AGGREGATES - Materials for Civil and Construction Engineers - page 168

Permeable
void

Moisture

Impermeable
voids

Solid

(a) (b) (c) (d)

FIGURE 5.7 Voids and moisture absorption of aggregates: (a) bone dry, (b) air dry,
(c) saturated surface-dry (SSD), and (d) moist.

On the other hand, some asphalt absorption is desired to promote bonding
between the asphalt and the aggregate. Therefore, low-absorption aggregates
are desirable for asphalt concrete.
Figure 5.7 demonstrates the four moisture condition states for an ag-
gregate particle. Bone dry means the aggregate contains no moisture; this re-
quires drying the aggregate in an oven to a constant mass. In an air dry
condition, the aggregate may have some moisture but the saturation state is
not quantified. In a saturated surface-dry (SSD) condition, the aggregate's
voids are filled with moisture but the main surface area of the aggregate par-
ticles is dry. Absorption is defined as the moisture content in the SSD con-
dition. Moist aggregates have a moisture content in excess of the SSD
condition. Free moisture is the difference between the actual moisture con-
tent of the aggregate and the moisture content in the SSD condition.

Sample Problem 5.1

A sample of sand has the following properties:

Wet mass = 625.2 g

Dry mass = 589.9 g

Absorption = 1.6 %

Determine: (a) total moisture content, and (b) free moisture content

Solution
a. Mass of water = 625.2 - 589.9 = 35.3 g

35.3
589.9 *

Total moisture content = 100 = 6.0 %

b. Free moisture

= 6.0 - 1.6 = 4.4 %