|Title:||Recycling alum sludge into controlled low-strength materials for backfill use|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Sewage sludge -- Recycling
Water treatment plants -- Waste disposal
|Department:||Faculty of Construction and Environment|
|Pages:||85 pages : color illustrations|
|Abstract:||A large amount of alum sludge was generated as by-product from water treatment plants around the world. This study proposed an innovative method to reutilize waste alum sludge into controlled low strength materials (CLSM) for backfill use. With the use of alum sludge as replacement of aggregate (0 % to 100 %), water-to-cement ratio (w/c ratio) has been increased from 0.95 to 2.60, final stiffening has been increased from 19 h to 55 h and 28-day compressive strength has been decreased from 3.21 MPa to less than 0.3 MPa. Thermal gravity analysis (TGA) showed high content of organic matters in waste alum sludge interfered the hydration process between cement and aggregates. To facilitate the hydration and to promote the strength performance, various additives and different cementitious materials were used. Coal fly ash was found to be effective in increasing flowability and maintaining compressive strength. MgO and MgClO based cement was more effective to incorporate with alum sludge compared with OPC. Organic material triethanolamine (TEA) and calcium salts can significantly accelerate the stiffening of produced CLSM. All the prepared samples showed little leachability of heavy metals, proved successful stabilization of contaminants in alum sludge by the immobilization of cement. The results of this study indicated that waste alum sludge could be reutilized as aggregate substitute to produce fast stiffening and environmental friendly CLSM for backfill use.|
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