Vacuum Sealing–Based Volumetric Density Measurement Approach for Cold In-Place Recycling

Recent economic limitations have fostered increased use of pavement rehabilitation methods such as cold in-place recycling (CIR). CIR could be more appealing to departments of transportation provided variability were lower and performance were more predictable. Because of the nature of the materials and construction processes, CIR is likely to be more variable than plant-mixed asphalt, and it is believed that the performance variability of CIR can be reduced through enhanced density control. The many density control methods described in the literature for CIR are often vague. This study used ASTM D6857 vacuum sealing to obtain the maximum theoretical specific gravity (G_mm) of reclaimed asphalt pavement (RAP) and a gravity-proportioning equation to estimate CIR G_mm (specific gravity after cement, emulsion, or a combination is mixed with RAP). Vacuum sealing was also used to obtain the bulk specific gravity (G_mb) of compacted CIR (AASHTO T 331). In all, 240 G_mm and 156 G_mb tests were conducted. D6857 and AASHTO T 209 detect differences between RAP and hot-mix asphalt G_mm, but the differences led to manageable errors for CIR density control that should still allow for some improvements over many current practices. The equation developed in the study estimated CIR G_mm with reasonable error, and T 331 suitably characterized CIR G_mb at the often high air void levels that were observed. The findings show that CIR G_mm and G_mb, as determined by vacuum sealing and the gravity-proportioning equation, constitute a reliable, convenient, and implementable approach to controlling density and likely reducing performance variability.