Sampling Aggregate and Aggregate-Soil Mixtures
A visual examination of the lot of aggregate should be carefully made. An accurate description of the material should be made for all materials examined. Slag aggregates shall be identified as to type, such as Basic Oxygen, Air-Cooled Blast Furnace, Open Hearth, etc. The nature and extent of segregation, if any, should be noted. Sample increments shall then be taken in such amounts, and in such locations, that the composite sample formed by combining the increments shall be of the same composition in all respects as nearly as possible as the lot from which it was taken.
Unless the lot of aggregate or aggregate-soil mixture samples is unusually small, the composite sample collected will be larger than that required for submission to the Laboratory for tests. In such instances, the amount of material shall be reduced to the proper size by use of a sample splitter.
Coarse Aggregate in Stockpiles
Once the pile has been examined and sample locations identified, care should be taken to minimize the segregation caused by the rolling of the larger coarse aggregate particles into the sample increment. Sample increments taken at spots designated by the inspector shall be placed in a separate pile. The pile shall be thoroughly mixed by the clamshell or front-end loader and a sample obtained from the combined and mixed increments.
If a loader is not available, then the sample is taken by digging perpendicular to the stockpile surface and placing the increment in the sample bag. This procedure is repeated at the selected locations about the pile until the proper number and type of sample increments have been collected to represent the condition of the stockpile.
Fine Aggregate in Stockpiles
A suitable method of securing sample increments from fine aggregate stockpiles consists of the following: Scrape off the outer layer of the material until damp sand is reached at the spots selected for taking the increments. Dig the material out with a shovel so that a vertical face 18 to 24 inches in height is exposed, insert the point of a shovel at the bottom of the face and move the shovel upward along the vertical face so as to obtain a shovel full of sand. The increment is then transferred to the sample bag. This procedure is repeated at the selected locations about the pile until the proper number and type of sample increments have been collected to represent the conditions of the stockpile.
Another satisfactory method of sampling a fine aggregate stockpile is by the use of a sampling tube. This tube should be one and one-fourth inches in diameter or larger and about six feet long. The tube is thrust into the stockpile perpendicular to the stockpile face at selected spots, the tube is then tilted down and removed. The contents of the tube are then emptied into the sample bag. This procedure is repeated about the pile until the proper number and type of sample increments have been collected to represent the conditions of the stockpile.
Aggregate in Trucks, Barges, etc.
A satisfactory method of sampling from a truck is to open the tailgate of the truck without lifting the bed, which will cause part of the material adjacent to the tailgate to slide off to the ground, thus exposing a sloping cross section of the truckload, from which several increments may be taken. Sample increments should be obtained from a number of truckloads, the increments combined and mixed, then split to the desired sample size.
Aggregate transported in railroad cars or barges will be found to have been loaded in three or more piles, each of which may be considered to be a small stockpile for purposes of sampling. The Inspector shall dig deeply enough into the piles to be sure that his sample increments accurately reflect the gradation of the carload or barge load. Sample increments should, of course, be taken to represent each condition of aggregate found and the same procedure of combining and splitting shall be followed to obtain the sample to be submitted to OMM.
At aggregate production or blending plants, a point where a conveyor belt can be safely and conveniently stopped long enough to remove a section of the flow of aggregate provides a satisfactory way of taking a sample. Select a sufficient length of the aggregate flow along the stopped belt so that three or four times the quantity of material needed for the sample can be removed. Carefully remove all of the material within the length of flow selected, place it on a clean surface, mix thoroughly and split by a splitter into the quantity needed for the sample to be submitted for test.
If aggregate in a bin must be sampled, the best procedure is to fill a truck from the bin, dump a load, mix thoroughly, then treat the pile as a small stockpile for sampling purposes.
Additional Sampling Methods may be found in the ODOT Level 1 Training Manual.