Abstract
With the rapid development of urbanization, many new buildings are erected, and old ones are demolished and/or recycled. Thus, the reuse of building materials and improvements in reuse efficiency have become hot research topics. In recent years, scholars around the world have worked on improving recycle aggregates in concrete and broadening the scope of applications of recycled concrete. This paper reviews the findings of research on the effects of recycled fine aggregates (RFAs) on the permeability, drying shrinkage, carbonation, chloride ion penetration, acid resistance, and freeze–thaw resistance of concrete. The results show that the content of old mortar and the quality of recycled concrete are closely related to the durability of prepared RFA concrete. For example, the drying shrinkage value with a 100% RFA replacement rate is twice that of normal concrete, and the depth of carbonation increases by approximately 110%. Moreover, the durability of RFA concrete decreases as the RFA replacement rate and the water–cement ratio improve. Fortunately, the use of zeolite materials such as fly ash, silica fume, and meta kaolin as surface coatings for RFAs or as external admixtures for RFA concrete had a positive effect on durability. Furthermore, the proper mixing methods and/or recycled aggregates with optimized moisture content can further improve the durability of RFA concrete.
Highlights
College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China; China Metallurgical Construction Engineering Group Construction Ltd., Chongqing 400084, China; Abstract: With the rapid development of urbanization, many new buildings are erected, and old ones are demolished and/or recycled
A comprehensive review of the mechanical properties of recycled aggregate concrete (RAC) has been conducted, and the results show that degradation of the mechanical properties of RAC is mainly related to the high water absorption of the aggregates and the weak areas formed by the mortar adhering to the old interface [19,20]
The acid presoaking method effectively breaks down the bond between the hydration products of the cement, removing the old mortar adhering to the recycled aggregate (RA) surface [28]; this method increases the cost of concrete production
Summary
With the rapid economic and social development of the 21st century, the urbanization process has produced a large amount of construction waste. An increase in the water-to-ash ratio (W/C) or the addition of additives or mineral additives is required to offset the lower workability of the RAC [23]. The acid presoaking method effectively breaks down the bond between the hydration products of the cement, removing the old mortar adhering to the RA surface [28]; this method increases the cost of concrete production. Some studies have broken away from the tradition and invented the process of crushing all waste concrete to obtain fully recycled fine aggregates [31]. The fully recycled fine aggregate obtained by this process has excellent physical properties and can replace 100% of the river sand in concrete [32]. Understanding the effect of RFA on the durability of concrete can provide a theoretical basis for the future large-scale application of RFA as a substitute for sand in practical projects
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