New sustainable technology for recycling returned concrete
Introduction
The production of construction and demolition waste (C&DW) is concurrent with the production of concrete, the second most consumed material, after water. It is estimated that roughly 25 billion tons of concrete are globally produced every year. Consequently, 510 million tons of C&DW are generated in Europe, about 325 million tons in the US and about 77 million tons in Japan. Given that China and India are now producing and using over 50% of the world’s concrete, their waste generation will also be significant as their development continues.
Recycling and recovery of both hardened concrete and returned concrete is an important issue for concrete sustainability. Returned concrete is the unused unset concrete that comes back to the plant in the concrete truck as excess material. This can be small amount of concrete leftover at the bottom of the drum, or more significant quantities not used by the costumer at the construction site. Typically, the amount of returned concrete generated by ready-mixed deliveries can be as low as 0.4–0.5% of the total production. However, during peak periods, returned concrete can increase to 5–9%. Globally, it can be estimated that over 125 million tons of returned concrete are generated every year, confirming that it is a relevant part of C&DW and represents a heavy burden for the ready-mixed plants [1].
Section snippets
Current methods of processing returned concrete
Current methods of processing returned concrete include:
- (1)
Discharging returned concrete at a location at the ready-mixed plant. Hardened concrete is then removed and stored before disposal to landfill or crushed to produce aggregates in recycling centres.
- (2)
Production of concrete elements, such as blocks for breakwaters or retaining walls. This possibility is limited by local market conditions and opportunities for the block production.
- (3)
Reclamation systems to reuse or dispose the separate
The new method to recover returned concrete
So far, environmental impact, working complexity and capital investment have limited the possibility of achieving a high level of recycling. The new method presented in this paper is based on a new additive that transforms returned concrete, in few minutes and without the need of specific equipments, into a granular material that can be fully reused as aggregates for new concrete. The new technology permits the complete recycling of returned concrete without the generation of wastes and,
Characteristics of the aggregates with the new method
The properties of the aggregates obtained by the new technology are related to those of the original aggregates and to the mix-design of the returned concrete. The composite layer of mortar that surrounds the core of the grains of the new aggregates influences their characteristics, both in terms of size and other physical/chemical properties. Fig. 4 shows the comparison between the cumulative aggregate distribution of the original aggregates (dotted line) and the recycled aggregates produced
Characteristics of concrete made with the new aggregates
Thirty per cent by weight of aggregates produced by the new process were used in substitution of natural aggregates for the production of new concrete, which was compared with a reference mixture prepared with natural aggregates. Both mixes were characterized by the same dosage of cement (CEM 32.5R II/A-LL, 320 kg/m3), water to cement ratio (W/C = 0.55) and consistency class (S4 according to EN 206-1). The characteristics of hardened concrete are compared in Table 2.
These results indicate that the
The assessment of the new technology in Japan
Japan is a highly industrialized country in a relatively small area (about 130 million inhabitants in 377,000 km2) and C&DW account for over 77 million tons/year. For this reason recovery and recycling is highly encouraged by the Government and protocols have been issued for many materials.
A full scale experimental program to assess the new technology has been set up in Japan by 15 members of GNN, a Japanese association joining more than 40 ready-mixed concrete companies whose mission is sharing
Economical impact of the new technology
The new technology has not only environmental and social benefits, but it also offers an economical advantage to the users, both to the ready mixed concrete plant and to the general contractor. In fact, one pack of the new additive – consisting of 0.5 kg of Part A and 6 kg of Part B – transforms 1 cubic metre of returned concrete into 2.4 tons of new aggregates that can be totally used to produce new concrete. Furthermore, returned concrete needs no longer to be disposed and therefore the costs of
Conclusions
- (1)
The new technology permits recovery of returned concrete by transforming it in a granular material and to prevent the production of wastes, both liquid and solid, with reduction of the impact on the environment, compared to the other methods.
- (2)
The granular material, once hardened, can be used for the production of concrete, in partial substitution of natural aggregates. In this way, the double objective is accomplished: (a) to preserve the natural resource by reducing the quarrying of aggregates
Acknowledgements
The authors would like to express their sincere thanks to the fifteen GNN Members that helped us developing this project: East-India Company (Tokyo), Kaneko Concrete (Yokohama), Yodagiichi-shouten Sakuragaoka RMC (Yokohama), Sanwa Kengyo (Saitama Prefecture), Futaba Corporation (Shizuoka Prefecture), Nomura Mapro (Shizuoka Prefecture), Fuji Ube (Shizuoka Prefecture), Seien Shoji (Shizuoka prefecture), Iwata (Shizuoka Prefecture), Ito Shoten (Aichi Prefecture), Remic Maruhachi (Gifu Prefecture),
References (7)
State-of-the-art review on delayed ettringite attack on concrete
Cem Concr Compos
(2003)- World Business Council for Sustainable Development. The cement sustainability initiative – recycling concrete....
- Obla K, Haejin K, Lobo C. Crushed returned concrete as aggregates for new concrete. Final report to the RCM research &...
Cited by (33)
Analyzing and mapping the current status, hotspots, and perspectives of lightweight cellular concrete: A bibliometric evaluation from 2000 to 2022
2024, Journal of Building EngineeringStudy on the use of CO<inf>2</inf> to strengthen recycled aggregates and pervious concrete
2024, Construction and Building MaterialsTechnical and environmental properties of recycled aggregates produced from concrete sludge and excavation materials
2023, Case Studies in Construction MaterialsAn overview of factors influencing the properties of concrete incorporating construction and demolition wastes
2023, Construction and Building MaterialsManagement and characterization of concrete wastes from concrete batching plants in Belo Horizonte - Brazil
2022, Journal of Materials Research and TechnologyCitation Excerpt :Furthermore, the development of alternatives for the use of concrete waste to promote the reduction of the amount of cement produced is extremely important, reducing environmental impacts associated with the CO2 emissions and the consumption of non-renewable resources. The aforementioned papers [6,8–22] present different information and/or evaluate a specific type of concrete waste (granular or fine). Furthermore, correlations between management and use of concrete wastes are not usually described in the literature.
Quality improvement of recycled aggregate
2022, Recycled Concrete: Technologies and Performance