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3D Printing Concrete Technology and Mechanics

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 technical paper

3D PRINTABLE CONCRETE TECHNOLOGY

AND MECHANICS
by S. Cho, P.J. Kruger, S. Zeranka & G.P.A.G. van Zijl

ABSTRACT A microcontroller unit (MCU), the core of the 3D printer, controls the
Growing interest in additive manufacturing in the construction industry input/output (I/O) signals and is powered by a 12 V power supply unit
has promoted research in 3D printing of concrete. A gantry-type 3D (PSU) to accommodate other electronic features like fans and lighting.
printer for concrete was designed and manufactured at the Department The software generated G-code according to the 3D model is interpreted
of Civil Engineering, Stellenbosch University. Characteristics of 3D by the MCU and communicates with the stepper motors to produce the
printable concrete are investigated and reported. In the fresh state, required nozzle movement.
thixotropic behaviour is required in the form of high static shear yield The gantry printer allows three translational degrees of freedom
stress, but relatively low dynamic yield shear stress when the material (DOF), with the option for future expansion to rotational DOF to enable
is agitated by pumping and extrusion in the 3D printing process. Once complex geometrical detail with alternative nozzle shape and size.
agitation stops, i.e. when a layer has been 3D printed, fast re-building of Currently, a 25 mm diameter nozzle is utilised to print a uniform cross-
the static yield stress is required to retain the printed shape despite self- section around bends in the absence of rotational DOF. The movements
weight and that of upper layers. In the hardened state, the interfaces in of the gantry system in the horizontal plane (x and y-direction) and
the layered structure may be regions of weakness. Results of rheometer vertical direction are allowed by the mounted linear guide and rail
tests to characterise thixotropy, mechanical strength and stiffness tests, systems. In the horizontal plane, a belt and pulley system driven by
as well as interfacial bond strength tests in the hardened state, are selected stepper motors are employed for each axis, while ball screws
presented. An evolution of 3D concrete printed elements is presented. are the chosen mechanism for vertical movement of the gantry in which
back drive can be prevented if there is a loss of power. The 3D printing
1. INTRODUCTION platform shown in Fig. 2 is a stabilized trolley with 12 polyurethane
A research program on 3D printing of concrete (3DPC) is executed by the wheels with an ultimate capacity of 700 kg each. The trolley facilitates
Centre for Development of Sustainable Infrastructure (CDSI) at Stellenbosch the removal and transport of the printed object from the gantry frame.
University. An industrial-grade gantry type 3D printer of roughly 1 m cube The gantry frame is paired with a 3-phase 380V 3kW locally
build volume, was designed and manufactured in 2017-2018. The point of manufactured concrete pump (Rockcrete TSL), originally purchased for
departure was to develop a robust, versatile laboratory printer that enables research on the sprayed application of fibre concrete, also known as
research on a range of concrete material classes, printing speeds and shotcrete, with a maximum aggregate size of 4 mm. A variable
geometrical complexity. Knowledge and experience in concrete pumping, frequency drive (VFD) was supplemented for pump motor speed control,
spraying and extrusion [1-3] informed the selection of an appropriate which is also manipulated by the MCU. This enables control of the
concrete pumping pressure range for the standard to high performance concrete pumping speed, required for instance when bends of small
(HPC) grades of concrete and fibre reinforced concrete (FRC). radius are printed and excessive deposition may result in inconsistent
filament thickness, or bulging.
The Marlin firmware based MCU is paired with two G-code based
2. DEVELOPMENT OF A 3D CONCRETE PRINTER
software packages in operator PC, namely ‘Slic3r’ and ‘Simplify3D’.
Three types of 3D concrete printers are typically used, gantry, robotic,
Both packages provide various customizing options for different types
and crane systems (see Fig.1). Each type has merits and drawbacks,
of printer and material. Particularly, vase mode printing, printing spirally
however, the gantry type was selected since it is relatively simple and
upwards instead of printing each level of layers, is functional in both
inexpensive to build, versatile and the most common type in the
software. The option saves time and improves the printing quality for
research field. Conceptual, mechanical and electrical design commenced
certain objects such as circular columns.
in 2017. The industrial-grade, laboratory scale, gantry-type 3D printer
The 3D concrete printer enables the research team to produce
with outer dimensions 1.3 x 1.3 x 1.67 m with a build volume of roughly
laboratory scale structural elements (walls, beams, columns etc.) for
1 m3 was constructed within 7 months.

