff and the workers of materials laboratory and Madampitiya depot of the Colombo Municipal Council for their contribution during this research.

I would like to acknowledge invaluable support given by many organizations specially to Mrs. Judith and the staff of road research laboratory of RDA.

Very special thanks to my wife, mother and father and friends who gave continuous encouragement throughout my study.

TABLE OF CONTENTS Page No

1. INTRODUCTION. 1 1.1 Background. 1 1.2 Objectives. 3 1.3 Methodology. 4

2. CAUSES FOR FAILURES OF ASPHALT CONCRETE SURFACES. 5 2.1 Introduction. 5 2.2 How to make cause and effect diagram. 5 2.3 How to use cause and effect diagram. 6 2.4 Development of cause and effect diagram for

asphalt concrete surfaces. 7

3. THE POSSIBLE CAUSES OF UNSATISFACTORY MIXES. 9 3.1. The effects of mix design procedure. 9

3.1.1. Objectives of mix design. 9 3.1.2. Mix design testing. 9 3.1.3. Mix design methods. 10

3.1.3.1. Marshall method of mix design. 10 3.1.3.2. Haveem method of mix design. 12

3.1.4. Evaluation of Marshall & Haveem mix design procedures. 12

3.2. The effects of bitumen quality & quantity. 14 3.2.1. The influence of bitumen properties

on performance. 14 3.2.2. Bitumen content. 18 3.2.3. The quality of bitumen. 22

3.3. The effects of the grading of aggregates in the mix. 23

3.4. The effects of mixing time. 30

t

4. THE POSSIBLE CAUSES OF EXCESS BITUMEN ON EXISTING SURFACES. 31

4.1. Introduction. 31 4.2. Sand sealing. 31 4.3. Tack coat. 32

Page No 5. THE POSSIBLE CAUSES OF {^BATHER. 33

5.1. t ntrodue ion. 33 5.2. Presence of water. 33 5.3 Hifih Temperature. 35

5.3.1. Permanent deformation at high service temperatures. 35

5.3.2. Fatting up at high service temperature. 39

6. THE POSSIBLE CAUSES OF UNSATISFACTORY BASES. 40 8.1. Introduction. 40 6.2. Strength of bases and sub bases in Colombo. 41 G.3. Non uniform layer thickness. 42

7 . THE POSSIBLE CAUSES OF POOR COMPACTION. 45 7.1. Introduction. 45 7.2. Mix Temperature. 48 7.3. Layer thickness. 46 7.4. Compaction equipment and method of compaction. 47

8 . THE POSSIBLE CAUSES OF ADVERSE TRAFFIC CONDITIONS 53 0.1. Introduction. 53 0.2. Type of loading. 53 0.3. Vehicle speed. 54 8.4. High stresses. 54

9. CONCLUSIONS AND RECOME3ENDATIONS 56 8.1 Conclusions 56 9.2 Recommendations 53

10. REFERENCES 3 0

11. APPENDICES Gi

r

LIST OF TABLES

Table Page No

Table. 3. 1. Marshall design criteria. 11 Table. 3. 2. Haveem method of mix design. 12 Table. 3. 3. Specification for penetration grade bitumen. 15 Table. 3. 4. Hardening of bitumen with age. 17 Table. 3. 5. Selection criteria for bitumen. 22 Table. 3. 6. Aggregate grading & mix design using cold agg. 25 Table. 3. 7. Hot bin gradins & actual agg. blend in B.C. 25 Table. 3. 8. Comparison of job mix (base course). 26 Table. 3. 9. Comparison of job mix (wearing course). 26 Table. 3. 10. Mix design ( Borella- Maradana road ) 27 Table. 3. 11. Difference of aggregate blend percentages. 27 Table. 3. 12. Comparison of job mix (Borella-Maradana). 28 Table. 5. 1. Road surface temperatures. 36 Table. 5. 2. Road survey for fatting up (Bambalapitiya). 37 Table. 5. 3. Road survey for fatting up (Wellawatta). 37 Table. 5. 4. Summery of road survey for fatting up. 38 Table. 5. 5. Weighted values for fatting up. 38 Table. 6. 1. Thickness of core samples. (1) 43 Table. 6. 2. Thickness of core samples 44 Table. 7. 1. Percentage compaction ( Test No 1 ). 48 Table. 7. 2. Percentage compaction ( Test No 2 ). 48 Table. 7. 3. Percentage compaction ( Test no 3 ). 49 Table. 8. 1. Time of loading Vs possible defects. 54

F

LIST OF FIGURES

FIGURE PAGE MO

Figure 2.1. Cause & effect diagram of unsatisfactory 8 asphalt concrete surfaces.

Figure 3.1. Temperature of mix Vs softening point 16

Figure 3.2. Core Sample, Bitumen content 4.85% 20

Figure 3.3. Core sample, Bitumen content 5.0% 20

Figure 3.4. Core Sample, Bitumen content 5.2% 20

Figure 3.5. Core sample, Bitumen content 5.5% 20

Figure 7.1. Positions of core samples collected (Test 1) 47

Figure 7.2. Positions of core samples collected (Test 2) 48

Figure 7.3. Direction of rollers 50

1.0 INTRODUCTION

1.1 BACKGROUND

The natural soil is seldom strong enough to support the repeated applications of wheel loads of vehicles without significant deformation. It is necessary to provide a structure between wheel and soil to improve natural strength of the soil foundation. This structure is called the pavement. The pavement is normally multi layered and in which the quality of the materials decrease with depth.

The two types of pavements used in road construction are rigid pavements and flexible pavements.Modern flexible pavements consist of three main layers, bituminous surfacing, road base and sub base ( sub grade ). The surfacing is generally sub divided into a wearing course and base course, which are laid separately.

Developments of asphalt concrete surfaces had come principally from United States of America. Open textured bituminous materials, using relatively low bitumen contents were developed as base materials in the early 1950"s and followed by the more durable dense mixes introduced in 1960's in U.S.A and U.K. ( Shell Bitumen handbook, 1972 ). In Sri Lanka asphalt concrete was introduced around 1959.

The pavement design is a process of developing the most economical combination of pavement layers ( in relation to both thickness and type of material ), to suit the soil foundation and the cumulative traffic to be carried during the design life. During the past 50 years, many empirical design procedures relating to flexible pavements have been developed. Although much progress has been made, the complex stress / deformation and fatigue properties of road materials make it extremely difficult to develop a viable theoretical method to design flexible pavements ( The asphalt handbook, 1989 ).

1

A road pavement suffers progressive structural deformation from the day it is opened to traffic. The objective of the engineer is to ensure that the degree of deterioration necessitating reconstruction or major structural repair is reached only at the end of the design life. The failure condition is judged in terms of deformation and cracking.

Urban motorways, bearing high traffic density due to their restricted width and always facing maintenance problems are designed for an initial design life of not less than 40 years.

The combined action of weather and traffic, reduces the life of bituminous road surface to a level below that of other civil engineering structures such as dams and bridges. The action of weather may be minimised by the use of " dense " surfacing but, the effect of traffic forces still remains. It is natural therefore to examine the mechanical properties of bituminous materials, particularly of the dense type, in an attempt to determine the properties required to resist mechanical failure under different climatic conditions and under different intensities of traffic.

Bituminous materials can fail mechanically by deformation at high temperatures or by fracture and disintegration, usually at low temperatures. Bituminous materials having a very high resistance to deformation, may well be expensive, difficult to lay and lacking in durability. On the other hand, although it is easy to formulate materials which will be very durable, in the sense that they will not fracture or disintegrate, they may well deform and become smooth. No single test can predict the ability of a material to satisfy the two requirements of continued resistance to deformation and continued resistance to fracture or disintegration.

Separate tests must be made to determine :-a ) , its resistance to deformation, b ) . its flexibility and resistance to fracture, c ) . the effect of weather on these properties.

D u r i n g t h e p a s t t w o d e c a d e s , S r i L a n k a a c h i e v e d r a p i d i n d u s t r i a l

a n d e c o n o m i c d e v e l o p m e n t . The i n c r e a s e d d e v e l o p m e n t a c t i v i t i e s h a s

c r e a t e d s u d d e n s u r g e o n t r a f f i c v o l u m e o n r o a d s a n d a l l a r e

c o n c e r n e d a b o u t t h e c o n d i t i o n o f r o a d s a n d d e l a y s i n t r a n s p o r t .

The g o v e r n m e n t h a s c h a n g e d t h e p r i o r i t y f r o m h o u s i n g d e v e l o p m e n t t o

i n f r a s t r u c t u r e d e v e l o p m e n t i n w h i c h r o a d r e h a b i l i t a t i o n p r o g r a m m e s

s h a r e t h e m a j o r c o m p o n e n t . I n t h e s e r o a d i m p r o v e m e n t p r o g r a m m e s

m o r e t h a n 75% o f t h e r o a d s a r e g o i n g t o b e o v e r l a i d by a s p h a l t

c o n c r e t e a n d t h i s w i l l b e c a r r i e d o u t b y s e v e r a l o r g a n i s a t i o n s o r

c o n t r a c t o r s .

I t w a s o b s e r v e d t h a t , a s p h a l t c o n c r e t e s u r f a c e s r e c e n t l y l a i d b y v a r i o u s c o n t r a c t o r s h a v e f a i l e d w i t h i n 5 y e a r s a f t e r c o n s t r u c t i o n . The f a i l u r e o f a b o v e a s p h a l t s u r f a c e s may b e d u e t o v a r i o u s p r o b l e m s a s s o c i a t e d w i t h d e s i g n i n g , m i x i n g , l a y i n g a n d e n v i r o n m e n t d u r i n g s e r v i c e .

1 . 2 OBJECTIVES

The o b j e c t i v e s o f t h i s r e s e a r c h p r o j e c t a r e ,

1. To i d e n t i f y t h e p r o b l e m s a s s o c i a t e d d u r i n g d e s i g n i n g , m i x i n g , l a y i n g a n d d u r i n g t h e p e r i o d o f s e r v i c e o f a s p h a l t c o n c r e t e m i x e s .

2 . To i n v e s t i g a t e t h e p o s s i b l e c a u s e s f o r t h e a b o v e p r o b l e m s .

3 . To s u g g e s t b e t t e r q u a l i t y c o n t r o l & a s s u r a n c e m e a s u r e s t o

e l i m i n a t e t h e a b o v e p r o b l e m s .

3

. 3 METHODOLOGY

1 ) . L i t e r a t u r e r e v i e w on q u a l i t y a s s u r a n c e

2 ) . I d e n t i f y t h e mode o f f a i l u r e s b y , a ) , s i t e o b s e r v a t i o n s , b ) . t e s t i n g c o r e s a m p l e s .

3 ) . S t u d y on p r e s e n t p r a c t i c e o f a s p h a l t c o n c r e t e m i x d e s i g n

m e t h o d s

4 ) . S t u d y on a s p h a l t p l a n t m i x i n g p r o c e s s .

5 ) . I d e n t i f y t h e c a u s e s o f f a i l u r e s .

6 ) . I d e n t i f y t h e r e m e d i a l m e a s u r e s .

7 ) . Make p r e l i m i n a r y c o n c l u s i o n s a n d d i s c u s s i o n s .

8 ) . C o n c l u s i o n s a n d r e c o m m e n d a t i o n s .

2 . 0 CAUSES FOR FAILURES OF ASPHALT CONCRETE SURFACES.

2 . 1 INTRODUCTION

The result of a process can be attributed to a multitude of factors, and a cause and effect relationship can be found among those factors. Any planning is based upon the concept that effects or events do not occur without a cause. Invariably, cause must precede effect, and cause does not merely assist, but is eminently necessary to produce the effect.

In 1953, Kaoru Isikawa, a professor at university of Tokyo, (Isikawa. K. 1979 ) discovered that a structure or a multiple cause and effect relationship could be found by observing a problem systematically. It was possible to solve complicated problems with multiple causes, using this structure which consisted of a chain of causes and effects. This structure is known as the " Cause and effect diagram " or the " Fish-bone diagram " ( due to its shape ) and is widely used as a management tool in solving practical problems.

2 . 2 . HOW TO MAKE CAUSE AMD EFFECT DIAGRAM

The following procedure could be used to develop a cause and effect diagram.

