TRANSPORT AND ROAD RESEARCH LABORATORY Department of Transport

RESEARCH REPORT 104

THE PREPARATION OF CUTBACK BITUMENS TO ASTM

SPECIFICATIONS BY BLENDING READILY AVAILABLE

CONSTITUENTS

by L S Hitch and M Stewart

The work described in this Report forms part of the programme carried out for the Overseas Development Administration, but the views expressed are not necessarily those of the Administrat ion.

Overseas Unit Transport and Road Research Laboratory Crowthorne, Berkshire, RG11 6AU 1987

ISSN 0266-5247

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on 1 st April 1996.

This report has been reproduced by permission of the Controller of HMSO. The work described in this report forms part of a programme carried out for the Overseas Development Administration, but the views are not necessarily those of the Administration. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

CONTENTS Page

Abstract 1

1. Introduction 1

2. Objectives 1

3. The American System of classification 2

4. Applications of cutback bitumens 2

4.1 Priming 2

4.2 Surface dressing 4

4.3 Stabilisation 4

4.4 Tack coats 4

4.5 Bi tumen-- aggregate mixes 4

5. Blending study 4

5.1 Blending procedure 4

5.2 Viscosity tests 4

5.3 Distillation characteristics 5

5.4 Discussion 9

5.5 Other requirements 9

5.5.1 Flash point 9

5.5.2 Residue from distillation 9

6. Manufacture of MC and SC cutback grades 10

7. Manufacture of cutbacks to BS 3690 Part I 11

8. Preparation of cutbacks under site conditions 12

9. Conclusions 12

10. References 13

11. Appendix 1. Properties of materials 14

12. Appendix 2. Conversion to kinematic viscosities 15

13. Appendix 3. Viscosity results for all blends 15

© CROWN COPYRIGHT 1987 Extracts from the text may be reproduced,

except for commercial purposes, provided the source is acknowledged.

THE PREPARATION OF CUTBACK BITUMENS TO ASTM SPECIFICATIONS BY BLENDING READILY AVAILABLE CONSTITUENTS

ABSTRACT The high viscosity of penetration grade bitumens can be reduced by the addition of volatile diluents (cutters) to make cutback bitumens suitable for specific road building applications. In many countries the choice of cutbacks available commercially is very restricted but cutbacks can often be made locally by blending more readily available components. A range of laboratory blends have been tested to examine compliance with the widely-used American classification system and recommended compositions are given for cutbacks using 50 pen and 100 pen base bitumens. With the latter both medium and slow curing cutbacks could be made but with the former only medium curing blends satisfied the specifications. Rapid curing cutbacks could not be made with either grade. Blends were also produced which complied with the main requirements for the three grades specified in BS 3690 Part I.

1 INTRODUCTION Cutback bitumens are manufactured by reducing the viscosity of a relatively hard bitumen using selected volatile diluents (cutters). Their composit ion is such that bitumen can be easily incorporated into a road structure for a variety of purposes, the diluent subsequently evaporating, thereby restoring most of the high viscosity associated with the parent bitumen. The rate at which evaporation occurs during the 'curing' process depends largely upon the volatility of the diluent but other factors such as exposed surface area, ambient temperature and the movement of air also contribute.

The individual demands of different road construction and maintenance operations require cutback specifications enabling both viscosity and curing characteristics to be selected. In the UK, and in Europe generally, cutbacks are used mainly for surface dressings and for some macadam compositions (BSI, 1973). Aw ide choice has been found unnecessary, only three grades being described in the relevant British Standard (BS11982a).

Road construction and maintenance in tropical countr ies encompasses a much wider range of cl imate condit ions and construction processes. The American system of cutback classification (ASTM, 1986) provides a broader range of binders from which suitable combinations of viscosity and curing characteristics can be selected. However the choice of binders is f requent ly restricted and it is not surprising that many problems with bituminous materials are attr ibutable to the use of unsuitable grades.

Fortu nately it is possible to prepare many cutback b i tumens from readily available components by blending in a central plant or on site. This report describes the results of a laboratory investigation which shows how this can be done.

