Journal of the Institute of Petroleum, Vol. 26, No. 197

P . WXf l / D ^ ' S )

J O U R N A L OF

T H E I N S T I T U T E

O F P E T R O L E U M

F O U N D E D 1 9 1 3 I N C O R P O R A T E D 1 9 1 4

V o l . 26 M A R C H 1940 N o . 197

C O N T E N T S

P A C K

Flow Properties of Bitum inous M aterials.

J. B. W arren and D . B. W aters

A. R. Lee, IOI Synthesis of L ubricating Oils. P art i. W

T . G. H u n ter and A. W . N ash .

R. Wiggins,

M anufacture and Use of T etraethyl Lead G . Edgar

T rinidad Geological Conference •

Obituary . . . . . •

Abstracts . . . . . i i

A

Book Reviews . . . .

A

Books Received . . . .

A

Institute N otes . . . .

¡ _H

Published by The Institute of Petroleum.

Emergency Address : c/o The University of Birmingham, Edghaston, Birmingham, 15.

Printed in Great Britain by Richard Clay and Company, Ltd., Bungay, Suffolk.

A l l rights o f Publication or Translation are Reserved. P r ic e 7s. 6 d .

T H E I N S T I T U T E O F P E T R O L E U M

COUNCIL, 1939-40

PRESIDENT : Prof. A. W. Nash, M.Sc.

Alfred C. Adams Lt.-Col. S. J. M. Auld,

O.B.E., M.C., D.Sc.

Prof. J. S. S. Brame, C.B.E., F.I.C.

The Rt. Hon. Lord Cadman, C.C.M.C., D.Sc.

PAST-PRESIDENTS :

T. Dewhursf, A.R.C.S.

A. E. Dunslan, D.Sc., F.I.C.

Sir Thomas H. Holland, K.C.S.I., K.C.I.E., D.Sc., F.R.S.

J. Kewley, M.A., F.I.C.

Ashley Carter, A.M.I.Mech.E.

C. Dailey, M.l.EE.

F. H. Carner, Ph.D., M.Sc., F.I.C.

VICE-PRESIDENTS:

J. McConnell Sanders, F.I.C.

F. B. Thole, D.Sc., F.I.C.

MEMBERS OF COUNCIL:

C. H. Coxon

A. Frank Dabell, M.I.Mech.E.

E. A. Evans, M.I.A.E.

E. B. Evans, Ph.D., M-Sc., F.I.C.

W. E. Gooday, A.R.S.M., D.I.C.

A. C. Hartley, O.B.E., F.C.G.I.

Prof. V. C. Illing, M.A.

E. R. Redgrove, Ph.D., B.Sc.

C. A. P. Southwell, M.C., B.Sc.

H. C. Tett, B.Sc., D.I.C.

A. Beeby Thompson, O.B.E.

A. Wade, D.Sc., A.R.C.S.

W. J. Wilson, F.I.C., A.C.G.l.

C. W. Wood, F.I.C.

J. S. Jackson, B.Sc., F.I.C.

Arthur W. Easllake, A.M.I.Mech.E., Honorary Secretary

HONORARY EDITOR: Dr. A. E. Dunstan HONORARY ASSOCIATE EDITOR: Dr. F. H. Carner HONORARY TREASURER: The Rt. Hon. Lord Plender, G.B.E.

SECRETARY: S. J. Astbury, M.A.

F) 1 VV o l .ol. 2

26. No. 197.

1940.

THE FLOW PR O PER TIES OF BITUMINOUS MATERIALS.*

A. R .

B .S

., P h.D ., A.R.C.S., D .I.C ., J . B.

B .S

., P h.D ., A .R.C.S., D .I.C ., A .In st.P ., an d D. B.

B .S

., Assoc.M .Inst.C.E.

SUMMARY.

Som e results are given of th e in vestigation s n ow in progress on th e funda­

m en tal flow properties of bitum ens and bitum en-aggregate m ixtu res. A coni-cylindrical viscom eter has b een used for m easuring th e effect of stress and tem perature on th e v isco sity and ela stic recovery of various ty p es of bitum ens. Tho rolation betw een rate of shear ( D ) and shearing stress (S) for a ll b u t th e m ost p lastic bitum ens m a y be represented b y an equation

ind ex p as a “ plastic-flow in d ex ” provides a m eth od of expressing tho degree of p la stic ity o f a bitum en, where th is is considered as th e divergence from id eal viscous flow. D ifferent bitum ens havin g th e sam e penetration (66) m ay have very different viscosities. T he bitum ens so far in vestigated have been found to differ chiefly in their p lastic a n d elastic properties.

T he effect of stress and tem perature on tho flow properties of roller- com pacted specim ens of bitum en-aggregate m ixtures has been in vestigated b y beam and tensile tests. The relation betw een stress ( S ) and m inim um rate of strain (li) m a y bo expressed b y tho equation I t — K S P , where K and

P are constan ts. The flow properties a t th e m inim um rate of deform ation under conditions of constan t tensile stress m ay be expressed com p letely b y a num ber o f constan ts—n am ely P , K 0 (tho m inim um rate of strain a t un it stress a t 0° C.), A7 (the rate of change of log. I C w ith change of tem perature), and th e ex ten sib ility a t failure, th e value of these constan ts being determ ined b y th e nature and grading of tho aggregate and b y th e nature of th e binder.

M ixtures o f a particular aggregate grading containing th e more plastic bitum ens have greater values for P th a n those containing non-plastic bitum en; tho value of P is affected m ore b y tho grading and proportion of th e aggregate th an b y tho nature of th e bitum en.

B i t u m i n o u s

m aterials are used for a large varie ty o f in d u strial purposes, b u t m ost extensively in ro a d construction. A lthough th e present p ap er deals w ith th is asp ect of th eir use, m uch o f th e inform ation presented is of m ore general in terest, since i t is concerned w ith fu n d am en tal properties.

T he m aterials used m u st be readily ad ap tab le to keep pace w ith th e developm ent o f m odern in d u strial m ethods, a n d this can be achieved only if th e essential properties o f th e m aterials are fully understood. D a ta on th e fundam ental flow properties o f bitum inous m aterials are being obtained w ith th ree m ain objects in view : first, to enable th e ir behaviour in service to be predicted, an d th u s to enable th e ir su itab ility for specific purposes to be ju d g e d ; second, to enable th e ir behaviour during m ixing an d laying to be predicted, an d so to enable th e m ost satisfactory conditions for application to be de term in ed ; an d th ird , to provide inform ation on

of tho form where r / ' and p are constan ts. T he uso of the

In t r o d u c t i o n.

* P aper received 16th O ctober, 1939. Crown C opyright R eserved.

H

102 L EE , WARBEN, AND WATERS :

th e n a tu re of th e in tern a l stru ctu re of th e bitum ens them selves, in order to indicate th e best m ethod of proparing a binder having an y required properties.

