This blog post discusses the nuances of concrete admixture storage and handling. Discover how these additives affect concrete, from modifying its consistency to enhancing its frost resistance. Dive into admixture weighing, dosing, storage and filling. And learn how Tecwill’s innovative solutions streamline operations while ensuring precision and efficiency for the concrete industry.
Admixtures play an important role in fine-tuning concrete production. Concrete admixtures are used to improve properties of concrete, modify its consistency, enhance frost resistance with small air bubbles or accelerate the hardening process.
Made primarily of liquid chemicals, admixtures contain a significant amount of water content. However, they are added to concrete in very small amounts compared to other raw materials, usually just a few kilos or pounds per cubic meter.
Admixtures typically fall into the following categories:
- Air entrainers
- Water reducers
- Set retarders
- Set accelerators
- Superplasticizers
- Corrosion inhibitors
- Shrinkage controllers
- Alkali-silica reactivity inhibitors
- Color pigments
Volumetric admixture dispensing options
There are two most common methods of adding admixtures into the concrete mix – volumetric and weighing.
In the volumetric method, the admixtures are measured by volume rather than weight.
This method involves pumping admixtures into a concrete mixer by a flow control device. This method is used when a fast admixture dispensing is needed, for example, in dry batch plants.
Alternatively, admixtures can be measured first in a bottle and then delivered to the concrete mix via a pump. This allows for slower dosing and higher accuracy.
However, as the accuracy of the volumetric method depends on the density of the admixture, it may not always be suitable for applications requiring very precise dosing.
Admixture weighing
An alternative way of measuring the required admixture amount is weighting using a scale.
Admixture scales are typically integrated into the concrete mixing plant as in-line scales and are the smallest scales used in the plant.
These scales feature stainless steel hoppers arranged horizontally side by side in the required number. Each hopper is equipped with its own discharge valve. This allows the batch system or operator to freely select and modify the timing and discharge order of admixtures into the mixer. When a hopper’s filling and discharge hoses operate as separate units, any possible chemical reactions between substances can be avoided.
Scales provide better accuracy because they measure the weight. This is particularly important for applications like self-consolidated concrete, where precise dosing of superplasticizers, water-reducing admixtures, is crucial. In this case, even a minor mistake can easily ruin the batch.
Admixture dosing to the scales
Admixtures are dosed to the scales by pumping. Pneumatic diaphragm pumps are simple and maintenance-free. If the pumps are further equipped with a pressure regulator, admixture dosages are even more precise. These pumps are also well suited for pumping liquids of higher viscosity.
Dosing valves mounted on top of the scale hoppers minimize overrun. They also allow admixture circulation 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, all hoses remain fully filled, and admixtures are always ready to be dosed. The control system automatically schedules circulation cycles.
Admixture storage
Admixtures are delivered to the concrete mixing plant either in bulk by tanker trucks or in intermediate bulk containers (IBCs). From there, they are pumped into the plant’s storage tanks. These tanks should be selected according to admixture delivery conditions and placed in an insulated room equipped with heating or cooling 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 tank storage room has double doors, as is the case with Tecwill’s plants, IBC tanks can be placed directly inside and are easy to relocate with a forklift.
Admixture filling
Equipping the admixture storage room or container with a level measuring and filling system makes delivery scheduling easy and reduces extra traffic on the plant’s site. It also allows refilling the tanks from outside without the need for delivery personnel to enter the facility.
Tecwill offers such a system. The solution ensures that the filling pipelines are clearly labeled and that signal lights connected to the level sensors indicate when a tank is filled.
If you want to know more about our concrete production and admixture handling solutions, please check our solutions page.
If you have any questions, contact Teemu Tuominen using the information below.
