Evaluation of workability parameters in 3D printing concrete

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Procedia Structural Structural IntegrityIntegrity Procedia1000(2018) (2016)155–162 000–000

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1st International Conference of the Greek Society of Experimental Mechanics of Materials

Evaluation of workability parameters in 3D printing concrete

XV Portuguese Conference on Fracture, PCF 2016, 10-12 February 2016, Paço de Arcos, Portugal

M. Papachristoforou, V. Mitsopoulos, M. Stefanidou*

Thermo-mechanical modeling of a high pressure turbine blade of an Laboratory of Building Materials, School of Civil Engineering, Aristotle University of Thessaloniki, University Campus 54124, Greece airplaneThessaloniki, gas turbine engine Abstract a

P. Brandãoa, V. Infanteb, A.M. Deusc*

Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa,

Portugalused as material for additive manufacturing. 3D concrete The baim of this paper was to examine workability of fresh concrete IDMEC, of Mechanical Engineering, Instituto Superior Universidade de Lisboa, Av.construction Rovisco Pais, 1, 1049-001 Lisboa, printing is anDepartment innovative construction method that promises to Técnico, be highly advantageous in the field in terms of Portugal optimizing construction time, cost, design flexibility, error reduction, and environmental aspects. Quality of the final printed c CeFEMA, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, structure is significantly affected by the properties of fresh concrete Portugal which must possess adequate workability in order to be extruded through an extruder head (printability), maintain its shape once deposited and not collapse under the load of subsequent layers (buildability). In the present paper, workability of fresh concrete used as material for additive manufacturing was measured Abstractto four different tests: flow table, ICAR rheometer, Vicat and an experimental applied in the laboratory by measuring according the electric power consumption of the motor that rotates the screw extruder. By measuring a wide range of mixtures produced During theiraggregates operation,(limestone, modern aircraft engine components are subjected to (cement, increasingly demanding operating with different river sand, combination of both) and binders fly ash, ladle furnace slag),conditions, printing especially the high system pressurewith turbine (HPT) blades. conditions these to undergo different of time-dependent them with a printing screw extruder andSuch setting printablecause criteria, theparts range of printability wastypes obtained. Flow table one of which is creep.toAthe model using the finite method (FEM) developed, to be to table predict testdegradation, was more consistent in relation other methods used.element Printability range was was found between in 18order and 24 cmable (flow the creep of for HPT blades.from Flight data records forwas a specific aircraft,andprovided by depended a commercial values). Timebehaviour after mixing moving the upper limit to (FDR) the lower also measured was highly on theaviation type to used. obtainAthermal and of mechanical data three different In order to create the 3D model of company, aggregateswere and used binders maximum 30 minutes wasforobtained without flight using cycles. any retarder additives. Electric power needed for was the considered FEM analysis, a HPT blade scrap wasreal-time scanned,workability and its chemical composition materialtoproperties consumption as a parameter of measuring of the mixture, makingand it possible modify it were on obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D time in real scale applications by adding chemical additives during printing. Regarding hardened concrete properties, density of rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The concrete was measured, between 1.9 and 2.1 g/cm³, depending on the aggregate and binder. Compressive strength and Ultrasonic overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a Pulse Velocity significantly affected by the type andblade proportions of raw in the mixtures. model can beare useful in the goal of predicting turbine life, given a setmaterials of FDR data. © 2018 The Authors. Published by Elsevier Ltd. ©© 2018 TheThe Authors. Published by Elsevier Ltd. B.V. 2016 Authors. Published This is an open access article under theby CCElsevier BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/) This is an open access article under the CC BY-NC-ND license Peer-review under Peer-review under responsibility the Scientific Committee of PCF 2016. Peer-review under responsibility of the of scientific committee of the 1st(http://creativecommons.org/licenses/by-nc-nd/3.0/). International Conference of the Greek Society of Experimental Mechanics st responsibility of Materials. of the scientific committee of the 1 International Conference of the Greek Society of Experimental Mechanics of Materials Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation. Keywords: 3D printing, fresh concrete; workability; printability; buildability

* Corresponding author: Tel.: +30 2310 995 635 E-mail address: [email protected] Received: May 04, 2018; Received in revised form: August 02, 2018; Accepted: August 08, 2018

2452-3216 © 2018 The Authors. Published by Elsevier Ltd.

