Cracking performance of asphalt mixtures containing taconite tailings using traditional and multiple freeze-thaw moisture conditioning methods.

Abstract

Crushed aggregate resources for use in infrastructural applications are depleting and use of alternative resources is necessary to meet the demand. With annual consumption of approximately 1.2 billion tons of aggregates in the United States, significant environmental impact is caused. Annually, more than 125 million tons of fine grained crushed siliceous material is generated through iron ore mining in Northern Minnesota. This material is typically referred to as “taconite tailings” and usually ends up as landfills near mining operations. Research is being conducted on the potential usage of taconite tailings in asphalt mixtures to improve sustainability of highways. This study is focused on the key pavement failure mechanism of moisture damage, typically evident in the form of pot-holes during winter and spring seasons. The mechanical performance of asphalt concrete rapidly deteriorates in presence of moisture and is significantly accelerated through incur of freeze-thaw cycles. Currently there are no standardized tests which condition asphalt mixtures through multiple freeze-thaw cycling. Therefore, this study explored a method for subjecting specimens to multiple freeze-thaw cycles using temperatures which better represent actual climatic conditions. A field conditioning method was also employed by placing samples outside over a period of winter and spring months. These proposed conditioning methods were compared with a conventional conditioning process used for AASHTO T-283 procedure. The evaluation of moisture damage in asphalt mixtures containing taconite tailings was conducted using the conventional AASHTO T-283 test procedure and a fracture energy based approach. Testing results indicate that mix containing taconite tailings has acceptable moisture damage resistance after multiple freeze-thaw and field conditioning, which more accurately represents typical climatic conditions. The mechanical behavior of field and multiple freeze-thaw conditioned samples was quite different as compared to those conditioned in lab using the traditional AASHTO procedure.