What are the best methods for pre-soaking lightweight aggregate for concrete that will be pumped?
Concrete containing lightweight aggregate can experience severe slump loss during pumping if the aggregate isn't wet enough. Because of this, some producers of lightweight aggregate use vacuum or thermal processes to saturate their material. The amount of water absorbed during these processes may be two or three times that absorbed in 24 hours under atmospheric pressure. These aggregates can be stockpiled for more than 90 days without significant moisture loss and will respond to pumping much the same as normal-weight aggregates. Most concrete producers, however, achieve an aggregate moisture content suitable for pumping by simply sprinkling their aggregate stockpiles. Depending on the aggregate absorption rate, three to seven days of uninterrupted soaking will normally bring the aggregate moisture content to within an acceptable 70% to 80% of the total absorption. The amount of water absorbed generally decreases sharply after the first 24 to 48 hours of sprinkling. The stockpiles should be remixed several times during the process to ensure thorough soaking. For large or ongoing projects, some producers form three separate piles to allow storage and soaking of newly delivered aggregate without interrupting a continuous supply of soaked aggregate. On a rotating basis, loader operators take aggregate from only one pile while a second pile is being soaked and a third is receiving newly delivered material. They closely monitor storage so unsoaked aggregate is never batched, and also sample aggregates from the fully saturated stockpile for moisture content several times a day. Consistent moisture contents help produce uniform slumps. Some producers have also stored lightweight aggregates in 2-foot-deep pits that are filled with water from constant sprinkling. Loader operators turn the material over frequently so it's alternately submerged and sprinkled.