CURRENT CHALLENGES AND FUTURE PERSPECTIVES OF 3D CONCRETE PRINTING

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Beryl Freeman
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1 2 nd International Conference on Progress in Additive Manufacturing (Pro-AM 2016) May 2016, Singapore Chua Chee Kai, Yeong Wai Yee, Tan Ming Jen and Liu Er Jia (editors) CURRENT CHALLENGES AND FUTURE PERSPECTIVES OF 3D CONCRETE PRINTING BIRANCHI PANDA *, YI WEI TAY, SUVASH CHANDRA PAUL, TAN MING JEN, KAH FAI LEONG Singapore Centre for 3D Printing, School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore IAN GIBSON School of Engineering, Faculty of Science, Engineering and Built Environment, Deakin University, Victoria, Australia ABSTRACT: The emphases on reduction of construction time and production costs have profound influences on construction process that has led us to investigate a new paradigm, known as 3D concrete printing. This printing system can fabricate complex 3D objects directly from the computer aided design (CAD) model without any tools and human intervention. However, compatibility of presently available materials, processes, build size and associated costs present significant barriers against widespread application and commercialization. This paper presents an overview of 3D concrete printing processes and some of the challenges that need to be addressed for fruitful implementation in the building & construction (B&C) industry. With global researchers working to explore the possibilities, it is believed that there may be a promising future for concrete printing in the B&C industry. INTRODUCTION The construction industry has traditionally relied on two-dimensional (2D) drawings and scale models for evaluation of the design process. Increasingly, 2D drawings and prototypes are being replaced by three-dimensional (3D) modelling in the virtual environment of building information modelling (BIM) (Perkin et al., 2015). With increasing population comes an increasing demand for large buildings. Although all buildings have unique features, the larger the building the more of these features will exist. Using BIM it is possible to maintain a digital model for as long as possible throughout the development process, thus allowing architects, designers and engineers to investigate possible modifications that would need to be made due to changes in design intent or unforeseen circumstances. A benefit in the use of BIM, backed up by 3D modelling, is that they can be used in combination with digital fabrication methods. Digital fabrication includes the use of 3D printing or Additive Manufacturing (AM) which uses a layer by layer deposition strategy to build complex 3D objects directly from the CAD model in a reasonable build time. In recent years, this technology has shown the potential to be used in B&C applications due to significant advantages in terms of reduced build time, less wastage and less human resources when compared to traditional methods. Whilst some demonstration systems have been developed in industry and research, there are still numerous challenges related to scale, materials and delivery system, suitability to adverse environments, etc. This paper introduces one specific area appropriate to B&C; concrete printing

2 and discusses it s associated challenges and future guidelines which could lead to success for B&C applications. CONCRETE PRINTING SYSTEMS The first published evidence of 3D concrete printing was in 1997 with an innovative approach suggested by Pegna (Pegna et al., 1997) that was part of a student project. Development of this field has grown slowly and currently three main categories (shown in figure 1) of this technology can be found in the public domain. 1. D-shape 2.Contour crafting 3.Concrete printing Figure 1. Large scale 3D printing process (a) D-Shape, top left, (b) Contour Crafting, right and (c) Concrete Printing, bottom left (Lim et al., 2012) All these three technologies have been proven as an effective means of printing complex geometrical concrete structures for B&C application. Though the three processes are similar in the sense that they build the product in an additive manner, they are developed for different applications and materials. Both the D-shape and concrete printing are gantry based offsite printing processes whereas contour crafting is for onsite, in-situ application. D-shape uses a powder deposition process, which selectively binds the powder such as sand by a chemical agent (binder) in the same way as the MIT 3DP process (Gibson et al., 2010; Mahapatra and Panda, 2013). Once sand is deposited over the print bed, D-shape ejects the binder to hold each layer of sand that forms a 3-dimensional shape as shown in Figure 1(a). This method has advantage over extrusion based methods because any unbound raw materials that are not used to form the shape may be used as supports for overhanging features. Also, due to the small incremental size of each layer, the produced part by this process has good mechanical strength, and good surface finish. However, as with all concrete printing, proper maintenance, cleaning and control processes remain a significant barrier.

Contour crafting (CC) is a material extrusion method that lays down concrete layer by layer to fabricate complex structures out of the 3D CAD model.