I n th e stu d y of th e Theological properties of m ixtures of b itu m en an d aggregate a knowledge of th e characteristics of th e binders is clearly o f first im portance. U n til recently little was known of th e fun d am en tal flow p ro ­ perties of bitum ens, although in th e testing o f bitum ens for in d u strial p u r­

poses m an y different em pirical te sts involving flow properties have long been used as aids to th e selection or specification o f m aterials. Such te sts are useful for ensuring th a t samples o f th e samo m aterial conform to a sta n d ard m easured u nder certain a rb itra ry conditions o f flow, b u t as a tru e com ­ parison o f th e behaviour in service of different m aterials a n d as a basis for im proving an d understanding existing techniques th e y are o f little value.

I n fact, certain o f these te sts (such as th e p en etratio n te st), w hen ta k e n alone, can often be m isleading. Moreover, in cases whero th e m easurem ents are reproducible to a high degree of accuracy, fun d am en tal im portance m a y freq u en tly b e atta c h e d erroneously to sm all differences. I n general, th e te sts m easure com plicated and variable functions of several fundam ental properties operating sim ultaneously. F o r exam ple, th e “ p en etratio n ” valuo depends on viscosity, elasticity, tensile strength, a n d adhesion;

an d tho “ d u c tility ” valuo depends, am ong other properties, on th e viscosity and th e in tern al cohesion. B ingham

has pointed o u t t h a t “ th e use of such em pirical te sts which are n o t based on an y so rt of th eo ry of th e fun d am en tal n a tu re of flow have m ore th a n an y other th in g prevented th e progress of th e a r t of rheology.” I t is probably tru e to ad d th a t it has also re tard ed th e developm ent of th e industries using th ese a n d o ther plastic m aterials.

A n investigation has therefore been sta rte d a t th e R o ad R esearch L ab o rato ry to correlate th e behaviour on th e road of bitum inous surfacings w ith th o Theological characteristics of th e ir binders an d of m ixtures p re ­ pared in th e laboratory. This investigation th u s involves initially an a tte m p t to evaluate in absolute u n its th e viscous an d elastic properties of b o th th e bitum inous binders a n d th e consolidated bitum en-aggregate m ixtures.

Sim ple p ro p o rtio n ality betw een stress an d stra in or ra te of stra in is n o t generally shown by these m ate rials; therefore, th e d eterm ination o f th e flow coefficients expressing these relations m u st be m ade u nder con­

ditions o f uniform stress. F o r th e bitum ens them selves th e use of suitable

viscom eters is therefore necessary; for th e bitum en-aggregate m ixtures

uniform stress d istrib u tio n across th o specim en m u st also be ensured,

involving either th e application o f a co n stan t stress or a co n stan t ra te

o f strain, w hichever is th e m ore convenient. E xtensibility, as defined

b y th e percentage elongation o f th e specim en a t failure, a n d th e elastic

recovery which occurs on rem oval of th e applied stress are fu rth er rhcological

properties which can be m easured b y either m ethod o f testing. Such

concepts as th e coefficient o f viscosity or th e m oduli of elasticity a n d o f

rig id ity are th e results of experim ent applied on th e one h an d to substances

definitely in th o liquid state , an d on th e o ther to those in th e tru ly solid

sta te . I t is n o t, therefore, to be expected th a t th e linear relationship

betw een stress and stra in or ra te of stra in im plied b y using such m oduli

THE FLOW PROPERTIES OF BITUMINOUS MATERIALS. 103

will necessarily apply to these m ore com plicated m aterials, which m ay exhibit bo th solid a n d liquid properties a t th e sam e tim e.

W hen th e stresses aro rap id ly applied, as in th e case o f im p act or v ibration forces from passing vehicles, bitum en-aggregate m ixtures exhibit th e properties of solids. Some progress has been m ade in m easuring th e tra n sie n t forces norm ally occurring on th e road, an d it is im p o rta n t to investigate th e relation betw een stress an d stra in for bitum inous m aterials u nder sim ilar conditions o f rap id stress application. The stresses applied by m ost im p a ct te sts are usually of a high, b u t indeterm inate, order, m aking

(a )

Fi g. 1 .

LO A D —T IM E CU R V ES G IV E N B Y R E P E A T E D T R A N S IE N T LOAD T E ST IN G M A C H IN E.

i t im possible to determ hie th e fu n d am en tal rheological properties involved, an d i t is open to question w hether such te sts reproduce p ractical con­

ditions, or have an y practical significance. A m achine has thereforo been constructed which subjects bitum inous specim ens to a repeated, suddenly applied, tra n sie n t stress of a given value m ain tain ed approxim ately con­

s ta n t for a sh o rt predeterm ined tim e. T he stress-stra in relations can

th u s be evaluated for “ im p act ” forces of know n m agnitude an d d u ratio n (of

th e order o f -¡V to second) w hich are repeated a t in terv als o f one second

to h a lf a m inute. Typical lo a d -tim e curves given by th e m achine are shown

in Fig. 1. Conditions o f stress sim ilar to those b en eath th e wheel of a

1 0 4 LEE , WARREN, AND WATERS :

passing vehicle are th u s obtained, b u t forces arising from v ib ratio n are n o t supplied. The extension o f th e m easurem ents to th e elastic properties exhibited u nder v ibrations o f audio-frequency would com plete th e field of investigation of th e rheological characteristics of bitum inous m aterials necessary for deducing th e stre ss-stra in -tim e relations m e t w ith in practice.

Some m easurem ents on these lines h av e already been rep o rted .2-

E xam ples of th e results of th e investigations now in progress on bitum ens an d on bitum en-aggregate m ixtures are given below, and servo to illu strate th a t, although these problem s are com plicated, th e evaluation o f th e fu n d a ­ m en tal physical characteristics in absolute u n its provides new insight into th e ir behaviour.

Riie o l o g y o f As p h a l t i c Bi t u m e n s.

W hen a bitum inous m aterial is subjected to a co n stan t shearing stress

set up, its m agnitude depending on th e m agnitude o f th e applied stress.

I n th e case of “ ideal ” liquids th ere is a sim ple p ro p o rtio n ality betw een these tw o quantities, expressed by th e N ew tonian Law

or viscosity

illu strated b y curve (A) in Fig. 2.

B itum ens an d bitum en-aggregate m ixtures do n o t obey th is ideal law.

