Title:
Leaching Composition and Associated Microbial Community of Recycled Concrete Aggregates
Author(s):
Adams
Publication:
Web Session
Volume:
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
10/17/2021
Abstract:
Recycled concrete aggregates (RCA) have been used as an alternative sustainable material in the construction industry, particularly as fill material and rip rap. Although RCA application has been successful, its long‐term environmental impacts in are still being considered. Currently, the most important known concern is the high alkaline pH of leachates when water moves through the RCAs due to their high content of calcium hydroxide
(Ca(OH)2). In this study, bacterial enrichment potential to reduce the alkalinity of two different sources of RCA were examined. One source of RCA was made from laboratory‐produced concrete that was crushed approximately 90 days after being cast. A second source of RCA was from a stockpile of demolished concrete that had been in service in transportation applications in New York City; the exact source(s) of the material are unknown. Washed and un‐washed lab and field RCAs were biostimulated by being exposed to an alkaline medium in batch experiments. pH, metal composition and microbial community changes in the leachates were monitored over time. Results show that pH of field RCAs could be decreased to less concerning values, as low as 8, while lab RCA samples were resistant to change. Furthermore, the long‐term effectiveness of this process was assessed by exposing these new bio‐enriched treated RCAs to DI water during 840 h after two times washing. Even though, the pH increased to high alkaline level again, it happened significantly slower; pH increased from 9 to 11 in 264 h and 504 h for field‐unwashed and field‐washed samples, respectively and stayed roughly constant over 840 h compared to an increase from 11 to 12 in 24 h for both original field RCAs. Metal concentrations in the leachate were much lower than initial releases in field bioleaching treatments except aluminum and copper, which were higher.