Evaluation of High and Low Temperature Properties of Heavy Trafficked

Asphalt Road Pavements in Poland

Dariusl Z. Sybilski l

Abstract

Four heavy-duty pavements were chosen for tests including methods developed at

Strategic Research Program (SHRP). Pavements chosen were constructed by various

contractors with application of various materials. Plain asphalt cement and binders modified

with Styren-Butadiene-Styren (SBS) block copolymer were used. Two methods of

modification were applied: industrial pre-blending of asphalt with SBS or modification during

production of asphalt-aggregate mixture in a pug mill at certain specified conditions. Two

types of mixtures were applied: asphalt concrete and Stone Matrix Asphalt (SMA).

The main objectives were the evaluation of reliability of the test methods, and adequacy

of the materials used in pavements to meet the requirements ortraffic loading and climate.

The program of work included testing oflow- and high-temperature properties of

specimens cored from pavements. Mixture properties were related to properues of the binders

recovered. Results of laboratory tests of rutting resistance oflhe wearing courses were related

to rut depth and rut rate measured in pavements. RSST -CA developed at SHRP, Static Creep

Test and Repeated Load Indirect Tensile Test were applied for evaluation of resistance to

defonnation. Shear Frequency Sweep was used to evaluate properties of the mixtures in a

wide range of temperature and frequency. Thermal Stress Restrained Specimen Tensile

Strength Test (TSRST) was applied to characterize low-temperature properties. Results of

rSRST were related to glassy modulus found from SFS results.

RSST -CH proved to be an effective tool for evaluation of rutting resistance of asphalt­

aggregate minures. It was concluded that shear stiffness modulus directly measured at the

end of testing should be used instead of extrapolating the number ofload cycles to 4.5% shear

strain.

Both methods RSST-CH and Static Creep underestimate rutting resistance of SMA.

SBS-modified layers exhibit superior behavior in service at high and low temperatures,

regardless of the modification method.

I Deputy Director, Chief orPavemenl Tecltnology Division, Roadand Bridge Researcb Institute. Poland

I

Keywords: Rutting Resistance, Repeated Simple Shear, Statie Creep, Indirect Tensile, Shear

Frequency Sweep, Low Temperature Resistance, Relaxation, Asphalt Concrete, Slone Matrix

Asphalt, SBS-modified Binders

Introduction

In the aftennath of political and economic changes in Poland and, in genml, in our pan

of Europe, importance of road transport ina-eased. significantly. Creation of market economy

and development of small and medium enterprises, among other changes, shifted

lransponation of goods from rail to roads. The implications were an increased traffic density

and loads, and a new type or loads - Super Singles. lnc:reased traffic and the lack of funds for

rehabilitation caused significant deterioration of road pavements. The range and speed of

deterioration afroad asphalt pavements in Poland caused that the new mix design, material

recommendations and lest methods had to be implemented immediately.

In 1995 a research project WAS initiated to evaluate a few chosen pavement sections using

new test methods developed in SHRP. Research project WAS financed by the Polish General

Directorlle of Public Roads and was executed by Road and Bridge Research Institute in

cooperation with Dr. lorge Sousa. Main aims of the project were to answer whether.

• materials and tochnologies applied in Poland for rehabilitation of the deteriorated and

construction of the new pavements designed for heavy traffic provide durability in certain

climatic and traffic conditions

• relatively simple test methods applied in Poland provide proper evaluation ohsphalt.

aggregate mixture comparing with sophisticated test methods newly developed in SHRP.

Test program was not based on Superpave system but applied some optional test methods

of asphalt-aggregate mixtures. Tesu were executed in lahoratories of Road and Bridge

Research Institute (lBOM) and SHRP Corp. ofDr Jorge Sousa.

Materials tested

To obtain an objective evaluat ion of the materials used in Polish road construction,

sections of road pavement were chosen which reflect the most recent development: the usc of

J

harder-grade asphalt cement, polymer-modified asphalt binder and SMA mix. Four sections

of heavy trafficked road pavements were chosen, which were constructed of various materials

and by different technologies, and various contractors,

Parement ddign rutd maurials

Section A

Section A is located on the road A4, in the south-west Poland. It has an asphalt pavement

laid on an old shattered cement concrete pavement. Rehabilitation was executed in 1994. The

pavement is constructed of the following layers:

• 5 em, wearing course, asphalt ooncrete 0116 mm, asphalt cement 050 (pen 45-60)

• 8 em, binder course, asphalt concrete 0/25 mm, asphalt cement 050 (pen 45-60)

• 5 em, base course, asphalt concrete recycled hot in place, old asphalt cement 070 (pen

65-85) + new (pen 45-60)

• 5 em, base course. old binder course. asphalt concrete 0112.8 mm, asphalt cement 070

(pen 6\-85)

• shattered cement concrete slabs.

Section B

Section B is located on the road OKl, in western Poland. The pavement is asphalt, semi

rigid. Rehabilitation was executed in 1995 and consisted in hot recycling in place of 4 em

existing wearing course with addi tion of coarse aggregate and overlaying with new wearing

course. Pavement has the following asphalt layers:

• 4 em, wearing course, SMA 0/12.8 mm with asphalt cement 050 (pen 45-60) and

cellulose fibers

• 6 em, binder course, hot recycled in place asphalt concrete. old asphalt cement 070 (pen

65-85) + new 0 50 (pen 45-60)

• 6 em, base course, old asphalt layer

• 18 em, base course old lean cement concrete.

Section C

Section C is a part of the A4 road in Katowice, in southern Poland. The pavement was

newly constructed in 1995. It is a flexible pavement of the following layers:

• 5 em, wearing course, SMA 0/12.8 mm with elastomer-asphalt (Styren-Butadiene-Styren

SBS modified asphalt cement) Elastofalt 50B and cellulose fibers

• 8 em, binder course, asphalt concrete ono mm, asphalt cement 050 (Pen 45-60)

• 22 em, base course, asphalt concrete 013 1.5 mm, asphalt cement 070 (pen 65-85)

• sub-base of crushed mineral aggregate (coal bass).

Section D

Section 0 is a part oftht city expressway 17 in Warsaw. The pavement was newly

constructed in 1993. The layers are as follows:

• 5 em, wearing course, SMA 0112.8 nun with asphalt cement 0 70 (pen 65-85) modified

with SBS directly in pug-mill

• 6 em, binder course, asphalt concrete 000 mm, asphalt cement 070 (pen 65-85) modified

with SBS directly in pug mill

• 15 em, base course, asphalt concrete om mm, asphalt cement D70 (pen 65-85)

• 25 em, sub-base, crushed mineral aggregate.

