Polymer Modified Binders (PMBs) are special binders contained additives designed to make asphalt more workable during application, and (once laid) more resistance to deformation, fatigue or cracking.
Recent advances in materials technology have increased the range of PMBs, each designed to suit a particular application. PMBs are used mostly within surface course, but there is much to be gained from using them in base layers. PMBs may consume more resources at the outset but can often hope a road to exceed its expected design life, requiring less maintenance over the longer term.
Advantages of Polymer Modified Asphalt
- High elasticity and higher softening point make Polymer Modified Asphalt lesser prone to both cracking and rutting.
- The resilience modulus of PMA is higher than HMA (e.g., PMA's resilient modulus value has been found as 793Mpa as compared to 677Mpa for HMA at 40 celsius).
- The softening point of bitumen is increased significantly. For example, Performance Grade (PG) 64-22 bitumen can be increased to PG 85-22.
- Elastomeric properties are also improved significantly, and overall polymer modification just makes a tougher binder.
- PMBs are most effective for wearing course. Stress absorbing membrane of 2-3mm of PMB over distressed surface helps arrest reflective cracking. Final overlay with PMBs based mix can help in rehabilitation of distressed wearing course and extend life in an otherwise structurally sound pavement.
- Micro surfacing is done by using PMBs for maintenance purpose. It prolongs the life of distressed pavement by delaying the reflection of cracks on the overlay surface.
Limitations/Constraints of Polymer Modified Asphalt
- The inadequate investigation in selecting the correct type of PMBs can lead to asphalt not performing in line with the expectations.
- PMBs are not necessarily a panacea for producing high performance asphalt materials; there is as much variation across different PMBs in terms of ageing characteristics etc. The research shows that performance of some of the PMBs was worse than the standard bitumen.
- The performance graded bitumen containing polymer modifiers is susceptible to separation of the modifier. So, the proper circulation or agitation in storage needs to be ensured.
- PMBs require high temperature to allow for proper pumping and coating of the aggregates. Temperature of up to 177 C may be used with the supplier recommendations.
- The contribution of PMBs towards riding quality is negligible.
- In hot climatic conditions, the pavement temperature at 10-20 mm below surface can reach up to 60C, the binder should be specified at least PG 76-10 in accordance with SPI, Asphalt Institute USA. If DSR (Dynamic Shear Rheometer) testing facility is not available, the supplier can be asked as manufacturer’s certificate to submit the test result of the binder before and after modification.
- It is essential to have a transparent and clear system for certification and quality control of new materials.
- The performance of PMBs needs to be carefully examined before making it a standard practice. The evaluation needs to address previous experiences, environmental impacts, cost/benefit analysis etc.
- When the PMBs are transported in bulk tankers or in drums, the bulk transfer must have good heating and circulation systems and shall have good functional insulation that can maintain the same temperature.
- Overall higher elasticity and softening point make Polymer Modified Asphalt suitable for roads in hot climatic condition. The said qualities will provide better resistance to rutting and cracking and they will be suitable in the local conditions with high temperature in summer.
- PMBs suppliers’ instructions with regard to the recommended application and storage should be carefully followed.
Design Manager @ Meinhardt Group | Project Management Professional (PMP)
2 年Very informative read. The sentence in recommendations where it is mentioned temperatures below 20mm of pavement surface can reach upto 600...seems incomplete and possibly a typo.