Figure 1 - 3D concrete printers: (a) Gantry (b) Robotic (c) Crane type [1]
1
Department of Civil Engineering, Stellenbosch University, South Africa

CONCRETE BETON 11
technical paper

and shape of a printed object also influence the print quality, but
the distinct rheological characteristics of the material will notably
influence the buildability and pumpability.
Rheology is the branch of physics that studies the deformation
and flow phenomena of matter. Material flow initiates when the
applied shear stress exceeds the static yield stress of the material.
Once the material starts to flow, the measured shear stress reaches
a quasi-equilibrium plateau, defined as the dynamic shear stress. A
distinct difference between the static and dynamic yield stress of
the material is required for 3DPC and is defined as thixotropic
behaviour. Thixotropic fluids as dispersions build an intermolecular
system of forces at rest, which results in flocculation of particles
that increases the viscosity of the fluid, enabling it to support its
own weight [7]. Flow initiates when the intermolecular structures
are broken by external energy via agitation, resulting in shear-
thinning of the material. This phase is called de-flocculation, which
Figure 2 - 3D concrete printer component layout and final assembly
reduces the viscosity of the material. Once the external energy is
removed, the thixotropic material starts to re-flocculate and
regains pseudo-solid behaviour as the original microstructure is
rebuilt and the original viscosity is restored. This 3-phase thixotropic
testing, with the goal to contribute towards fundamental research for
behaviour is depicted in Fig. 3 (c). Each phase illustrated in the
the 3DPC industry. The printer complies with structural design criteria of
figure can be closely associated with the following timescales:
strength and stiffness, in order to accommodate high volume concrete
• Flocculation: concrete is placed into the hopper of the pump.
printing and nozzle head speed without excessive vibration.
• De-flocculation: the material is agitated by rotational paddle or
auger, and pumped through the hose.
3. MATERIAL CHARACTERISTICS FOR 3D PRINTABLE • Re-flocculation: the material is extruded and deposited onto
CONCRETE the printing bed or a previous layer.
3.1 Rheology
3D printing is widely used in various industries, such as the The thixotropic behaviour is determined by several factors including
automobile, aviation, biomedical, dental, food, fashion and the water content, temperature, chemical admixtures, cement
manufacturing industries. Despite the various and sophisticated extenders, aggregate grading, and rate of hydration. The
additive manufacturing techniques developed, the material restoration rate between the static and dynamic yield stress can be
deposition and formation are mainly thermal-processed. Hence, considered as the degree of thixotropy. A higher degree of
heating and cooling techniques are vital features of the printing thixotropy is desired for 3D printing application in concrete. The
process. However, the conventional 3D printing deposition and degree of thixotropy can be characterised by measurement of the
thermal-processed formation, such as metals or plastics, are not shear stress of the fresh concrete with a rheometer. The measured
essential for concrete, although heating to 60 – 70 ºC can be used initial static and dynamic yield stresses are 1860.4 Pa and 1474.4
for faster setting and strength development. Note that no thermal Pa according to Fig. 3 (b). The test result further shows rapid
activation was used in the 3DPC research results reported here. restoration and build-up of the static yield stress within a short
Instead, concrete requires modified rheology through optimised period of less than 1 minute. Note that return of the 3D printer
mix design, admixtures and other additions including nano- nozzle to deposit an upper layer varies according to nozzle speed
materials [4,5] and fibres [6] to be suitable for 3D printing in terms of and the printed structural element’s geometry and size. Typical
transport (pumpability) and buildability, or extrudability and shape return periods can be several minutes. For a laboratory test 3D
retention under self-weight and subsequently deposited upper print of a 400 mm diameter circular hollow column, the return
layers. period is 21 seconds with a 60 mm/s printing head speed. The re-
As additive manufacturing is formwork free, the freshly extruded building rate of the material static shear yield stress, is used to
material must have appropriate shape retention, and develop design a 3D concrete printing process, in order to prevent instability
sufficient strength and stiffness rapidly to support subsequent and collapse of the unsupported printed object, considering the
layers. Hence, traditional concrete designed for casting in formwork geometry and print settings [8]. Fig. 4 presents a bilinear time-
cannot be directly used. Concrete can be designed to be stiff, or evolution of static yield shear stress, collecting the peak shear
highly viscous, in the form of so-called zero slump / pseudo-solid stress values from Fig. 3 (b), and more at longer waiting periods up
concrete, by modification of the constituents and their proportions to initial set of the concrete. The graph in Fig. 4 serves as a 3DPC
to retain the extruded shape without significant deformation. design tool for the time-dependent resistance, which must exceed
Shape retention is one of the prime factors influencing the quality the demand, typically the weight of upper layers as 3D printing
of the extruded layer. In contrast, the material is required to have progresses. The initial gradient of static yield shear strength
low viscosity at transport during pumping, minimizing the evolution is depicted by RThix, referring to the rapid rebuilding by
probability of ingredient segregation under high pumping pressure re-flocculation. The second gradient is depicted AThix, which refers
in the range of 1 to 4 MPa [1]. Segregation may lead to blockage or to a lower rate of strengthening, brought about a structuration
poor dispersion and associated inferior mechanical and durability process following re-flocculation (Fig. 3 c).
properties of the extruded product. The printing speed, path, size

