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

Abstract

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.

Fresh, Mechanical, and Thermal Properties of Cement Composites Containing Recycled Foam Concrete as Partial Replacement of Cement and Fine Aggregate

“…It is difficult to compare exact values of compressive strength and thermal conductivity coefficient with results from the literature due to differences in the materials used and their proportions. The reported development of mechanical properties, density, and absorbability is similar to those reported in the literature for other lightweight aggregates [37,[65][66][67][68]71]. In shaping the mechanical properties of composites containing lightweight aggregates, the effective w/c ratio has a strong influence [36,42].…”

“…Deterioration of mortar consistency by substituting part of the natural aggregate with recycled concrete aggregate is normal. This is caused by the increased absorbability of the recycled aggregate [65,66]. The magnitude of the phenomenon is even greater as the aggregate used is a lightweight aggregate, being obviously more porous [67,68].…”