Antioxidant depletion from five geomembranes of same resin but of different thicknesses immersed in leachate

The effect of thickness on the antioxidants depletion time for five high density polyethylene geomembranes (with nominal thicknesses of 0.5, 1.0, 1.5, 2.0, and 2.4 mm) immersed in synthetic leachate at six different temperatures (25, 40, 55, 70, 85 and 95 °C) is investigated. The geomembranes were manufactured from the same geomembrane resin (i.e., polymer resin, antioxidant/stabilizer package, and carbon-black batch). Four (1.0, 1.5, 2.0, and 2.4 mm) of the five geomembranes were manufactured during the same production run by changing the pulling speed of the geomembrane from the extrusion die. The depletion of antioxidants/stabilizers inferred from both standard (Std-) and high pressure (HP-) oxidative induction times (OIT)s show that increasing geomembrane thickness resulted in longer depletion times for temperatures above 40 °C but little to negligible difference in projected depletion times below 40 °C for this antioxidant package. The increase in depletion times was not proportional to the square of the geomembrane thickness as theoretically predicted if depletion was diffusion controlled and the diffusion coefficient was the same for each GMB. Thus, the depletion of antioxidants is not fully governed by diffusion and/or the GMB's diffusion coefficients are different. Regardless of the GMB thickness, the time for Std-OIT depletion was shorter than the time to residual HP-OIT above 70 °C but was longer at or below 55 °C. For example, for 2.4 mm GMB, the inferred time for Std-OIT depletion was 0.2–0.3 (at 85 °C), 2–3.5 (at 55 °C) and 9.5 (at 40 °C) times that for the HP-OIT to deplete to residual. The projected Std-OIT depletion times for 1.0 and 2.4 mm GMBs were: 2.7 and 4 years, respectively, at 60 °C; 23 and 26 years, respectively, at 40 °C; and about 330 years at 20 °C.     

Effect of high temperatures on antioxidant depletion from different HDPE geomembranes

The effect of elevated temperatures, typically 95–115 °C, on antioxidant depletion from a high-density polyethylene (HDPE) geomembrane (GMB) incubated in air, water and synthetic leachate is examined. It is shown that the antioxidant depletion in synthetic leachate at 95–115 °C is consistent with what would be expected from Arrhenius modeling based on data from lower temperatures (25–85 °C). A similar finding is reached for incubation in air. However, when incubated in water the antioxidant depletion is more complicated. At temperatures above 100 °C a four-parameter exponential model was needed to fit oxidative induction time data that exhibited quite different early-time and later-time depletion rates. The early-time depletion rate decreases with an increase of the temperature while the later-time depletion rates follow the more typical pattern of increasing with increasing temperature. Three additional HDPE GMBs with different antioxidant packages are examined at elevated temperatures in air. The GMB with the lowest initial standard (Std) oxidative induction time (OIT) and without hindered amine light stabilizer (HALS) has the longest antioxidant depletion stage based on Std-OIT at these elevated temperatures. GMBs stabilized with HALS showed only a slight change in their high pressure OIT during the current study. It is shown also that degradation in physical properties can start at Std-OIT values above the residual OIT values.     

Manufacturer''s perspective on liners

Presented in this paper is a brief historical perspective of the origins of polymeric liners and the growth of the industry to the present. The orientation is on the seams themselves and on the appropriate seaming method with respect to the particular liner type. Emphasis is placed on the proper seaming material and/or proper combination of temperature, pressure and dwell time to create a good seam. Focus is placed on workmanship, seaming conditions and the related aspects of construction quality control (CQC) and construction quality assurance (CQA).     

Interaction of antioxidants with carbon black in polyethylene using oxidative induction time methods

Carbon black (CB) is added to the geosynthetics for ultraviolet protection. However, CB can interact with antioxidant (AO) in the geosynthetics, and their interaction has been documented to be synergistic and/or antagonistic towards the oxidation reaction. In this paper, two oxidative induction time (OIT) methods, a standard (Std) OIT test and a high pressure (HP) OIT test, were used to evaluate the interaction of CB with two types of antioxidants during the oven aging. Test samples made from high density polyethylene (HDPE) blended with different amounts of Irganox^®1010 (I-1010) and Irgafos^®168 (I-168) together with 0 or 2.5wt.% of carbon black were studied. The sample were incubated in a forced air oven at 85 °C to accelerate the oxidation reactions. After 1000 days, Std-OIT values of samples with 500 ppm and 1000 ppm I-1010 exhibited only 10% drop from their initial values from 19.42 min and 34.01 min to 17.53 and 31.0 min respectively. In comparison, a continuous decrease of Std-OIT value was observed for samples contained both I-1010 and I-168; a 40% drop was measured after 1000 days, corresponding to 16.4 and 26.8 min reduction. For samples contained 2.5% CB and I-1010, an exponentially decrease of Std-OIT and HP-OIT with aging time was obtained. However, adding I-168 to those samples did not change the OIT decreasing trends, indicating that the interaction of CB with I-168 is negligible. The test data further verify that the effectiveness of the OIT test is strongly correlated to the functional temperature range of the AO. The Std-OIT test with testing temperature of 200 °C can detect both I-1010 and I-168, while the 150 °C testing temperature of the HP-OIT test can only detect the I-1010.     

