Performance enhancement of recycled concrete aggregate – A review

Construction and demolition waste generation and properties of recycled aggregate concrete: A global perspective

Recycling of waste concrete has become an important issue worldwide due to the continued increase of construction wastes. Also, the growing global construction activities urge to find sustainable resources to replace natural materials for the production of concrete. In the past few decades, many researches have been carried out on the use of recycled aggregate (RA) derived from construction and demolition wastes to produce concrete products. This paper reviews the previous findings on the effects of use of RA on durability of concrete. In general, the amount of adhered mortar and the quality of the original concrete have a significant effect on the properties of resulting concrete. The increase of RA content and w/c ratio results in poorer durability of concrete. In comparison, the negative effect of recycled fine aggregate is more obvious than that of recycled coarse aggregate. The use of pozzolanic materials either for surface coating of RA or intermixed within the concrete are effective and feasible to improve the overall durability of concrete. Recent researches on CO2 treatment indicate that it can enhance the properties of RA and durability of concrete significantly.

Durability of recycled aggregate concrete – A review

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Carbonation of cement paste : Understanding, challenges, and opportunities

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.

Properties of recycled concrete aggregate and their influence in new concrete production

The cement paste attached to natural aggregates has a significant effect on the quality of recycled concrete aggregates (RCAs) because it usually has higher porosity and lower strength than natural aggregates. This work attempted to improve the quality of RCAs through carbonation of the attached cement paste. During carbonation reactions, CO2 reacted with Ca(OH)2 and calcium silicate hydrate (C─S─H) to form CaCO3 and silica gel, which filled the pores in the attached cement paste. Thus, carbonation increased the density, and decreased the water absorption and crushing values of the RCAs. It, thus, increased the flowability and compressive strength and decreased drying shrinkage of the recycled aggregate mortars.

Performance Enhancement of Recycled Concrete Aggregates through Carbonation

Influence of carbonated recycled concrete aggregate on properties of cement mortar

Permeability is an important indicator of the durability of cement-based materials. Surface treatments are effective in reducing permeability, and thus improving durability. In this study, CO2 surface treatment, as a new method, was investigated explore the efficiency on cement-fly ash-slag ternary concrete. The results show that the CO2 surface treatment densified surface microstructure and reduced both air and water permeability of concrete. With increase in fly ash and slag contents, the efficiency of CO2 surface treatment in reducing concrete permeability was enhanced. The results of thermogravimetric analysis (TGA), X-ray diffraction (XRD), environmental scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) indicated that CO2 surface treatment consumed calcium hydroxide (CH) and formed calcium carbonate (CaCO3). Moreover, the calcium-to-silicon ratio (Ca/Si) of calcium silicate hydrate (C–S–H) decreased after surface treatment and CaCO3 was covered by C–S–H during further hydration.

Zhaobin Xie

Papers

Performance enhancement of recycled concrete aggregate – A review

Performance Enhancement of Recycled Concrete Aggregates through Carbonation

Influence of carbonated recycled concrete aggregate on properties of cement mortar

Effect of CO2 surface treatment on penetrability and microstructure of cement-fly ash–slag ternary concrete