Effect of high levels of alkalinity on geotextiles. Part 1: Ca(OH)2 solutions

The adverse effect of high alkalinity solutions on certain polymers has long been recognized by the polymer industry. Most chemical resistance charts and summary tables give an approximate indication of where problems might occur. Lacking, however, is the degree of this effect and the general conditions in which problems might exist. Furthermore, there is no testing methodology to quantitively assess the possible effects.

This paper investigates six geotextiles using alkaline solutions of pH = 12 and pH = 10; and it compares the resulting flow and strength behavior to the as-recieved fabric incubated at the neutral condition of pH = 7. All tests were conducted at the temperature of 25°C (77°F). The flow rate is seen to decrease with the duration of the experiment, and is caused mainly by the formation of a precipitation filter layer on top of the fabrics. The strength data showed a significant reduction in strip tensile strength for both polyester fabrics in the pH = 12 solution. No significant trends were seen in the pH = 10 solution within the 120 days of these tests.

The results point out the necessity of knowing site-specific information about the groundwater (and perhaps soil conditions) so as to properly select a geotextile. Furthermore, the results seem to question the effects of groundwater with moderate alkalinity for longer time periods than evaluated here, and perhaps under elevated temperatures as well. Additional work into these potentially adverse effects seems to be warranted.