The use of marine sands
Both of our deposits have been surveyed in a 2016 study by the Ministry of the Environment, which has mapped the potential of Italian offshore sand deposits for the purpose of beach nourishment in erosion. From this study it emerges that Arenaria, with its two concessions, has about 30% of the suitable sands and immediately usable to rebuild the eroded beaches in Italy.
Arenaria is therefore proposed primarily as an authorized supplier of large volumes of marine sands for the reconstruction and maintenance of beaches in erosion. As part of a re-launch of infrastructure works, Arenaria’s marine sands can also be used in the design mix for the production of concrete and other blends for construction.
LAND RECLAMATION – ITALY AND ABROAD
On behalf of the land extension works taking place in Monaco at the Anse du Portier, Jan De Nul Monaco has been appointed as the main dredging contractor. The project consists in the construction of an eco-quartier on a total surface of 6 ha. In order to be able to pump a total amount of 600,000 m³ of sand and to fulfil the soil requirements, JDN Monaco proposed the use of sand from the Arenaria concession in Termini Imerese. The borrow area is located at approximately 450 nautical mile from Monaco and 5 nautical miles away from the shore in Sicily. The borrow area has a surface of 2,000 ha and water depths going from 120m to deeper.
After having performed soil investigations in 2010 and 2016, an area of 7.5 km long and 100m width has been defined as dredgeable in order to meet below requirements:
· Lowest overburden of clay top layer
· Water depths shallower than 140m
· High percentage of calcareous soil to be avoided
· Focus on zones with lowest interest for fishermen communities
Due to the presence of calcareous soil in the centre of the area which could have a negative impact on the soil characteristics when being backfilled, JDN has further in detail defined 2 preferential areas located in the North Western Area and the utmost South East Area.
Besides that, an additional area in the South Eastern part of the borrow area also meets JDN requirements. This area has a length of 500m and would be dredged in the event that North Western Area would not be sufficient or not available.
Dredging activities will be performed with one of the most prestigious vessel of the JDN fleet.
The vessel Leiv Eiriksson is 223m long and 41m wide, she has a hopper capacity of 46,000 m³.
In order to be able to dredge in deep water, the vessel will be mounted with the longest possible
suction pipes, which allows her to dredge up to 155m depth.
During trailing (or dredging) the two dragheads are lowered on the seabed while the ship is sailing with a speed of approximately 2 knots. The soil is loosened because of the weight of the draghead on the seabed and the water that is injected under high pressure into the soil and cutting tools that are
installed on the draghead. The injected water is called jetwater and is pressurized by jetpumps.
These jetpumps are always placed inside the ship. The tools inside the draghead are called teeth or scrapers. While the soil is loosened, at the same time, it is also mixed with water. Dredgepumps pump the mixture of soil and water into the ship. The cargo area of a TSHD is called a hopper. In this hopper, the soil mixture is loaded. Since the sand is heavier than water, it is therefore causing the sand to settle in the hopper while the water remains on top. The water on top of the sand can flow overboard, which permits the hopper level to remain the same whilst more mixture enters the hopper and sand settles. This principle is called overflowing. Once the ship has been fully loaded, she will sail to Monaco to pump out the sand into the reclamation area.
Since the dragheads will be penetrating the seabed, the amount of the top clay layer dredged will be reduced to a minimum. During each pass, typically, a layer of 30 to 50cm sand will be removed. Due to high tech DGPS positioning, the accuracy of the vessel and her draghead will be within the order of meters. As such, it is at all times guaranteed that the vessel operates within the defined limits and never performs dredging activities out of the permitted zones.
The sea sand coming from the bottom of the Adriatic Sea is a medium-fine sand, gray, well-classed and clean, both in terms of presence of fine fraction (passing to 0.063 mm less than 3%) and in terms of settling organic, polluting and / or toxic. Its features make it suitable for the use in the design mix of:
- bituminous conglomerates
as well as material for landfills, surveys and drains.
As evident from the granulometric curve, the sand has an average diameter of about 200 mμ, estimated by analysis with a laser granulometer. The tests conducted in collaboration with the University of Ancona and with the ELLETIPI laboratory of Ferrara have demonstrated the perfect suitability from sea sand to use in the mix design for concrete and bituminous conglomerates. In detail, the sand did not show any reactivity to alkalis (ASTM C289), nor significant absorption in water (UNI EN 1097-6) and equally negative were the results of the corrosion tests on the reinforcing rods, carried out on specimens of cement conglomerate. The experimentation carried out on packaged specimens, both for concrete and for bituminous conglomerates, with sea sand extracted from Arenaria has highlighted the particular property of “curve corrector” of the material, linked to the size and the particular shape of the grains, angular but blunt. Furthermore, the experiment conducted by mixing sand with cement, to make it suitable for structural geotechnical uses, has shown that the mix achieves excellent performances with modest amounts of cement (6-8%).
THE MARINE SAND AND THE CEMENTITIOUS CONGLOMERATES IN EUROPE
The aggregates for civil uses are, if the mineral resources destined for energy production are excluded, the most critical resources for the national economies and are essential in order to generate and maintain the structure of the construction world and the drive towards infrastructural development. Unfortunately, Italy, to date, does not have a great variety of aggregate supply sources, and this, in general, helps to make the supply of sand and gravel less secure. In the rest of Europe, instead, the use of marine aggregates in cement conglomerates is now a custom: Great Britain, Denmark, Holland and Belgium make responsible and environmentally friendly use of marine aggregates, and are a very useful reference for our activity. The incidence of marine aggregates in the British national aggregates market is so important that the Government, strongly encouraging the use of this resource, has brought together all the subjects involved in dredging and in the commercialization of the same in a single association, known by the name of BMAPA (The British Marine Aggregate Producers Association – www.bmapa.org) which has the role of standardizing the management of materials and methods of extraction, in compliance with the law and, above all, with the codes for the protection of the marine environment, submarine and coastal. It is a policy that involves not only companies connected purely to mining itself, but also the state bodies and the whole industry directly and indirectly related industries, as well as environmental groups aimed at verifying the impact of these activities. both from an environmental and archaeological point of view.
FURTHER MORE …
The extraction of marine aggregates has a long series of positive aspects, both from an economic and environmental point of view, just think of the enormous landscape damage produced by the land quarries that are much discussed in Italy, where many resources are spent for the recovery of degraded areas. The sea sand presents in fact obvious advantages for:
- energy and raw materials: the sea sand is extracted with large effluent dredges, whose operation is energetically optimized with respect to the small dredges operating in the pit quarries visible on the mainland and compared to other mechanical means generally used for the handling of aggregates. Moreover, it does not require a process, energetically very expensive, to crush. The chloride washing cycle, where necessary, requires a minimum use of fresh water, capable of removing the chlorides contained in the sand by simple immersion, until saturation of the recirculation water.
- waste generation: sea sand, controlled according to Ministerial Decree 367/2003, does not present pollutants and / or toxic substances. The possibility of diffusion in the marine and coastal environment of substances dangerous for the environment, let alone waste, does not arise.
- emissions in air, water and earth: sea sand, extracted and moved, does not generate emissions either in the air or on the ground.