Table I. Traffic loads or pavements tested

A B C 0

Numher of vehicles:

• trucks l2S 1310 1873 l2S

• trucks with trai lers 12801 2071 1997 12M

• buses 149 21J 206 149

Total 1758 363 01 J776 1758

ESALs IOOkN/day 1723 2812 2813 1723

ESALs lOOkN/day/lane 77l 1283 1266 77l

ESALs 80kN/day/lane \892 JI ll J090 1892

N20, ESALs lOOkN in 20 years, Mia 11 .6 19.2 18.9 11.6

Traffic category, 7% rate KRl KR6 KR6 KRl

In service until May 1998, years II 2.5 2.l 4.l

In service until May 1998, ESALs l00kN, Mio 0.99 1.17 1. 16 \.27

In service until May 1998, ESALs 80kN, Min 242 2.86 282 111

Average rut depth (May \998), mm lJ 6.1 1.9 l .2

Runing Rate, mmlES AL1 00 l.J9E-6 5.24E-6 1.67E-6 01.0SE-6

Traffic load rondiriolu

Traffic data of road sections tested are given in Table I. According to Polish

classification the traffic is of the highest categories KR5 and KR6. According to Superpave

classification traffic exceeds 10' ESALs in 20 years - asphalt-aggregate mixtures should be

designed according to Level 3.

Tlble 1. D6ign pavement temperature and required binder PC grldes

S«tion A B C 0

Latitude 51°10' 52°25' 50° 10' 51 °10'

Maximum Average 7-Days Air Temperature (± 3604 31.19 31.97 36.04

Standard Deviation), C ±l.ll ±l.l3 HIS ±l.l l

Minimum Air Temperature (± Standard 27.7 28.1 27.4 27.J

Deviation), C ±5.71 ±5.58 ±5.56 ±S.71

Maximum Pavement Design Temperature (50% 46.29 41.21 44.94 46.29

Reliability), C

Maximum Pavement Design Temperature (980/. 12.]] 11.2J 10.16 12.]]

Reliability), C

Minimum Pavement Design Temperature, C -22.09 -22.78 -21.84 -22.09

Binder PO grade required:

• normal traffic conditions 18-28 12-28 52-22 18-28

• slow traffic OR high traffic 64-28 18-28 58·22 64-28

• slow traffic AND high traffic 70-28 64·28 64-22 70-28

Qimtllic condiri0ll5

Climate data are given in Table 2. Average air temperature is based on dala from JO-year

period 1965-1995. Based on this data the maximum and minimum pavement design

temperatures were calculated and the binder PO grades required were established according to

(1]. Considering the traffic loading, the use of one or two higher PO grades is recommended in

the case of sections A and D, while in the case of sections B and C. it is even required.

It should be noted thallhe PG-grades required for Polish climatic and traffic conditions

are very high. Comparing these grades with the asphalt cements gathered in SHRP materials

6

libruy it becomes evident that only few conventional binders meet these requirements. Use of

polymer-modified binders is especially justified in thest conditions.

Testing program

Testing of pGlIOnOfts

The following pavement properties were measured:

• deflect ions and bearing capacity by means of FWD

• transverse evenness (rut depth) by means orlhe mOM rut·lesler

• skid resistance by means oClhe mOM skid·resistance tester SRTJ .

The first, reference, measurements were executed after work completion, the second

measurements, in 1996. Rut depth was measured for the trurd time in May 1998.

Laboralory rests

Samples of asphalt layers were cored from sections of road pavemenlS, from the right

wheelpath, after trafficking, in the spring 1995. Samples were distributed for testing at mDM

and SHRP Corp. The laboratory testing program included:

lt mDM

• layer thickness

• air voids content

• composition of asphalt-aggregate mixtures

• propenies of bind en recovered fiom layers (penetration, Softening Point R&B, Fraass

Breaking Point)

• SIalic creep test 8l4OC

• stiffness modulus Repeated Load Indirect Tens ile in Nottingham Asphalt Tester al 0, 10,

2DC

The tests al JBDM were separately executed on samples of each oflhe asphalt layer.

al SIiRP Corp

• ai r voids content (wi th and without para6lm)

• Repeated Simple Shear Test - Constant Height RSST-CH

• Shear Frequency Sweep Test SFS at temperatures - 10, 0, 20, 40C and frequencies 10, 5,

2, 1,0,5, 02, O. I, 0.05, 0.02 Hz

• Thermal Stress Restrained Specimen Tensile Strength Test TSRST.

RSST -CH was executed on samples oflhe wearing and binder courses, while SFS and

TSRST· on samples of the wearing courses only.

7

Testing temperature ofRSST -CH was calculated from the climatic data of the Polish road

sections. For all sections th is temperature was 51.5e. Other conditions were the following:

shear stress 0.069 MFa (10 psi), tire pressure 0.69 MFa (100 psi). Intcfllretation of the RSST­

CU lest results was provided by Dr.lorge Sousa according to procedure presented in [1,3]

[v,l u. lion of pavement conditions

Bearing capacity

Bearing capacity was estimated on the basis ofthe FWD measurements. Backcalculation

was done using ELMOD program. Pavement of section A exhibited a strange behavior in

deflection measurement and bearing capacity backcalculation: on average, the residual li fe

was above 20 years but several points showed nil residual life. Explanation of this

phenomenon is that asphalt pavement ;s overlaid on shattered cement CQnaete slabs. but over

joints the bearing capacity is low, giving the nil rest life. After three years in service the

pavement of this section showed extensive regular fatigue cracking in lines over joints.

All other three sections exhibited proper bearing capacity with residual lire over 20 years.

S~id Raistance

Measurements of skid resistance showed average coefficients in 1996 as follows: A

0.362, B 0.38 1, C 0.302, D 0.350.

Trallsvuse evt"lIl1 tsS (rut depth)

Evolution of average rut depth detennined in three consecutive measurements in years

1995, 1996, 1998 is shown in Fig. I. In all cases the rut depth after three to five years service

does not exceed the safety limit. It is however interesting to observe that evolution of rutting

varies in pavements with plain asphalt cement (A and B) and with SBS modified binder (C

and D). The pavements with plain asphalt cement showed regular inaease in rut depth, while

with SBS modified binders there was an increase of rut depth in the beginning or service. yet

rutting rate was then lower. In 1998 the highesllUl was measured on section B (SMA with

asphalt cement 050 and cellulose fibers), the lowest section C (SMA with SBS modified

binder and cellulose fibers).

