Periodic Reporting for period 4 - SmartCast (Smart casting of concrete structures by active control of rheology)
Reporting period: 2021-04-01 to 2022-09-30
Concrete production processes do not take full advantage of the rheological potential of fresh cementitious materials, and are still largely labour-driven and sensitive to the human factor. The ERC Advanced Grant project 'SmartCast' proposes a new concrete casting concept to transform the concrete industry into a highly automated technological industry. Currently, the rheological properties of the concrete are defined by mix design and mixing procedure without any further active adjustment during casting. The goal of the 'SmartCast' project is the active control of concrete rheology during casting, and the active triggering of early stiffening of the concrete as soon as it is put in place. The ground-breaking idea to achieve this goal, is to develop concrete with actively controllable rheology by adding admixtures responsive to externally activated electromagnetic frequencies. Inter-disciplinary insights are important to achieve these goals, including inputs from concrete technology, polymer science, electrochemistry, rheology and computational fluid dynamics. In the short term, achieving the active control of the pumping slip layer will have an immediate impact on concrete industry, as this can be applied on pump trucks without interfering with the elements to be cast. In the longer term, making possible concrete casting with active control of flow and stiffening will be a totally new paradigm for concrete industry. Moving from ‘passively’ relying on evolving properties of fresh concrete, to ‘actively’ controlling rheology and stiffening will revolutionize concrete industry and bring quality levels to higher standards. The developed active rheology control will also provide a fundamental basis for the development of future-proof 3D printing techniques in concrete industry. For society, it will mean more reliable construction, with less damage cases and less failures, while better preserving the environment (reduced carbon footprint, reduced noise and vibration levels, reduced exposure of technicians to safety and health risks).
Within SmartCast, two main routes to achieve Active Rheology Control (ARC) and Active Stiffening Control (ASC) have been studied, as schematically summarized in Figure 1.
The first route is based on the concept of magnetorheological fluids (MRF). Magnetizable solid particles are added to the cementitious material, e.g. magnetizable nanoparticles (MNP) consisting of Fe3O4 or more traditional cement-replacing materials like fly ash with some magnetic response. Upon applying a magnetic field, the magnetizable particles can form clusters, inducing stiffening on demand. Alternatively, the acceleration of the magnetizable particles due to the electromagnetic forces temporarily gives the cementitious material some more liquid-like properties. Variable magnetic fields can be applied to actively control rheology, using the magnetizable particles as internal actuators. As a conceptual illustration, Figure 2 shows the window of opportunity for active magneto-rheological control of a cement paste containing magnetisable nanoparticles (MNP). The evolution of the storage modulus in absence of magnetic field is shown as the central curve. When a constant magnetic field is applied, a controlled faster stiffening is obtained as shown by the top curve. In case of a varying magnetic field, a controlled reduced stiffening is obtained as shown by the staggered lower curve. In principle, the area in between these two extreme curves, is the potential field of application for active rheology control for the considered cement paste with MNP.
The second route is the development of switchable superplasticizers. This technology further builds on the working principle of the latest generation of superplasticizers, which are comb copolymers consisting of a backbone with negative charges in view of adsorption onto the surface of cement grains and of side chains in view of providing steric hindrance to disperse cement particles. Instead of using classical polycarboxylate ethers (PCE), additional functionalities are given to the superplasticizers by incorporating responsive elements into the polymer architecture.
One example is a comb copolymer consisting of a classical backbone with negative charges (MAA) and of side chains of a new type, namely TEMPO. This side chain on the one hand can provide steric hindrance, and on the other hand can be triggered by an electric signal to become positively charged. Upon electric triggering, the positive charges of TEMPO+ will counterbalance negative charges form the backbone, reducing the adsorption capacity to the cement grain surface. In this way, a controllable superplasticizer is obtained, enabling active rheology control by moderating the adsorption capacity through external electric signals. The potential of the newly developed switchable superplasticizer is conceptually illustrated in figure 3. Implementing the newly developed admixture, initially without external control signal, leads to a reduced flow curve compared to the reference paste, showing the plasticizing effect. Upon application of a redox signal, pTEMPO is given a positive charge, resulting in pTEMPO+. This is influencing (reducing) the adsorption to the cement grains, and thus the plasticizing effect, as illustrated by the higher flow curve. The dotted area conceptually shows a potential window of operation for the active rheology control by means of the redox-switchable plasticizer.
Another example of a switchable superplasticizer is a magnetizable polymer composite consisting of polymer chains linking MNP (by means of a chelator) to the surface of a cement grain (by means of electrostatic adsorption). These polymers act as a superplasticizer, due to adsorption on the cement surface and steric hindrance by the side chains. By means of an externally applied magnetic field, the MNP will try to cluster in a similar way as the previously mentioned responsive mineral additions, now also involving the cement particles to which the polymers are electrostatically adsorbed. This can provide a strong active stiffening effect.
