Application of Fly Ash to Improve the Mechanical Properties of Paste Tailings

摘要

Fly ash (FA) as supplementary cementing material (SCM) or a single binder agent can have two potential applications in mining. In this study the application of class C fly ash both as a single binder agent to improve the mechanical properties of tailings at the paste consistency and as an SCM to substitute Portland cement (PC) in cemented paste backfill (CPB) was evaluated through unconfined compressive strength (UCS) testing. Gold mine tailings were mixed with PC and/or class C fly ash at the initial solid content of 78%. Specimens were prepared by mixing tailings with 3% PC, 1.5% PC: 1.5% FA, 1.5% PC:3% FA, and 7% FA binder contents and cured for 90 days maximum. The specimens with 3% PC and 1.5% PC:3% FA binder contents yielded fairly similar 90-day UCS values. The specimen with 7% FA binder content yielded a 90-day UCS value of 109 kPa. Vicat needle tests were performed to investigate the impact of PC replacement with fly ash in CPB on the initial and final setting times. The replacement of 50% PC with class C fly ash resulted in approximately 3.5 times longer initial and final setting times. Based on the test results class C fly ash can be successfully used to develop the most economical CPB mix design; however, longer setting time is needed. Moreover, the test results indicate a potential application of class C fly ash to be used as a single or major binder content to improve the mechanical properties of tailings at the paste consistency.