Examination of Rutting and
Weathering Characteristics of
various Danish Road Classes
Danish Road Institute
Report 111
2001
Ministry of Transport - Denmark
Road Directorate
Danish Road Institute
Elisagaardsvej 5
P.O. Box 235
DK-4000 Roskilde
Denmark
Telephone: +45 46 30 70 00
Telefax:
+45 46 30 71 05
e-mail:
vd@vd.dk
web:
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Title:
Author:
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Examination of Rutting and Weathering Characteristics of various Danish Road Classes
Jørn Raaberg, Jeanette Rosenberg
September 2001
Road Directorate, All rights reserved
Road Directorate, Danish Road Institute
87-90145-88-7
0909-1386
Examination of Rutting and
Weathering Characteristics of
various Danish Road Classes
Jørn Raaberg
Jeanne Rosenberg
Danish Road Institute
Report 111
2001
1
1
Contents
Contents.........................................................................................................................3
Abstract ........................................................................................................................4
1. Introduction ..............................................................................................................5
2. The investigated road sections.................................................................................6
3. Material composition................................................................................................7
4. Stripping test.............................................................................................................9
5. Dynamic creep test .................................................................................................10
6. Discussion ................................................................................................................12
7. Conclusion...............................................................................................................14
8. Literature ................................................................................................................15
3
Abstract
The Danish road network is divided into four classes: Motorways, main roads, rural
roads and local roads. In order to optimise the lifetimes of the bituminous surfacings
in these road classes economically, it is necessary to consider the rutting and weathering resistance of road pavements. Optimisation of rutting resistance often results in a
lean, stone rich layer that is less weather resistant than a bitumen rich layer. For low
trafficked roads it is therefore, important to optimise weathering resistance, whereas
for heavily trafficked roads, optimising rutting resistance is more important.
A three year project commenced in 1998 to research the functional performance of
bituminous wearing courses and road base materials designed and produced by Danish
asphalt contractors. The objective of the project was to ensure that bituminous materials tested in the Danish Asphalt Rut Tester can be related to other well known testing
methods and to measurements of rutting actually occurring on roads so that a basis can
be established for evaluating the rutting and weathering resistance of future bituminous materials.
Ten pavements were selected that were due for overlaying and which suffered from
rutting generated mainly in the bituminous layers. Cores were taken from these pavements in and between the wheeltracks. On the basis of their rutting and weathering resistance a number of laboratory tests were conducted to determine whether these different bituminous materials could be classified as suitable surfacing materials for three
road classes. These laboratory tests included material composition, stripping and dynamic creep test on the samples from the upper 10 to 18 cm of the surfacing in the selected pavements.
This paper describes the part of the project in which the observed in situ conditions
were compared to the results from the laboratory tests carried out on the samples taken
from the ten pavements. This comparison resulted in a classification of the bituminous
mixes investigated in terms of their rutting resistance and weathering resistance.
4
1. Introduction
This paper describes the properties of flow rutting and stripping of the bituminous layers of selected road pavements. Research regarding flow rutting and stripping of samples prepared in the laboratory have been performed previously at the Danish Road Institute (DRI) [1]. A great difference in the structural design has however been observed between laboratory prepared samples and samples taken in situ [2, 3, 4]. Some
uncertainty must therefore be expected when test results of these two types of sample
preparations are compered. In the light of the previously mentioned, it was decided in
this project exclusively to use samples taken in situ for the laboratory testing and
compare data from these tests with data from in situ measurements of selected pavements
In Denmark, it is common practice to measure rutting of the pavements of the Danish
road network regularly with the Profilograph. The criteria for the selection of the
pavements for this investigation were thus road pavements where there had been or
currently was rutting to a greater or lesser extent generated in the asphalt layers.
In order to characterise the individual asphalt types and pavement designs of the selected road pavements, the following laboratory tests were performed on samples
taken in situ:
Material composition of the individual layers.
