TRANSPORT A N D ROAD RESEARCH LABORATORY Department of Transport
RESEARCH REPORT 122
THE EFFECT OF EVA-MODIFIED BITUMENS ON ROLLED
ASPHALTS CONTAINING DIFFERENT FINE AGGREGATES
by J Carswell
The views expressed in this report are not necessarily those of the Department of Transport
Pavement Materials and Construction Division Highways Group Transport and Road Research Laboratory Crowthorne, Berkshire, RG11 6AU 1987
ISSN 0266-5247
Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on I st April 1996.
This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.
CONTENTS
Page
Abstract 1
1. Introduction 1
2. Binders 1
2.1 Penetration 1
2.2 Softening point 1
2.3 Viscosity (45°C) 1
2.4 Viscosity (100-200°C) 2
3. Discussion of rheological changes 2
4. Aggregates 3
5. Properties of asphalt mixes 3
5.1 Marshall design 3
5.2 Deformation resistance 9
6. Relationships between different properties of materials 11
7. Conclusions 14
8. Acknowledgements 15
9. References 15
© CROWN COPYRIGHT 1987 Extracts from the text may be reproduced,
except for commercial purposes, provided the source is acknowledged
THE EFFECT OF EVA-MODIFIED BITUMENS ON ROLLED ASPHALTS CONTAINING DIFFERENT FINE AGGREGATES
ABSTRACT
The changes in the rheological properties of petroleum bitumens after the addition of ethylene- vinyl acetate co-polymer (EVA) are described and the consequent effect on their use in rolled asphalt wearing course mixtures is reported. In particular, the changes in the Marshall stability and deformation resistance using four asphalt sands of different stability are quantified. The relationship between these properties and the effect of the EVA component is discussed in detail, and equations are derived relating the Marshall stability of a conventional rolled asphalt wearing course to the Marshall stability of a rolled asphalt containing bitumen modified with 5 per cent EVA for the same resistance to permanent deformation.
1 INTRODUCTION
The use of bitumens modified with an ethylene-vinyl acetate co-polymer (EVA) is now fairly widespread in the UK particularly in weather conditions likely to affect adversely the laying of conventional wearing courses or where more deformation-resistant surfacings are required. Denning and Carswell (1981) have detailed the effect of a particular grade of EVA on the physical properties of the bitumen and on the rolled asphalt mixtures made with this binder. This work has led to a draft specification being introduced to cover the use of this particular grade (18_+2 per cent vinyl acetate, melt f low index 150_+40) in rolled asphalt wearing courses. The principal effect of adding 5 per cent of this EVA to a petroleum bitumen is to increase the resistance to permanent deformation of a rolled asphalt wearing course material to a far greater degree than would be expected from the measured change in Marshall stability. This finding raises the question as to whether low stability fine aggregates, at present unsuitable for surfacing heavily-trafficked sites, may be used with an EVA modified bitumen to achieve a performance similar to that of conventional asphalts made with higher stability fine aggregates. As a result of this research the option would be available to use either a locally-available, lower-stability sand with a more-expensive modified binder or a higher stability sand, with high haulage costs, with a conventional binder.
This report quantifies the effect of two petroleum bitumens modified with ethylene-vinyl acetate co- polymer on rolled asphalt wearing course mixtures
containing four different fine aggregates. The fine aggregates were chosen to represent a wide range of stability characteristics.
2 BINDERS
The fol lowing binders were used in this project: a 50 pen bitumen, a 70 pen bitumen, the 50 pen bitumen plus 2.5 per cent and 5.0 per cent EVA (18 per cent vinyl acetate, 150 melt f low index) and the 70 pen bitumen plus 5.0 per cent of the same EVA. The bi tumen/EVA binders were blended using a low shear mixer for a period of approximately 2 hours at a temperature of 160°C. Rheological tests were carried out on the 5 binders.
2.1 PENETRATION The penetration of each binder at 25°C was determined according to the Institute of Petroleum method 49/1984 (Institute of Petroleum 1984a). The results are given in Table 1 and show that the addition of EVA to a bitumen reduces the penetration by about one grade.
2.2 SOFTENING POINT Ring and ball softening point measurements were carried out according to the Institute of Petroleum method 58/1984, (Institute of Petroleum (1984b)) and the results are tabulated in Table 1. The increase in softening point is marked, being 5°C for the 2.5 per cent addition, 12°C for the 5.0 per cent addition to the 50 pen bitumen and 15°C for this level of addition to the 70 pen bitumen. It appears from this limited information that the change in softening point with the addition of EVA may be linear, particularly for a given bitumen and polymer.
2.3 V I S C O S I T Y (45°C) The viscosity of each binder at 45°C was measured using the Sliding-Plate Rheometer (Denning and Carswell 1981). The values of viscosity at a shear rate of 0.05s -1 and at a strain of 1 are shown in Table 1. Previous work (Denning and Carswell 1981) has shown a good correlation between this measure of viscosity and the wheel-tracking rate of a rolled asphalt (with 30 per cent coarse aggregate) made with the same binder. Table 1 also shows the nominal elastic recovery of each binder measured with the same rheometer, determined after a period equal to the loading time; it can be seen that the EVA confers a degree of elasticity to the binder, in proportion to the polymer content, indicating that the
binder is less Newtonian in character than a bitumen at this temperature.
