Effect of Cold Central Plant Recycled Mixture Stockpiling on Mixture Performance

Paving roads in the traditional manner using hot mix asphalt is a very intensive process that requires a lot of energy and virgin material. Meanwhile, there are many piles of reclaimed asphalt pavement (RAP) available to use which reduces the need for virgin material. As of now, this usage is limited to about 30% by the Virginia Department of Transportation (VDOT), which is higher than most state DOTs allow. One of the methods that reuses a large quantity of RAP is cold central plant recycling (CCPR), a type of cold recycling. For this method, RAP is taken to a cold recycling asphalt plant, and after being graded and sorted is mixed with binder, water, and other aggregates to create a new mix for paving. Although this method has been around for a while, there is currently been interest by contractors to try and stockpile this mix, however, the effects of this on cold recycled asphalt are unknown. The purpose of this study was to understand the behavior of CCPR asphalt after it has been stockpiled with varying times between creating the mix and compacting specimens to the required density. For this study, the asphalt mix was processed at the plant and stored in plastic 5-gallon buckets that were lined with a large plastic bag to simulate a stockpile and keep moisture loss to a minimum. Specimens were created at varying time intervals and, after properly curing, were tested for characteristics such as indirect tensile strength and dynamic modulus. In addition to the strength characteristics of the CR mix, information about fabrication, such as moisture content and number of gyrations, was also recorded. This study found that even after 24 hours, the strength properties of the asphalt drop significantly and reach a plateau after 72 hours. If mix is stored properly, it is possible to maintain the moisture content over a long period of time however the number of gyrations required to create the specimens as well as its stiffness iv increase the longer the mix is stored. When running the dynamic modulus test to determine the overall stiffness of the specimen, this study found that the material became stiffer as time went on for three days after which it remained constant. However, plugging in the values for the dynamic modulus into a mechanistic empirical program, PavementME, suggested that this loss of stiffness has little effect on pavement performance.