3 Contour crafting (CC) is a material extrusion method that lays down concrete layer by layer to fabricate complex structures out of the 3D CAD model. Compared to other thick-layer extrusion based methods, CC is able to achieve a smooth external surface whilst maintaining a large layer thickness utilizing an integrated trowel system. A big advantage of CC is that the system allows steel reinforcement to be embedded in the component (Figure 2) which improves the overall strength of the component (Khoshnevis et al., 2005). Other than reinforcement, different subsystems like plumbing, electrical and embedded sensors can also be integrated with this technology by combining the 3D printing with robotic assembly, which eliminates the need of post processing for different household applications. Usually, the mix design for CC consists of cement, fly ash, plasticizer, silica fume, sand and water. The average size of the sand particle in the mix design is selected in such a way that it should not be too large to clog the delivery pipe or the nozzle tip during extrusion of material. Like CC, concrete printing is an extrusion based manufacturing process that fabricates complex part geometries layer by layer without the use of labour intensive formwork. Today many universities and industries like Winsun, Apis-Cor, etc. have developed their own concrete printing systems that are claimed to reduce production times by percent and reduce labor costs by percent ( Figure 2. Reinforcement in Contour crafting CHALLENGES OF 3D CONCRETE PRINTING Material: Recent research into 3D concrete printing proves that proper material development is one of the biggest challenges that need to be tackled for successful printing of the concrete structures. The following five key benchmarking properties have been identified in order to prepare the mix specifically for concrete printing (Le et al. 2012): (1) Extrudability (2) Flowability (3) Buildability (4) Open time and (5) Layer adhesiveness Extrudability and flowability are related to the concrete extrusion, flow, and workability, as it is important for 3D printing that the materials have a continuous easy-flowing behavior from the source to the printing nozzle. Buildability refers to the ability of a concrete bead layer to hold another bead layer on top it without collapsing. Open time studies the change of concrete flowability with time. The goal is to ensure that each bead layer has the capacity to hold itself and harden when poured onto the build plate or onto preceding layers. Once all the layers are

4 deposited, a proper bonding between these layers (layer adhesiveness) must be maintained in order to avoid structural collapsing in heavy rainy or windy conditions. This all relates to the curing dynamics of the concrete so that it is relatively easy to extrude yet viscous enough to hold together and adhesive enough to create an integrated structural result. Structural integrity: Concrete printing method has a limitation of not being able to fabricate significantly overhanging parts since this would need support material for stability in the design. This would restrict AM of complex freeform structures. Voids and hollow designs also may not be achieved with this limitation, unless a sacrificial support system is used. An alternative approach that would permit more complex designs to be fabricated would be for these structures to be built in multiple sections and later assembled to build the complete structure. However, in this approach proper care should be taken for structural integrity (especially in joining the multiple sections in one position) since material shrinkage, or vibration in the structure from seismic action can cause tolerance errors in the printed and assembled structure. Post-Processing: Poor surface finish (due to volumetric error) has also been seen as a limitation in concrete printing. Improper control and excess deposition of material also causes poor surface quality in the part, which is not desired at all. Insufficient material may be even worse since voids may become trapped and incorporate weakness into the structure. Therefore proper care (Integration of trowels) needs to be taken during the printing as well as after the printing to improve the surface quality and dimensional accuracy. Concrete layers should be deposited in such a way that it should stick to previous layers without any change of volume and if necessary reinforcement (like fibers, nanoparticles) can be added that will help to improve the structural properties. Apart from material, the printing system must also be robust enough to work continuously without creating any mechanical issues in what is typically a dirty and disorganized environment. Waterproof and corrosion resistant material should be chosen while developing the printing system for the concrete deposition process. FUTURE PERSPECTIVES OF 3D PRINTING IN B&C Despite the above challenges, concrete printing can improve the current fabrication methodology by automating the complete process. Automating also reduces the reliance on skilled labour and can lead to increase in accuracy through lowering of potential defects due to human errors. However considering the challenges, there is a need for intelligent system design as well as advance material development that can lead to environment friendly affordable housing. Printing System: One of the limitations of current concrete printing system is that it is unable to print overhanging geometries since they need support structure which is difficult to generate. In this case, modular printing has gained remarkable attention due to the ease in printing objects and assembling. However, sometimes assembling is not preferred since it is likely to cause poor structural strength at the boundaries and may also cause gaps between the layers due to fabrication tolerances. In this regard, Khoshnevis suggested that this issue can be addressed by using an ancient technique of constructing support-less structure as described in Khoshnevis, Concrete structures generally need addition of reinforcement for improved mechanical properties as well as structural integrity. Therefore in future a hybrid printing system can be developed that

can print concrete along with the reinforcement in different arrangements which will eliminate the need of adding reinforcement to the structures.

