Use of uncontaminated marine sediments in mortar and concrete by partial substitution of cement

Globally, shallow shipping lines and harbors require continuous dredging for efficient navigation. Large volumes of sediments are dredged annually and dumped as waste. For instance, in France, about 50 million m³ of sediment is produced annually, while in China the value skyrockets to about 400 million m³. These sediments can contain pollutants, thereby, they present a global economic and environmental issue. Consequently, scientists and engineers have resolved into sequestration as an alternative means of dealing with such menace. As such, studies considering bricks and foundation road layers made from disposed sediments have been reported.

Over the last decade, researchers have successfully demonstrated partial replacement of aggregates and cement in concrete with alternative materials, such as recycled aggregate and fly ash. Following this trend, it appears that the use sediment in the manufacture of mortars and concretes is very promising. Unfortunately, very few studies have been devoted to the valorization of uncontaminated marine sediment just subjected to drying at ambient temperature for long period or at moderated temperature if the process has to be accelerated.

To this note, University of Lille scientists: Dr. Zengfeng Zhao, Dr. Mahfoud Benzerzour, Dr. Nor-Edine Abriak, Dr. Denis Damidot in collaboration with Dr. Luc Courard at University of Liège and Dr. Dongxing Wang at Wuhan University conducted a study where they focused on assessing the use of marine sediments, as partial substitution of cement in the manufacture of mortars and concretes. They showed that cheaply obtained uncontaminated marine sediments could be effectively used to lower cost of cement during concreting works. Their work is currently published in the research journal, Cement and Concrete Composites.

The authors obtained uncontaminated marine sediments dredged in the harbor of Dunkirk (France), which they dried and ground. The resultant material was then used as partial replacement for cement in the manufacture of mortars and concretes. In particular, three contents of sediments were used as cement CEM I 52.5 substitution (10%, 20%, 30%) to produce mortars. Fresh properties, such as: fresh density, slump and the mechanical properties of mortars were measured and the microstructural properties of mortars were also studied. Lastly, concretes were designed from the results obtained on mortars.

The scholars found out that both flexural and compressive strengths of the mortars decreased when the sediment replacement content increased. On the contrary, the mechanical properties of the mortar with 20% replacement of cement with sediments were seen to better than those of a mortar made from cement CEM II/A-LL 32.5 containing a proportion of limestone similar to the sediment substitution. Furthermore, the total porosity measured by mercury intrusion porosimetry of different types of mortars showed that the porosity increased as the sediment substitution content increased but the pore size distribution was shifted toward smaller pores.

In summary, the study demonstrated the successful use of uncontaminated marine dredged sediments as partial cement replacement in the manufacture of mortars and concrete. Generally, it was observed that the beneficial effect of sediment was more efficient on mortars than on concretes with respect to their mechanical properties. Altogether, dried and finely ground uncontaminated sediments have been demonstrated as a very interesting constituent for partially substituting up to 20% of cement as its efficiency overpass limestone filler.