Evaluation of Type C Fly Ash in Cold In-Place Recycling

Abstract

The Kansas Department of Transportation has developed an innovative method of rehabilitating low-volume pavements using cold in-place recycling (CIR) and Type C fly ash. Previous field test sections have indicated that fly ash improves constructability and moisture sensitivity. However, the same field test sections have exhibited increased cracking with increased fly ash content and a drop in pavement modulus with time. A laboratory study was undertaken to evaluate the effect of fly ash content on CIR. Reclaimed asphalt pavement (RAP) was mixed with 3, 7, 11, and 15 percent Type C fly ash and the fatigue life, durability, freeze-thaw resistance, and thermal cracking potential of laboratory-compacted samples were evaluated. RAP mixed with asphalt emulsion and asphalt emulsion with hydrated lime were evaluated as well. The results indicated that 7 to 11 percent Type C fly ash provided optimal laboratory freeze-thaw and moisture sensitivity performance. Increasing the fly ash content resulted in a brittle fatigue behavior as well as an increased thermal fracture temperature. AASHTO T283 is recommended for selecting the optimum fly ash content.

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