T he relation betw een ra te of shear an d shearing stress o f all bitum ens so far investigated is represented by a curve of th e form (B ) in Eig. 2. The ra tio S /D varies according to th e value of S , b u t th e curve still passes through th e origin, no experim ental evidence of a yield value having y e t been obtained for bitum ens w ith viscosities up to ab o u t 10

poises. I n these cases th e relation betw een D and S has been found to be m ore nearly expressed b y a n em pirical equation of th e ty p e

where V an d p are constants, v{ resem bling (b u t n o t in dimensions) th e viscosity Tfj in th e earlier equation. As pointed o u t b y S co tt B lair

this equation has been found b y m any investigators to ap p ly to a g rea t num ber of m aterials. I t has as y e t no theoretical significance, b u t provides a convenient m eans, a t th e present stage of rheological knowledge, o f express­

ing th e flow-curves in term s of certain num erical constants.

F o r a satisfactory evaluation o f th e ra te o f flow -stress-tem peraturo

relations, such m aterials m u st be subjected to a range of uniform shear

stresses o f know n values a t various know n tem peratures. F u rth e r, th e

ra te of shear u n d er con stan t stress generally varies for some tim e after

th e in itial application of th e stress, and th e m aterial m u st undergo some

continuous deform ation before th e ra te of shear becomes constant. The

ro ta tin g cylinder viscom eter, which gives a closer approxim ation to these

conditions than any other viscometer, has been found most satisfactory for these investigations.

THE FLOW PROPERTIES OF BITUMINOUS’ MATERIALS. 1 0 5

Fi g. 2.

R E L A T I O N B E T W E E N S H E A R S T R E S S A N D R A T E O P S H E A R . (a) I D E A L R E L A T I O N

( D = - S ) . ( b ) r e l a t i o n f o r b i t u m i n o u s m a t e r i a l s ( D — —, S r).

V V

No m e n c l a t u r e.

Owing to certain difficulties that arise when considering some of tho results of these investigations, attention is directed to the terminology which has been adopted.

The scientific description of naturally occurring products frequently presents some measure of difficulty. Obviously no ono would regard

“ British coal ” as a clear scientific description. Similarly, it is inaccurate

and misleading to refer to “ Californian bitumen,” since several types of

crude oils occur in tho large area of California. On the other hand, a fuller

description associating any particular oil with the well from which it was

obtained at a particular date would not be any more helpful, since such a

description would only be imperfectly understood even locally. In the

circumstances the best that can be done is to refer to the products under

65 pen 65 >>

65 )) 65

2 2 i i

65

200

65

65

65 >>

consideration as “ a ty p e o f Californian b itu m e n ,” etc., an d to rely upon th e chem ical d a ta to supplem ent th e description.

T he asphaltic bitum ens an d asphalts d ealt w ith in this p ap er will th e re ­ fore bo described as follows :—

A. A ty p e of Californian, steam distilled B. A ty p e of Venezuelan, steam distilled C. A ty p e of Mexican, steam distilled . D. A typo of Borneo, “ Miri,” steam distilled E . A ir blow n from a Mexican Crude

F . F lu x ed air blown, fluxed w ith a 200 pen. Mexican G. A ty p o of Mexican, steam distilled .

H . T rinidad asphaltic cem ent, 5A, specified as ab o u t 23-0 per cent, m ineral m a tte r, calculated solubility 62 p er cent. . I. T rinidad asphaltic cem ent, 5B, specified as a b o u t 18-5 per cent, m ineral m a tte r, calculated solubility 77 per cent. . J . C uban asphaltic cem ent, 22-24 p er cent, insoluble m aterial

I n th e te x t which follows th e bitum ens are referred to individually by th e reference lette rs in th e above list.

Plasticity is th e general p ro p erty b y v irtu e of which a m aterial m ay be

m oulded, and has been defined b y W ilson

as “ th a t p ro p erty which enables a m aterial to be deform ed continuously an d p erm anently w ith o u t ru p tu re during th e application o f a force th a t exceeds th e yield value o f th e m aterial.” I n a tte m p tin g to define th is p ro p e rty m ore rigidly for purposes o f physical m easurem ent, th e idea has become p rev alen t th a t a plastic m aterial is one for which a yield value can be determ ined. This value represents th e stress above w hich continuous deform ation occurs, and below w hich th e re is no appreciable continuous deform ation

*

N o satisfactory term , however, has been generally adopted for describing a liq u id (a m aterial having zero yield valuo) for w hich th e ra te of shear is n o t d irectly proportional to th e shearing stress. Such term s as non- N ew tonian flow, pseudo-plasticity, quasi-viscosity, an d stru c tu ra l viscosity have been em ployed, b u t th e y become inconvenient w hen used to com pare m aterials which differ in th eir degree o f deviation from ideal flow. I t has consequently been found desirable, in order to preserve a reasonable degree of clarity, to refer to th e plastic flow o f such m aterials even though th e y have a zero yield value. I t is considered th a t if such an artificial division is necessary, th e term plastic solid should be applied to m aterials having a definite yield value an d th e te rm plastic liquid to those which do not.

W ith m an y plastic solids th e yield valuo is indefinite an d th e classification depends largely on th e sensitivity of th e m easurem ent or on th e choice of a n a rb itra ry m inim um yield stress such as g rav itatio n al stress.

Th e Co n i-Cy l i n d r i c a l Vi s c o m e t e r.

A viscom eter sim ilar to th a t used b y Saal

has been used. I n th is in stru m e n t th e difficulty o f estim ating th e lower end effect is overcome b y

1 0 6 LEE , WARREN, AND WATERS :

* R oller distinguishes betw een p lasticity, w hich depends on tho actu al m agnitude of th e deform ation, and plastic flow, w hich depends on tho rate of deform ation.

THE FLOW PROPERTIES OF BITUMINOUS MATERIALS. 1 0 7 MIRROR

HOLDER

TORQUE PULLEY CLUTCH

SQUARE SHAFT

VERNIER

^ 'GRADUATED

DISC

BRAKE SURFACE

TOP BEARING OIL RETAINING CUP HOLES

NORMAL A8CDSIZE

SIZES NVEST SLIP E,

GATINGFOR C2 R. CMS 1250 IOOO rooo

tsoo 1-500 1250 L INNER CMS 7-960 7,704 7734 L OUTER

CMS 6-019 7ß/J 7017

X VISCOMETER SHOWN IN DIAGRAM ACTUAL SIZE

BAYONET FITTING

HOLES FOR WATER CIRCULATION

STAINLESS STEEL INNER CYLINDER

BRASS OUTER CYLINDER

HARDENED STEEL FOOT BEARING

Fi q. 3.

C O N I-C Y L IX D R IC A L V ISC O M ETE R .

