One of the most pressing problems confronting the New York Metropolitan area is caused by the Port of New York and New Jersey. In order to keep shipping lanes open, they need to be dredged constantly to prevent silting. Until recently, the Port’s operator, the Port Authority of New York and New Jersey, disposed of the dredged material in the ocean. Recognizing the environmental hazards posed by this material, which contains all kinds of toxins and heavy metals, the Federal Environmental Protection Agency is now prohibiting ocean dumping, forcing the Port Authority to search for environmentally acceptable methods of disposal. This is a formidable task, since several million of cubic yards of dredged material, much of it heavily contaminated, need to be disposed of, and the costs are staggering. Existing facilities do not offer indefinite capacities to store additional material for much longer. Yet, if an acceptable solution is not found soon, the Port of New York may lose important shipping business, and the potential losses of jobs in the region are politically and economically unacceptable. Thus, the demand for beneficial uses is increasing rapidly. Can our background in concrete technology guide the way to find a solution to the dredged material problem?

Making Dredged Material Safe

Dredged material contains clays, silts, salts, and various hazardous substances such as heavy metals and organics. Since untreated dredged material tends to form conglomerates a prior treatment is required, e.g., by reorganizing the microstructure (Figure 1). Such treatment effectively permits decontamination, e.g., by encapsulation of heavy metals, immobilization of organics or, more general, the containment of pollutants. Different treatment methods obviously lead to different products (Figure 2). The treatment procedure developed at Columbia gave promising first results, giving rise to hope that treated dredged material can be used in various applications, for example, as filler material in plaster, paints, mortars, and concrete.

 

Figure 1: Microstructure of dredged material before and after treatment (100X Magnification)

 

Figure 2: Dredged material before and after various treatments

Adding Value to Treated Dredged Materials

Many of the constituents of dredged materials may affect the hydration of Portland cement and react chemically with other concrete components. Due to its fineness, it changes also the aggregate grading in an undesirable way. Delayed setting time, poor workability and performance under load may be the consequences.