Robert J. Flatt

Last Name

Flatt

First Name

Robert J.

ORCID

0000-0002-5609-8487

Organisational unit

03891 - Flatt, Robert J. / Flatt, Robert J.

Show all metadata

Search Results

Publications 1 - 10 of 97

On sustainability and digital fabrication with concrete
Flatt, Robert J.; Wangler, Timothy (2022)
Cement and Concrete Research
Digital fabrication with concrete has been touted as an avenue to more sustainable construction through more material efficient design, but notably has produced materials with higher carbon footprints and a strong likelihood of reduced durability compared to standard construction. In this short article, a relationship to give a sense of the environmental impact of a structure is introduced, and it is emphasized that shape efficiency is the only unique environmental benefit that digital concrete brings. However, efforts should still continue to bring digital concrete more in line with standard concrete, especially through incorporation of large aggregates and better characterizing the durability. Finally, it is shown that while most 3D printed concretes appear to be overdesigned due to processing requirements, the use of aluminum based accelerators in a 2K system can be beneficial in decoupling buildability from structural strength, allowing greater freedom to lower carbon footprints in mix design.
Processing of Set on Demand Solutions for Digital Fabrication in Architecture
Szabo, Anna; Reiter, Lex; Lloret-Fritschi, Ena; et al. (2019)
Early-age hydration of accelerated low-carbon cements for digital fabrication
Das, Arnesh; Wenger, Cedric; Walpen, Lukas; et al. (2025)
Cement and Concrete Composites
Digital fabrication processes with concrete offer several advantages compared to conventional processes, however, a major criticism with related concrete mixes has been with regard to their high cement paste content and consequent carbon footprint. One of the ways to address this is to reduce ordinary Portland cement (OPC) content in such mixes by using supplementary cementitious materials. This paper reports on such an approach for two different digital fabrication methods: digital casting system and 3D concrete printing. Results focus on the combined use of such low carbon blends with a calcium aluminate cement (CAC) based accelerator. Two such accelerators were studied: one being mainly crystalline based and the other mainly amorphous. Their performance is assessed at different temperatures. It is concluded that crystalline CAC is more suitable for applications above 20 °C while at temperature below 20 °C, amorphous CAC should be preferred. This paper also delves deeper into the effect of amorphous CAC on the hydration of tricalcium silicate present in OPC. It shows that the effect of amorphous CAC on that silicate depends on the OPC content of the system as well as on the type and amount of calcium sulfate used in the accelerator formulation.
Revisiting Folded Forms with Digital Fabrication
Szabo, Anna; Lloret-Fritschi, Ena; Reiter, Lex; et al. (2019)
eCAADeSIGraDi ~ eCAADe SIGraDi 2019. Architecture in the Age of the 4th Industrial Revolution
Robustness of Digital Concrete: Effects of Temperature, Accelerator Type and Dosage
Mahmoudi, Matineh; Wangler, Timothy; Flatt, Robert J. (2024)
RILEM Bookseries ~ Fourth RILEM International Conference on Concrete and Digital Fabrication
Digital fabrication of concrete has increasingly gained attention from scholars and industrial investors during the past several years. However, the proper concrete mix for such applications needs to meet stricter criteria compared to conventional concrete casting, due to the higher process demands. This leads to a shortcoming in this technology, which is that digital concrete mixes are more sensitive to minor variations in mix proportioning, properties of the incoming materials, and environmental conditions such as temperature. 3D printing of concrete, which is one of the main subdivisions of digital concrete, can be further categorized into 1k and 2k systems. This work focuses on 2k systems, which includes a secondary mixing step for the addition of an accelerator, omitted in 1k systems. In this study, the robustness of different accelerating systems was investigated and compared. Two accelerating systems were studied respectively based on Calcium Aluminate Cement pastes (CAC) and Aluminum Sulfate solutions (A$). The accelerated mixes are subjected to dosage as well as temperature variations. The obtained results are discussed in view of enhancing the robustness of digital concrete.
Eggshell Pavilion: a reinforced concrete structure fabricated using robotically 3D printed formwork
Burger, Joris Jan; Aejmelaeus-Lindström, Petrus; Gürel, Seyma; et al. (2023)
Construction Robotics
