Measurements of Moisture Conditions of Cold In-place Recycling Layer

Cold In-place Recycling (CIR) is one of the most common rehabilitation techniques applied in Iowa. Currently, the CIR layer should be dried below a moisture content of 1.5% before an overlay is applied. However, it does not only require a contractor to make frequent measurements of the moisture content using a nuclear gauge but also it is difficult to achieve such a low moisture content, particularly in a rainy summer in Iowa. To address this curing issue in a more systematic way, the moisture contents and temperatures of both CIR with foamed asphalt (CIR-foam) and CIR with emulsified asphalt (CIR-emulsion) layers were monitored. Moisture contents were measured by embedding capacitance moisture sensors at both midpoint and bottom of the CIR layer. These measurements were then compared against moisture contents measured using a nuclear gauge. The modulus and stiffness were measured using a falling weight deflectometer (FWD) and a geo-gauge, respectively. Based on the field data obtained from the embedded moisture sensors and a weather station, a moisture prediction model was developed as a function of the initial moisture content, CIR layer temperature and humidity. By utilizing the developed moisture prediction model, a contractor can predict an optimal timing for the placement of the wearing surface without continually measuring moisture contents of the CIR layer using a nuclear gauge. It was discovered that the stiffness of CIR layer measured by the geo-gauge continued to increase as the curing time increased in spite of an increase in moisture content due to a rainfall. This interesting finding may lead to a new practice that, to determine the optimum timing of an overlay, the stiffness of CIR layer should be measured rather than the moisture content. The use of moisture prediction model and/or geo-gauge will not only save money by not having to continually measure moisture measurements using a nuclear gauge but also will allow more use of CIR by public agencies.