Environmental assessment and geomechanical properties of controlled low-strength materials with recycled and alternative components for cements and aggregates

Industrial by-products and construction and demolition wastes could be used in building materials and composites in place of natural aggregates and/or ordinary binders. This study investigated the use of cement kiln dust, cement by-pass dust combined with powdered incinerator bottom ash) and aggregates (saw-mill silt, concrete demolition waste, and incinerator bottom ash sand) to form unconventional controlled low-strength materials (CLSM). These CLSM mixtures were then compared with traditional CLSMs obtained by combining natural sand with ordinary Portland and sulpho-alluminate cements. A number of different mixtures were prepared and tested to explore the environmental and geo-mechanical properties related to the laying-construction phase and in-situ service. The results indicate the effects and possible limits of each alternative mixture element on the properties of both fresh and hardened CLSMs. The use of alternative binders may result in mixtures with properties comparable to those of reference mixtures. Very fine aggregates (saw-mill silt) significantly improve workability and reduce setting-times, without promoting any strength gain in the long term. Recycled CLSMs proved effective only when used as a substitute for 50% of natural sands. The high concentration of some hazardous contaminants was reduced to acceptable levels using hydrophobic agent and stannous sulphate. Such results encourage the use of unconventional CLSMs as a surrogate for conventional geo-materials in a variety of civil and environmental engineering applications