2.4 VISCOSITY (100-200°C) Measurements of viscosity in the range 100 to 200°C were made on each binder using a Haake viscobalance, which utilizes the principle of a falling sphere in a fluid. This temperature range is useful as it corresponds to the mixing, laying and rolling temperatures of rolled asphalt wearing course materials. The viscosity curves for each binder are shown in Figure 1 and equiviscous temperatures, relating to mixing and rolling temperatures, are
B I N D E R
o 5 0 pen B i t u m e n
o 50 pen B i t u m e n + 2 .5 per cen t E V A
• 50 pen B i t u m e n + 5 per cen t E V A
70 pen B i t u m e n
• 70 pen B i t u m e n + 5 per c e n t E V A
3.0
O t~ v
d
2 . 0 -
1.0 -
0.0 -
I I I I I I I I I I I 100 120 140 160 180 200
Temperature (°C)
Fig . 1 R e l a t i o n s h i p b e t w e e n H A A K E v i s c o s i t y a n d t e m p e r a t u r e
-1.0 80
shown in Table 1. The temperature values shown for 300 poise are extrapolated from the experimental results and should be treated with caution.
The effect of the EVA co-polymer is to render the binder more viscous, but not markedly so, and is in keeping with the increased softening point values. However, previous work has shown that the EVA- modified bitumens do not require higher mixing and laying temperatures in commercial practice, possibly because the EVA confers a degree of shear susceptibility to the binder as it departs from Newtonian behaviour.
3 DISCUSSION OF RHEOLOGICAL CHANGES
For a 2.5 per cent addition of EVA to a 50 pen bitumen the high temperature viscosity characteristics remain relatively unchanged but, over the typical temperature range experienced on the road, the binder is generally stiffer and slightly more elastic. At 45°C it is nearly twice as viscous as the 50 pen bitumen, indicating an increased resistance to permanent deformation when used as a binder in a wearing course material.
The effects of adding 5 per cent EVA to the 50 pen and the 70 pen bitumens are virtually the same; the penetration is reduced by about one grade and there is a substantial increase in the ring and ball softening point. At 45°C, the elasticity of the polymer modified binders were an order of magnitude greater than the respective base bitumens and their viscosities were also increased by a factor of 4 to 5. This stiffening effect was observed in the normal mixing and laying temperature range but not to the extent that modifications to existing commercial practice were required.
T A B L E 1
Rheological properties of the binders
Binder
50 pen 50 pen + 2.5
per cent EVA
50 p e n + 5 per cent EVA
70 pen 70 pen + 5
per cent EVA
Pen- etration
(0.1 mm)
53 39
34
73 50
RSB Softening
Pt. (°C)
54 59
66
48 63
Apparent viscosity (45 ° ) S t r a i n = l ,
Shear rate = 0.05s -1 (poise)
1.35. 105 2.60. 10 s
7.60. 10 s
7.80. 104 3.30. 10 s
*extrapolated values
Elastic recovery
(per cent)
2 10
20
2 20
Equiviscous mixing and rolling temperatures (°C)
2 poise 10 poise
162 130 169 133
187 146
150 120 164 129
50 poise 300 poise
104 106
115
9 8 102
80* 84*
8*
75* 78*
TABLE 2
Properties of aggregates and filler
Coarse aggregate (granite)
Fine aggregates
Southport Bristol Beach Channel Whitegate AImington
Sieve size per cent (by mass passing)
14 mm
10 mm 3.3 mm 3.35 mm 2.36 mm 300/~m ]00/~m ;)12/~m 75/~m
D
99.97 99.79 96.38 55.02
0.51
100 5O
16.7 m
95.80 85.00 52.30 24.70
2.20
m
m
99.4O 100.00 98.70 99.50 72.10 86.25 44.20 55.5O
0.20 4.96
2.70 2.68
1.526 1.511
Filler l imestone
100.00 91.54
Specific gravity 2.59 2.69 2.71 2.75 (Mg/m 3)
Bulk density -- 1.507 1.510 -- (Mg/m 3)
The 70 pen bitumen modified with 5 per cent EVA showed a similar viscosity-temperature relationship over the mixing and laying range to that of a 50 pen petroleum bitumen but had a higher softening point and an increased viscosity at 45°C. This suggests that in commercial production an asphalt containing this binder would provide a more deformation resistant surfacing without involving additional energy cos ts .
Denning and Carswell (1981) have shown that asphalt surfacings containing EVA modified bitumens may show better workability, with adequate compaction being achieved below the rolling temperature, equivalent to 50 poise, as measured by the Haake viscobalance. At present, the reasons for this are not clear and may be due either to the non- Newtonian behaviour of the binder at these temperatures or to physical-chemical reactions within the EVA itself. This effect, if reproduced generally, should allow more time for compaction of an asphalt, thereby either extending the working season, or allowing more successful laying in adverse weather conditions. The problems associated with adverse weather working are the subject of a report by Daines (1985). Further work is needed to quantify the effect of the EVA co-polymer on the compaction of asphalt in the temperature range 80-100°C.