",-------------------------------,

'r-----------------------------4 E E

" ,

• ~ • ~ • • , 0:

2

0

199. 1995 1996 1997 1998 1999

Fig, I. Evolution of rut depth

Properties of tbe binden recovered from the pavements

8

Basic properties oflhe binders recovered from particular layers of pavements are given in

Tables 3, 4, S (the recovery preccdure based on RILEM recommendations was used (4] with

trichloroethylen solvent), Properties of tile binders recovered reflect the materials and

technologies used. The best properties are shown by SBS modified binders, both industrially

produced (wearing course, section C) and modified directly in a pug mill (wearing and binder

course, sections 0) These binders exhibited low Fraass Breaking Point, high R&D Softening

Point and high Penetration Index.

Binders from binder and base course of section B exhibited high stiffness (high PI, Fraass

Breaking Point, R&B Softening Point and low penetration). They show excessive hardening

effect, which may be explained by conditions crealed by hOI recycling in place.

Table 3. Basit properties of bindm recovtrtd (rom the wearing courses tested

Property Section (binder)

A B C 0

(050) (050) (Elastor.1t SOB) (070+4%SBS)

Penetration al 25C, 0. I mm 39 \6 53 38

R&D Softening Point, C 54 SI 54 61

Frws Breaking Point, C -1 -2 .\ -7

Penetration Index PI (penlR&B) -0.80 ·0.69 -0.11 0.57

Table 4. Bisic properties of binders reconred from the binder courses tested

Property Section (binder)

A B C 0

(050) (!) (050) (070+4'/,S8S)

Penetration at 25C, 0.1 mm 42 25 45 41

R&D Softening Point, C 52 68 52 6<J

Fraass Breaking Point, C -1 +1 4 -6.5

Penetration Index PI (pen/R&8) -1.10 0.91 .{).95 0.55

Tlble S. Buit properties of biDders recovered from the base counes tested

Property S«lioo (binder)

A B C 0

(070) · (!) (050) (070)

Penetration at 25C, O.lmm 11m J4 46185 46

R&D Softening Point, C 49150 n 54.5/46.5 52.5

Fraas! Breaking Point, C -314 +9 -51-9 -6

Penetration Index PI (pen/R&8) ·0.60/'{)30 1.15 -0331-0.81 '{)78

Evaluation urlhe resistance 10 permlnent deformalion of asphalt-aggregate mixtures

Evaluation of the rutting resistance of the pavements tested was based on three test

methods:

• Repeated Simple Shear Test - Constant Height RSST-CH at 5 L5C

9

• Slatic Creep Test S.C. at 40C

• Repealed Load Indirect Tensile RLiT NAT at 20C.

RSST -CH presented a great scatter ortlle results for samples of the same layer. For the

analysis the average of two results was used. Fig. 2 shows comparison of evolution of

stiffness modulus during shear testing. II is evident that the behavior of asphalt concrete of

layers AI , A2 is different from other mixtures. Layers AI, A2 exhibit decrease of stiffness

modulus, while all other mixtures increase. Samples oflayers 8 1 (SMA) and 82 (asphalt

concrete) became destroyed during testing before reaching the end orlest (5000 cycles).

RSST-CH

10

10 .00

Cycles

.000 .0000

!-O-A1-6-B1 4-C1-o- 01 -0- A2 -6- B2 -o- C2 -0- O~

Fig. 1. Evolution of stirrness modulus at RSST-CH

Presentation cr lcst results of RSST·CH were done in two ways:

• original way developed by Dr Sousa - the number of eydes required to obtain 4,5%

strain or the number ofESALs to reach 12,5 mm rut depth

• slifTness modulus calculated ITom test data after SO cycles (to compare all samples

including the prematurely destroyed ones during the test) or 4999 cycles at the end of

testing.

Evaluation of asphalt-aggregate mixture depends to a great extent on the presentation method

used. Difference may be due to the extrapolation of test resuln in the case of mixtures

resistant to deformation Laboratory test is executed until strain 4.5% is achieved or to 5000

" cycles. In the case of resistant mixtures, the number of load repetitions extrapolated from the

test data may be much higher than 5000, e.g. for mix Allhe numbers orload repetitions

extrapolated arc 1.8JE+87 and 4.6JE+ 13. These numbers seem to be unreasonably high. Both

asphalt concrete mixtures exhibited relatively low air voids content (A I: 1.86%v/v, A1:

2.8S%v/v acoordinglo mOM results, confirmed by SHRP Corp. results), with relatively low

binder content. One possible explanation is that eruapolalion of lest data does not take into

consideration the third phase of now rutting, which accelerates evolution of rutting. On the

other hand it is interesting to observe that A I and A2 samples exhibited decrease of stiffness

modulus during testing. Partl (5] gives explanation orlhi! as malerial fatigue. To avoid

probable error of extrapolation, author used direct test results - modulus after 50 or 4999

cycles.

Results of Static Creep and RLiT were presented as stiffness modulus.

AJI three tests data (RSST -CH, SC, RLlT) were correlated with each other in various

combinations of data: all layers, panicular layers, various mixtures. The effect of air voids

content and asphalt cement content on test results was analyzed. Further, the test data were

correlated with rut depth measured on the pavements and rut rale per ESAL IOOkN calculated

from rut depth and traffic data.

Comparison 0lrest results lor l'Ilrious methods

Rating oflhe materials tested depends on the test method and the way of presentation

chosen. Table 6 presents comparison of rating of mixtures, separately for the wearing and

binder courses. Rating of pavements according to rut depth (or rut rate) measured in May

1998 is also given. The best correlation of the results from laboratory testing and field

measurements provide stiffness modulus G(4999) from RSST -CH and Slatic creep Sliffness

modulus. It must be kept in mind that A I is asphalt concrete and other wearing course

mixtures are SMA. Development ofRSST -CH was hased on the testing of the asphalt

concrete minures rather than SMA. The type of the mix affects the behavior of the material

during testing.

Tables 7, 8, 9 present the correlation coefficients Rl ofregressions between results of the

tests. Various groups of materials were considered: layers or minures, combined or separated .

Fig. 3,4,5 illustrate some of the relationships.

