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

The unique achievements of Japanese industries in the super-aged society.

Study on mechanism of drying shrinkage and water loss of recycled aggregate concrete

1. はじめに 既設火力発電所等,大規模電力建物の解体に伴い大量に発生する コンクリート塊の持続可能なリサイクルシステムの構築を目的に, 筆者らはかねてより,品質・安全性,環境負荷および経済性による 評価に基づくリサイクルシステムの実用化について検討を行ってき ている 1), 2), 3), .このうち,再生粗骨材を用いたコンクリート(再生 粗骨材コンクリート)は,既に国土交通大臣認定を取得し,2 棟の 実構造物へ利用されている .一方,コンクリート用再生骨材に関 する規格(JIS)は整備されたが ,普及を促進するためには,共通認 識の保持,合意形成の確立,意志決定および適正な技術競合とコス ト競合に基づく循環市場の自立が必要となる .そのためには,図 1 に示すように,リサイクルに対する要求性能としての品質・安全 性,環境負荷および経済性の観点から最適なバランスを総合的に評 価し,リサイクルの行為自体の影響を適切に示すことが必要となる. 中でも環境負荷の評価は重要で,これまで筆者らは,リサイクル の行為が環境負荷に及ぼす影響ついて,CO2 排出量を指標として評 価を行ってきた 1), 2), .しかし,環境負荷を客観的に評価するために は,CO2 排出量のみではなく,リサイクルを行った結果として削減 される廃棄物量,あるいはリサイクルされない場合に本来消費され ていたはずの天然資源などの消費削減効果を含めた評価が必要とな る.すなわち,CO2排出量といった単一の環境影響要因のみでなく, 資源循環に係わる複数の要因を反映し,総合的にみた評価を行うこ とが評価の客観性を高めることとなる.その一つに,ライフサイク ルアセスメント(LCA)の環境影響評価に用いられている統合化の 手法として,被害算定型環境影響評価手法 LIME (Life-cycle Impact assessment Method based on Endpoint modeling) 7), による評価がある. 本検討は,コンクリート塊のリサイクルに対して,適切な評価に 基づく持続可能なシステムの構築を目的に,LIME を用いた評価指 標により,これまで筆者らが検討してきた技術 3), 4), 9), 10), の適用 を主体に,既設火力発電所の建替えをモデルにシミュレートし,リ サイクルシステムの有効性評価について検討を行った結果を示す.

RECYCLING SYSTEM OF CONCRETE WASTE INCURRED FROM BUILDING DEMOLITION : Production of recycled aggregate by real-scale plant and quality of recycled aggregate concrete

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Masafumi Narikawa

Papers

Application of recycled coarse aggregate by mixture to concrete construction

The unique achievements of Japanese industries in the super-aged society.

Study on mechanism of drying shrinkage and water loss of recycled aggregate concrete

RECYCLING SYSTEM OF CONCRETE WASTE INCURRED FROM BUILDING DEMOLITION : Production of recycled aggregate by real-scale plant and quality of recycled aggregate concrete

Practical application of environmentally-friendly recycled aggregate concrete