4 AGGREGATES
All wearing course mixtures were made with granite coarse aggregate (Croft) and limestone filler
(Flowers). The coarse aggregate and the fil ler gradings, together with their specific gravities are shown in Table 2. The variables in the mixtures were the type of binder and the type of fine aggregate. Four fine aggregates were used ranging from rounded to angular shaped particles, yielding a wide range of Marshall stabil i ty values. The fine aggregates were all sands and their gradings, specific gravities and bulk densities are recorded in Table 2. The Southport Beach and Bristol Channel fine aggregates are composed mainly of rounded particles, the difference between them being that the Southport material is more single-sized. The Whitegate fine aggregate was chosen to represent an average stabil i ty sand and the Almington fine aggregate for producing high Marshall stabil i ty asphalt wearing course mixes.
5 PROPERTIES OF ASPHALT MIXES
5.1 M A R S H A L L D E S I G N The optimum binder content for each binder for each fine aggregate was determined using the procedure in British Standard BS 594 (1973) (British Standards Institution 1973) except that 30 per cent coarse aggregate was also included in the test specimens. The values of mix density, compacted aggregate density, Marshall stabi l i ty and percentage voids are plotted against binder content for each fine aggregate and binder in Figures 2 to 5.
2.26
I I 2.21 5.5
7.0
j/ 2.25
~ 2.24
g "o 2.23 x
2,22
I 6.5 7.5 9.5
I 8.5
2.11
~-" 2.09 -
2.07 -
" 0
m m 2.05 --
==
o_
E 2.03 -- o £3
2.01 5.5
B INDER
[] 50 pen Bitumen
O 50 pen Bitumen + 2.5 per cent EVA
• 50 pen Bitumen + 5 per cent EVA
ix 70 pen Bitumen
• 70 pen Bitumen + 5 per cent EVA
I 6.5 7.5 8.5 9.5
A z v
o3
6.0
5.0
4.0
3.0
2.0 5.5 6.5 7.5 8.5 9.5
Binder con ten t (per cent)
F i g . 2
8.0
E
Q.
X
E . E
o >
7.0
6.0
5.0
4.0 -
3.0 5.5
I I I 6.5 7.5 8.5
Binder content (per cent)
Marshall Design on rolled asphalt (30 per cent stone content) with Southport Beach sand
9.5
\
\
2.28 --
E 2.27 -
-~ 2 . 2 6 - x
2 .25 -
2.24 5.0
B I N D E R
D 50 pen Bi tumen
O 50 pen Bi tumen + 2.5 per cent E V A
• 50 pen Bi tumen + 5 per cent E V A
z~ 70 pen Bi tumen
• 70 pen Bi tumen + 5 per cent E V A
2.29
9 . 0
5.0
E
&
o~
Q.
E 0
2.15
2 .125
2.10
2 .075
2.05
• 5 . 0 I I I
6.0 7.0 8 .0
I I I 6 .0 7.0 8 .0 9 .0
A z
>
U3
4.0
3.0
5.0 6.0 7.0 8.0
Binder con ten t (per cent)
F ig. 3
9.0
+~
Q .
x ~=
O >
7 .0 ' - -
6.0 -
5.0 -
4 .0 -
3.0 -
2.0
5.0
I I I
6 .0 7.0 8 .0
B inder c o n t e n t (per cent)
M a r s h a l l Des ign on r o l l e d a s p h a l t ( 3 0 per c e n t s t o n e c o n t e n t ) w i t h B r i s t o l C h a n n e l sand
9 .0
2.22
8.0
7.0
A
6.0
_~ 5 .0
4 .0
3 .0
BINDER
O 50 pen Bitumen
O 50 pen Bitumen + 2.5 per cent EVA
• 50 pen Bitumen + 5 per cent EVA
z~ 70 pen Bitumen
• 70 pen Bitumen + 5 per cent EVA
2.20 ---(3
2.18 --
2.16 -
2.14
6.0
2.06
~" 2.04
• ~ 2.02 E
2.00
j E O ~J
10.0
1.98 -
I I I 1.96 I I I 7.0 8.0 9.0 10.0 6.0 7.0 8.0 9.0 10.0
2.24
E
v
E
. X
6.0
Fig . 4
8.0
X
E
>
m
B
= . .