In general, low correlat ion was achieved between various test methods applied. Improved

correlat ion coefficients were obtained, if mixtures were divided into separate groups of

asphalt concrete and SMA. As far as RSST-CH results are concerned. high values of

11

correlation coefficients were provided by the relationships of stiffness modulus 0(4999) to

sialic creep stiffness modulus for asphalt concrete and SMA analyzed separately.

Table 6. Rating of milturu regarding rutting resistance depending on ttst method or

way of prescntation wilb comparison 10 rut ... te of in-se,.,.ice plvemenu

layer RSST-CH SC RUT Average Rut Depth

Number G(IO) G(4999) M~$) 1;20 (or Rut

of cycles Rate)

to 4.5% '" sheM pavement

strain

Wearing Course

AI , AC I 1 ] 2 1 1.6 ]

BI,SMA 4 4 4 4 4 4 4

CI , SMA 2 ] 2 ] 2 2.4 1

D1 , SMA ] 2 1 1 ] 2 2

Binder Course

Al, AC I 1 ] 2 2 1.8

B2, AC 4 4 4 4 4 4

Cl,AC 2 2 1 1 1 1.4

D2, AC ) ] 2 2 ] 2.6

r.ble 7. Comlation coefficieots Rl of RSST-CH venus EIO RLiT NAT

Layer(s) Number of R RSST·CH

samples Cycle G(IO) G(4999)

E10 W' B 8 0,4971 0.50]0 0.5 197

W 4(' ) 0.8420 0.4978 0.9499'

B 4(']) 0.4907 0.8048 0.OOS8"

SMA' W ]( ' 2) OJ817 0,0211 1.0000'

AC: W+B 1('4) 0.606\ 0.87S] 0 2)70'

Average 0.5639 0,5404 0.5425

Table 8. Correlation coefficients RI orRSST·CB versUI Static Cr« p

Layer(s) Number of R RSST-CB

samples Cycles G(50) G('999)

l\h(s) W+B 8 0.0632 0.4050 0.0199

W ' (' 3) 0.4448 0.712] 0.0\04 '

B ' (' 3) 0. 2972 0.1121 0.5416'

SMA: W 3(' 2) 0.6831 0.9541 1.0000'

AC: W+B 5(" ) 0.0024 0.2076 0.8263 '

Average 0.1981 0,5982 0.47%

Table 9. Correlation coefficients R' of Static Crttp venul RLJT NAT

Layet{s) Numbel'of R [ 20

samples

Ms(s) W+B+8a I' 0.0276

W+8+8a: AC 11 0,0343

W+B 8 0.3805

W , 0.1909

B , 0.7605

SMAW 3 0.0049

AC: W+8 5 0.2435

Average (exc. two first rows) 0.3161

Abbrcy;at;o1tS:

W· wtaring course, B - binder course, Ba -~ course, AC - asphalt concrete, SMA -

Slone Matrix Asphalt

13

1.DEtU

1.0E+12

.! 1.0E+l0

~ U. 1,DE t CIII l:

~ 1,OE +06

III « 1,0E +04

1.0E t 02

1,OE+OO

Wearing and Binder Courses

• AI;.t(:,OSO

y: 10,133eo ....

R2 = 00632

Cl ,SUA.OE50

• • 01".SWA.071)oS8S

• • 82;.t(:,D50 81 :$I.IA.05G

14

A1;.t(:,OSO

• C2,,oc ,l)5O

• 0'l;.t(:.o1O+S8S

" " 20

Ms(sl,4OC, MPa

25 30

Fig, J, The Dumbu of cycle! RSST·CU vs. Static Creep StiITDtsS Modulus, Asphalt

Concrete and SMA

,; 1.0E+l0

~ U 1.0E+0f!

:i ~ 1,OE+06 III III « l ,oe+04

I ,DE +Q2

l .oe+OO

"

Wearing and Binder Courses: AC

• Al ;.t(:,P50

Y = 9E+{)1e ... ·U1h

R2 = 0,0024

A2;.t(:f)50

• C2;.t(:,050

I • • 82.JrCDSO

~;AC.o1O+S8S

: " 20 " 30

Ms(s,,40C, MPa

Fig. 4, The number of cycle! RSST-CR V$, Static Creep StilTne!S Modulus, Asphalt

Concrete

Wearing and Binder Courses: AC

H" I y:8,1718x . I5.(,18 C2:IrCD50

r- Rl :: 0,8263 A2:ACD50 /" •

/ V •

" • ~

" ~

-m m m ~ "

V~= 02:ACD1O<S8S -

" 20

o 10 15

/ 20

Ms(s),40C, MPa " 30

Fig,S. Shur Stillness Modulus after 4999 cydes RSST-CH VI. Siltic Creep Stillness

Modulus. Asphalt Concrtle

Effect of air VQids (Ufd bindu content

RSST ·CH and static creep test resul ts were correlated to the air voids and binder content.

The group of milCtUres analyzed included wearing and binder courses with both asphalt

concrete and SMA If a test method were universal, the relationship achieved would be

common for alt types of mixtures and the same criteria could be applied.

More reliable trends were obtained when G(4999) was use instead of the number of

cycles to failure. The latter increases with decreasing air voids content and is very little

affected by the binder content (Fig. 6). 0(4999) shows opposite correlation with air voids,

which is more logical (Fig. 7). On the other hand, the relationship between 0(4999) and

binder content at first sight seems to be opposite to the expected: increase in the binder

content causes increase in the modulus. Consiering, however, that SMA milctures contain

more binder showing better resistance to deformation, this relationship seems to be proper.

Relationship between the air voids content, binder content and stalic creep stiffness

modulus is similar to that for 0(4999) but a decrease in binder content causes an increase in

the stiffness modulus.

9

• 7

~ 6 .. , " .. . > " l <,

,

• - - --•

Wearing and Binder Courses

• • ---I ---. . . . . . .. _.

•

•

, , E 7E 6~ ~ : ~ o

l ;;

, 1l ,iii ,

1,OE.oo l ,OE+02 I ,OE.04 l ,OE+ai l ,OEl-OII l ,OE +l0 l ,oe.'2 ' ,oe".

RSST -CH, cycle

e MVoids HBinder I Fig, 6, EfT«t of Air Voids and Binder Conlent on Number orCydes RSST-CB

, • 7

~ , i' .. ' " ... > .. l

" , , , "

Wearing and Binder Courses

30

---

. . . - . •

40 so 60

G(4999), kPa

• •

--- . . ..;.r---

•

10

eAirVoids EI Binder

;.:a

•

,

" 90

• , 7 ~ .... , ~ 4 ~

o l ;;

" , f

, '00

In

.'ig, 7, Effect of Air Voids and Binder Content on G(4999) RSST-CH

16

II

£fJ~d of properties of the binckr rec01'tred

Trends orlhe relationship between RSSr -CH results and properties orlhe binder confirm

earlier conclusion as to higher reliability of G(4999) than the number of cycles to failure.

