3-D printing of concrete is becoming an attractive option for construction because of its several unique advantages. These sessions are intended to let researchers, engineers, designers, constructors/contractors and students obtain a ringside view of the global advances happening in this rapidly advancing field. The sessions will provide new information on 3-D printable binders, their characteristics, processing techniques, and test methods for 3-D printed components. Details on recent large-scale 3-D printers, efforts on developing protocols, and aspects of importance related to material design and specifications will be covered.
(1) To familiarize the research community with latest research on 3D printing of cementitious materials;
(2) To understand the fundamental mechanisms influencing early-age behavior and its control in extrusion-based 3D printing
(3) To elucidate the influence of microstructure on the properties of 3D printing of cementitious materials;
(4) To explore modifications in cement-based materials to better tailor them for 3D printing.
This session has been AIA/ICC approved for 2 CEU/PDH credits.
Binary and Ternary-blended Systems as Means to Tailor the Structural Build-up of Cementitious-based Matrices for 3-D Concrete Printing
Presented By: Wilson Ricardo Da Silva
Affiliation: Danish Technological Institute
Description: This presentation provides insights to researchers and engineers working on material development for extrusion-based 3D Concrete Printing (3DCP). Our main goal is to share experiences and results on the use of blended binder systems to tailor concrete buildability, which is a key characteristic to increase the vertical production rate in 3DCP. This characteristic is strictly related to the cementitious matrix’s early-age structural build-up and strength development. In our presentation, we will walk through an experimental program focused on the characterization of the structural build-up of cementitious-based mortars using oscillatory rheometry tests. The suggested test protocol was developed by the Danish Technological Institute in collaboration with Imerys Aluminates. The evaluated binder systems comprise a blend of Ordinary Portland Cement (OPC), Calcium Aluminate Cement (CAC), and Calcium Sulphate (C$). The former serves as a basis for a retarded mortar, whereas the latter one’s help modulate the matrix’s structural build-up for a given structural build-up demand. In other words, CAC and C$ serve as hydration modifiers for the OPC system. Through the suggested experiments, we identified the structural build-up curves for mortar compositions with various dosages of OPC+CAC (binary systems) or OPC+CAC+C$ (ternary systems). These curves allowed us for tailoring the mortar composition for a case study where 3DCP was used to produce elements at vertical build rates ranging from 0.85 to 1.35 m/h (2.78 to 4.42ft/h). The overall results show that both binary and ternary-blended binder systems help modulate the matrix’s structural build-up. Moreover, the oscillatory rheometry characterization helps provides information that helps linking material properties to design and 3DCP process requirements. While the presented results give valuable insights into the link materials-process, complementary investigations are suggested to further validate our findings.
Using Hydration Control for Digital Fabrication Processes - Controlling Structural Build-up
Presented By: Lex Reiter
Affiliation: ETH Zürich
Description: With the growing interest in digital fabrication technologies employing concrete, a new set of challenging questions has arisen with respect to material control. Increasingly early age strength and its development are emphasized as many processes require concrete to sustain its own weight and subsequently, as more layers are placed, layers placed on top. In this work we show how such strength build-up is achievable by controlling hydration rate, by triggering hydration in a mixing chamber just before concrete placing, using combinations of set retarders and set accelerators. This concept is then practically applied to processes such as slip forming, layered extrusion, spraying, to different binders depending on process specific strength development requirements and verified with early age rheology characterization methods such as penetration.
Influence of Internal Architecture of 3-D-Printed Elements on Microstructure, Compressive Strength and Fracture Behavior of Cement-based Materials
Presented By: Jan Olek
Affiliation: Purdue University
Description: This presentation will focus on mechanical properties and fracture behavior of 3D-printed cement-paste elements with two types of nature-inspired internal architectures: “lamellar” and “Bouligand”. The cement paste elements were fabricated via layer-by-layer 3D-printing process that results in formation of interfaces between the individual filaments. In addition, companion (control) specimens were produced using the traditional casting technique. Prior to mechanical testing, both, the 3D-printed and the cast elements were examined by micro-CT tomography technique to obtain size and spatial distribution information regarding porosity within the filaments and at the interfaces between individual layers.
The mechanical properties (compressive strength and work-of-failure) of 3D-printed and cast elements were evaluated and analyzed in terms of the role of interfaces and internal architecture. It was found that interfaces created during the 3D-printing process have the following effects: (i) they induce connectivity between the pores in the microstructure, (ii) they introduce anisotropy of mechanical properties and alter load-displacement response of 3D-printed elements compared to cast elements, and (iii) they promote microcracking and crack twisting (in specimens with Bouligand architecture).
