Building 3D Printing: The Anisotropy Mechanical Properties and Printing Time

  • Penghao Xin
  • Ziming Wang
  • Wenbo Xi
  • Jingying Peng
  • Huan He
  • Ruifeng Tang
Conference paper
Part of the Springer Proceedings in Energy book series (SPE)

Abstract

Three-dimensional technology is different from the traditional construction in process, which has many advantages like personal customization, reduced energy, rapid manufacturing. Therefore, to study the performance and test methods of 3D printing cement-based materials has significance effects on research and promotion of building three-dimensional technology. In this paper, addictive manufacturing and mould cast were used to manufacture samples. The results show that compressive strength of the printing samples is about 14 MPa at 1 day, 17 MPa at 3 days and 26 MPa at 7 days, which are about 55, 61 and 53% of the mould cast; the compressive strength of printing samples is anisotropy in the vertical and parallel directions for the printing direction, and the difference decreases with the flowbility increasing; the bonding layer gets weaker with the printing time increasing, especially at 10 min initially.

Keywords

Three-dimensional technology Cement-based materials Anisotropy Compressive strength 

Introduction

3D printing technology, commonly called additive manufacturing [1], sets most advanced technology of software architecture, mechanical engineering, materials science, laser technology in one [2]. 3D printing is also known as “The important tool of production in the third industrial revolution [3]”. It applies in industrial design, art design, mold manufacturing, jewelry, bio-engineering, aerospace, metal manufacturing, scientific research, cultural relics protection and other rapid development fields. In recent years, its development of architecture has aroused the interest of scholars both at home and abroad.

Building 3D printing is a way to extrude cement-based materials through a nozzle, which uses a layer stacking technology to build components of construction. Professor B Khoshnev is from University of Southern California, invented the Contour Crafting (CC) [4]. The CC machine printed a hollow wall structure troweled by side trowels firstly and filled the inside space with concrete, shown in Fig. 1. Professor R. Buswell of Loughborough University in the United Kingdom has developed Concrete Printing [5], which extruded concrete filament continuously through a 9 mm diameter nozzle to build layer-by-layer structural components in a printing process, shown in Fig. 2.
Fig. 1

Concrete wall completed by contour crafting

Fig. 2

Printed bench by concrete printing

Building 3D printing research also starts in many international commercial company. In June 2016, China Yingchuang successfully built an office in Dubai using 3D printing technology, which covers an area of 250 m2. The building uses a special cement mixture as a printing material. In July 2016, Tongzhou District in Beijing, the first 3D printing villa completed. The villa, which covers an area of 400 m2, has two floors. The giant printing machine used special reinforced concrete to build the villa with only 45 days. In December 2016, a Spanish Civil Engineering Company named Acciona, printing a concrete bridge with a length of 12 and 1.75 m wide, was put into use.

Due to the forming process, layer-by-layer, mechanical properties of specimens may have some differences in various direction [6]. Lin studied the mechanical properties of 3D printing samples in vertical and transverse [7]. In addition, the bond strength between the layers may also be the weakness point for printing specimens. This paper studies the anisotropy of the 3D printing specimen and the relationship between the interval time and the inter-layer strength.

Materials and Method

Materials. Cement tape P.I 42.5, fly ash, silica fume were formed the binder component. An agent that accelerates early strength and reduce drying shrinkage was used. Besides, accelerator formed by sulphuric, aluminium salt and diethanolamine was also maxed in to control setting time. Polycarboxylate superplasticizer was added to change flowability of mortar.

  • Cement: Reference cement was produced by China United Cement Group Corporation, the performances of the cement are shown in Tables 1 and 2.
    Table 1

    The chemical compositions of Portland cement [%]

    Name

    SiO2

    Al2O3

    Fe2O3

    CaO

    MgO

    SO3

    Na2Oeq

    f-CaO

    C3S

    C2S

    C3A

    C4AF

    Percentage

    22.06

    4.25

    3.39

    64.95

    2.98

    0.46

    0.69

    0.85

    56.87

    20.33

    6.32

    10.18

    Table 2

    The physical performance of cement

    Fineness 0.08 [%]

    Specific surface area [m2/Kg]

    Setting time [min′]

    Bending strength [MPa]

    Compressive strength [MPa]

    Initial

    Final

    3d

    28d

    3d

    28d

    0.8

    338

    138

    215

    6.4

    8.3

    29.7

    54.5

  • Sand: Standard sand was adopted.

  • Additive: Superplasticizer: The Polycarboxylate superplasticizer was produced by Beijing Construction Engineering Research Institute Co., Ltd.

  • Accelerator: The accelerator were made of sulphuric, aluminium salt and diethanolamine.

  • Fiber: The polypropylene micro fibers have length of 9 mm and diameter of 20 μm.

  • Mix proportions: In this paper, the dosage of superplasticizer was changed to adjust the motor flowability. The mix proportions are shown in Table 3.
    Table 3

    The mix proportions

    Number

    Cement: fly ash: silica fume

    Water/binder ratio

    Binder/sand ratio

    Dosage of superplasticizer [%]

    Dosage of accelerator [%]

    Dosage of fiber [Kg/m3]

    Dosage of HPMC [%]

    C1

    7:2:1

    0.26

    0.67

    0.50

    4.00

    1.2

    0.20

    C2

    7:2:1

    0.26

    0.67

    0.75

    4.00

    1.2

    0.20

    C3

    7:2:1

    0.26

    0.67

    1.00

    4.00

    1.2

    0.20

  • Experimental Procedures. The preparation of cement mortar was manufactured according to GB/T17671-1999 [8], and samples were curing in standard curing box for 1 day, 3 days and 7 days. The flowability of the mortar was determined according to GB/ T2419-2005 [9]. The setting time of mortar was tested with JGJ70-90 [10]. The bonding strength of layers was testing by LBY-VI drawing test instrument.

