In recent years many artificial lightweight aggregates have been introduced and marketed widely as structural concrete aggregates. The water absorption property of lightweight aggregates exerts influence on the fundamental properties of fresh and hardened concretes.
Since the absorption property of the aggregates shows wide variations, 15 kinds of aggregates, including 11 artificial lightweight aggregates, one expanded slag, 2 pumices and one river gravel, were selected as the specimens for several water absorption tests under various conditions such as in normal water, boiling water, pressurized water and vacuum in order to find the common nature and interrelation among them. The rapid absorption tests such as boiling or pressurized test were not applied to the fine aggregates because of their high absorbability.
The main results obtained are as follows :
(1) The water saturation coefficient is about 70% by volume for fine artificial lightweight aggregates after one-day immersion in water, but it is generally lower for the coarse aggregates except for the natural aggregates.
(2) The water absorption of the heat-treated aggregates is very high and it is proportional to the heat-treatment temperature.
(3) From the water absorption after 30 minutes boiling, the long-term absorbability and pumpability of the lightweight aggregates can be estimated rapidly and easily.
(4) The absorption in boiling water is proportional to that under pressurized condition for lightweight aggregates. This correlation is particularly notable for the oven-dried aggregates.
(5) The absorption from the crosscut section of artificial aggregates is proportional to those under boiling and pressurized conditions as well as to the aggregate particle size of non-pelletized artificial aggregates. Such absorption characteristics enables us to estimate the permeability of these internal structures.