Unfortunately, it is well known that cement production causes environmental pollution and also consumes lots of energy.

Also, functional materials such as fibre reinforced concrete (FRC) and engineered cementitious composite (ECC) may be beneficial to 3D concrete printing, since they have higher tensile and flexural

5 can print concrete along with the reinforcement in different arrangements which will eliminate the need of adding reinforcement to the structures. Material: Cement-based mortar has been used most frequently to investigate the potential of 3D concrete printing. Unfortunately, it is well known that cement production causes environmental pollution and also consumes lots of energy. Therefore there is a need of developing green construction materials (where production requires less energy and has minimum or no impact on the environment) that can reduce this effect. Also, functional materials such as fibre reinforced concrete (FRC) and engineered cementitious composite (ECC) may be beneficial to 3D concrete printing, since they have higher tensile and flexural strength than conventional concrete properties thus allowing structural components like columns, beams and trusses to be fabricated (Laurent et al., 2014). Structure: Though concrete printing has gained increasing popularity for B&C application, the issue with structural strength has still remained as a largely unanswered question for the 3D printing experts. Instead of printing layer by layer in straight pattern, a different pattern (shown in figure 3) can be tried out in future for better strength and robust structural design. Figure 3. Proposed concrete printing patterns for robust structure Application: Concrete printing has potential in several areas, three markets and example product types being shown in Figure 4. As media interest grows in small-scale printing, research into large-scale systems is beginning to reveal the potential for applications in construction. Figure 4. Future applications of concrete printing

6 CONCLUSION Three concrete printing processes have been explored and compared in terms of their key characteristics and advantages and disadvantages during application. Though there are many challenges, in future, concrete printing is believed to have the capacity to change or improve the traditional construction process in some extent. Designers and architects need to understand the benefits of this technology in terms of improved design features and hence should be able to unleash their design potentiality that s was previously restrained by traditional construction methods. Furthermore, engineers need to understand the capability of the technology in terms of reducing inventory and making timelines shorter and more predictable. However, the need to abolish conventional methods completely may not be necessary. The future of construction is most likely to be an integrated process that allows organizations to take advantage of both conventional and AM technologies at the same time. ACKNOWLEDGEMENT The authors would like to acknowledge National Research Foundation Singapore (NRF) for funding and support for this research project. REFERENCES Perkins, I. and Skitmore, M., (2015) Three-dimensional printing in the construction industry: A review, International Journal of Construction Management, 15(1), 1-9. J. Pegna, (1997) Exploratory investigation of solid freeform construction, Automation in Construction, 5(5), , S. Lim, R.A. Buswell, T.T. Le, S.A. Austin, A.G.F. Gibb, T. Thrope, (2012) Developments in construction-scale additive manufacturing processes, Automation in construction, 21, , Gibson, Ian, David W. Rosen, and Brent Stucker (2010) Additive manufacturing technologies, New York: Springer. Mahapatra, S. S & Panda, B.N (2013) Benchmarking of rapid prototyping systems using grey relational analysis, International Journal of Services and Operations Management, 16(4), Khoshnevis, B, Bodiford, M.P, Burks, K.H, Ethridge, E, Tucker, D, Kim, W, Toutanji, H and Fiske, M. R. (2005) Lunar contour crafting a novel technique for ISRU-based habitat development, in American Institute of Aeronautics and Astronautics Conference, pp [Accessed: 29-Nov-2015] Le, T.T., Austin, S.A., Lim, S., Buswell, R.A. (2012) Mix design and fresh properties for highperformance printing concrete, Materials and Structures, 45(8), Khoshnevis, B., (2004) Automated construction by contour crafting related robotics and information technologies, Automation in construction, 13(1), Laurent, P., Erica, M., Laurent, F. and Safaâ, M. (2014) Advanced building materials, Bus. Innovaion Obs., 2 14

This document is downloaded from DR-NTU, Nanyang Technological University Library, Singapore.

This document is downloaded from DR-NTU, Nanyang Technological University Library, Singapore. Title Properties of 3D Printable Concrete Author(s) Citation Van Zijl, Gideon P. A. G.; Paul, Suvash Chandra;