Journal Aug 2020

Sustainable and durable - with recycled concrete aggregate? Chris Goodier, Wayne Dodds

The responsible sourcing of materials and the potential to reduce waste and increase sustainability is an increasingly important topic of debate in the global construction industry. As part of this, innovative recent research from Loughborough University in the UK has challenged common industry perceptions regarding the use of recycled concrete aggregate (RCA) in new structural concrete, and brought into question the existing limitations currently imposed by the international design standards [3].

The research analysed the effects of RCA, also referred to as crushed concrete aggregates (CCA), on the durability performance of structural concrete and hence their suitability for increased use in the civil engineering and infrastructure sectors. More than 1,400 concrete specimens were cast and tested as part of an extensive laboratory programme across 100 different mix designs.

The findings have provided authoritative peer-reviewed evidence that sustainable structural concrete can be a viable option for future responsibly sourced infrastructure projects, which highlights the requirement and need for a new and more robust framework for the efficient re-use and recycling of concrete.

The next step is for the findings of this research to be implemented in real-scale 'trial' structures or structural elements, and consequently monitored to determine the effect on long-term durability.

Brief overview on 3D construction printing Werner H. Bittner

Since about 1994, the construction sector generally faces an increasing productivity gap when compared with other classic manufacturing sectors like equipment manufacturing, the automotive or the aerospace industry. This gap has further increased meanwhile and many studies from well-reputed strategy and consultancy firms state this. Not all studies are identical, but the bottom line is.

In the author´s view, the reason for this increasing gap is the successful and ongoing implementation of the principles of standardization, industrialization, automation and - increasingly – digitalization by firms that are active in the sectors of mechanical engineering, automotive and aerospace whereas the overall construction sector has ignored either these developments or simply hasn´t done its share yet. In addition, in current times of many break-throughs, new technologies combined with striking business models increasingly show disruptive effects in their markets. In other words, competitors from unexpected angles and industry newcomers with disruptive ideas now threaten major players in the traditional and monolithic sectors.

Finally, we have arrived at one of these new technologies. It generally can be addressed as 3D Construction Printing.

Policies and business strategies for C&D waste management in India Kshemendra Nath P., Gaurav Bhatiani

Indian economy is expected to grow rapidly over the coming decades with increasing urbanization, industrialization and consequent demand for infrastructure. Generation of increasing amounts of construction and demolition (C&D) waste is a natural consequence of these processes. While there has been recognition of the challenge of managing C&D waste at the policy level, on the ground, progress remains limited. C&DWaste Management Rules, 2016 require all states to implement a policy and each city with a population of 500,000 to have established a functional waste processing facility by March 2019. This analysis concluded that compliance was less than a fifth (20%), i.e. only six out of thirty-six states and union territories had issued a policy or a draft version of the policy for managing C&D waste. Further, of forty-four cities in the dataset, nine i.e. less than fourth (25%) had an operational facility. The overall compliance level is well below one in ten i.e. compliance is more an exception, than a norm. Even the cities with an operational facility require significant upgradation, management support and capacity development to ensure compliance with the spirit and the word of the law. Therefore, a systematic approach towards data collection, capacity development, raising awareness, attracting private sector capital and management expertise in developing recycling facilities and quality control of recycled materials is recommended to address the challenge of scientifically managing large quantities of C&D waste.

Performances and applications of recycled aggregate concrete components in Chinese Mainland Yuxi Zhao, Weilai Zeng, Hongru Zhang

With the fast development of construction industry in Chinese mainland, lot of problems also appear simultaneously, for example, the scarcity of natural construction resources and the huge discharge of construction and demolition wastes. In order to solve these problems, recycled aggregate concrete (RAC) is proposed by recycling the wastes as substitute aggregates. Researchers have discovered the mechanical performances of reinforced RAC beams and columns to provide the theoretical support for the application of RAC in the practical engineering. Furthermore, the long-term behaviors of RAC components applied in practical projects also have been monitored.

Detailed assessment of the technical properties of recycled aggregates from mixed C&D waste Christian J. Engelsen, Sandeep K. Malhotra, Gaurav Bhatiani, Kshemendra Nath P.

An extensive assessment of the product quality has been conducted at Shastri Park C&D waste recycling plant in Delhi. The assessment was conducted during a 5-month period and when challenging mixed C&D waste was processed and recycled. The performance mostly complied to existing IS: 383 limits. The grading of 10/20 mm directly complied with the limits of IS: 383 for graded aggregates. In general for all fraction, the grading properties were found to be of sufficient quality when a proper concrete mix design is applied. Furthermore, the 0/3 mm may contribute to strength when used as aggregates in concrete block production due to the increased content of fines. The study revealed that with proper recycling technology, competitive recycled products can be produced from mixed C&D waste containing more than 20% clay masonry and excavated soil. Hence, the valorisation of the low-graded mixed C&D waste, contributes significantly to circular economy. It reduces the consumption of virgin raw materials and the CO2emission in addition to preserve the groundwater and surface water resources.

