Weathering of a Nonwoven Polypropylene Geotextile: Field vs. Laboratory Exposure

Abstract

Like other plastic materials, geosynthetics can undergo changes in their properties due to weathering. These changes must be known and, if necessary, duly accounted for in the design phase. This work evaluates the resistance of a nonwoven polypropylene geotextile to weathering, both in the field (under natural degradation conditions) and in the laboratory (under accelerated degradation conditions). The damage experienced by the geotextile in the field weathering tests was evaluated by monitoring changes in its physical (mass per unit area and thickness), mechanical (tensile, tearing and puncture behaviour) and hydraulic (water permeability normal to the plane) properties. Microscopic damage was assessed by scanning electron microscopy. In the laboratory weathering tests, only the tensile behaviour of the geotextile was monitored. The results showed that all geotextile properties were affected by weathering. The mechanical strength of the geotextile decreased in the field weathering tests. Microscopic transverse cracks were found in the weathered polypropylene fibres, which may explain the reduction in mechanical strength. The accumulation of dirt on the nonwoven structure altered the physical and hydraulic properties of the geotextile. Comparing the field and laboratory weathering tests, the reduction in tensile strength found after 24 months outdoors (roughly 30%) was very similar to that observed after 4000 h in the laboratory. This relationship may not be valid for other geotextiles or other exposure locations.

Keywords: Chimassorb 944; UV-ageing; carbon black; durability; geosynthetics; geotextiles; polypropylene; weathering.

Figure 1

Schematic representation of the specimens used in: (a) tensile tests according to EN ISO 10319 [31]; (b) tensile tests according to EN 29073-3 [28]; (c) tearing tests; (d) static puncture tests. The roll arrows indicate the machine direction of production. The gripping area is indicated in grey.

Figure 2

Schematic representation of the equipment used in the water permeability normal to the plane tests (the water course is indicated by arrows).

Figure 3

Reduction (in percentage) of mechanical strength over time. (Notation: T—tensile strength; F_R—tearing strength; F_P—puncture strength).

Figure 4

Mean curves head loss vs. v₂₀ of GT500, before and after the field weathering tests.

Figure 5

PP fibres of GT500 before and after natural weathering: (a) unexposed (2000×); (b) 6 months (500×); (c) 6 months (2000×); (d) 12 months (500×); (e) 12 months (2000×); (f) 18 months (500×); (g) 18 months (1000×); (h) 24 months (500×); (i) 24 months (2000×). The magnifications correspond to original on-screen values.

Figure 6

Comparison of the residual tensile strength of GT500 after the field and modified laboratory weathering tests.