6.0
4.0
2.0 -
0.0 I I I 7.0 8.0 9.0 10.0 6.0 7.0 8.0 9.0
Binder content (per cent) Binder content (per cent)
Marshall Design on rolled asphalt (30 per cent stone content) with Whitegate sand
10.0
6
2.30
2.28
2.26
~ 2.24 X
2.22
BINDER
n 50 pen Bitumen
O 50 pen Bitumen + 2.5 per cent EVA
• 50 pen Bitumen + 5 per cent EVA
z~ 70 pen Bitumen
• 70 pen Bitumen + 5 per cent EVA
2.12
~ 2.10
~ 2.oa
2.06 (~
E o 2.04
2.20 I I I 6 .0 7.0 8 .0 9 .0 10.0
2.02
m
I I I 6.0 7.0 8.0 9.0 10.0
I 0.0
9.0
8.0
7.0
6.0
10.0
8.0
6.0
X
E
.~ 4.0
2.0
\ 5.0 I I I 0.0
6.0 7.0 8.0 9.0 10.0 6.0
Binder content (per cent)
I I I
7.0 8.0 9.0
Binder content (per cent)
Fig. 5 Marsha l l Design on ro l l ed aspha l t (30 per c e n t s t o n e c o n t e n t ) w i t h A l m i n g t o n sand
10.0
TABLE 3
Marshall properties at optimum binder content for each binder and for each fine aggregate
MATERIAL PROPERTIES AT OPTIMUM
Compacted Marshall Optimum binder aggregate Marshall
content Mix density density Stability Flow Quotient (per cent by mass) (Mg/m 3) (Mg/m 3) (kN) (ram) (kN/mm)
50 pen 50 pen+2 .5 per cent EVA 50 pen + 5 per cent EVA 70 pen 70 pen + 5 per cent EVA
50 pen 50 pen+2 .5 per cent EVA 50 p e n + 5 per cent EVA 70 pen 70 p e n + 5 per cent EVA
50 pen 50 pen +2 .5 per cent EVA 50 pen + 5 per cent EVA 70 pen 70 p e n + 5 per cent EVA
50 pen 50 pen + 2.5 per 50 pen + 5 per cent EVA 70 pen 70 pen + 5 per cent EVA
7.3 7.3 7.6 7.3 7.3
6.9 6.6 6.9 6.9 6.7
SOUTHPORT BEACH FINE AGGREGATE
2.255 2.085 3.80 3.60 2.252 2.086 4.65 3.87 2.255 2.079 5.60 3.87 2.249 2.088 3.35 3.55 2.254 2.085 4.35 3.83
BRISTOL CHANNEL FINE AGGREGATE
2.285 2.124 3.59 3.83 2.282 2.128 4.51 3.13 2.280 2.120 5.23 3.78 2.275 2.118 2.74 3.84 2.278 2.124 4.12 3.53
WHITEGATE FINE AGGREGATE
8.4 8.4 8.6 8.4 8.4
8.1 8.0 8.1 7.9 7.9
2.216 2.018 5.17 3.60 2.231 2.047 5.75 4.37 2.231 2.023 7.81 3.95 2.216 2.029 4.12 3.90 2.219 2.043 5.96 4.20
ALMINGTON FINE AGGREGATE
2.269 2.084 8.86 5.55 2.284 2.104 9.60 4.85 2.261 2.078 9.50 4.77 2.267 2.087 7.50 5.00 2.266 2.084 8.10 4.75
Voids in mix
(per cent)
1.06 5.30 1.20 5.20 1.45 4.75 0.94 5.05 1.02 5.27
0.94 3.65 1.44 4.85 1.38 3.75 0.71 4.70 1.17 4.95
1.44 5.50 1.32 4.42 1.98 5.25 1.06 4.75 1.42 4.65
1.60 3.60 1.99 4.80 1.99 3.95 1.50 3.85 1.70 3.90
Table 3 shows the properties of each mix at optimum binder contents; these were calculated in the normal way as the mean of the binder contents of the maxima found for mix density, for compacted aggregate density and for Marshall stability.
The results showed that for each fine aggregate the type of binder made little difference to the opt imum binder content, to the mix and compacted aggregate densities or to the void content of the mix.
The only differences found were in the values of Marshall stabilit ies where the EVA modified bitumens gave higher results. For the 50 pen bitumen plus 2.5 per cent EVA the increase in Marshall stabil i ty was just over 10 per cent for the Whitegate and Almington sands, and over 20 per cent for the Southport Beach and Bristol Channel sands. Marshall quotient values were also higher because the f low
values remained relatively unchanged, except in the case of Whitegate sand where an unusually high f low value resulted in a slightly lower Marshall quotient.
For the two grades of bitumen modified with 5 per cent EVA the percentage increases in Marshall stabil i ty were of the order of 40-50 per cent for the lower stability sands, but only about 10 per cent for the Almington sand, probably because the angular- shaped particles of this sand have an over-riding effect. A lower than expected increase in Marshall stabil i ty was recorded for the 70 pen bitumen plus 5.0 per cent EVA when using the Southport Beach sand; the reason for this is not clear.
One point of particular interest from the Marshall design studies was that the optimum binder contents were about 1 per cent lower for the lower stability sands than for the higher stability materials; when
TABLE 4
Wheel-tracing rates (45°C) at optimum binder content for 30 per cent wearing course mixtures containing different fine aggregates
Binder
50 pen 50 pen + 2.5 per cent EVA 50 pen + 5 per cent EVA 70 pen 70 pen + 5 per cent EVA
50 pen 50 pen+2.5 per cent EVA 50 pen + 5 per cent EVA 70 pen 70 pen + 5 per cent EVA
Optimum binder
content (per
cent)
7.3 7.3 7.6 7.3 7.3
8.4 8.4 8.6 8.4 8.4
Density (Mg/m 3)
SOUTHPORT BEACH
2.217 2.217 2.225 2.215 2.212
WH ITEGATE
2.199 2.224 2.191 2.192 2.191
Wheel- tracking
rate (ram/h)
2.88 1.35 0.95 5.53 1.30
2.00 1.20 0.72 3.20 0.95
Optimum binder
content (per
cent)
BRI, (
6.9 6.6 6.9 6.9 6.7
8.1 8.0 8.1 7.9 7.9
Density (Mg/m 3)
~TOL CHANNEL
2.241 2.199 2.240 2.242 2.243
ALMINGTON
2.234 2.234 2.242 2.237 2.232
Wheel- tracking
rate (mm/h)
3.30 1.85 1.00 4.33 1.29
1.50 1.10 0.53 2.70 0.83
translated into commercial practice, this would reduce bitumen costs by about 12 per cent and, to some extent, compensate for the increased cost of the polymer modified binder. But, an asphalt surfacing with this reduced binder content may be less durable and the results of these Marshall designs must be interpreted cautiously. However, the results of an experiment on the Winchester by-pass (Jacobs 1983) have shown that low binder content rolled asphalts can perform well and some rolled asphalts with 1.5 per cent below target binder content (derived from the procedure given in Section 3 of BS 594: 1973) performed adequately for 7 years.
