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EU-LIFE+ Environment Policy and GovernanceLIFE 09 ENV/GR/304ROADTIRE
Integration of end-of-life tires in the life cycle of roadconstructionROADTIRE
Deliverable 4.4.1
Report on laboratory results of rubberizedasphalt mixtures made by the dry process
ByAthanasios Kalofotias, DATSE
Sofia Mavridou and Nikolaos Oikonomou, LBM
December 2011
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TABLE OF CONTENTS
1. INTRODUCTION......3
2. DRY PROCESS-GENERAL... .3
3. PRODUCTION OF ASPHALT MIXTURES......4
4. EXAMINATION OF PROPERTIES OF BITUMINOUS MIXTURES AND
EXPERIMENTAL RESULTS ...12
5. EXAMINATION OF THE MICROSTRUCTURE OF MODIFIED WITH TIRE RUBBER
BITUMINOUS MIXTURES...17
6. CONCLUSIONS...19
ACKNOWLEDGEMENTS.20
REFERENCES.20
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1. INTRODUCTION
This report is dealing with experimental results on asphalt mixtures produced by the dry process. In
the frame of LIFE+ project with Acronym ROADTIRE (Integration of end-of-life tires in the life
cycle of road construction) conventional and rubberised asphalt mixtures containing with various
percentages of tire rubber have been produced and examined as far as their basic characteristics are
concerned. Production of mixtures and examination of their properties have been conducted
according to Greek and European Standards, and according to similar activities on conventional
asphalt mixtures (with no tire rubber), while laboratory test results are presented in details below.
2. DRY PROCESS-GENERAL
Rubberized asphalt mixtures, produced by the dry process, include the addition of tire rubber
particles as substitutes for the natural aggregates of similar gradation. This technique permits the
utilization of a solid waste material that is produced worldwide annually in very large amounts.
According to former experience, tire rubber can modify the rheological properties of the bituminous
binder-wet process-, leading this way to mixtures, which are characterized by increased elasticity,
improved bonding between binder and aggregates, increased fatigue life and resistance to rutting as
well as reduced thermal and reflecting cracking of the mixtures [1-8]. However, by the use of the
dry method, mixtures perform inferior characteristics compared to the ones of the wet method. This
is attributed to the poor interaction between tire rubber particles and the bitumen, which resulted in
lower resistance to moisture, the detachment of the aggregates and the reduction in the bearing
capacity of the pavement [9]. Moreover, dry process, compared to the wet process has been far less
popular method because of the increased costs of having to use special graded aggregate to
incorporate the reclaimed tire rubber in addition to constructions difficulties and of course due to
higher cost compared to the one of natural aggregates. However, this method has the potential to
consume larger quantities of rubber from worn mobile tires while it is environmentally beneficial
compared to the wet process since it consumes less energy-there is no need for increased mixing
time, higher mixing temperatures and as a result less negative environmental effects during
production procedure. Furthermore, inclusion of tire rubber particles is much easier, since tire
rubber is added simply with the natural aggregates. In this process, the interaction between rubber
particles and bitumen starts as soon as aggregates are mixed with bitumen, so there is no time for
chemical interactions and modification of the binder.
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In the frame of the ROADTIRE project, tire rubber of max size 1mm has been added to asphalt
mixtures at percentages up to 3% w/t substituting natural aggregates and especially sand, whose
gradation is similar to the one of tire rubber particles.
3. PRODUCTION OF ASPHALT MIXTURES
The Marshall mix design procedure as specified by EN12697-34:2004 [10] was used in this study.
