An overview of study on recycled aggregate concrete in China (1996-2011)

Durability of recycled aggregate concrete

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

In this study, the fresh and hardened properties of self-compacting concrete (SCC) using recycled concrete aggregate as both coarse and fine aggregates were evaluated. Three series of SCC mixtures were prepared with 100% coarse recycled aggregates, and different levels of fine recycled aggregates were used to replace river sand. The cement content was kept constant for all concrete mixtures. The SCC mixtures were prepared with 0, 25, 50, 75 and 100% fine recycled aggregates, the corresponding water-to-binder ratios (W/B) were 0.53 and 0.44 for the SCC mixtures in Series I and II, respectively. The SCC mixtures in Series III were prepared with 100% recycled concrete aggregates (both coarse and fine) but three different W/B ratios of 0.44, 0.40 and 0.35 were used. Different tests covering fresh, hardened and durability properties of these SCC mixtures were executed. The results indicate that the properties of the SCCs made from river sand and crushed fine recycled aggregates showed only slight differences. The feasibility of utilizing fine and coarse recycled aggregates with rejected fly ash and Class F fly ash for self-compacting concrete has been demonstrated.

Properties of self-compacting concrete prepared with coarse and fine recycled concrete aggregates

This paper reports an experimental study to improve the properties of recycled concrete aggregates (RCA) by their impregnation with polyvinyl alcohol (PVA). The effects of PVA on the development of strength and durability properties of the recycled aggregate concrete were evaluated. The experimental investigation was conducted in two parts. Firstly, the optimal concentration of PVA solution required to improve the recycled aggregates was determined. The RCA was soaked in 6%, 8%, 10%, 12% PVA solutions, and impregnation was conducted under a controlled laboratory environment. Density, crushing value (10% fines value), and water absorption of the PVA impregnated RCA (PI-RCA) were determined. Secondly, the slump, slump loss, compressive and tensile splitting strength, dimensional change (shrinkage) and chloride penetrability of the concretes prepared with the RCA that had been impregnated with the optimal (10%) PVA concentration were determined. It was found that the 10% fines value of the PI-RCA was higher, and the water absorption of the PI-RCA were lower when compared to the untreated RCA. The results show that there was not only an improvement in the mechanical properties of the concrete made with PI-RCA, but also the shrinkage of PI-RCA decreased while the resistance to chloride-ion penetration of the concrete produced increased.

Properties of concrete prepared with PVA-impregnated recycled concrete aggregates

Application of recycled coarse aggregate by mixture to concrete construction

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Practical application of environmentally-friendly recycled aggregate concrete

PURPOSE: To prevent the lowering of the manifestation of the strength of concrete by placing concrete into a formwork, in which a polymer mixing mortar layer is formed beforehand on a sheeting board, and attaching and unifying the mortar layer onto the surface of concrete as a curing layer. CONSTITUTION: A polymer mixing mortar layer 3 is shaped previously onto the surface of a sheeting board 2 constituting a formwork 1, and the formwork 1 is assembled by end branching material 4, separators 5, clamps 6, etc., by using the sheeting board 2. Concrete C is placed into the formwork 1, the formwork 1 is left as it is for a fixed time, the polymer mixing mortar layer 3 is attached and unified onto the surface of concrete C while curing placing concrete C and a curing layer is formed, and the sheeting board 2 is removed after a specified period under the state and concrete C continues to be cured. Accordingly, the evaporation of moisture from concrete can be prevented continuously even after the removal of the sheeting board immediately after concrete placing. COPYRIGHT: (C)1989,JPO&Japio

Hitoshi Kishimoto

Papers

Application of recycled coarse aggregate by mixture to concrete construction

Practical application of environmentally-friendly recycled aggregate concrete

Method of curing formwork placed concrete