1 0 8 L E E , WARREN, AND WATERS :

term in atin g th e cylinders in cones having a common apex w hich acts as th e lower bearing p o in t of th e ro ta tin g inner cylinder. T he viscous r e ­ sistance due to th e fluid betw een th e tw o conical surfaces can be calculated

(according to Mooney an d E w art 8), an d b y choosing suitable dim ensions th is has been reduced to one te n th of th e resistance due to th e cylindrical p o rtio n ; in addition, th e m ean shearing stress in th e conical p o rtio n is m ade equal to th a t in th e cylindrical portion b y suitable choice of th e angular separation of th e cones. The in stru m en t, shown diagram m atically in Fig. 3, is provided w ith a quick release brake an d a dog-clutch m echanism which, while transferring th e applied torque to th e inner cylinder, provides a simplo m ethod of instantaneously releasing th e to rq u e w hen elastic recoveries are to be m easured. T he shape of th e upper end is designed to allow a slight overfilling w ithout appreciable errors. A detailed description of th e in stru m en t will be given elsewhere.

T he viscosity (i.e., ratio o f m ean shearing stress to th e m ean ra te of shear) is calculated from th e form ula

an d th e corresponding m ean shearing stress in tho fluid annulus is given by th e form ula

n g

JR. “ | 2

a n d m ean ra te o f shear D — Q j —---

-it o 1*"

w here 0 is th e applied.torque (dyne cm.),

D. is th e m easured angular velocity (radians/sec.),

f

an d i

are th e rad ii of tho cylinders,

L 0 is tho effective length o f tho cylindrical portion, 0

o is th e m ean of th e h a lf apex angles of th e cones, and is equal to / 22^ E 2

0 H

A 'lij

+ It,r

These equations apply to b o th N ew tonian an d non-N ew tonian flow.

W hen th e bitum ens are m ade m ore fluid by increase o f tem p eratu re, it is found th a t th e y te n d to conform m uch m ore closely to ideal liquids.

Viscosities m ay th e n be m easured b y a capillary U -tube viscom eter, and th e m odified O stw ald in s tru m e n t

designed p rim arily for ta rs a n d pitches has been found convenient, p articu larly for determ ining tem p eratu re coefficients.

So m e Ex p e r i m e n t a l Re s u l t s.

N o b itum en so far exam ined has been found to possess a yield value, w hatever th e con stan t shear stress applied, a n d a fter sufficient tim e tho

7

] (poises) — —

3L

sin Gq.

THE FLOW PROPERTIES OF BITUMINOUS MATERIALS. 1 0 9

inner cylinder o f th e viscom eter u ltim ately a tta in s a con stan t angular ro ta tio n . W hen th e load is rem oved th e elasticity of th e b itu m en produces a recovery. A ty p ica l angular ro tatio n -tim e curve is shown in Pig. 4, an d indicates th e four processes w hich operate during th e flow of th e m aterial. The sm all initial curved portion A B arises from elastic elongation of th e b itu m en as well as from some viscous flow, an d is related to th e final elastic recovery. W ith fluid binders th is elastic fore-effect occupies only a fow seconds of tim e a n d is scarcely noticeable, b u t w ith h ard er

Fi g. 4 .

T Y T IC A I . A N G U L A R R O T A T I O N /T I M E C U R V E S F O R B I T U M E N U N D E R C O N S T A N T S H E A R IN G S T R E S S .

Section A B . In itia l E la stic Foro-Effect.

,, BC. T hixotropic Region.

,, CD. F in al Constant Angular V elo city R egion.

,, D E . E la stic R ecovery. [E xaggerated A n gle Scale.]

binders i t occurs for a ra th e r longer tim e. The section B C , which indicates

a reduction in viscosity w ith continued working, is associated w ith thixo-

tro p y or th e in te rn a l stru ctu re o f th e m aterial. W hen th e stru c tu re has

been broken dow n to a n equilibrium sta te corresponding to th e stress

applied, th e curve straightens o u t (CD). I t is from th is p o rtio n o f th e

curve (i.e., w here th e angular velocity is constant) th a t th e viscosity

(applied stre ss/ra te o f strain) is calculated for th e p a rticu lar shearing stress

applied. The elastic recovery, a fter rem oval of th o applied stress, is

1 1 0 LEE, WARREN, AND WATERS :

S H E A R I N G S T R E S S ( D Y N E S P E R S Q . C M . )

F io . 5.

e f f e c t o f s h e a r i n g s t r e s s o n v i s c o s i t y o f e, a i r-b l o w n b i t u m e n, a t D I F F E R E N T T E M P E R A T U R E S .

(1) Temperature 30-7° C. (3) Temperaturo 44-9° C.

(2) Temperaturo 40-2° C. (4) Temperature 49-2° C.

T in ; FLOW PROPERTIES OF BITUMINOUS MATERIALS. I l l

represented b y B E . Tho corresponding angular velocities an d ap p aren t viscosities are also shown.

T he viscosity of each m aterial has been determ ined over a range of shearing stresses an d tem peratures. As previously sta te d , tho viscosities v a ry w ith th e shearing stress. A n extrem e case is shown in Fig. 5, in which th e viscosity o f th e blow n Mexican bitum en, E , is p lo tte d against th e corresponding shear stress a t four tem p e ratu res from 30° C. to 49° C.

The o ther bitum ens have show n v ariations of th is type, b u t to a less degree; th e Californian bitum en, A , shows tho least variatio n w ith stress.

Si g n i f i c a n c e o f t h e Pe n e t r a t i o n Va l u e.

The viscosities a t 25° C. are given in T able I for different bitum inous binders all having a p e n etratio n of 65 (a t 25° C.).

Table I .

V i s c o s i t y o f 65 P e n e t r a t i o n B i t u m e n s .

(Measured w ith Ostwald ty p e V iscom eters.) T ypo of B itu m en . V iscosity a t

25° C. (e x ­ V iscosity a t 40° C. in

Logarithm ic temporature coefficient

Code. Source.

trapolated)

poises.

D Miri 1-28 X 10" 3-55 X 10* 12-0

A Californian 1-70 X 10° 4-87 x 10* 11-9

B V enezuelan 2 ’64 x 10« 9-12 X 10* 11-2

C M exican 3-92 X 106 14-3 X 10* 11-1

F M ixture of B low n M exican 4-1%

and 200 P en . M exican 56%

22-1 x 10» 57-9 X 10* 12-2

H Trinidad A.C. 5A 4-66 x 10« 15-9 X 10* 11-3

I Trinidad A.C. 5B 2-78 X 10« 8-91 X 10* 11-5

J Cuban A.C. 44-7 x 10« 84-1 X 10* 13-3

I t will be seen th a t a t th e p artic u la r m ean shearing stress in th e visco­

m eters th e extrem e m aterials show a difference in viscosity o f 35 tim es.

These differences indicate th a t th e p e n e tratio n m easurem ent has little significance as a m easure o f tho viscosity o f a bitum en. Tho precise d ep th to w hich th o needle will sink in 5 seconds will be g reatly affected b y th e degree o f non-N ew tonian flow, a n d will also depend on th e thixotropic, elastic, an d adhesive properties. W ith th is in stru m en t th e effect o f these properties is exaggerated in relation to th a t of tho viscosity, an d w ith some bitum ens w ill hav e a predom inating influence on tho m easurem ent.