* Corresponding author. Tel.: under +351 218419991. This is an open access article the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under E-mail address: [email protected] responsibility of the scientific committee of the 1 st International Conference of the Greek Society of Experimental Mechanics of Materials 2452-3216 © 2016 The Authors. Published by Elsevier B.V. 2452-3216  2018 The Authors. Published by Elsevier Ltd. Peer-review underarticle responsibility of the Scientific Committee of PCF 2016. This is an open access under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Peer-review under responsibility of the scientific committee of the 1st International Conference of the Greek Society of Experimental Mechanics of Materials. 10.1016/j.prostr.2018.09.023

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1. Introduction 3-D printing is an additive manufacturing technique for constructing numerous types of products and structures using various raw materials, directly from three dimensional (3D) model data. The process consists of printing successive layers of materials on top of each other. There has been a growing interest upon 3D printing for civil engineering applications over the past decades due to the advantages this method possesses compared to traditional construction methods, such as the ability to construct complex geometry without the need of formwork, construction speed and minimize waste material and labor cost. There are many examples of such applications both from private companies and researchers. Khoshnevis (2004) has developed Contour Crafting (CC) which is based on the extrusion of cementitious materials in order to construct automatically a single house or a colony of houses, each with possibly a different design, or even habitats on other planets. The extruded surface roughness of every layer is smoothed out using a trowel while performing the extrusion. The 3D printhead is mounted on an overhead crane as the system is designed for on-site construction operations. Lim et al. (2011) from the department of Civil Engineering at Loughborough University were the first to study and develop a high-performance 3D printable concrete. They used a 3D printer that had a small printhead to 3D print in many layers a bench-looking structure. They were among the first to study the fresh and hardened properties of printable concrete and they maintained a lower limit of about 10 MPa of flexural strength in order the concrete to be characterized as high-performance. Also, using admixtures they were able to create a relatively flowable mixture. Cesaretti et al. (2014) created D-Shape, a technique using sand that can be hardened in pre-arranged places to create structures of different shape and size. The main advantage of this method is that the sand bed is used as the support, making it possible to built complex 3D structures. The main drawbacks of the D-Shape printing method are that building dimensions are limited by the dimensions of the printing equipment, the need for a constant supply of sand and the fact that needs a significant amount of time for the creation of a new design. Institute for Advanced Architecture of Catalonia, IAAC (2016) from Barcelona has developed a technique that uses robots to create any shape and form of buildings. It was one of the first to 3D-print a bridge in Madrid in fullscale and now is planning on continuing this trend with other materials such as metal and plastic. They use high-tech drawing technology at state of the art laboratories to design and build complicated structures and they even have partnerships with MIT in some projects. Many other companies around the world have developed different techniques and equipment for concrete 3D printing (ApisCorTM, WASP, CyBe Constructions, WINSUN). Limited research has been carried out on properties of printing concrete and especially on its fresh state. Kazemian et al. (2017) proposed a framework for performance-based laboratory testing of cementitious mixtures for constructionscale 3D printing, where workability of a fresh printing mixture was studied in terms of print quality, shape stability, and printability window. Print quality described using measures of surface quality and dimensions of printed layers. Experimental study of four different mixtures revealed that inclusion of silica fume and Nano-clay significantly enhances shape stability. The results of five conventional test methods, as well as four proposed tests were used to discuss the performance of mixtures as printable or not. In 2016, Perrot et al. (2016) compared the vertical stress acting on the first printed layer with the critical stress related to the plastic deformation and defined a critical failure time as a function of concrete specific weight, concrete yield stress with no time at rest, structuration rate, construction rate and a geometric factor. In this paper, criteria based on printing quality and dimensions of printed layers were established in order to accept a concrete mixture as printable or not. Concrete mixtures with different raw materials were produced and printed. Measurements of workability of fresh concrete by four different methods were conducted and printability windows were obtained. Finally, properties of hardened concrete such as compressive strength, ultrasonic pulse velocity and density were also measured. 2. Experimental program 2.1. Materials and printing system Crushed limestone, siliceous river sand and a combination of both (50% limestone + 50% river) were used as aggregates in the concrete mixtures, and their granulometry is given in Fig.1. It can be seen that river sand is much



