Conference Agenda

<p>High-density polyethylene geomembranes (HDPE GMBs) are a crucial component of the liner system for many municipal solid waste landfills and mining applications. The GMBs should be in-situ welded to create an impermeable seal. Extrusion welds are primarily used for repairs, curves, and other welds not accessible to the fusion welding machines. In a municipal solid waste (MSW) landfill, an extrusion weld facing upward will be in contact with leachate that can lead to chemical degradation. In view of the paucity of research investigating the long-term performance of the extrusion weld in MSW applications, this paper investigates the effect of extrusion welding parameters (i.e., preheat and barrel temperature, and GMB over-grinding) on standard oxidative induction (STD-OIT) depletion rate of extrusion weld GMBs area in a synthetic MSW leachate at elevated temperature. The paper discusses the results and implications.</p>

High-density (HDPE) and linear low-density polyethylene (LLDPE) geomembranes are used in barrier systems in various containment applications. The former is known for its better chemi-cal resistance, while the latter is known for its higher stress-crack resistance (SCR). The SCR of high-density polyethylene is well defined in the literature, but the SCR of LLDPE as well as its failure mechanism are rarely addressed. This paper investigates the SCR of LLDPE ver-sus HDPE geomembranes based on the fractured plane of unaged and aged specimens exam-ined using the single-point notched constant load tensile test method. The GMBs were aged using a synthetic heap leaching solution with pH 13.5 at 85°C. Failed specimens are analyzed using optical and scanning electron microscopy, after which the differences in fracture surface for both LLDPE and HDPE resins are discussed. The relationship between SCR, tensile break elongation, and melt flow index is also presented for the geomembranes examined.

<p>White Polyethylene Geomembranes have been available in the market for two decades and have been used broadly, often in demanding and sensitive applications. The performance of these materials has exceeded the initial (circa 1990’s) exceptions dramatically and there is increasing evidence that the durability and lifespan of a white geomembrane in an exposed application is perhaps longer, not only than projections, but perhaps longer than that of traditional black colored geomembranes of comparable composition. Data and evidence from forensic evaluations as well as laboratory testing for durability is presented and new estimates on lifespan are presented.</p>

<p>The resilience of mechanically stabilized earth structures in elevated pH backfill conditions have typically been a concern due to the potential for elevated degradation due to hydrolysis. Based on limited information on the performance of polyester (PET) geogrids in backfill with pH above 9, restrictions are placed on the use of PET geogrids. A detailed multi-year investigation of the reduction in tensile strength of coated PET geogrids exposed to a pH value of 11.4 was performed. Arrhenius modeling was used to extrapolate the degradation rate of the geogrid tensile strength to 20⁰C over a 75 to 100-year design life and determine appropriate durability reduction factors for a pH range of 11.4. </p>

<p>The paper will highlight the determination of the Long-Term Design Strength of geogrid reinforcement in high pH backfill conditions. LTDS is obtained by reducing the ultimate tensile strength by applying reduction factors for creep, installation damage, and durability. Durability default reduction factors are typically based on minimum molecular weight (Mw) and maximum carboxyl end group (CEG) concentration of the high tenacity polyester fibers used in geogrid production. Mw, CEG, and pH are important variables in the rate of loss of tensile strength due to hydrolysis, or the chemical reaction of PET and water, in reverting back to acid and glycol. </p>

<p>This study also identifies the importance of product specific testing by evaluating two types of PET geogrids and the limitations of only using Mw and CEG as guidelines for determining reduction factors. The two geogrid types exhibited distinctly different tensile strength degradation. The disparity in tensile strength degradation confirms the importance of the materials and the geogrid manufacturing processes in selecting appropriate durability reduction factors for field applications.</p>

The aim of this research was to compare the performance of cotton textiles when exposed to different environmental conditions namely categories “A” to “G”, herein. The testing method complied with standard soil burial methods. The tensile strength of the cotton samples was examined after one week buried in different soil conditions, including gravel only (without compost), clay only, clay with 3, 6, and 10% compost. Also, to investigate the effect of water drainage, the clay soil with undrained condition was considered. Generally speaking the tensile strength of the samples was reduced due to biodegradation after one-week exposure. Moreover, the results highlighted the important role of water in degradation of the samples. Although the soil burial testing method prescribed by the standards was followed and the cotton samples recommended by the standard and, a good bio-degrading soil were utilized, arguably the reductions in tensile strength of the buried specimen were very low (few percent). Therefore, an exposure time much longer than that stated by the standards is required to reach more than 75% tensile strength reduction for the proposed cotton samples.

<p>The article deals with the assessment of damage accumulation in polypropylene woven geotextiles subjected to cyclic fatigue tests. To make this assessment, the test specimens were submitted to tensile tests considering two factors: the material’s tensile strength average value percentage and the number of loading and unloading cycles. For the first factor, the load percentage was considered three levels, 10, 20 and 30% of the intact material tensile strength. For the second factor, the number of cycles, four levels of request were adopted, 10, 20, 30 and 90 cycles. The study was preceded with the combination of factors, that is, with factorial planning, and for each situation, after the fatigue request, strip method tests were performed, with ten test specimens’ replicas, in order to assess retained resistance. The results obtained were compared with the result of the intact material tensile strength average value. Therefore, a set of data was generated to assess the effect of fatigue on the material and, using statistical tools, an estimate of the retained strength of the material was demonstrated, with 95% reliability, that as the load and cycles level increases the material loses its tensile strength and becomes brittle. Promising results were obtained regarding the methodology adopted for the study of the durability of geosynthetics subjected to cyclic fatigue, by laboratory simulation of field situations in which they may be subjected to loading and unloading cycles before, during or after application in certain works.</p>

<p><em>Understanding the life expectancy and performance characteristics of geosynthetic products is critical in the design of containment and storage systems. As adoption of standard testing methods does not enable assessment of the expected long term performance of products exposed to challenging exposure conditions such as those related to storage of unique solid and liquid waste by-products generated by industrial and mining sectors the implementation alternate approaches for assessment of material durability under anticipated exposure conditions is necessary.   </em></p>

<p><em>Accelerated exposure testing programmes was undertaken on samples of a number of different HDPE geomembrane products to assess the material performance of under different expected service conditions. The laboratory testing programmes included the simulation a very high pH environment, low pH environment and extreme UV exposure conditions and were used to assess the performance of a number of candidate products proposed by manufacturers for use in different applications. The outcomes of the testing indicated significant variability in expected long term durability under the different assessed conditions for the different HDPE geomembrane products. These results indicate the need for this type of testing to provide evidence to support the choice of geomembrane materials for applications involving exposure to challenging conditions.</em></p>

<p><em>The findings of the testing provided an indication of each product’s mechanical performance and chemical durability under the assessed conditions and was used to inform the geosynthetic selection process and provide an indication of expected service life under the assessed service conditions. </em></p>

<p><em>Additional ‘fingerprint’ laboratory testing was undertaken on samples of candidate geomembranes to identify the composition of antioxidant and stabiliser packages as a QA measure to help confirm geomembrane materials supplied for construction had properties consistent with the supplied candidate samples.</em></p>