Mirza Abdul Basit Beigh
Bio: Mirza Abdul Basit Beigh is an academic researcher from Dresden University of Technology. The author has contributed to research in topics: Cement & Cementitious. The author has an hindex of 4, co-authored 4 publications receiving 63 citations.
TL;DR: In this paper, the structural build-up of concrete pastes of varying compositions and rheological properties is investigated, and it is demonstrated that applying low shear rates over short measurement periods does not always result in the achievement of flow-onset in stiffer cementitious materials, commonly used in digital construction.
Abstract: As a first step toward characterising structural build-up of high-strength, printable concrete mixes, the structural build-up of cement pastes of varying compositions and rheological properties is investigated. It is demonstrated that applying low shear rates over short measurement periods does not always result in the achievement of flow-onset in stiffer cementitious materials, commonly used in digital construction. For such materials, a characteristic delay exists before the effective shear rate reaches the applied shear rate. This leads to effective strains in the materials tested and consequently to the erroneous characterisation of structural build-up. A strain-based approach is suggested here as a more appropriate method for characterising structural build-up in the case of stiff materials. Maintaining a low, constant shear rate among various measurements is not necessary if the total effective strain is kept constant. Investigations on pastes with different compositions show that pastes in which a portion of the cement was replaced with micro-silica and fly ash exhibited high structuration rate. The use of secondary cementitious materials (SCM) appears to be similarly appropriate measure to make cementitious materials ‘printable’ when compared to using set-accelerators, in the absence of inline mixing of accelerators in the printhead.
TL;DR: In this article, a prospective approach to conduct sustainability assessment based on the life cycle of 3D printed structures is presented, which also highlights the importance of considering the functional requirements of the mixes used for 3D printing.
Abstract: This paper explores the sustainability aspects of binders used in concrete 3D concrete printing. Firstly, a prospective approach to conduct sustainability-assessment based on the life cycle of 3D printed structures is presented, which also highlights the importance of considering the functional requirements of the mixes used for 3D printing. The potential of the material production phase is emphasized to enhance the sustainability potential of 3DCP by reducing the embodied impacts. The literature on the different binder systems used for producing 3D printable mixtures is reviewed. This review includes binders based on portland cement and supplementary cementing materials (SCMs) such as fly ash, silica-fume and slag. Also, alternative binders such as geopolymer, calcium sulfo-aluminate cement (CSA), limestone calcined clay cement (LC3) and reactive magnesium oxide systems are explored. Finally, sustainability assessment by quantifying the environmental impacts in terms of energy consumed and CO2 emissions of mixtures is illustrated with different binder systems. This paper underlines the effect of using SCMs and alternative binder systems for improving the sustainability of 3D printed structures.
TL;DR: In this article, Limestone Calcined Clay Cement (LC3) was used to produce sustainable high-strength strain-hardening cement-based composites (HS-SHCC).
Abstract: High-strength strain-hardening cement-based composites (HS-SHCC) demonstrate excellent mechanical and durability properties. However, high cement content typical to HS-SHCC results not only in high carbon footprint, but also in excessive hydration heat and severe autogenous shrinkage. In this investigation, Limestone Calcined Clay Cement (LC3) was used to produce sustainable HS-SHCC. The LC3 substitution resulted in higher energy consumption during mixing and in shorter setting times of the fresh, plain matrices. Although the LC3 substitution slightly reduced the compressive strength, the formation of highly polymerized C-A-S-H gel and abundant ettringite benefited the flexural strength of the plain matrices. Additionally, single-fiber pullout experiments showed that the use of LC3 led to increased fiber-matrix bond strength and pullout energy. Finally, the replacement of Portland cement by LC3 resulted in HS-SHCC with similar mechanical performance to the reference composite, indicating a high potential for using LC3 in high-performance cement-based composites.
01 Jan 2020
TL;DR: In this paper, the structural build-up of LC3 paste was investigated by using the single batch testing approach, and two different calcined clays (CC), one from India and one from Germany, were studied, which were characterized by 58 and 66% amorphous phase, respectively.
Abstract: Ensuring sustainability of printable concretes while complying with the complex requirements to their rheological properties in the fresh state is challenging yet absolutely essential. In this context, the limestone calcined clay cement (LC3) is of high relevance. In the study at hand, the structural build-up of LC3 paste was investigated by using the single batch testing approach. Two different calcined clays (CC), one from India and one from Germany, were studied, which were characterized by 58 and 66% amorphous phase, respectively. Both CCs enhanced the static yield stress of the cementitious materials, showing benefits of their use for digital concrete construction. However, the structural build-up of LC3 made with Indian CC was significantly more pronounced in comparison with that made of the German CC. Most likely, such quick and intense structural build-up can be attributed to the presence of kaolinite in the Indian CC which interacts with the high-range water-reducing admixture used in a particular way.
TL;DR: In this paper, the authors investigated the influence of binder composition and time interval between layers on layer-interface strength in 3D-printable cement-based compositions (3PCs).
