Mix Design

The Asphalt Institute has recommended a modified Marshall mix type procedure for the design of CIPR mixes.(13) Such a design initially involves obtaining samples of the candidate pavement to determine the gradation of the aggregate, the asphalt content, and the penetration and viscosity of the asphalt binder. Marshall specimens are prepared at various emulsion percentages, as initially determined by calculating the asphalt demand on the basis of aggregate gradation and deducting the percentage of asphalt in the RAP.(16) The optimum asphalt content can be determined by a stability and air voids analysis, with target air voids in the 8 to 10 percent range, or the specimens may be evaluated using indirect tensile strength or resilient modulus testing.(17)

It has recently been shown that the addition of virgin aggregates (20 to 25 percent) in the CIPR process results in less voids and, consequently, less flushing, and improved stability.(14) The amount of recycling agent (either new asphalt or modifying oil) also has a significant effect on the behavior of the mix, with the ideal range of recycling agent being somewhere between 2 and 3 percent by weight of dry RAP.(18)

Structural Design

CIPR is generally considered for rehabilitation of pavements showing distress to depths about 100 to 150 mm (4 to 6 in). It can handle a pavement section in poorer condition and with more cracking than HIPR, provided that the pavement section (when recycled) is structurally sound and adequately drained.

The AASHTO Design Guide (15) is recommended for the thickness design of cold in-place recycled asphalt mixes. Since there is essentially little or no difference in the composition and structural properties of recycled cold mix and cold in-place recycled paving materials, the range of structural layer coefficients recommended for recycled cold mixes (0.25 to 0.35) are also applicable for cold in-place recycled mixes. CIPR mixes are not recommended for use as a wearing surface.