Confusion often arises as to the scope of the term 'cutback' since the addition of about ten per cent or less of di luent to moderately hard bitumens can produce binders whose consistency can be measured by the penetration test. These binders are more viscous than those covered by the cutback specifications. For most practical purposes the term cutback is usually associated wi th bi tumen-di luent blends whose v iscosi ty does not exceed 6000 centistokes at 60°C (ASTM, 1986). Such a definit ion is used in this report. More viscous blends are referred to as 'blended binders'.

2 OBJECTIVES The objectives of the study and this report are

a) to describe the American system of cutback classification and to discuss the selection of cutbacks for application in tropical developing countries,

b) to present the results of a laboratory blending investigation and to show how to prepare cutbacks to the American specifications using readily available components,

c) to provide practical guidelines for the manufacture of cutbacks on site.

3 THE AMERICAN SYSTEM OF CLASSIFICATION

Prior to 1962, American practice differentiated cutbacks using a system of six viscosity bands, numbered from 0 to 5, and three different curing rates wi th in each band, namely rapid, medium and slow. There were therefore eighteen grades available.

In 1962 a more rational system was introduced. The six viscosity bands were reduced to five new ones which were defined by kinematic viscosities at 60°C. The range of allowable viscosity within each band was defined in such a way that the upper limit was twice the lower limit, the lower l imit itself being used for identifying the viscosity grade. The three curing rates were retained for each grade except that only a medium curing cutback was specified for the most fluid grade ie MC 30. The current American specifications are as fol lows.

Specifying body Cutback curing type and specification reference

American Society for Testing and Materials (ASTM)

American Association of State Highway and Trans- 3ortation Officials (AASHTO)

Rapid (RC)

D2028

M81

Medium (MC)

D2027

M82

Slow (SC)

D2026

Slow-cur ing cutbacks are sometimes referred to as 'road oils' in the USA.

Because of the wide range of cutback grades available, the American system has been adopted in most tropical developing countries. The 1962 viscosity graded system is most often used but some countries still retain the original classification. Figure 1 shows the relationship between the two systems.

4 APPLICATIONS OF CUTBACK BITUMENS

The fo l lowing list of applications is presented in the order of their frequency of use with the most common first.

4.1 PRIMING The main purpose of a prime coat is to help

Current American cutbacks

(Viscosity range (centistokes at 60°C) is f rom value shown to double that value eg. 800 to 1600)

RC MC SC 3000

Tradit ional American cutbacks

RC MC

5 sc 1

RC MC SC

800

RC MC SC

4

RC MC SC

3

RC MC SC [ j 250 RC MC SC

2

RC MC SC

70

MC 30

RC MC SC

1

RC MC SC 0

These Kinematic Viscosity values at 60°C have been calculated f rom Viscosity Temperature charts and Viscometer conversion factors. They are therefore only approximate values

Fig. 1 American cutback grades

1 0 4

- - 103

o O ~o

8 =u >

102

=..~ I01

maintain adhesion between a layer of non- bi tuminous material and a bituminous surfacing. Its function is to bind the surface of the underlying layer by penetrating the voids to a depth of 5-10 millimetres. The prime coat must therefore be capable of wetting and penetrating the dust film covering aggregate particles and coating the aggregate. Surface porosity affects binder choice and low viscosity must be maintained for several hours. MC 70 is commonly used or MC 30 at lower temperatures or for very close textured surfaces. MC 250 is occasionally used for very open textured surfaces.

2

Coated chippings. Reduce lower temperature limit by about 10°C

Too stiff (poor wett ing) Too f luid (drainage and wh ip-o f f )

8

>

107 8 6 4

106 8 6

105 8 6

10 4 8

6

4

UJ d nr~ LU

o~ Z

_l

103

8

6

100 10

I 5O

20 3O 4O 50 6O 70

I I I I I 77 100 122 140 160

Surface temperature

Fig. 2 Relationship between road surface temperature and suitable binder for surface dressing

8O 90

I 180

(°C)

(OF)

3

4.2 SURFACE DRESSING For a surface dressing the binder must be fluid enough to wet the chippings yet viscous enough at road temperatures to retain the stone and prevent 'whip off' by traffic. Once wetting has been achieved, a rapid increase in viscosity is advantageous. Figure 2 may be used to assess the binder grade required. Road temperatures in many tropical countries are too high for surface dressing using cutbacks. MC 3000 is the most common ly used cutback. RC 3000 would be preferable but the risk of fire at the spraybar is increased.