12 NUMBER 158 | SEPTEMBER 2019

 technical paper

Shear Stress
Static Yield Stress

Dynamic Yield Stress

Time
(a)

3000 2,880.9 (+5) Test Interval (min)

2,421.2 (+2) Initial
2,246.1 (+1) +0
1,723.6 (+0) +1
Shear Stress (Pa)

2000 1,860.4 (ini) +2

+5

1000

0
0 2 4 6 8 10 12
(b) Time (s)

(d)

Figure 3 - (a) Stress growth rheological test result depicting the

clear difference between the static and dynamic shear yield
stresses of a thixotropic material,
(b) static yield stress re-building test result with different resting
periods. The result shows rapid static yield restoration after
agitation
(c) break-down and build-up phases of thixotropic materials
Initial Flocculation De-Flocculation due Re-Flocculation illustrated by means of particle flocculation,
to Agitation after Agitation (d) German Instruments ICAR Rheometer direct viscosity
(c) measurement setup used in the work reported here.

water-to-cement ratio of 0.45, is presented in Table 1. Note that

Static Yield Stress
polypropylene (PP) fibres are included in the mix. The relatively low
volume content and stiffness of PP fibres incorporated here control
plastic shrinkage cracking and reduces brittleness of the printed
Athix
product [6]. In continued research, the authors are investigating
incorporation of high strength and high stiffness polymeric fibres
to enhance hardened mechanical properties, including flexural
strength and toughness.

Table 1 - Mix design of a 3D printable mortar

Material Resting Time/
Re-Flocculation Structuration
Time After Deposition Constituent Mass [kg]

Cement (CEM II 52.5N) 579

Figure 4 - Static yield shear strength as a function of time illustrated
by re-flocculation and structuration mechanisms [13] Fly Ash 165

Silica Fume 83
The 3D printable mix was designed mainly based on the rheological
Sand 1167
performance of the material. From the literature [9,10], the optimal
mix design was developed with locally available constituents, Water 261
including CEM II/A 52.5N cement, Class S fly ash, silica fume Superplasticizer 1.48% by mass of binder
(Microfume supplied by Silicon smelters), and natural Malmesbury
Viscosity Modifying Agent 0.13% by mass of binder
sand with fineness modulus of 2.12. The final mix design, with

CONCRETE BETON 13
technical paper

100 appropriately binding layers to respond as a continuum. To verify the

Fuller Ideal Grading
interfacial bond, flexural tests were performed on beam specimens of
Standard HPC Mix 80 roughly 40 mm x 40 mm x 160 mm cut from a 3D printed structure, as
schematised in Fig. 6. Flexural tests were performed in a Zwick Z250
60 materials testing machine (MTM) with a span length (l) of 150 mm, and

