Circular floor system for residential buildings

Abstract

Sustained economic growth based on a linear production model is not feasible on a planet with finite resources and a limited capacity to absorb wastes. By 2050, the world's population has grown exponentially to 9.7 billion and a tripling of the global use of materials can be realistically expected. Therefore, the transition towards a circular economy has become one of the top priorities of the European Union and its national governments. The Dutch government has stated the ambition to achieve a fully circular economy by 2050 at the latest.

Worldwide, the construction sector contributes to approximately 13\% of the global economy and employment of over 110 million workers. However, the construction sector is also responsible for 50\% of the total raw material consumption, 40\% of the energy usage and for 39\% of all carbon dioxide emissions. The construction sector therefore shows excellent potential for the transition to a more circular production model. One of the initiatives in the Netherlands to accelerate this transition is called 'het betonakkoord'. This initiative aims to make the concrete supply chain more sustainable by focusing on high quality application of recycled or reused building materials and on circular design.

Another interesting development is ongoing in the Netherlands. Since 2019, the housing shortage is 300.000 units and is continuously increasing to approximately 400.000 units by 2025. Combined with the economic growth of the past decade has resulted in skyrocketing house prices. One of the most effective solutions to overcome this problem is to simply built new houses. However, taken into consideration the transition towards a circular economy, raises a fundamental question of how to design sustainable residential buildings with regard to circular principles. This question is quite extensive and consists of a variety of both structural and non-structural aspects. This thesis project focuses on the circular design of a load-bearing floor system for utilisation as a storey floor.

First, extensive literature review is performed in order to identify circular principles and strategies in the design phase of buildings. This thesis project adopted the framework of Cheshire. The framework consist of six nested circles which represent the hierarchy of the framework. Within the framework, Cheshire proposes five design principles in his book: building in layers, designing-out waste, design for adaptability, design for disassembly and material selection. This thesis project expanded the design principles of Cheshire, by defining and providing hands-on strategies or criteria for each design principle. In total, 42 criteria are proposed for transposition into a comprehensive framework for application in practice.

Next, several recent residential and utility building projects are reviewed to determine the state-of-the-art regarding the implementation of circular design principles in practice. The general tendency is that these projects take the deconstructability and, to a limited extent, the selection of materials of the buildings into account. The common denominator in all recent projects, and especially for residential buildings, is the reduction of environmental impact through the realisation of net zero energy buildings.

Concrete floor systems are still widely used in newly built residential and utility buildings, due to their favourable characteristics. Therefore, the four most commonly used concrete floor systems are reviewed and discussed, These four floor systems are primarily designed in accordance with the demands of users and contractors. As a result of this thesis project, a newly designed floor system is proposed which is fundamentally based on the theoretical design framework developed in this report. Implementation of all five design principles was not considered feasible given the current state-of-the-art and regulatory barriers. Therefore, the newly proposed floor system is based on strategies and criteria related to the design principles of adaptability and disassembly. These design principles form the starting point of the multi-criteria analysis conducted in this report. The multi-criteria analysis is conducted in the first place to evaluate the performances of the four most commonly used concrete floor systems in the context of the considered circular design principles and secondly to compare the newly proposed floor system with the four most commonly used concrete floor systems. Based on the weighted rating scale, a maximum score of one hundred can be obtained. Results from the multi-criteria analysis reveal that three out of four commonly used concrete floor systems score well (scoring between 60 and 80) regarding the circular design principles. The newly proposed floor system scores excellent (scoring between 80 and 100).

The structural resistance of the newly proposed floor system is verified in accordance with codes of practice and state-of-the-art research under normal loading conditions. Horizontal wind loading is taken into consideration as well with respect to the stability of floor systems. Moreover, several stakeholder prerequisites are included in the design. Possibilities for recesses, staircases or vertical shafts for example, and building services are provided and suggested. Buildability aspects, such as the fabrication and assembly process are discussed in the report as well.