The specimens were manufactured in both mould-cast and printed states. According to the mix design (number C1, C2, C3), the specimens made in mould were named M1, M2, M3, and printed specimens were named P1, P2, P3. The printed samples were manufactured with mortar-gun layer-by-layer, shown in Fig. 3a, then saw into 40 mm × 40 mm × 40 mm cubes for strength test. The compression surfaces were divided into three based on three-dimensional space like Fig. 3b. So, depending on the different compression surfaces, the printed samples were numbered P11, P12, P13, P21, P22, P23, P31, P32, P33.
Fig. 3

Process in 3D printing (a) and testing directions (b)

Results and Discussion

  • Flowability. The water reducing agent had the characteristic of changing fluidity when the water/cement ratio is constant. When the water/binder ratio was unchanged, the amount of effective component of water reducing agent was 0.5, 0.75 and 1% respectively. In this regard, the printing motor has good performance to be printed. The sample fluidity and compressive strength are shown in Figs. 4 and 5.
    Fig. 4

    Effect of superplasticiser on flowability

    Fig. 5

    Effect of superplasticiser on compressive strength

As shown in Fig. 5, the samples had early strength, and the strength of the M1 at 1 day was as high as 26.85 MPa. Cause of early strength agent, the early strength of the material was high resulting in 1 day. And relative to the strength of 3 days, the growth of strength was not so much. In the case of the same water/cement ratio, with the amount of the water/reducing agent increasing, the fluidity of the mortar was obviously increased, but the compressive strength of the test piece was reduced.

  • The Effect of the Printing Process. The compressive strength of the molded samples and printed samples in three mix proportions at 1 day, 3 days and 7 days are shown in Fig. 6. It can be seen from the Fig. 6, the compressive strength of printed samples was lower than the normal molded samples, and for different compressive surface, the compressive strength was different. The strength of the direction 1 in vertical was the highest. The strength of P11 was 72.5% of the mold forming at 3 days, and the compressive strength of direction 3 was 56.19%. During the whole curing process, the strength of direction 2,3 were almost the same. But they were about 2–14% lower than the strength of direction 1. It is there are more pores or weaker point between the layers, resulting in different compressive strength in every direction, that is, printed samples have anisotropy of mechanical properties. During the test, the bonding strength between layers became weakness, as shown in Fig. 7.
    Fig. 6

    The anisotropy caused of printing for three mix proportions

    Fig. 7

    The destruction in direction 2 (a) and direction 3 (b)

  • The Effect of Flowability on Materials Mechanical Properties. The compressive strength of 1 day, 3 days, and 7 days for the different flowability mortars is shown in Fig. 8.
    Fig. 8

    Effect of flowability on compressive strength

With the flowability of the mortar increasing, the difference of the compressive strength in three directions for the printed samples was reduced, as shown in Fig. 8. Compared with the standard mould formed samples, the maximum strength of C1 in the printed sample was 7.27% and the maximum strength of C3 was 5.49%. The maximum strength difference of C1 was 13.79%, the strength of C3 was 5.36% at 7 days. The results confirmed that with the increase of the water reducing agent, the flowability of the mortar increases and the interlaminar adhesion increases, so that the anisotropy difference between the different directions surfaces decreases.
  • The Effect of Time between Layers on Bonding Strength. During the printing process, there was an interval between the layers. The printing speed is too slow or process have a large intermission between every layer, will cause the bond strength of printing layers decreased, even cold joints and other issues, so that the mechanical properties of the specimens will be impacted.

It can be seen from the Fig. 9 that the bond strength of the inter-layer decreased as the interval time increased. At 5 min, the bond strength can reach 58.77% of the contrast sample, the loss strength was fast and large. Between 10 and 20 min, the inter-layer bond strength was roughly the same, the strength was mainly depending on the fresh cement slurry which was not completely set. After 20 min the bond strength decreased rapidly, and the bond strength became lower.
Fig. 9

Effect of printing time between layers on bonding strength of layers

Conclusion

Building 3D printing has the characteristics of no mould forming, which is quite different from traditional construction, so its mechanical properties will be some differences. The strength of building 3D printing samples compared to the traditional mold specimens is lower, and the mechanical strength shows anisotropy, but the anisotropy decreases with the increasing of mortar fluidity. With the increase of the interval between layers, the bonding strength of layers is decreasing, so the appropriate interval interval is one of the important conditions to ensure the mechanical properties of the specimen.

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Copyright information

© Springer Nature Singapore Pte Ltd. 2018

Authors and Affiliations

  • Penghao Xin
    • 1
  • Ziming Wang
    • 1
  • Wenbo Xi
    • 1
  • Jingying Peng
    • 1
  • Huan He
    • 1
  • Ruifeng Tang
    • 1
  1. 1.Colloge of Material Science Engineering, Beijing University of TechnologyBeijingChina

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