The produced mixtures consisted of conventional bitumen, tire rubber particles in the form of
powder (of gradation 0-2mm) supplied by Karabas S.A. [11] and natural aggregates of limestone
origin from a quarry near the city of Lamia Kaltsas Techniki S.A-. Properties of the mixtures were
tested in compliance withGreek standards A265-A[12] which are in force for conventional
bituminous mixtures and for surface bituminous layer. All mixtures were produced at the
Laboratory of the Department of Materials Control and Public Works Quality of Sterea Ellada in
cooperation with Laboratory of Building Materials of the Department of Civil Engineering of
Aristotle University of Thessaloniki. Tests on properties of raw materials (aggregates and tire
rubber) took also place at the above laboratories. Gradation curve of natural aggregates mix used is
showed in Figure 1 and main characteristics on Table 1. Aggregate mix design was 60% sand (size
0-4mm), 10% aggregates of size 4-12mm and 30% aggregates of size 12-25mm. Rubber, which
acted as substitution for part of the natural aggregates at percentages up to 3% had the gradation as
given in Figure 2.
0
20
40
60
80
100
120
1''3/4''3/8''No4No10No40No80No200
Sieves (mm )
Cummulat
ivepassing(%)
Lower limit Upper limit Mixture
Figure 1. Indicative gradation curve of aggregates used for the production of bituminous mixtures
with conventional bitumen (limits of-A265[12]).
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0
20
40
60
80
100
0,01 0,1 1 10
Siev es (mm)
Cummulativepassing(%)
Tire rubber
Figure 2. Gradation curve of rubber added to binder.
Moreover, basic properties of natural aggregates are given in Table 1.
Table 1. Main characteristics of aggregates used for the production of asphalt mixtures as well as
relevant test Specifications [13-24]
Specification
EN Property Particle size Value1367-2 Magnesium sulfate test Coarse (4-12mm) 3%
1097-2 Resistance to fragmentation (LA) Coarse (10-14mm) 20%
1097-1 MICRODEVAL Coarse (10-14mm) 12%
1367-5 Thermal shock (VLA) Coarse (10-14mm) 3%
933-8 Sand equivalent (SE) Sand (0- 4mm) 75
933-9 Methylene Blue (MBE) Sand (0- 4mm) 0,9
1097-8 PSV Coarse (4-12mm) 59
AAV Coarse (12-25mm) 8,2
933-04 Shape index Coarse (12-25mm) 10%
933-04 Shape index Coarse (4-12mm) 11% 933-03 Flakiness index Coarse (12-25mm) 14%
Flakiness index Coarse (4-12mm) 13%
1744-1:98 Loss on ignition Sand (0- 4mm) 42%
1744-1:98 Total sulfur content Sand (0- 4mm) 0,0015%
1744-1:98 Acid soluble sulfates Sand (0- 4mm) 0,001
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Bituminous binder was a typical 50/70 while its rheological characteristics are showed in table 2.
Table 2. Rheological characteristics of bituminous binder 50/70[25]
Rheological
characteristic Value
Penetration at 25oC, pen 55
Softening point, oC 46
Ductility at 25oC, cm 110
Viscosity at ~1000cps, oC 123
Elastic recovery, % 10
All specimens tested have been produced in the Laboratory of the Department of Materials Testing
and Control of Quality of Public Works of Sterea Ellada in cooperation with Laboratory of Building
Materials. Production of all samples has been conducted according to European Standards as well
as according to similar of conventional ones. The same procedure has been followed in order to be
able to examine the effect of tire rubbers inclusion into the mixes, keeping the rest of the
parameters constant.
Two series of compositions have been produced and examined in the laboratory.
The first one was a conventional mixture produced by asphalt binder 50/70 with no tirerubber.
The second one included the use of asphalt binder 50/70, containing tire rubber as fineaggregate at percentages up to 3%, which means 0,5-1-1,5-2-2,5 and 3% w/t of the total
mix.
As far as production is concerned, aggregates (including tire rubber) prior to mixing with asphalt
binder have been heated for 4 hours into an oven at temperature equals to ~160
o
C, which is theheating temperature for the binder before mixing.
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Photo 1 a,-d. Production stages of rubberized asphalt mixtures
All specimens have been compacted by 75 blows per face with the standard Marshall hammer
(photos 2 a-e).
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Photo 2 a-f. Compaction procedure of samples and samples ready for testing
Specimens were stored for 24 hours prior to testing, while the procedure for the tests of Marshall
characteristics is the following:
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Photo 3a,b. Testing for Marshall Deformation and stability
According to Marshall Procedure (based on EN12697-34:2004), deformation and stability have
been measured for all of the mixtures.