1. Identify all the relevant factors through examination and discussion with many people

2. Express the characteristic as concretely as possible.

3. Make the same no of cause and effect diagrams as that of characteristics.

4. Choose a measurable characteristic and factors.

5. Discover factors amenable to action.

5

2 . 3 . HOW TO USE A CAUSE AND EFFECT DIAGRAM.

C a u s e a n d e f f e c t d i a g r a m s a r e d r a w n t o c l e a r l y i l l u s t r a t e t h e

v a r i o u s c a u s e s a f f e c t i n g p r o d u c t q u a l i t y , b y s o r t i n g o u t a n d

r e l a t i n g t h e c a u s e s . T h e r e f o r e , a g o o d c a u s e a n d e f f e c t d i a g r a m i s

t h e o n e t h a t f i t s t h e p u r p o s e , a n d t h e r e i s n o s i n g l e d e f i n i t e

f o r m . The i m p o r t a n t t h i n g i s t h a t t h e y f i t t o e a c h p u r p o s e a n d

t h e r e a r e s e v e r a l w a y s o f u s i n g t h e m .

The a d v a n t a g e s i n u s i n g c a u s e a n d e f f e c t d i a g r a m a r e :

1. M a k i n g a c a u s e a n d e f f e c t d i a g r a m i s e d u c a t i o n a l i n i t s e l f .

2 . A c a u s e a n d e f f e c t d i a g r a m i s a g u i d e f o r d i s c u s s i o n

3. The c a u s e s a r e s o u g h t a c t i v e l y a n d t h e r e s u l t s a r e w r i t t e n i n on t h e d i a g r a m .

i

4 . I t a s s i g n s i m p o r t a n c e t o e a c h f a c t o r o b j e c t i v e l y on t h e b a s i s o f d a t a .

A 5 . D a t a a r e c o l l e c t e d w h i l e d r a w i n g a c a u s e a n d e f f e c t d i a g r a m .

6 . C a u s e a n d e f f e c t d i a g r a m i s c o n t i n u o u s l y i m p r o v e d w h i l e u s i n g i t .

7 . A c a u s e a n d e f f e c t d i a g r a m s h o w s t h e l e v e l o f t e c h n o l o g y .

8 . A c a u s e a n d e f f e c t d i a g r a m c a n b e u s e d f o r a n y p r o b l e m .

6

2 . 4 DEVELOPMENT OF CAUSE AND EFFECT DIAGRAM FOR ASPHALT CONCRETE

SURFACES.

S e v e r a l v i s i t s w e r e made t o a s p h a l t p l a n t s i t e s , m a t e r i a l l a b o r a t o r i e s , a n d t o a s p h a l t l a y i n g s i t e s , d i s c u s s i o n s w e r e made w i t h t h e p e o p l e who w e r e i n v o l v e d i n a s p h a l t c o n c r e t e w o r k , s e v e r a l s u r f a c e s i n s e r v i c e w e r e o b s e r v e d , I n f o r m a t i o n w e r e c o l l e c t e d f rom t e x t b o o k s , m a g a z i n e s , r e s e a r c h p a p e r s e t c , a n d my p a s t e x p e r i e n c e i n a s p h a l t c o n c r e t e c o n s t r u c t i o n s w a s u s e d t o i d e n t i f y t h e f a c t o r s w h i c h c a u s e a s p h a l t c o n c r e t e d e f o r m a t i o n s .

The f o l l o w i n g f a c t o r s w e r e i d e n t i f i e d a s t h e m a i n p o s s i b l e f a c t o r s :

1. U n s a t i s f a c t o r y m i x e s . 2 . P o o r c o m p a c t i o n .

3. A d v e r s e t r a f f i c c o n d i t i o n .

4 . F a i l u r e o f b a s e s . 5 . W e a t h e r c o n d i t i o n . 6 . T a c k c o a t s a n d s e a l c o a t s .

T h e n , t h e s e m a j o r f a c t o r s w e r e a n a l y z e d t o i d e n t i f y t h e r e a s o n s b e h i n d t h e m . S e v e r a l f i e l d a n d l a b o r a t o r y t e s t s a n d s i t e o b s e r v a t i o n s w e r e made f o r d e t a i l a n a l y s i s .

Unsatisfactory Mixes

Weather Condition

Adverse Traffic Conditions

Mix Design Procedure

Rain

Mixing, Time

Too Much

Wind or Drainage

Less or Excess Fines

Nature .of Existing

Bleeding

reriou dck Coats Application

E x c a v a t i o n -

for services

Tack Coat and Seal Coats

Brgkin

ser hdviour^* Turning

- H o o d i n g and Stagnation of Water

Non hemogeneous Layers

Thickness not enough

Roller Movements

Direction

Standing loads ^ Vehicl ' N . Spee

low High Moving Speed

Wheel Loads

Exceeding Design Loads

Unsatisfactory Asphalt Cone Surface

irregularties

J»4 . Un Continuous Laying

Too. Many Joints

Top Thick Nor Layer Thickness

["op \A Non uniform

Too Thin

Failure of Bases

Poor Compection

o 1 C a u s e & E f f e c t D i a g r a m of U n s a t i s f a c t o r y A s p h a l t ^ C o n c r e t e S u r f a c e /

3.0 THE POSSIBLE CAUSES OF UNSATISFACTORY MIXES:

The possible causes of unsatisfactory mixes are described in this section.

3.1 THE EFFECTS OF MIX DESIGN PROCEDURE

3.1.1 OBJECTIVE OF MIX DESIGN

The overall objective of the design of asphalt paving mixes is to determine an economical blend and gradation ( within the limits of the project specifications ) of aggregates and asphalt that yields a mix having the following characteristics :

1). sufficient asphalt to ensure a durable pavement,

2 ) . sufficient mix stability to satisfy the demand of traffic without distortion or displacement,

3 ) . sufficient voids in the total compacted mix to allow for a slight amount of additional compaction under traffic loading without flushing, bleeding and loss of stability, but low enough to keep out harmful air and moisture,

4 ) . sufficient workability to permit efficient placement of the mix without segregation.

Further more, the final mix design must maintain a favourable balance between stability and durability requirements for the intended use ( The asphalt handbook, 1989 ).

3.1.2 MIX DESIGN TESTING

Normally, mix design testing have four important applications during the construction of flexible pavement. They are,

1). Preliminary design testing :-To determine whether the local prospective sources of aggregates are of satisfactory quality

9

2 ) . Source - Acceptance testing :-To determine the most economical blend of aggregates that will satisfy both the gradation and mix design requirements.

3 ) . Job mix control testing :-Is performed at the start of plant production and in conjunction with the calibration of the mixing plant for the job mix formula.

4 ) . Routine construction control testing :-The results of these tests are compared with the job mix control tests and the overall specification requirements.

3.1.3 MIX DESIGN METHODS

The Marshall and Haveem methods of mix design are widely used for the design of hot-mixes. In Sri Lanka, most of the organisations use Marshall method of mix design.

3.1.3.1 MARSHALL METHOD OF MIX DESIGN

This method was formulated by Bruce Marshall, a former bituminous engineer of the Mississippi state highway department. Marshall test procedures had been standardised by American Society for Testing and Materials (ASTM). ( Mix design methods for asphalt, 1986 ).

Prior to this operation, it is required to ensure,

1). that the materials proposed to use meet the requirements of project specifications,

2 ) . that the aggregate blend combination meet the gradation requirement of the project specification,

3 ) . that, the bulk specific gravity of all aggregates used in blend and the specific gravity of the asphalt cement have been determined, for the use in density and void analysis.

10

The two principal features of the Marshall method of mix design are density-Voids analysis and stability-flow test of the compacted test specimens. The stability of the test specimens is the maximum load resistance that the standard test specimen will develop at 60° C. The flow value is the total movement or strain (in units of 0.25mm ) in the specimen between no load and maximum load during stability test.

A series of test specimens are prepared on the basis of 0.5 percent increments of asphalt content, so that the test data curves show well defined optimum value. In Marshall method each compacted test specimen is subjected to the following tests and analysis in the order listed. 1). Bulk specific gravity determination, 2 ) . Stability and flow test, 3 ) . Density and voids analysis,

The equipments used are Marshall testing machine and water bath suitable for the test. The results and data are prepared accordingly and illustrated by the following graphs : 1). Stability Vs Asphalt content, 2 ) . Flow Vs Asphalt content, 3 ) . Unit weight of total mix Vs Asphalt content, 4 ) . Percentage of air voids Vs Asphalt content, 5 ) . Percentage of voids in mineral aggregates Vs Asphalt

content. The optimum asphalt content of mix is determined from data

out lined above. The suitability of the designed mix is determined using Table 3.1 which was recommended by The Asphalt Institute. ( Mix Design methods for asphalt, 1986 )

Table 3.1 : MARSHALL DESIGN CRITERIA

TRAFFIC CATEGORY HEAVY MEDIUM LIGHT MO OF (EACH

BLOWS ESXO

75 SO 35

TEST EROPK&TY M a x w a x M1J3 Stability C W ) 3336 - 2224 - 222-4 -Floe? C Q-25sca ) 8 16 G 18 8 20 SX A l l ' 3 5 3 5 3 6 Voida Baca 3 8 3 8 3 8

11

3.1.3.2 HVEEM METHOD OF MIX DESIGN

The concepts of Hveem method of mix design was developed by Francis N. Hveem of California division of highways. Hveem method of test procedures have been standardized by the ASTM Designation D 1560. The principal features of the Hveem method of mix design are the centrifuge kerosene equivalent test on the aggregate to estimate the asphalt requirements of the mix, followed by a stabilometer test, a swell test, and a density - voids analysis on test specimens of the compacted paving mixtures. The suitability of the hot mix design by the Hveem method is determined on the basis of whether the asphalt content and aggregate grading will satisfy the requirements given in Table 3.2. ( The Asphalt Handbook, 1989)

Table 3.2: Hveem Design Criteria

Test category Heavy Medium Light

Test property Min Max Min Max Min Max

Stabilometer value

Swell

37

Lei

35

5S than 0.76i

30

2 mm

3.1.4. EVALUATION OF MARSHALL AND HAVEEM MIX DESIGN PROCEDURES

Most asphaltic paving technologists and literature agree that for good performance asphaltic concrete must have high stability and durability., For asphaltic concrete to have good stability (resistance to 3tress ), it must have adequate strength in tension to prevent cracking and adequate strength in shear to prevent deformation or rutting.

Past research work ( Transportation research record 1317, 1991 ) has indicated that Hveem stability stands for the resistance to rutting, and that the Marshall stability stands for the tensile strength to resist cracking in pavement.

12

The mix design procedure currently used in Sri Lanka is the Marshall method of mix design which does not measure shear strength of the paving mixture. Due to the unavailability of testing apparatus such as stabilometer, swell test apparatus and mechanical compactor etc^ required for Hveem method of mix design, it is not possible to explore and evaluate other design procedures such as Hveem method of mix design.

A research had been carried out to evaluate Marshall and Hveem mix design procedures by Mr Abdul Wahhab ( Civil engineering department, king Fahd university Saudi Arabia ) and Mr Z.A. Khan ( consulting engineer ). ( Transportation Research record 1317, 1991). They designed five mixes for five gradations, according to their specifications using the marshall mix design method and the Hveem mix design method. Five gradations selected were three wearing courses and two base courses. In addition to the above tests, they performed resilient modulus test, split tensile strength test and static creep test' for a range of asphalt contents, including optimum asphalt contents obtained by both methods. Based on literature search and experiments conducted in their study, they made following conclusions.

1). Marshall mix design tends to predict optimum asphalt i

contents that are higher than those predicted by the Hveem mix design method ( about 0.5% ).

2 ) . Hveem specimens have a higher bulk density and a lower air void content than Marshall specimens, indicating that a different orientation of particles is obtained and that more aggregate interlock is achieved by kneading compaction.

3 ) . Mixes designed by Hveem method gave higher resilient modulus values, higher stiffness values, and lower creep values than those obtained from mixes designed by the Marshall method.

4 ) . Resilient modulus tests on marshall samples predicted optimum asphalt contents that were similar to those predicted for Hveem samples. The deficiency of the Marshall mix design, could be improved by using the resilient modulus test.

