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Product Properties, Classification, Selection and Application T Distin Colas South Africa.

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Presentation on theme: "Product Properties, Classification, Selection and Application T Distin Colas South Africa."— Presentation transcript:

1 Product Properties, Classification, Selection and Application T Distin Colas South Africa

2 Product Properties Section 3

3 Product Properties Major properties influencing performance: –Cohesion –Adhesion –Rheology –Elasticity –Stiffness –Ageing –Compatibility/storage stability

4 Product Properties cont… Modified products should be assessed as a whole –full asphalt mix design to ascertain desired properties achieved Thermo-mechanical history will have major effect on behaviour in terms of: –blending technique –blending temperature –high shear pumping –storage temperature

5 Cohesion A measure of the tensile stress to break the molecular bond A binder with high cohesion requires high tensile stress to cause failures Binders with low cohesion break easily Cohesive properties if measured by empirical tests (eg penetration or R&B) are significantly changed by modification with thermoplastic polymers

6 Cohesion cont… Increase in polymer gives large increases in softening point but small increases in penetration Standard ductility not appropriate for modified binders Force-ductility gives a better indication of cohesive strength Cohesive properties influence how: –soon a surface seal is opened to traffic –its ability to withstand traffic shear stresses

7 Typical Force-ductility relationship Elongation Force Elastic phase Toughness

8 Adhesion Measure of the stress required to break the binder aggregate bond “Wetting” of aggregate is controlled by the binder’s viscosity properties Adhesion influenced by presence of water (during construction and in-service) It is more difficult to achieve good adhesion with hydrophilic aggregates Hot modified binders –develop increased cohesive strength at the expense of increased adhesion –are less able to “wet” and adhere to the aggregate

9 Influence on cohesion/adhesion properties Force Cohesion Adhesion Mode of failure % Modifier

10 Adhesion cont… Failure mode in seals using highly modified binders more likely to be adhesion (especially during cold weather) Higher binder thickness improves bond Aggregate needs to be clean and dry Time between binder and aggregate application kept to a minimum Pre-coated aggregates helps adhesion Use of cutters to help early adhesion not recommended Addition of commercial adhesion agents may be considered in high risk areas

11 Adhesion testing No test available showing clear performance-based relationship Modified Vialit test (MB-7) recommended to predict adhesion of binder to the aggregate Pull-out test (MB-8) and Pliers test (MB- 9) are useful early indicators of adhesion

12 Rheology (flow behaviour) At high temperatures and/or long loading times, binders behave as viscous liquids resulting in large permanent deformation At low temperatures and/or short loading times, binders behave as elastic (brittle) solids, with recovery of deformation Rheology of conventional binders is easy to predict with simple tests (Penetration, R&B and Viscosity) Rheology of modified binders highly complex

13 Influence of Softening Point and Viscosity on modifier content Viscosity EVA SBS SBR Polymer content (%) Softening point SBR EVA SBS

14 Rheology cont… Softening Point of modified binders decreases during storage over time Long haul distances or delays may require a small increase in modifier Addition of polymer results in lower moduli at low temperatures giving rise to more flexibility At high temperatures binder shows improved stiffness

15 Rheology tests Dynamic Shear Rheometer –Behaviour of binder over a range of loading and temperature conditions –Typical design parameters are Dynamic Stiffness (G*) and Phase Angle (δ) –Phase angle measures relative elastic and plastic properties –Not included as a mandatory test –Recommended for special or high risk applications

16 Elasticity Indicates binder recovery to its initial shape when a load is removed Used to measure – fatigue resistance in a binder – its ability to absorb large stresses without cracking Elastic property influenced by type and degree of modification –SBS has high elastic recovery –SBR relatively lower elastic recovery –EVA no elastic recovery but high stiffness Torsional Recovery (method MB-5) has been introduced as a quality control tool

17 Torsional Recovery relationship % POLYMER CONTENT TORSIONAL RECOVERY

18 Stiffness Property indicates the strain under particular stress conditions Stiffness modulus is a function of load: –size –time –temperature Direct correlation between stiffness of the binder and permanent deformation under repetitive loading in asphalt layer Binders with higher stiffness should be used in asphalt layers exposed to high stress conditions

19 Ageing Measurement of gradual changes in engineering properties over time caused by: –heat –oxidation –UV radiation –loss of volatiles Modified binders are generally more resistant to ageing Binders and polymers degrade if not stored correctly

20 Ageing Most significant ageing of binders occurs during asphalt mixing in the drum Binders continue to age in service Ageing characteristics determined by the modified RTFOT (MB-3) Pressure Ageing Vessel test models ageing but no requirement in current guideline

