Periodic Reporting for period 1 - TexTaConStruct (Textile-reinforced tailored concrete structures)
Période du rapport: 2021-10-01 au 2023-01-31
There is a compelling need to urgently reduce carbon emissions. A huge part of carbon emissions worldwide can be attributed to the construction industry, of which the concrete industry is responsible for a great part thereof. The Textile-Reinforced Tailored Concrete Structures (TexTaConstruct) project addressed a potential reduction of building industry-related carbon emissions through the use of textile reinforcement in combination with advanced structural engineering.
Textile reinforcement is characterised by high strength and excellent durability, which has recently enabled the creation of lightweight filigree high-performance structures. The concrete used in combination with such reinforcement typically has a high strength. This is due to the small mesh width of the textile reinforcement, which only allows for the use of small aggregate sizes. Thus, a higher binder content is needed in the concrete mix design. Moreover, the concrete grade is typically chosen according to the most stringent requirements that occur within a structure. While the high-strength concrete complements the high-performance reinforcement in those critical areas, such high-performance concrete is not needed elsewhere. Considering that high-strength concrete typically requires a higher cement content this is coupled with high carbon emissions due to the CO2 intensity of cement production. Hence, more sustainable structures can be achieved if the concrete mix is graded within a structural element according to the performance requirements. The overall objective of the Fellowship was the realisation of the full potential of such functionally graded TRC structures to reduce carbon emissions through the explicit exploitation of the inert characteristics of the reinforcement material and cement minimisation.
Textile reinforcement is characterised by high strength and excellent durability, which has recently enabled the creation of lightweight filigree high-performance structures. The concrete used in combination with such reinforcement typically has a high strength. This is due to the small mesh width of the textile reinforcement, which only allows for the use of small aggregate sizes. Thus, a higher binder content is needed in the concrete mix design. Moreover, the concrete grade is typically chosen according to the most stringent requirements that occur within a structure. While the high-strength concrete complements the high-performance reinforcement in those critical areas, such high-performance concrete is not needed elsewhere. Considering that high-strength concrete typically requires a higher cement content this is coupled with high carbon emissions due to the CO2 intensity of cement production. Hence, more sustainable structures can be achieved if the concrete mix is graded within a structural element according to the performance requirements. The overall objective of the Fellowship was the realisation of the full potential of such functionally graded TRC structures to reduce carbon emissions through the explicit exploitation of the inert characteristics of the reinforcement material and cement minimisation.
To ascertain the promise of functionally graded TRC as a route for CO2 reduction, a multi-dimensional optimisation strategy that was pursued throughout the project that ranged from (a) investigations into the early age properties of layered concrete cast wet on wet, (b) quantification of the mechanical performance of functionally graded concrete, (c) fabrication techniques to combine concrete layers and TRC, (d) parametric design studies where a stepwise grading of concrete was implemented within a structure and (e) numerical modelling of functionally graded TRC beams to gain a better understanding of the structural behaviour.
Different mixes were developed throughout the project, with a wide spectrum of compressive strength and cement consumption, that allowed fur a stepwise grading of the concrete in TRC structures. The uniqueness of the approach followed here is, that the same raw materials were used where only the quantities varied, which facilitates the manufacturing process and reduces logistical challenges. The placement of multiple layers of concrete enables to grade the concrete according to the requirements within a structure, however, it also increases complexity. Results from the project demonstrate the high variability of stresses due to restraint shrinkage in dependency of different boundary conditions. These different influences were studied so that optimal settings, e.g. delay time of casting, were determined. The potential of a functional grading to increase performance was demonstrated on bond tests, where it was shown that when the reinforcement is fully enclosed by a high-strength mix, an increase in splitting resistance can be expected.
The functional grading in TRC components was subsequently realised on a structural level. Starting from an initial design of a lightweight TRC structure that was taken from literature, a stepwise refinement of the concrete grade was implemented, so that all requirements for the structure were still fulfilled. It was shown that such a functional grading would result in a reduction of 73.8 % of the cement mass compared to the original design. Moreover, inspired by an experimental campaign from members of Cambridges Concrete Infrastructure Research Group, comparative numerical calculations showed, that through the judicious replacement of concrete in an RC beam with a novel low-strength TRC shear panel, not only the ultimate capacity of the beam could be increased but also the structural stiffness could be retained at a high level. Finally, methods for the fabrication of functionally graded TRC beams were introduced, showcasing how functionally graded TRC beams can be produced.
The work cumulated in a tailored TRC prototype, where it was proven that a significant amount of material, and in particular cement, can be saved when designing concrete structures, while simultaneously achieving a high load-bearing capacity.
