Understanding Acoustic Emission Testing- Reading 1 Part B-A

16.7.7 High Alumina Cement
In concretes made with high alumina (calcium aluminate) cement, the
conversion from CAH 10 * to C 3 AH 6 * on prolonged aging can lead to a large
increase in porosity and therefore a large decrease in strength. There has
thus been considerable interest in finding a nondestructive technique to
monitor high alumina cement concrete (HAC) members. Parkinson and
Peters concluded that the conversion process itself is not a source of acoustic
emission activity, since no acoustic emissions were generated during the
accelerated conversion of pastes at the critical w/c ratio of 0.35. However, at
the high w/c ratio of 0.65, conversion was accompanied by a high level of
acoustic emission activity, due to the fracture processes taking place during
conversion, associated perhaps with the liberation of excess water. Arrington
and Evans suggested that the structural integrity of HAC could be evaluated
from the shape of the acoustic emission vs. load plot, the emissions recorded
while the specimens were held under a constant load, and the decay of
emission activity with time.
*Note that cement chemistry notation is being used: C= CaO; A= Al 2 O 3 ; H=
H 2 O.
Charlie Chong/ Fion Zhang