Date of Award

December 2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Konstantin Sobolev

Committee Members

Nikolai Kouklin, Marina Kozhukhova, Xiaoli Ma, Habib Tabatabai, Jian Zhao

Keywords

3D printing, 4D printing, Auxetic concrete, Fly ash beneficiation, Magnetorheology, Nano-particles

Abstract

Existing concrete technology relies on the use of considerable volumes of raw materials, large energy consumption and so associated with severe corresponding environmental impacts. This impact is the driving force for the development of sustainable concrete including a wide range of concrete with supplementary cementitious materials and advanced manufacturing. Recent developments in the field are further inspired by the digital concrete based on 3D printing (3DP) technology which require tailor-made concrete mixtures. The main challenge for 3D printing of concrete is to develop printable ink material, thus this research focuses on characterisation of cementitious materials based on smart materials-materials that respond to specific stimuli and can be tuned as needed. The 3DP using smart material or resulting in a smart materials response is termed as 4D printing (4DP). The smart materials used in this research are tuned for the magnetorheological and auxetic responses, where the former controls the green strength while the latter controls the mechanical response of the hardened composite based on of the proposed cementitious ink. The design methodology for the cementitious ink and auxetic concrete is proposed here, along with supporting experimental data based on experiment planning approach as no specific standards or guidelines are available yet for the design of new composites.

Systematically designed cement based mixtures incorporating various proportions of portland cement (PC), high-ferrous Class-F fly ash (FA), nano-silica (NS), and nano-alumina (NA) were characterized for rheological response with and without the application of a magnetic field in order to better understand the effects of potential doping of cement with magnetic material for application in ‘4D-printing’ of cementitious ‘smart materials’ (SM). Control groups doped with industrial-grade magnetite powder (commonly used as pigment) were likewise mixed and characterized to provide contrast to low cost ferromagnetic components based on beneficiated coal-combustion byproduct fly ash. Mixtures supplemented with ferromagnetic particles had demonstrated the amplified yield stress when exposed to the magnetic field, leading to non-Newtonian rheological response exhibiting ‘sticky particles’ paradigms as discussed herein. Further, control portland cement systems were doped with cobalt powder at varying dosage to study the effect of strong ferromagnetic dopant on yield stress and stiffening stress. In order to develop a sustainable printable ink, ferromagnetic particles were extracted from fly ash using fly ash beneficiation technique, and were characterized for rheological and magnetorheological response. The heat of hydration, X-ray diffraction for individual components and products of the hydration, and compressive strength parameters were used to characterize the proposed cementitious inks. These results suggest that the idea of utilizing an applied magnetic field to modify the flow and slump of cementitious materials extruded through 3D-printing apparatus is worthy of further pursuit and development. In addition, the ferromagnetic particles used in this smart mix composition did not influence cement hydration or compressive strength, however, the applied magnetic field slightly accelerated the hydration process of portland cement.

Another smart material approach used in this research was focusing on the development of auxetic concrete elements that exhibits a negative Poison's ratio due to it's geometrical configuration. Based on the principle of origami and kirigami, the geometry of the auxetic concrete was designed. The nano-engineered fiber-reinforced cement composites were used to create the auxetic samples and were tested to confirm their auxetic behavior. The result of this research provided a substantial confidence in the potential of additive manufacturing and the use of auxetic concrete contributing to a broader practical application of 4DP. This research enabled to establish the theoretical framework and fundamental understanding of magnetorheological cementitious ink materials with ultimate active control of rheological behavior, the formation of patterned microstructures as required for an auxetic response, and improved fracture toughness capable of scaling up to 4D printing of smart origami and kirigami (OAK)-oriented structures. The advancement of engineered cementitious inks based on ferromagnetic nano-particles, nano-fibers, and micron-sized powders combined with magnetite-rich fly ash particles can result in a smart rheological response of the ink, enabling immediate on-demand stiffening, the formation of “patterned” microstructures, and accelerated strength development under short-term electro-magnetic (EM) fields as required for the long-term auxetic response of structural elements. The promising outcome of this research along with future study will led to the development of EM-induced on-demand stiffening and strength development of digitally-deposited cementitious ink materials shall represent a foundational paradigm shift in the approach and methodology of additive manufacturing which will be applicable to a range of auxetic biomaterials, ceramics, and concrete enabling the materialization of future cyber infrastructure with capabilities to deploy permanent structures and habitations here on earth, underwater, up to the Moon, Mars, and beyond.

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