Hydraulic and Mechanical Properties of Recycled Materials

Construction and maintenance of roads requires large volume of aggregates for use as base and subbase materials. Because of the cost of virgin aggregates, federal and state agencies are encouraging the recycling of waste materials including materials in old pavements. This study assessed the suitability of four recycled materials relative to virgin aggregates for use as base and subbase materials. The four recycled materials were the reclaimed asphalt pavement (RAP), fly ash (FA), reclaimed concrete material (RCM), and foundry sand (FS). Assessment of these materials was done in terms of their hydraulic, mechanical, and leaching properties when mixed in with various proportions of virgin aggregates. Except for slightly higher fine content in some RAP-aggregate mixtures, particle size distribution of all mixtures was within the Mn/DOT specification band for Class 5 materials. Water retention (pore size distribution), hydraulic conductivity, resilient modulus, and shear strength measurements were generally similar to that of 100% aggregates. Exception was the mixtures of FS. Heavy metal concentrations in the leachate were also generally less than the EPA drinking water standards. We concluded that FA, RAP, and RCM mixtures will be good substitutes of virgin aggregates as base and subbase materials.Minnesota Department of Transportatio