% passing
loaded at third points (x = 50 mm). All specimens failed at an interface
within the uniform bending moment zone (between load points). From
40
the ultimate load, the maximum flexural strength was calculated,
considering linear elastic behaviour, i.e. the modulus of rupture was
20 calculated. These flexural strengths are denoted as the interfacial
(flexural) bond strength (IBS) in Table 2, and determined at 28 day age
0 only on three specimens. Note that the 3D printed column was kept in
Pan 0,075 0,15 0,3 0,6 1,18 2,36 4,75 laboratory conditions at 23 ±2ºC and 65 ±5% relative humidity until
Sieve Size (mm) sawing the specimens and subsequent testing.
The 19% lower interfacial flexural strength (IBS) of 6.8 MPa,
Figure 5 - Particle size distribution of the binder and sand combined, compared with the cast specimen flexural strength of 8.4 MPa could be
compared to Fuller-Thompson’s ideal curve ascribed to both the curing regime and the interfacial bond
characteristics. Note that there was a short time lapse of less than one
The Fuller Thompson theory [11], which aims to achieve maximum
packing density, is used as optimal aggregate grading target. The Table 2 – Mechanical characteristics of 3D printable mortar
shear rate of cement paste is inversely proportional to granular (coefficient of variation in brackets)
aggregate packing fraction [12] in which the shear rate is determined
Age ffl (MPa) fcu (MPa) E (GPa) IBS (MPa)
by the state of flocculation. Maximum packing and minimum voids
are expected to yield lower shear rates and higher state of 1 day 1.7 (0.081) 7.9 (0.026)
flocculation. A recent study by Weng et al. [13] confirms that the 7 days 7.3 (0.050) 55.6 (0.006) 26.6 (0.023)
Fuller Thompson theory can serve as a reasonable rheological
28 days 8.4 (0.057) 70.6 (0.103) 30.8 (0.020) 6.8 (0.021)
design approach for 3DPC. A natural sand available in the Western
Cape is selected for use in the 3DPC mix reported here. It is 56 days 8.7 (0.02) 80.0 (0.151)
possible to achieve a Fuller-Thompson grading curve by sieving and
re-mixing, which is generally an expensive process. Given the
reasonable agreement with the ideal curve shown in Fig. 5, and
associated cost of re-grading, the natural sand is accepted. Note
that Fig. 5 shows the combined grading of the binder and sand
particles.

3.2 MECHANICAL PROPERTIES

Rheology in the fresh state determines 3D print quality, however the
mechanical robustness in the hardened state is also crucial. The
compressive strength, fcu determines the particular structural application
Figure 6 – Interlayer bond strength (IBS) (a) specimen cut from a
class and is conventionally used as a quality control parameter of
3DPC column, (b) flexural test setup
concrete. It is often linked to several other mechanical properties of
concrete, such as Young’s modulus, E, and flexural capacity, fflex of
minute between printing successive layers in the 3DPC column.
concrete by correlation, making it an important material property.
Interfacial bond is the subject of continued research by the authors. To
The concrete further gains strength through crystallisation and
investigate the potential of plastic shrinkage and cracking of 3DPC
structuration inside of the concrete mass over time, through the process
structures, due to the lack of mould protection, plastic shrinkage tests
of hydration. High strength concrete (HPC) is defined by the American
were recently performed and reported by the authors[6]. For the
Concrete Institute (ACI) as concrete with 28-day compressive strength
particular mix presented here, no plastic shrinkage cracks occurred,
of at least 55 MPa [14]. Table 2 summarises the compressive and flexural
even at extreme climatic conditions of 20 km/h wind, 40ºC air
strengths, as well as Young’s modulus of the concrete used here for
temperature and 10% relative humidity.
3DPC. Note that standard specimen preparation and testing were
performed according to EN 196-1 for four-point flexural tests, and
ASTM C469-02 for Young’s modulus. Flexural specimens of size 40 mm 4. 3D CONCRETE PRINTING PROCEDURE AND PRODUCT
x 40 mm x 160 mm and Young’s Modulus specimens of 100 mm EVOLUTION
diameter and 200 mm height were cast in regular moulds, protected 4.1 Printer Calibration
and stripped after 1 day, and water cured at 23 ±2ºC until the age of Since the concrete material is novel to 3D printing, none of the
testing. However, the 3DPC process might alter the material commercially available 3D printing software has material pre-
microstructure and thus also the mechanical properties. Also, without set values for concrete. Hence, the determination of the primary
the protection of moulds, earlier drying might occur. In addition, the printing parameters, such as the extrusion rate, print head speed
interface between layers may significantly alter mechanical behaviour. and layer height, was necessary before printing an object. The fixed
To a large extent, strong interfacial bond may counter such changes, by parameters are shown in Table 3.

14 NUMBER 158 | SEPTEMBER 2019

 technical paper

Table 3 - Fixed printing parameters based on the printer

specification

Nozzle diameter 25 mm

Filament diameter 25 mm

Extrusion width 25 - 30 mm

Build volume 990 x 860 x 980 mm (X, Y and Z)

(a)

Mixed concrete material

(Rheology)

Choose
Print head speed

(b)
Calibrate
Extrusion Rate
(Using G code)

If unacceptable

Extrude layer
width check

(c)
If acceptable

Ready to print
(Save the setting for future)

Figure 7 - Flowchart depicting the process of obtaining correct layer

width for various concrete materials with different rheology.

