AGGREGATES - Materials for Civil and Construction Engineers - page 193

Sampling from stockpiles must be performed carefully to minimize seg-
regation. Typically, aggregate samples are taken from the top, middle, and
bottom of the stockpile and then combined. Before taking the samples, dis-
card the 75mm to 150mm (3 in. to 6 in.) material at the surface. A board
shoved vertically into the pile just above the sampling point aids in prevent-
ing rolling of coarse aggregates during sampling. Samples are collected using
a square shovel and are placed in sample bags or containers and labeled.
Sampling tubes 1.8 m (6 ft) long and 30 mm (1.25 in.) in diameter are
used to sample fine aggregate stockpiles. At least five samples should be col-
lected from random locations in the stockpile. These samples are then com-
bined before laboratory testing.
Field sample sizes are governed by the nominal maximum size of aggre-
gate particles (ASTM D75). Larger-sized aggregates require larger samples to
minimize segregation errors. Field samples are typically larger than the sam-
ples needed for testing. Therefore, field samples must be reduced using sam-
ple splitters (Figure 5.17) or by quartering (Figure 5.18) (ASTM C702).

FIGURE 5.17 Aggregate sample

splitter.

(a) (b) (c)

(d) (e)

FIGURE 5.18 Steps for reducing the sample size by quartering: (a) mixing by
rolling on blanket, (b) forming a cone after mixing, (c) flattening the cone and quar-
tering, (d) finishing quartering, (e) retaining opposite quarters (the other two quarters
are rejected). (ASTM C702). Copyright ASTM. Reprinted with permission.