Modification of strength of wasteforms during leaching

This paper reports on some of the results of a project aiming to devise a test method for characterising wasteforms in terms of their likely physical stability, using the NEN 7375 testing method coupled with cube strength measurements as its basis. The experimental programme was devised to establish the influence of loss of material from specimens on strength with variables of specimen size and pH. Results from cement- and glass-based matrices are presented. The results indicated a leaching mechanism in which the leachable constituents of the specimens started to become depleted within the timescale of the test. While smaller specimen sizes usually leached at higher rates, they displayed high variability in performance. Acidic leaching conditions had variable effects on leach rates, depending on the wasteform matrix. Cement-based specimens displayed behaviour indicative of continued strength development of the cement matrix during the test. A method for predicting strength deterioration in wasteforms is proposed, based on curve-fitting of strength data to predict the growth of the degraded zone of a wasteform. A tentative attempt has been made to establish an appropriate performance limit for the predicted ultimate strength of a wasteform.