Durability test, where the material's resistance to stripping was tested.
Dynamic creep test, where the material's resistance to permanent deformation was
tested.
In the following sections, a characterisation of the pavements, the laboratory tests and
the results obtained are described in detail.
5
2. The investigated road sections
In 1998, DRI selected in a co-operation with four road administrations possible road
pavements as investigation objects, based on the above criterion. Ten road sections
were selected, based on the following road classes:
·
·
·
2 motorways (M) with an ADT > 20,000 and with an EASELs >1400.
7 main roads (MR) with an ADT between 6,000 and 12,000 and with an EASELs
between 300 and 1300.
1 rural road (RR) with an ADT < 4,000 and with an EASELs < 300.
On the ten road sections, the following material types are included in the upper three
to four asphalt layers, Table 1.
Type
Classification
Air voids
(%)
ABS *)
£ 8.0*)
60*)
£ 9.0
60, 85, 180
GAB S
Hot rolled asphalt with
chippings
Asphalt concrete, dense
Asphalt concrete, gap
graded
Soft asphalt,
dense
Stone mastic
asphalt
Binder course
GAB
Basecourse
Course
Wearing
course
AB t
AB aa
PA t
SMA
Binder and
Basecourse
Bitumen
content
(%)
Penetration
(1/10 mm)
300 or softer
£ 7.0
60
£ 8.0
³ 4.8
60
£ 8.0 / £ 10.0
³ 5.0 / ³ 4.5
60, 85
*) The requirements are based on a previous Road Standard [5], since hot rolled asphalt with chippings is not
included in the present Road Standard [6].
Table 1: Grade of materials and some selected requirements from the Road Standard.
6
3. Material composition
In order to substantiate the results from the dynamic creep tests and weathering resistance tests, the material composition was determined for each layer of the upper 10-18
cm, corresponding to the upper three to four asphalt layers of the pavements. Drilled
cores from the pavements were used for the material examination with a diameter of
100 mm, taken in and between the wheeltracks. Table 2 shows some of the data of the
material composition from the ten road sections.
All data is determined according to Danish Test Methods [7,8].
It can be observed from Table 2 that the road sections 152/614 (layer 1 and 3), 332B
(layer 3), 332C (layer 3), 363 (layer 1) and 608 (layer 1) contain one or several layers
with a relatively low calculated air voids content. Furthermore, Table 2 shows that
layer 3 of road sections 14 and 608 has a relatively high calculated air voids content.
On several of the pavements there is a marked difference in the calculated air voids
content in cores taken in and between the wheeltracks. Also it can be observed that
road sections 125, 152/614 and 608 contain one or several asphalt layers with a relatively high penetration, corresponding to a soft binder. This can be considered acceptable for the rural road section 608, as a pavement of this type of road class according
to the Road Standards does not require a hard type of binder. However, it is critical for
main roads such as road sections 125 and 152/614, since the traffic intensity is higher.
The third layer of road section 363 consist of an asphalt layer with relatively low
penetration and low bitumen content.
