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1 This document is downloaded from DR-NTU, Nanyang Technological University Library, Singapore. Title 3D printable high performance fiber reinforced cementitious composites for large-scale printing Author(s) Citation Weng, Yiwei; Qian, Shunzhi; He, Lewei; Li, Mingyang; Tan, Ming Jen Weng, Y., Qian, S., He, L., Li, M., & Tan, M. J. (2018). 3D printable high performance fiber reinforced cementitious composites for large-scale printing. Proceedings of the 3rd International Conference on Progress in Additive Manufacturing (Pro-AM 2018), doi: /d4b591 Date 2018 URL Rights 2018 Nanyang Technological University. Published by Nanyang Technological University, Singapore.

2 ABSTRACT: 3D printing cementitious composites require special rheological properties, which are affected significantly by the materials constituents. In this work, a novel mixture of 3D printable fiber reinforced cementitious composites (3DPFRCC) was developed. The rheological performance, settingtime, and mechanical properties were characterized, a printing test was carried out as well to test the buildability and pumpability. Results indicate that the new material possesses appropriate rheological and mechanical performances. Rheological properties are designed based on previous practical printing test. The static and dynamic yield stress are 3289 Pa and Pa, respectively. The plasticity viscosity is 32.5 Pa s. The initial setting time is 59.2 minutes. The flexural strength and compressive strength are 8.6 MPa and 71.2 MPa, respectively at 28 days. Then, a cm (L W H) structure was printed successfully in 150 minutes, which demonstrates that this novel 3DPFRCC possesses excellent buildability and pumpability, which is capable of large-scale printing. KEYWORDS: 3D printing; fiber reinforced cementitious materials; rheological properties; buildability; pumpability 1. Introduction 3D PRINTABLE HIGH PERFORMANCE FIBER REINFORCED CEMENTITIOUS COMPOSITES FOR LARGE-SCALE PRINTING YIWEI WENG, SHUNZHI QIAN Singapore Centre for 3D Printing, School of Civil and Environment Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, , Singapore LEWEI HE, MINGYANG LI, MING JEN TAN, Singapore Centre for 3D Printing, School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, , Singapore The process of 3D printable cementitious materials forms the objectives in a layer-atop-layer manner (Bos et al., 2016; Chua & Leong, 2014; Lao et al., 2017; Tay et al., 2018). During the printing process, the cementitious materials should sustain the weight of higher layer and can be delivered in the pumping system (Lu et al., 2016), which require the materials should possess special rheological performance, namely yield stress and plastic viscosity that determine the buildability and pumpability of 3D printable cementitious materials (3DPCM), respectively (Weng et al., 2018). Much research has been done to investigate the relationship between the rheological performance, buildability, and pumpability. Perrot et al. established a model to correlate the relationship between yield stress and buildability (Perrot et al., 2016). And a model to relate the relationship between the plastic viscosity and pumping pressure was proposed by Chhabra and Richardson. (Chhabra & Richardson, 2011). Based on Perrot et al. s research, Weng et al. proposed a modified method to predict and directly verify the buildability for 3DPCM. All these research results prove that optimizing Proc. Of the 3 rd Intl. Conf. on Progress in Additive Manufacturing (Pro-AM 2018) Edited by Chee Kai Chua, Wai Yee Yeong, Ming Jen Tan, Erjia Liu and Shu Beng Tor Copyright 2018 by Nanyang Technological University Published by Nanyang Technological University ISSN: :: 19