5.2 D E F O R M A T I O N R E S I S T A N C E Laboratory samples were manufactured at the optimum binder contents and at __1 per cent of optimum for each binder and fine aggregate; they were subjected to the TRRL wheel-tracking test at 45°C described by Jacobs (1981). The variations in wheel-tracking rate with binder content for each material are shown in Figures 6-9. Density values and wheel-tracking rates at the optimum binder contents are recorded in Table 4.
For the 50 and 70 pen bitumens the wheel-tracking rates showed a similar pattern, with the more stable sands giving the lower tracking rates. Only the asphalts made with 50 pen bitumen and with the Whitegate and the Almington sands had wheel- tracking rates less than 2mm/h, indicating suitability for use on very heavily trafficked roads; see Jacobs (1981).
For the materials made with 50 pen bitumen plus 2.5 per cent EVA the wheel-tracking rates for three of the sands were reduced by a factor of 1.8, with all rates being less than 2mm/h. For the Almington sand the effect was less marked (reduction factor 1.35), probably because the high particle interlock of this sand was more significant than the contribution made by the EVA polymer.
The wheel-tracking rates for the asphalts containing the bitumens modified at the 5 per cent EVA level were substantially reduced for all the fine aggregates, with all values below 1.5 mm/h, a reduction factor of 3 to 4. This indicates that asphalts containing low stability sands, when mixed with bitumen plus 5 per cent EVA, should perform satisfactorily under the severest traffic loading conditions, even though the Marshall stability values for the Bristol Channel and Southport Beach sands suggest otherwise. The plots of variation of wheel-tracking rate with binder content in Figures 6 to 9, show that the addition of ethylene-vinyl acetate to a bitumen improves the tolerance of the rolled asphalt to variations in binder content. In practice, this would enable a higher-than- optimum binder content to be specified without adversely affecting deformation resistance and this could be of benefit in certain applications. While the optimum binder content, determined by the Marshall design method, gives low wheel-tracking rates for each material, Figures 6 to 9 also show that, for a minimum deformation resistance, a lower binder content could be chosen, especially for the Whitegate and Almington fine aggregates. This confirms earlier work by Jacobs (1983). However, this trend is not apparent for all the fine aggregates in this study.
E E
--L ==
BINDER
o 50 pen Bitumen
o 50 pen Bitumen + 2.5 per cent EVA
• 50 pen Bitumen + 5 per cent EVA
70 pen Bitumen
• 70 pen Bitumen + 5 per cent EVA
!0.0
8.0
6.0
4.0
2.0
0.0
!
D
I I I
5.0 6.0 7.0 8.0
Binder content (per cent)
Fig. 6 Whee l - t r ack i ng rates o f ro l l ed asphal t (30 per cen t s tone c o n t e n t ) w i t h var ious b inders using Br i s to l Channe l f i ne aggregate
E E
z=
BINDER
50 pen Bitumen
o 50 pen Bitumen + 2.5 per cent EVA
• 50 pen Bitumen + 5 per cent EVA
70 pen Bitumen
• 70 pen Bitumen + 5 per cent EVA
10.0
8.0
6.0
4.0
2.0
0.0
D #
7.0
I !