Moreover, rutting resistance has been examined through the use of the appropriate equipment, as
showed in photo 5a,b according to -5-03-11-04[26] based on EN12697:22-2003[27] after
the production of samples of specific dimensions photo 4a-e. Specimens used had dimensions of
40x30x5cm. European Standard used for this test describes test method for determining thesusceptibility of bituminous materials to deform under load. The Wheel tracking test is applicable to
mixtures with upper sieve size less than or equal to 32 mm. The tests are applicable to specimens
that have either been manufactured in a laboratory or cut from a pavement; test specimens are held
in a mould with their surface flush with the upper edge of the mould. The susceptibility of
bituminous materials to deform is assessed by the rut formed by repeated passes of a loaded wheel
at constant temperature (45oC).
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Photo 4a-e. Production of samples for rutting test
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Photo 5 a,b. Testing for rutting resistance
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4. EXAMINATION OF PROPERTIES OF ASPHALT MIXTURES AND EXPERIMENTAL
RESULTS
Experimental test results for the two series are showed in tables below.
Table 2. Marshall Characteristics of series with no rubber (conventional one)
Characteristics
Binders content
Limit according to
-265 A (standard)-
Heavy traffic
4,5 5 5,5 5-7,5
Compaction (No of hits) 75 75 75
Marshall stability at 60oC (lbs) 2900 2625 2504 1500
Deformation at 0,01'' 10,4 11,5 14,2 10-16
Specific gravity (kg/m3) 2362 2375 2390 NA
Voids on aggregates (%) 16 16,4 16,2 15
Voids on bituminous mixture (%) 5,8 5,1 3,7 3-5
Mixture -BIT-0 is the conventional mixture with no addition of tire rubber. As noted, increase on
binders content leads to decrease on Marshall stability, increase on deformation, increase on
specific gravity and voids on aggregates, while there is a decrease on voids on bituminous mixture.
Optimum percentage of binder was found to be around 5%w/t.
Results of the series with the addition of asphalt binder 50/70, containing tire rubber asfine aggregates at percentages up to 3%, which means 0,5-1-1,5-2-2,5 and 3% w/t of the
total mix.
Table 3a. Marshall Characteristics of series with tire rubber at percentage of 0,5% w/t of the total
mix
Characteristics
Binders content (%)
Limit according to
-265 A (standard)-
Heavy traffic
4,5 5 5,5 5-7,5
Compaction (No of hits) 75 75 75Marshall stability at 60
oC (lbs) 2810 2450 2412 1500
Deformation at 0,01'' 11,5 12,7 14,8 10-16
Specific gravity (kg/m3) 2355 2374 2388 NA
Voids on aggregates (%) 16,9 16,3 16,2 15
Voids on bituminous mixture (%) 5,7 5,0 3,7 3-5
Mixture -BIT-0,5 is the one, containing 0,5% of tire rubber as part of the sand. As noted, increase
on binders content leads to decrease on Marshall stability, increase on deformation, increase on
specific gravity and decrease on voids on aggregates, while there is a decrease on voids onbituminous mixture. Optimum percentage of binder was found to be around 5.25%w/t.
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Table 3b. Marshall Characteristics of series with tire rubber at percentage of 1% w/t of the total
mix
CharacteristicsBinders content (%)
Limit according to
-265 A (standard)-
Heavy traffic4,5 5 5,5 5-7,5
Compaction (No of hits) 75 75 75
Marshall stability at 60oC (lbs) 2760 2418 2374 1500
Deformation at 0,01'' 12,7 13,5 15,3 10-16
Specific gravity (kg/m3) 2347 2372 2387 NA
Voids on aggregates (%) 16,8 16,3 16,2 15
Voids on bituminous mixture (%) 6,7 5,1 3,8 3-5
Mixture -BIT-1 is the one, containing1% of tire rubber as part of the sand. As noted, increase on
binders content leads to a decrease on Marshall stability, increase on deformation, increase on
specific gravity and decrease on voids on aggregates, while there is a decrease on voids on
bituminous mixture. Optimum percentage of binder was found to be around 5.25%w/t.