Generally. harder binder should produce mixture more resistant to deformation. This is

obtained when G(4999) is used instead or lhe number of cycles (Fig. 8 and 9).

III

• --•

•

Wearing and Binder Courses

----• •

- ---~ ----• •

RSST -CH, cycles

l+Pen25 0 R&BI

-- -

.,

.....

.

Fig. 3. Erred of binder propert ies on tbe Number ofeydes of RSST-CB

III

10

E ., E

" o

,

"

Weartng and Binder Courses

--- ----- -•

., G(4999), kPI

l.pef125 'R&BI

--, ------•

•

III

Fig. 9. Errecl or binder properties on G(4999) of RSST-CH

III

D

" ""

Static creep lest results do not show reliable correlation with properties orthe binders

recovered.

/8

When analyzing relat ionship of binder properties and the resistance of asphalt layer to

runing, it must be born in mind that the binder hardness is one of critical facto rs. The data

analyzed were obtained from the testing of various mixtures (asphalt concrete and SMA) with

very different binders (plain asphalt and polymer modified binders with an additional

admixture of cellulose fibers) . Some outlying results may be explained in terms OflecMOlogy

applied, e.g. hot recycling in place in the case of the seaion B binder course. This asphalt

ooncrete showed low resistance to deformation, despite very hard asphalt recovered. It

confirms that hoI recycling in place rarely allows to improve significantly composition of the

existing layer.

Apparently illogical trend afthe effect of binder properties on evaluation of runing

resisllUlCe can be obviously explained by the predominant role of the mix composition and

properties of the mineral aggregate. For instance, SMA with a softer or polymer modified

binder will be generally more rutting resistant than asphalt concrete.

Wearing COUl"$e

• A", • B SMA _

o SMA

• CSMA

1.0E4S i

• , , Binder Content, 'Iomlm

Fig. 10. Rut lUte vs. Binder Conltnt in tbe Wuring Count

Relationship of rut depth measured in pavement and mix properritS from laboratory testing

It must be emphasil.ed that all road sections tested are in service for a rela tively short

period oD-S years. The rut depth is low being in the range of2-6 mm. If, however, under

certain traffic conditions, rutting resistance of these pavements were nol proper, pennanenl

defonnation would develop already during three hoI summer seasons, as it was observed on

many other road sections constructed in earlier years.

19

Fig. 10 shows relationship between rut rale calculated for pavements tested and binder

oontent in the wearing course, indicating the type of mil( (it is assumed that all ru t depth was

created in the wearing course, which is reliable assumption in this case, considering the range

of rut and pavement design - nol trench study was performed to confirm this assumption and

to evaluate a contribution of the lower layers).

In 1998 the lowest rut depth (and rut rate) was measured on section C (SMA with SBS

modified binder and cellulose fibers), followed by section 0 (SMA with SBS modified

binder) and section A (asphalt concrete with conventional asphalt OSO). The highest rut depth

was measured in section B (SMA with conventional asphalt 050 and cellulose fibers).

The first conclusion is that, when analyzing the whole group of mi~tures of various

types, binder content has very liltle influence on rutting resistance. SMA mixtures containing

more binder perform better than asphalt concrete with a lower binder content. The second

remark is that both SBS-modified SMA show lower rut depth and rut rate than either of tile

mixtures with plain conventional asphalt, including SMA with 050 and cellulose fibers. Both

methods of SBS modification (directly in a pug mill,as well as industrially produced binder)

appeared to be effective.

"

.. o I.OE.a5

C ·

•

Wearing Cou,,"

, + A

,

~ 0 0

, ~ 0

8 , +

, 3.OE.a5 4.OE.Q!I 5,OE.a5

Rut Rate, mm/ESAl

IQMS(S) + RSST-CHI

Fig. II . Static Crttp Stiffness Modulus and Number orCydes or RSST-CB "s. Rut Rate

in Pavements

" • ~ ,. ~" • ... ,.

" o

'''' ...

C

•

•

Wearing Course

A

• 0 I

• B •

3,OEA16 ~,Cf.{)6 5,DE.o&

Rut Rite, mmfESAL

".

" 50 ~

" o

'''' ...

"

20

Fig. 12. Static Creep Stiffness Modulus and Modulus .rter SO or 4999 Cycles of RSST­

CD vs. Rut Rate in Pavements

Relationship between rut rar.e and properties of mixtures is shown on Fig. 11 and 12.

Static creep stiffness modulus does not describe correctly mixtures ofvanoos types. II

underestimates runing resistance of SMA: if two mixtures, asphalt concrete and SMA. have

the same value of the static creep stiffness modulus, SMA will exhibit better resistance to

runing.

Similarly, RSST-CH underestimates the performance of SMA mixtures. Expression of

RSST -CH as 0(4999) gives much better agreement with rut rale Ihan the Dumber of cycles to

4.5% shear strain. On the other hand, significallt overestimation of section A asphalt concrete

is to be noted. Also in this case a better correlation with in-service bebavior or pavement was

obtained when 0(4999) was used.

Vuijication wi,h Whul Tracking Test LCPC

During construction or pavements or sections A and D the Wheel Tracking Test (WIT)

was executed ror mixtures orthe wearing courses of A and D and the binder course 0(0 T~

slab samples were compacted in the laboratory from the mixes taken al the construction sile

LCPC apparatus was applied al test temperature of 4SC. Results are presented in Fig. lJ

Number of wheel passes a to rut depth or 100/. was calculated from linear regression of the

rutting results in the log-log scale. Fig. 13 illustrates that the WIT results for two mi:Ktures

laid in the wearing courses are in agreement with the rut rate calculated for in-service

pavements.