8.0 9.0
Binder content (per cent)
10.0
Fig. 8 Wheel - t rack ing rates o f ro l led asphal t (30 per cent s tone con ten t ) w i t h var ious b inders using Whi tegate f ine aggregate
E E
¢0
¢0 L
==
BINDER
o 50 pen Bitumen
o 50 pen Bitumen + 2.5 per cent EVA
• 50 pen Bitumen + 5 per cent EVA
70 pen Bitumen
• 70 pen Bitumen + 5 per cent EVA
10.0
8.0
6.0
4.0
2.0
0.0
/
I I I
6.0 7.0 8.0
Binder content (per cent)
Fig. 7 Whee l - t r ack i ng rates o f r o l l ed aspha l t (30 per cen t s tone c o n t e n t ) w i t h var ious b inders using S o u t h p o r t Beach f ine
aggregate
9.0
A .¢E E E v
BINDER
o 50 pen Bitumen
o 50 pen Bitumen + 2.5 per cent EVA
• 50 pen Bitumen + 5 per cent EVA
70 pen Bitumen
• 70 pen Bitumen + 5 per cent EVA
6.0
5.0
4.0
3.0
2.0
1.0
0.0 6.0
Y ~1 O ~
I I I
7.0 8.0 9.0
Binder content (per cent)
Fig. 9 Wheel - t rack ing rates o f ro l led asphal t (30 per cent s tone con ten t ) w i t h var ious b inders using A l m i n g t o n f ine aggregate
10
6 RELATIONSHIPS BETWEEN DIFFERENT PROPERTIES OF M A T E R I A L S
The changes in the rheological properties of modified binders have already been discussed and provide a consistent pattern in this limited study. Relationships have been found between the softening point of a binder and the wheel-tracking rate by Jacobs (1981) who used Redhill sand and this information together wi th the data from four fine aggregates from this study are shown in Figure 10. Similarly, the effect of the apparent viscosity of a binder (45°C) on the wheel-tracking rate has been reported by Denning and Carswell (1981) for Redhill fine aggregate and regression lines for each fine aggregate are constructed in Figure 11. The relationships shown in both Figures 10 and 11 are distinct for each fine aggregate; it wil l be noted that the slopes are generally the same and the values are tabulated in Table 5. These different relationships probably reflect or are a function of material differences;
In order to examine the role of the ethylene-vinyl acetate component in the Marshall stabil i ty values and wheel-tracking rates, these are considered with and w i thou t the addit ion of polymer. The ef fect of the addit ion of EVA to bi tumen on the Marshall stabilities for each f ine aggregate is shown in Table 6 and on the wheel- tracking rates in Table 7. For the 2.5 per cent level of addit ion to the 50 pen bitumen, the increase in Marshall stabi l i ty values averaged 17 per cent, and the wheel- t racking rates are reduced by a factor of 0.6 (range 0.5 to 0.7). A t the 5.0 per cent level of addit ion to both grades of bi tumen the resultant Marshall stabilit ies were 35 per cent higher, wi th the increase for the A lmington sand being somewhat smaller for the reasons discussed earlier. The wheel-tracking rates were reduced by a factor of 0.3 (range 0.25 to 0.35) wh ich was found to be independent of type of f ine aggregate.
Currently, bitumen modif ied w i th 5 per cent EVA is used in some asphalts therefore the results for this material wil l be examined in more detail. Figure 12 shows the relationship between Marshall stabil i ty and wheel-tracking rate on a logari thmic scale for both the unmodif ied and EVA modif ied asphalts.
A J =
E 0.5 E v
0.0
-~ -0.5
- 3
Bristol Channel --0.037
~ - " ~ Southport --0 042 \
W h i t e ~ Almington --0.036
Redhill--0.05
I I I I 45 50 55 60 65
Ring and ball softening point (°C)
Fig. 10 Relationship between log wheel-tracking rate and ring and ball softening point for each fine aggregate
A . C
E E
v
. J
~.='q~:--~ Southport --0.79 0.5
- _ -- -~.-,r- ~ . = = " ~ , ~ ~ Bristol Channel --0.70
o o . e o .
Almington --0.70 ~ ~ ~ ~ ' - " " - ~
Whitegate --0.74 ~'~ --0.5 -- -0.9 I I
4.7 - 5.0 5.5
Log apparent viscosity (poise)
Fig. 11 Relationship between log wheel-tracking rate and log apparent viscosity for each fine aggregate
T A B L E 5
Regression slopes and correlation coeff icients for f ine aggregates
Softening point /Wheel tracking Apparent viscosity (45°C)/Wheel- t racking rate regression rate regression
Fine aggregate Slope Correlation coefficient Slope Correlation coeff ic ient
Southport Beach Bristol Channel Whitegate Almington Redhill
- 0.042 - 0.037 - 0.037 - 0.036 - 0.05t
0.98 0.99 0.99 0.99
- 0.79 - 0.70 - 0.74 - 0.70 - 0 . 6 3 *
0.91 0.98 0.98 0.99
t basis: LR 1003 * basis: LR 989
11
TABLE 6 Effect of EVA con ten t on Marshall stabi l i ty
Fine agg rega te
Br isto l Channel
S o u t h p o r t Beach
W h i t e g a t e
A l m i n g t o n
50 pen
D
m
Factor increase w i th b inder modi f icat ions
50 pen +
2.5 per cent EVA
1.26
1.22
1.11
1.08
50 pen +
5.0 per cent EVA
1.46
1.47
1.51
1.07
70 pen
M
m
m
70 pen 4-
5.0 per cent EVA
1.50
1.30
1.45
1.08
A V E R A G E FACTOR INCREASE - - 1.17 1.38 -- 1.33
T A B L E 7
Effect o f EVA con ten t on whee l - t rack ing rate (45°C)
Factor reduct ion
Fine agg rega te
50 pen +
2.5 per cent
50 pen +
5.0 per cent 50 pen EVA EVA 70 pen
Br isto l Channel - - 0.56 0.30 -- 0.30
S o u t h p o r t Beach - - 0.47 0.33 - - 0.24
W h i t e g a t e 0.60 0.36 -- 0.30
A l m i n g t o n -- 0.73 0.35 -- 0.31
A V E R A G E REDUCTION FACTOR - - 0.59 0.33 -- 0.29
70 pen +
5.0 per cent EVA
A J~
E E
1.3
1.1
0.9
0.7
0.5
0.3
0.1
-0.1
-0.3
Fig. 12
W = 1.32--1.34M (unmodified -- all work) (W = 21/M(1.34)
W = 1.125--1.04M I (unmodified -- present work only)
- . / (W = 13.3/M (1-04)
~ / WE=0-7--0.93ME "~ ~ . ~ ' ~ (5 per cent EVA modified)
" ~ W E = 5/ME(0"93))
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 i.O 1.1 .2
Log Marshall Stability (30 per cent stone content) of mixes, M (kN)
Relat ionship between wheel - t rack ing rate and Marshall S tab i l i t y fo r asphalts conta in ing unmod i f i ed and E V A mod i f i ed b i t umen
8 O . . c :
• ,-, ¢, = 6 i-- ~ u J ~ o . ~ _ ~_a~ 5
~)~< 4 o .E "' o'J co ~ 3 > c g • ~ -8~ 2
Nx 1
~ o
/ Design curves constructed at / ~ ,
- - . / / /
85 per cent confidence level / j ~ /
. J - ~ ME=0"21M1"44 -
i i i I I I I I 1 2 3 4 5 6 7 8 9 10 11 12
Marshall Stability (30 per cent stone content) of mixes containing unmodified bitumens, M (kN)
Fig. 13 Marshall Stabi l i ty curves for equivalent wheel- tracking rates for materials with modi f ied and unmodi f ied bi tumens
12
The equation derived for the unmodified asphalt is
13.3 W-M~.04 . . . . . . (1) where W=whee l tracking
rate (mm/h) and M = Marshall stability (30 per cent stone content) (kN).