Table 3c. Marshall Characteristics of series with tire rubber at percentage of 1,5% w/t of the total
mix
CharacteristicsBinders content (%)
Limit according to
-265 A (standard)-
Heavy traffic4,5 5 5,5 5-7,5
Compaction (No of hits) 75 75 75
Marshall stability at 60oC (lbs) 2630 2367 2244 1500
Deformation at 0,01'' 13,2 13,7 15,8 10-16
Specific gravity (kg/m3) 2340 2370 2386 NA
Voids on aggregates (%) 17,5 16,4 16,2 15
Voids on bituminous mixture
(%) 6,3 5,4 4 3-5
Mixture -BIT-1,5 is the one, containing1,5% of tire rubber as part of the sand. As noted, increase on
binders content leads to a decrease on Marshall stability, increase on deformation, increase on
specific gravity and decrease on voids on aggregates, while there is a decrease on voids on
bituminous mixture. Optimum percentage of binder was found to be around 5.3%w/t.
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Table 3d. Marshall Characteristics of series with tire rubber at percentage of 2% w/t of the total
mix
CharacteristicsBinders content (%)
Limit according to
-265 A (standard)-
Heavy traffic4,5 5 5,5 5-7,5
Compaction (No of hits) 75 75 75
Marshall stability at 60oC (lbs) 2580 2233 2163 1500
Deformation at 0,01'' 14 14 16,5 10-16
Specific gravity (kg/m3) 2332 2370 2385 NA
Voids on aggregates (%) 17,3 16,4 16,3 15
Voids on bituminous mixture (%) 7,3 5,7 4,2 3-5
Mixture -BIT-2 is the one, containing 2% of tire rubber as part of the sand. As noted, increase on
binders content leads to a decrease on Marshall stability, increase on deformation, increase on
specific gravity and decrease on voids on aggregates, while there is a decrease on voids on
bituminous mixture. Optimum percentage of binder was found to be around 5.35%w/t.
Table 3e. Marshall Characteristics of series with tire rubber at percentage of 2,5% w/t of the total
mix
Characteristics
Binders content (%)
Limit according to
-265 A (standard)-
Heavy traffic
4,5 5 5,5 5-7,5Compaction (No of hits) 75 75 75
Marshall stability at 60oC (lbs) 2465 2116 1976 1500
Deformation at 0,01'' 14,7 15,3 17,5 10-16
Specific gravity (kg/m3) 2286 2305 2314 NA
Voids on aggregates (%) 19,4 18,7 18,8 15
Voids on bituminous mixture (%) 8,5 7,7 6,7 3-5
Mixture -BIT-2,5 is the one, containing 2,5% of tire rubber as part of the sand. As noted, increase
on binders content leads to a noticeable decrease on Marshall stability, increase on deformation-
even outside the limits set by Greek specifications for binders content 5,5%-, increase on specific
gravity and decrease on voids on aggregates, while there is a decrease on voids on bituminous
mixture. As far as voids on bituminous mixture are concerned, all values were found to be outside
the limits set by Greek specifications.
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Table 3f. Marshall Characteristics of series with tire rubber at percentage of 3% w/t of the total
mix
Characteristics
Binders content (%)
Limit according to
-265 A (standard)-Heavytraffic
4,5 5 5,5 5-7,5
Compaction (No of hits) 75 75 75
Marshall stability at 60oC (lbs) 2320 2010 1860 1500
Deformation at 0,01'' 15,5 16 18,4 10-16
Specific gravity (kg/m3) 2216 2257 2274 NA
Voids on aggregates (%) 21,8 20,4 20,2 15
Voids on bituminous mixture
(%) 11,3 9,7 8,3 3-5
Mixture -BIT-3 is the one, containing 3% of tire rubber as part of the sand. As noted, increase on
binders content leads to a noticeable decrease on Marshall stability, increase on deformation-even
outside the limits set by Greek specifications for binders content 5-5,5%-, increase on specific
gravity and decrease on voids on aggregates, while there is a decrease on voids on bituminous
mixture. As far as voids on bituminous mixture are concerned, all values were found to be outside
the limits set by Greek specifications.
