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Dredging is crucial for ports and waterways navigability, as well as water and flood management. Following the Circular Economy concept, dredged material can be reused in several ways. Contaminated sediments, although they occur in minor volumes, can only be reused after special treatment. Treated sediments must comply with strict environmetal standards in their final uses. Lime and lime-based binders are used advantageously to solidify and stabilize dredged sediments for reuse.
Prior to any reuse, sediment must meet basic technical parameters for a given application. Depending on the final kind of reuse, sediment must also comply with complex legislation in sea, inland water, waste and soil protection fields.
Sediment cannot be reused in a sludge form. In all cases, it must be dewatered to obtain typical soil consistency. If contaminated, dredged sediments must undergo special treatment in order to eliminate their harmful effects. Stabilization processes are used here to keep all pollutants under control.
Lime can react selectively with individual parts of dredged material and provide:
- Flocculation together with iron or aluminium salts; therefore it is widely used in the first treatment step in sediment dewatering processes.
- Drying and solidification thanks to exothermic hydration of quicklime when used.
- Further dewatering thanks to reaction with clay minerals in sediments, releasing physically bound water: this changes their nature to sandy or granular.
- Reduction in solubility of most contaminants in dredging sludge (mainly heavy metals), thanks to alkali pH of lime, and preventing contaminants from leaching to the environment.
- Sediment stabilization thanks to a pozzolanic reaction between lime and clay minerals to a solid and low-permeable matrix, contributing to contaminants leaching blockage.
For most sediments, customized lime-containing binders combine the effects above with increased cementitious reaction of hydraulic admixtures. This synergetic effect results in stable and durable final products wherever required.
Carmeuse offers the StabiCalco® range of products targeting the complex treatment, solidification and stabilization of dredging sludge and sediments.