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coarser than limestone filler and this is the reason why a mixture of both was also used. Maximum size of 1 mm was selected as the diameter of the printing nozzle was relatively small (~2 cm). Regarding the binder, cement type II 52.5 was used at a quantity of 500 and 830 kg/m³. Fly Ash (FA) with relatively high CaOfree content (≈5%), a by-product from lignite fired power plants, and Ladle Furnace steel Slag (LFS), a by-product of steel industry, were also used as alternative cementitious materials along with Silica Fume (SF) in the mixtures. CFA or LFS replaced 20 wt.% and SF 10 wt.% of cement. CFA and LFS replaced an amount of cement not only for cost reduction, but also to reduce concrete shrinkage due to high cement paste quantity. Water/binder ratio ranged from 0.34 to 0.56, depending on type of aggregates and binders used. A superplasticizer (Sika Viscocrete 300) at various addition rates (0-2.5 wt.% of binder) was used in order to obtain different levels of workability for the same mixture. The purpose of the relatively large number of mixture parameters was the production of a large number of concrete mixtures (over 20) with different workability in order to establish the limits for accepting them as printable or not. Limestone filler

River Sand

Passing (%)

100 75 50 25 0 0.01

0.1 Sieve (mm)

1

Fig. 1. Granulometry of various aggregate mixtures used.

A prototype printing system was introduced to print and check all the latter parameters in small scale experiments. The system includes the 2 cm diameter nozzle for linear extrusion as well as the base where the nozzle prints the layers of the mixtures, which in each turn is also able to move in z axis. Regarding the extrusion mechanism, a screw-kind extrusion system was selected for the extrusion process due to some of the advantages and easiness it offers in comparison to other extrusion methods (syringe extrusion). 2.2. Concrete tests Workability of fresh concrete was estimated using various tests that include a rotational rheometer (Koehler and Fowler (2004)), flow table test according to EN 1015-3 (1999), and Vicat apparatus according to EN 196-3 (2005). All these tests were conducted 0, 15 and 30 min after mixing in order to determine the rate of which the workability is lost for the given 3D printing system. However, for performing these tests, an adequate quantity of the material must be extracted from the printing system and results are obtained after the required testing time. Additionally, in real scale applications, workability of 3D printing concrete is prone to even small variations of environmental conditions (temperature, humidity, moisture of raw materials, etc). For these reasons, a novel method was implemented on selected mixtures in order to estimate real-time workability of fresh concrete during printing. The electric power consumption of the electric motor that rotates the screw extruder was measured and correlated with the corresponding values of workability obtained from the flow table test. This way, the properties of fresh concrete can manually or automatically be corrected by adding chemical additives in the print-head (superplasticizer, viscosity modifier, retarder etc.), using appropriate equipment as proposed by Gosselin et al. (2016). The final workability parameters that were measured are presented in Table 1. The threshold values of all the above parameters in order to characterize the concrete mixture as printable were obtained during the printing procedure, where the material must be able to be extruded from the nozzle. On the other hand, buildability can be estimated by the number of layers of the printing specimen that can be achieved without

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collapse. Malaeb et al. (2015) proposed that 5 layers were considered to be the target and this was the method that was adopted. Additionally, dimensions of the first and fifth layer were also a criterion for buildability. The height ratio of the first layer versus fifth layer should be kept around 1 in order to accept the mixture as printable. Final criteria for printability and buildability are given in Table 2. Table 1. Parameters tested for measuring workability of 3D printing concrete. Standard

Test apparatus

Parameter tested

ASTM C 1749

Rotational Rheometer

Static Yield Stress (Pa)

EN 1015-3:1999

Flow table

Expansion (mm)

EN 196-3:2005

Vicat

Vicatscale reading (mm)

-

Real-time monitoring of workability

Electric power consumption of electric motor rotating screw extruder (W)

Table 2. Criteria for accepting concrete mixture as printable or not. Characteristics of 3D printing concrete

