However well a recipe is designed, the quality of concrete is decided at the scales. Aggregate, cement, water and admixture are weighed on separate scales and combined in the mixer. If one scale is systematically off by a few kilos, that error repeats in every cubic metre. This page explains how a concrete batching plant weighing system works and how automation brings discipline to weighing.
What is weighed and how?
- Aggregate: weighed cumulatively from bin gates onto the weigh belt or aggregate scale; each fraction is added on top of the previous one.
- Cement: taken from the silos by screw conveyor into the cement scale. With more than one cement type, each silo is managed separately.
- Water: weighed on a water scale or measured with a flow meter. If the moisture carried by the aggregate is not accounted for, the real water/cement ratio drifts from the recipe.
- Admixture: because the quantity is small, it is weighed on a separate, sensitive scale.
Cumulative weighing and jog feeding
In cumulative weighing the software adds each fraction’s target to the actual total of the previous fractions. Near the target the gate is not left open continuously; short open/close pulses feed the last kilos in a controlled way so the target is not overshot.
In-flight compensation
When the gate closes, material is still falling between the gate and the scale. Without compensation every fraction ends up above target. The right approach is to measure the in-flight amount separately for each bin and close the gate that much earlier. Details in what is in-flight material and how to set it.
Tare and running out of material
Material left on the scale after discharge into the mixer is added to the next weighing; an automatic tare after discharge stops this error from accumulating. Another critical check: if the gate is open but the weight does not increase, the silo is empty, the material is bridging or the gate did not open. The automation must detect this and stop production so an under-weighed batch never reaches the mixer.
Moisture correction: the invisible half of weighing
Recipe aggregate values are dry weights; the aggregate in the bins is wet. Without moisture correction, too little aggregate and too much water is added. Moisture correction raises the wet aggregate and lowers the water, keeping the effective water/cement ratio constant. For a step-by-step calculation see how to calculate moisture correction in a concrete batching plant.
How DKT CPlants handles weighing
DKT CPlants uses cumulative weighing, per-bin in-flight compensation, jog feeding near the target and automatic tare after discharge. If the gate is open but the weight does not increase, production stops. The weighing line and the mixer line run independently: the next batch is weighed while the mixer is mixing, but no new weighing starts while the scales discharge into the mixer. Moisture correction is applied to the recipe automatically.
Frequently asked questions
Where do weighing errors in a concrete plant come from most often?
The most common sources are uncompensated in-flight material, missing tare after discharge, scales with drifted calibration and aggregate moisture that is not accounted for.
How often should the in-flight value be measured?
Separately for each silo, and re-checked whenever the material, the gate or the drop height changes.
Water scale or water meter — which is better?
Both can be used; what matters is correct calibration and deducting the moisture carried by the aggregate from the water quantity.
Do I need to replace my scales and load cells?
No. Scales and load cells stay in place; what changes is the PC software that talks to the PLC.
Related pages
- Concrete batching plant software (DKT CPlants)
- Concrete batching plant recipe management
- Moisture correction in a concrete batching plant
- What is in-flight material and how to set it?
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The plant’s input/output list and PLC model are enough. We check compatibility together and show your own plant running in simulation with DKT CPlants. WhatsApp: +90 547 909 99 90