21 Compatibility/Storage Stability Definition of compatibility –Where the bitumen and polymer consist of a single phase with no separation during storage without agitation –Where the bitumen and polymer can be combined into a two-phased product behaving essentially as a single-phased product Solubility of the polymer in bitumen dependant on two main parameters: –Difference in solubility of the polymer and the maltene phase of the bitumen –Amount and type of asphaltenes in the bitumen

22 Compatibility/Storage Stability cont… Storage stability test recommended for assessment of stability/suitability of modified products Test should not be seen as a performance indicator Manufacturer should supply method statement on circulation and storage techniques

23 Modified Binder Classification Section 4

24 Generic classification of modified binders Modified Binders Non-homogenousHomogenous Bitumen-rubber Crumb rubber Plastomer EVA Elastomer SBRSBS

25 Classification System Classified according to: Applications in which they perform surfacing seals asphalts crack sealants Modifier group use in the binder elastomer type polymer plastomer type polymer crumbed rubber Product properties Numerical – higher number indicates improved product performance properties

26 Letter coding S - surfacing seal (hot applied) SC - surfacing seal (cold applied) A - hotmix asphalt C - crack seal (hot applied) CC - crack seal (cold applied) E - elastomer type polymer (SBR, SBS) P - plastomer type polymer (EVA) R - crumbed rubber

27 Classification for Surface Seals Modified Binder Class (S) Application S - E1Surface Seal - Hot applied S - E2Surface Seal - Hot applied S - R1Surface Seal – Bitumen rubber SC - E1Surface Seal - cold applied (emulsion) SC - E2Surface Seal - cold applied (emulsion)

28 Classification for HMA Modified Binder Class (A) Application A - E1Hotmix asphalt - Fatigue A - E2Hotmix asphalt - Fatigue / Deformation A - P1Hotmix asphalt - Deformation A - R1Hotmix asphalt - Bitumen rubber

29 Classification for Crack Sealing Modified Binder Class (C) Application C - E1Crack Sealant - Hot applied CC - E1Crack sealant - Cold applied C - R1Crack Sealant - Hot applied

30 Selection and Application Criteria Section 5

31 Environmental Influences - Seals Climatic conditions more restrictive for application of hot modified binders Aggregate loss due to rain soon after application is a real risk due to poor aggregate “wetting” Addition of cutter may solve the problem in the short term but this may cause future bleeding problems –expert advice needed Cutters should not be considered for high stress applications

32 Minimum Road Surface Temperatures for Surface Sealing Binder ClassMinimum Road Surface Temp. (°C) S - E1; S - E225 SC - E1; SC - E 210 S - R125

33 Environmental Influences - HMA Rapid increase in viscosity due to cooling could cause compaction problems Mainly in cold weather and when constructing thin layers Rolling must commence and be completed as soon as possible after application

34 High Stress Surface Seals Durability of seals determined by: –residual binder properties –associated film thickness Highly stressed area is one of following: –>30 000 elv per lane per day (TRH 3:1998 classification) –Curve radii < 50m –Steep gradients >5% Moderately stressed area is one of following: –10 000 to 30 000 elv per lane per day –Curve radii < 100m –Gradients < 5%

35 Selection Criteria for Surface Seals Modified Binder Class Condition S-E1S-E2SC- E1 SC- E2 S-R1 Active cracks Passive cracks Moderately stressed areas Highly stressed areas Surface temp at application (>10 deg C) Very high road surface temperatures

36 Stress Absorbing Membranes SAMIs applied to absorb strains that could result in reflection cracks Selection criteria same as previous Table for active cracks Local experience with bitumen- rubber seals More information in TRH 3

37 Hotmix Asphalt Binder Class Condition A-E1A-E2A-P1A-R1 High deformation resistance on stiff base High deformation resistance on flexible base High fatigue resistance on flexible base Moderate fatigue resistance and moderate deformation resistance Reflective cracking High stress areas Open graded mixes with high film thickness Low road surface temperatures

38 Crack Sealing Active cracks indicate deep structural deficiencies Generate high vertical and horizontal movements Performance of crack sealant dependant on its stiffness at the minimum pavement temperatures Widening narrow cracks reduces stresses on sealant Sabita Manual 20 gives more details of best practice for crack sealing

39 Crack Sealing properties Specific binder properties for range of environmental conditions: Adequate adhesion Low flow values at high temperatures (60ºC) Low moduli at low temperatures (-10ºC) Sufficient elasticity to accommodate crack movements without cracking

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