General
Admixtures play an important role when it comes to the fine-tuning of the concrete production process. Admixtures are chemical, usually liquid, pumpable substances that, compared to other raw materials of concrete, are dosed and weighed in small amounts only, mostly just a few kilos per cubic meter. Concrete admixtures for instance are used to modify of the concrete consistency, to add small air bubbles for increasing the frost resistance and to accelerate the concrete hardening process. Admixtures though, to a very high percentage, consist of water.
Dosing and weighing of admixtures
The admixture scale is the smallest of all scales used in the concrete mixing plant. The weighing of admixtures can be carried out in many ways, but certainly the most well-known scale model is the "inline scale". The scale hoppers are made of stainless steel and they, with the number as required, are placed in horizontal position side by side.
Possible chemical reactions between different substances are avoided when the scales hoppers and their filling and discharge hoses operate as separate units. Each hopper is equipped with its own discharge valve. This allows the operator to freely select and modify the timing and the discharge order of the admixtures into the mixer. Dosing valves mounted on top of the scale hoppers minimize overrun and allow the admixtures to be circulated within the system: from the container to the pump, from the pump to the scale and back into the container. This ensures that even sticky admixtures do not settle and all hoses always are filled completely, admixtures ready to be dosed at any time. Circulation cycles are automatically scheduled by the control system.
The admixtures are dosed to the scales by pumping. The pneumatic diaphragm pump construction is simple and maintenance-free. When, furthermore, the pumps are equipped with a pressure regulator, precise dosing can be guaranteed. The diaphragm pumps are also well suited for pumping liquids of a higher viscosity.
Storage of admixtures
Admixtures are delivered to the customer by a tanker or in IBC containers, from which they are pumped into the customer's storage tanks. The customer choses the size of the admixture tanks according to the admixture delivery conditions. Admixture tanks and pumps should be placed in an insulated room equipped with heating facilities. The location and distance between the tanks and the scale are determined by the lifting and pumping capacity of the dosing pump. If the storage room for the admixture tanks is equipped with double doors, as it is the case with modules/containers of Tecwill plants, IBC tanks can be directly put inside. In this case, the tanks can also be easily moved from one place to another by a fork lift.
It is easier to amend the timetables and reduce extra traffic on the concrete mixing plant site if the admixture storage room or container is equipped with a level measuring and filling system. This allows the customer's admixture tanks to be filled from outside at any time. Tecwill’s system offers this possibility, the filling pipelines are labelled and signal lights connected to the level sensors indicate when a tank is filled.
Do you have any questions? Contact Teemu Tuominen by email teemu.tuominen@tecwill.com,
respectively, if you are a customer located in BENELUX, UK or Ireland Holger Reinecke, by email holger.reinecke@tecwill.com