F u rth e r, besides th e large change in stress w hich occurs during a m easure­

m en t, a low -penetration b itu m en is te ste d u n d e r m uch higher stresses th a n a h igh-penetration bitum en. The p e n e tra tio n te s t m ay therefore bo quite m isleading if i t is used alone for com paring one bitum inous m aterial w ith another.

Pl a s t i c Pr o p e r t i e s.

I t is found th a t for m ost bitum ens th e relatio n betw een D (rate o f shear) an d S (shearing stress) m a y bo oxpressed b y th e em pirical equation

D ^ ~ S P

(

)

LOG(ANGULARVELOCITY)

1 1 2 LEE , WARBEN, AND WATERS :

LOG (SHEARING STRESS DYNES/ C M 2)

© AT S&4 ' C Q) AT 3 0 -9 "C

© AT 4 4 5 °C @ AT 2 4 3 'C

Fi g. 6 .

R E L A T IO N B E T W E E N A N G U LA R V ELO C ITY A N D SH E A R IN G S T R E S S F O R I , T R IN ID A D ASF1IALT 5 B , A T D IF F E R E N T T E M P E R A T U R E S .

TIIE FLOW PROPERTIES OF BITUMINOUS MATERIALS. 113

The results from th e “ plastic ” air-blow n bitum en, however, do n o t fit even th is equation.

Fig.

shows th e straight-line relatio n obtained on p lotting log. angular velocity ag a in st log. shearing stress for th e T rin id ad A.C. 5B (I), a t tem p eratu res from 24° to 56° C. The slope of tho lines gives th e value of th e index p . O ther w riters

havo referred to th e deviation from ideal flow exhibited b y bitum inous m aterials, b u t no m eth o d based on fu n d a ­ m e n tal considerations lias y e t been proposed for defining th e degree of p lasticity . The “ p en etratio n index ” used b y Pfeiffer and V an D o o rm a l

is largely determ ined b y tho plastic properties o f th e m aterial. T he uso of th e index p in th e above equation as a “ plastic flow index ” provides for th e tim e being a m ethod, based on th e fund am en tal flow properties, of expressing th e degree o f p la sticity where th is is considered as th e divergence from ideal viscous flow. T he values o f p for tho different m aterials are given in T able I I , w hich contains o th er d a ta on these m aterials.

As n o ted b y previous w riters, th e deviation from ideal flow decreases as tho m aterials are m ade m ore fluid b y rise of tem p eratu re. The effect o f te m p era tu re on th e plastic flow index of th e m aterials is show n in F ig. 7.

Te m p e r a t u r e

-* - ° c

E F F E C T OF T E M P E R A T U R E O X P L A ST IC F L O W IN D E X O F 65 P E N E T R A T IO N B IT U M E N S .

I. M ixture of B low n M exican and Spramox. F . 2. M oxican. C.

3. Trinidad A.C. 5A . H . 4. Venezuelan. B .

5. Trinidad A.C. 5B. I . 6. Californian. A .

1 1 4 LEE, WARREN, AND WATERS :

Ef f e c t o f Te m p e r a t u r e o n Vi s c o s i t y.

All bitum inous m aterials are characterized by th e very large changes in viscosity produced b y changes in te m p e ra tu re; th is p ro p erty is o f v ita l im portance in th e use of th e m aterials.

The curves given in Fig. 5 show values of th e viscosity o f E , th e blown bitum en, obtain ed for a range of shearing stresses a t tem p eratu res betw een 30° a n d 49° C. The change in viscosity produced b y th is change in tem p e ratu re is large w hen th e shearing stress is

dynes/sq. cm., a n d com paratively sm all w hen tho shearing stress is 80,000 dynes/sq. cm.

T hus th e tem p eratu re susceptibility of highly viscous bitum ens showing m arked plastic properties will v a ry according to th e shear stress a t w hich th e viscosities are m easured, being g reater a t low an d sm aller a t high shearing stresses. However, a t higher tem peratures, or, ra th e r, w ith m ore fluid products (viscosities less th a n

poises), th e variations in viscosity arising from changes in applied stress are g reatly reduced, a n d eventually become insignificant w hen th o tem peraturo is raised sufficiently. F o r all tho 65 p en etra tio n m aterials th e v ariatio n in viscosity w ith stress is of a m uch sm aller order th a n th a t duo to change in tem p eratu re (Fig. 9).

Ta b l e I I .

R e s u l t s f o r s a m e o f t h e F l o w C h a r a c t e r i s t i c s o f B i t u m e n .

T y p e of b itu m en . A ir- blow n M exican,

E .

44%

air-blow n 56%

200 P en . M exican,

F .

M exican 60/70 P en ., C.

V en e­

zuelan 60/70 P en ., B .

C ali­

fo rn ian 60/70 P e n ., A.

T rin . A.C.*

5A, H .

T rin . A .C .f 5B,

I .

M exican 200 P en .,

G.

Specific g ra v ity :—

A t 15° 0 . 1-051 1-042 1-015 1-025 1-244 1-164 1-035

A t 25° 0 . __ 1-028 1-039 — 1-015 1-237 1-152 1-025

P en e tra tio n s :—

A t 15° 0 . 13 29 26 26 _ 24 28

A t 25° 0 . 22 60 63 64 66 59 66 199

S oftening p o in t, I t . and

B ... S5-5 57-2 52 49-7 45-6 51-1 66 40

P e n e tra tio n in d ex 4-3-2 4-1-2 - 0 - 1 - 0 - 6 - 1 - 7 5 - 0 - 5 - 1 - 5 0

A sphaltenc co n te n t, % . 37 27 20 13 4 2 1 1 15 I 17-7

V iscosity a t 25° 0 . :—

(a ) D eterm in ed in O stw ald v isco ­ m e te r m ean stress a b o u t 3,000

d y n es/sq . cm . . 22-1x10* 3 - 9 2 x 1 0 ' 2-64x10* 1-70x10* 4 -66x10* 2 -7 8x10* 2 -98x10*

(6) D eterm in ed in C onicylindric v is ­ c o m eter m ean s tre ss 36,130

d y n es/sq . cm . . 3 -0 x 1 0 * 5-61x10* 3-47x10* 2-11x10* 1-91x10* 3 -6 5x10* 1-94x10* 2-32x10*

L og te m p e ra tu re coeffi­

c ien t 11-1 11-4 11-6 11-8 11-0 10-6 9-7

P la s tic flow in d ex (p ) a t

25° 0 . . 3 1-44 1-22 1-10 1-02 1-2 1-08 1-19

M axim um elastic r e ­ co v e ry , degrees in C o u ette v isco m eter a t

25° C. . 8 5 4 2 0-5 1 1 3-7

* T rin id a d A.O. 5A co n sists of 83*5% of T rin id ad E p u rc a n d 16-6% of F lu x Oil.

f T rin id a d A.O. 6B consists of 49*5% of T rin id ad E p u re , 5% o f F lu x OH, 45*5% 200 p en . V enezuelan B itu m en .