Rutting resistance
Results of laboratory experiments concerning rutting resistance through measurement of rut depth
and rate of rutting are showed in diagram 3 for the conventional and the rubberized mixtures.
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0
1
2
3
0 500 1000 1500 2000 2500 3000 3500
Cycles (No)
Rutdepth(mm)
BIT0 BIT-0,5 BIT-1,0 BIT-1,5 BIT-2,0 BIT-2,5 BIT-3,0
Diagram 3. Rut depth of samples of the series one and two (conventional-BIT0- and with the
addition of tire rubber particles)
0
1
2
3
0 500 1000 1500 2000 2500 3000 3500
Cycles (No)
Rateofrutting(mm/h)
BIT0 BIT-0,5 BIT-1,0 BIT-1,5 BIT-2,0 BIT-2,5 BIT-3,0
Diagram 4. Rate ofrutting of samples of the series one and two (conventional-BIT0- and with the
addition of tire rubber particles)
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Photo 7. Tire rubber particles
Photo 8. Conventional bituminous mixture
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As far as microstructure of the bituminous mixture is concerned, it was found to be very solid
and concrete, while aggregates (natural and tire rubber) seemed to very well cooperate with the
bituminous binder despite the fact that tire rubber particless presence was difficult to be easily
specified due to its low percentage of use and its very fine gradation.
Photo 9. Modified with tire rubber bituminous mixture
6. CONCLUSIONS
Present report includes laboratory test results of rubberised asphalt mixtures produced by the dry
process containing various percentages of tire rubber from worn mobile tires.
Marshall Characteristics as well as rutting resistance has been studied for all of the mixtures.
General comments on the results of the research are presented below: The first series included
composition -BIT-0, which is the conventional mixture with no addition of tire rubber. Increase onbinders content leads to decrease on Marshall stability, increase on deformation, increase on
specific gravity and voids on aggregates, while there is a decrease on voids in bituminous mixture.
The second series included use of tire rubber as substitutes for the fines-natural sand- at percentages
0-3% and especially 0,5%-1%-1,5%-2%-2,5%-3%w/t of the total mix.Laboratory results showed
that, for the majority of compositions, increase on binders content leads to decrease on Marshall
stability, increase on deformation, increase on specific gravity and relative decrease on voids on
aggregates and on voids in bituminous mixture. The amount of tire rubber added, was found to be a
determining factor of the mixs resistance to rutting, since higher amounts of tire rubber improved
their response to plastic deformation. In particular, according to Marshall characteristics,
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substitution of fines by tire rubber at percentage of up to 2% w/t of the total mix is possible, leading
to mixtures with satisfactory characteristics and values inside the limits set by Greek Specifications
265. Higher percentages lead to mixtures with extremely high void content, which is far
outside limits of specifications. As far as rutting resistance is concerned addition of tire rubber
leads to a relative decrease of rut depth showing an improved performance compared to the
conventional one. This means that addition of tire rubber increase resistance to rutting. However, all
compositions behave worse than the ones produced by the wet method and which are presented in
details in deliverable 4.2.1 [28].
So, taking into account all laboratory results, it can be concluded that production of asphalt
mixtures by the dry process behave relatively well for the whole of the properties examined for
percentages of added tire rubber up to 2%w/t of the total mix. However, results are inferior to the
ones of the mixtures produced by the wet method, so for the pilot application, which took place in
the city of Lamia, second method has been suggested.
ACKNOWLEDGMENTS
This reports authors would like to thank the personnel of the Department of Materials Control and
Quality of Public Works of Sterea Ellada and especially: Mr Christos Tsimbouris, Mr Dimitrios
Tsoros and Mr Dimitrios Rizopoulos, Chemical Engineer, Electronical Engineer and Technician
respectively. Moreover, special thanks to the personnel of the Laboratory of Building Materials of
the Department of Civil Engineering of Aristotle University of Thessaloniki and especially Mrs
Stefanidou Maria, Ass. Professor.
