Batching with load cells

May 2016 Mass Measurement

The first task when preparing a concrete mixture is batching the raw materials. This means collecting raw materials, either by using methods of weighing or checking volume, or a combination of the two. During batching, there are certain permissible tolerances that are typically part of project specifications and/or noted in the “NPCA Quality Control Manual for Precast Concrete Plants”. A load cell and read-out combine to weigh the correct amounts for the desired mixing pattern (referred to as the mix design), which ensures the concrete is of the right consistency.

Materials are usually stored in hoppers. By using load cells to weigh the content of the hopper, an accurate measurement can be made of the contents, and maintenance issues, such as water leaks or holes, can easily be detected (the weight of the content will change).

Typically, admixtures are batched by volume through a dispenser. Usually the supplier will provide the dispenser at no cost to the producer and manufacturers should investigate this option. Dispensers reduce the likelihood of improper dosing and ensure the admixtures form the concrete mix in accordance with the requirements.

Aggregates are usually batched by weight. Whether in a hopper, on weigh belts, or directly from storage bins, load cells measure the weight of the material. The most common method used is weigh belts. However, ‘weigh belt’ is a misnomer. A true ‘weigh belt’ weighs while it is moving. In most batch plants, Live Bottom-Weigh Hoppers (LBWHs) are used. An LBWH’s belt is stationery while weighing aggregates. This type of belt can start under load to move the weighed aggregates to a transfer belt, hopper or skip hoist.

Load cells improve the overall accuracy in all of the above processes. Weighing each component gives an accurate measurement of the batched material and the result is the desired consistency achieved through a continuous timesaving method.

For more information contact Glen Webster, Loadtech Load Cells, +27 (0)12 661 0830, [email protected], www.loadtech.co.za

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