Auxetic Cementitious Composites by 3D Printing

Project Information

ACC-3D

Grant agreement ID: 101041342

DOI

10.3030/101041342

EC signature date 8 March 2022

Start date 1 April 2022

End date 31 March 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 498 201,00

EU contribution

€ 1 498 201,00

Coordinated by

TECHNISCHE UNIVERSITEIT DELFT
Netherlands

Periodic Reporting for period 1 - ACC-3D (Auxetic Cementitious Composites by 3D Printing)

Reporting period: 2022-04-01 to 2024-09-30

Summary of the context and overall objectives of the project

In ACC-3D I propose a completely new class of cementitious composite materials. I aim to develop cementitious composites with damage resistant behaviour and high ductility which can absorb at least 2 times more energy compared to current cementitious composites during deformation and fracture. This will provide important civil engineering structures such as nuclear power plants and protective structures, which demand high level of safety and functionality, with significantly better resistance to earthquakes and impacts.
In current building materials and structures, the role of reinforcement is passive: it reacts to cracks propagating in the cementitious matrix and arrests them. As a result, damage in the system is needed in order to activate the reinforcement which might negatively affect the functionality of the structure after the hazard. I will take advantage of additive manufacturing to create complex reinforcement architectures with a negative Poisson’s ratio. I believe that such reinforcement, due to its negative Poisson’s ratio, can enable active role of reinforcement and work together with the brittle cementitious matrix already before cracking and damage, something that has never been attempted before. This will result in paradigm shift in building materials and structures, bringing the effectiveness of reinforcement to the next level and enabling that with the same constituent materials (matrix and reinforcement) the performance of materials and structures is perfected. To achieve this, I need to:
1. Understand and predict the impact of 3D printing techniques and resulting imperfections on the mechanical properties of reinforcement, reinforcement architecture and its auxetic behavior.
2. Understand, predict and tailor the bond between 3D printed reinforcement and cementitious matrix.
3. Understand and tailor the composite action of auxetic reinforcement and cementitious matrix.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work so far has focused on the three objectives described above as follows:
1. It is well known that 3D printed parts have imperfections resulting from the layer-by-layer nature of most printing processes. We have developed a computer model which can predict the mechanical behavior of such 3D printed polymeric parts while taking these imperfections into account. This is extremely important because, as our models show, considering these parts as perfect solids would result in overestimation of their stiffness and (especially) strength, which can result in non-conservative designs of 3D printed parts.
2. Bonding between reinforcement and concrete is crucial for their cooperation. However, mechanical bonding between 3D printed polymers and concrete is very weak. We are developing and testing ways of improving this bond by coating the reinforcement and thereby adding artificial "roughness", which should result in stronger cementitious composites.
3. The 3D printed reinforcement and the concrete both have good mechanical properties in some sense. The ambition of this project is to combine them in such a way that the composite properties (for example energy absorption capacity) are better than the sum of the parts. We have tested different combinations of reinforcements, including different designs and different polymers, together with cementitious matrices. Some combinations do indeed fulfill our ambition, while others are unfortunately not successful. We have made initial steps in understanding the composite action of our composites, but will expand on this further in the coming period.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In the field of concrete materials, the work performed in terms of material structure optimization (generative deep neural networks and reinforcement design) is the first of its kind. Furthermore, our combination of a soft auxetic reinforcement printed using a deformable polymer (TPU) with a cementitious matrix has shown unique properties which have never been achieved before: extremely high deformability coupled with strain hardening behavior in compresson. This was something completely unexpected for us, but now we are thinking of possible applications of this material.
In addition, our two-scale approach of modelling mechanical properties of 3D printed (FDM) lattices, which considers printing orientations explicitly in the formulation, is to the best of our knowledge the first of its kind.
Finally, our ongoing study of printed reinforcement-concrete bond and ways of improving it has never been attempted before. Using such improvement in our ACC’s may further improve their mechanical performance, but this will be validated using our models before further laboratory experiments.

(a) Deformation and damage mode of the ACC (T20) under uniaxial compression at different strain, (b)

Deformation and damage mode of the printed auxetic structures with increasing compressive strain