Life prediction of the oxidation of geogrids by three different methods

Life prediction tests have been performed on a polypropylene geogrid using three methods for accelerated oxidation: the wet autoclave and dry autoclave tests using pressurised oxygen, and oven ageing in normal air. The predictions from the two autoclave tests agree sufficiently well with one another, but are 40 times less than the prediction from oven ageing tests. This indicates that the autoclave and oven ageing methods cannot be regarded as equivalent for this material. The discrepancy is explained by assuming that the rate of degradation depends on oxygen pressure in a nonlinear manner, in addition to which no reduction in activation energy at lower temperatures was observed. Preference is given to the longer lifetime predicted by oven ageing.