For a variety of reasons, reuse of concrete waste by the construction industry is becoming increasingly important. This “It is too early to predict the future of corrosion-inhibitors, epoxy coated reinforcing bars, surface coatings, and cathodic protection technology... their
high cost and low environmental friendliness would clearly be a major disadvantage.” is
reflected in several research papers from different countries which were presented at a special session on concrete for environmental enhancement at a recent international con-ference, “Concrete in the Service of Mankind,” held in Dundee, Scotland. In addition to environmental protection, conservation of natural aggregate resources, shortage of waste disposal land, and increasing cost of waste treatment prior to disposal are the principal factors responsible for growing interest in recycling concrete waste as aggregate.
According to Hendriks, presently the European Union countries produce 200 million tonnes of building and demolition waste every year, which is expected to double in 10 years. In the Netherlands where waste recycling has become a growth industry since 1970s, 60 percent of the demolition waste is reused. Uchikawa and Hanehera estimated that 29 million tonnes, which is one-third of the 86 million tonnes of the construction waste produced in Japan in 1992, consisted of concrete rubble. Twelve million tonnes was recycled as road-base aggregate; the rest was disposed. Saeki and Shimura reported the satisfactory performance of recycled concrete aggregate as a road-base material in cold regions. In the United States, in 1983, deteriorated concrete from a 9 km (6 mi) long freeway pavement in Michigan was crushed, and the rubble was used as aggregate for concrete that was needed for the construction of the new pavement.
The end-use of the aggregate recovered from concrete waste depends on its cleanness and soundness, which are controlled by the source of origin of the rubble and the processing technology. Aggregate recovered from surplus fresh concrete in precasting yards and ready-mixed concrete plants is generally clean and similar in properties to the virgin aggregate. Concrete rubble from demolition of road pavements and hydraulic structures requires screening to remove the fines. Many laboratory and field studies have shown that the size fraction of the concrete rubble corresponding to coarse aggregate can be satisfactorily used as a substitute for natural aggregate.
A comparison of properties of concrete from natural aggregate and the recycled concrete aggregate shows that the latter would give at least two-third of the compressive strength and the elastic modulus of natural aggregate. Demolition wastes from buildings are more difficult to handle. The concrete is usually contaminated with deleterious constituents, such as wood, metals, glass, gypsum, paper, plastics, and paint. In combination with selective demolition of building components, such wastes can be handled in a cost effective way by processing into a number of subflows, which can be recycled separately. Evidently, due to the processing cost, at times the recycled concrete aggregate from building rubble may be more expensive than natural aggregate. However, this situation will rapidly change as the natural sources of good aggregate become scarce and the alternative waste disposal costs are included in the economic analysis.
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