and for the EVA asphalt
5 W E = M E 0'93
. . . . . . (2) where WE= wheel tracking rate of EVA asphalt (ram/h) ME = Marshall stability of EVA asphalt (30 per cent stone content) (kN).
For the case of equivalent wheel-tracking rates, W=WE, we have
13.3 5 M~.04 ME0.93
or ME = 0.35M 1'12 . . . . . . (3)
This equation is shown in Figure 13 and suggests that if the Marshall stability of a conventional mix is known, then, for the same performance in the wheel- tracking test, a much lower Marshall stability is required with a binder containing 5 per cent EVA. This finding would permit sands, currently considered unsuitable, to be used for heavily-trafficked roads when used in a mix containing EVA.
The standard deviation of the data used in the derivation of equation (3) has been used to develop the design curve in Figure 13 corresponding to the 85 per cent confidence level, which can be simplified for general use (in the range 4-12 kN for conventional materials) to the following approximation.
ME = 0.5M + 0.75 . . . . . . . . (4)
This is given in Figure 14.
The work described in this report covers only four fine aggregates and two unmodified bitumens. However earlier work by Jacobs (1981) and (1983), provides a greater range of both these variables for unmodified binders. Assuming that Marshall values for stone filled mixtures (30 per cent) are 1.3 times those for mortar mixtures (Jacobs 1983), all the reported work, together with the results of this project can be combined to form a general equation relating these two properties for conventional asphalts. The equation is
W = 21 M1.34 . . . . . . (5)
which differs to some extent from equation (1) above, and from earlier work (Jacobs 1981). The relationship in equation (5) is shown in Figure 12.
If it is assumed that the relation between wheel tracking and Marshall stability of mixes containing EVA that could have been made with the sands of Jacobs earlier work is also that obtained from the present work, then equation (5) can be combined with equation (2) to derive a relationship between
X
"6.,.
o,,,
O O
u'.C:
8 ~
~ 8
7
6
5
4
3 --
2 --
1 --
M E = 2J3M (all work) J
I I I I I I I I 3 4 5 6 7 8 9 10 11 12
Marshall Stability (30 per cent stone content) of mixes containing unmodified bitumens, M (kN)
Fig. 14 Marshal l Stabi l i t ies of modi f ied and u n m o d i f i e d materials w i th equ iva lent wheel - t rack ing rates
Marshall stabil i ty for EVA modif ied and for unmodified asphalts at equivalent tracking rates (W = WE):
21 5 M1.34 ME0.93
or ME = 0.21 M T M . . . . . . (6)
This equation is plotted in Figure 13. A similar design curve at the 85 per cent confidence level for Marshall stabil i ty values of mixes containing 5 per cent EVA- modified bitumen is also shown. For all work the approximate design equation relating Marshall stabil i ty of unmodified asphalts to that of modified- EVA asphalts for equivalent wheel-tracking rates is
ME = 2M . . . . . . . . (7)
This relationship is shown in Figure 14.
It is equally plausible to assume that the proportional shift in relations between wheel tracking and stabil i ty obtained from the present work and from all results combined (shown in Figure 12) is the same as would be obtained for these two groupings of materials with EVA added: in this case equation (3) would apply. However Figure 14 shows that at stabilities of greater than 4 kN equation (7) is more conservative and is therefore recommended for use.
The recently revised British Standard 594 (1985) (British Standards Insititution 1985) requires a minimum Marshall stabil i ty of 6 kN for roads carrying over 6000 commercial vehicles per day. From equation (7), for the same deformation resistance, an EVA asphalt would require a Marshall stabi l i ty of 4 kN. Alternatively, if the Marshall stabil ity of the EVA asphalt was 6 kN, it would correspond to using a conventional asphalt of 9 kN stabil i ty with the equivalent deformation resistance.
