elongated using the criteria shown in Table 2.

surement of the aggregate dimensions (shortest,

These criteria were developed basically for iden-

intermediate, and longest lengths). Based on

tifying flat and elongated aggregate and not as a

these lengths, the shape of the aggregate is quan-

tified in terms of both the flatness and elongation

general tool for describing the shape of coarse ag-

ratios or by the shape factor. The flatness ratio (p)

gregates.

is the ratio of the short length to intermediate

length, and the elongation ratio (q) is the ratio of

Description of roundness

the intermediate length to the longest length.

Roundness, as opposed to shape, has to do

An alternate method for describing the shape

with whether the edges are sharp or round

of the aggregate involves the shape factor (F) and

(Wadell 1932). The roundness of a particle is sen-

sphericity (ψ) of the aggregate particles. The

sitive to abrasion and wear to which aggregates

shape factor (F) is the ratio of the elongation ratio

are subjected during processing and construc-

(q) and the flatness ratio (p), i.e.,

tion. The process for determining the roundness

of a particle is fairly complex and involves tracing

p

a magnified image of the particle. An inscribed

F= .

q

circle is drawn within the aggregate tracing and