Reinforcing 3 D Printed Concrete: The Missing Link
Presented By: Gideon Zijl
Affiliation: Stellenbosch University
Description: Interfaces between filaments of 3-D printed concrete structures have been shown to have lower resistance than the virgin material in mechanical action. The adhesive tensile and shearing resistance is influenced by amongst others the pass time, i.e. the duration between printing the filament layer and its substrate layer, the consistency of the material, the filament layer shape and deposition height. Recent studies have shown that the interface may dominate the response in fire, forming a debonding failure mechanism due to the thermal gradient and associated tensile stress. The debonding failure could lead to structural instability. Whereas fiber reinforcement of the 3-D printable material is possible and reported, transverse reinforcement across interfaces presents the missing link for in-plane and out-of-plane shear and flexural resistance, as well as thermo-mechanical reinforcement. This contribution presents comparative flexural responses of 3-D printed elements with and without reinforcing links, comparing the responses of reference unheated specimens with those of specimens cooled down from elevated temperatures. The concept of automated link reinforcement of a 3-D printed fiber-reinforced concrete modular load-bearing walling system is presented. Preliminary mechanical characterization test results on linked wall parts will be presented at the conference.
Fiber and Particulate Reinforcement for 3-D Printed Cementitious Systems
Presented By: Narayanan Neithalath
Affiliation: Arizona State University
Description: One of the significant impediments in the development of 3-D printing concrete is the complication arising from the need to pre-place reinforcement. Studies have attempted co-printing reinforcement (polymeric or steel) with concrete, but it is expected that the economy of scale will not be favorable for such an approach in the near term. This study hence attempts to judiciously use fiber and particulate reinforcement for 3-D printed mortars. The inclusion type, content, and placement strategies are tuned to provide structural capabilities to 3-D printed vertical sections. Rheological properties that influence printing are evaluated. While this strategy is less useful for horizontal members such as beams, it is expected that a majority of 3-D-printed structural elements will be placed in a vertical configuration and thus this approach can be beneficial. Structural design aspects are also discussed.
Early-Age Mechanical Performance of Fiber-Reinforced Mortars Used in 3 D Printed Concrete Construction
Presented By: Liberato Ferrara
Affiliation: Polytechnic University of Milan
Description: The digital fabrication with cement-based materials requires to pay specific attention to the rheological and mechanical material properties in both fresh and hardened state. For the layered extrusion process, the cement-based material needs to satisfy the so called “printability” requirement. Generally, printable mortars exhibit a brittle mechanical behavior due to the absence of physical reinforcement; to overcome this issue, many different strategies can be implemented. Among them, the addition of short fibers in the mortar represent a first step towards the development of robust materials for 3-D printing in construction. In this context, the paper focuses on the early stage properties of fiber reinforced cement-based material to be used in the layered extrusion process. The embedment of discrete fibers in a printable mix is expected to improve the fresh and hardened mechanical behavior but, at the same time, it implicates a loss of workability in the mix, which could lead to problems during the printing process (in terms of extrudability and pumpability of the mix). In particular, the mechanical response under direct tensile and shear load conditions are investigated as a function of the type/concentration of fibers as well as the mortar resting time. Furthermore, the effect of varying the amount of the superplasticizer to guarantee the printability requirement of the printable mortar is also investigated. In a quality control framework, the development of tensile and shear fracture properties, in the considered production time frame, is fundamental to discriminate about the printability of the mix, with reference not only to the quality of the finishing but also to the speed of the printing process.
Using Placed Fibers as Vertical Reinforcement in 3-D Printed Wall Elements
Presented By: Manu Santhanam
Affiliation: Indian Institute of Technology Madras
Description: The integration of reinforcement with 3-D printing is a challenge and provides for a large part of the current research worldwide. Research on 3-D printing at IIT Madras has led to the development of a systematic method for design and control of mixtures required for 3-D printing, and two full scale rooms have already been printed. The first project involved the printing of 30 cm height modules (in 20 layers) and then joining like in a masonry structure. The latest print involved just two modules, each of 1.4 m height, that were stacked to make the full-size room. During this print, it was seen that the interfacial effects caused due to the printed layers led to a reduction in the flexural capacity of the wall in the transverse direction. This could be a critical issue in the large-scale behavior of 3-D printed walls. The current presentation discusses the strategies to mitigate the interfacial effects and also to provide minimum vertical reinforcement by manually placing crimped fibers after the print of every second layer. The process attempted during the printing of the second full scale room was similar to pinning or stapling with crimped fibers after every two layers - this could be easily mechanized in the 3-D printing system. An experimental study was subsequently conducted at the laboratory to assess the out-of-plane flexural response of 3-D printed wall elements with manually placed fibers. The influence of fiber dosage was also assessed in the study.
New Reinforcement Concepts for Digitally Fabricated Concrete Structures
Presented By: Jaime Mata-Falcon
Affiliation: ETH Zürich
Description: Most digital concrete technologies do not allow adding reinforcement during the production, which complicates the compliance with structural integrity requirements and limits their market to (try to) compete with inexpensive masonry walls. In this work, we present a wide range of new possibilities to reinforce digitally fabricated structures, namely the aligned interlayer fiber concept, the use of knitted textiles and the Mesh Mould concept. We will also discuss the potential to reduce the required minimum amount of reinforcement when using 3D printing processes generating weak interfaces between layers. These new possibilities illustrate that digital fabrication offers a wide range of yet unexplored opportunities for fast, sustainable economic design and production of reinforced concrete structures.