Periodic Reporting for period 1 - CodeDEMO (Construction and Demolition Waste-based “Green” Demountable Structural Components)
Berichtszeitraum: 2021-09-15 bis 2023-09-14
Traditional concrete is the main building block of our infrastructure and it uses Portland cement (PC) as the main binding agent, production of which is fast increasing globally and responsible for about 7-10% total man-made annual anthropogenic CO2 emissions significantly contributing to global warming. Negative impacts of PC manufacturing are coupled with the quarrying of natural aggregates. Concrete also constitutes more than half of the 800 million tons of construction and demolition waste (CDW) generated each year, which is the largest waste stream in almost all countries. CDW industry is recognized one of the main sectors contributing to the global solid waste production, constituting 30-40% of total urban waste and its landfilling is responsible for about 35% of the deposition area worldwide. On the other hand, reinforced concrete structures lack of longevity due to their high deterioration tendency under simultaneous mechanical and environmental effects, which leads to increased needs for new demolition and reconstruction activities furthering the quantity of CDW generated and raw materials for the manufacturing of new construction materials. This is also exacerbated by catastrophic events such as earthquakes.
In an effort to tackle the issues related to generation of massive amounts of CDW as well as traditional concrete, CodeDEMO project proposes a new paradigm of manufacturing construction materials and demountable structural components by using resources coming entirely from CDW, with the following main objectives: (i) the development of structural geopolymeric green concrete mixtures with both binder and aggregate phases based on CDW and (ii) the use of green structural concretes in the design and production of pre-fabricated demountable structural components for a more resource- and eco-efficient designs for building circularity.
In an effort to tackle the issues related to generation of massive amounts of CDW as well as traditional concrete, CodeDEMO project proposes a new paradigm of manufacturing construction materials and demountable structural components by using resources coming entirely from CDW, with the following main objectives: (i) the development of structural geopolymeric green concrete mixtures with both binder and aggregate phases based on CDW and (ii) the use of green structural concretes in the design and production of pre-fabricated demountable structural components for a more resource- and eco-efficient designs for building circularity.
The project CodeDEMO was progressed smoothly and in accordance with the initially proposed plan. In first work package (WP1) of the project, the mineral portion of CDW was used in complete recycling to develop truly green geopolymer concrete mixtures having compressive strength grades similar to traditional cement-based counterparts. To do this, first, different types of CDW-based source materials (precursors) including different masonry and wall elements (e.g. bricks, tiles), concrete and glass, which form the majority of CDW were acquired and categorized. The precursors were subjected to initial crushing and ball milling process to obtain powdery samples suitable for geopolymerisation. Within the scope of WP1, production of suitable geopolymer binder phases by taking different parameters (e.g. single/combined use of precursors, curing conditions, types/combined use of alkali activators) into account was focused. After, both fine and coarse aggregates originating from waste concrete were characterized for the determination of their properties and selected for suitable utilization in the CDW-based geopolymer binders. Following the characterization of waste concrete aggregates, first, geopolymer mortars have been developed and then, suitable mortar mixtures were incorporated with coarse waste concrete aggregates to develop fully CDW-based concrete mixtures. Special attention has been paid to achieving compressive strength levels adequate for the majority of structural purposes. Durability-related aspects have been investigated for both mortar and concrete mixtures. Our findings showed that completely CDW-based concrete mixtures with compressive strength in the range of 30-40 MPa can be manufactured, although modification in the mixture compositions with traditional supplementary cementitious materials (e.g. ground granulated blast furnace slag) is necessary specifically in achieving improved strength levels and reasonable durability performance.
In the second work package (WP2) of the project, the main emphasis was placed on the design and testing of structural components allowing easy demountability for future reuse. Physical tests of connections between different types of structural components as well as validation via numerical analyses have been performed. In order to develop structural elements in the forms of beam, column, wall, and slab and their connections, half- and real-scale specimens were manufactured and tested. Connections, which are the most vulnerable part of structural elements under the effect of seismic actions, have been of special focus to allow easy demountability and future reuse. During the development phase of connections of different structural elements, dry connections, which are generally obtained by using bolts in connection parts of structural elements instead of welding or wet concrete, were employed instead of wet connections. The proper detailing and design of these connections play a critical role in ensuring a sufficiently-ductile performance under seismic loading. Accordingly, structural performances of the beam-to-column, column-to-base, slab-to-beam, and shear wall-to-base connections were experimentally obtained and validated using finite element simulation against the experimental results. It has been shown that properly designed and manufactured connection details can lead to structural elements with performances similar to those having monolithic connections in seismic regions and this is irrespective of the use of CDW-based green concrete mixtures in the structural elements. The comparison of the experimental results with the numerical predictions indicated that the equations and assumptions in the numerical practices made for conventional reinforced concrete products provide conservative estimations for CDW-based geopolymer concrete products.
In the second work package (WP2) of the project, the main emphasis was placed on the design and testing of structural components allowing easy demountability for future reuse. Physical tests of connections between different types of structural components as well as validation via numerical analyses have been performed. In order to develop structural elements in the forms of beam, column, wall, and slab and their connections, half- and real-scale specimens were manufactured and tested. Connections, which are the most vulnerable part of structural elements under the effect of seismic actions, have been of special focus to allow easy demountability and future reuse. During the development phase of connections of different structural elements, dry connections, which are generally obtained by using bolts in connection parts of structural elements instead of welding or wet concrete, were employed instead of wet connections. The proper detailing and design of these connections play a critical role in ensuring a sufficiently-ductile performance under seismic loading. Accordingly, structural performances of the beam-to-column, column-to-base, slab-to-beam, and shear wall-to-base connections were experimentally obtained and validated using finite element simulation against the experimental results. It has been shown that properly designed and manufactured connection details can lead to structural elements with performances similar to those having monolithic connections in seismic regions and this is irrespective of the use of CDW-based green concrete mixtures in the structural elements. The comparison of the experimental results with the numerical predictions indicated that the equations and assumptions in the numerical practices made for conventional reinforced concrete products provide conservative estimations for CDW-based geopolymer concrete products.
Mineral components arising from CDW are predominantly used in downcycling operations such as non-structural road sub-base/base filling significantly losing the value imparted to these materials. CodeDEMO project has contributed to a better understanding of how resources related to CDW can be used in upcycling operations by increasing the added-value of these materials not only on the basis of innovative and green construction materials but also on structural engineering aspects, extending the project’s reach beyond the current state-of-the-art. The project results are important from multiple aspects of lowering the amount of wastes going to clean landfills, reducing the need for clean raw materials and avoiding destructive demolishment of structures, all of which contribute towards reducing the impact of global warming, thereby having significant and meaningful impact on the research community, industry, policy makers and regulatory authorities and the lay public. The outcomes of CodeDEMO project are also in line with and contribute to nation- and EU-level priorities and policies such as Net Zero Strategy, European Green Deal, European Green and Digital Twin Transition, Circular Economy Action Plan, and Strategy for the sustainable competitiveness of the construction sector and its enterprises.