Finally, this research has been realized with the contribution of the LIFE financial instrument of the
European Union.
REFERENCES
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2. http://www.rubberpavements.org3. Goulias D.G. and A.H. Ali, 1998, Asphalt Rubber Mixture Behavior and Design-Wet
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Testing Materials, W4est Conshohocken, PA.
4.
Goulias D.G. and A.H. Ali, 1997, Use of Tire Rubber in Hot Mix Asphalt :Binder andMixture Evaluation, Journal of Solid Waste Technology and Management, Vol 24, no. 24,
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5. Goulias D.G and A. Ntekim, 2001, Durability of Asphalt Mixtures with Recycled TireRubber, The Journal of Solid Waste Technology and Management, Vol 27 No 3&4, pp.170-
174, Philadelphia, PA.
6. Heitzman M.A., 1992, State of the Practice- Design and Construction of Asphalt PavingMaterials with Crumb Rubber Modifier, FHWA ReportSA-92-022, Washington D.C.
7. Fernandes Jr.J.L., Bertollo S.A.M, Bernucci L.L.B, E. de Moura, 2002, Laboratoryevaluation of dense asphalt mixtures modified with addition of rubber, 3
rdInternational
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8. Mavridou S, 2010. Utilization of recycled tire rubber in mortars and concrete based oncement or asphalt for special applications, PhD Thesis, Department of Civil Engineering,
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9. F. Moreno, M.C. Rubio, M.J. Martinez-Echevarria, 2012, The mechanical performance ofdry-process crumb rubber modified hot bituminous mixes: The influence of digestion time
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10.EN12697-34:2004: Bituminous mixtures-Tests methods for hot mix asphalt-Part 34:Marshall test.
11.Karabas S.A, European Hellenic Recycling; http://www.karabas.gr/gr_index.html12.265-, Bituminous concrete, Greek Specifications, 196613.EN 933-01:1997 entitled: Tests for geometrical properties of aggregates Part 1.
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14.EN 933-03:1997 entitled: Tests for geometrical properties of aggregates Part 3:Determination of particle shape Flakiness index.
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16.EN 933-08:1999 entitled: Tests for geometrical properties of aggregates - Part 8:Assessment of fines Sand equivalent test.
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18.EN 1097-02:1998 entitled: Tests for mechanical and physical properties of aggregates - Part2: Methods for the determination of resistance to fragmentation, through the Los Angeles
method.
19.EN 1367-02:1998 entitled:Tests for thermal and weathering properties of aggregates, Part2: Magnesium sulfate test.
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20.EN 1367-05:2002 entitled: Tests for thermal and weathering properties of aggregates Part5: Determination of resistance to thermal shock.
21.EN 1097-03: 1998 entitled: Tests for mechanical and physical properties of aggregates - Part3: Determination of loose bulk density and voids.
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24.EN 1744-01:1998 entitled: Tests for chemical properties of aggregates -Part 1: Chemicalanalysis.
25.A. Kalofotias, S. Mavridou, E. Aloupis and Nikolaos Oikonomou, Deliverable 4.2.1:Report on rheological characteristics of rubberised asphalt binder, July 2011, EU-LIFE+
Environment Policy and Governance LIFE 09 ENV/GR/304ROADTIRE, Integration of
end-of-life tires in the life cycle of road construction ROADTIRE.
26. 05-03-11-04, Bituminous layers of closed type, Edition 1, May 2006 (GreekSpecifications).
27.EN 12697-22:2003 Bituminous Mixtures-Tests methods for hot mix asphalt-Part 22:Wheel tracking.
28.A. Kalofotias, S. Mavridou and Nikolaos Oikonomou, Deliverable 4.3.1: Report onlaboratory results of rubberized asphalt mixtures made by the wet process, December
2011, EU-LIFE+ Environment Policy and Governance LIFE 09
ENV/GR/304ROADTIRE, Integration of end-of-life tires in the life cycle of road
construction ROADTIRE.