Abstract Manager

The performance of an asphalt pavement structure is depicted by several limiting values of observed or expected distresses including cracking, rutting and moisture related stripping. The most desirable options to improve the stripping resistance of asphalt concrete (AC) mixes are the provision of good quality aggregates, reduced air voids and improved pavement drainage. However, challenges exist to economically source or process aggregates that will ensure good resistant to stripping. An anti-stripping agent is added to asphalt mixtures to improve the adhesion between the asphalt binder and aggregates and thereby, preventing undesirable extent of moisture-induced premature to AC layer and ensuring sustainability of pavement structures.

Manitoba has been using several types of liquid anti-strip (LAS) chemical agents to address the stripping issues, mostly for aggregates in south-western area of the province. The province requires a minimum wet to dry tensile strength ratio (TSR) of 70% for acceptance of AC mixes. However, some pits have aggregates for which the available LAS agents do not provide the desired TSR. In addition, the specified minimum TSR may not ensure adequate long-term resistance to stripping because the specified TSR does not target any minimum indirect tensile (IDT) strength, specifically in wet condition. The objective of this study was to benchmark aggregates from different areas of the province in terms of TSR and wet IDT strength; recommend the desired minimum thresholds of TSR and wet IDT strength for acceptance; thresholds of TSR and wet IDT strength for which a LAS agent or hydrated lime should be used; thresholds of TSR and/or IDT strength values for which the use of hydrated lime should be considered mandatory, and recommend the process of adding the hydrated lime for producing sustainable AC mixes. 

Based on the preliminary assessment of test data, a minimum TSR of 70% and wet IDT strength of 350 kPa seem to be acceptable targets to ensure adequate anti-stripping performance of AC mixes in Manitoba. A suitable LAS agent and/or hydrated lime may be used if any of the above stated criteria are not met for any aggregate combination. However, hydrated lime may be mandated if the TSR falls below 60% and/or the wet IDT strength falls below 300 kPa. The paper will present the details of historical test data, their assessment, basis for the specified thresholds and recommendation, and the future plan for sharing knowledge with interested participants.