(d)
Recall from Section 3 that freshly mixed concrete has a certain stiffness
and flowability based on the constituents. Since the material rheology Figure 8 - Typical poor condition or failure during the printing
process
cannot be modified simply without changing mechanical properties,
the stiffness and flowability of the material must be characterised or
investigated in advance to be acceptable for printing, while also directly affects the interlayer bond strength, which influences the
attaining appropriate mechanical properties in the hardened state. integrity of the structural component and its mechanical properties.
Thus, the print head speed is only considered as a variable parameter to The layer thickness was obtained in the range of 10 – 15 mm depending
determine the optimum extrusion rate. The printing speed was tested on the condition of the material.
within a range of 50 – 100 mm/s based on the previous study by Nerella
et al.[9]. Since the standardised test for printability of the material has During the calibration process, a few typical observations (Fig. 8) of
not yet been developed, the determination of the parameter was trials performed show imperfection and irregularity in quality or global
judged by the authors. For each printing speed, the extrusion rate must failure:
be calibrated until the extruded layer width does not exceed the nozzle (a) A loose translational pulley not engaged properly with stepper
diameter by 5 mm, thus a layer width in the range of 25 – 30 mm. motors resulting in a slip. The slip causes an inaccurate print path
The structural component in the construction environment is, first or shifting of the printing plane entirely.
of all, desired to have global stability. In a first approach the buckling (b) Residual water inside of the hose altering the flowability of the
effect as a cause of failure is disregarded to investigate the buildability material.
of the concrete material. Hence, cylindrical hollow column is chosen for (c) At the vertical lifting position for each layer, extra material is
a buildability test model. The printing time, the compressibility of each deposited due to gravity feed. Thus, an actuator at the nozzle is
printed layer under the self-weight and printed object height were required to control material flow more accurately.
compared in each printing outcome. The optimum layer thickness was (d) Printing a bathtub. The action described in (c) causes global
investigated by printing the buildability model. The layer thickness deflection of the wall.

CONCRETE BETON 15
technical paper

4.2 Printing Quality and Shape

Retention
A 400 mm diameter circular hollow column
is 3D printed and shown in Fig. 9 (a) and
(b) to demonstrate progressively improved
control and material performance. The
nozzle translational speed while printing
of 60 mm/s was maintained for all prints.
The very first 3D printed specimen of the
group is shown in Fig. 9 (a), using a mortar
material by another research group [1].
The specimen exhibited inconsistent layer
thickness and some discontinuity in printing
Figure 9 - Progression in 3D concrete printing control and material rheology at SU:
(a) First printed circular column; (b) improved layer uniformity and surface quality due to due to pump feeder air ingress and poor
improved rheology and pump speed control at the onset of new layers; control in pump speed. The air ingress is
(c) the buildability test model was printed with increased height before collapse due to caused by the high viscosity of the material,
plastic yield of bottom layers. which required more agitation energy in the
hopper to feed uniformly. The poor surface
quality is shown in the figure which indicates
inadequate rheology for 3DPC. The average
layer thickness was not recorded since the
specimen collapsed due to operator error
just after the print process.
The subsequent specimen, shown in
Fig. 9 (b) showed a near perfect cylindrical
column of 47 layers (height 471 mm)
despite the presence of additional material
deposits at the layer print start position. The
rheological improvement of the material led
to the notably improved uniformity of the
extruded layer and the surface quality. Since
a discontinuity is observed at some points,
an extra energy source (poker vibrator
in hopper) was considered to improve
consistency.
Figure 10 –3D printing of (a) fibre concrete column with a 90 degree twist over 0.6 m of the Lastly, Fig. 9 (c), the Ø250 mm circular
0.8 m height of 70 layers, showing a top and side view on the right; (b) benchmark dome[15]. hollow column was printed to validate
buildability model. The small addition of
retarder helped to reduce the required
agitation energy for consistent layer printing
Table 4 - 3D printed object geometry. Average of 2-4 readings by extending the period of the fresh state
(coefficient of variation in brackets) and reducing dynamic yield stress. A concrete
Average layer Remarks on poker vibrator was employed to provide
Figure Layers Width Height 3DP duration
thickness (mm) material/control additional agitation energy in the hopper.
(mm) (mm) (min:s)
Base Top improvement The material modification, together with the
Collapsed due to
poker vibrator usage, resulted in 59 layers
9a 40 - - 13 - - operator error, (height 590 mm). The use of vase mode
poor quality surface improved the uniformity in layer thicknesses.
9b 47 402.5 478.0 21 11.9 9.3 Best print. Good As the specimen was printed until failure
(0.002) (0.033) (0.046) (0.141) quality surface, for the buildability test, the average layer
improved software
control. thickness was not recorded.
The geometrical complexity was also
9c 59 - 590 13 - - Uniform layer and
best buildability. validated with a 90 degree twisted square
column (Fig. 10 a). Irregular layers are seen
10a 70 250.5 792.5 26 11.9 12.6 Good print; but
(0.003) (0.003) (0.046) (0.152) irregular layers to be reduced, but still appear due to pump
shown due to feeder air ingress. However, both specimens
air ingress. could be 3D printed while remaining stable
10b Dome 14 300 125 3:04 - - Reasonable print of even with the geometrical complexity
varying ascending and high construction rate – see Table 4.
slope geometry
Finally, benchmark structures for 3DCP