J E s tim a te d o n th e e x tra c te d b itu m en .

Fig.

shows th e values of log. viscosity over a tem p eratu re range from

25° C. to 90° C. for six bitum ens (each having a p en etratio n of 65 a t 25° C.)

THE FLOW PROPERTIES OF BITUMINOUS MATERIALS. 1 1 5

EFFECT OFTEMPERATUREONLOO. VISCOSITY OF BITUMENS(65 PENETRATION).

1 1 6 LEE , WARBEN, AND WATEKS :

£ 6 - 0 ioo oto S hf 0 5 - 0

totQ N tao

te sted under a shearing stress of 2,063 dynes/sq. cm. These curves show th a t th e variations in log. viscosity of th e different m aterials w ith change

I S 1-6 1 7 1-8 1 9 2 0 2 1 2 - 2 ~ 2 3

LOG TEMPERATURE f ‘F j F io . 9.

R E L A T IO N B E T W E E N LO O . T E M P E R A T U R E ( ° F .) A N D LO G . V ISC O SITY F O R B , V E N E Z U E L A N B IT U M E N .

1. Shearing stress 2,003 dyn es/sq . cm .

“ • f f >* 0 ,j3 0 ,, ,,

3 ...36,130

o f tem p eratu re are very sim ilar, even w hen a com parison is m ade betw een

th e fluxed blow n Mexican, C, an d th e steam -distilled V enezuelan bitum en,

B. T here are differences betw een th e viscosities th ro u g h o u t th e whole

THE FLOW PROPERTIES OF BITUMINOUS MATERIALS. 117

range, b u t these arise m ainly from th e in itial differences in viscosity a t 25° C. Curves o f th is type provide no m eans of defining th e te m p eratu re coefficient of viscosity, since a given change in tem p eratu re produces a greater change in viscosity a t low tem peratures th a n a t high tem peratures.

V arious viscosity/tem perature coefficients have been proposed for b itu ­ m inous m a te ria ls; for exam ple, T rax ler

assum es th a t th e curved lines relating log. viscosity an d tem p era tu re (° C.) are sufficiently stra ig h t over a sm all range to define an “ A sphalt Viscosity In d e x ” as th e percentage decrease in viscosity for

° C. rise in tem p eratu re. I n order to obtain a single num erical coefficient for extrapolation and com parison purposes, i t is necessary to use functions of viscosity and tem p eratu re which give a linear relation over as large a tem p e ratu re range as possible. A ccurate stra ig h t lines have so far been obtained over a range o f 70° C. for any bitum inous binders up to viscosities of

poises on plo ttin g th e logarithm of th e ap p aren t viscosity against th e logarithm of th e tem p eratu re F ah ren h eit, th e viscosities being m easured a t the sam e shearing stress th ro u g h o u t th e tem p era tu re r a n g e ; some ty p ical curves are given in Fig. 9.

The equation

log.

] = a — n log. T ,

which also holds for coal-tars an d pitches, th u s provides a sim ple em pirical expression for v aria tio n of viscosity w ith tem p eratu re defined b y one constant, viz. :—

„ _ log. vjj - log.

log. '1\ - log. 1 \

n has been called th e “ logarithm ic tem p eratu re coefficient.”

This expression for the tem p eratu re susceptibility, while in accu rate for extrapolation to th e high tem p era tu res necessary for m ixing, is valid for a tem p eratu re range sufficient to indicate th e relative susceptibilities of different bitum ens.

The eq u atio n t\ = a T ~ n is a p articu lar case o f S lottes’ form ula

•/] = C/(b + t)n, where I is th e tem p eratu re Centigrade, and where th e value 5 X 32

of b becomes ——— - and th e o ther contents are su itab ly chosen.

The theoretical form ula of A ndrade

an d Sheppard

) = A e~ k,°

where

is absolute te m p eratu re, which was derived for pure monomolecular liquids, would n o t be expected to hold for the com plicated m ixtures which constitute bitum ens and tars.

The values of n in th e equation tj = a T ~ n for the different bitum ens are given in T able II.

El a s t ic Pr o p e r t i e s o f Bi t u m e n s.

I t has already been m entioned th a t th e elastic or solid properties of a bitum en are m ost prom inent when th e stress is rap id ly applied o r varied, b u t, even when a bitum en has been sheared slowly u nder co n stan t stress, elastic recovery occurs on th e sudden rem oval o f the stress. T he am ount

i

AND WATERS L E E . W A R R E N

S 3 3 3 0 3 0 - A d 3 A 0 0 3 d 3 0 3 1 0 N V

RELATION BETWEENSHEARINGSTRESS ANDTOTALELASTIC RECOVERYOFF, 65PENETRATIONMIXTUREOF BLOWNAN- 200 PENETRATIONMEXICANBITUMEN.

THE FLOW PROPERTIES OF BITUMINOUS MATERIALS. 11 9

of recovery depends on th e stress applied a n d th e degree to which th e m aterial has been previously sheared. F o r a given stress, th e recovery increases to a definite m axim um value w ith increase in th e previous shear.

Fig. 10 shows th e relation betw een th e applied stress and th e m axim um recovery for th e fluxed blow n bitum en, F (G5 pen.).

F rom th e angular recovery values which occur on th e rem oval of definite applied stresses an a p p a re n t rig id ity m odulus, ta k e n as th e ra tio of shear stress to shear recovery, has been calculated for various values of th e shearing stress. Allowing for th e dim ensions of th e viscom eter an d assum ing th a t th e recovery corresponds to a sim ple shear m otion w ith no flow, th e shear recovery is equal to five tim es th e m easured angular recovery (a) of th e inner cylinder. These calculated values are ta b u la te d in Table I I I .

T

III.

A p p a r e n t M o d u l i o f R i g i d i t y f o r F l u x e d B l o w n B i t u m e n F .

T e m p e r a t u r e .

S h e a r i n g s t r e s s ( d y n e s / s q . c m .)

S .

A n g l e o f r e c o v e r y ( d e g r e e s )

a.

A p p a r e n t m o d u l u s o f r i g i d i t y ( d y n e s / s q . c m .)

S / 5 a .