A study on the use of construction and demolition waste as coarse aggregate in self-compacting concrete for sustainability S. Girish, N. Ajay, Sasha Azimi

In this experimental study, a simple unique mixture proportioning method starting with volume of paste was successfully adopted for developing self - compacting concrete (SCC) using construction and demolition waste as recycled concrete aggregate, for sustainability. A systematic experimental programme with wide range of volume of paste, powder, water, and cement contents were chosen keeping in mind the field requirements. Results showed increase in compressive strength as paste volume is increased for the same w/c ratio and higher compressive strength when compared to normal concrete. The enhancement in compressive strength can be factored in the mix design. SCC can be the preferred choice when recycled coarse aggregate are used.

Mechanical properties and permeability of pervious concrete made with recycled concrete aggregates Shoukai Chen, Zhengnan Zhang, Jialin Chen, Yajing Bie

The mix proportion of the pervious concrete is designed based on that the ratio of water-cement is 0.3 and the ratio of sand is 10%. Then, the effect of different replacement level, aggregate gradation, superplasticizers, steel fiber, fly ash and silica fume on the recycled aggregate pervious concrete (RPC) are investigated. The results show that the compressive strength of RPC with coarse aggregates increases along with the replacement level of recycled coarse aggregates growth. When using the double graded aggregates and the replacement level of recycled coarse aggregates is 30%, the maximum of the RPC compressive strength was increased by 35.4% comparing with the natural pervious aggregate concrete.

Study on the nano-hardness of the interfacial transition zone of recycled concrete with graphene oxide Kai Guo, Fengshuo Yang, Jinghai Zhou, Ming Liu

The nano-hardness of the interfacial transition zones of recycled concrete with graphene oxide were studied by using nanoindentor. The results showed that the average hardness and width of the interfacial transition zone of recycled concrete with graphene oxide between new paste matrix and natural aggregate were about 0.84GPa and 30-35?m, respectively; The hardness and width of the interfacial transition zone between new paste matrix and old paste matrix was about 0.76GPa and 25-30?m, respectively. Compared with ordinary recycled concrete, it was found that the proportion of calcium silicate hydrate and the content of calcium hydroxide crystal group in the hydrate were enhanced. The nano indentation hardness distribution in the interfacial transition zone were more uniform and the microstructure was more stable. According to the relationship between the microscopic mechanical properties and the macroscopic mechanical properties of recycled concrete, it can be concluded that graphene oxide can enhance the mechanical properties and microstructure of the interfacial transition zone of recycled concrete so as to improve the macroscopic mechanical properties of recycled concrete.

DeConcrete: Eco-efficient arctic technologies for construction and demolition practices Priyadharshini Perumal, Iveta Novakova, Victor Danilov

Increasing the reuse potential of construction and demolition waste (CDW) in building industries is one of the main focus of several projects funded by European Union. One such example is DeConcrete which is exclusively addressing the issues in the Arctic region and to improve the co-operation between countries under Kolarctic CBC (cross border co-operation). The project is planned based on the current scenario of CDW handling in this region, and ways to improve the quality applications of CDW in construction industries other than backfilling/ earth applications. The main objective is to eradicate the linear model, create a circular economy in construction business, and increase interconnection between building industry and CDW management businesses in the Arctic. This starts with exploring the demolition practices, processing of the material, identifying the reuse potential, treatment methods to improve the quality of recycled concrete aggregates (RCA) and the waste management strategy. Any project would not be successful without the practical implementation of the finding in industrial platform. DeConcrete gives importance to the ripple effect of the discoveries from the project in construction industries through the network of industrial partners and research organizations.

Sustainability of magnadense in civil engineering Richard Hunt, Mark Moriarty

Swedish magnetite, mined within the arctic circle, is predominantly utilised in Steelmaking. However, due to its naturally high density of around 5 kg/m3, the mineral is regularly utilised for many applications outside of steelmaking.

In many civil engineering projects, the use of heavy weight concrete and ballast can prove to be a cost effective solution, with the higher cost per tonne offset by savings in other areas on the project. Alongside, this use of high density concrete can provide CO2 advantages due to the reduction in concrete on a project and other related groundworks such as excavation and piling.

This paper provides an overview of the properties of magnetite and the benefits of its use in civil engineering applications.

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