Properties of Portland cement made from contaminated sediments

Abstract

Hundreds of millions of cubic meters of contaminated sediments are dredged from US harbors and waterways annually for maintenance of navigation, environmental remediation, or both. In recent years, inexpensive ocean dumping has been largely eliminated as a disposal alternative causing a crisis in the management of sediment. This paper presents a new beneficial use alternative for contaminated dredged material, which is to use dredged material as a feedstock in the conventional manufacture of Portland cement. The paper demonstrates the efficacy of the process at the bench and pilot scales, and presents a summary of practical and economic considerations. A bench scale manufacture was carried out with feedstock mixtures containing 1–12% dredged material from the New York/New Jersey (NY/NJ) harbor. The clinkers were quantitatively analyzed with X-ray powder diffraction and differences in phase concentrations were observed in the clinker samples manufactured with dredged material (decreased alite and increased belite) suggesting that additional burn time was needed to account for the quartz present in the sediments. The free chloride concentrations in the clinker samples were below ACI limits for cement used with reinforcing steel; however, the chloride in the dredged material remains a manufacturing concern and is expected to increase annual maintenance costs. A pilot scale manufacture was carried out in a batch rotary kiln; X-ray diffraction analysis and ASTM tests for strength, soundness, and setting time suggested that with better optimized burning conditions, dredged material can be successfully incorporated into full scale manufacture.