2 5 ° C . 1-5 X 1 0 3 0-4 4 -3 X 10*

1 0 -0 X 1 0 3 2 -0 5 -7 X 10*

17-5 X 1 0 3 3 -0 6 -8 X 10*

3 0 '0

x

»»

4 5 ° C . 2 -5 X 1 0 3 1 1 5 2 -5 X 10*

5 0 X 1 0 3 1-87 3 0 5 X 10*

1 0 -0 X 1 0 3 2 -8 5 4 0 X 10*

2 0 0 X 1 0 3 4 -0 2 5 -4 X 10*

>•

Fig. 10 shows th a t for th e 65 p e n etratio n fluxed blow n bitum en, F , a change of te m p era tu re from 25° to 45° C. produces little change in th e elastic recovery. I t has been found th a t for th e bitum ens investigated th e re is a te m p eratu re range w ithin which th e recovery is a m a x im u m ; above an d below th is range th e recovery dim inishes, an d a t high te m p e ra ­ tu res, a t which th e m aterials are quite fluid, th e elastic recovery eventually disappears. Over th e range of tem p e ratu re from 25° to 45° C. th e change in th e a p p a re n t rig id ity m odulus o f th e b itu m en is o f a m uch lower order th a n th e change in viscosity. As would be expected from consideration of viscous in tern al dam ping, th e ra te of recovery increases as th e te m ­ p e ra tu re o f th e b itum en is raised or its viscosity reduced. The values for th e a p p a re n t rig id ity m odulus

to

x

dynes/sq. cm.) are o f a lower order th a n values of th e rigidity m odulus o f b itu m en obtained by dynam ic m ethods (e.g., Lonsdale an d W ilson

10

dynes/sq. cm.).

C

B

.

The results given in T able I I show th a t th e bitum ens so far investigated

differ chiefly in th eir plastic an d elastic properties, an d th e tem p era tu re

differences found necessary in p ractice in th e use of th e m aterials appear

/r/v- Nonosi^sa

Ag g r e g a t e Co m p o s it io n Leig h to n Bu z z a r d Sa r d807.

Po r t la n d Ce u e n t Fil l e r B O Z

to be due p rim arily to differences in these properties, an d to th e difference in in itial viscosity of th e bitum ens arising from th e adoption of a sta n d a rd p en etra tio n to which th e various m aterials m u st conform.

There is little difference betw een th e logarithm ic te m p eratu re coefficients of viscosity, although th e Californian bitum en, A , has th e highest coefficient, an d th e blow n bitum en, F , th e least. These facts are su b stan tially in agreem ent w ith th e conclusions of Pfeiffer a n d V an D oorm al (loc. cit.), a n d th e ex p lan atio n p u t forw ard b y these au th o rs to account for th e differences in rheological properties o f different ty p es of b itu m en are so far su pported b y th e p resent results.

120

R h e o lo g y

AsrHALTic R o a d M ix tu r e s .

The flow properties of a bitum en-aggregate m ixture are d irectly in ­ fluenced b y th e flow properties of th e bitum inous binder. The large

O lO 2 0 3 0 4 0 SO 6 0

T IM E -K U N U TES Fi g. 11.

E F F E C T O F B I N D E R C O N T E N T O N T H E D E F L E C T I O N O F B E A M S O F S A N D A S P H A L T .

Storago tim e 8 (lays. Tem perature of te st 25° C. D im ensions of beam s 10

” x

” x

".

Binder—Trinidad A sph altic Cement— T y p o 5 A . Percentage of Soluble B itum en Marked on Curves.

am o u n t of work on m easuring th e m echanical properties o f such m ixtures

done b y earlier investigators is, on exam ination, usually found to comprise th e m easurem ent of flow properties under various a rb itra ry conditions of stress.

Am ong a considerable num ber of te sts investigated those selected for

th e p resen t purpose are th e beam and tensile tests. The m ethods and

technique ad o p ted for preparing an d testing specimens have been described

elsew here.18' ltf A lthough for certain purposes th e tw o te sts give th e

sam e inform ation, the tensile te s t lias th e ad v an tag e th a t th e results m ay be expressed q u an titativ e ly , are in dependent of th e dim ensions o f th e specim en, and th a t th e m aterial is subjected to a co n stan t uniform stress or ra te of strain. The experim ental procedure has been to obtain th e deform ation-tim e curves given b y roller-com pacted rectangular specimens.

Two fu n d am en tal characteristics are th u s obtained—nam ely, th e ra te of flow u nder a know n stress and th e ex tensibility or to ta l flow before failure. Inform ation on th e flow properties o f th e m ixtures involves a stu d y of th e variations of these q uantities w ith stress, tem p eratu re, and age-

Some typical deform ation-tim e curves are show n in Fig. 11. The resulting deform ation o f th e tensile specim en m ay be considered as due to tw o shear stresses of one-third th e tensile stress

The ra te of elongation m ay be shown to be equal to th e ra te o f shear strain.

The ratio of th e stress to th e slope of th e straight-line portion of the curves (the m inim um ra te of deform ation) m ay be considered a m easure of the viscosity of th e m aterial. On th is basis, from th e curves shown in Fig. 11, th e specim en containing 7 p er cent, of bitum en exhibits th e m axim um resistance to deform ation, an d from th is p oint of view 7 per cent, m ay be considered th e optim um binder co n ten t for th e p articu lar aggregate. T his optim um binder co n ten t has been determ ined for each bitum en-aggregate m ix tu re referred to below.

E

S

R

S

.

I n Fig. 12 some ty p ical stre ss-ra te of stra in curves are shown for specim ens o f sand asphalt, each m ade w ith its optim um binder content.

W hen, from such results, log. stress is p lo tte d against log. m inim um ra te o f strain , stra ig h t lines are obtained, as shown in F ig. 13. T hus these results show th a t th e relation betw een stress a n d m inim um ra te of stra in m ay be expressed by th e equation

R = K S P ...(3)

where I? is th e m inim um ra te of strain ,

S is th e applied stress, K a n d P are constants.

In Fig. 13 th e slope o f th e stra ig h t lines is co n stan t over th e tem p eratu re range investigated. P m ay th u s be considered to be a characteristic of th e m a terial representing th e divergence o f th e flow from th a t expressed by a linear relatio n betw een stress an d ra te of flow. B y analogy w ith the equation applicable to bitum ens, P m ay therefore be term ed th e “ plastic flow index ” o f th e bitum en-aggregate m ixture. The value o f th e co n stan t K in th e above equ atio n represents th e m inim um ra te of de­

form ation a t u n it stress, an d is th u s a m easure of th e “ m obility ” o f th e m aterial (i.e., ra te o f flow /unit stress).

E

T

R

S

.

I t has been found th a t a straight-line relatio n exists betw een log. K and tem p eratu re over a tem p e ratu re range o f a b o u t 25° C .; Fig. 14 shows

THE FLOW PROPERTIES OF BITUMTNOTJS MATERIALS. 121

MINIMUMRATEOFSTRAIN/ MINUTE.

LEE , WARREN, AND WATERS :

AO 6 0 8 0 /OO 120

STRESS ~ LB/SQJN.