7
Road
classes
Section
11
Motorway
14
125
152/614
332 A
Main road
332 B
332 C
363
401
Rural road 608
Materials
Types
Air voids
in wheelbetween
track
wheeltrack
(volume-%) (volume-%)
4.1
3.4
4.6
4.5
5.2
5.9
2.6
3.5
4.0
3.2
10.9
11.3
3.9
5.2
3.4
5.4
2.1
2.7
0.3
1.4
3.6
5.8
-0.2
3.1
4.1
3.4
4.6
4.5
5.2
5.9
5.2
7.2
2.7
4.4
1.3
1.2
4.7
7.4
7.6
7.8
0.2
0.6
1.6
2.0
4.9
4.5
6.2
6.8
2.0
2.6
3.7
6.3
2.4
8.4
8.0
7.7
1.8
1.4
Bitumen data
Bitumen
Penetracontent
tion
(weight-%) (1/10 mm)
6.6
65
5.5
41
4.9
40
6.9
44
5.6
24
4.6
45
5.1
101
5.1
109
5.5
122
5.3
95
6.7
99
6.4
245
6.7
69
4.9
85
5.3
59
5.3
45
5.3
54
5.0
64
5.2
56
5.0
46
5.6
62
5.6
69
5.3
49
4.3
16
5.1
28
4.9
67
5.9
57
4.6
50
5.1
146
ABS
GAB
GAB
ABS
AB
GAB
AB t
GAB
GAB
AB t
AB
PA t
SMA
GAB
GAB
AB aa
GAB S
GAB
AB
GAB
GAB
GAB
GAB
GAB
AB t
AB
AB t
GAB
AB t
Layer
thickness
(mm)
35
30
40
40
40
50
30
40
90
30
15
25
35
70
30
30
45
75
30
50
80
60
65
60
25
20
15
55
30
GAB
60
5.6
7.1
4.8
50
AB
30
10.9
9.1
4.8
25
Table 2: Selected data of the material composition of samples from the ten road sections.
8
4. Stripping test
The test method used in Denmark to determine the adhesion between an aggregate and
a bitumen is normally the "Rolling Bottle Method" [9]. This method tests only a certain fraction of the aggregate and does not give any information about the properties of
the asphalt mix. In this particular project, the Danish Road Institute has used a method
where the mix itself is tested.
The weathering resistance test is performed by determining the Stiffness Modulus of
the individual layer of the pavement samples (cores with a diameter of 100 mm) before and after the test samples have been exposed to an accelerated condition procedure according to Lottman, 1982 [10].
The Stiffness Modulus was determined by the Nottingham Asphalt Tester (NAT) according to British Standard DD 213:1993 [11]. It should be mentioned that only asphalt layers with a thickness greater than 30 mm have been tested, as required in the
test method. The result of this test is shown in Figure 1 as the mean change of the
Stiffness Modulus in percent.
Difference in Stiffness Modulus (%)
10
0
-10
40
50
60
70
80
-20
90
100
Basecourse
Binder course
Hot rolled asphalt with
chippings
-30
-40
-50
-60
-70
Voids filled with bitumen (%)
Figure 1: Results from the weathering resistance test shown as the difference in Stiffness Modulus as a function of the air voids filled with bitumen of samples
taken from the road sections.
Only the changes of more than 20% in the Stiffness Modulus after accelerated conditions are significant.
Based on the results shown in Figure 1 the materials have been divided according to
the amount of voids filled with bitumen with regard to their resistance to stripping, as
follows:
· Good resistance to stripping: voids filled with bitumen > 80%.
· Medium resistance to stripping: 60%< voids filled with bitumen < 80%.
· Poor resistance to stripping: voids filled with bitumen < 60%.
9
5. Dynamic creep test
In order to test the pavements' resistance to rutting, samples were taken as drilled
cores with a diameter of 150 mm of the entire pavement construction between the
wheeltracks. By using samples taken between the wheeltracks it is possible to obtain a
material structure and properties which are similar to the material which originally
was used for paving, since the pavement in this area only has been exposed to low
traffic load. There is however a hardening of the binder, which will influence on the
rutting properties of the pavement.
Dynamic creep tests were performed according to FAS method 468-97 [12]. The
method prescribes that on samples with a layer thickness less than 30 mm the test
should be performed on a stacked layer of the same material. This was done for two
different types of asphalt mixes and compared to the dynamic creep test performed on
the entire pavement construction of the two layers. The results showed that the two
tests were comparable. It was therefore decided to perform dynamic creep tests of the
entire pavement construction of the three to four upper asphalt layers corresponding to
a layer thickness of 10-18 cm.
