Test methods adapted for alternative and recycled, porous aggregate materials (Part 3 – Water absorption) (NT TR 550)

Abstract

  This is the third report in a series of projects dealing with test methods for mainly alternative and recycled aggregates (1292-96 and 1393-97). This study focuses on the problem of water absorption of porous aggregates in atmospheric pressure in accordance with EN 1097-6 Determination of particle density and water absorption, and the implication on durability aspects. The water absorption has been measured on incinerator bottom ash, crushed concrete, porous basalt and lightweight aggregate (expanded clay). The test procedure followed EN 1097-6 for atmospheric pressure. In addition a long term test of 300 days water soaking was performed. Boiling and vacuum were also used in order to see whether a quick method could be developed. The results clearly show that water absorption for 24 hours in atmospheric pressure and conditioning is not suitable for these very porous materials. They also show that there is a significant difference when pre-drying the materials before testing compared to soaking the materials in a natural state, “as delivered”. The four tested materials performed quite differently during long term saturation in relation to the quick tests, which indicates that it may be difficult to find one unique quick test method valid for all of them. The long time to water saturate the materials also has implications for other tests, e.g. durability, when the materials shall be conditioned and/or tested in a wet condition. One such example is compaction before tri-axial dynamic testing which is usually performed in a wet condition. Also when assessing the frost resistance, the materials shall be saturated before the freeze-thaw cycles. If this is done for only 24 hours the results could be unreliable. It has not been possible to develop one unique, quick test methods valid for all materials. Until such a method is developed, one has to let the materials absorb water until steady state is reached or develop an indirect method validated for each type of material!