Wheel Tracking Test at 45C

" "

~ .. t • ~ • , •

• • • , o

/ .~ . "" .......... . ..". ,"" .·0 ' . .. ... - --.

p' _ .. -t,. .. -~)'

O~2OOXIDDl«XIXI!!lXOO8XIXI7OOXIIIOO'.DSIDXl

Number of Wheel PlSseS

I-+- 01 SMA,070tSBS ' 0 'D2AC,D7D+SBS -tr-AI AC rD501

Fig. 13. Wheel Tracking Test resul ts

UlE+11 r------- 01 :SMA,D10tS:S ~ 100

A1 :BA,050 I • 1,DE" 2 f------"---+---r- 02:BA,D70+S8S - 75 ~

i A i .,: ',0£00II 1----- - ---,7'-1';,--------1 ~ i ~ ~ a: 1.O£o(W f-----f'.===+-~'O'·;------1 ~ i

,« .. '-_______ -L _______ -4 0 10000 ltmJO IIOX1lO

N(10"lo ]

I_RSST-CH o Ms(s) AG(4999)1

Fig. t4. Results of RSST-CR and Static Creep vs. WIT

Fig. 14 shows the relationship between RSST -CH. static creep test results and WIT

results. WIT rating of miKlures confi rms the results of RSST -CH expressed by G(4999) and

21

22

of slatic creep lest. Rating by the number of cycles ofRSST -CH or by 0(50) is opposite to the

WIT results.

TIe lempenture and frequency effects 00 propertiet of asphalt-aggregate mixtures

Stiffness moduJus1fUU(er curu

Resubs of two tests exeruted were used to chancterize the temperature and frequency

effects on properties of asphalt-aggregate mixtures. Shear Frequency Sweep Test SFS was

carried out at the SHRP Corp. laboratory and RUT at the mOM laboratory. One sample only

was tested in SFS and three samples in RUT.

The master curve of stiffness modulus was derived from the values measured at various

temperature and frequency in SFS and RUT. applying time-temperature SUpefllOsllion

principle derived in (6]. Complex stiffness modulus P from the indirect tensile teSI was

shifted to the shear modulus G' using relationship:

where: v' complex Poisson coefficient.

For noo-compressible materials Poi~n coefficient equals 0.5 and then:

E'olG ' (1)

Shift factor IT was calculated according 10 Arrhenius equation after Francken and

Vanelstraete [7]:

iii I I 10", 0-(- - - ) (l)

R T r. where:

~H activation energy, assumed value 50 kcaVmol

R universal gas constant, 1.98 callmoVK

T temperature, K

T. reference temperature, K.

Arrhenius equation was successfully applied in the imerlaboratory lestS ofRILEM

Te 152PBM [8] for both bituminous binders and asphalt-aggregate mixtures. In this work

reference temperature was 2OC.

Additionally, stiffness modulus ITom SIalic creep teSl at 40C was also included in setting

up the master curves. This is based on the Cox-Merz principle (9J, al lowing comparison of

dynamic and static test results, e.g. in the case of viscosity 11 .. 11* for dy/dt .. C1) or in the case

of stiffness modulus E '" E* for t ::: T, where T - dynamic load period at frequency f(T c lIf).

If at static creep lest the loading time is 3600 5, then the frequency is f = 1/3600 s = 0.000277

Hz. Further, slatic creep stiffness modulus Ms(s) '" 30", assuming that v = 0.5. Fig. 15 shows

the master curve for mixtures of the wwing courses tested. Presentation of the results in a

form of master curve allows to find the irregularities and erroneous results. For instance the

modulus of mixture B at 40C or of mixture D at 0 and -IOC. Unfortunately, it was not

possible to repeat the testing.

The milCtures modified with SSS demonstrate a better behavior. AI a high temperature

andlor low frequency their modulus is higher, while at a low temperature an<Vor high

frequency is lower than that of the non-modified mixtures. Elastic part of the modulus of lhe

SBS-modified mixtures is higher than non-modified at high temperature and/or low frequency

and both pans oflhe modulus, elastic and viscous, are lower at low temperature andtor high

frequency. Service performance of modified mixtures proved to be better compared with the

non-modified ones both at high and low temperatures and in a whole range of frequency.

Complex Modulus, G', SFS i G""'El3, Ms(s)l3

'OOOOr---------------------------~~~~y_,

•• j;1I ~~~!!!!: "'"

10

.1. • 0 • • 1

I' , .' I ( ..

•• i· , • 'I i i .. , .. '

, ~--------------------------------~ • ., o Log{r.Tj

I_A.a. c 001

, •

Fig. 15. Muler curves or modulus for wuring courses mil.lurts

•

Fig. 16 presents the results of the modulus testing at 40C in static creep and dynamic

shear. It 's obvious from Fig. 15 and 16 that the results for section B should be omiued The

modulus curve for A shows a regular shape - the static creep st iffness modulus coincides with

the curve extrapolated from shear measurements. Results of the creep test for SBS-modified

mixtures lay below the lines extrapolated from the shear tests. This confinns the known

principle that static creep test underestimates the hehavior of elastomer-modified mixtures in

comparison with the non·modified mixtures (e.g. [10, II]). Dynamic test are more favorable

for elastomer-modified mixtures.

• • • ,; , , • 0 •

"'" ,.----,----,-----,-----.-- --,

'00

"

,~--+---~--~--~--~ 0,'" 0.001 0.01 0,1

Frequency. Hz

I .. A4OC ..... e4OC ..... C4OC .... 0 4OC 1

Fig. 16, Modulul al40C (rom SFS and Static Crttp

"

Pltas~ IUIg/~ master aln'e

The master curve of phase angle was constructed from shear test resuhs only. The same

values of parameters for the Arrhenius equation were used as for the modulus. Run of the

auves of phase angle is much less regular than for stiffuess modulus (Fig. 17), which

confirms the conclusion reached by Francken and Vanelstraete that optimum activation

energy for phase angle and for stiffuess modulus is different. Adjusting the values assumed

would probably improve the precision of shifting.

