sand patch and british pendulum tests of the recently built l3 road

SAND PATCH AND BRITISH PENDULUM TESTS OF THE RECENTLY BUILT L3
Eng. Charles Silva de Aguiar
Road Engineering Laboratory
CEFTRU/UnB
Brazil
Eng. Paulo Roberto Farias Falcão
Road Engineering Laboratory
CEFTRU/UnB
Brazil
Prof. Márcio Muniz de Farias
Road Engineering Laboratory
CEFTRU/UnB
Brazil
Eng. Li Chong Lee Bacelar de Castro
Road Engineering Laboratory
CEFTRU/UnB
Brazil
ABSTRACT
The surface course of a flexible pavement must be stable and provide a safe and comfortable ride
for its users. The adherence between the vehicle tires and the pavement surface is of great relevance for
user’s safety. This interaction is controlled by the macro and micro texture of the surface. Several
researches confirm the relation between surface texture and surface friction, and their influence on the
skid resistance against aquaplaning under wet conditions and critical speeds. One of the most busy roads
of Brasilia (capital of Brazil), the L3 avenue, was recently duplicated. A dense concrete asphalt layer was
constructed using the most common mineral aggregate applied in pavement services in Brasilia
(limestone). This kind of aggregate becomes easily polished and projects using dense mixtures generally
produce deficient pavement surfaces in terms of macro and micro texture. This paper presents the results
of a survey about the macro and micro texture of the recently built L3 pavement, based on sand patch and
British pendulum tests.
INTRODUCTION
Studies about tire-pavement adherence in the middle-west roads of Brazil are still insufficient.
The present work aims to characterize the macro and micro texture of the recently built L3 pavement,
based on sand patch and British pendulum tests.
The L3 road is the main access to the University of Brasilia (UnB). The federal transportation
department has classified the L3 road traffic as one of the most dangerous of the Federal District. Data
provide by the administration of the University of Brasilia has shown that 25% of the accidents on the
university roads happened in the L3 road between 1999 and 2004.
The duplication of the L3 road started in November of 2005. The construction cost approximately
U$ 2.2 millions. The first deadline for finishing the construction (90 days after the begging of the works)
was not achieved due to the extended raining season. Almost six months later (in July of 2006) the
construction was then finished and the road was opened to the traffic.
EXPERIMENTAL PROGRAM
The sand patch and British pendulum tests were carried out on both traffic directions
(North/South and South/North). Table 1 summarizes the number of experiments on both traffic flow
directions.
1
Table 1 - Number of experiments for each traffic direction
Direction of the traffic
Experiment
North / South
South / North
British Pendulum
16
16
Sand Patch
8
8
Sand Patch Experiments
Sand patch tests were carried out in accordance to ASTM E 965-96 guidelines. Tests were
performed at every 400 m and 3 sand patches were made for each point. The average of three
measurements of diameter was taken for each sand patch to calculate the average diameter for an
individual sand patch. The medial diameters of the three sand patches were used to calculate the
macrotexture depth for each local point.
Before the beginning of each experiment the surface of the pavement were carefully cleaned and
the sand patch were then made as illustrated in Figure 1.
Figure 1 – Sand Patches
British Pendulum Experiments
The British Pendulum tests were carried out in accordance to ASTM E 303-93 guidelines and 32
different points were analyzed for the two traffic flow directions (16 for each direction, one test every
200 m). Five determinations of British Pendulum Number (BPN) were taken discharging the first one to
calculate the mean value for each point.
All the experiments were performed on the right line of the road for both traffic flow directions in
the same area of the sand patch tests. Figure 2 presents the British Pendulum apparatus used for this study.
Figure 2 – British Pendulum Apparatus
2
RESULTS AND DISCUTIONS
Table 2 (South/North traffic flow direction) and Table 3 (North/South traffic flow direction)
present the results of the sand patch tests and the macrotexture classification in accordance with the
French standard RG-2/1971 for each point analyzed.
Table 2 – Results of Sand Patch Experiments for South/North Traffic Flow Direction
Table 3 – Results of Sand Patch Experiments for North/South Traffic Flow Direction
It can be observed from the results shown in Tables 2 and 3 that the macrotexture of almost all
the points analyzed were classified as smooth according to the French standard RG-2/1971. In order to
facilitate visualization, the results of the evaluation according to the French standards are summarized in
Figure 3.
3
Very
Smooth
Medium
Rough
Very Rough
1,50
1,40
1,30
1,20
1,10
1,00
0,90
0,80
0,70
0,60
0,50
0,40
0,30
0,20
0,10
0,00
0
1
2
3
4
5
6
South / North
Direction
7
8
9
10
11
Analized Points
12
13
14
15
16
Smooth
Height (mm)
Macrotexture Evaluation - RG-2/1971
17
North / South Direction
Figure 3 – Macrotexture Evaluation
The results of the British Pendulum tests, for both longitudinal and transversal directions, are
presented in Figure 4. It can be observed that the BPN values for all the analyzed points were classified
as good or excellent (BPN > 65).