13

5 ) . Hveem mix design seems to have a potential application for Saudi Arabia's roads because it more closely simulates field conditions and can better identify mixes with high rutting susceptibility and deformation than does the Marshall method. ( H. Al-Abdul Wahhab & Ziauddin A. Khan, 1990 )

3.2 THE EFFECTS OF BITUMEN QUALITY AND QUANTITY

3.2.1 THE INFLUENCE OF BITUMEN PROPERTIES ON PERFORMANCE

Bitumen is defined as a viscous liquid or a solid consisting essentially of hydrocarbons and their derivatives, which is soluble in trichloroethylene and is substantially no volatile and softens gradually when heated, possess water proofing and adhesive properties. ( B.S. 3690 Part 3, 1989 ). Penetration grade bitumens are specified by the penetration and softening point and are being used for asphalt concrete production.

It is essential to investigate the relationship between laboratory measured properties of penetration grade bitumen and their performances on road, with changing traffic loading conditions and more demanding performance requirements. Although bitumen is in terms of its volume , a relatively minor component of a bituminous mix, it has a crucial role acting as a durable binder and conferring visco-elastic properties to the mix.

Satisfactory performances of a bitumen on the road can be ensured if, the following four properties are controlled. ( Shell Company USA, 1972 ).

1) . Rheology - is adequately characterised by penetration and penetration index.

2 ) . Cohesion - low temperature ductility. 3 ) . Adhesion - assessed by a retained Marshall test. 4 ) . Durability - Durability can be defined as the ability to

maintain satisfactory rheology, cohesion and adhesion in long term service. As part of the quality criteria for bitumen, the following have been identified as the prime durability

14

There are two groups of bitumen hardening described in most of the literatures, namely, a ) . Oxidative hardening and evaporative hardening; b ) . Exudative hardening;

The performance of bitumen-bound mixes in practice is significantly influenced by the mechanical properties, and to a lesser extent by the chemical constitution of the bitumen. The latter is particularly important at the road surface, because the constitution of bitumen, influences the rate of oxidation and their by how rapidly the bitumen is eroded by traffic.

During mixing, hot bitumen must be readily able to coat the dried and heated aggregate in a relatively short period of time. Whilst the mixing temperature must be sufficiently high to allow rapid distribution of the bitumen on the aggregate. ( Bituminous materials, Shell USA, 1972 ). Table 3.3 gives the required specification for penetration grade bitumen.

Table 3.3 : Specification for penetration grade bitumen

PROPERTY GRADE OF BITUMEN PROPERTY 15 pen 35 pan 50 pon 70 pen lOO pan

Ponotration at 26°C 15-5 35-10 50-10 70-10 100-20 Softenino point °C 63-73 52-84 47-58 44-64 41-51 LOG a on heating £ o v 6hr at 163°C I.LO Q G by maaaSS 2.drop in ponotration

0.1 20

0.2 20

0.2 20

0.2 20

0.5 20

( Source T.3.1-BS 3690:Part 1 )

The higher the mixing temperature, the greater will be the oxidation of bitumen exposed in thin films on the aggregate surface. Experiments carried out by Shell bitumen limited were published in Shell bitumen hand book, ( 1972 ) which shows an increase of 5.5°C in mixing temperature, for a standard mixing time of 30 seconds, results in an increase of 1°C in the softening point of bitumen.

15

If Asphalt concrete is mixed too hot, drainage of bitumen off the aggregate may occur during hot storage or transport, leading to variations in bitumen content. The mixing temperature may be fixed by adding 110°C to the softening point of bitumen. ( Shell petroleum Co, 1972 ).

In Sri Lanka only pen 80/100 bitumen is available at the Petroleum Corporation. The softening point of pen 80/100 bitumen is between 44°C - 47°C. Therefore the mixing temperature of asphalt should be kept around 155°C.

Using the relationship between the temperature of the mix and change in softening point, it could be assumed that the softening point of bitumen in the mix lie between 46°C - 47°C ( An increase of 2°C at mixing temperature of 155°C ).

C h a n g 8 e

140 150 160 170 180 190 200 210 220 Mix temperature °C

Fig 3.1 :Relationship between the Temperature of the mix and change in softening point

( Source :- Shell Bitumen Handbook 1972 ).

16

Hardening of bitumen in the mix may take place during hot storage, or in the transport vehicle. When a mix is discharged into a storage or into a truck, air enters into the mix and some air get is trapped in the voids of the material. During storage, some of the oxygen in this entrained air will react with the bitumen. If no additional air enters into the storage, oxidation of the bitumen will cease. The majority of bitumen hardening occurs during mixing and to a lesser extent during storage and transport. However, under site conditions, hardening of bitumen can also occur on the road. Therefore, the main factor which influences bitumen hardening on the road is the void content of the mix.

Table 3.4 : Hardening of bitumen with age for different void contents

VOIDS IN MIX % SOFTENING POINT °C VOIDS IN MIX %

AFTER MIXING & LAYING AFTER 15 YRS SERVICE

4 64 68

5 63 76

7 66 88

( source : Bitumen in road surfacing, Shell Petroleum Co, 1969 )

Table 3.4 clearly shows that the bitumen recovered from the mix with the lowest void content had hardened very little, however, where the void content is high, substantial hardening had occurred.

Therefore, if the void content of the mix is kept close to its upper allowable limit, while satisfying all other design requirements, there is an advantage when using pen 80/100 bitumen, due to high road surface temperatures ( The effects of high temperatures will be discussed under adverse weather conditions. ).

17

3.2.2 BITUMEN CONTENT

If bitumen in the mix is too high, it creates a situation like individual stones floating on bitumen. In that situation, the framework of stones will be destroyed, and the pavement will not carry appreciable load and there will not be any voids in asphalt. This condition results in bleeding, shoving, or rutting of the pavement.

Other extreme is the addition of asphalt only in sufficient quantity to serve its function as a binder, which leaves high volume of air voids. In this case, the pavement may still have good resistant to movement, it may increase the hardening of asphalt cement through weathering and allow water to enter into the pavement.

Bitumen content of the mix should lie between 5.0% to 7.0% for wearing courses and 3.5% to 5.5% for base courses according to RDA specifications. ( Standard Specifications RDA, 1989 )

During this research a comparative study was made to find out the percentage of binder available in core samples collected from Galle road and Prince of Wales avenue. ( Refer Appendix B ) The results of the study was compared with the specification limits given by RDA and the following conclusions were made based on the study. ^ ,-\x^

* a„ Normal road surface:

The bitumen content was less than the lower limit of the specifications( 5% ), and the percentage of fines passing No 200 sieve was closer to the lower limit specified by ASTM.

b._ Normal road surface with excess bitumen on the surface:

The bitumen content was closer to the lower limit of the * specifications, and percentage of fines passing No 200

sieve was around the medium of ASTM specifications. 18

c Surface with full of corrugations.

The bitumen content of most of the samples were between the mid value and the upper limit of the specification, and the percentage of fines passing No 200 sieve were close to the upper limit given by ASTM specifications.

It was observed from the core samples collected from the surfaces where there were lot of corrugations, the top of the core samples were mainly made with finer particles blended with bitumen,and the bitumen content is higher than 5.0%. The cause may be due to the higher percentage bitumen and very fine particles in the mix, fines may separate from the coarse aggregate forming a mastic with bitumen. Such mastic, when presents in excessive amounts, may cause flushing of the pavement, resulting in an unstable mix. This condition become even worse when the percentage of binder is higher and the percentage of voids is less. ( Low void content may result instability or flushing of the pavement after it has been exposed to traffic, specially at high temperatures. This is due to the re-orientation of particles by the excessive traffic loads at these temperatures.)

It was identified from the core samples that the samples having bitumen contents less than 5.0% in wearing course, the joint between base course and wearing course was clearly identified. In contrast core samples having bitumen contents higher than 5.0% in wearing course joint between base course and wearing course was not clearly identified and some photographs of these core samples are given in Figures 3.2, 3.3, 3.4 and 3.4.

Under the Colombo road rehabilitation programme Galle road and Prince of wales avenue were rehabilitated between 1988 and 1991. Deformations were visible in 1992 and there was a large no of deformations on surface by 1993. Asphalt produced by Colombo Municipal Council was criticised and several studies were carried out to find out the causes for these asphalt failures. By thorough investigation of the previous laboratory records it was found that the bitumen content of the asphalt wearing courses laid on these road3 lie between 5.1% to 5.8% and the design method used for designing asphalt mixes was Marshall method of mix design.

67984 1 9

Suspecting the role of bitumen content it was then decided to reduce the bitumen content of wearing course mixes still satisfying the requirements of Marshall method of mix design and several trial sections were laid from 1994. Wearing course laid on one section of the Reclamation road 1994 had bitumen content between 5.0% to 5.2% . Bluemandol road had bitumen content between 4.9% - 5.1. Wearing course laid during latter part of 1994 on George R. De Silva Mawatha and replacement surface of downhill at Prince of Wales Avenue ( Totalaga ) had bitumen contents between 4.7% to 4.9%. Wearing course having bitumen contents between 4.5% - 4.7% was used to lay another section of Reclamation road close to Church at Kochchikade. The percentage of fines were kept close to allowable limit and the road formation was prepared to take uniform thickness of overlay.

The performance of those roads were monitored regularly. Although there is not much deformations appeared on the road surfaces with bitumen contents between 4.9% - 5.2%, in some sections fatting up on the surface was observed. Specially at the junctions and roundabouts where sections laid with wearing courses having bitumen contents between 4.5 % - 4.7% fine aggregates at the top of the surface was eroded by traffic. Nearly after 3 years in service the best asphalt surface so far was produced from the mix having bitumen content between 4.7% to 4.9%, but still it is too early to make conclusions.

Laying asphalt wearing course on Olcott Mawatha commenced in June 1996 and the bitumen content used was 4.8%. Mineral filler was not used for the production of asphalt and the fines requirement was fulfilled from the fines in quarry dust, and more coarser mix was used, Galle road, Prince of Wales Avenue and Olcott Mawatha has similar traffic characteristics. In Galle road and Prince of Wales avenue few surface deformations were visible after single year in service , but in Olcott Mawatha No signs of deformations appeared yet.

These trials are not enough to make conclusions and these type of experiments must be continued and the developments to be monitored during the design life of the pavement. But it could be suggested to use bitumen content between 4.7% - 4.9%, when using pen 80/ 100 bitumen for wearing course mixes.

21

3.2.3 THE QUALITY OF BITUMEN ( TYPE )

The type of bitumen used in Sri Lanka is pen 80/100 bitumen having softening point between 44°C to 47°C

Research work done in the past show that in the hot climates , the asphalt cements with the lower penetrations may be used to prevent the pavement from becoming too soft during the hot weather, and in the cold climates , the softer asphalt cements may be used to prevent the pavement from becoming too brittle in extremely cold weather. Although asphalt cements with a penetration as low as 60 are used in South of U.S.A, the more recent trend has been to a minimum penetration of 70 for all climates." ( Bituminous construction handbook, Baber Green Co. 1972 )

From Table 3.5 it is clear that the type of bitumen should be selected giving due consideration to the prevailing field conditions. Data from field surveys done in Sri Lanka show that the deformations are severe at bus stops, traffic signals, close to roundabouts etc. Due to unavailability of different types of bitumen all the asphalt producers in Sri Lanka have to use pen 80/100 bitumen, which is the only type of bitumen available in local market.

Table 3.5 : Selection criteria for the selection of suitable type of bitumen.

FIELD CONDITIONS PENETRATION ( pen )

SOFTENING POINT °C

DUCTILITY

At situations where high rainfall and / or colder conditions prevail

60-80 45-55 50 min

For general application 40-60 50-60 50 min

At bus stops and situations with equable climate where heavy standing loads are encountered

30-40 52-62 50 min

( Source : Bituminous materials in road construction. Road research laboratory UK, 1980 )

22

3.3 THE EFFECTS OF THE GRADING OF AGGREGATES IN THE MIX

The manufacture of asphalt concrete involves mixing aggregates in appropriate proportions with binder to provide a homogeneous mix of the specified composition at the right temperature.

There are three basic types of asphalt plants. They are,

a. Batch heater plant.

A batch of aggregate is accurately proportioned at the cold-feed, then heated and discharged into the mixing chamber where binder and aggregates are added.

b. Drum mix plant.

Mixing occurs in the heating drum and is a continuous process.

c. Conventional asphalt batch process.