4.3 STABILISATION Local materials such as sands and natural gravels can be stabil ised with cutbacks, usually at ambient temperature. The viscosity of the binder needs to be low to begin wi th to coat the aggregate but a rapid increase in viscosity is desirable once coating has been achieved. RC 80 and RC 250 are commonly used, depending on ambient temperatures. MC 250, MC 800 and MC 3000 have also been used but extended aeration is needed to remove a proport ion of the volatiles before compaction

4.4 TACK COATS A tack coat is a very thin layer of bitumen used to ensure a good bond between two layers of asphalt. It is essentially a glue hence thick films and low viscosities must be avoided. RC 250 is often specified but it is difficult to avoid excessive fi lm thickness with this grade. The area must be closed off to permit curing before paving commences. Quick breaking emulsions are usually preferable.

4.5 BITUMEN-AGGREGATE MIXES Mixed materials, using cutbacks are usually manufactured only for maintenance patching. The mixes must remain workable in the stockpile over long periods. MC 3000 is normally used for this purpose. RC 250 is sometimes used for preparing precoated chippings.

5 T H E B L E N D I N G S T U D Y

The pr imary characteristic of the various grades of cutback bitumen designed to the American classification is the kinematic viscosity at 60°C but the rate of curing, the residual bitumen content and the properties of the residual b i tumen are also important.

The fol lowing stock samples of bitumen were used

i) Nominal grade 100 pen, specification 80-120 pen, actual penetration 90.

ii) Nominal grade 50 pen, specification 40-60, actual penetration 61.

The diluents used were automotive diesel and kerosene and a blend of kerosene and diesel in the proport ion 3:1 by volume. Kerosene is popularly referred to as 'paraffin', ie the distillate oil used for heating and lighting purposes. The properties of these materials are given in Appendix 1.

Blending quantities were based on a fixed mass of bitumen namely 750 grams. At a blending temperature of 120-130°C this occupies a volume of 773 ml. In the blending programme total blended volumes ranged from 800-1300 ml.

5.1 BLENDING PROCEDURE Preweighed batches of bitumen were heated with continuous stirring to between 120 and 130°C in lever-lid tins.

When all lumps had been dispersed, calculated volumes of diluent were added slowly, again with continuous stirring. The stirring action was considerably more vigorous than is normally attainable under field conditions. The recommended procedure for blending on site, described in section 8 below, emphasises the importance of the tank filling operation, in which a vigorous swirling motion is generated, to obtain good mixing.

5.2 VISCOSITY TESTS Blends were allowed to stand for at least 24 hours in t ightly closed tins before being reheated as necessary and again stirred prior to removing samples for testing as follows:-

Penetration at 25°C (BS 2000 Pt 49) for diluent percentages up to 10 per cent by volume.

ii) Viscosity at 60°C using a Brookfield HATD torsional viscometer for absolute viscosities above 200 centipoise.

iii) Viscosity at 60°C using a Rion model VT-03 viscometer for absolute viscosities below 200 centipoise.

iv) Viscosity at 40°C using a Standard Tar Viscometer (BS 2000 Pt 72) to test compliance with BS 3690 Part 1.

4

Absolute viscosit ies were converted to kinematic viscosit ies using calculated densit ies for each blend as described in Appendix 2. The viscosity measurements are i l lustrated in Figures 3 and 4 and the results tabulated in Appendix 3. The penetrat ion results are shown in Table 1.