Degradation behaviour of HDPE geomembranes with high and low initial high-pressure oxidative induction time

The degradation of three high density polyethylene geomembranes (GMBs) (denoted xA, xB and xC) when immersed in simulated landfill leachate at 85 °C is examined. All three GMBs met the requirements of the generic industry specification GRI-GM13 with respect to their performance properties. The large high-pressure oxidative induction time (HP-OIT) (i.e., 790 min for xB and 960 min for xC) combined with the relatively high level of trace nitrogen detected, suggest the presence of hindered amine light stabilizers (HALS) as part of the antioxidant package in these GMBs, whereas, the relatively low initial HP-OITs (i.e., 260 min) and the low level of trace nitrogen for xA, suggest the absence of HALS in xA. Although xA had the lowest initial standard Std-OIT (Std-OIT was 115, 158 and 175 min for xA, xB and xC, respectively) it exhibited the longest time to antioxidant depletion based on Std-OIT. For the three GMBs, the HP-OIT depleted following exponential decay model until reaching a residual value. xB had the slowest HP-OIT depletion (0.016 month⁻¹) and was still depleting without reaching a residual value at the end of this study (after 46 months). xA experienced the fastest HP-OIT depletion (∼62 times faster than of xB) and reached a residual value of 78 min. For xC, HP-OIT depleted 40 times faster than for xB reaching a residual value (∼610 min) that was still higher than the HP-OIT of 400 min specified by GRI-GM13 for a new GMB. xB had the longest time to nominal failure despite having the lowest initial SCR value (330 h for xB compared to 910 and 800 h for xA and xC, respectively) and not having the highest OITs values. Although xC had a residual HP-OIT of 610 min, the SCR, melt index (MI) and tensile properties for xC had decreased to the point that xC was at nominal failure, indicating that the degradation can take place without the total depletion of antioxidants/stabilizers captured by the HP-OIT.     

Geomembrane factory and field thermally welded seams comparison

This technical paper presents a unique comparison of geomembrane factory and field welded thermal seams for a large off-stream water reservoir project. The results of the comparison show that factory welded seams exhibit higher seam peel and shear strengths at yield, less variability, and more consistency than field welded thermal seams. In particular, the results show that factory seams are about 10% stronger than field seams in shear and about 9% stronger in peel strength at yield. More importantly, this resulted in 100% of the factory welded seams passing the project seam strength requirements even though the factory welding speed was 1.1–1.6 times faster than the field welding speed. Conversely, about 25% of the field welded seams did not pass the initial specified field seam shear strength requirement, which caused significant delays, scheduling, and other construction issues. As a result, the field seam shear strength requirement was reduced from 9.6 kN/m to 8.2 kN/m to increase the number of field seams that achieved project requirements. Because the geomembrane was primarily factory fabricated, there were about 78% less field seams on this project than if the geomembrane was entirely field fabricated.     

Technical note on hot air seaming of high-density polyethylene geomembranes

Hot air fusion welding is widely used as a secondary seaming method for welding high-density polyethylene (HDPE) geomembranes, although seldom as a primary seaming method. This method is based on a very simple principle and can withstand comparison with the other main seaming methods. However, the strength and long-term durability of seams made with this method are still poorly known, and should be explored, as compared to the other welding methods.     

Geonet seams

In most geonet applications, seaming of geonets is not considered to be critical because the primary function is that of drainage rather than reinforcement (as with geotextiles or geogrids) or use as a barrier (as with geomembranes). However, when geonets must be joined, and the method of joining interferes with the drainage function, seaming becomes important. To date, geonet seaming has evolved from the empirical judgement gained in the field. This paper attempts to examine this limited experience and quantify the effects of seaming on flow capacity of disjointed geonet seams. Several different and new methods of joining geonets are also evaluated based on the strength of the unseamed geonet. Finally, the influence of confining pressure on geonet and geonet seam strength is evaluated.     

Durability of chlorosulfonated polyethylene geomembrane seams after accelerated aging tests

Accelerated aging tests have been conducted on seam specimens prepared by the different methods used to seam chlorosulfonated polyethylene (CSPE) geomembrane. These included factory seams prepared by dielectric seaming, by hot air and with a bodied solvent as well as a field seam made with a bodied solvent. Accelerated aging tests were conducted in hot air at 100°C and in a 63°C Xenon Arc Weather-O-Meter. Shear strengths of seams increased significantly during the early aging exposures, as the CSPE cured, and they remained at the higher level for the duration of the tests. This was true for both potable and industrial CSPE grades.     