A C C .R F C A T F / S O P E R C E N T S A N O .

I 2 0 PERCENT PORTLAND CEMENT FILLER.

Fio. 12.

R E L A T IO N B E T W E E N STR ESS AND R A T E O F S T R A IN F O R SAN D A SPH A LTS AT VARIO U S T E M P E R A T U R E S .

--- L aboratory Prepared Material containing V enezuelan B itum en.

--- M aterial from Public R oad.

T ttE FLOW PROPERTIES OF BITUMINOUS MATERIALS. i 23

STRESS - L B PER SO. IN

+ MEXICAN BITUMEN

O VENEZUELAN « a TRINIDAD {TYPE 5 A)

O MATERIAL FROM PUBLIC ROAD Fi g. 13.

R E L A T IO N B E T W E E N LO O . STR ES S A N D LO O . M IN IM U M R A T E O F S T R A IN O F SAND A SPH A L T A T V AR IO U S T E M P E R A T U R E S .

1 2 4 L EE , WARREN, ANI) WATERS i

th e curves for tw o m aterials. (Note.— In th e case o f m aterials having binders which possess N ew tonian flow properties th e slope o f such lines is th e sam e as for th e binder alone. This is illu strated by th e curves in Fig. 15 obtained from m ixtures m ade w ith a soft p itch binder.)

F ia . 14.

R E L A T IO N B E T W E E N T E M P E R A T U R E °C . A ND LO O . R A TE O F S T R A IN PR O D U C ED B Y U N IT STR ESS

(1) N — 0-147 (Log Strain/M inute)/°C .

Standard A ggregate w ith M exican B itum en and V enezuelan B itum en and Trinidad f)A.

(2) Ar = 0-111 (Log Strain/M inute)/°C . P u b lic R oad (Good Section).

The relation betw een I i an d tem p eratu re over a range of ab o u t 25° C.

m ay therefore be expressed b y th e equation

log. K = log. K 0 + N ( T - T 0)

. . (4) where A

is th e value of K a t a tem p e ratu re T 0,

N is th e ra te of change of log. K w ith change of tem p eratu re, T is te m p era tu re (°C.).

E q u atio n (3) m ay therefore be w ritten

log. I i = P log. S + log. K 0 + N ( T - T 0).

Thus, over a range o f tem p eratu re o f ab o u t 25° C. th e flow properties a t

th e m inim um ra te of deform ation of a bitum en-aggregate m ix tu re under

conditions o f co n stan t tensile stress m ay be expressed by th e constants

THE FLOW PROPERTIES OF BITtTMINOPS MATERIALS.

10 2 0 ■ 3 0 4 0 SO 60 TEMPERATURE — DEGREES CENTIGRADE

Fi g. 15.

E F F E C T O F T E M P E R A T U R E ON M IN IM U M R A T E O F D E F L E C T IO N OF BEAM S A N D V ISC O S IT Y T] O F B IN D E R .

(1) Sand 80% ) 10»/ Binder Portland Cement, 2 0 % / iU /°

(2) Sand 60% 1 1 1 07 Binder Lim estone D u st 4 0 % / 11 0

(3) Temperature F lu id ity Line for th e 300 Pen. P itc h Binder.

9-3 x/O*

OO/

126 LEE , WARREN, AND WATERS :

Values obtained for these constants for specimens m ade w ith a v ariety o f bitum ens are given in T able IV . All th e specim ens h a d th e same aggregate grading, an d contained th a t q u a n tity of binder w hich from a se t o f results sim ilar to those shown in Fig. 10 gave th e m axim um resistance to deform ation. A few results are also included of specimens cu t from asp h alts on public roads.

T a b l e

TV.

F l o w C h a r a c t e r i s t i c s o f B i t u m i n o u s S p e c i m e n s u n d e r C o n s t a n t T e n s i l e S t r e s s .

Specim ens c o n tain in g o p tim u m b in d e r c o n ten ts.

Soluble b itu m en c o n te n t (per cen t.).

Change of r a te of

s tra in w ith stress (p la stic llow in ­ d ex ), P , a t 25° C.

Log. r a te of s tra in fo r u n it stress a t

0

Change o f log.A w ith te m ­ p era tu re,

X.

E x ten sib ility , 50 lb ./sq . In.

E.

25° C. 0° C.

S ta n d a rd A g gregate an d C alifornian B itu m e n A .

,, ,, ,, V enezuelan B

,, ,, ,, M exican 0

„ ,, „ T rin id a d A.O.

(T y p e 5A) H

„ T rin id a d A.O.

(T y p o 5B) I

„ „ ,, B low n M exican

an d S p ram ex . F 7-5 7-5 I

8-0

7-0 7-0 8*75

2-0 2-8

3-2

- 8 - 3 5

— 9*31

- 9 - 1 2

0-170

0-117 -

0-115 8-7 G-l 7-1 3-0

10-0

7-3 G-0

6-2

3-1 <*

7-0

f P u b lic R o ad N o. 2—G ood . 10-25 3-91 -1 1 -7 8 1

0-111

t ,, „ N o. 12—C racked 8-70 3-95 - 1 2 - 9 5 0-137

2-0

„ ,, N o. 22—C racked — 5-28 — 1G-25 0-129

1-1

* A t 100 lb ./sq . ill.

f R o a d s N o. 2 a n d N o. 12 w ere 13 y e a rs old a n d b o th c o n tain ed th e sam e b itu m en a n d aggregate.

t A t - 2° 0 . 5 A t 150 lb ./sq . in .

T he plastic properties of th e m aterials are determ ined p a rtly b y th e aggregate com position a n d p a rtly b y th e n a tu re of th e binder. Specimens containing th e non-plastic Californian bitum en, A , as binder have a value o f 2-0 for th e Plastic Flow In d ex (P), a value which is also found for speci­

m ens containing a viscous ta r as binder. The variations from th is value given b y th e o th e r m aterials are related to th e plastic properties of th e bitum ens.

I t will be seen from th e results in T able IV th a t th e m aterials containing th e Californian bitum en, A , have a m uch lower resistance to deform ation th a n th e others (the com parison being m ade betw een m aterials having th eir optim um binder contents). This difference arises from th e fa c t th a t although th e bitum ens have a pen etratio n of 65 a t 25° C., th eir viscosities u n d er th e p articu la r shear stress of th e te s t differ considerably, th a t of th e Californian bitum en, A , being m uch less th a n th a t o f th e o th er bitum ens.

C

.

T he exam ples given in th is paper of th e results o f th e investigation of th e fu n d am en tal flow properties of bitum inous m aterials illu strate th e progress m ade in u nderstanding th e problem s.

T he flow properties of a bitum en-aggregate m ix tu re are determ ined by

th e n a tu re an d grading o f th e aggregate and by th e q u a n tity , th e viscosity,