The aggregate drying and heating is a continuous process, but mixing is carried out in batches

( G.P.Jackson & D. Brian, 1972 ).

The asphalt concrete analyzed in this research were produced using the batch type asphalt plant owned by Colombo Municipal Council and mixing procedures of similar type of asphalt plants are discussed in this report.

The different sizes of aggregates are loaded to feeder hoppers and fed to the aggregate drier. Next, heated aggregates are discharged from the drier, is conveyed vertically up in bucket elevator, and screened into different sizes and temporarily stored in hot aggregate bins. Then different sizes of aggregates stored in hot aggregate bins are weighed separately to get the proper blend and discharged into the mixer. Finally, bitumen and filler (if necessary) are added and mixed.

23

Blend proportions of cold feed aggregate obtained by mix design cannot be directly used in asphalt plant because aggregates are heated and re-screened prior to mixing. According to BS 812, artificially heated aggregates shall not be used for relative density calculations in mix designing. Therefore samples from heated and re-screened aggregates cannot be used for mix designing. The blend proportions of aggregates for the asphalt plant should be re-calculated using the gradins of heated and screened aggregates and the ideal combined mix should have the same blend obtained from mix design.

During this research a comparative study was made to identify the grading differences of aggregate blend, between the combined aggregate blend obtained in mix design and the actual blend of aggregates in asphalt produced by the asphalt plant. Always there is a difference between the blend of aggregates obtained in mix design and the blend used for mixing at asphalt plant using hot bins aggregates. These differences were analyzed using aggregate blend proportions obtained in asphalt concrete mix design, hot bin aggregate mix proportions used in asphalt plant and actual aggregate blend of asphalt concrete obtained from extraction tests during this research and produced in Tables 3.6., 3.7., 3.8. and 3.9. Optimum bitumen content obtained from mix design was used for asphalt mixing at the plant.

Similar test was carried out for the asphalt concrete produced at R.C.D.C. asphalt plant at Peliyagoda on 24-07-96. The mix design details were obtained from research division of R.D.A. at Rathmalana and the findings are tabulated in Tables 3.10., 3.11. and 3.11.

24

Table 3.6 : Aggregate blend ( job mix formula) of mix design (C.M.C base course on 06/08/96)

Sieve size

% Passing Blend J.M.F obt*

%

J.M.F req.% (mid. v. of ,spec.

Sieve size

20mm under

(A)

12mm under ; (B)

Quarry dust

(C)

A*30 %

B*35 %

C*35 %

J.M.F obt*

%

J.M.F req.% (mid. v. of ,spec.

28mm 100 100 100 30.0 35.0 35.0 100.0 100

20mm 89.1 100 100 26.7 35.0 35.0 96.7 94.0

10mm 19.1 75.2 100 5.7 26.3 35.0 67.0 67.0

5mm 4.0 17.9 100 1.2 6.3 35.0 42.5 45.0

2.36mm 1.5 4.9 85.7 0.45 1.7 27.8 32.0 29.5

1.18mm 1.2 3.4 67.8 0.4 1.2 23.7 25.3 24.0

600pm 1.1 2.8 55.5 0.3 1.0 19.4 20.7 18.0

300pm 0.9 2.2 38.5 0.3 0.8 13.5 14.6 13.0

150pm 0.5 1.5 21.2 0.15 0.5 7.4 8.1 8.0

75pm 0.3 0.8 10.3 0.1 0.3 3.6 3.9 4.0

Table 3.7: Hot bin gradins & theoretical aggregate blend of B.C

Sieve size

Passing J.M.F. obt. % *

J.M.F req. %

Sieve size

Binl Bin2 Bin3 Bin4

J.M.F. obt. % *

J.M.F req. %

28mm 100 100 100 100 100.0 100.0

20mm 100 100 100 99 98.8 94.0

10mm 100 97 32 12 70.1 67.0

5mm 99 7 0 0 45.9 45.0

2.36mm 67 3 - - 30.8 29.5

1.18mm 48 0 - - 21.6 24.0

600pm 35 - - - 15.8 18.0

300pm 22 - - - 9.5 13.0 150pm 12 - - - 5.4 8.0

75pm 5 - - 2.3 4.0

25

Table 3.8 : Comparison of actual J.M.F. (B.C) with design J.M.F. & required J.M.F. ( % passing B.S sieve)

Sieve Design, Actua! L Req. Difj :. . Diff. Allowabl' size J.M.F J.M.F. "J.M.F. tolerance

A i B C B-. \ . B-C +/_ 28mm 100.0 100.0 100.0 0.0 0.0 6.0

20mm 96.7 98.8 94.0 +2.1 +4.8 6.0

10mm 67.0 70.1 67.0 +3.1 +3.1 6.0

5mm 42.5 45.9 45.0 +3.4 +0.9 4.0

2.36mm 32.0 30.8 29.5 -1.2 + 1.3 4.0

1.18mm 25.3 21.6 24.0 -3.7 -2.4 4.0

600um 20.7 15.8 18.0 -4.9 -2.2 4.0

300um 14.6 9.5 13.0 -5.1 -3.5 4.0

150um 8.1 5.4 8.0 -2.7 -2.6 4.0

75um 3.9 2.3 4.0 -1.6 -1.7 2.0

Similar study was carried out for the wearing course mixes.

Table 3.9 : Comparison of actual J.M.F. (Wearing course) with. design J.M.F. and required J.M.F. (%Passing B.S. sieve)

Sieve size

Design J.M.F.

A

Actual J.M.F

B

Req. J.M.F.

C

Diff

B-A

Diff

B-C

Allowable tolerance

+/_ 28mm 100.0 100.0 100.0 0.0 0.0 6.0

20mm 98.0 99.6 95.0 + 1.6 +4.6 6.0

10mm 79.0 76.1 79.0 -2.9 -2.9 6.0

5mm 57.0 55.2 59.0 -1.8 -3.8 4.0

2.36mm 45.0 42.8 46.5 -2.2 -3.7 4.0

1.18mm 36.0 33.6 37.0 -2.4 -3.4 4.0

600um 30.0 26.5 28.0 -3.5 -1.5 4.0

300um 21.0 18.8 19.5 -2.2 -0.7 4.0

150um 13.0 10.6 14.0 -2.4 -3.4 4.0

75um 6.5 6.0 8.0 -0.5 -2.0 2.0

26

Table 3.10 : MIX DESIGN ( RCDC plant Peliyagoda )

Sieve size

% Passing Blend J.M. obt.

%

F. J.M.F. req. % ( mid. v. of spec.)

Sieve size

20mm under

12mm under

Quarry dust

A*20 %

B*25 %

C*55 %

J.M. obt.

%

J.M.F. req. % ( mid. v. of spec.)

19.0mm 100.0 100.0 100.0 20.0 25.0 55.0 100. 0 100.0

9. 5mm 8.1 73.4 100.0 1.6 18.4 55.0 75. 0 75.0

4.75mm 3.4 16.8 94.0 0.7 4.2 51.7 56. 6 56.6

2.36mm 0.7 9.1 73.7 0.1 2.3 40.5 42. 9 42.9

1.18mm 0.0 6.7 56.1 0.0 1.7 30.9 32. 6 32.6

600pm - 5.4 42.5 - 1.4 23.4 24. 8 24.8

300pm - 3.9 26.8 - 1.0 14.7 15. 7 15.7

150pm - 2.4 14.7 - 0.6 8.1 8. 7 8.1

75pm - 1.3 7.0 - 0.3 3.9 4. 2 3.9

The actual job mix used on 24-07-96 defers from the designed mix and the reason for that was explained as the variations of hot bin and cold bin gradines.

Table 3.11 : Difference of Designed and actual aggregate blend percentages.

Aggregate size

Blend percentages Aggregate size

Actual Design

20mm agg. 20% 20%

12mm agg. 20% 25%

Quarry dust 1 60% 55%

27

Table 3.12 : Comparison of actual J.M.F with designed J.M.F. and required J.M.F (R.C.D.C. asphalt plant at Peliyagoda on 24-07-96)

Sieve size

Design J.M.F.

A

Actual J.M.F

B

Req. J.M.

C F

Diff.

B-A

Diff

B-C

19.0mm 100.0 100.0 100. 0 0.0 0.0

9. 5mm 75.0 76.0 75. 0 + 1.0 + 1.0

4.75mm 56.6 58.0 56. 6 + 1.4 + 1.4

2.36mm 42.9 44.1 42. 9 + 1.2 +1.2

1.18mm 32.6 32.9 32. 6 +0.3 +0.3

600pm 24.8 24.1 24. 8 -0.7 -0.7

300pm 15.7 14.9 15. 7 -0.8 -0.8

150pm 8.7 7.9 8. 1 -0.8 -0.2

75pm 4.2 3.3 3. 9 -0.9 -0.6

It is clear from the above comparisons, there is a significant difference between the aggregate blend of mix design and actual aggregate blend of asphalt, although both gradations satisfy the specification requirements. The reasons for the reduction of fine particles in hot bins, may be blowing away of fine particles during heating inside the drier, and loss of fines during transfer through bucket elevator which is collected by wet dust collector and finally discharged into the sedimentation tanks. At CMC asphalt plant in sedimentation tanks gets filled up after every 1000 tonnes of asphalt production. Samples from sedimentation tanks were analyses and found that 100% of these particles passed through 150 urn sieve and 85% passes through 75 urn sieve. The actual mix has more coarse aggregate and less fine aggregates. Hence, the surface area of particles in actual mix is lesser than the surface area of particles in the designed mix. Therefore, the amount of bitumen added may be more than the bitumen required to wet the surface of aggregate particles. The percentage of bitumen for the mix is decided during mix design and therefore, the excess bitumen available in asphalt may reduce the voids in mix and create floating of fine aggregate particles.

28

To minimize the problems of grading differences following method may be introduced.

1. Select suitable aggregate combination for the production of asphalt which satisfy the mix design requirements.

2. Mix an aggregate sample using the aggregate combination obtained in step 1.

3. Sieve the mix aggregate sample obtained in step 2, and store each and every portion retained on each sieve separately.

4. Feed different aggregate sizes received from suppliers (same type of aggregates used in step 1 ) to asphalt plant, collect hot bin samples and perform sieve analysis to get their gradins.

5. Work out a suitable blend using hot bin aggregate gradins which falls within the grading limits of the required asphalt mix.

6. Combine the different sizes of materials retained on different sieves in step 3, to get a similar gradation as obtained in step 5.

8. Use the aggregate blend from step 6 for the mix design. 9. Repeat the above procedure until a satisfactory mix is

obtained and decide the optimum bitumen content.

The disadvantages of the above procedure is,

1. The mix design could only be carried out after receiving bulk quantities of aggregates and not before awarding the tenders to aggregate suppliers and therefore,it is not possible to use the samples supplied by tenderers for mix design to find out the suitability of aggregates for asphalt production prior to awarding the tender.

2. It is common that grading of aggregates supplied by the same' supplier from the same source varies within the limits given in the his order for the supply of aggregates, which also leads to difference in blend gradins. It is not possible to pez^form mix designs at short intervals and therefore excessive controls in mix design may be wasted due to the grading fluctuations of the aggregate supply.

29

3.4 THE EFFECTS OF MIXING TIME

The mixer of asphalt batch plant comprises two contra-rotating sets of paddles and mixing time is determined by the composition of the mix. Mixing to be carried out until there is complete coating of the aggregate with binder. Excessive mixing should be avoided to prevent rounding of aggregate particles and undue hardening of binder at the relatively high temperatures.

More mixing time is required for the denser mixes to ensure adequate coating of the high proportion of fines. Usually mixing time is not specified in mix design. Therefore the mix designer and the production engineer must decide the mixing time considering the above and the asphalt plant manufacturer's specifications. Most of the new asphalt plants are computerised and it is only required to set the correct mixing time.

30

4 . 0 THE POSSIBLE CAUSES OF EXCESS BITUMEN ON EXISTING SURFACES

4.1 INTRODUCTION

In Sri Lanka, asphalt concrete is mainly laid on the rehabilitated roads, where the existing surface was made from bituminous material. Sand sealing for surface improvements and the U D C of cold mix asphalt for pot hole patching is common practice. Application of tack Coat over the existing surface prior to the laying of asphalt concrete, provides a bond between two layers. All these applications may leave some percentage of bitumen on the surface which might mix with newly laid asphalt due to high temperatures and this may lead to increase the binder content.