In summary, this research revealed that the ability to control the internal architecture of the elements via 3D-printing can be used to indirectly control their microstructure, to tailor their mechanical response, and to enhance the fracture properties of inherently brittle hardened cement paste materials.
How Clay Particulates Affect Shear Jamming and the Coiling Stability of Yield Stress-matched Suspensions
Presented By: Gaurav Sant
Affiliation: University of California, Los Angeles
Description: The remarkable increase in the flow resistance of dense suspensions (jamming) can hinder 3D-printing processes on account of flow cessation and filament fragility in the extruder. Understanding the nature of rheological changes is critical to tailor flow conditions or to design flow modifiers for 3D-printing. Therefore, this paper elucidates the influences of clay particulates on controlling jamming and shape stability of dense cementitious suspensions that typically feature poor printability. A rope coiling method with varying stand-off distances was used to probe buckling stability and filament fracture of dense suspensions that undergo stretching and bending during deposition. The contributions of flocculation and short-term stiffening on the kinetics of structure formation was deconvoluted using a stepped isostress method. It is shown that the shear stress features divergence with a power-law scaling when the particle volume fraction approaches the jamming limit. Such a power-law divergence of the shear stress is decreased by a factor of nearly 10 with increasing clay dosage. Such behavior in clay-containing suspensions arises from decreasing relative packing fraction and forming fractally-architected aggregates, whose uniform arrangement and collective movement control shear jamming and suspension homogeneity, thereby imparting greater buckling stability. These insights create new understanding and methods for assessing and controlling shear jamming behavior during slurry-based 3D-printing processes.
Assessment of Extrudability and Buildability of 3-D Printable Concrete
Presented By: Manu Santhanam
Affiliation: Indian Institute of Technology Madras
Description: Research on 3D printing at IIT Madras is currently focusing on understanding the material characteristics required for printability. Apart from studying the factors governing the choice of specific materials, the assessment of phase separation in concrete under the application of pressure, and the quantification of the early age structural build up is an objective of the current phase of study. The phase separation is studied using a modified version of the pressure bleed test typically adopted for grouts, which leads to a parameter called desorptivity. Experiments have shown that printability is affected significantly by the desorptivity characteristics exhibited by different blends of materials. Further, the early age mechanical response is studied with the measurement of green strength and modulus in a uniaxial compression arrangement. The change in material characteristics from a plastic type behavior to strain softening behavior is clearly captured using these tests, which help in quantifying the structural buildup of the system. Additionally, the use of lightweight aggregate in 3D printable mixtures and increase in the rate of build up by using accelerators is discussed in the study.
Controlling Nanoclay Processing to Enhance Yield Stress and Elasticity of Fresh Cement Pastes for Extrusion-based 3-D Concrete Printing
Presented By: Ala Eddin Douba
Affiliation: Columbia University
Description: Nanoclays (NC) have been explored as a thixotropy modifier for many concrete applications, including reducing self-consolidating concrete formwork pressure, improving slipform paving, and reducing rebound during shotcreting. Given their ability to enhance structural build-up, they are also a strong candidate for achieving shape stability of deposited layers during extrusion-based 3D concrete printing. However, early studies have indicated that typical dosing of ~ 0.5 wt % is not sufficient to meet the high rheological demands of this technique. And with current processing methods, higher dosing while achieving sufficient dispersion is difficult to achieve. This study explores various NC processing techniques and examines their efficiency in altering yield stress and elasticity of cement pastes, as well as reaching higher dosages. Results show that with the new processing technique a 16x increase in yield stress and 6x increase in storage modulus is achieved with 4 wt % NC, with limited impact on steady-state viscosity. Insights into underlying mechanisms and connections to 3D printing performance will also be discussed.
Examining the Significance of Polymer Rheology on the Mechanical Properties of 3-D-Printed Polymer Concrete
Presented By: Mahmoud Reda Taha
Affiliation: University of New Mexico
Description: 3D printing concrete technology is making good progress, placing itself as an alternative to conventional concrete production, specifically when complex geometries are needed. Concrete mixtures used for 3D printing typically incorporate high cement concrete and low water to binder ratio with some inherent limitations stemming from the significant time-variable rheological properties. Polymer concrete has been widely used in the construction industry for decades with remarkable mechanical properties, low permeability, and superior bond to different substrates. We report on a new 3D-printed polymer concrete using Novolac epoxy. Compression, flexural, and shear strength tests for 3D-printed hardened polymer concrete are performed and analyzed. We examine the significance of polymer rheology characteristics on the 3D-printing process and the mechanical properties of 3D-printed polymer concrete.