Advantages of Polymer Modified Asphalt

Polymer Modified Asphalt (PMA) contains 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 PMAs, each designed to suit a particular application. PMAs are used mostly within surface course, but there is much to be gained from using them in base layers. PMAs 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 (PMA) lesser prone to both cracking and rutting.
• The resilience modulus of PMA is higher than Hot Mix Asphalt (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.
• PMAs are most effective for wearing course. Stress absorbing membrane of 2-3mm of PMA over distressed surface helps arrest reflective cracking. Final overlay with PMAs 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 PMAs 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 PMAs can lead to asphalt not performing in line with the expectations.
• PMAs are not necessarily a panacea for producing high performance asphalt materials; there is as much variation across different PMAs 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.
• PMAs require high temperature to allow for proper pumping and coating of the aggregates. Temperature of up to 177C may be used with the supplier recommendations.
• The contribution of PMAs towards riding quality is negligible.

Recommendations

• 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 PMAs 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 PMAs 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 PMA 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.
• PMAs suppliers’ instructions with regard to the recommended application and storage should be carefully followed.