4.2 SAND SEALING

The binders used for the seal coats may be cut back bitumen or road emulsions. The rate of application is normally between 0.75 litre to 1.0 litre per square metre (R.D.A. specifications 1989). Seal coat must be covered with blotting material before bitumen hardens, and the surface must be rolled immediately with a pneumatic roller. Re-brushing of blotting material collected at the road edse, back to the road surface must be carried out until surface bleeding completely disappears.

In practice only a covering of seal coat is put and traffic is left to do the rolling. The blotting material is never brushed back to the surface. In some roads, at noon when the temperature is hifih, it is difficult even to walk because the melted bitumen available on the surface, stick to the shoes. If excess bitumen is available on surfaces, it might melt due to the high temperatures of asphalt concrete and fill the voids left in the mix and increase the bitumen content. As a remedy to the above problem the surface whore excess bitumen is available, may be re-compacted after scarifying, before the placement of asphalt overlay.

31

4.3 TACK COAT

The need for a tack coat is to promote adhesion between bitumen layers. Normally, tack coats are used, when it is considered that the underlying surface will not provide sufficient bond or mechanical key. The material may be cut back bitumen or road emulsions and generally the rate of application is between 0.25 litre to 0.55 litre per square metre (Standerd specifications RDA 1939). The commonly used road emulsion here is CRS1.

If the asphalt concrete is laid in thick layers there is no need to apply tack coat. For a thin layer (less than 37.5mm) or for an old surface, which is very smooth, tack coat may be advisable (Shell Petroleum Co. 1969 ). But it has become a common practice in Sri Lanka to apply tack coats before laying asphalt concrete, irrespective of layer thickness or surface conditions. The spreading rate of the tack coat must be uniform, and no puddles should be allowed to form, as these will lead to fat spots in the subsequently applied surfacing. The tack coat emulsions must be allowed to break ( indicated by a change of colour from brown to black ) before the bituminous mix is applied, other wise, it will tend to act as a slip layer. Tack coating should not be carried out far in advance of surfacing work as it may be removed by site or public traffic. (Standerd specifications RDA, 1989)

It is observed that 3ome laying staff do not pay much attention and adopt correct method of tack coat application. High rate of application, fat spots due to nonuniform applications etc, may reduce voids in asphalt layer which are left for additional compaction under traffic.

32

5.0 THE POSSIBLE EFFECTS OF WEATHER

5.1 INTRODUCTION

Weather plays a crucial role in asphalt concrete manufacturing and laying process. If materials are not stored under a roof and allowed to be exposed to rain, excessive moisture in aggregates will lead to unsatisfactory mix of asphalt concrete. Loss of temperature by 20° C is usually experienced when discharging the asphalt into a paver. The temperature loss during spreading is dependent on the thickness of the layer, ambient temperature, wind speed and the temperature of the substrate on which the new material is placed. The two most crucial factors influencing the cooling effect of the layer are wind speed and the layer thickness ( The asphalt handbook, 1989).

The behaviour of the mix in service after laying and compaction, mu3t also be considered. The critical conditions for the performance of bituminous mixes are generally associated with either high service temperatures ( 30° to 60° C ) or low service temperatures (< 5° C ). At high temperatures the problems are deformation and fatting up and at low temperatures cracking and surface fretting ( Prediction of pavement performance, 1976 ).

5.2 PRESENCE OF WATER

One of the principal functions of bitumen is to act as an adhesive to bind aggregate particles together. The presence of water causes few problems to the adhesive effect of bitumen, because aggregate is wetted more easily by water than bitumen. Adhesion problems by the presence of water arise in two ways. Firstly, due to the aggregate being wet before mixing and secondly due to the effect of rain on the material, after it has been laid. The displacement of one liquid by another on a solid surface arises from the physio-chemical forces acting on the system. If the surface of an aggregate is wet, it is almost impossible to disperse the water with bitumen and for the bitumen to adhere with aggregate. However it is possible for water to penetrate a film Of bitumen and detach the bitumen from the aggregate. ( Prediction of pavement performance, 1976 )

33

When aggregate passes through the drier of the asphalt plant, moisture evaporates and the evaporated moisture is drawn off by exhaust fans. The drier is a long rotating metal drum, which is slightly inclined, with oil fired burner, located at the discharge end. Metal flights inside the drum lift the aggregate and cause it to fall on a curtain, through hot gases produced by burner flame. Control of the burner ensures the correct aggregate temperature for any particular mix. Most driers are designed for an average moisture content of about 5 percent. Over wet aggregate kept open for rain requires more heat than dry aggregates if the aggregate flow remains constant. However, their is an upper limit for the increase of heat and beyond that limit the aggregate flow must be reduced for proper drying hence reducing the capacity of the plant. Usually producers do not want to reduce the rate of production and prefer to increase the heat up to the maximum limit and work during rainy season.

If aggregates are not properly dried, particularly if it is of a porous nature, then this could result in the production of unsatisfactory mixes due to the presence of water ( moisture). This is frequently apparent; the mix will appear rich, and tend to slump; white smoke could be seen when discharged in to trucks. In colder climates or during heavy rains or on long hauls where there is likely to be any appreciable loss of temperature, the mix should be properly covered over to prevent loss of heat.

When the asphalt plant and the asphalt laying site are located far away, during rainy season, these two places may experience different climatic conditions. It may be possible that asphalt ordered during fair weather may be produced in wet weather, or when asphalt arrive, the site may experience rain. In such caces neither the producer nor the contractor prefers to throw the material, due to the high cost of the material and prefer to lay rather than throwing away. It is common in Sri Lanka that most of the asphalt laying contractors and asphalt producers work during rainy season.

34

Asphalt concrete produced using extremely wet aggregate results poor bonding between bitumen and aggregate. When asphalt is laid on a wet road surface, rapid cooling will occur and there will be a poor bond between the existing surface and the new asphalt layer. Although the percentage of compaction, binder content, surface irregularities etc. could be tested , the effects of the presence of water cannot be tested and identified immediately after asphalt laying, poor bonding between aggregates may result in relative movements between layers. Presence of excess moisture leads to poor bonding between aggregate particles and the formation of thin film of bitumen due to excess moisture and they may separate during service. Excess moisture or water evaporated with time leave voids on asphalt surfaces and, during rain, water filled into voids creep through asphalt and destroy the surface. It is advisable to avoid asphalt laying and production during rain and instead, carry out the other construction activities.

5.3 HTGH TEMPERATURES

r>.3.1 PERMANENT DEFORMATION AT HIGH SERVICE TEMPERATURES

Plastic deformation may occur under moving or stationary traffic, and particularly when the high sheering stresses imposed by breaking, accelerating or turning traffic. The primary factor influencing plastic deformation is the mix composition. But for a given composition, behaviour will be governed by the viscosity of •the bitumen ( Prediction of pavement performance, 1976).

At-.pha.l t mixes have a low thermal conductivity. In practice the majority of the asphalt defi H'matioti is plastic deformation . >f wearing n< «urses in reha.>>j litatad roads in Colombo.

Plastic deformation is high at high service temperatures, for which 60"C may be taken a y maximum in-Bifcu temperature (Prediction of pavement performance, 197R). Road surface temperatures were recorded during March and April 1996 for ten days, along the Prince of wales avenue between 11.00 am to 3.00 pm and shown in Table 5.1.

35

Table 5.1 : Road surface -temperatures

DATE ROAD SURFACE TEMPERATURE <=>C ATMOSPHERIC TEMPERATURE

°C

DATE

11 AM 12 AM 13 PM 14 PM 15 PM 16PM

ATMOSPHERIC TEMPERATURE

°C

24-04-96 40.0 46.5 51.5 52.0 52.0 46.0 35.0

25-04-96 42.0 49.0 54.0 55.0 54.0 48.0 37.0

26-04-96 42.5 50.0 55.0 57.0 55.0 48.5 38.0 J

06-05-96 42.0 48.0 52.5 54.0 52.5 47.5 1

36.5 07-05-96 41.0 47.0 52.5 53.0 52.0 47.0 36.0

08-05-96 39.0 45.0 49.5 50.0 49.5 45.5 33.0

09-05-96 40.0 46.0 53.0 53.5 52.5 46.0 36.0

10.05-96 1

43.0 51.0 55.0 56.0 54.5 48.0 38.0 i

20-05-96 43.0 51.0 56.0 58.0 56.5 48.5 39.0

21-05-96 42.0 51.0 55.0 57.0 56.0 49.0 38.5

Highest surface temperature observed was 58 °C at 14.00 hrs when the atmospheric temperature was 39 °C. Type of bitumen used for asphalt was pen 80/100 and its softening point was between 44°C-4S°C. From Table 5.1 it was clear that between 12.30pm and 3.30pm the road surface temperatures were higher than the softening point of bitumen. At surface temperatures higher than softening point of bitumen, bitumen in asphalt is more viscous and plastic deformations may be the cumulative effect of repeated loadings at short durations.

Road survey was conducted to measure deformations along the Galle road ( See appendix A ) over 1.0 km in length and given in Tables 5.2, 5.3, 5.4 and 5.5.

36

Table 5.2 : ROAD SURVEY - GALLE ROAD FROM BAMBALAPITIYA JUNCTION TOWARDS GALLE ( 500m ) FOR DEFORMATIONS.

LOCATION DEFORMATIONS (NO OF LOCATIONS)

LOCATION SEVERE MEDIUM MILD NIL

LOWER SIDE

SOUTH BOUND CARRIAGEWAY 23 22 6 0

LOWER SIDE NORTH BOUND CARRIAGEWAY 13 28 9 1

MIDDLE


MIDDLE NORTH BOUND CARRIAGEWAY 2 13 19 17

HIGHER SIDE


HIGHER SIDE NORTH BOUND CARRIAGEWAY 1 5 5 40

Table 5.3 : ROAD SURVEY - GALLE ROAD FROM WELLAWATTA (HOTEL SAPPHIRE) TOWARDS GALLE (500m) FOR DEFORMATIONS.

1 LOCATION

(DEFORMATIONS (NO OF LOCATIONS) ' 1 LOCATION

SEVERE MEDIUM MILD NIL

LOWER SIDE



MIDDLE



HIGHER SIDE



37

Table 5.4: SUMMERY OF DATA ALONG GALLE ROAD FOR DEFORMATIONS.

LOCATION DEFORMATIONS ( NO OF LOCATIONS )

LOCATION SEVERE MEDIUM MILD NIL

LOWER SIDE



MIDDLE



HIGHER SIDE



The following weighted values were given for the deformations to compare deformations of different lanes.

Severe - 1 . 0 0 ( Deformed length > 5.0m ) Medium - 0.5G { 2.5m < Deformed length < 5.0m Mild - 0.25 ( 0.0m < Deformed length < 2.5m Nil - 0.0C ( N o deformations )

Table 5.5: WEIGHTED VALUES FOR DEFORMATIONS ALONG THE GALLE ROAD.

LOCATION DEFORMATIONS (WEIGHTED VALUES)

LOWER SIDE

SOUTH BOUND CARRIAGEWAY 74.25

LOWER SIDE NORTH BOUND CARRIAGEWAY 64.75

i i MIDDLE

SOUTH BOUND CARRIAGEWAY 49.0 i

i MIDDLE NORTH BOUND CARRIAGEWAY 37.0

HIGHER SIDE

SOUTH BOUND CARRIAGEWAY 24.0

HIGHER SIDE NORTH BOUND CARRIAGEWAY 11.5

Following observations could be made using table 5.5.

a. More deformations occur along the lower side of the road, in both north bound, and south bound carriageways and less close to the centre median ( higher side ) of the road.

b. Deformations along the south bound carriageway is more than the north bound carriageway.

It was observed that along the north bound carriageway traffic flow is heavy during early mornings, and along the south bound carriageway traffic flow increases after 12.00 hrs.

Along the South bound carriageway when the traffic was more and road surface temperature is high, it deformed more than the north bound carriageway. Therefore it could be concluded that there may be a relationship between fatting up and high service temperature. Most of the heavy vehicles travels along the lower edge of the read. Therefore, in both sides deformations at lower ends were higher.

5.3.2 FATTING UP AT HIGH SERVICE TEMPERATURES.

Fatting up occurs due to the consolidation of aggregate in asphalt by traffic. It reduces the void content of the mix, eventually forcing bitumen to the surface. This will be exacerbated, if the bitumen content is too high or if the void content is too low.