100 000

c) (o

>

10 000

1000

100

i,O,e,e, 3:1 Kerosene/d iesel

10 I I I l I | I ! 0 5 10 15 20 25 30 35 40

D i luen t (per cent vo l . o f b lend)

Fig. 3 Viscosity of 100 pen base bitumen blends

Diesel

O 3 :1 Kerosene /d iese l

10 000

% c.o

1000

8 100 --

100 000

10 I I I I I i , J a 0 5 10 15 20 25 30 35 40 45 50

D i l uen t (per cen t vo l . o f b lend)

Fig. 4 Viscosity of 50 pen base bitumen blends

5.3 DISTILLATION CHARACTERISTICS On the basis o f these results, selected blends hav ing v iscos i t ies w i th in or close to the ASTM specification ranges (Figure 1 ) were examined for the i r d is t i l la t ion characteristics. To i l lustrate the results, those for two blends for each of the cur ing rate categor ies ie MC, SC and RC for the 50 pen base b i tumen are shown in Tables 2, 3 and 4 and for the 100 pen base b i tumen in Tables 5, 6 and7 .

T A B L E 1

Penetration at 25°C of b i tumen/d i l uen t blends

Diluent )er cent 3f blend

4 6 8

10

Base bitumen, 50 pen (nominal)

Kerosene

153 226 265 424

3:1 Kerosene-

diesel

140 222 241 470

Diesel

144 210 241 371

Base bitumen, 100 pen (nominal)

Kerosene

3:1 Kerosene-

diesel

232 361 392 536

236 383 432 602

Diesel

211 317 363 553

5

C (13

..gl

i - -

-",.'2.

(,- (]3

O O . . , - O ~ u - ~ v

II II c ~

35

0

0

(.3

¢-

0

I - - ._~ f f l . ~ _

Or)

e- 0

I - - . ~

o 0

0

0

O

f ~

--ff

.-ff 0

r,- "o ~

A r -

E

(.0

A I -

E

0

c,4

0

~ 4

E

r-

E o (.) t - o

Z

I 'N

14.1 . , ,4

( -

n--

C

0

I--

O o 03

e- 0

( /3

i -

II ( ~ o

I . - . ~

0

0

o o

I E ('~ r--

¢- c -

E E E tO O O (v) (.O OO

70 A

r,.- - o

A

E O Q0

a~

'E

E I..o

0O

=o 7O

n "

O

00

O o4

o0

o= 7O

"6 F:,

O z

¢ 0 0 o Z

(J C it0

13..

E O (.3 ¢-

O Z

(/')

C:

0 mr"

C

w , o

I - -

Q.

o

0

C~

T--

II :-)

c t~ o~ O .

E 0

C 0

Z :,it

LILI u l DO

I--

(/) " 0

(1) ..Q C_)

o

- i

r r"

I -

to

c II

o ~

0 o

0 L~ C~

c 0

Q.

t - O

~2

0 .

0 C~ t.O

0 O0

0

o o L~

c~ L~

oo ~ oo

o

0

0 r'-

0 Z

¢-

0 - 0

I -

cO

a

i -

<~

q.)

Q .

0 0

to o~ :_~ "-i Q . . ~

CC

0 z z

e,-

ffl

ffJ

I--

o --1

II

55

~ ._0 o

a . ~

~ ~ o o

0

"0 A

8 = " ~

LO

O0

0

(I)

O0

0

(/)

ffl

>-

e - 0

E ~ 8 ~ g ~

0 ,Zz

¢y-

F--

o 0

I.-.~_ u)~ E

I-- .~-

f f l

" 0 A

0 "--" o

E v

A CZ

. _

E I .N

0

&

0

0

0 z

f..

c'0

Q .

E o r

0 z

A general summary of all the results is given in Table 8.

TABLE 8

Cutback disti l lation tests; volati l i ty characteristics of recovered disti l late

Diluent 50 pen blends I 100 pen blends l

Kerosene Volatility too low for RC grades Volatility too high for MC grades

Kerosene/diesel 3:1

Diesel

Volatility satisfactory for MC 3000, 800 and 250 grades. Marginally high for MC 70

Total distillate (as per- centage of cutback) is generally too high (ie residual bitumen too low).

Volatility satisfactory over entire MC range

Total distillate (as per- centage of cutback is satisfactory for the SC range.)