Abstract: Interfaces between layers in 3D-printed elements produced by extrusion-based material deposition were investigated on both macro- and micro-scales. On the macro-scale, compression and flexural tests were performed on two 3D-printable cement-based compositions (3PCs), namely Mixtures C1 (with Portland cement as sole binder) and C2 (containing pozzolanic additives) at testing ages of 1 day and 28 days. The influences of binder composition and time interval between layers on layer-interface strength were critically analyzed. The investigated time intervals were 2 min, 10 min and 1 day. The investigations revealed that Mixture C2 exhibited lower degrees of anisotropy and heterogeneity as well as superior mechanical performance in comparison to Mixture 1. In particular, Mixture C2 showed a less pronounced (below 25%) decrease in interface bond strength as observed in flexural tests for all time intervals under investigation. In contrast, the decrease in flexural strength measured for C1 specimens amounted to over 90% due to the higher porosity at the interfaces of the printed concrete layers. Microscopic observations supported the findings of the macroscopic investigations. SEM images also delivered additional information on morphology of interfacial defects as well as “self-healing”.
TL;DR: In this article, a comprehensive overview of the underlying physics relevant to an understanding of materials processing during the various production steps in extrusion-based 3D concrete printing (3DCP) is presented.
Abstract: This article offers a comprehensive overview of the underlying physics relevant to an understanding of materials processing during the various production steps in extrusion-based 3D concrete printing (3DCP). Understanding the physics governing the processes is an important step towards the purposeful design and optimization of 3DCP systems as well as their efficient and robust process control. For some processes, analytical formulas based on the relevant physics have already enabled reasonable predictions with respect to material flow behavior and buildability, especially in the case of relatively simple geometries. The existing research in the field was systematically compiled by the authors in the framework of the activities of the RILEM Technical Committee 276 “Digital fabrication with cement-based materials”. However, further research is needed to develop reliable tools for the quantitative analysis of the entire process chain. To achieve this, experimental efforts for the characterization of material properties need to go hand in hand with comprehensive numerical simulation.
TL;DR: The article at hand evaluates the state-of-the-art with respect to these requirements and presents the CONPrint3D concept for on-site, monolithic 3D-printing as developed at the TU Dresden.
Abstract: The construction industry faces severe problems resulting from low productivity and increasing shortages of skilled labor. The purposeful digitalization and automation of all relevant stages, from design and planning to the actual construction process appears to be the only feasible solution to master these urgent challenges. Additive concrete construction has a high potential to be a key part of the solution. In the first place, technologies are of interest which would enable large-scale, on-site manufacturing of concrete structures in accordance with the demands of contemporary architectural and structural design. The article at hand evaluates the state-of-the-art with respect to these requirements and presents the CONPrint3D concept for on-site, monolithic 3D-printing as developed at the TU Dresden. This concept is driven by the demands and boundary conditions of construction practice. It complies with common architectural norms, valid design codes, existing concrete classes and typical economic constraints. Furthermore, it targets the use of existing construction machinery to the highest possible extent. The interdisciplinary team of authors illuminates various perspectives on the new technology: those of mechanical engineering, concrete technology, data management, and construction management. Some representative results of completed work in these fields are presented as well.
TL;DR: In this paper, an analytical model based on the novel rheological characterisation of a material is presented as a method for quantifying the buildability performance of a 3D printable concrete/mortar.
Abstract: Concrete structures are 3D printed in the plastic state, therefore emphasis should be placed on the rheological characterisation of these materials to ensure that they are appropriate for 3D printing as well as for quality control. In this research, an analytical model based on the novel rheological characterisation of a material is presented as a method for quantifying the buildability performance of a 3D printable concrete/mortar. Structural instability of a freshly printed object e.g. elastic buckling is not accounted for as this model is only based on physical nonlinearity, in particular plastic yielding. The failure mechanism is based on the Mohr-Coulomb failure criterion, and incorporates Tresca and Rankine limit functions, dependent on the degree of confinement. The model is considered a lower bound theorem as stress redistribution occurs in the printed filament layers. The model is verified via an experimental study that yields a conservative error of
TL;DR: In this article, a rheological thixotropy model for 3D printing of concrete is presented, which accounts for both physical and chemical influences on a material's microstructure, denoted by re-flocculation and A t h i x (structuration) respectively.
Abstract: This paper presents a novel rheological thixotropy model that specifically appertains to the characterisation of materials that are suitable for 3D printing of concrete (3DPC). The model accounts for both physical and chemical influences on a material’s microstructure, denoted by R t h i x (re-flocculation) and A t h i x (structuration) respectively. Rheological analyses are performed on a reference material with varying superplasticizer (SP) and nano-silica (nS) dosages in order to determine their effects on the aforementioned parameters. Specific focus is placed on the re-flocculation thixotropy mechanism. The advantages of adding nanoparticles to concrete for 3DPC is practically validated by printing circular hollow columns until failure occurs. The result is supported by the thixotropy model, which is applied to the materials that are used for the 3DPC tests. It is concluded that, for this study, R t h i x is a better measure of thixotropy behaviour that is suitable for 3DPC than A t h i x .