According to the method described above the total strain should be stated after 3,600
pulses. Two dynamic creep test series reached a state of tertiary flow before the 3,600
pulses were reached. Therefore, the creep rate was additionally given. Based on the results of the dynamic creep tests, the road sections can be divided into the following
categories of rutting properties:
Rutting
performance
Good
Medium
Poor
Section
332 B
332 C
14
363
401
608
11
332 A
152/614
125
Road
classes
M
M
M
MR
MR
RR
M
MR
MR
MR
Creep rate
(me/pulse )
Total
strain
(me)
Year of
construction
E10
1999
ADT
1999
1.0
1.0
1.1
1.2
1.2
1.5
3.0
5.5
6.0
7.5
11,652
13,814
12,112
11,133
12,738
12,614
24,695
33,510
+
+
1994
1995
1983
1998
1987
1984
1987
1983
1988
1986
695
695
1916
760
680
213
1466
1223
900
399
6363
6363
32,834
6923
7688
3,531
24,432
11,376
11,193
6500
*
Rutting has been repaired three times
+
Tertiary flow before 3,600 pulses
Mean
rutting in
situ
(mm)
3.0
1.6
8.5
5.8
4.7
3.4
11.3
6.9*
8.1
8.8
Table 3: Results from dynamic creep test of samples taken from the ten road sections.
10
As can be observed from Table 3, it could be considered appropriate to divide the road
classes according to the creep rate with regard to their resistance to rutting, as follows:
· Good resistance to permanent deformation: Creep rate ≤ 2.0 me/pulse for motorways and heavily trafficked main roads.
· Medium resistance to permanent deformation: 2.0 me/pulse < creep rate ≤ 4.0
me/pulse for main roads.
· Poor resistance to permanent deformation: Creep rate > 4.0 me/pulse for rural
roads.
Table 3 shows that the pavement of the rural road section 608 has good resistance to
permanent deformation, which - seen from an economic point of view is not appropriate - since the traffic load is relatively low. On the motorway such as road section 11,
the pavement has a medium resistance to permanent deformation, which again is not
appropriate since the pavement has a relatively high traffic load. Also the materials on
main road sections 332A, 152/614 and 125 are not sufficiently resistant to permanent
deformation in relation to the traffic load on the pavements in question.
It should be mentioned that the data measured by means of dynamic creep test do not
give a particularly good correlation to the mean rutting measured in situ. This can be
due to the fact that the permanent deformations measured in situ partly come from
lower-lying asphalt layers and/or unbound layers.
11
6. Discussion
Variations in compaction of asphalt pavements in situ lead to a variation in material
properties. Variation in test results based on in situ samples is therefore larger than test
results based on laboratory prepared samples. It was however, decided to perform
laboratory tests using in situ samples to obtain a good basis for comparison to measurements performed in situ.
A comparison of the material composition and the creep tests shows clearly that the
pavements where a soft binder was used have the highest creep rates. This could lead
to rutting problems, for pavements exposed to high traffic loads. Other mix design parameters, such as aggregate size distribution and the type of aggregates used, can also
lead to less rut resistant roads.
A comparison of the material composition and the weathering resistance test shows
that asphalt materials with a high content of air voids have a poor weathering resistance in contrary to asphalt materials with a high content of bitumen. The testing of
the pavement's resistance to stripping has made it possible to differentiate between the
different materials from the content of voids filled with bitumen.
Figure 2 below shows the correlation between weathering resistance of the asphalt
layer with the highest difference in Stiffness Modulus after accelerated conditions and
rutting properties for the full construction for the ten road sections investigated.
85
Voids filled with bitumen (%)
80
332 A
75
152/614
125
70
0
1
2
3
65 11
332 B
363
4
5
6
7
8
Creep rate (me/pulse)
60
332 C
401
55
Motorway
608
50
14
45
Main road
Rural road
40
Figure 2:
Characteristics of rutting properties and weathering resistance for the
ten road sections shown as the correlation between creep rate and air
voids filled with bitumen.