5.4 DISCUSSION Al though SC cutbacks are rarely used in tropical countries, satisfactory blends are attainable using 100 pen bi tumen and diesel fuel. The mixture of kerosene and diesel in the ratio 3:1 is a suitable di luent for preparing MC cutbacks. The sl ight ly high volati l i ty noted above for the MC 70 blend prepared using 50 pen bitumen reflects the higher proport ion of diluent required in compar ison wi th that needed for 100 pen bitumen. It is unlikely that this small deviation f rom the ASTM specifications will affect performance.

The disti l lation range of the kerosene was too high for making RC type cutbacks. The percentages of di luent recovered to 190 and 225°C were too low. It is likely that this could be rectified by the use of 'power kerosene' ( 'vapourising oil') which has been recommended by other authorit ies (eg NAASRA, 1965).

5.5 OTHER REQUIREMENTS In addit ion to the principal test criteria, ie viscosity and disti l lation characteristics, ASTM Specifications D2026-28 include other requirements as discussed below.

5.5.1 Flash Point This test est imates the temperature at wh ich an igni table a i r /vapour mixture is present at the surface of a l iquid under specif ied test condit ions. For the successful MC and SC blends prepared using 100 pen b i tumen, low values are unlikely since the blends had sat isfactory dist i l lat ion characteristics. For the 50 pen blends, the quant i t ies of recovered disti l late were general ly high wh ich could adversely affect the flash point.

5.5.2 Residue from distillation The percentages of residue were satisfactory for the MC and SC type cutbacks blended using 100 pen b i tumen. For the 50 pen b i tumen blends, the percentage of residue was satisfactory for the MC grade but the SC b lends produced excessive dist i l late (Tables 2-7).

The consis tency of the residue was measured using the penetrat ion test. The kerosene blends were unsuccessful RC candidates and were not tested further. The SC blends are of little interest in t ropical env i ronments and therefore the tests were not done. Table 9 summar ises the results for the MC blends.

9

TABLE 9

Penetration of residues

Base bitumen (pen)

31 (nominal 50)

)0 (nominal 100)

Diluent range (per cent vol)

15 to 45

10 to 35

Range of observed penetrations

163-316

188-350

Specification ASTM D2027

120-250

The specif ied upper l imit of 250 pen was approached by the fo l lowing blends.

Base bitumen Diluent Cutback produced Pen of residue (per cent vol)

31 (nominal 50) 30 MC 250 242 )0 (nominal 100) 20 MC 800 233

These results suggest that blends prepared for surface dressing, MC 250 and higher viscosity blends, should not give problems arising from a low v iscos i ty residue after curing. At higher d i lu t ions, eg MC 70, softer residues are expected but th is should not seriously affect the per formance of these cutbacks when used as p r imes which is their principal application.

6 THE MANUFACTURE OF MC AND SC CUTBACK GRADES

The exact composi t ion of cutbacks to ASTM speci f icat ions may be estimated using Figures 3 and 4. Table 10 shows the blends which were found to meet the viscosi ty and dist i l lat ion

TABLE 10

Diluent blending range for American grade cutbacks (per cent by volume of blend).

a) 50 pen bi tumen, nominal (61 pen actual)

Cutback

MC

3000 800 250

70

Acceptable range of 3:1 Kerosene/diesel

(per cent)

Lower limit

14 21 27 37

Upper limit

18 24 32 45

b) 100 pen bitumen, nominal (90 pen actual)

Cutback

MC

3000 800 250 70

Acceptable range of 3:1 Kerosene/diesel

(per cent)

Lowe r limit

12 17 24 35

Upper limit

14 21 30 44

c) 100 pen bitumen, nominal (90 pen actual)

Cutback Acceptable range of diesel (per cent)

SC Lower Upper limit limit

3000 14 17 800 20 24 250 27 33

requirements and indicates the range of diluent percentages which were found acceptable. The Table shows that for a given cutback, the percentage of diluent needed when using 50 pen base bitumen is about 3 per cent more than for 100 pen base bitumen.

The data in the Table should be regarded as a guide. The precise properties of blends wil l depend on those of the constituent materials.

