Assignment Task

Reuse of Concrete Components in New Construction Projects

Background

The reuse of concrete components in the construction process holds the promise of transforming the architecture industry and significantly contributing to a more sustainable future. Utilizing recycled concrete from demolished buildings is far more efficient than simply demolishing existing infrastructure without regard for resource conservation. Repurposing concrete components can diminish the need for new raw materials in construction projects and mitigate the negative environmental impact of buildings. By prioritizing sustainably sourced materials, architects and engineers can make a meaningful difference in communities, both large and small.

Reusable concrete components play a pivotal role in sustainable construction projects by offering customization to meet specific project needs while also minimizing waste and maximizing resource utilization. These components have found applications in various sustainable building projects, including floors, walls, and bridges (Hui et al., 2018). Moreover, recycled concrete components can be repurposed in different forms, such as insulation or fire protection, further reducing the reliance on primary materials (Shrirao et al., 2017). Additionally, the reuse of concrete components can lead to cost savings since they obviate the need to acquire new materials (Buhl, 2012). Furthermore, reused concrete components offer significant environmental benefits, including enhanced energy efficiency and durability (Chliya, 2016). By integrating reusable concrete components into sustainable construction projects, architects and engineers can construct structures that are both cost-effective and resource-efficient, while also fostering safe and comfortable living environments.

Introduction to Compound Concrete (CC) and Concrete-filled Steel Tubes (CFST)

Firstly, there are two types of recycled materials obtained from demolished structures: Recycled Aggregate Concrete (RAC) and Compound Concrete (CC). RAC is produced from a mixture of recycled concrete aggregates (RCA) less than 31.5mm (Jian and Wu, 2021) and fresh concrete (FC). On the other hand, compound concrete (CC) is a blend of fresh concrete and demolished concrete lumps (DCL) with a size greater than 40mm (Wu et al., 2015).

Concrete-filled steel tubes (CFST) find application in various structural roles such as piles, building columns, and bridge piers (Wang et al., 2017) owing to their high elastic stiffness and axial strength (Han et al., 2014). The steel tube used in CFST members serves as permanent formwork and reinforcement, reducing building costs and time. The concrete core confines the steel tube, preventing localized buckling inward and enhancing the mechanical performance of the member (Han et al., 2014). Compound concrete-filled steel tubular (CCFST) members, structurally similar to CFST members, use CC instead of regular concrete. Consequently, CCFST members require less cement and natural aggregates compared to CFST members, thus benefiting the environment.

The Dazhi Bridge in Kaohsiung, Taiwan

The Dazhi Bridge in Kaohsiung, Taiwan, stands as a prominent example of a steel tube bridge. Comprising concrete-filled steel tubes, the bridge offers structural support and features three box girder spans of varying lengths and a single cantilever length (Gu et al., 2008). Employing a compound concrete method, the bridge achieves a tight "monolithic connection" between concrete and steel, bolstering its strength and longevity (Gu et al., 2008). This landmark structure exemplifies how engineering innovations, such as compound concrete-filled steel tubes, enhance infrastructure by delivering strength, durability, and efficiency.

Circular Economy

The circular economy (CE) represents a development strategy aimed at ensuring continuous reuse or recycling of resources. It leverages the "3 Rs" (reduce, reuse, and recycle) to mitigate the adverse impacts of human activities (Li et al., 2010), emphasizing the redesign of products, manufacturing processes, and consumer practices to maximize resource retention and value extraction. In the UK, building construction and maintenance account for approximately 50% of all CO2 emissions. With the goal of reducing greenhouse gas emissions by 80% by 2050, the UK seeks to enhance the energy efficiency of new buildings (Borchers, 2010). Within a circular economy framework, structures must incorporate reusable and adaptable components like recycled aggregate concrete (RAC). Conversely, reinforced concrete (RC) members, being expensive and non-reusable, can only be recycled upon demolition, necessitating substantial energy expenditure. Preliminary tests indicate that CCFST members offer mechanical performance equivalent to or slightly below that of CFST members while delivering greater environmental benefits (Zhao et al., 2016). However, structural components made from recycled concrete are not fully embraced by the construction sector, limiting their use to non-structural applications like road subbases (Wu et al., 2019).

Aims of the Project

Construction and the built environment are significant consumers of energy and natural resources, with the construction industry generating substantial waste (Ekanayake & Ofori, 2000). Concerns regarding the environmental impact of waste generated during the demolition of old structures have prompted increased attention from the construction industry. The objective of this project is to gain a comprehensive understanding of the compressive behavior of compound concrete-filled steel tubular (CCFST) members. The study aims to reduce greenhouse gas emissions associated with concrete usage and mitigate resource depletion rates (Tam et al., 2018). With the UK targeting an 80% reduction in greenhouse gas emissions by 2050 (Borchers, 2010), achieving these goals is imperative. The project will pursue three objectives:

1. Investigating the axial compressive behavior of concrete-filled steel tubes.
2. Examining the material properties of compound concrete.
3. Proposing designs for recycled concrete-filled steel tubes.

Research Methodology

The research will commence with a comprehensive literature review detailing the types of concretes under investigation, including compound concrete utilizing demolished concrete lumps, compound concrete-filled steel tubes, and concrete-filled steel tubes. Subsequently, experimental investigations will be conducted in the concrete lab, encompassing compressive tests to elucidate the compressive behavior of both compound concrete and fresh concrete. Comparative analyses of strengths will be performed to demonstrate the suitability of recycled concrete for sustainable construction. The process will be repeated for different recycled aggregates to eliminate anomalies and ensure robust findings.

Literature Review

Compound Concrete and Demolished Concrete Lumps

This section will focus on the compressive behavior of CCFST, CFST, and CC. Compound concrete (CC) incorporates DCLs greater than 40mm, with a significant amount of mortar adhered to their surface, reducing the requirement for natural aggregates