Investigation of Water Absorption Behavior of Recycled Aggregates and its Effect on Concrete Strength

The water–cement ratio (w/c) has a significant effect on the strength of recycled concrete. In this study, considering the effects of water/cement ratio, strength, and water content of recycled aggregates, two kinds of pulse sequences of low-field nuclear magnetic resonance (LF-NMR) were applied to investigate the water migration behavior between simulated recycled aggregates (SRA) and water or fresh mortar. Three sets of concrete strength tests were designed and the results were used to verify the findings of LF-NMR imaging tests. The results showed that the depth of water migration in the SRA increases with time: at first the change rate is rapid, then slows down, and eventually tends to remain stable. When the SRA is in contact with fresh mortar with low w/c, no water migration occurs because the hydration of the cement in the mixture consumes a large amount of water, resulting in the inability of water to migrate into the SRA through capillary pressure. For the recycled aggregate concrete with high strength, the addition of extra water will increase the effective w/c and reduce the compressive strength of the concrete.