10

7 THE MANUFACTURE OF CUTBACKS TO BRITISH STANDARD 3690 PART 1

Brit ish Standard 3690 Part I (BSI, 1982a) defines three grades of cutback b i tumen by means of the standard tar v iscometer namely 50, 100 and 200 seconds (10 mm cup at 40°C). To relate these grades to the ASTM system several blends of 100

pen b i t umen and kerosene/d iese l cut ter were tested for v iscos i ty us ing the s tandard tar v iscometer . The results are p lo t ted against d i l uen t content in Figure 5. The percentage of d is t i l la te recovered to 360°C is shown in Figure 6. Table 11 i l lust rates the proper t ies of three b lends wh ich sat isf ied the BS 3690 v iscos i ty requ i remen ts and shows h o w they are related to the Amer i can classi f icat ion. The cutbacks fall into the m e d i u m cur ing (MC) category.

T A B L E 11

Cutback blends of 100 pen b i tumen and kerosene/diesel sat isfy ing BS 3690 Part 1

Grade (seconds, STV)

Per cent diluent (of blend)

Viscosity STV (10 mm 40°C) (seconds)

Distillate (per cent volume to 360°C)

Approximate kinematic viscosity at 60°C (cSt)

Relationship to ASTM system

50

Blend 1 Spec

16 45 40-60

11 8-14

2000

Blend 2

13

91

8

4500

100

Spec

80-120

6-12

Blend 3

11

161

6

7000

Between MC 800 and 3000

200

Similar to MC 3000

Spec

1 6 ~ 2 ~

~ 1 0

More viscous than MC 3000

O o O ~ r

E E

O

>- }- ~3 v

>

400

300

200

100

0 - I I I 0 5 10 15

Di luent (per cent vo lume)

Fig. 5 Viscosity (STV, 10mm) at 40°C versus per cent diluent

¢J o 0 LO

o

"o

E

o .

20

30

20

I0

I I I I I 0 5 10 15 20 25

D i l u e n t (per cen t vo l ume)

Fig. 6 Per cent distillate recovered to 360°C for different blends

30

11

8 P R E P A R A T I O N O F C U T B A C K S U N D E R S I T E C O N D I T I O N S

In most tropical and subtropical countries 80/100 penetrat ion grade bitumen is most frequently used for surfacing mixes and for surface dressing. In very hot areas such as the Gulf States, 60/70 pen grade is more common.

Since the base bitumen in commercially produced cutbacks is usually 100 pen grade it is a relatively s imple matter to produce otherwise unobtainable cutbacks under field conditions; it is only necessary to establish the appropriate manufactur ing techniques, diluents and blending proport ions.

Cutbacks are manufactured commercial ly using blender units. These contain proport ioning devices and are designed to produce an efficient mix ing action. Typical units produce about 40-50 tonnes per hour but smaller units are available. It is advisable to use a blender unit if at all possible because it el iminates the possibil i ty of Iocalised concentrat ions of di luent during blending and also the risk of generating large amounts of solvent vapour wi th the attendant fire hazard. It must be remembered that all cutbacks are potent ial ly dangerous and strict precautions must be taken to avoid sources of ignition such as cigarettes, fires, heating devices and particularly the burners on bitumen distr ibutors and decanters.

Simple equipment can also be effective in preparing cutbacks. The requirements are:

ii)

iii)

suppl ies of hot bitumen and of diluent (unheated), together wi th a means of propor t ion ing each (eg dipstick, contents gauge and, drums of known volume for di luent)

a storage tank fitted wi th a filling and circulating pump system and also provision for heating tank contents

a small hand pump of approximately 40-50 litres per minute capacity, with delivery hose.

Items (i) and (ii) are available as part of the equ ipment for mechanised surface dressing in the form of the bitumen heater/decanter and dist r ibutor respectively. Older distributors which are no longer suitable for spraying work can be employed for blending. The procedure given be low for preparing blends assumes a distr ibutor is used but is equally applicable to static plant.

1 ) Calculate the volumes of bitumen and diluent required based on the total volume of blend

to be prepared. If a bitumen distributor or similar vessel is to be used, a dipstick or a contents gauge is usually fitted. Prepare the diluent in suitable containers eg 200 litre drums.

