The D35.04 Subcommittee on Geosynthetic Clay Liners has a reputation of being open and direct in discussions regarding GCL technology, dedication to develop high quality pertinent GCL standards, and aggressive re-evaluation of the performance of GCL products and their standards. Such was the scope and approach of the presenters and attendees at ASTM’s 2nd Symposium on Geosynthetic Clay Liners. The topics of the symposium were broken down into the following categories:
– Assessment of Clay Component,
– Durability of Clay Component,
– Evaluation of Current and Proposed GCL Standards,
– Movement of Compounds through the GCL, and
– GCL Specifications.
The presenters and attendees received a formal welcome by the President of IGS, Danielle Cazzuffi; Chairman of D 35, David Suits; and Symposium Co-Chairs Kent von Maubeuge and Bob Mackey.
After formal inductions were complete, Charles Landis, Bentonite Performance Materials, presented an excellent paper over the use of isotopes for clay identification. As natural sodium bentonite stockpiles decrease and activated sodium bentonite finds more acceptance in the GCL marketplace, this identification technique may become a valuable tool to assess the Na+/Ca2+ content in the montmorillonite and expected performance of various activated sodium bentonites. Kent von Maubeuge discussed the need of the free swell, fluid loss and water absorption test to determine whether a bentonite will meet its indicated low permeability value. He then presented test results comparing the performance of natural bentonite and activated bentonite using glass cylinders to measure the velocity of liquid movement which might be a quicker quality control method to determine the bentonite permeability. Jim Olsta presented new information to the old argument over which test method “swell index” or “fluid loss” is a better indicator for the hydraulic conductivity of the GCL. Jim’s assessment of variables to each test was highly enlightening.
Under the discussion of clay durability, Randal Osicki presented results from his Master’s Thesis in which a Fann viscometer and filter press testing can be used to assess bentonite compatibility when subjected to various salt solutions. Bob Mackey presented the test results for GCL samples taken from landfill closure caps located in coastal regions of Florida, USA. One landfill had cover soil with a high concentration of shells (CaCO3). The test results for each landfill showed a dramatic decrease in the swell index values. However, only the landfill with a high concentration of calcium in the cover soil showed a significant increase in the GCL’s hydraulic conductivity. There was some variability in the hydraulic conductivity results between testing laboratories, indicating that the increase in hydraulic conductivity might not be as significant as the worst case results. One source of the variability could be the storage of the GCL samples under unconfined conditions prior to testing. Additional research was recommended to investigate the source of the variability and to verify the conclusions of the paper.
Richard Erickson presented a paper noting that the ASTM standard practice for GCL manufacturing quality control (ASTM D5889) and guide for construction quality assurance (ASTM D6495) have, for the most part, achieved their goal of normalizing specification standards for GCL materials, as specified by design engineers. Scott Lucas presented recommended changes in the GCL Peel Test (ASTM D6496) to allow the easier use of this standard during the manufacturing quality control process. Patrick Fox presented an excellent, wide ranging paper regarding GCL shear strength testing (ASTM D6243). Fox listed critical testing criteria and recommended improvements to this extremely important GCL test. Scott Lucas presented another paper reviewing the variability of the GCL index flux test (ASTM D5887) and how the results can be affected.
Kerry Rowe presented a paper in which the behavior of a GCL subjected to thermal gradients in basal liner application was investigated. The research indicated that no adverse effect on the GCL was noticed due to thermal gradients for the set design conditions. Toshifumi Mukunoki presented a paper on the effect of freeze-thaw on the permeation of diesel fuel through a GCL. Although subjected to numerous freeze-thaw cycles, Mr. Mukunoki concluded that the GCL performed well as a hydraulic barrier in the short to medium term, with additional research ongoing to assess long-term performance.
The permeation of gas/vapors through the GCLs and/or composite liners has become a new topic of interest in the USA and in CEN. Bernard Myles gave a short presentation on the test method being developed by CEN to measure gas permeation, included the proposed test apparatus and procedure. Mr. Mukunoki also gave a short presentation detailing the apparatus used in his research. Symposium Co-Chairman Bob Mackey noted that gas permeation of GCLs is going to be a new area of testing that will be mandated by international standards bodies and possibly in the near future by regulators.
The symposium concluded with a presentation by Sam Allen, representing the Geosynthetic Institute (GSI), detailing the current status of the GCL specification being developed by GSI. Mr. Allen’s presentation noted the current issues to be resolved in finalizing the specification. There was no indication when the GCL specification would be complete and available to the GCL marketplace.
The presenters and attendees had a full day of discussions, with many new and interesting issues to ponder upon. The pace of the symposium left little time for anyone to relax, with provocative questions consistently raised regarding the state of GCL technology. It was a long day and well spent.