Different mixes were developed throughout the project, with a wide spectrum of compressive strength and cement consumption, that allowed fur a stepwise grading of the concrete in TRC structures. The uniqueness of the approach followed here is, that the same raw materials were used where only the quantities varied, which facilitates the manufacturing process and reduces logistical challenges. The placement of multiple layers of concrete enables to grade the concrete according to the requirements within a structure, however, it also increases complexity. Results from the project demonstrate the high variability of stresses due to restraint shrinkage in dependency of different boundary conditions. These different influences were studied so that optimal settings, e.g. delay time of casting, were determined. The potential of a functional grading to increase performance was demonstrated on bond tests, where it was shown that when the reinforcement is fully enclosed by a high-strength mix, an increase in splitting resistance can be expected.
The functional grading in TRC components was subsequently realised on a structural level. Starting from an initial design of a lightweight TRC structure that was taken from literature, a stepwise refinement of the concrete grade was implemented, so that all requirements for the structure were still fulfilled. It was shown that such a functional grading would result in a reduction of 73.8 % of the cement mass compared to the original design. Moreover, inspired by an experimental campaign from members of Cambridges Concrete Infrastructure Research Group, comparative numerical calculations showed, that through the judicious replacement of concrete in an RC beam with a novel low-strength TRC shear panel, not only the ultimate capacity of the beam could be increased but also the structural stiffness could be retained at a high level. Finally, methods for the fabrication of functionally graded TRC beams were introduced, showcasing how functionally graded TRC beams can be produced.
The work cumulated in a tailored TRC prototype, where it was proven that a significant amount of material, and in particular cement, can be saved when designing concrete structures, while simultaneously achieving a high load-bearing capacity.
During the Fellowship it was addressed how a functional grading of the concrete can be realised most effectively in TRC structures. This approach is unique and the results of the fellowship added significant knowledge beyond the current state of the art. Overall, a multidimensional optimisation routine was implemented, to seek concrete grading options for TRC structures such that all the requirements in the serviceability and ultimate limit state are fulfilled, while simultaneously the cement consumption and hence the embodied CO2 is reduced to a minimum. The project yielded substantial results, which have already been published in two Q1 journals during the Fellowship. Additional three papers in tandem with members from CIRG are currently in preparation and at advanced stages. These papers address the behaviour of functionally graded TRC at both the material and structural level. The expectation is that all of these manuscripts will be published in 2023. Moreover, a state-of-the-art paper on the bond behaviour of TRC that evolved from the Fellows involvement in RILEM TC 292: “Mechanical characterisation of textile-reinforced concrete” is almost finished.
The expertise that the Fellow has gained in the course of the Fellowship is valued by the scientific and professional community. He was recently elected by the Austrian Society for Construction Technology as Head of a working group that deals with the application of non-metallic reinforcement in new build structures. The mid-term goal is to establish a guideline on the design and construction of concrete structures reinforced with such materials. Moreover, the innovative research paths that were pursued throughout the Fellowship have already created a significant impact. New research projects that build upon the fundamental knowledge gained during the Fellowship were successfully acquired. One of the projects is an industry collaboration that aims at creating resource-efficient TRC elements, that can be produced in large volumes in a prefabrication plant. With these projects, a further step towards a sustainable transformation of the building industry will be taken.
Climate protection measures are a vital part of the UN Sustainable Development goals. The research that was conducted during the course of this Fellowship as well as the areas of research that will be explored in the future, address these challenges by following a high-performance principle that we must use less material and that we must use material more efficiently. The results of the Fellowship clearly highlight the great potential of that principle.
The expertise that the Fellow has gained in the course of the Fellowship is valued by the scientific and professional community. He was recently elected by the Austrian Society for Construction Technology as Head of a working group that deals with the application of non-metallic reinforcement in new build structures. The mid-term goal is to establish a guideline on the design and construction of concrete structures reinforced with such materials. Moreover, the innovative research paths that were pursued throughout the Fellowship have already created a significant impact. New research projects that build upon the fundamental knowledge gained during the Fellowship were successfully acquired. One of the projects is an industry collaboration that aims at creating resource-efficient TRC elements, that can be produced in large volumes in a prefabrication plant. With these projects, a further step towards a sustainable transformation of the building industry will be taken.
Climate protection measures are a vital part of the UN Sustainable Development goals. The research that was conducted during the course of this Fellowship as well as the areas of research that will be explored in the future, address these challenges by following a high-performance principle that we must use less material and that we must use material more efficiently. The results of the Fellowship clearly highlight the great potential of that principle.