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Section 3: Stockpiling Aggregate

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TxDOT’s Standard Specifications allow the contractor to stockpile aggregate to be used on the project at locations approved by the engineer. For the sake of efficiency, most contractors will elect to do this. There are, however, some steps that must be taken before stockpiles are placed on the job site.

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Before the contractor submits a bid on the project, he will have already received a tentative agreement from a supplier that the required materials will be made available. When the contract is awarded, the contractor identifies his supplier to the engineer.

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Aggregate Sampling and Testing

The plans, specifications, and special provisions identify the required tests for the aggregate. Test methods are defined in TxDOT’s Manual of Testing Procedures (2002). The sampling and testing locations and frequencies are in TxDOT’s Construction Contract Administration Manual (2002), "Guide Schedule of Sampling and Testing."

Item 6.1 of the Standard Specifications states, “All materials being used are subject to inspection or tests at any time during preparation or use. Any material which has been tested and accepted at the source of supply may be subjected to a check test after delivery, and all materials which, when re-tested, do not meet the requirements of the specifications will be rejected.”

The method and location of sampling materials should be consistent and uniform. The AE can retest accepted materials if the material shows visible changes, does not conform to specifications, or if further testing is called for by the specifications or Guide Schedule. Construction Materials and Pavements (CST M&P) Material Inspection Guide contains additional material specific information on sampling and testing responsibilities.

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Stockpile Locations

Normally, the contractor proposes the stockpile locations to the project engineer for approval. TxDOT Standard Specifications for surface treatments ( Item 316) gives broad restrictions on stockpile locations as follows:

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It is important for stockpiles to be placed so that they are not contaminated. Extreme care must be taken that clay and mud do not pose a problem. Stockpiling should not be situated such that roadway drainage will cause the aggregate to remain excessively wet.

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Area Preparation

If necessary, the Contractor may be required to prepare a stockpile area before the aggregate is placed on it. He may be required to level it with a dozer or motor grader, and to clear it of any debris, such as vegetation, rocks, and sticks. Appropriate storm water pollution prevention devices should be placed as necessary.

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Proper Stockpile Techniques

Stockpiles should be placed in a manner that will minimize (or prevent) segregation and degradation.

Segregation. The separation of the different sized aggregate particles. Segregation would result in one part of the stockpile containing only the coarser particles and another area containing only finer particles. Ideally, any sample taken from any area of the stockpile should contain a representative sampling of the complete range of sizes.

Degradation. The breaking apart of the aggregate particles. This, of course, would result in a finer gradation of aggregate than desired. Degradation occurs most commonly from improper operation of the front loader, rather than improperly constructed stockpiles. Figure 6-1 shows a properly placed stockpile. Note the series of loads that have been placed adjacent to each other. Stockpiles should not be placed in one high cone-shaped heap, because segregation is almost certain to occur.

Properly Placed Aggregate Stockpiles. (click in image to see full-size image) Anchor: #i998959grtop

Figure 6-1. Properly Placed Aggregate Stockpiles.

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