3 Chee Kai Chua, Wai Yee Yeong, Ming Jen Tan, Erjia Liu and Shu Beng Tor (Eds.) the rheological properties of materials to satisfy the requirement of buildability and pumpability is essential for 3DPCM. Rheological properties are affected by many aspects, such as materials constituents (Yang et al., 2009; Ruan et al., 2018), chemical additive (Li & V.C. Li, 2013), and particle size gradation (Weng et al., 2018). Weng et al. achieved a meter-level printing through optimization the particle size gradation of sand. However, the material used in Weng s research is plain concrete, which is brittle with low tensile strength and crack resistance. Since fiber reinforced cementitious composites is widely used to enhance tensile property and prevent cracks, a type of 3D printable fiber reinforced cementitious composites (3DPFRCC) should be developed for large-scale printing based on the rheological performance. In this work, a novel mixture of 3DPFRCC is developed. The rheological properties were characterized by yield stress and plastic viscosity, open time was characterized by setting time (Lim et al., 2012). The mechanical performances (flexural and compressive strength) were tested as well. Finally, printing test was used to test the performance in actual printing process of developed materials. 2. Methodology, materials, mixing, rheological characterization, mechanical properties testing and printing test 2.1 Methodology, materials and mixing Build-up and pumping pressure models indicate that printing height and pumping pressure are corresponding to the yield stress and plastic viscosity of materials, respectively (Weng et al., 2018). A meter-level printing was carried out by Weng et al. via optimizing the materials rheology. Based on the rheological properties of materials used in his meter-level printing, the materials used in this work were designed by optimizing materials constituents to meet the requirement of rheology for large-scale (meter-level) printing. Besides, setting time indicates the workable time for 3D printing process, which should be enough for 3D printing process to ensure the pumpability and appropriate bonding performance. In this study, the mixture consists of Ordinary Portland Cement type I 42.5, natural river sand, class F fly ash with a fineness of 386 m 2 /kg, silica fume, and PVA fiber with 40 μm in diameter, 8 mm in length and 0.8% oil coating. Superplasticizer was added with the content of 3 g/l. The gradation curve of natural river sand can be found in Weng s research (Weng et al., 2018). The mixture proportion can be found in following Table 1. Table 1 Mixture proportions S/B W/B FA/C SF/% Fiber/% A 80L Screed Mortar Mixer (Soroto) was used for mixing. As materials rheology performance is affected by many external factors, such as temperature, mixing time, etc (Yang et al., 2009; Zhou et al., 20

4 Proc. Of the 3 rd Intl. Conf. on Progress in Additive Manufacturing 2012), the mixing process is fixed to ensure rheology performance constituency. Firstly, the powder of all solid ingredients was dry mixed for 1 min in stir speed; then water was added with the mixing process continued for 1 minute in stir speed; after that, the superplasticizer was added, the mixing process continued for 1 minute in speed I followed by 1 minute in speed II. Finally, the fiber is introduced, and the mixing process continued for 2 minutes in speed II. 2.2 Rheological characterization, mechanical properties testing and printing test Bingham model is a classic rheological model of cementitious materials (Weng et al., 2016). According to the Bingham model, fresh cementitious materials can flow after it overcomes its static yield stress. During the flow, dynamic yield stress is the minimum yield stress to maintain its flow. The plasticity viscosity measures how easily the materials can flow once the yield stress is overcome. In this study, the rheological performance was characterized by a Viskomat XL with a six-blade vane probe and a cage, the detailed dimensions of probe, cage, testing program and typical test result can be found in Weng s research (Weng et al., 2018). Then, the static/dynamic torque and torque viscosity can be converted into static/dynamic yield stress and plastic viscosity via the following equation: RR 1 2 l 4RR 1 2 l0 R = ln (1) 2 2 R R R R R here (N m) is the torque, 2 (rad/s) is the rotational speed of outer barrel, l (m) and R 1 (m) are the length and radius of the probe, respectively, and R 2 (m) is the radius of the outer barrel. Setting time is another essential parameter, which determines the working time of 3DPFRCC (Zhu et al., 2017). In this work, the setting time of the cement pastes was determined according to ASTM C with using an automatic Vicat apparatus. The 1.13 diameter needle is fixed on a movable rod. A specimen of normal consistency fresh cement paste is prepared and placed in a 40 mm high container with a diameter of 40 mm. The test consists in the measurement of the penetration depth of the needle, which penetrates the specimen every 4 minutes (Sleiman, Perrot, & Amziane, 2010). The initial setting time in this study is calculated from following: ( H E) Initial setting time = ( ( C 25) + E (2) ( C D) where E (minutes) is the time of last penetration greater than 25 mm; H (minutes) is the time of first penetration less than 25 mm; C (mm) and D (mm) are the penetration depth reading at time E and H, respectively. A gantry concrete printer was used to fabricate flexural specimens. The nozzle used for printing was 30 mm 15 mm (L W). The printing and pumping speeds were 4000 mm/min and 1.8 L/min, respectively. The standoff distance was 15 mm for each layer. Then, the printed specimen was cut into separate filaments with 350 mm in length and 300 mm in height (two layers). Afterwards, a four-point bending test with a span length of 240 mm was conducted at 28 days (Weng et al., 2018). 21