BPN Average for All Analyzed Points
BPN Average
BPN Longitudinal
BPN Trasnversal
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233
South / North Direction
Analyzed Points
North / South Direction
Figure 4 – Longitudinal and Transversal BPN values
It can be concluded form the results presented in Figure 4 that, in average, there is no anisotropy
between the BPN longitudinal and transversal values for both studied traffic flow directions. Based on a
statistical analysis, it was concluded that all the BPN results comprise the same data family.
Tire-pavement adherence may be better analyzed by considering macrotexture and BPN values
together. The international friction index (IFI) was calculated for each analyzed point using the average
values of longitudinal BPN (Figure 4) and macrotexture results presented in tables 2 and 3 for each traffic
flow direction. Table 4 presents the calculated (Sp, F60) pair for each analyzed point, where (Sp) is the
Speed Constant and (F60) the friction Index.
Yeaman (2005) established thresholds values for macro and microtexture in pavements
evaluations of New Zealand and Australia. These limits are expressed in terms of (Sp) and (F60). Based
4
on these limits, Yeaman proposed a graphic to identify when to make further investigations or
rehabilitations in class 1 highways pavements (speed limit of 70 kph).
Two combinations of (Sp, F60) are plotted in Figure 5. The average of Sp and F60 values for each traffic
flow direction were used to estimate the pavement adherence conditions in both directions.
Sp, F60 and FR60 were calculated using empirical formulations developed by the international
committee of surface characteristics in 1992 and are calculated using the sand patch and the British
Pendulum testes results.
It can be observed in Figure 5 that the results for both traffic flow directions the of L3 road are
deficient according to the restrictions suggested on Yeaman´s graphic. Although the results of macro and
microtexture of L3 road are compatible with the road class when analyzed individually, the combined
analyses of Sp and F60 values show the necessity of further investigations of the pavement surface
texture.
Table 4 – (Sp, F60) Values
F60
HDT Average
Local Average
FR 60 ( 60 km/h Adjusted
Sp
Point
(Friction
(mm)
(BPN)
Friction Index)
index)
1
76
16,26
3,51
0,08
2
85
16,26
3,92
0,09
3
80
16,26
3,69
0,09
4
82
16,26
3,78
0,09
5
75
16,26
3,48
0,08
6
78
16,26
3,60
0,08
7
75
16,26
3,46
0,08
8
80
16,26
3,69
0,09
0,25
9
81
16,26
3,74
0,09
10
81
16,26
3,74
0,09
11
86
16,26
3,97
0,09
12
80
16,26
3,69
0,09
13
93
16,26
4,29
0,09
14
83
16,26
3,83
0,09
15
84
16,26
3,88
0,09
16
83
16,26
3,83
0,09
17
87
29,17
15,67
0,18
18
82
29,17
14,77
0,17
19
82
29,17
14,77
0,17
20
78
29,17
14,05
0,17
21
81
29,17
14,59
0,17
22
75
29,17
13,51
0,16
23
85
29,17
15,31
0,18
24
66
29,17
11,89
0,15
0,36
25
71
29,17
12,79
0,16
26
83
29,17
14,95
0,18
27
76
29,17
13,69
0,17
28
85
29,17
15,31
0,18
29
85
29,17
15,31
0,18
30
80
29,17
14,41
0,17
31
80
29,17
14,41
0,17
32
80
29,17
14,41
0,17
5
F60 Values
0,55
0,50
0,45
0,40
0,35
0,30
0,25
0,20
0,15
0,10
0,05
0,00
Do not investigate for combinations
above and to the right of this point
Macrotexture Problems in
this Region
No intervention for
combinations above and to the
right of this point
Macro and Microtexture
Problems in this Region
0
10
20
30
40
50
60
70
80
90
100
110
Sp Values (kph)
(F60 x Sp) South/North Direction
(SP x F60) North/South Directionl
Figure 5 – (F60,Sp) restrictions (modified – Yeaman, 2005)
CONCLUSIONS
The results of the sand patch tests of the recently duplicated L3 road pavement indicate that the
macrotexture of this road is smooth according to the French standard RG-2/1971. Although a smooth
macrotexture is considered to be acceptable for this kind of road class (speed limit < 70 kph), one should
consider that the type of aggregate used (limestone) may be easily polished and the macrotexture will
tend to deteriorate due to traffic action.
Although the British Pendulum tests results were considered to be satisfactory (BPN >65), the
combined analyses of Sp and F60 values show the necessity of further investigations of the L3 pavement
surface texture according to restriction proposed by Yeaman (2005).
REFERENCES
ASTM-E-965, (1996). Test for Measuring Surface Macrotexture Depth Using a Sand Volumetric
Technique, in 1995 Annual Book of ASTM Standards American Society for Testing and Materials, vol.
04.03, USA
ASTM E-303-93 (1998). Standart Method for Measuring Frictional Properties Using the British
Pendulum Tester. Annual book of ASTM Standarts, Road and Paving Materials; Vehicle Pavement
Systems, Volume 04.03, USA, 5p.
Yeaman, J (2005). “Are We Afraid of IFI?” International Conference on Surface Friction. 17p.
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