At high road temperatures, migration of bitumen particles to the surface results in a smooth shiny surface, which has poor resistance to skidding in wet weather. Fatting up is most likely to occur at high servibe temperatures. If bitumen with much lower softening points wexfe used for the asphalt production the effects of fatting up would be high. It is the cause for fatting up problems of most of our roads because, the type of bitumejD^-used here is pen 80/100 which has lower softening point whe-with road temperature. Thus limiting the softening po: viscosity of the bitumen will limit fatting up.

39

6 . 0 THE POSSIBLE CAUSES OF UNSATISFACTORY BASES 6.1 INTRODUCTION

The basic idea in building a road for all-weather use by-vehicles is to prepare a suitable subgrade or foundation, to provide necessary drainage and to construct a pavement that will,

1). have sufficient total thickness and internal strength to carry expected traffic loads,

2 ) . have adeeuate compaction to prevent the penetration or internal accumulation of moisture, and

3 ) . have a top surface that is smooth, skid resistant, and resistant to wear, distortion , and deterioration by weather and deicing chemicals. ( The asphalt handbook, 1989. )

The subgrade ultimately carries all traffic loads. Therefore, the structural function of a pavement is to support a wheel load on the pavement surfece and transfer and spread that load to the subgrade without exceeding either the strength of the subgrade or the internal strength of the pavement itself.

An asphalt pavement structure consists of all layers above the prepared subgrade. The upper or top layer is the asphalt wearing surface. It may vary from 25 mm to 75mm in thickness depending on road design.

Base and subbase are structural elements of the pavement in conjunction with the overlying asphalt surface. Their purpose is to distribute traffic wheel loads over the subgrade to foundation. To perform this function bases and subbases must be built with necessary internal strength properties.

Based on the comprehensive analysis of vast volumes of accumulated data, The structural design of asphalt pavement has now been developed into a reliable engineering procedure. ( A guide to the design of pavements, 1970 ). There is no standard thickness for a pavement. Required total thickness is determined by engineering procedures. Factors considered in the procedures are,

1). Traffic tc be served initially and over the design service life of the payment,

2 ) . Strength end other prominent properties of the prepared subgrade,

3 ) . Strength and other influencing characteristics of the materials available or chosen.

6.2 STRENGTH OF EASES AND SUBBASES IN COLOMBO

Most of the roads in Colombo are narrow streets widened time to time to cope up with the heavy traffic demand. Various bases and sub bases had been constructed over the last decades. They consist of compacted granular material, set stones, single sized aggregates etc, in Colombo. As modern traffic increases in weight and volume some of these untreated bases and subbases show performance limitations. Road bases of some of the major roads, like Prince of Wales avenue and Olcott Mawatha, was made using different types of material at different times. Roads are excavated to provide various services and different agencies adopt different backfilling materials. These bases has different strength characteristics, which results non homogeneous base strength. Unless the weakest base is identified before the design, specially before deciding on the layer thicknesses, pavement might fail at the locations where the base strength is lesser than the value used in design.

Regardless of the design method employed, it is desirable that preliminary data to be gathered through road surveys and laboratory tests. Where there are different bases exist, it is necessary to expose the existing pavement across the road at suitable intez^vals and test all types of base materials used.

Weight and traffic volume normally increase each year, pavement originally built thick enough to handle immediate traffic volumes may not be thiak enough and strong enough to handle future needs. The design load must be decided giving due consideration to the future characteristics of traffic, at least up to the design life of the pavement.

An asphalt pavement structure deflects downward under a moving load, returning virtually to its original position after the load has passed. Because it falls infinitesimally short of recovering completely after each application of heavy load, it xindergoefj a continuous rate of deterioration as a result of continuous traffic (The asphalt handbook 1939 ). The damage of the above effect is serious along service excavations and places where the bases are week, and may alter transverse and longitudinal profiles, and, possibly crack.

Strength characteristics of bases must be analysed at the pavement design stage and it is not within the scope of this project.

6.3 NON UNIFORM LAYER, THICKNESS

One of the first requirements is that, the layer on which the mix is being laid, must be at the correct level and is of satisfactory regularity.

In road rehabilitation projects, changes are always there in vertical alignment and cross fall. Design engineers prefers to keep minimum overlay over the highest points of the existing surface, rather than excavating the existing surface, which results in different thicknesses of asphalt overlay.

Road rehabilitation work is carried out while these roads are still in operation. In most cases due to the non availability of alternative routes these roads cannot be closed completely for traffic during construction. Forming existing surfaces up to the road formation by scarifying and re-metalling, takes time and the working sections should be closed till the surface is covered with asphalt concrete. Therefore building up of the road profile using

i

asphalt concrete regulating courses only, is preferred by most of the contractors, because it reduces the closing down time of roads when compared \*ith the process of re-metalling. Now, due to the reason mentioned above, cases are arising, where the thickness of a regulating course is maximum at the sides of a road and reduced towards crown.

42

The excessive variations in thickness of a bituminous mix, laid on a poorly shaped substrate, can cause variations in initial compaction,! due to uneven temperature drop ) result in variable durability and reduce riding quality.

Prince of Wales avenue was rehabilitated and asphalt surfacing were completed on 1990. Section from railway bridge at Totalange to Totalange roundabout of Prince of Wales avenue along north bound carriageway was severely deformed. The deformed surface was removed in 1993 and it was observed that the asphalt layer was thicker at the lower edge of the road and thinner at the centre median. The total thickness of asphalt layer close to the centre was between 90mm to 120mm while thickness close to side was between 140mm to 300mm. This section was reconstructed up to formation level, to take only 110mm of asphalt overlay (40mm wearing course and 70mm base course). Graded aggregates having maximum particle sise of 50mm, were compacted in 75mm thick layers for the road base and then covered with 70mm asphalt base course and 40mm wearing course. In this section, after more than 3 years in service, no visible movement or deformation or fatting up observed, although it is subjected to severe stresses due to, the steep slope, bus halt and approach to the roundabout.

During this research 10 no of core samples were taken from Galle road, where there were large surface corrugations. The thicknesses of the core samples were given in Table 6.1.

Table 6.1: THICKNESS OF THE CORE-SAMPLES WHERE THERE WERE LARGE CORRUGATIONS

SAMPLE NO 1 3 4 5 6 7 8 9 10

THICKNESS (mm) 158 210 160 145 150 120 100 110 105 155

The designed total thickness of asphalt overlay was of 110mm. The above data shows that 70% of the corrugated places have overlay more than 110mm and the maximum is 210mm.

43

Another 10 no Of core samples were collected from the same road where there wer£ no deformations. The thicknesses of the ^omples were given in Table 6.2.

Table 6.2: THICKNESS OF THE CORE SAMPLES WHERE THERE WERE NO CORRUGATIONS

SAMPLE NO 1 2 3 4 5 6 7 8 9 10

THICKNESS (mm) 115 108 110 105 110 100 98 120 107 108

This shows the over lay thickness of nondeformed areas were closer to the designed over lay thickness. The thickness variations in core samples (overlay) are created by irregular road bases. Therefore it could be assumed that the possibility of occurring deformations on asphalt surfaces are high when asphalt is laid over irregular bases, specially when the overlay thickness exceeds the designed thickness.

44

7.0 THE POSSIBLE CAUSES OF POOR COMPACTION 7.1 INTRODUCTION

Rolling of various bituminous layers requires skill and care. A well engineered and executed construction job, employing the most advanced grading and levelling techniques and the best material and workmanship, can fail entirely due to poor methods in rolling and finishing. The goal of compacting an asphalt concrete pavement io to achieve the optimum air void content and provide a omoobh riding surface. Behind the paver, the mat has 15% to 20% air voids. It is the task of the rollers to reduce that void content to lees than 7% or less for dense-graded mixes. Caution must be exercised, however, not to compact the pavement to a air void level I o n s than 3%. this minimum void level is necessary to allow for thermal expansion, without causing flushing and mix instability. Compaction and rolling equipment for this purpose includes steel and pneumatic tired rollers (The asphalt handbook, 1989 ).

During compaction of asphalt, three very important factors which affect pavement performance will take place. The asphalt coated aggregate particles are pressed together, air voids are reduced, and mix density increases.

1) . Squeezing together of the aggregates, increases their surface to surface contact and inter-particle friction, resulting in higher mix stability and pavement strength.

2 ) . The reduction of air voids to the optimum level in the mix produces a pavement that is nearly impermeable.In an under compacted mix, the entrapped air oxidizes the asphalt binder, making it brittle and crack under repeated deflections of traffic loads. Water permitted into the pavement can lead to stripping of the asphalt from aggregate, weakening of the base and sutagrade.

3 ) . If hifch level compaction is not achieved during construction, subsequent traffic will further consolidate the mix non uniformly.

Improving compaction significantly improve load spreading Capability, resist fatigue cracking and resist internal deformation Of bituminous material. ( Asphalt handbook 1989 ).

45

7.2 MIX TEMPERATURE AT SITE

The temperature at which an asphalt is produced, affects both the initial time of compaction and the time it takes for the mix to cool up to 85°C ( The lowest temperature at which the compaction process ends). The upper limit of the temperature to begin rolling is the temperature at which the mix will support the roller 'without moving horizontally.

Most of the laying staff concern about the temperature at the initial compaction, but pay less attention to the temperature at which the compaction process must end up. At temperatures below 85°C, asphalt in combination with the fines in the mix, begins to bind the aggregate particles firmly in place. Consequently, compaction of the mix is extremely difficult once the mix has cooled to 85°C. The pate of reduction of temperature of asphalt varies with pi'evailing weather condition at the time of compaction. Care should be taken to achieve the required compaction before the asphalt layer reaches? 85°C. The number of rollers to be used, Eiethod of compaction etc. must foe decided accordingly.

7.3 LAYER THICKNESS \

At the time oif placement, the mix temperature is uniform i

throughout the thickness of the mat. However, the top and bottom surfaces cool more rapidly than the interior because they are in contact with the cooler air and subgrade or underlying pavement. The ability of thicker layers to retain heat longer, increases the time available for effective compaction to be carried out. If thick layers are laid in adverse weather conditions, a skin of relatively cold , stiff material rests on hot asphalt. Under these circumstances movement of the relatively fluid hot material may result cracking of the stiff surface crust during rolling ( The asphalt handbook, 1989 ). Cool air temperatures, high humidity, strong winds and cool surfaces alone or together shorten the time in which compaction must take place.

The optimum thickness of asphalt layer must be decided after giving due consideration to the capacity of compaction equipment, and to the prevailing weather conditions.

46

7.4 COMPACTION EQUIPMENT & METHOD OF COMPACTION

A common sequence of roiling begins with the steel three wheeled or two wheeled breakdown roller, followed by a pneumatic tire, intermediate rolling operation, and final or finish rolling by a steel wheeled tandem roller. The principal requirement of any roller is that it will compact the material being laid in an effective manner without introducing unacceptable irregularities. To ensure that a particular roller is capable of achieving the required leveL of compaction, it is necessary to carry out comparative trials.

To test effectiveness of the present method of compaction, core samples were collected 24 hrs after the asphalt concrete was laid from Olcott Mawatha close to Maradana Technical College junction. The positions of the core samples collected along the cross section of the road is shown in Figure 7.1

LANE 1

4

LANE 2

5

Fifjure. 7.1 : Positions of core samples collected.

*" - Positions where core samples were collected.

The width of the road was 7.3m and the asphalt concrete was laid by two 3.65m strips. Two wheeled tandem roller was used as break down roller and followed by pneumatic roller and finished by steel wheeled tandem roller. Each Roller made five no of passes over each and every place with an over lap equal to half of the width of the roller drum. The percentage of compaction achieved in the field were compared with the laboratory compaction, using collected cope samples collected, and the results are given in Table 7.1.

47

Table 7.1 : Percentage compaction

SAMPLE NO 1 n A 3 4 5 6

PERCENTAGE COMPACTION

97 102 102 100 102 99

From table 7.1 it is clear that both edges of the road were under compacted compared with the centre of the road. The method of rolling make every point on the road surface passed by each roller ten ( 5*2 ) times ( over lapping of layers ), except the points along the lower and upper edges ( near the kerb edges ). Points on stripa, having half of the width of the roller drum along the road edge were passed by rollers only 5 times ( no overlapping ). To verify the above results another eight no of core samples were collected, with two no of additional core samples collected from the edges, within Half of the roller width from the edge. The positions of the samples collected are given in Figure 7.2 and the results obtained are; given in table 7.2.