2) Heat the bitumen in the supply vessel to the lowest temperature consistent with efficient pumping (for 80/100 pen grade bitumen this is approximately 140°C).

3) Extinguish all flames, cigarettes etc, and ensure that fire extinguishers are on hand. Remove non-essential and unauthorised persons from the area. Essential personnel must wear protective clothing, boots and gloves (if handling hoses etc). Eye protection is also required.

4) Pump the hot bitumen from the supply vessel into the storage tank (eg the distributor), control ling the delivery such that the required volume of diluent can also be pumped in before the total volume of blend has been attained. The diluent delivery hose must dip below the level of the binder inthe tank at all times. Dispersion of the diluent in the bu Ik of the binder is then promoted by the vigorous swirling action created by the incoming binder.

5) When the constituents have been loaded, circulate contents of tank for approximately one hour in order to complete mixing.

It is not advisable to pump diluent into a tank already charged with a large volume of bitumen since the circulatory pumps usually available will disperse diluent very slowly. Local concentrations of diluent may also precipitate asphaltic sludge but there is little danger of this occurring if the blending procedure described above is followed.

9 C O N C L U S I O N S Cutback bitumen blends have been prepared in the laboratory using 100 pen and 50 pen bitumens with three diluents namely kerosene, a 3:1 mixture of kerosene and diesel and diesel. The blends have been examined for compliance with established US specifications.

It has been shown that:

a) blends made using kerosene as diluent do not contain sufficiently volatile 'cutter' for compliance with 'RC' type specifications;

12

b) blends which meet the 'MC' type specifications can be made using a 3:1 kerosene/diesel mixture with both 100 and 50 pen bitumen;

c) 'SC' type cutbacks can be prepared using 100 pen bitumen blended with diesel fuel. If 50 pen bitumen is used the residual binder after distillation is below the required minimum.

Diluent blending ranges have been established for both MC and SC cutbacks meeting the ASTM classification system and blending proportions have also been established for three cutback grades which are included in British Standard 3690 Part 1. These results should be regarded as a working guide since, in practice, the precise properties of the blends will depend on those of the constituent materials which may differ from those used in this study.

A recommended procedure for field production of cutbacks based on previous experience has been described.

BSI, 1983. Methods of test for petroleum and its products: Part 49. Penetration of bituminous materials. BS 2000:1983. London: British Standards Institution.

HITCH, L S, 1981. Surface dressing in developing countries: research in Kenya. TRRL Laboratory Report 1019. Crowthorne: Transport and Road Research Laboratory.

NATIONAL ASSOCIATION OF AUSTRALIAN STATE ROAD AUTHORITIES, 1965. Principles and practice of bituminous surfacing Vol 1. Sprayed work. Sydney: National Association of Australian State Road Authorities.

ROAD RESEARCH LABORATORY, DSIR, 1962. Bituminous materials in road construction. London: HM Stationery Office.

TRANSPORT AND ROAD RESEARCH LABORATORY, DOE, 1981. Recommendations for road surface dressing. Road Note 39.2nd edition. London: HM Stationery Office.

10 REFERENCES ASPHALT INSTITUTE, 1983. Principles of construction of hot-mix asphalt pavements, Manual Series No. 22. College Park, Maryland. The Asphalt Institute.

AMERICAN SOCIETY FOR TESTING AND MATERIALS, 1986. Annual book of ASTM Standards, Section 4 (Volume 04.03), Philadelphia. American Society for Testing and Materials.

BSI, 1973. Specification for coated macadam for roads and other paved areas BS 4987: October 1973. London: British Standards Institution.

BSI, 1980. Laboratory determination of density or relative density of crude petroleum and liquid products (hydrometer method). BS 4714: 1980. London: British Standards Institution.

BSI, 1982a. Specification of bitumens for road purposes. BS 3690 Part 1: February 1982. London: British Standards Institution.

BSI, 1982b. Methods of test for petroleum and its products: i) Part 27 Distillation of cutback asphaltic

(bituminous) products ii) Part 72 Viscosity of cutback bitumen and road

oil. BS 2000: 1982. London: British Standards Institution.

