Resumen de The beneficial use of dredged marine sand as an alternative material for concrete
Within the field of construction and civil engineering, concrete is the most commonly used material, mainly due to the favorable cost performance ratio provided by this material. In order to reduce the impacts related to the concrete fabrication, numerous lines of research consider the use of fly ash, silica fume and recycled aggregates; these have in common the use of a constituent material of a residual character for the molding of a new concrete, which at the same time also favors an optimization of the existing resources. On the other hand, one of the maintenance activities carried out in ports is dredging, in order to maintain the suitable functionality conditions for sea traffic; this leads to the extraction and stockpiling of the material resulting from dredging, which traditionally has been mainly used for beach regeneration.
Within this general framework, the main objective of this doctoral thesis is studying the potential use of the fine materials resulting from dredging as constituents of concrete. To this end, a research has been carried out making use of dredged marine sand DMS from the Port of Sant Carles de la Ràpita and the Port of Barcelona. This research comprises two main levels of action: one concerns the works carried out at the laboratory, and the other concerns the execution of a pilot experience at an industrial scale corresponding to the construction of a port pavement, under standard conditions of execution, at the Port of Sant Carles de la Ràpita.
At the laboratory, the first step was the characterization of DMS. Studies at the level of paste, mortar and concrete were carried out. The reference used for the concrete was that of a standard concrete for port pavements. In these studies the main variable used was the percentage of DMS to be used in order to reach a certain performance framework fresh behavior and hardened behavior.
Dredged material DMS was characterized following the directives from the CEDEX Recommendations for the Management of Dredged Material in Spanish Ports grain size analysis, mineralogical characterization, determination of heavy metals, determination of the content in organic matter, determination of total polychlorobiphenyls PCBs.
Likewise, the contents of chlorides and sulfates were also determined.
For the studies on pastes and mortars several tests were carried out: normal consistency test, Marsh cone, mini slump, truncated cone, flexural strength and compressive strength tests. During the studies concerning concrete, the following aspects were characterized: workability; compressive, flexural and splitting tensile strengths; impact and abrasion strength; water penetration; capillary suction; and the volume of accessible pores.
The studies carried out on pastes and mortars have highlighted that even if the fineness of the dredged material is higher than the fine fraction of the sands, its effect on the fresh state of the mixtures makes it impossible for a behavior such as addition to take place. On the other hand, its incorporation as corrective sand in percentages of substitution of natural sand of up to 25% has proved to be effective, both as regards the behavior in fresh state and the behavior in hardened state.
The research carried out on concretes with partial substitution of natural sand by dredged sand have highlighted the viability of achieving the reference features with an optimum percentage of 25%.
The pilot experience at an industrial scale carried out in the Port of Sant Carles de la Ràpita has highlighted the feasibility of using dredged sediments in the context of work site conditions. In this sense, with respect to the concrete with a compressive strength of 30 MPa used in the work, the concrete with dredged sand has followed the same sequence and the same means of execution than the reference one stockpiling, fabrication, transportation and placing showing no problems at all and maintaining the project features of the reference concrete.
