An experimental study on controlled low strength material (CLSM) for utilization as sustainable backfill

Abstract

Disposal of ash produced by coal-based power plants is a global problem because of its fineness and lack of space for its pondage. In recent years, efforts have been made to reutilize ash for different applications, viz., manufacturing of cement, bricks, tiles, in concrete, for soil stabilization, construction material for roads and bridge abutments, etc. However, there is a need to find more applications for the complete utilization of ash. In this direction, the present work explores potential of fly ash and pond ash for development of controlled low strength material (CLSM), an alternative material for backfilling applications. The performance of different compositions of CLSM have been studied, by partially replacing sand and cement, with pond ash and fly ash, respectively. Experimental studies have been performed to obtain flowability, hardening time and compressive strength (soaked and unsoaked conditions) for different CLSM combinations. In the present study, 20% binder content and 80% filler content has been considered, with a water/binder (w/b) ratio of 1.7 based on initial trials. Further, variation in percentage of fly ash and pond ash as partial replacement of cement and sand, respectively, have been evaluated. From the test results, it can be concluded that upto 75% replacement of sand by pond ash (60% of overall mix) is possible for development of CLSM with desired properties. Furthermore, the 28-days average compressive strength observed for CLSM varies from 0.4 MPa to 1.8 MPa for the studied combinations. This range of strength is favourable for backfilling applications, wherein, excavation in future may be necessary. Though the study results are quite encouraging towards development of CLSM using pond ash and fly ash, further studies on durability properties and minimizing the variation in properties would help towards developing sustainable CLSM for environmentally friendly infrastructure development.