Fig 7.2 : Positions of core samples collected ( test no 2 ).

Lane 1 LANE 2

4 6 7

Table 7.2 : Percentage compaction ( Test B O 2 )

|'SAMPLE N 0 ~ 7 T 7 2 ~ 7 3 ~ 7 M 1 6 ~ 7 7 ~ 7 ^ l'

PERCENTAGE 97 97 102 100 103 104 COMPACTION

1

43

The results Obtained by the second test proved that the area close to the both sides of the road, within half of the width of the roller., were under compacted.

Under compacted layers consolidate with traffic and lead to nonuniform compaction. This may be one of the reasons for the severe deformations along the edge of the roads. This problems of under compacted edges could be eliminated by providing additional compaction to both edges. The required additional number of passes of rollers along the edges must be decided by compaction trials.

Compaction trial was performed on the same road to eliminate the area of under compaction. In addition to the method of compaction used earlier 5 no of passes were made using small roller with 1.0 m wide drum along the both edges. Percentage compaction was obtained and shown in Table 7.3.

Table 7.3 : Percentage compaction ( Test No 3 ).

Sample No 1 2 3 4 5 6 7 8

Percentage Compaction

99 101 102 103 102 100 102 100

It was clear from Table 3 that the problems of under compaction could be minimised by proper method of compaction which should be identified by compaction trials.

In addition to the workability of the mix and weight of the roller, the technique of rolling is important to obtain adequate compaction and good surface.

49

The following is considered as good practice: ( Transport & Road research Laboratory UK, Report 833 1976)

1. With static, steel wheeled rollers, the operation should always progress with the drive wheel forward in the direction of paving, because the direct vertical load applied by drive wheel is greater than the tilter wheel. If the breakdown pass of the roller is made with the tilter wheel forward, then the pushing force and the weight is slightly ahead of vertical and will cause material to push up in front of the wheels shown in fig 7.3.

FIGURE 7.3 : DIRECTION OF ROLLERS 50

2. Roller should never be allowed to stand on newly laid material.

4. Tho roller speed should not exceed 5km/hr. for steel wheeled static or vibratory rollers or Skm/hr. for pneumatic rollers.

5. Each pass over the material should be straight with the reverse pass in the same lane.

6. Changes in lateral position should be made only on material which has already' been well compacted.

7. Points of reversing of the roller on newly laid material should be staggered by one meter or so.

8. Longitudinal joints should be rolled directly behind the paving operation. The roller should be shifted to the previously placed lane so that not more than 150mm rides on the edge of the newly spread material. The roller should continue to roll along this line, until a thoroughly compacted, neat joint is obtained. Vibration should not be used when operating on a cold mat.

9. When transverse joint is placed next to an adjoining lane, ensure that, a ) , the first pass is made with steel wheeled roller moving along

the longitudinal joint for a short distance, b ) . the surface is then straightened and corrections are made if

necessary. 1

c ) . the joint is then rolled transversely same as in "8".

51

3. Rolling should be in a longitudinal direction from sides to centre, with the lower edge being rolled first, and then working over the araa in successive overlapping passes. The reason for this is that asphalt mixes, when hot, tend to migrate towards the lower side of'. the spread under the action of roller. If rolling is started on the high side, this migration is more than rolling starting from low side.

From interviews with asphalt laying staff and roller operators and from site observation, it was found that from the Huide lines above, only the fifth guide line i as correctly performed.

For example, it was found some roller operators park their rollers standing on newly laid surfaces waiting for the compaction of adjacent asphalt laying area. Therefore, it can be said that incorrect methods of compaction may cause deformations in asphalt.

52

8.0 THE POSSIBLE CAUSES OF ADVERSE TRAFFIC CONDITIONS

8.1 INTRODUCTION

Largo differences in traffic and other factors make greatly varying problems. Some streets and highways must accommodate vehicles with heavy loads, while others are subjected to only light vehicle traffic. Some roads are experiencing heavy traffic flows, while others subjected to less traffic. Roads experiencing different traffic conditions are subjected to different patterns of deformation characteristics and these differences are discussed in this chapter.

8.2 TYPE OF LOADING

The main external factor affecting the performance of a pavement structure is traffic loading. A wide range of vehicles use a road, from private (Jars to the heaviest lorries. The wear on the pavement structure due to cars and other light vehicles has been found insignificant and therefore the assessment of traffic loading for design purposes is based on commercial vehicles. The concept of equivalent load has been developed for this purpose and expresses mixed traffic in terms of an equivalent number of standard 80kN axle loads. Structural design is based on the cumulative number of jtandered axles to which the pavement will be subjected during its design life, taking account of the anticipated growth of commercial vehicles over the design life and the average wear factor per commercial vehicle. Due to the visco- elastic nature of bituminous materials, it can deform under heavy loading at high pavement temperatures ( The asphalt handbook, 1989 ).

Deformations are most likely where heavy vehicles are channelled into specific lanes, and is more severe on uphill gradients receiving direct sun. This is proved by the survey conducted along the Galle road to study deformations (T.5.5). ,The weighted values of fatting up along the lower side where most'c?f the heavy vehicles travels are three times more than the highs?;;* side.

53

8.3 VEHICLE SPEED

The low speeds increase the time of loading at any point on . the road surface. Relationship between time of loading and possible dofeoto obtained by Road Research Laboratory is given in Table S.i

Tabic 8.1 : Relationship between time of loading and possible defects

TIME OF LOADING

CONDITION IN PRACTICE

POSSIBLE DEFECT RELATIVE ! STIFFNESS AT 25"C

1 Month Settlement Cracking 4*10-7 i

1 Day Standing loads Deformation 1.2*10-5

1 Hour

0.4 Second

ij... . ,, , i n

Standing loads Deformation 3.0*10~ 4 1 Hour

0.4 Second

ij... . ,, , i n

(Penetration Test)

Deformation 1

ID - 3- Second Slow moving traffic, Effect on surfacing

1.Fatting up due to compaction

2.Deformation

o. o

1 0 ~ 2 Second Fast moving traffic, Effect on surfacing

1.Fretting 2.Cracking 3.Progressive

deformation

2.3*10i

10"'-' second l

Fc.st- moving traffic, Effect on surface particles

Fretting 1.0*102

( As a basis cf comparison, all the stiffness values are related to that of 100 pen bitumen under the conditions of the penetration test at 25°C.).

( A guide to the design of pavements, 1970. )

8.4 HIGH STRESSES

On gradients, tractive and breaking forces are greater and some redistribution of vehicle weights between axles occurs; one or more axles bear greater loading.

54

In areas of high traffic stress, such as approaches to junctions and pedestrian crossings, at roundabouts and where tight manoeuvring by heavy vehicles occurs, the fine texture of the aggregate particles themselves is more important than the coarse text are between aggregate particles. A high strength unchipped wearing course such as high stone content asphalt, or high strength surface dressing based on a bitumen extended epoxy-resin binder xtfith a high PSV (' resistance to polishing ) such as calcined bauxite, are normally considered necessary for these places. Where excessive indenting loadings or very high stress turning are envisaged, special typet; of surfacing may be necessary and very cvtrong foundations may be needed ( British Aggregate Construction Materials, 1920 ). Examples of such situations are,

* where tight manoeuvring by heavy vehicles produces abnormally high-stress wheel scuffing

* where heavy vehicles travel in tightly defined wheel tracks * where forklift trucks are operated *' where solid metal support feet or dolly-wheels of heavy

trailers rest on the surface.

High strength asphalt or dense macadam mixes may be suitable in these situations but in extreme cases may not be adequate. In which case special surfacing materials or alternative types of construction may need to be considered ( British aggregate construction materials 1990 . - "BACMI" information sheet No. 2 " Construction of parking areas for medium and heavy vehicles " and No. 6 "bituminous surfacing for high stress situations " ).

It can be clearly seen from the deformation survey data of Galle road that most of the the severe deformations exists close to bus halts or junctions ( turning points ), where high stresses are developed. Cut of the section of Galle road rehabilitated by R.C.D.C. from Mount Lavinia to Moratuwa the badly deformed section is the down hill at Mount Lavinia. In Kandy Colombo road, down hill close to Kclani bridge at Peliyagoda also deformed much more than the adjoining sections where the same type of asphalt concrete was laid. Presently in i Sri Lanka, nominal mixes are used in all situations irrespective of the stress situation which may lead to the failure of surfaces after few year in service.

55

9.0. CONCLUSIONS AND RECOMMENDATIONS: From the literature review , site observations, tests performed during this research the following conclusions could be made.

9.1. CONCLUSIONS :

1. The only method of mix design used in Sri Lanka is Marshall method of mix design. It may not be the best method of mix design suitable to local conditions.

2. If conventional asphalt batch plants are used for the production of asphalt, there may be grading differences between the actual grading of aggregates in asphalt and combined grading of aggregates used in mix design, specially in the region of fine aggregates.

3. It is evident from the literature review that different types of bitumen or special types of mixes have to be used for different field conditions.

4. The only type of bitumen available in Sri Lanka is pen 80/100 bitumen and it is used for all the applications, but it was not recommended by any literature.

5. Although the specifications recommended by RDA for bitumen content for wearing course asphalt mixes is between 5.0% - 7.0%, it has been proved that most of the asphalt wearing course surfaces with bitumen contents more than 5% in Colombo city deformed after very short period of service.

6. Asphalt production during rain and the using over wet aggregates cause excessive moisture presence in mix.

7. Laying asphalt during rain or cold and windy climate cause problems by rapid loss of temperature and it leads to under compacted asphalt surfaces.

8. Excessive variation of thicknesses of asphalt overlay due to surface irregularities of existing surfaces leads to nonuniform compaction and early deformations.

56

9. Some of the methods specified for the proper compaction of asphalt are not carried out.

57

10. There is a relationship between the characteristics of traffic and the mode of failure of asphalt surfaces.

11. Excessive application of tack coats and previously applied seal coats may increase the rate of deformation.

9.2 RECOMMENDATIONS:

58

From this research the following recommendations could be made.

1. Mix design methods other than Marshall method of mix design should be introduced to find out the most suitable method of mix design to Sri Lanka.

2. Production and laying asphalt during adverse weather should be restricted.

3. Guide lines for the proper compaction of asphalt to be introduced and laying staff and the roller operators must specially be trained for the compaction of asphalt.

4. Where excessive indenting loading or very high stress turning are envisaged, special types of surfacing may be necessary and very strong foundations are required. Further research is required to develop special types of mixes for such situations.

5. If the layer thickness is greater than 37.5mm application of tack coat should be restricted to special cases like the existing surface is very smooth.

6. Prior to asphalt overlay road formations should be prepared to take uniform thickness of asphalt overlay.

7. Harder bitumen than pen 80/100 bitumen must be introduced for few roads with different traffic conditions and their performances should be monitored.

8. For pen 80/100 bitumen

a ) . Voids in the mix should be kept close to the allowable upper limit ( 7% ) which leave space for further consolidation by traffic and to reduce the flow of bitumen during high temperatures without deforming the surface.

b ) . Bitumen content for the wearing course mixes should be kept between 4.7% and 5.0% keeping all other Marshall method of mix design requirements are satisfied, specially for the roads subjected to heavy and slow moving traffic in the city of Colombo till a decision is made through the first recommendation. The performance of these roads should be monitored and recorded.

59

REFERENCES

A guide to the design of pavements, (1970). Transport & Road Research Laboratory UK.

Asphalt Mixes: Design, Testing and Evaluation. (1991). Transportation Research Board, National Research Council, Washington, D.C.

Asphalt paving manual (1972). Asphalt Institute Maryland USA.

B.S. 3690 part 3 (1989). The British Standard Institute.

Bituminous construction handbook (1972). Barber Green Co Ltd. U.K.

Bitumen in road surfacing (1969). Shell International Petroleum Co Ltd., London.

Bituminous materials (1972). Shell International Petroleum Co Ltd., London

Bituminous materials in road construction (1980). Transport and Road Research Laboratory UK.

