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REVIEW OF LITERATURE AND MANUFACTURERS' DATA
Parameters of PVC degradation
The degradation of mechanical properties over time discussed in the previous section is of
concern for the users of sheet piles. The outdoor atmospheric exposure parameters, which
influence the mechanical properties of PVC in sheet piles, include UV radiation, air temperature,
rain, pollutants, and relative humidity.
The dosage of UV (ultraviolet energy) from solar radiation varies with location. The
wavelengths of the radiation that are of most concern are in the range of 295380 nanometers
(nm). At these wavelengths, the UV has sufficient energy to break the chemical bonds (Summers
and Rabinovitch, 1999). Outdoor air temperatures usually vary between 40 and 120F, but
when exposed to the sun, sheet pile temperatures may exceed 120F, because they would be the
composite of air temperature, infrared radiation, effect of wind, and surface evaporation of water.
Rainfall varies with location, ranging from 0 to 100 inches per year. Rain usually washes away
the loose materials from the sheet pile surface, but it may also deposit dissolved gas if it reacts
with the PVC. The atmospheric relative humidity usually varies between 10 and 100%, and
sometimes it may allow pollutants to be deposited on the surface of the sheet piles. The range of
pollutants is variable and includes CO2, NO2, O3, SO2, and dust.
Changes in properties during weathering
The chemical degradation processes of PVC have been well studied and well summarized by
Rabinovitch et al. (1993a, 1993b). These processes lead to discoloration, surface erosion, and
embrittlement. However, this type of aging is limited to a depth of no more than 150 micrometer
(0.006 in). Rabinovitch and her coworkers weathered extruded rigid PVC samples at 45 facing
south, according to ASTM D1435, in Arizona (hot, dry, high-UV climate), Florida (hot, humid,
high-UV climate), and Ohio (northern industrial climate). The exposure was continued for one,
two, and five years. Mechanical properties were then measured on the exposed and unexposed
samples. Figure 10 shows the mechanical properties as they changed over the five years. The data
indicate that in general, properties such as flexural strength, flexural modulus, tensile strength,
and tensile modulus do not change or, if anything, increase very slightly during the five years of
outdoor exposure for all U.S. climates. However, the data also show that, in contrast with the
above properties, the impact strength decreases significantly over time, with the greatest
reduction observed in hot, high-UV climates of Arizona and Florida.
Changes in creep properties
Unconfined tension creep tests were performed on vinyl sheet piling materials by one of the
manufacturers according to the ASTM test method D5262-92. At the test duration of 10,000
hours the total strain was 1.80% for a constant load of 43% of ultimate strength, and 2.78% for a
constant load of 65%. The progressive increase in strain with time is shown in Figure 11, and the
progressive decrease in the strain rate in Figure 12.
Regarding creep, another manufacturer (Materials International) notes "Creep failure is the
deformation or plastic flow of the vinyl when subjected to constant loading over time and can be
precluded if the stresses are maintained below 5% strain. A 75-year tensile strain on the order of
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