13

11 APPENDIX 1 PROPERTIES OF MATERIALS USED FOR BLENDING PROGRAMME

1. B i t u m e n s

Test

Penetrat ion at 25°C Sof ten ing Point (R and B)(°C)

M e t h o d 50 pen 100 pen

BS 2000 Pt 49 61 90 ASTM D36 47.5 44.5

2. D i luen ts

Diluent

Density at 15°C (IP 365) 1 kg/I Flash point (IP 303) 1 °C Dist i l la t ion (IP 123) 1 Initial Boi l ing Point °C 5% recovery at °C 10% recovery at °C

Kerosene

0.7853 51

Diesel

0.8485 73

20% recovery at °C 30% recovery at °C 40% recovery at °C 50% recovery at °C 60% recovery at °C 70% recovery at °C 80% recovery at °C 90% recovery at °C 95% recovery at °C Final Boi l ing Point °C

Recovery % vol Residue % vol Loss %vo l

165 179 184 189 192 196 200 205 210 217 225 233 246

177 205 225 247 261 273 285 296 307 320 339 353 368

98 1 1

99 1

Kerosene/diesel

0.8011 54

166 182 187 193 199 205 211 219 231 247 289 323 341

98.5 1

0.5

1. Inst i tute of Petroleum, 1986. IP Standards for Petroleum and its Products, Part 1. (2 vols) IP 45. London: Inst i tute of Petroleum

14

12 APPENDIX 2

CONVERSION OF ABSOLUTE TO Absolute viscosities were converted to kinematic viscosities using the calculated density at 60°C for each blend based on composition and component densities.

Densities 15°C, kg/I Kerosene 0.7853 Diesel 0.8485 Kerosene/diesel blend 3:1 by volume. 0.8011

A

(J o Q cD

>,

1.00

0.99

0.98

0.97

0.96

0.95

0.94

0.93

0.92

0.91

~,~sel

" ~ ' ~ 3:1 Kerosene/diesel

j

Kerosene / ~ ~

I i I I I I I I I 5 10 15 20 25 30 35 40 45 50

Diluent (per cent by volume)

Fig. 7 Density of blends using 100 pen base bitumen

KINEMATIC VISCOSITIES A temperature correction coefficient of 0.00063 per °C (Appendix B of BS 4714) was applied to obtain densities at 60°C. The densities of the blends has been plotted against content in Figures 7 and 8. Kinematic viscosities are obtained from the absolute viscosities by dividing by the density.

1.00

0.99 ~ Diesel -- 0.98 ~;\" ~ , , /

0.97 , ~ . ~ 3:1 Kerosene/diesel 096o9 0.95

°09 0.92 ,~ %~.~

0.91 I I I I I I I I I 0 5 10 15 20 25 30 35 40 45

Diluent (per cent by volume)

Fig. 8 Density of blends using 50 pen base bitumen

13 APPENDIX 3

50

VISCOSITY RESULTS FOR ALL BLENDS Viscosity (kinematic) at 60°C of bitumen/diluent blends (in centistokes)

Bitumen 50 pen (nominal) 100 pen (nominal) 61 pen (actual) 90 pen (actual)

_•luent Per c e n t ~ of blend " ~

4 6 8

10 15 20 25 30 35 40 45 50

Kerosene

113,800 46,605 25,560

3:1 Kerosene/diesel

88,620 43,825 27,230

Diesel

101,510 63,270 41,240

Kerosene

51,600 30,550 12,120

3:1 Kerosene/diesel

71,330 48,240 15,140

21,980 4,890 1,420

710 320 160 120

18,790 5,150 1,930

860 350 170 130

45

25,810 7,180 2,730 1,130

620 310 170

8,530 2,800 1,040

420 220 180 100

8,620 2,870 1,140

510 250 180 110 61

Diesel

59,720 35,330 20,100 11,100 4,480 1,620

800 400 190 180

Printed in the UK for HMSO by Bocardo Press Ltd, Oxford Dd No. 8222677 C8 1/87. 15