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T A B L E 8
Marshall stabilities required for wheel-tracking equivalence
Wheel-tracking rate
(mm/h)
5 4 3 2 1 0.5
Marshall stability required for
conventional asphalts M* (kN)
2.9 3.4 4.3 5.8 9.7
16
Marshall stability required for EVA-modified
asphalts MEt (kN)
1.9 2.3 2.9 3.9 6.5
10.7
* from W = 21 M1.34
2 [ design equation ME=~M
Table 8 sets out the Marshall stabilities of conventional materials calculated for a range of wheel-tracking rates from the general equation (5). The Marshall stabilities of the EVA-modified materials for the same wheel-tracking rates are also calculated using the design equation (7).
In Table 9 the values calculated for the Marshall stability of the asphalt made with the EVA-modified bitumens using equations (4) and (7) are recorded for a range of Marshall stabilities of conventional materials for wheel-tracking equivalence. The two equations provide similar values over a wide range of Marshall stabilities.
7 CONCLUSIONS
The addition of ethylene-vinyl acetate (EVA) co- polymer to a petroleum bitumen produces the following rheological changes:
1. A decrease in the penetration of the binder by just under one grade at the 2.5 per cent level of addition and by about one grade at the 5.0 per cent level.
2. An increase in the ring and ball softening point, with the increase being dependent on the concentration of EVA.
T A B L E 9
Prediction of Marshall stability for EVA asphalts (5 per cent EVA in bitumen)
Marshall stability (M) of unmodified
asphalt (kN)
2 3 4 5 6 7 8 9
10 12
Predicted Marshall stability for EVA asphalts (ME) (using design equations) for equivalent wheel-tracking rate
1 M E = ~M + 3/4*
(kN)
1.8 2.3 2.8 3.3 3.8 4.3 4.8 5.3 5.8 6.8
ME=2M +
(kN)
1.3 2.0 2.7 3.4 4.0 4.7 5.3 6.0 6.7 8.0
* Basis: work done in this project + Basis: * plus work by Jacobs (1981) and (1983)
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3. An increase in the elasticity of the binder at higher road temperatures while at the same time making the binder more viscous.
4. An increase in the viscosity at typical mixing and laying temperatures but not to the extent that the increase in the softening point value would imply.
When EVA-modified bitumens are used in rolled asphalt wearing course the following changes are produced:
1. Marshall stabilities are increased by about 20 per cent for the 2.5 per cent EVA level, irrespective of fine aggregate and by about 35 per cent at the 5 per cent EVA level, though the effect is less marked for the high stability sands.
2. The wheel-tracking rate is reduced by a factor of 0.6 for the 2.5 per cent level of EVA addition and by a factor of 0.3 for the bitumen containing 5 per cent EVA, with the reductions being generally independent of type of fine aggregate.
Relationships between the Marshall stability of the conventional asphalt (M) and the Marshall stability of the EVA modified asphalt (ME) with the same resistance to permanent deformation was
ME=~M for the range of Marshall stabilities normally encountered. Thus EVA-modified binders can be used to enhance the properties of fine aggregates which produce low Marshall stability rolled asphalts with conventional binders.
8 ACKNOWLEDGEMENTS
The work described in this report forms part of the research programme of the Pavement Materials and Construction Division (Division Head: G F Salt) of the Highways Group of the TRRL.
The research team included J H Denning, J Carswell, D M Colwill and Miss F Tetley.
9 REFERENCES
BRITISH STANDARDS INSTITUTION (1973). Rolled asphalt (hot process) for roads and other paved areas. British Standard BS 594 British Standards Institution, London.
BRITISH STANDARDS INSTITUTION (1985). Hot rolled asphalt for roads and other paved areas. Part 1 Specification for constituent materials and asphalt mixtures. British Standards BS 594 British Standards Institution, London.
DAINES, M E (1985). Cooling of bituminous layers and time available for their compaction. Department of Transport TRRL Report RR4: Transport and Road Research Laboratory, Crowthorne.
DENNING, J H and CARSWELL, J (1981). Improvements in rolled asphalt surfacings by the addition of organic polymers. Department of the Environment, Department of Transport, TRRL Report LR 989: Transport and Road Research Laboratory, Crowthorne.
INSTITUTE OF PETROLEUM (1984a). IP Standards for Petroleum and its Products. IP4a/84 Penetration of bituminous materials. London, Institute of Petroleum.
INSTITUTE OF PETROLEUM (1984b). IP Standards for Petroleum and its Products. IP58/84 Softening point of bitumen, ring and ball. London, Institute of Petroleum.
JACOBS, F A (1981). Hot roled asphalt: effect of binder properties on resistance to deformation. Department of the Environment, Department of Transport. TRRL Report LR 1003: Transport and Road Research Laboratory, Crowthorne.
JACOBS, F A (1983). A33 Winchester by-pass: the performance of rolled-asphalts designed by the Marshall Test. Department of the Environment, Department of Transport. TRRL Report LR 1082: Transport and Road Research Laboratory, Crowthorne.
Printed in the United Kingdom for Her Majesty's Stationery Office (2774/87) Dd8222700 12/87 C10 G426 10170
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