Accepted

Not accepted

Printability

1. The mixture is extruded through the nozzle

If 1 or 2 do not apply

2.Good printing quality meaning no voids, no dimensional variations of extruded material Buildability

3. Five layers of printing material can be achieved without collapse

If 3 or 4 do not apply

4. Height of 1st layer versus height of 5th layer ~ 1

Regarding hardened concrete, compressive strength was measured on 40x40x40 mm cubes after 28 days of curing in the humidity chamber. Additionally, density and Ultrasonic Pulse Velocity (UPV) of concretes were also recorded. Volume stability of selected mixtures, which is very important since shrinkage problems can be severe in 3D printing concrete due to high cement paste quantity, was also tested according to Le Chatelier apparatus (EN 196-3:2005). 3. Results Concrete mixtures produced with different aggregates, binders and different amount of water and superplasticizer were produced, tested for workability according to four different tests and printed in order to have available a wide data range of measured workability parameters and finally define their threshold values that characterize a concrete mixture as printable. In Fig.2, the mixture with river sand as aggregate, binder of cement, LFS and SF, and 2.5 % (left speci-

Fig. 2. River sand, cement, LFS, SF mixture with higher (left) and lower (right) amount of superplasticizer.



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men) and 1 % (right specimen) superplasticizer by weight of binder can be seen. It is obvious that the mixture with higher quantity of superplasticizer, even though it fulfills criteria 1,2 and 3, does not meet criteria 4 regarding buildability, since height ratio of 1st layer versus 5th is 0.3, so it is characterized as not printable. On the other hand, the right specimen fulfills all 4 criteria and is characterized as printable. Mixture with limestone as aggregate and cement as binder can be seen in Fig.3. By adjusting water and superplasticizer amount, three different workability levels were achieved, high, moderate and low, however all of them where considered as not printable. Mixture with high workability does not meet criteria 3 and 4. Mixture with moderate workability does not meet criteria 4. Mixture with low workability does not meet criteria 2, since the final layer is printed with voids. a

b

c

Fig. 3. Limestone and cement mixture with (a) high (b) moderate and (c) low workability level.

By applying the criteria of Table 2 on all the printed mixtures, upper and lower limits of workability parameters that were tested by four different tests and characterize concrete as printable were obtained and results are presented in Table 3. Expansion measured according to flow table test was found to be more consistent than Yield stress or Vicat value, since the printability lower limit of 18 cm and upper limit of 24 cm applied to all the mixtures that were tested and printed. On the contrary, threshold values of Yield stress and Vicat for accepting concrete mixture as printable were not so clear. For example, some mixtures with Vicat value lower than 1mm were found to be printable according to criteria of Table 2, while others with 10mm were not printable. The above can also be seen in Figs. 4 and 5 where expansion is correlated with yield stress and Vicat respectively. In Fig.4. It can be seen that for flow table value of 18 cm, yield stress ranges from 200 to 6000 Pa. Even higher fluctuations are observed in Fig.5, for example for 22 cm expansion, Vicat value was measured 0.5 mm in one mixture and 30 mm in another one. Power consumption of the electric motor rotating the screw extruder was also considered as a workability parameter. Unfortunately, it could only be measured on two mixtures with river sand, one with 500 kg/m³ and the other with 830 kg/m³ cement as binder. Threshold values of power consumption that were obtained are also given in Table 3, while in Fig.6, expansion versus power is given. It can be seen that regardless the quantity of cement, for the upper limit of expansion (24 cm), the limit of power consumption is the same for the two mixtures (630 W). On the other hand, for the lower limit of expansion (18 cm), the mixture with higher quantity of cement (830 kg/m³) has lower power consumption than the mixture with 500 kg/m³. This can be attributed to the fact that lower quantity of cement renders to higher quantity of aggregate in a given volume of concrete and consequently, more friction induced by the aggregates in the moving parts of the screw extruder, especially in the case of low workability mixture. Another important parameter of workability in 3D printing concrete is the loss of workability with time. Expansion of mixtures with the three different aggregates used was measured 0, 15 and 30 minutes after mixing and results are Table 3. Threshold values for accepting concrete mixture as printable. Parameter tested

