This grant provides funding for the development of Sensor-Enabled Geosynthetics (SEG) as a new generation of geosynthetics with embedded sensing capabilities that will allow their mechanical strain to be measured without the need for conventional instrumentation such as strain gauges and extensometers. The focus of the study is on polyvinyl chloride (PVC)-coated, polyethylene terephthalate (PET) yarn geogrids which are commonly used in soil reinforcement applications. Carbon black (CB) will be used as the primary type of conductive filler material. An advantage of this geogrid material is that only the coating will contain the CB content that is required for strain-sensing capability. This will help ensure that the underlying mechanical properties of the geogrid will not be affected, since the inner PET yarns are the load-bearing component of the geogrid. The primary objective of this proof-of-concept study is to solve the chemical and materials aspects of developing SEG specimens to attain reliable, accurate and reproducible strain-conductivity properties.
Upon successful proof-of-concept, and future verifications involving large-scale in-soil testing in the lab and in the field, this study will result in a novel approach to measuring mechanical strain in geosynthetics with important advantages over existing technology. These advantages include: 1) ability to measure reinforcement strains at greater number of locations within the structure, 2) a less complex and costly data acquisition system, 3) reduction/elimination of mechanical interference of the sensors at the locations of measuring strains, and 4) measuring larger strains than what is currently possible using strain gauges. Through these advantages, the SEG technology will facilitate health monitoring of geosynthetic-reinforced soil structures using smart materials leading to a better understanding of their field response and improved design methodologies with respect to their safety and economy. Consequently, it will help engineers prevent costly failures and repairs of infrastructure involving geosynthetics resulting in significant savings in both private and public sectors. The study will also provide a better understanding of the piezoresistivity of conductive-filled polymers at very low strains; a region that is of practical significance in multi-disciplinary applications including civil and chemical engineering.
Geosynthetics, as construction materials, have become an indispensable part of infrastructure development and renewal due to their proven advantages in construction speed, cost, durability and a wide range of design possibilities. Geosynthetic engineering and the related manufacturing and construction industries have experienced tremendous growth over the past few decades and are now an established technology involving several billions of dollars annually in material production and construction projects worldwide. At the same time, as geosynthetic-related structures and facilities become more widespread, it becomes more important to ensure that these structures are not only safe but also offer a satisfactory level of serviceability. Health monitoring of structures is especially important where they support crucial infrastructure in urban areas and along transportation corridors, or protect the environment from hazardous waste, fuel or other contaminants. However, in spite of significant advancements in manufacturing and testing of geosynthetics and analysis and design of related structures, an important aspect of their sustainable development; i.e. their instrumentation and health monitoring, has received comparatively little attention with costly consequences. A significant impediment has been the fact that installation of instruments that are at the forefront of monitoring technology (e.g. strain gauges and extensometers) is typically costly and tedious with a rather unreliable outcome. Technical Merit of the Study: The primary objective of this study was to establish the proof-of-concept of sensor-enabled geosynthetics (SEG) as a new generation of geosynthetics with embedded sensing capabilities by developing conducting carbon black (CB) networks in their polymer formulation in order to measure their mechanical strain without the need for conventional (and often costly) instrumentation. This objective was achieved by studying the tensoresistivity property (i.e. tensile strain-conductivity response) of polymer composites that were filled with electrically conducting particles. Specific goals of the study along its broad objective were to determine the influences of the polymer type, filler type and properties, blending technique and loading régime on the tensoresistivity and mechanical properties of the composite samples. This information was necessary to resolve the chemical and materials issues related to the fabrication of conductive-filled SEG materials and determine promising formulations of the filled composites and procedures to fabricate SEG samples. One main objective in this proof-of-concept study was to develop reproducible, strain-sensitive and accurate SEG samples in the laboratory using a method similar to the actual industrial manufacturing process. The study has resulted in a better understanding of the influences of the above factors on the electrical and mechanical performance of SEG specimens based on extensive laboratory testing and preliminary numerical simulation of filled polymers. Broader Impact: This study is the first of its kind in geotechnical engineering and specifically in the field of geosynthetics. At the same time, it adds to the body of knowledge in the areas related to smart materials and sensors in other disciplines. As a result, the study offers a new direction and exciting opportunities in the field of geosynthetics with significant scientific and technological impacts in the broader field of engineering. This proof-of-concept study resulted in several peer-reviewed publications including an invited paper (all co-authored by students involving in the research), a Middlebrooks award by the American Society of Civil Engineers (ASCE), a U.S. patent and a pending international patent, significant graduate and undergraduate participation with award-winning presentations in specialty conferences (seven students, five of which were female), establishment of a SEG laboratory at the University of Oklahoma (OU), and interdisciplinary collaboration within OU (CEES, CBME and AME Schools within the college of engineering, and the Office of Technology Development) and with the industry (TenCate geosynthetics). Development of SEG technology will offer an effective and economical health monitoring technique using smart materials for various infrastructure facilities that involve geosynthetics. A sample of numerous benefits include: improving the safety of these structures by incorporating a monitoring and warning system in their design; expediting their construction and/or making necessary adjustments in the construction process using real-time response data; and, preventing costly serviceability problems, failures and repairs yielding significant savings in both private and public sectors. Another very important aspect of the proposed research is training of civil engineering students in the field of geosynthetics and polymers as construction materials. Currently, in spite of tremendous advancements in the science and technology of geosynthetics, their footprint in the civil engineering curriculum and continuing education (and hence, their exposure to students and practicing engineers) has been fairly limited. The multidisciplinary aspect of this research has offered (and will continue to offer) unique educational benefits for the recruitment and retention of talented students at OU and other universities through REU and OU outreach programs. It has enabled the PIs to continue their successful history of providing research experience for underrepresented students. Further details and outcomes of the study can be found in the peer-reviewed publications listed in the final report of the study.
