United States Department of Transportation
i
Field Study of Recycled Concrete Aggregate in French Drain
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2019-01-01
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[PDF-15.91 MB]
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Edition:Final Report, February 2016 – January 2019
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Abstract:A field study of recycled concrete aggregate (RCA) in French drains was conducted to evaluate in situ exfiltration drainage performance of RCA as a pipe backfill material. The project was aimed at: (i) developing field test protocols to measure the exfiltration drainage performance of the RCA French drain, (ii) long-term monitoring (12 months in this study) of the field drainage behaviors of RCA French drains, and (iii) investigation of clogging buildup in the drains over time. Four French drains were designed and constructed with different aggregate type and condition, which involve limestone, RCA ‘as is’, RCA with 2% fines, and RCA with 4% fines. Field and laboratory tests were conducted. First, the flow rate and discharge rate of French drains were monitored for 12 months to evaluate the short- and long-term performances of RCA French drains. Second, permittivity testing was conducted on the geotextile samples taken from the four French drains after 12 months of field conditioning. Third, visual inspection inside the pipes was conducted at 3, 6, 9, and 12 months. Lastly, X-ray diffraction (XRD) tests were conducted on RCA field models, which were embedded underground for 6, 12, and 18 months to identify re-cementation and calcite precipitation. The results of laboratory and field tests indicated that the drainage performance of RCA French drain is mainly controlled by soil conditions (e.g., groundwater table, permeability of surrounding soils, etc.) and the amounts of excessive fines in the drain system; however, the aggregate type is not a critical factor affecting exfiltration drainage performance. Therefore, it was concluded that RCA in French drains performs similarly to limestone and causes no significant reduction in exfiltration drainage performance.
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