The SmartCast project successfully reached the intended goals. A laboratory proof of concept has been successfully obtained at paste level, both for the approach using responsive mineral additions and the approach applying switchable responsive plasticizers. This shows the great potential of active rheology control (ARC) and active stiffening control (ASC) of cementitious materials. Nevertheless, further technological and valorisation studies are still needed (and have been initiated) to bring the new technology to the market.
The first route is based on the concept of magnetorheological fluids (MRF). Magnetizable solid particles are added to the cementitious material, e.g. magnetizable nanoparticles (MNP) consisting of Fe3O4 or more traditional cement-replacing materials like fly ash with some magnetic response. Upon applying a magnetic field, the magnetizable particles can form clusters, inducing stiffening on demand. Alternatively, the acceleration of the magnetizable particles due to the electromagnetic forces temporarily gives the cementitious material some more liquid-like properties. Variable magnetic fields can be applied to actively control rheology, using the magnetizable particles as internal actuators. As a conceptual illustration, Figure 2 shows the window of opportunity for active magneto-rheological control of a cement paste containing magnetisable nanoparticles (MNP). The evolution of the storage modulus in absence of magnetic field is shown as the central curve. When a constant magnetic field is applied, a controlled faster stiffening is obtained as shown by the top curve. In case of a varying magnetic field, a controlled reduced stiffening is obtained as shown by the staggered lower curve. In principle, the area in between these two extreme curves, is the potential field of application for active rheology control for the considered cement paste with MNP.
The second route is the development of switchable superplasticizers. This technology further builds on the working principle of the latest generation of superplasticizers, which are comb copolymers consisting of a backbone with negative charges in view of adsorption onto the surface of cement grains and of side chains in view of providing steric hindrance to disperse cement particles. Instead of using classical polycarboxylate ethers (PCE), additional functionalities are given to the superplasticizers by incorporating responsive elements into the polymer architecture.
One example is a comb copolymer consisting of a classical backbone with negative charges (MAA) and of side chains of a new type, namely TEMPO. This side chain on the one hand can provide steric hindrance, and on the other hand can be triggered by an electric signal to become positively charged. Upon electric triggering, the positive charges of TEMPO+ will counterbalance negative charges form the backbone, reducing the adsorption capacity to the cement grain surface. In this way, a controllable superplasticizer is obtained, enabling active rheology control by moderating the adsorption capacity through external electric signals. The potential of the newly developed switchable superplasticizer is conceptually illustrated in figure 3. Implementing the newly developed admixture, initially without external control signal, leads to a reduced flow curve compared to the reference paste, showing the plasticizing effect. Upon application of a redox signal, pTEMPO is given a positive charge, resulting in pTEMPO+. This is influencing (reducing) the adsorption to the cement grains, and thus the plasticizing effect, as illustrated by the higher flow curve. The dotted area conceptually shows a potential window of operation for the active rheology control by means of the redox-switchable plasticizer.
Another example of a switchable superplasticizer is a magnetizable polymer composite consisting of polymer chains linking MNP (by means of a chelator) to the surface of a cement grain (by means of electrostatic adsorption). These polymers act as a superplasticizer, due to adsorption on the cement surface and steric hindrance by the side chains. By means of an externally applied magnetic field, the MNP will try to cluster in a similar way as the previously mentioned responsive mineral additions, now also involving the cement particles to which the polymers are electrostatically adsorbed. This can provide a strong active stiffening effect.
The SmartCast project successfully reached the intended goals. A laboratory proof of concept has been successfully obtained at paste level, both for the approach using responsive mineral additions and the approach applying switchable responsive plasticizers. This shows the great potential of active rheology control (ARC) and active stiffening control (ASC) of cementitious materials. Nevertheless, further technological and valorisation studies are still needed (and have been initiated) to bring the new technology to the market.
At the end of SmartCast, a clear scientific break-through can be confirmed. The lab-scale proof of concept of active rheology control, based on the newly developed switchable plasticizers is a major scientific breakthrough. This was the first time ever switchable plasticizers have been used to adjust concrete rheology in an active way, on demand. Also the further study of active rheology control based on responsive mineral particles can be considered as a scientific breakthrough, going far beyond some preliminary ideas previously published in literature. As a side result of the development of switchable plasticizers, the project also enabled the development of a new type of plasticizers, called PCA (poly carboxylate amines), with alternative side chains compared to PCE (poly carboxylate ethers).