12
Figure 2 supports the conclusions reached in part 5: Dynamic creep test. The rural
road section 608 has good rutting resistance, but poor durability, which is not optimal
seen from an economic point of view in relation to the actual traffic load. The motorway section 11 has only medium rutting resistance despite the fact that the actual traffic load is considerably higher. The main road sections 125, 332 A and 152/614 has
poor rutting resistance and the pavements are not economically viable.
The material tests have shown that on some of the road sections, an inexpedient selection of pavement type for the actual traffic load has been made. This could be due to
the fact that there in general has been a considerably larger increase in traffic load than
expected.
13
7. Conclusion
No simple correlation was found between in situ rutting and the laboratory tests of
samples taken in situ. This may be due to the fact that there are too many variable
factors which have an influence on the rutting properties of asphalt materials, such as
the hardness of the binder, the amount of bitumen, the aggregate size distribution, air
voids content, etc.
The ten road sections have however been classified according to their rutting properties based on creep rate determined by dynamic creep tests and their stripping properties based on the voids filled with bitumen. It is demonstrated that the resistance to
stripping and resistance to permanent deformation of the asphalt materials were not
always optimised in relation to traffic load. By performing a few simple tests of the in
situ asphalt materials, a more economically viable solution can be ensured.
It should however be mentioned that the tests described in this paper regarding the
rutting and stripping properties are not suitable for mix design, where laboratory samples usually are used. The tests described are relevant when an existing road pavement
is due for repairing. The tests could improve the evaluation whether it would be economically profitable if one or several asphalt layers should be removed before overlaying.
14
8. Literature
[1]
Raaberg, J., et al., Fællesafprøvning af diverse asfalttyper (i forbindelse med revision af vejregel for varmblandet asfalt). Eksternt notat 8, Vejteknisk Institut,
1998. [Testing of various types of asphalt - in connection with a revision of the
Road Standard for hot-mixed asphalt].
[2]
Eriksen, K., Wegan, V., Krarup, J., Air void content and other air void characteristics of asphalt concrete by image analysis. Contract No.: SHRP-88-AIIR13, Phase 2.
[3]
Eriksen, K., Air void characteristics in asphalt-concrete samples from the compaction study, Contract No.: SHRP-88-AIIR-13, Phase 3a.
[4]
Raaberg, J., Investigation of gyratory compaction used for asphalt mix design.
Proceedings of the 7th Euroseminar on Microscopy Applied to Building Materials, Delft, June 29-July 2, 1999.
[5]
Udbuds- og anlægsforskrifter, varmblandet asfalt, Almindelig arbejdsbeskrivelse. November 1994 [Danish Road Standard - hot-mixed asphalt].
[6]
Udbuds- og anlægsforskrifter, varmblandet asfalt, Almindelig arbejdsbeskrivelse. November 1998. [Danish Road Standard - hot-mixed asphalt].
[7]
Prøvningsmetoder - Vejmaterialer, 0-59. Vejdirektoratet. [Test methods - Road
materials 0-59].
[8]
Provisoriske prøvningsmetoder, 1-99.Vejteknisk Institut. [Provisional test
methods 1-99].
[9]
Bituminous mixtures - Test methods for hot mix asphalt - Part 11: Determination of the compatibility between aggregate and bitumen, prEN 12697-11:1999.
[10] Lottman, R. P., Predicting Moisture-induced damage to asphalt concrete, Field
evaluation. National Cooperative Highway Research Program, Report 246,
Transportation Research Board, May 1982.
[11] BSI, DD213:1993 Draft for development, Technical Committee B/510.
[12] Bestämning av deformationsresistens med dynamisk kryptest. FAS Metod 46897. [Determination of resistance to deformation by means of dynamic creep
tests].
15
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(Electronic edition)
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Danish Road Testing Machine RTM2: 1998
(Wei Zhang, Robin Macdonald)
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(Wei Zhang, Robin Macdonald)
(Electronic edition)
102/00
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Danish Road Testing Machine RTM3: 2000
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(Electronic edition)
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Motorway Pavements
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