All the miKlures tested exhibit a maximum value of phase angle in the high temperature

range. The master curve for pure binder would show regular monotonic run of the increasing

phase angle value from rt to 9(f with temperature In the case of asphalt·aggregate mixture at

the certain, high temperature the bi nder becomes tOO fluid to prevent aggregate grains to get

into a direct contact and the phase angle decreases as the mixture behavior would become

more elastic. The maximum value of phase angle is higher for mixtures with plain bitumen (A

65°) and lower for mixtures with elastomer·modified binder (D 45°). It proves Ihal in the [aller

cast the viscous part of the modulus is lower al high temperature and the mixture is more

res istant to flow deformation.

ro

., '" ... • " -» " " 0

•

Phase Angle, SFS

0 0 • . " ", '1,1i. ••• • II

.1' , •• :', • · . ·0·· III.. . Ii ... ,... o '111!Il~' •• ,'

., o

Log(raT)

IIiIA.a. c .ol

,f' '.',"i t· •• . •• , ,

Fig. 17. Phase angle master turves ror the miltures wuring [oursu

Us~ of th~ SFS usllltl for comfHU"ati~ fflIlllation of asphalt.aggregat~ mixtures

•

SFS test conducted in a wide temperature and frequency range provides a basis for an

analysis of mixture behavior in various load and temperature conditions. From the test

conditions applied, the following temperatures and frequencies were chosen to analyze the

materials with regard to the different deterioration modes:

• pennanent deformation, nonnaJ traffic speed:

high temperature, short load time (medium frequency)

chosen: 4OC, 1Hz (1Hz is respective to speed -60kmIh)

• permanent deformation, slow traffic speed:

high temperature, long load time (low frequency)

chosen: 4OC, O.02Hz

• fatigue under traffic loads:

intermediate temperature, short load time (intermediate frequency)

chosen: 2OC, 1 Hz

• thermal fatigue

low temperature, intermediate load time (intermediate frequency)

chosen: -IOC, O. 1Hz

25

• low temperature aacking:

low temperature, long load time (low frequency)

chostn: · IOC, 0.02Hz.

Table 10. Raling of the wuring course miltures bued 00 the SFS results

Mixture, Rutting Fatigue Low Average

Binder Normal Slow Traffic Thermal Temperature General

Traffic Traffic Load Cracking Rating

Al , AC 3 3 4 4 4 3

050

B] , SMA . . ] 2 ] . 050

C], SMA 2 2 3 3 3 2

ElastofahSOB

D] , SMA ] ] 2 ] 2 ]

070+40/.S8S

'OOOO r----------------------------,

• • ~

, .. ,OJ

,,~----------------------~--~ ." ." o 20 JO " " Tempenture, C

I -<>-A1 .... 61 -<>-C1 .... D1

26

Fig. 18, Syntbetic presentation of the SFS resulls - evaluation of miltures: rulling

rcsisu nte (slow traffic) 40C, O.GZaz, load fatigue zoe, I Hz, low lemperalun cradting ­

IOC, O.OlHz

27

Shear stiffness modulus and phase angle for the wearing course mixtures tested were

compared at chosen test conditions. Results of this comparative analysis are given in Table 10

which shows the rating of the mixtures tested_ The SBS-modified mixtures were rated higher

than their non-modified counterparts. Mixture B I could not be rated. From other mixtures

both SMA mixtures SBS-modified were rated higher than asphalt concrete with 050 plain

asphalt cement.

The analysis of the SFS results is summerized in Fig. 18 which presents the shear

stiffness modulus at chosen frequencies and temperatures reflecting recommended properties

to meet the re1juiremenls at low, intennediate and high temperatures. Samples taken from the

wearing courses of sections C and D proved to perfonn better than from section A with

respect to cracking resistance (lower modulus at low temperaturellow frequency), load fatigue

(lower modulus at intermediate temperaturelintermediate frequency) and rutting resistance

(higher modulus at high temperaturellow frequency) .

Resisllnre to low-temperaturt cracking

Results of two tests were analyzed with regard to low-temperature properties of the

mixtures tested:

• Thermal Stress Restrained Specimen Tensile Strength Test TSRST

• Shear Frequency Sweep Test SFS.

Thermal Stnss Restrained Specimen Tensile Strength Test TSRST

Repeatability ofTSRST was very low, with a substantial scatter of results (Fig. \9). It

illustrates the reason why an AASHTO standard does not provide the precision and bias data

for this test method (11). Nevertheless, an average of two results of every mixture was taken

to the analysis.

Fig. 20 gives a simplified, synthetic version ofTSRST results showing three

characteristic points on the TSRST diagrams:

• P I end of relaxation zone

• P2 end of linear range temperature susceptibility of tensile stress

• Pp point of crack.

18

TSRST

,,----,----,----,-----,----,----,

. ~---+----~_=~1_----+_--~----_1

-30 ." ." , "

Temperaturt,e

-- A1-1 .... Al-J -- B1-2 -- B1·3 --Cl· t - Cl-4 - 01-1 ....... 01-2 -- 01-3 -- 01-4

Fig. 19. TSRST rtsulU

TSRST Characteristic points: Pl, P2, Pp

,

• 4>.,~ ~

..... . 'til

=-- ~

. , 1i =- 1 ! -

.,. .lD . ., Temperature,

I ..... A<>- B+C .. ol

Fig. ZO. Simplified presentation ofTSRST resUlt5

After passing the end of rel axation zone, microcracks may appear in specimen. These

microcracks can affeCllesi resul ts influencing both characteristic points P I and Pp, making

them \0 shift to lower temperatures [Il]. Therefore, it may be assumed (hal the most reliable

is point P2. Both mixtures containing SBS-modified binder have lower P2 temperature than

non-modified mixtures.

]9

Glassy modulus Goo/rom Sweep Frequency Shear Test SFS

It is possible to derive glassy modulus Om from Black diagram of lhe SFS results as the

limiting value of modulus at (f phase angle (Fig. 21). Glassy modulus at shear of asphalt­

aggregate mixtures tested is, respectively: A 11 998 MFa, B 9]32 MPa, C 6398 MFa, D 7650

MPa_ Rll.EM interlaboratory lest (7) provided the value of glassy modulus ED<> of about

30000 MFa for non-modified asphalt concrete. Regarding that E '" J *0, the glassy modulus

E .... orlhe mixtures tested are, respectively, for non-modified: A 35994 MFa and B 27996

MPa, and for 5BS-modified: C 19194 MPa and 0 22950 MPa. These values confirm earl ier

conclusions that the SBS-modified mixtures are less stiff at low temperatures and therefore

more resistant 10 [ow-temperature cracking.

b • , 3 ~ o ~

:

i • • ~ •

100

10

1

~ ~ I'" Y",

R1 .. 0,9836

I'" o 10

iii W· O,95(2

, R'· 0,98

" " " Phase Angle, deg

l'A'8'c 001

-

50

Fig. 21. EIInpolation of Glassy Modulus from lineAr rtgmsion of part of Black

dilgram ofSFS - 10 and OC

Rt:/QriOll of I(})P-/empua/lln propt:rlies of mixtures tll,d bindm

Low·temperature propenies of four mixtures were related to Fraas! Breaking Point for

the binders recovered , II confirms the predominant influence of binder low temperature

properties on mixture behavior at low temperature.

• ~ ~

,,,.

