Polymer modified binder (PMB) is a co-blend of polymer and bitumen that is formulated for both spray sealing and asphalt applications. PMB have been used with success at locations of high stress, such as intersections of busy streets, airports, vehicle weight stations, and racetracks. The polymers that have been used to modify bitumen in Australia include:

  • Styrene-butadiene-styrene (SBS)
  • Polybutadiene (PBD)
  • Ethylene vinyl acetate (EVA)
  • Crumb rubber (CR) 

The processes of bitumen modification involving natural and synthetic polymers were patented as early as 1843. In the 1930s, test projects using PMB were ongoing in Europe and neoprene latex began to be used in North America in the 1950s. Europe was ahead of USA in the use of PMB because the European use of contractors, who provided warranties, motivated a greater interest in decreased life cycle costs, even at higher initial costs. The history dates back in time but how is Queensland in Australia managing the technical aspects of PMB use, handling, quality amongst many other critical must know. 

In this article, Global Road Technology dives deeper into understanding the latest PMB scene in Queensland, Australia. 

PMB Technical specifications in Queensland, Australia

In Australia, the current National Asphalt Specification includes guides and specifications regarding PMB. The sole focus of our discussion borders around Technical Specification: Transport and Main Roads Specifications MRTS18 Polymer Modified Binder (including Crumb Rubber) July 2020. You must have access to the Austroads documents to understand what applies in Queensland. This Technical Specification sets out the requirements for the supply (including transport and storage) of PMB and CR modified binders for use in both sprayed sealing and asphalt applications. Polymer modified binder shall be supplied in accordance with the requirements specified in ATS 3110 Supply of Polymer Modified Binders unless those requirements are specifically amended by MRTS18. In addition, MRTS18 shall be read in conjunction with MRTS01 Introduction to Technical Specifications, MRTS50 Specific Quality System Requirements. Overall, MRTS18 forms part of the Transport and Main Roads Specifications Manual. 

Binder quality procedures in Queensland, Australia.

The Contractor shall prepare documented procedures for all required processes as defined in Clause 6 of MRTS50 and be consistent with the requirements of ATS 3110 and MRTS11 Sprayed Bituminous Treatments and the binder manufacturer’s recommendations. These procedures shall be included in the respective asphalt quality plan or construction procedure specified in MRTS30 Asphalt Pavements or MRTS11 as appropriate. For field or plant blended CR modified binders, the procedures shall address the following specific issues:

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  • the management of CR blending, digestion, and storage times and temperatures
  • the maximum time / temperature conditions that field produced / plant blended product can be stored and / or transported without loss of properties
  • circulation of the product during transportation and storage 
  • method for achieving a homogeneous product that can be sprayed to achieve a uniform application of binder across the pavement during sealing operations, free of streaking, and 
  • requirements for spraying plant and spraying practices including adjustments to nozzles (if required).

Manufacture and handling of binders

MRTS18 accepts with amendments Clause 5 Manufacture of Binders, Items 5.1 to 5.3 of ATS 3110 Supply of PMB. Polymer modified binders shall be manufactured using SBS, PBD, EVA and CR as is listed in table 5.1 of MRTS18. The handling, storage, transport, heating and transfer of PMB shall comply with the requirements and practices outlined in the latest version of the following documents: 

  • Austroads – Bituminous Materials Safety Guide, AP-G41
  • Austroads – Guide to the Selection and Use of Polymer Modified Binders and Multigrade Bitumens, AP-T235-13
  • AAPA – Guide to the Heating and Storage of Binders for Sprayed Sealing and Asphalt Manufacture, Advisory Note 7, and
  • AAPA – Guide to the Manufacture, Storage and Handling of Polymer Modified Binders, HSE Guide 5.

PMB shall not be heated to temperatures greater than the maximum values listed in the latest version of AAPA Advisory Note 7 – Guide to the Heating and Storage of Binders for Sprayed Sealing and Asphalt Manufactures and the binder manufacturer’s recommendations. The rate of increase in temperature shall not exceed 15 °C per hour. 

The good, the bad and the ugly about PMB

The good of PMB is achieved in so many ways than one. Roads with polymer modification exhibit the following characteristics:

  • greater resistance to rutting 
  • thermal cracking resistance 
  • decreased fatigue damage
  • reduced susceptibility to stripping
  • greater elastic recovery 
  • a higher softening point 
  • greater viscosity
  • greater cohesive strength 
  • increased ductility 

The bad of PMB is in the many challenges associated with its different applications. These challenges include: 

  • overheating of PMB
  • storage of PMB
  • transportation of PMB
  • need for purpose-built containers
  • risk of contamination on transfer between containers 
  • need to flush or clean with appropriate solvents 
  • removal of residue of flushing and cleaning 
  • additional sampling on any suspicion of contamination

The ugly of PMB includes extreme cases of failure in intended application owing to the following reasons:

  • foaming of PMB can render the whole batch unusable 
  • time constraints between supply and application are limiting 
  • nonconformance can lead to further tests at the projects expense 
  • there is a fine line between lab results and field performance 
  • formulation should go through anticipated extremes to meet specifications.

Conclusions

It is a long way from formulation, meeting the specification, sampling, material handling to the actual application of PMB. Across the value chain, each step is important to achieve project deliverables for either a spray seal or asphalt application. The good, the bad or the ugly must motivate the supplier, contractor, manufacturer to meet the best of quality requirements for PMB to realize the intended project goals. 

References:

Behnood, A. and Gharehveran, M.M. 2018. Morphology, Rheology and Physical Properties of Polymer-Modified Asphalt Binders. European Polymer Journal. 

Moreno-Navarro, F., Sol-Sánchez, M., and Rubio-Gámez, M.C. The effect of polymer modified binders on the long-term performance of bituminous mixtures: The influence of temperature. Materials and Design. 

Polacco et al. 2015. A review of the fundamentals of polymer-modified asphalts: Asphalt/polymer interactions and principles of compatibility. Advances in Colloid and Interface Science.

Yildirim, Y. 2007. Polymer modified asphalt binders. Construction and Building Materials.