Rotterdam 55 / Custom made (industrial) sand
Rotterdam 55 for custom made (industrial) sand
A floating plant
The flagship of Dekker Natural Resources, the sand classification plant ‘Rotterdam 55′ is built to produce (industrial) sand products with a pre-described grain size and composition.The majority of the manufactured sand is intended for use with
concrete and bitumen plants, which demand several requirements with the sand they use(also called aggregates). These requirements are primarily about the particle size distribution and the purity of the sand.
Particle Size Distribution
A well balanced grain distribution (also called grain size composition, grain size classification and grain gradations) of the aggregates has a big impact on the processing properties, strength, possible shrinkage of the concrete and the cement usage of the concrete. When the aggregates exist primarily out of grains with the same diameter, spaces will start to emerge within the grains and those spaces will have to be filled up with cement which is not cost efficient and will eventually lower the hardness and strength of the concrete. If the rate of smaller and larger grains is not proportionate then there will be a surplus of smaller grains. Consequently, the smaller grains keep the bigger grains at a further distance from each other which does not help the maximum reachable concrete strength either.
These two examples justify the need for a grain size composition with several sizes of sand grains which is of importance when making good quality concrete. The ‘Rotterdam 55′ is equipped with a so-called sand installation which divides the rough sand from the soil into 4 separate sand grain sizes (sand gradations). These 4 gradations of sand are added to each other based on a recipe and in this way we can make industrial sand within the very specific requirements and demands of the concrete and road construction industry.
Sand classification plant
The system which the Rotterdam 55 uses for the grain size classification (the classification process) consists of screens and upstream tanks. With this system, the raw material which is dredged by a suction pump of the sand suction dredger ‘Rotterdam 58’ goes on the ‘Rotterdam 55′ and is separated in 5 gradations in order of size: >8mm (gravel), 2-8mm (pebble), 0.5-2mm(coarse sand), 0.25-0.5mm(medium sand) and 0-0.25mm(silt).
The gradation gravel and pebble is screened by size through the tumbler screens. Screening does not work with grains smaller than 1 mm so therefore the ‘Rotterdam 55′ uses the so-called upstream tanks which are tanks where the grains of a variety of sizes can be separated by using the strength of upstream water in combination with the differentiating falling speeds of the different grain sizes in water; we use the Archimedes number or the ‘gravitational acceleration’ technique to determine the speed and through this process we are able to separate different grades of sand. This is a situation which belongs to physics where not only the mass plays a role but also the size of the sand grain when it comes to the speed of falling into water. The classified gradations are stored temporarily on board and will be mixed according to a recipe and loaded onto ships to be directly transported to the client.
Besides the right grain sizes, the purity of the sand is also important. On the bottom of a waterway or soil there is often rough sand together with layers of clay, humus and layers of pre-historic wood. These ‘iniquities’ should never end up in the end product which is the industrial sand. In order to remove the clay, the installation has a screening machine cross beam which lets the grains grind against each other at a rate which grinds the clay and lets it dissolve in the rinsing water. The end result is clean gravel, pebbles and sand.
The present pre-historic wood (wood from forests which thrived a couple of thousands of years ago at the sand mining location) is dredged together with the sand in the suction dredger and is removed on board through a wood removal tank.In this tank the water and sand mixture is pumped and a mixture is created so thick that it is also known as quicksand.This mixture of sand and water has a voluminous mass(density) which is larger than the pre-historic wood in the mixture.This results in the prehistoric wood floating to the surface of the quicksand and the pre-historic wood can easily be removed by letting the wood removal tank overflow slightly. By using the above mentioned equipment we can always guarantee the demanded purity of the industrial sand.
The ‘Rotterdam 55′ provides a large amount of the present Dutch concrete and asphalt plants(usually near a body of water) with industrial sand. This is always done in large quantities which makes it nearly impossible to transport by truck. Furthermore, transport by water is highly sustainable and that is why we also chose to have a ‘floating’ installation because only then it is possible to ship the custom made industrial sand directly to the client per vessel. The installation is designed to produce and transport a maximum of 10.000 ton sand per day. Just imagine if you had to transport this load by truck; that would mean 600-800 loads up and down the same route!
Naturally, the sand classification plant Rotterdam 55 runs on sand. In order to get the sand to the ‘Rotterdam 55′, the ‘Rotterdam 58′ is used which is an electrical low-noise sand suction dredger which uses a rubber floating pipe combined with the ‘Rotterdam 55′. The sand suction dredger can mine sand up to a depth of 40 metres and is equipped with two centrifugal sand pumps and an underwater suction pump to get the sand dredged from the soil and a press pump in order to get the sand through the rubber pipe and transport it to the sand classification plant. The suction dredger is not with diesel or generator driven. Instead, the electricity is facilitated through an electrical wire from the ‘Rotterdam 55′. This solution takes care of any noise and makes it possible to work on critical low-noise sites such as natural reserves.