construction and refurbishment of earthen irrigation channel banks

PVC is very flexible, easy to handle, readily conforms to the channel shape,surface preparation can be less than ideal and can be pre-fabricated into largepanels. However PVC does not have good UV performance and overseasdurability experience in exposed situations may not translate to Australianconditions where the UV exposure is more severe.PVC is susceptible to damage from burrowing aquatic animals, will stiffen withage and becomes brittle at 0°C making it difficult to handle in cold climates.22.8.2.3 Chlorosulphonated Polyethylene (Hypalon or CSPE)CSPE is based on the use of chlorine and sulphur to modify and soften thepolyethylene structure in order to make the material more workable and facilitateseaming. CSPE geomembranes are always scrim reinforced for dimensionalstability.CSPE materials are capable of factory fabrication using semi-automatic weldingpractices but field installation requires the use of solvent seaming. Theconstruction methods used with CSPE do not allow effective non-destructivetesting of the welds. A CSPE quality control program depends on the diligenceand competence of the factory and field fabrication techniques.When fresh it is amenable to seaming by both solvent bonding and thermalmethods but it crosslinks or cures with exposure such that normal weldingbecomes more difficult and in fact impossible after one year. Once cured,modifications or repairs must be carried out using two part solvent-basedadhesives with extensive abrasion and solvent scrubbing of the seam area. Thesolvent bonded field seams also tend to suffer a decline in strength after a numberof years primarily due to polymer softening and scrim pullout.CSPE provides very good chemical resistance, excellent UV exposureperformance and are not subject to cracking and embrittlement with long termexposure. Recently it has been suffering from cost pressures due toenvironmental aspects of its manufacture.The specific gravity of Hypalon is generally around 1.45 which means that it willnot float without assistance.22.8.2.4 Flexible Polypropylene (FPP)Flexible Polypropylene has developed as a result of recent polymer catylisationdevelopments that have enabled flexible FPP sheets to be produced by extrusionor calendering. They are provided in both unreinforced and reinforced form andprovide a choice in terms of tensile behaviour.The unreinforced polypropylene membrane materials are typically very flexiblewith excellent elongation capability. The reinforced materials have lowelongation but also have very low coefficients of thermal expansion.Seaming of FPP is very easy using thermal methods on both old and new sheet.The welding methods allow a full destructive and non-destructive QC/QAregime.Construction and Refurbishment of Earthen Channel Banks August 2002 - Edition 1.0 22-46