Lower limit

Upper limit

Expansion (cm)

18

24

Yield stress (Pa)

500±300

1800±500

Vicat value (mm)

2±1.5

20±10

Power consumption of electric motor rotating screw extruder (W)

7501/6702

6301/6302

1: mixture with river sand and 500 kg/m³ cement 2: mixture with river sand and 830 kg/m³ cement

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8000

40

6000

30

Vicat (mm)

Yield Stress (Pa)

160 6

4000 2000 0

10

15

20

20 10 0

25

10

Expansion (cm)

500kg/m³ 830kg/m³ Expansion (cm)

Power (W)

30

700 650

25 20 15

15

20

Expansion (cm)

25

Limestone aggregate River sand aggregate 50% Limestone + 50% River sand

800

600

20

Fig. 5. Flow table expansion versus Vicat along.

Fig. 4. Flow table expansion versus Yield stress.

750

15 Expansion (cm)

25

Fig. 6. Electric power consumption of screw extruder motor vs. flow table expansion for mixtures with 500 and 830 kg/m³.

0

10

20

30

Time (min) Fig. 7. Loss of workability with time of concretes with different cement aggregates quantity.

presented in Fig.7. Concrete with limestone filler lost workability in a higher rate than ones with river sand or combination with limestone and river sand. This can be explained by the granulometry of aggregates. Limestone filler has more fines that absorb more water from the mixture. Regarding hardened concrete properties, density of concrete was measured, between 1.9 and 2.1 g/cm³, depending on the aggregate and binder. Density decreased when limestone filler rate increased, or when cement is replaced by FA or LFS. Compressive strength and UPV, as expected, are significantly affected by the type and proportions of raw materials in the mixtures. As seen in Fig.8, compressive strength is decreased when the Water/Binder ratio is increased and a maximum strength of 70 MPa was achieved for W/B ratio of 0.4. Regarding the type of aggregates, when the W/B ratio was kept constant, mixture with river sand and limestone filler showed the best strength results followed by the one with 100% river sand. An example of strength development for mixtures with 500 kg/m³ cement and different aggregates is given in Fig.9. The substitution of part of cement by supplementary materials such as FA and LFS decreased compressive strength. In Fig.10, mixtures with combination of river sand and limestone as aggregates, 500 kg/m³ quantity of total binder and different binders is given. When FA or LFS replaced part of cement, compressive strength was reduced by 30%. UPV, a non destructive method for estimation of strength, was also measured and correlated with experimental results of compressive strength (Fig.11). Soundness of selected printable mixtures was also tested according to EN 196-3:2005. The difference of distance measured between the indicator points after boiling was low (0.5-1.5 mm), which means that the possibility of expansion of concrete due to free CaO and MgO is also low. 4. Conclusions Workability of fresh concrete used as material for additive manufacturing was measured according to four different tests. By measuring a wide range of mixtures produced with various raw materials (aggregates, binders) with different

100 80 60 40 20 0

0.3

0.4

0.5

0.6

0.7

Compressive strength (MPa)

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Compressive strength (MPa)



50

47.97

40

32.95

30

31.86

20 10 0

Cement

Cement + FA

Cement + LFS

Fig. 10. Compressive strength for different binders.

40.24

40

38.83 27.34

30 20 10 0

50% river sand + 100% river sand 100% limestone 50% limestone

Fig. 9. Compressive strength for different aggregates.

Compressive strength (MPa)

Compressive strength (MPa)

60

Binder 500kg/m³

Cement 500kg/m³

50

Water/Binder ratio Fig. 8. Compressive strength versus Water/Binder ratio.