Destructive testing of polyethylene geomembrane seams: Various methods to evaluate seam strength

The incidence of high-density polyethylene geomembrane liner failures makes it essential that as much information as possible regarding seam performance be extracted from testing. The durability of polyethylene geomembrane seams can be determined largely by the data resulting from conventional seam peel and shear destructive tests.

Unfortunately, current test parameters and acceptance criteria are not used to a great enough extent. Specifically, the seam peel and shear tests can and should be used more fully to assess the effect of seaming on the strength and durability of the seam and the adjacent geomembrane. Specific minimum values for seam shear strength and elongation as well as peel separation should be established by a project's geosynthetic design engineer. In addition, functional seam test acceptance criteria for very low-density polyethylene need to be defined. Another type of testing that can provide valuable information on the aging behavior and defect distribution within field seams is hydrostatic, biaxial burst testing.     

Extrusion flatwelding

Extrusion flatwelding of HDPE geomembranes is a fully automated and field proven technology for the seaming of HDPE geomembrane sheets. This paper describes and illustrates the mechanics and details of the process and of its several variations. These variations are (a) motor driven bottom flatwelder, (b) winch driven slope welder, (c) universal bottom and slope combination welder and (d) Extru-Wedge® welder systems.     

自升式海洋起重平台齿条板对接工艺

ZPMC自升式海洋起重平台为非自航自升式起重平台,配有4根桩腿。桩腿采用齿条板连接形式,结构新颖,施工难度大。由于桩腿齿条板受钢板长度的影响需对接,但因材质结构强度高、板材厚等,经过反复对接试验及对方案的分析研究后,最终确定利用螺栓胎架工具对接齿条板,取消了常规齿条板对接缝处焊接卡板问题,既保证了对接缝焊接质量,又减少焊缝约束产生裂纹的可能性及去除卡板的清理工作,经济效益显著。     

TPO防水卷材接缝剥离强度影响研究

通过试验系统地研究了焊接参数特别是温度和速度对TPO自粘复合防水卷材中TPO层接缝剥离强度的影响,并确定了TPO的焊接窗口.结果表明,在较大范围的焊接温度和速度下,TPO的接缝剥离强度从9.10 N/mm变化到11.88N/mm,符合相关标准规范的要求.根据试验数据确定的焊接窗口较宽,表明TPO可焊性良好,焊接操作较易.     

Temperature and pressure effects on the degradation of polypropylene tape yarns—depletion of antioxidants

Polypropylene (PP) tape yarns with a specific antioxidant package consisting of hindered amine light stabilizers were used to evaluate the effects of high oxygen pressures on the depletion of antioxidants. In order to emphasize the pressure effects, relatively low temperatures at 35, 45, 55 and 65 °C were utilized for the incubation. The high-pressure environments were created using air or oxygen at levels of 0.02, 1.3, 2.8, 4.9 and 6.3 MPa. The depletion of antioxidants was effectively monitored using the high pressure oxidative induction (HP-OIT) test, whereas the oxidation of the polymer was evaluated using tensile and melt index tests. The test data indicate that the depletion of antioxidants was governed by the oxygen partial pressure, not the total pressure of the gas. The oxidation of the polymer did not start until the HP-OIT value dropped below 10% of the original when the antioxidant was essentially depleted.

The reaction rate of antioxidant depletion increased with temperature according to the Arrhenius equation, whereas the rate increased exponentially with oxygen pressure. The antioxidant reaction was found to be a rate controlling mechanism. Analytical models were developed to predict the antioxidant depletion rate and antioxidant lifetime of this particular PP tape yarn.     

Evaluation of the slenderness ratio in built-up cold-formed box sections

According to section D1.2 of AISI S100-2007 for compression members composed of two sections in contact whose buckling mode involves shear forces in the connectors, a reduction must be made, KL/r must be replaced by (KL/r)_m. This new modified slenderness ratio takes into account the connection weld spacing and the minimum radius of gyration of an individual shape in the built-up member. Under the provisions of section D1.2 a reduction in load capacity must be made for built-up welded box members, which are the subject of this study. An experimental investigation on 48 samples was addressed to determine the comparative behaviour under compression load of box sections composed of two C-section members in contact by seam welds with different weld spacings (ranging from 100 to 900 mm). The studs were tested simulating rigid and flexible end support conditions. The length of the samples was 900 mm with a cross-section of 100 mm×100 mm. The base material thickness was 1.5 mm (gauge 16) for 24 samples and 2.0 mm (gauge 14) for the rest. The testing done on the samples did not show a statistical reduction in the ultimate compression load capacity for these members except for a weld spacing of 900 mm and a flexible end support condition. The reduction considered in AISI S100-2007is not applicable to determine the ultimate load capacity for the rest of the members.     