16 NUMBER 158 | SEPTEMBER 2019

 technical paper

quality assessment and standardisation

have recently been proposed by the References
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21:56-57.
this regard, with the construction of the first
industrial-grade gantry type 3D concrete printer [15] Bester, F.A., van den Heever, M., Kruger, P.J., van Zijl, G.P.A.G. 2019. Paper ID 395
on the African continent and preliminary tests Benchmark structures for 3D concrete printing. fib Symposium Krakow, Poland,
on high strength fibre-reinforced concrete for 27-29 May 2019.
3DPC. The following conclusions are drawn.

CONCRETE BETON 17
technical paper

• For successful 3D printing of concrete, Seung Cho is a PhD-student in Structural Engineering

a thixotropic material is required to and Civil Engineering Informatics at Stellenbosch
enable pumping and extrusion without University (SU). As member of the Centre for Development
segregation and blockage. Once agitation of Sustainable Infrastructure, his research involves 3D
by pumping and extrusion stops, a high printing of foam concrete. Nanotechnology is essential for
static shear yield stress must develop at developing appropriately thixotropic foam concrete to be
a rate higher than the building or layer 3D printable. He obtained BEng(Civil) with distinction in
deposition rate, in order to resist the 2017, enrolled for MEng(Civil) in 2018, but was upgraded
weight of upper layers. Structural collapse to PhD in 2019.
will occur at too low rebuilding rates due
to plastic yielding of lower filament layers.
• From rheometer stress growth test results
the evolution of static shear yield strength
can be determined and represented Jacques Kruger is a PhD-student in Structural
by a bi-linear approximation. From this Engineering and Civil Engineering Informatics at
resistance curve and the demand of Stellenbosch University (SU). As member of the Centre
upper layer weight, a building rate can be for Development of Sustainable Infrastructure (CDSI), his
determined that will prevent collapse by research involves the development of analytical models
plastic yielding. to quantify constructability performance of 3D concrete
• An average interfacial flexural bond printing. The design and manufacture of the SU 3D concrete
strength of 6.8 MPa, 19% lower than printer formed part of his research. He obtained BEng(Civil)
the inherent composite flexural strength cum laude in 2016, enrolled for MEng(Civil) in 2017, but
of 8.4 MPa was determined in four point was upgraded to PhD in 2018.
bending tests.
• An evolution in successful 3D printing
of concrete elements has been
presented. This has led to the proposal Stephan Zeranka (PhD, BEng in Structural/Civil
of standardisation through benchmark Engineering) is the Laboratory Manager for the Structures
structures for 3D printing of concrete. Division at Stellenbosch University since 2013. His research
This presents a stringent test of material interests are multi-scale structural optimisation towards
suitability, as well as 3D printer precision. innovative structural systems and construction methods
utilising additive manufacturing and high-performance
Current work involves developing a range of and recycled composites.
3D printable concretes, and the development
of prefabricated structural elements and
connections for on-site assembly, towards
industrialised hybrid construction of low to
medium-rise housing. s

Gideon van Zijl (DEng, PrEng) is professor of Structural

Engineering at Stellenbosch University since 2001. His
research interests are structural and computational
mechanics, structural durability and retrofitting, façade
structural engineering and recently, 3D printing of
concrete. Concurrently, structural design guidelines for
cement-based construction materials are developed in his
research group, the Centre for Development of Sustainable
Infrastructure (CDSI).

18 NUMBER 158 | SEPTEMBER 2019

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