Determination of length to thickness ratio of armor stone test.
Principle.
The individual pieces of armor stone shall be classified on
the basis of their maximum length L and minimum thickness T, as determined by
visual inspection by using straight laths and carpenter’s rule or a tape-
measure or by using a caliper.
Preparation of test portion.
The sample shall be taken and reduced if necessary in
accordance with the requirements of clause 4 to produce the required test
portion. Fragments shall be discarded.
Test portions obtained for the determination of the mass
distribution of a light and heavy grading may be used for this test. Each stone
in the test portion shall have the weight above the extreme lower limit (ELL)
of the designed grading class. The number of pieces of armor stone for the
testing may vary from minimum 25 to 200 with different grading class.
Procedure.
Measure the length (L) of each stone as the maximum distance
between tow portions on the stone and measure the thickness (T) of each stone
as the minimum distance between two parallel straight lines through which the
stone can just pass. The tape measure, caliper, or carpenter’s rule shall be
used for measuring length and thickness.
Take the total weight and total number of the stone with a
length- thickness ratio of greater than 3.
Calculation and expression of the results.
For heavy grading, calculate the percentage ,X, of pieces of
armor stone with a length/ thickness ratio greater than 3.
X = N1 /N2 * 100
Which,
N1 is the number of pieces of armor stone with a L / T ratio
greater than 3.
N2 is the total number of pieces of armor stone tested.
For light grading, calculate the percentage ,X, of pieces of
armor stone with a length/ thickness ratio greater than 3.
X = M1/M2*100
Which,
M1 is the total mass of pieces of armor stone with a L / T
ratio greater than 3 (kg).
M2 is the total mass of pieces of armor stone tested.
References.
The rock manual, CIRIA C 683 : 2007/ BS EN 133-2: 2013.