Performance of CFTST column to steel beam joints with blind bolts under cyclic loading

The objective of this research is to investigate the seismic performance of the composite joint consisting of square concrete filled thin-walled steel tubular (CFTST) column and steel beam with end plate and blind bolts. The cold-formed square tube in each CFTST column connection was fabricated by seam welding together four pieces of lipped angle with nominal wall thickness 1.5 mm or 3 mm. Four exterior joint specimens were tested under axially compressive load on the top of the columns and cyclic loads on the beam tip. The experimental parameters in the study were the thickness of the steel tube and the type of end plate. The seismic response of the blind bolted moment joints to CFTST columns was analyzed and evaluated in terms of the hysteretic behavior, failure modes, stiffness and strength degradation, ductility, and energy dissipation capacities of the joints. To improve the tension behavior of the blind bolted moment connections to the thin tube wall, the anchorage action of reinforcing rebar welded to the bolts with concrete-filled steel tubes was also investigated to consider the effect of cyclic loading. The experimental and analytical results indicated that when the end plate thickness is not less than 3 mm, the flush or extended end plate joints to CFTST columns exhibited large hysteretic loops and excellent seismic performance, such as ductility and energy dissipation capacity. The proposed innovative blind bolted joint was verified as a reliable and effective solution applied in mid- and low-rise buildings through properly design and detailing.     

低压湿式储气罐底板计算探讨

通过对低压湿式储气罐底板强度及焊缝强度的计算,探讨了确定底板厚度的计算公式。     

土工膜焊缝剪切强度与充气时间和充气压强的关系

土工膜焊缝剪切强度是整个防渗结构可靠性保障的关键因素之一。为了得到充气时间和充气压强对土工膜焊缝质量的影响,本文选择七种不同厚度的HDPE土工膜在不同充气时间和充气压强条件下进行焊缝剪切强度试验。试验结果表明:相同充气时间和充气压强条件下,土工膜焊缝剪切强度随着土工膜厚度的增加而增大,且曲线变化几乎一致;无论充气压力多少,充气时间长短,相同土工膜厚度试验条件下,不同厚度的HDPE土工膜在焊缝剪切强度方面表现出良好的稳定性,所有试验组的焊缝剪切强度值大小及其变化相近,剪切强度变化系数最大为6.72%,最小为0.81%,充气压力和充气时间对土工膜焊缝剪切强度影响很微小;土工膜焊缝剪切破坏主要发生在焊缝区域与土工膜母材的连接处薄弱部位,应当引起重视。     

Gaseous formaldehyde removal: A laminated plate fabricated with activated carbon,polyimide, and copper foil with adjustable surface temperature and capable of in situ thermal regeneration

Formaldehyde is one of the most common indoor air pollutants in Chinese residences. This study introduces a novel laminated plate with adjustable surface temperature to remove gaseous formaldehyde. The plate is fabricated with activated carbon, polyimide, and copper foil via thermal compression. The plate can be regenerated in situ by applying a direct current to the copper foil. Adsorption‐regeneration cycle tests were conducted to evaluate the plate's formaldehyde removal performance. The overall removal efficiency of the fabricated laminated plate with glue mass fraction of 25% and thickness of 1.5 mm was about 30% at the face velocity of 0.8‐1.2 m/s. The pressure drop was about 5 Pa. Its removal ability can be regenerated in situ in 8 minutes by increasing the surface temperature to 80°C. The fabricated laminated plate showed good durability after 52 cycles of adsorption‐regeneration tests. The results indicate that the proposed laminated plate can enhance the purifying efficiency and enlarge the life span of ordinary, cheap sorbents. It makes cheap materials with low performance suitable for air purification.     

The 17 February 2006 Guinsaugon rock slide-debris avalanche, Southern Leyte, Philippines: deposit characteristics and failure mechanism

The Guinsaugon rock slide-debris avalanche was the most catastrophic single landslide event in Philippine history, with 14–18 M m³ of debris instantly burying an entire village. Hummocky topography, pressure ridges and other internal structures suggest that the landslide deposit was emplaced as a debris avalanche and debris flow. Susceptibility to planar and wedge failures as well as to toppling due to rock discontinuities were demonstrated using kinematic analysis and SMR. Limit equilibrium analysis on planar failures yielded factors of safety ranging from 0.8 to 1.5. The study showed that pore pressure on discontinuities had a more significant effect on the slope stability than seismicity. For wedge failures, there is a sudden drop in the factor of safety at pore water pressures of 258–306 kPa. At the site, the pore water pressure may have been as high as 490 kPa. The possibility of such a landslide event in the future is discussed.