Dr. Timothy Wangler
Dr. Timothy Wangler
Lecturer at the Department of Civil, Environmental and Geomatic Engineering
Additional information
Timothy Wangler is a postdoctoral researcher and senior research assistant in Physical Chemistry of Building Materials since 2012. His research interests center primarily on the intersection of three fields: chemical engineering, material science, and civil engineering. His education is primarily in chemical engineering, with a bachelor's degree from the New Mexico Institute of Mining and Technology. After working some years in semiconductor manufacturing at Intel Corporation in Rio Rancho, New Mexico, he joined the PhD program at the Princeton University Department of Chemical Engineering, ultimately earning his PhD in 2009 under the guidance of Prof. George Scherer, on the topic of understanding and inhibiting damage to heritage sandstones by swelling clays. He then joined the Laboratory of Building Science and Technology at the Empa in Dübendorf, Switzerland as a postdoctoral researcher, where he researched the topic of leaching of biocides from building facades into surface waters. He then joined the group of Prof. Robert J. Flatt, where he has since expanded his research scope.
Digital Fabrication with Concrete
The digital revolution that has transformed many industries such as manufacturing has yet to take hold in a big way in the construction industry. The recent surge of interest in digital fabrication with concrete (DFC) processes in construction is a consequence of the notion that the construction industry is on the cusp of a true revolution, one that will pave the way to truly industrialized construction. Advances in robotics and the overall trend to digitalization are leading the way. There is great potential to increase productivity in construction while simultaneously allowing for more sustainable, shape-efficient designs.
Concrete is the most widely used manmade material in the world, and with good reason: its raw materials are widely available, the production of its components (most notably cement) is simple and relatively inexpensive, and it transforms from a fluid material to a hardened material that can bear a structural load durably. It is this last quality makes it attractive for DFC processes such as 3D printing, and the major reason for research interest in this topic within PCBM.
The introduction of these technologies raises interesting new challenges due to the more stringent requirements on the material with respect to when and how its rheology must be controlled. In particular, hydration control ("set on demand") creates new process engineering challenges, usually requiring the intermixing of an accelerator just before placement. Having a reliable cement chemistry, as well as the requirement of a matrix-rich material, has led to DFC mixes with high CO2 impact, which negates potential benefits from shape efficiency. Additionally, until now, processing has limited the maximum aggregate sizes of these mixes.
Thus, within the context of the external page NCCR Digital Fabrication, the major thrusts of research on this topic have to do with:
- Minimizing paste content in DFC mixes through better mix design
- Minimizing clinker content within the paste through increased SCM and inert substitutions
Improved mix design includes increasing the maximum aggregate size, which introduces equipment upscaling challenges. Minimizing clinker content means the use of robust accelerators or rheology modifiers, introducing both processing and chemistry challenges. Finally, in addition to this, improving sustainability of DFC processes means also assessing the durability of structures produced via DFC, which is also being investigated within PCBM.
Swelling Clays in Cultural Heritage
Many stones used in buildings and monuments of cultural and historical significance contain clays which swell upon contact with water. This swelling can lead to stresses on the order of the strength of the stone, and also leads to incompatibility with current consolidation treatments. Certain molecules, such as the diaminoalkanes, can reduce swelling in sandstones such as the molasse of the Swiss plateau. Understanding the mechanism of swelling clays as well as the mechanism of swelling inhibitors in these sandstones is an interesting topic, not only for cultural heritage conservation, but also for geotechnical problems such as tunneling and borehole stability. Additionally, how these swelling clays lead to the stresses that lead to damage is not a completely answered question, and an additional focus of research.
Swelling Anhydritic Claystones in Swiss Tunnels
Tunnels in Switzerland and southwest Germany that go through the Gipskeuper formation have been having issues with tunnel floor heave for decades, even centuries. This formation contains anhydrite and clay together, and the floor heave is believed to arise from both swelling of the clay and crystallization pressure from the anhydrite-to-gypsum (ATG) transformation. Above a temperature of approximately 40 C, the solubility of anhydrite is lower than that of gypsum. By running experiments above this temperature, we make use of this novel "thermodynamic switch", and we are able to decouple both swelling phenomena and test chemical inhibition of each process. The project has led to the development and patenting of an ATG inhibitor for tunnel construction under these circumstances.
Transport in Building Materials: Leaching and Ingress
Biocides are often added to the final coatings of exterior finishes to buildings to prevent unsightly and destructive microbial growth. These biocides can eventually find their way into the ecosystem, however, through runoff from wind-driven rain events at the building façade. Understanding the mechanism of biocide transport during and between rain events, as well as other factors such as biocide degradation, is vital to understanding their potential impact to the environment. These biocides are typically added to coatings and then applied, where they are then allowed to dry. This means the coatings function as a de facto controlled release system, and can be modeled as such, as well as ultimately designed.
Concrete Material Science
Concrete Material Science is taught with Prof. dr. Robert J. Flatt, and examines how concrete properties are affected by its microstructure and how its microstructure is controlled by processing and composition. To achieve this, the course comprises a comprehensive presentation of the different techniques used to characterize concrete and its constituents, both in research and construction practice.
Concrete Technology
In the course concrete technology, taught in conjunction with Dr. Martin Bäuml, Dr. Giovanni Martinola, and Felicia Constandopoulos (all of Concretum AG), students receive a deeper understanding of material technology in concrete construction, including the most recent advances. Both the fundamental science behind the technology and the practical implementation of them are emphasized, especially useful for civil engineers who will be designing, specifying and executing concrete structures.
Science and Engineering of Glass and Natural Stone in Construction
The course Science and Engineering of Glass and Natural Stone in Construction is taught in conjunction with Dr. Falk Wittel. The course offers an overview of relevant practical issues and present technological challenges for glass and natural stones in construction. Students gain a good knowledge of the basics of glasses and natural stones, their potential as engineering materials and learn to apply them in the design of civil engineering constructions and to evaluate concepts.