161 7

80 60 40 20 0 4500

5500

6500 UPV(m/s)

7500

Fig. 11. Compressive strength versus UPV.

workability levels, printing them with a printing system with screw extruder and setting criteria for accepting them or not as printable, printability windows were obtained. The criteria that were applied of either accepting or not the mixture as printable were proven adequate. Experimental data showed that flow table test was more consistent than the other methods and printability window for the printing system used was found between flow table expansion values of 18 and 24 cm. Time after mixing for moving from the upper limit to the lower was also measured and was highly depended by the type of aggregates used. A maximum of 30 minutes was obtained without using any retarder additives. Electric power consumption of the motor that rotates the screw extruder was considered as a parameter of measuring real-time workability of the mixture, making it possible to modify it on time in real scale applications by adding chemical additives during printing. Very strong correlation was observed with expansion values from the flow table test, however it should be noted that the threshold values of power obtained by the experimental data refer only to the specific equipment and materials used. Nevertheless, after calibration, the method can be applied to other printing equipment and materials. Regarding the type of aggregates, an adequate number of river sand and combination of river sand and limestone based concrete mixtures were able to be printed successfully. On the other hand, most of limestone based mixtures were considered as not printable. Additionally, the limestone mixtures required higher amount of water and superplasticizer in order to achieve the same level of workability with the other mixtures, leading to lower values of compressive strength. Higher strength levels (maximum 70 MPa) were obtained for the combination of river sand and limestone. The use of alternative cementitious materials such as fly ash and ladle furnace slag as a replacement of cement (20wt.%) results to average reduction of compressive strength by 30% and density by 10%, compared to mixtures with

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100% cement as binder. It should also be mentioned that in most cases during printing, it was observed that fly ash mixtures showed reduced values and higher loss rate of workability with time compared to other mixtures. However, lower cost and volume stability of hardened concrete are expected to be the advantages of using fly ash or ladle furnace slag in concrete for 3D printing. References Apis CorTM, [Online]. Available: http://apis-cor.com/en/(Accessed 15/04/2018). Cesaretti, G., Dini, E.,Kestelier, X.D.,Colla, V.,Pambaguian, L., 2014. Building components for an outposton the lunar soil by means of a novel 3d printing technology. Acta Astronaut. 93, 430-450. CyBe Constructions, [Online]. Available: https://cybe.eu/(Accessed 15/04/2018). EN1015-3, 1999.Methods of test for mortar for masonry, Part 3: Determination of consistence offresh mortar (by flow table). EN196-3, 2005.Methods of testing cement-Part 3: Determination of setting timeand soundness. Gosselin, C., Duballet, R., Roux, Ph., Gaudillière, N., Dirrenberger, J., Morel, Ph., 2016. Large-scale 3D printing of ultra-high performance concrete - A new processing route for architects and builders. Materials and Design 100, 102-109. IAAC. 2016. Institute for advanced architecture of Barcelona. Available: https://iaac.net/research-projects/large-scale-3d-printing/3d-printedbridge/ (Accessed 15/04/2018). Kazemian, A., Yuan, X., Cochran, E., Khoshnevis, B., 2017. Cementitious materials for construction-scale 3D printing: Laboratory testing of fresh printing mixture. Construction and Building Materials 145, 639-647. Khoshnevis, B., 2004. Automated construction by contour crafting-related robotics and information technologies. Automation in Construction13, 5-19. Koehler, E., Fowler, D., 2004. Development of a portable rheometer for fresh Portland cement concrete. Available: https://repositories.lib.utexas. edu/bitstream/handle/2152/35338/105-3F_completed.pdf?sequence=2 (Accessed 15/04/2018). Lim, S., Buswell, R.A., Le, T.T., Wackrow, R., Austin, S.A., Gibb, A.G., Thorpe, T., 2011. Development of a viable concrete printing process. Proceedings of the 28th International Symposiumon Automation and Robotics in Construction, (ISARC2011), Seoul, SouthKorea, 665-670. Malaeb, Z., Hachem, H., Tourbah, A., Maalouf, T., El Zarwi, N., Hamzeh, F., 2015. 3D Concrete Printing: Machine and Mix Design. International Journal of Civil Engineering and Technology 6, 14-22. Perrot, A., Rangeard, D., Pierre, A., 2016. Structural built-up of cement-based materialsused for 3D-printing extrusion techniques. Mater. Struct. 49, 1213-1220 WASP, [Online]. Available: http://www.wasproject.it/w/ (Accessed 15/04/2018). WINSUN, [Online]. Available: http://www.winsun3d.com/En/Contact/ (Accessed 15/04/2018).