Field Performance of Drainage Systems in Highways with RCA Base Course 

Recycled Concrete Aggregate (RCA) is a highly desirable yet underused construction and demolition (C&D) reclaimed waste material within the U.S. and other parts of this planet to replace the use of crushed natural rock. One of the highest demanding construction market for use of RCA is roadway construction. However, current federal and state regulations prohibit or impose extreme restrictions on the use of RCA adjacent to any geotextile fabric used in subdrain systems. These restrictions are due to existing concerns about the potential for leaching high levels of calcareous constituents and precipitate formation of such constituents (known as calcareous tufa or simply tufa) in or around various parts of a subdrain system specifically the geotextile. The excessive deposition of such formations may lead to the clogging of the geotextile fabric and reduce the drainage capacity and consequently the service life of the subdrainage. A subdrainage system mainly consists of a perforated pipe in a trench filled with granular free-draining aggregate and wrapped around by non-woven geotextile fabric (French drains). The subdrain is a vital part of a geo-infrastructure and its proper performance has a direct impact on the serviceability of the infrastructure. Any reduction in drainage capacity or service life of the subdrain can lead to loss of serviceability of the entire infrastructure.

A comprehensive experimental and theoretical study has been was conducted previously in the SGI laboratories at George Mason University focusing on the different clogging phenomena, governing mechanisms, the potential of the occurrence and the loss of serviceability of the geotextile as a result of the use of RCA as unbound base course/subbase layer. The two major phenomena investigated in this research were the chemical clogging, as a result of chemical precipitation reactions and deposition of RCA tufa within the fibers of the geotextile, and the physical clogging, as a result of fine particles movement and entrapment within geotextile fiber structure under seepage forces. New analytical and mechanical models are suggested based on the results of experimental tests to enable engineers to understand the extension of occurrence of geotextile clogging and estimate the loss of serviceability of such systems due to the occurrence of both phenomena.

The laboratory scale findings and proposed analytical models are needed to be confirmed in a field scale study prior to the implementation of any policy for or against the use of RCA in infrastructure construction. This field research study is planned to evaluate the validity of the RCA behavior observed in the laboratory and confirm that the developed models are also true under the field conditions. Other objectives of this study are to develop a threshold percentage for the blending of RCA with virgin aggregate and to provide recommendations for VDOT to generate specifications to allow the use of RCA/virgin aggregate blends as an unbound aggregate when geotextile is present in the drainage system. The monitoring program includes monitoring a variety of the chemical characteristics of the leachate as well as the changes in the overall performance of the side French drains in a long time period. The study of the changes in the pore structure of the geotextiles with time will enable the researcher to answer the questions and concerns about RCA tufa problem.



Our speciall thanks to Hallaton team for their inkind material donation and technical support for GMU team during construction of this project. 

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