Brien, D., and Jackson, G.P. (1962). Asphaltic Concrete. Shell International Petroleum Co Ltd, London.

British Aggregate construction materials , (1990). Transport & Road Research Laboratory UK.

Flaherty, C.A. 0', ( 1976 ), Highway engineering volume 2.

Highway Research Board bulletin 105, (1985). National Academy of Science & National Research Council USA.

Ishikawa, K. (1979). Guide to quality control.

Kume, H. (1990). Statistical methods for quality improvement.

Mix design methods for asphalt concrete and other hot mix types (1986). The Asphalt Institute Maryland USA.

Prediction of pavement performance and the design of overlays (1976). Transport and Road Research Laboratory report 833.

Shell Bitumen handbook (1972). Shell Petroleum Co Ltd., USA.

Standard specifications for construction and maintenance of roads and bridges (1989). Road Development Authority of Sri Lanka.

The asphalt handbook (1989). Asphalt Institute Maryland USA, Manual series no 4 (MS- 4 ) .

Wahhab, H. Al- Abdul, & Khan, Z.A., (1991). Evaluation of Marshall & Hveem mix design procedures for local use, Transportation research record No 1317. National Research Council USA.

60

11. APPENDICES:

11.1. APPENDIX "A"

SURFACE DEFORMATION DATA ALONG GALLE ROAD FROM BAMBALAPITIYA ( UNITY PLAZA ) , TOWARDS GALLE ( 500m )

Sheet 1

L.H. SIDE SOUTH BOUND NORTH BOUND R.H. SIDE CARRIAGEWAY CARRIAGEWAY

Chainage

0 *** *** o *** 10 #** *'** o * ** 20 **# ** o o #* 30 **# #* * o o * 40 *** ** o o o *

50 ##* ** * o * 60 #** ** o o * 70 ** ** o o ** 80 ** o o * #* 90 * * o o **

100 **# #* * o **• #*# 110 *** *•* * o o *# 120 **# * o * ## 130 w o o * *# 140 *** * * o o *

B 150 *#* ** * o * ## 160 ** *•* # o o ** 170 * *• o * * 180 ** * o o o ** 180 o o * * 190 o o o **

*** - Severe deformation **• _ Medium -do-* - Mild -do-o - No , -do-B - Bus halts J - Junctions

i

SURFACE DEFORMATION DATA ALONG GALLE ROAD FROM BAMBALAPITIYA ( UNITY PLAZA ) TOWARDS GALLE ( 500m ) Sheet 2

L.H SIDE

Chainage

200

210

220

230

240

250

260

270

280

290

300

310

320

330

340

350

360

370

380

390

SOUTH BOUND CARRIAGEWAY

I

*

o

o

*

o

*

o

o

o

NORTH BOUND CARRIAGEWAY

R.H SIDE

o

o

*

o

o

o

o

o

o

*

o

o

o

o

o *

**• ## ##

*#* *#

##

o

*

*#

- Severe deformation ** - Medium deformation * - Mild deformation

B - Bus halt J - Junction

ii

SURFACE DEFORMATION DATA ALONG GALLE ROAD FROM BAMBALAPITIYA ( UNITY PLAZA ) TOWARDS GALLE ( 500m ) Sheet 3

L.H SIDE

Chainafie

400 J

410

420

430

440

450

460

470

480

490

500


* * *

O

o


o

o

*

R.H SIDE

***

### - Severe deformation ** - Medium -do-* - Mild -do-o - No -do-

B - Bus halt J - Junction

iii

SURFACE DEFORMATION DATA ALONG GALLE ROAD FROM WELLAWATTA (HOTEL SAPPHIRE), TOWARDS GALLE ( 500m ) Sheet 1

L.H SIDE

Chainage

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190



R.H. SIDE

XX

*#

XX

xx

.XX

XX

XXX

xx-a

XX

XX

XXX

XXX

XXX

XXX

XXX

XXX

xxx

XX

XXX

XXX

X •

X

XX ,

XX

XX

XX ,

XXX

XX

XX

XX

X

x :

X

X

XX

XX

XX

X ,

XX

xxx

o

o

*

X

XX

X

X

o

o

o

o

o

o

X

X

X

X

XX

xxx severe deformations XX medium - do -* mild - do -o no - do -

B - Bus halt3 J - Junctions

xx

xx

XXX

xx

xxx

X

X

X

X

X

xxx

X

X

X

XX

X

XX

XX

XX

X

xxx

xxx

xxx

xxx

xxx

XX

X

X

XX

X

xxx

xxx

XX

xxx

xxx

xxx

xxx

XX

XX

X

iv

SURFACE DEFORMATION DATA ALONG GALLE ROAD FROM WELLAWATTA (HOTEL SAPPHIRE) TOWARDS GALLE(500m) Sheet 2

L.H. SIDE

Chainage


200

210 B

220

xxx

XXX

XXX

XXX

XXX

XXX

*** XXX.

** XX

* *

XXX

** XX

XX

XX

XX

X

XX

XX

XXX

XXX

xxx

XX

xxx

xxx

xxx

XX

XX

X

X

XX

X

X

X

X

o

o

o

X

XX

XX

XX

X

X

X

XX

X

X

X

X

X

X

o

o

o

o

o

o

xxx Severe deformations xx Medium - do -* Mild - do -o No - do -

B - Bus halts J - Junctions


o x

o X

o *

* xxx

x xxx

X XX

X xxx

o x

o X

X XX

XX XX

X X

X XX

o x

o x

o *

* ** X X xxx

XX XX

R.H. SIDE

X

X

X

XXX

XX

XX

xxx

XX

XX

XX

xxx

xxx

xxx

XX

X

XX

xxx

xxx

xxx

XX

V

SURFACE DEFORMATION DATA ALONG GALLE ROAD FROM WELLAWATTA (HOTEL SAPPHIRE, TOWARDS GALLE (500m) Sheet 3

Chainage

400 * 410 o

420 o o * 430 o o *

440 * o o * * 450 >fc o

460 #*# #* o * J

470 o

480 * * 490 ** 500 o o o

*## Severe Deformations #* Medium - do -* Mild • - do -o No - do -

B - Bus halts J - Junctions

vi

L.H. SIDE SOUTH BOUND NORTH BOUND R.H. SIDE CARRIAGEWAY CARRIAGEWAY

Appendix B

Summery of core sample data analysis :

SAMPLE NO

LOCATION Amount of Deformation

Sample Height (mm)

Binder content W.C (%

% Passing 75um Sieve

1 P.of Wales Av Severe 140 6.0 9.0

2 - Do - , Nil 115 4.9 4.2

3 - Do - Mild 115 5.1 7.5

4 - DO - Nil 105 5.0 5.1

5 - Do - Severe 105 5.9 10.0

6 - Do -1

Severe 165 5.8 8.8

7 - Do - Mild 110 5.2 7.9

8 - Do - Mild 120 5.3 8.1

9 - Do - Nil 105 4.8 4.9

10 - Do - Severe 190 6.1 9.3

11 Galle road i Severe 100 5.9 9.6

12 - Do - Severe 140 6.2 11.1

13 - Do - Mild 120 5.1 7.8

14 - Do - Nil 120 5.0 5.2

15 - Do - Nil 100 4.8 5.4

16 - Do - • Severe 115 5.9 9.5

17 - Do - Nil 110 4.9 5.6

18 - Do -: Mild 130 5.4 i 7.4

19 - Do - Severe 210 6.1 9.0

20 - Do - ' Severe 145 6.2 10.7

M A T E R I A L S L A B O R A T O R Y

Colombo Municipal Council-Colombo 14

DETERMINATION OF PERCENTAGE OF BITUMEN IN ASPHALTIC MIXTURES AASHTO zT164 z76 iASTM_p2172 : :75_ .y

SOURCE: t ~ - ' PROJECT:- J T - " r----7 y . ----r-, A -> LOCATION:- - - ^ g - ^ — ° / - ^ — C J ^ A i ^ i . . ^ ^ " V SAMPLE:-DATE : ~

(W. C/S-i-G) , RECIPE No.'

EXTRACTION

l.Wt.of Pan + Filter Paper-2.Wt.of Pan + Filter Paper + Sample

3.Wt.of Sample (2) - O )

4.Wt.of Pan + Filter Paper +_• Extracted Sample {oven dried)

5.Wt. of Extracted Sample (4) - (1)

6.Wt. of Bitumen (3) - (5)

7.Percentage of Bitumen by Wt. of Mix {6J_ x 100 (3)

. . - ? f f f gm

6 • o %

.gm

. gm

. gm

, gm

. gm

GRADING OF EXTRACTED AGGREGATE

Sieve Size Wt. Retained % Retained % Passing % passing (Soecificatxoi

2 8 m m O o a /'OO fc* \S 1 1 1 1 1 1

7 Omm c o / o o

10mm 7/-S 6qjJ2- — 5 m m m>A '6- <? • C T - O

2 . 3 6 i t l t i /*6-J • f 1.18mm <r<6 < o 600um 7 S-2-300pm 7 0 - 4 8 J 150um • 9 0

0 . : ."_ . 1 76'S p. o — Total | * * ? - 9 J

M A T E R I A L S L A B O R A T O R Y Colombo Municipal Council-

Colombo i 4 .

DETERMINATION OF PERCENTAGE OF BITUMEN IN ASPHALTIC MIXTURES AASHTO-T164-76,ASTM D2172-75

SOURCE: r- : . PRO J ECT: ^ - - r - 7 7 - 7 3 " - ] - - / ~ 7 —

LOCATION:- *-l^r^L_SJ--£LtL*P. JTL^L^ 111-Lcg±t.IL'lA.'* ' SAMPLE: (5* (W.C/B-s-€-), RECIPE No. — DATE :-_ £S^/J_^yj>__

EXTRACTION

l.Wt.of Pan + Falter Paper- .... ,./. gm 2.Wt.of Pan + Filter Paper + Sample » 9 m

3.Wt.of Sample (2") - ( jr) . . .t?. .. .gm

4.Wt.of Pan + Filter Paper Extracted ??.^A '. Pi. .9™

Sample _(oven dried)

5.wt. of Extracted Sample (4) - (1) .g">

6.Wt. of Bitumen (3) - (5) f ^ ' t . 9™ 7.Percentage of Bitumen by Wt. of Mix

(_6_l x 100 (3)


Sieve Size Wt. Retained % Retained % Passing % Passing (Soecificatioj

*) R mm 0 • 0 /rio

0 Dram c c /&o rcrO

1 Omm 9 6?- O

5 mm IS h £/•*'

. .• 2.3 6mm i n 2 /6 • 3 as-3 1.18mm a c 7-7 *?• 6 600pm jji • 1 s i

300pm i s h S-c

150pm *iT 0 3 •£ 9-6 7 511 -Ti 3g • 3 • V S A

i—f.—i l h • h . . . — - —

Total

V I & a

Colombo Municiool Council-Colombo \4

SOURCE: t PROJECT:-L O C A T I O N ^ " - ^ ^ SAMPLE:- — ® - (W.C/-B^e), RECIPE No. -•— DATE : ~ _ f f / j L / f - L

DETERMINATION OF PERCENTAGE OF BITUMEN IN ASPHALTIC MIXTURES AASHTO-T164-76,ASTM D2172-75 .+

EXTRACTION

l.Wt.of Pan + Filter'• Paper-2.Wt.of Pan + Filter Paper + Sample

3.Wt.of Sample (2) - ($)

4.Ht.of Pan + Filter Paper +L-Extracted Sample _(oven dried)

5.Wt. of Extracted Sample (4) - (1)

o.Wt. of Bitumen (3) - (5)

7.Percentage of Bitumen by Wt. of Mix j_6_2 x 100 (3)

. "?.*V>o gm

•ApM'A 9m

, .gm

• •••••••••3 7 • 3 gm


Sieve Size Wt. Retained % Retained % Passing % Passing_ (SDecificai ? ft m m o . c /OO /o o 2 0mm o c 1 Omm 70-1 So-so 5 mm £ 3 0

. . 2.3 6 mm 12/ • fe iS% 1.18mm y - 2 i i - o

600um 9 • SI *s- •) 3 00pm e ' S - ; To /Si 150um s-j? o S • 7 7 5 u-Ti 4 -7 T-S i-=LyM L i

66-/ Total

a study on quality control and assurance measures …

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