دانلود رایگان مقاله انگلیسی مصالح بتنی بازیافت شده و تاثیر آن در تولید بتن جدید - الزویر 2018

ABSTRACT

This manuscript presents a review of the potential and challenge of using recycled concrete aggregate (RCA) as the substitute for natural aggregate (NA) in concrete mixtures. Using RCA in concrete preserves the environment by reducing the need for opening new aggregate quarries and decreases the amount of construction waste that goes into landfill. The properties of RCA such as specific gravity, absorption, and the amount of contaminant present in it contribute to the strength and durability of concrete. The quality of RCA depends on the features of the original aggregate and the condition of the demolished concrete. Some researchers have reported that the use of RCA degrades concrete properties while others have successfully produced RCA concrete with a performance that matched normal concrete (NC). In addition to the influence of RCA to concrete properties, this paper also evaluates multiple techniques to improve the performance of RCA concrete, reported cost savings in concrete production and recommendations regarding the application of RCA in concrete.

9.1. Conclusions

-The difference in properties of RCA with respect to NA is mainly driven by the presence of old mortars that adhere on the surfaces of RCA particles. This remnant of mortar responsible for the lower specific gravity, higher absorption, lower abrasion resistance of RCA as compared to NA.

-Assuring the quality of RCA (both fine and coarse) is crucial prior to its use as aggregate in the mixture in order to make a good quality concrete and/or mortar. One of the ways is by minimizing the amount of the attached old mortar on the surfaces of the coarse and/or fine RCA particles.

-The handling of RCA prior to the mixing process influences the quality of the batched concrete. Combined with proper mix design and batching process, the use of partially saturated to fully saturated RCA has shown to improve concrete performance relative to that of concrete batched with dry RCA.

-There are several ways to improve the quality of concrete containing RCA such as using saturated RCA, incorporating sufficient amounts of SCMs (i.e., FA, GGBFS, metakaolin and SF) in the mixture and performing other mixture-design modification (i.e. increasing the amount of cement, using superplasticizer to lower the w/b), coating RCA surfaces with PP, applying new ways of mixing concrete techniques (i.e., TSMA, TSMAS, TSMASC, MMA, SEMA), surface-modification technology, self-healed the RCA prior to its usage in the concrete mixture, reducing the amount of old mortar and other impurities in RCA particles, incorporating fiber into RCA concrete mixture.

-The loss of workability when incorporating RCA in the concrete mixture can be addressed by several methods such as wetting the aggregate prior to the mixing, using plasticizer and/or a superplasticizer, incorporating SCMs as partial replacement of OPC and the combination of the aforementioned techniques.