Hydration Characteristics of Recycling Reduction Slag and Waste Sludge by Co-Sintered Treatment Produced as Eco-Cement

Abstract

Waste materials have traditionally been discarded in landfills and often dumped directly into ecosystems without adequate treatment. However, possible reuse and recycling alternatives should be investigated and implemented. Recent environmentally friendly approaches have been aimed at achieving sustainable development by conserving natural resources and minimizing the discarding of materials. The objective of the present study was to investigate the hydration characteristics of reduction slag, limestone sludge, stone sludge, and iron-oxide sludge for fabricating four types of eco-cement clinkers. The compound raw materials were burned for 2 h at 1400°C to form eco-cement clinkers. The results showed that the major components of ordinary Portland cement (OPC), namely C₃S, C₂S, C₃A, and C₄AF, were present in the eco-cement clinkers. The compressive strength development of EcoA pastes (containing 78% limestone sludge, 19.51% stone sludge, and 2.49% iron-oxide sludge) was similar to that of the commercial OPC products. The compressive strength of the EcoD pastes (containing 71% limestone sludge, 19.51% stone sludge, 2.49% iron-oxide sludge, and 7% reduction slag) decreased as the amount of α-C₂S increased. Mercury intrusion porosimetry indicated that the pore volume of the pastes gradually decreased with an increase in the curing time. Furthermore, the results of physical-mechanical tests showed that reduction slag, limestone sludge, stone sludge, and iron-oxide sludge can be used as raw materials in cement production at no cost to the producer, thereby reducing the production costs.