This paper discusses the design, fabrication, and assembly of the ‘Eggshell Pavilion’, a reinforced concrete structure fabricated using 3D printed thin shell formwork. Formworks for columns and slabs were printed from recycled plastic using a pellet extruder mounted to a robotic arm. The formworks were cast and demoulded, and the finished elements were assembled into a pavilion, showcasing the architectural potential of 3D printed formwork. The Eggshell Pavilion was designed and fabricated within the scope of a design studio at ETH Zurich. The structure was designed using a fully parametric design workflow that allowed for incorporating changes into the design until the fabrication. The pavilion consists of four columns and floor slabs. Each column and floor slab is reinforced with conventional reinforcing bars. Two different methods are used for casting the columns and floor slabs. The columns are cast using ‘Digital casting systems’, a method for the digitally controlled casting of fast-hardening concrete. Digital casting reduces the hydrostatic pressure exerted on the formwork to a minimum, thereby enabling the casting of tall structures with thin formwork. The floor slabs are cast with a commercially available concrete mix, as the pressure exerted on the formwork walls is lower than for the columns. In this research, 3D printed formwork is combined with traditional reinforcing, casting, and assembly methods, bringing the technology closer to an industrial application.
Structural build-up at rest in the induction and acceleration periods of Portland Cement
Michel, Luca; Reiter, Lex; Sanner, Antoine; et al. (2024)
Cement and Concrete Research
Structural build-up in fresh cement paste at rest is characterized by time evolutions of storage modulus and yield stress, which both increase linearly in time during the induction period of hydration, followed by an exponential evolution after entering the acceleration period. Here, we investigate structural build-up by coupling calorimetry and oscillatory shear measurements of Portland Cement at different w/c ratios and in the absence of admixtures, capturing how the storage modulus evolves with changes in cumulative heat. This allows the decoupling of hydration kinetics from the mechanisms dictating build-up at rest. We obtain an exponential relation between stiffness and heat, with the same exponent in both the induction and acceleration periods. This suggests that, at least in the absence of admixtures, the same mechanism dictates build-up at rest in both periods. Since it is understood that C-S-H dictates build-up at rest in the acceleration period, we deduce that the same mechanism holds in the induction period.
Rehabilitating and Rebuilding in Ukraine in the context of CO2 emissions
Troian, Viacheslav; Flatt, Robert J.; Angst, Ueli (2025)
SBE Conference Series ~ Sustainable Built Environment Conference 2025 Zurich - Extended Abstracts
Phase assemblage and microstructure of burnt oil shale-containing blended cements
Boscaro, Federica; Londono-Zuluaga, Diana; Kruspan, Peter; et al. (2025)
CEMENT
Burnt oil shale (BOS), obtained from the combustion of oil shale, is a promising supplementary cementitious material (SCM) based on its chemistry and mineralogy. This paper summarizes the use of BOS and its hydration in blended cements. It presents new data on the effect of combinations of alkali activators and Ca(NO3)2 in blended cements containing 50 % Portland cement (OPC) where BOS is combined with limestone, fly ash and ground granulated blast furnace slag. These chemical admixtures increase the slope of the correlation between compressive strength and heat of hydration of BOS containing mixes, providing an increase in compressive strength from 1 to 7 days for similar heat release to the control system. In contrast, the slope is not affected in absence of BOS. The change is due to a higher volume of hydrates from BOS increased hydration for a given C3S degree of hydration, likely from a less exothermic dissolution of BOS amorphous component. These admixtures increase the reactivity of both BOS and OPC at different curing times and depending on the type of alkali activator. They promote ettringite and portlandite precipitation, inducing a refinement of the microstructure, particularly around BOS particles. The information presented should pave the way to a broader and more effective use of BOS in blended cements with particularly low clinker contents.
Machine Learning-Based Detection of Stone Degradation using TLS, Photographs and HBIM: A Case Study on the Lausanne Cathedral
Tennenini, Camilla; Laasch, Helena; Patankar, Yamini; et al. (2025)
STONE 2025 - Proceedings of the 15th International Congress on the Deterioration and Conservation of Stone, Volume 1 & 2
Historic sandstone structures are vulnerable to environmental degradation, requiring efficient damage assessment and documentation for effective conservation. Traditional manual mapping methods are time-intensive, cost-intensive, and challenging to standardize. Herein we present a semi-automated workflow for damage classification and integration into a historic building information model (HBIM) using terrestrial laser scanning (TLS), orthophotos, and machine learning. A Random Forest model, optimised through forward feature selection and Bayesian hyperparameter tuning, classifies degradation types (contour scaling, biodeterioration, black crust formation and exfoliation) based on geometric and radiometric features. Finally, degradation information is linked to individual stone blocks in the HBIM, and degradation maps can be generated. In a case study on the Lausanne Cathedral, we achieve an overall classification accuracy of 80% using this approach. The results highlight the potential of using machine-learning techniques with TLS data for an efficient and scalable heritage condition assessment.

Publications 1 - 10 of 97

Robert J. Flatt

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results