8100X1 o • , , ~ ~

:5OOJ ~ o

. ,

•

•

,

•

."

• 0 •

C

• • Tfraul, C

B

A

.,

Fig. 11. Glassy Modulus vs. Fl1IlSs BreakiDg Point

B

C

• D

•

• • ., TFraaSl,C

•

A

•

Fig. 23, Temperature or point Pl of TSRST YS. Fruss Breaking Point

'"

•

Fraass Breaking Point is in particularly good agreement with glassy modulus derived

from SFS test (Fig. 22) and with temperature of point P2 - the end of relaxation zone from the

TSRST (F;g. 23).

Influence or lhe type of miKture is nol observed in the low-temperature behavior - the

difference in behavior of mixtures is obviously related 10 the binder properties rather than to

J/

the type of mixture. Setter properties of SMA taken from sections C and 0 should be related

to the use orSBS·modified binders, not to the composition of mineral aggregate. II confirms

earlier conclusions, e.g. [1 4].

Conclusions

Sections offour heavy trafficked asphalt pavements were tested with application of the

testing methods developed under SHRP and wi th mort traditional methods used at mOM.

High- and low-temperature behavior of the materials cored from pavements were evaluated.

Asphalt concrete and SMA mixtures were tested. Binders applied were plain asphalt cement

and SBS-modified, Two various modification methods were used during production orlhe

mixtures: blending of base asphalt with SSS, or direct modification orlhe mixture in a pug

mill under certain conditions.

RSST-CH applied for the evaluation of rutt ing resistance proved to be a useful method.

The author reoommends, however, to present the test results as stiffuess modulus at the end of

test (after 5000 load cycles). The original method developed by Dr. Sousa may lead to

erroneous results in the case of enrapolation of direct results.

None of the methods applied: nither RSST-CH nor Static Creep may be used universally

for various types of asphalt-aggregate mixtures like asphalt concrete or SMA Rutting

resistance of SMA is underestimated. The most suitable verification of runing resistance.

which finds confinnation in nomal service is obtained by Wheel Tracking Test. The

recommended WIT is its French version ofLCPC.

Shear Frequency Sweep at various temperatures and frequencies allows to characterize

mixture over a wide range of load conditions. Presentation of the results in a form of master

curve gives a synthetic view on mixture behavior at low and high temperatures.

TSRST is a useful tool to characterize low temperature behavior of asphalt-aggregate

minure but its precision must be improved. From the test parameters the most reliable seems

to be the temperature of the end point of relaxation zone.

Evaluation of materials cored from in-service pavements after three to four years under

heavy traffic and in hard climatic C(Inditions proved that SOS-modified minures behave

bener than the non-modified ones. Both methods of modification proved to be effective in the

actual industrial construction and service conditions regarding both low- and high-

temperature propcnies. Application of SMA mixture modified with SSS and a fibrous

stabilizer proved to have superior properties over a wide temperature range.

Acknowledgments

32

Author would like to express his gratitude 10 General Directorate of Public Roads in Poland

for financial support oflhis research project. Special thanks and gratitude are extended to Or.

Jorge Sousa, subcontractor of the project, who executed or organized the SHRP tests.

Rererences

1 SoI.imIOi.lD M.. Kenntdy T.: Predicting Maximum Pavement Temperature using

Maximum Air Temperature and Hourly Solar Radiation. TRB 1993, Washington

2 SOUSI J.B., Solaimloiln M., Weissman 8.L.: Development and U$I!. oj till Repealed

Shear Test (Constant Height): An Optional Superpave Mix Design Tool. Report SHRP-A-

698, SHRP, NRC, Washington, DC 1994

3 Sousa J.B., Solaimanian M.: Abridged Procedure To Determine Permanent Deformation

oj Asphalt Concrete Pavements. TRR 1448, TRB, NRC, Washington, DC, 1994

4 Duet J.: Recovery method with rotary evaporator of the soluble binder from bituminous

mixes: interlaboratory test comparisons and test procedure recommendation. Rll..EM r C56-

MHM, Materials&Structures, 1988, p. 151·160

5 Plrt! M.N., Vinsoll T.S., Sousa J.B., Hicks R.C.: PtrJonnanct and proptrtiu oj Swiss

asphalt concrete surface courses. EMPA, Report No. IIJn, Oaober 1994

6 Williams M.L.. Lalldel RF., Fcrry J.D.: Journal of Amer. Chern. Soc., 77, 1995

7 Franckcn 1... Vane1strlttt A.: Complex moduli oj bitumil10us materials: A rational

method Jar the inttrpretatiO/1 oJ test results. ?roc. oftht 5111 International Rll.EM Symposium,

Mechanical Tests for Bituminous Materials, MTMB Lyon, 14·16 May 1997, Edited: A.A.

Balkema, RonerdamlBrookfield, 1997

8 Par11 M.N., Francken L.: RlLEM il1terlaboratory tests all stiJ/IltSS modullls oj bituminolls

mixtures. Pree. of the 5" International RJLEM Symposium, Mechanical Tests for Bituminous

Materials, MTMB Lyon, 14·16 May 1997, Edited: A.A Balkema, RonerdamIBrooldield,

1997

9 Cal W.P., Men E.B.: Journal of Polymer Science, 28, 619,1958

10 Vllktring c.P., Vonk W.: Thermoplastic rubbers for Ihe modification of bitumens:

improved elastic recovery for high de/ormation resistance of asphalt mixes. Pmc, of \5111

AR.RB Conference, Part 2

JJ

11 Sybihki D •• Dorodeckl R : Oetna odpornoici na koleinawonie mieszanek mine/alno­

asJallowych w zaleirlo.sci ad zastosawanego /epimza i melody hadania. IV Mi~dzynarodowa

Konferencja "Trwa!e i bezpieczne nawierzchnie drogowe", Kielce 1998

12 AASIDO Provisional Standard TPIO: Standard Test Method for T1Iennaf Stress

Restrained Specimen Tensile Strength.

13 Partl M.N., Vinson T.S., Sousa J.B., Hick.! R.G.: Performance and properties a/Swiss

asphalt concrete surface courses. EMP A, Report No. ]13n, October 1994

14 Arand W., Sybilski D.: Wplyw zastosowollio poIslcich asfa/taw drogowych Ttl wlaSdwoSci

belonu asfallowrgv w niskirj Irmperarune (Influence of Polish Road Asphalt on Properties of

Asphalt Concrete at Low Temperature). Prace mDM 1. 1992, s. 5 ~ 26 (in Polish)