5 Chee Kai Chua, Wai Yee Yeong, Ming Jen Tan, Erjia Liu and Shu Beng Tor (Eds.) 22

6 Proc. Of the 3 rd Intl. Conf. on Progress in Additive Manufacturing The large-scale printing test result was shown in Figure 3. During the printing, the standoff distance was 10 mm for each layer, the gantry movement speed is 6000 mm/min and the pumping speed is 1.8 L/min. A preprinted concrete plate was used to form the overhang structure. Table 2 Testing results of rheological and mechanical performance, and open time Flexural strength /MPa Compressive strength /MPa Plastic Viscosity /Pa s Static Yield Stress/Pa Dynamic Yield Stress/Pa Conclusion Figure 3 Large-scale printing, 78 cm 60 cm 90 cm (L W H) 3D printable cementitious composites require special rheological performance to satisfy the requirement of printability (buildability and pumpability). In this work, a novel 3DPFRCC was developed. The rheological performance (yield stress, plastic viscosity), setting time, mechanical performance and printability were characterized. The results show that the static yield and dynamic yield stress of this 3DPFRCC are 3289 Pa and Pa, respectively; the plastic viscosity is 32.5 Pa s; initial setting time is 59.2 minutes; the flexural strength and compressive strength are 8.5 MPa and 71.2 MPa respectively at 28 days. Finally, a 78 cm 60 cm 90 cm (L W H) structure was printed in the printing test, which demonstrates that this new material possesses excellent printability and is capable for large-scale printing. ACKNOWLEDGEMENTS The authors would like to acknowledge National Research Foundation, Prime Minister s Office, Singapore under its Medium Sized Centre funding scheme, Singapore Centre for 3D Printing and Sembcorp Design & Construction Pte Ltd for their funding and support in this research project. 23

7 Chee Kai Chua, Wai Yee Yeong, Ming Jen Tan, Erjia Liu and Shu Beng Tor (Eds.) REFERENCES ASTM, C109-16A, Standard Test Method for Compressive Strength of Hydraulic Cement Mortars, American Society for Testing and Materials, Philadelphia, PA, 2016 Bos, F., Wolfs, R., Ahmed, Z., & Salet, T. ( 2016). "Additive manufacturing of concrete in construction: potentials and challenges of 3D concrete printing", Virtual and Physical Prototyping, 11(3), Chhabra, R. P., & Richardson, J. F. (2011). Non-Newtonian flow and applied rheology: engineering applications, Butterworth-Heinemann. Chua, C. K., & Leong, K. F. (2014). 3D PRINTING AND ADDITIVE MANUFACTURING: Principles and Applications (with Companion Media Pack) of Rapid Prototyping. World Scientific Publishing Co Inc. Li, Mo, & Li, V. C. (2013). "Rheology, fiber dispersion, and robust properties of engineered cementitious composites", Materials and structures, 46(3), Lim, S., Buswell, R. A., Le, T. T., "Austin, S. A., Gibb, A. G., & Thorpe, T. (2012). Developments in construction-scale additive manufacturing processes", Automation in Construction, 21, Lu, B., Tan, M. J., & Qian, S. Z. (2016). "A Review of 3D Printable Construction Materials and Applications", Proceedings of the 2nd International Conference on Progress in Additive Manufacturing (Pro-AM 2016), Perrot, A., Rangeard, D., & Pierre, A. (2016). "Structural built-up of cement-based materials used for 3D-printing extrusion techniques", Materials and structures, 49(4), Ruan, S., Qiu, J., Yang, E. H., & Unluer, C. (2018). Fiber-reinforced reactive magnesia-based tensile strain-hardening composites. Cement and Concrete Composites. 89, Tay Y W D, Panda B, Paul S C, et al (2017). 3D printing trends in building and construction industry: a review. Virtual and Physical Prototyping, 12(3): Weng, Y., Li, M., Tan, M. J., & Qian, S. (2018). "Design 3D printing cementitious materials via Fuller Thompson theory and Marson-Percy model", Construction and Building Materials, 163, Weng, Y., Lu, B., Tan, M. J., & Qian, S. (2016). "Rheology and Printability of Engineered Cementitious Composites-A Literature Review", Proceedings of the 2nd International Conference on Progress in Additive Manufacturing (Pro-AM 2016), Yang, E.H., Sahmaran, M., Yang, Y., & Li, V. C. (2009). "Rheological control in production of engineered cementitious composites", Materials Journal, 106(4), Zhou, J., Qian, S., Ye, G., Copuroglu, O., van Breugel, K., & Li, V. C. (2012). "Improved fiber distribution and mechanical properties of engineered cementitious composites by adjusting the mixing sequence", Cement and Concrete Composites, 34(3), Zhu J., Tao Z., Mansour F, Chen W. (2017). "3D printing cement based ink, and it s application within the construction industry",matec Web of Conferences. EDP Sciences, 120: