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State of California, Department of Transportation - page 25 / 52





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fall to one side of each bin and coarse aggregates will fall to the other side. This condition is most critical in the fine bin.

The following will help to eliminate improper samples from being taken. The sampling tray must be wider than the flow of aggregate being sampled. The sampling tray must be sized large

enough section When through

to accommodate a full cross of the aggregate stream. pulling the sample trays the stream of aggregate they



smoothly on



Samplers must entire stream constant speed.

be pulled through the of aggregate at a The aggregate sample

must not overflow during this process.




The sample tray must be pulled through the stream of aggregate at a constant speed to obtain a representative sample. The aggregate sample must not overflow the sampling tray during this process.

If the AC Plant Inspector is not familiar with the plant or the sampling device, always ask the Contractor’s plant personnel for assistance.

Batch plant aggregate samples must be lowered from the sampling platform down to the ground level, sometimes twenty to thirty feet below. The contractor is required to provide a means to deliver hot bin samples to ground level. This may include a length of rope with a hook, which can be used to lower the sample container to ground level. Another device for delivering samples to the ground may be a long piece of piping that extends from the sampling area to ground level. This system allows the sample to be poured into a chute at the top of the pipe, the aggregate then falls through the tube to a bucket or sample sack located on the ground.

Aggregate Weigh Hoppers Aggregates are discharged into the weigh hopper from the hot bins. Normally coarse aggregate is weighed first, succeeded by the next smaller size, and so on. Aggregates weighed in this sequence, prevent fines from leaking out through the gate at the bottom of the weigh hopper. Aggregate discharged from the hot bins should be deposited near the center of the weigh hopper. If aggregates are deposited on one side of the weigh hopper, an imbalance will occur and the scales will not indicate the correct weight.

Caltrans specifications require interlocks be in place, so that "not more than one bin can discharge onto any given scale at one time, and that the weigh box cannot be tripped until the required quantity from each bin has been deposited therein".

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