Next Article in Journal
Environmental Impact Assessment of Waste Wood-to-Energy Recovery in Australia
Next Article in Special Issue
3D-Printable Concrete for Energy-Efficient Buildings
Previous Article in Journal
The Faster the Better? Optimal Warm-Up Strategies for a Micro Combined Heat and Power Plant
Previous Article in Special Issue
Application of Alkali-Activated Sustainable Materials: A Step towards Net Zero Binder
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Energies
Volume 16
Issue 10
10.3390/en16104181
energies-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

Development of Alkali-Activated 3D Printable Concrete: A Review

by
Syed Mujeeb
1,
Manideep Samudrala
1,
Bhagyashri A. Lanjewar
1,
Ravijanya Chippagiri
1,
Muralidhar Kamath
2 and
Rahul V. Ralegaonkar
1,*
1
Department of Civil Engineering, Visvesvaraya National Institute of Technology, Nagpur 440010, India
2
General Manager—Technical Services, Apple Chemie India Private Limited, Nagpur 440022, India
*
Author to whom correspondence should be addressed.
Energies 2023, 16(10), 4181; https://doi.org/10.3390/en16104181
Submission received: 30 March 2023 / Revised: 11 May 2023 / Accepted: 13 May 2023 / Published: 18 May 2023
(This article belongs to the Special Issue Challenges and Research Trends of Energy Efficient Buildings)
Browse Figures
Versions Notes

Abstract

:
The construction world has changed day by day and is becoming more digitalized by introducing new technologies. Three-dimensional concrete printing (3DCP) is one such technology that has automated building process along with several benefits such as reduced material waste, reduced human hazard, and time savings. Traditionally, this technique utilizes cement to construct numerous structures, resulting in a significant carbon footprint and negative environmental impact. There is a need to find alternate solutions to reduce cement consumption. Alkali activation technology has replaced cement completely. The scope of development of alkali-activated 3D printable concrete utilizing agro-industrial byproducts is presented in this study. A review of the fresh and hardened properties of alkali-activated 3D printable concrete was the primary objective. The change in properties of 3D concrete mixes with the variation of additives that influence the ultimate strength parameters is presented. This study explores the curing conditions and in-depth behavior of uses of 3DCP in the construction industry. The environmental benefits over conventional concreting technology are presented. As per previous studies, the optimum mix composition per cubic meter concrete is 600–700 kg/m3 of binder content, 450 kg/m3 of alkali activator solution, and 600–800 kg/m3 of fine aggregate content. This study contributes to the making of 3D printable alkali-activated concrete.

1. Introduction

Three-dimensional concrete printing (3DCP) is a new technology in the construction world with a systematic placement of material to construct a component without formwork using a computer [1,2]. This procedure, known as contour crafting, was introduced years ago and involves employing a Cartesian machine with a concrete extruder [3]. The construction industry faces many challenges to eliminate the problems associated with poor quality, slow productivity, fatal accidents, and insufficient skilled labor [4]. This 3D concrete printing technology is the one suitable alternative to overcome many of these problems [5]. This technology has spread all over the world and rapidly conquered the construction market [6,7]. Three-dimensional concrete printing is performed using the layer deposition method to retain any structure in shape [8,9]. The actual printing of concrete comprises two main parts, namely, hardware and software. In terms of hardware, a 3D printing machine [10] is required for material mixing, along with a delivery system. In terms of software, tools are implemented to print a building information modeling (BIM) file [11,12].
In 3D printing, printers are categorized into three types, gantry, robotic, and crane, which have been successfully used in many studies. The gantry type printer [13] has a fixed height, whereas the crane type is flexible with height adjustment. Both of these are easy to handle and adjustable to any scale. On the other hand, a robotic printer has a fixed dimension and is difficult to rescale [14]. The robot printer has movement in six axes, which facilitates the accomplishment of tasks that are not possible using a four-axis gantry printers. Gantry printers are much preferred over others, unless there is no complexity in the studied objects.
The fundamental advantage of 3DCP is its design flexibility as there are no geometric restrictions for designers and architects. Moreover, 3DCP technology has been employed to produce many curved buildings and gabled roof buildings. However, structural stability was considered in a large-scale building. The entire structure was separated into sections and joined in a correct way to withstand earthquake or vibration activities [10]. A 4 m high support structure for a playground roof was constructed with a complex truss while optimizing shape for good carrying capacity in compression compliance [15].
To print the concrete successfully, many parameters are adjusted such as the maximum acceleration and maximum speed in all directions. Different types of nozzles with circular (diameter 25 mm) and rectangular (25 mm × 25 mm) shapes were tested to check for printability and buildability [16]. The programming for movement of the printer head was established in such a way that the orientation of the nozzle always remained tangent to the tool path to avoid twisting of the filament [16,17]. The 3DCP technical categorization is divided into seven categories: binder jetting, material extrusion, directed energy deposition, material jetting, sheet lamination, powder bed fusion, and vat photo polymerization [18]. The difference between conventional and 3DCP technology is shown in Figure 1. Specifically, 3D printing covers the phases of concrete mixing, block making, labor work, and tools required into a single unit. The distinctive feature of 3DCP eliminates the use of formwork and creates the ability to print any nonstandard geometries [14,19].
Cement is the second most consumed material after water [20]. Conventional concrete production involves many processes from the extraction of each raw material to the final mix, which causes a huge impact on the environment. Among all its constituents, cement is accountable for 5% of global anthropogenic CO2 emissions [21,22]. The 3DCP technology was developed using conventional ordinary Portland cement (OPC).
Alkali activation is a geosynthetic process that chemically binds silicon- and aluminum-rich products in alkaline circumstances to form a 3D chain [23] (via polycondensation), making the concrete strong, durable, and chemically resistant [20]. Inclusion of alkali activation technology in 3DCP has less impact on the environment and releases less CO2 into the atmosphere compared to OPC-based 3DCP [20,24]. Hence, alkali-activated concrete is considered a sustainable alternate to OPC-based concrete [25]. This review is focused on the application of alternate precursors, as well as their effect on the fresh, rheological, and hardened properties of 3D printable concrete along with the environmental impact.

2. Materials and Mix Design

Alkali-activated 3D concrete is a mixture of precursors, fine aggregates, and other modifiers. The raw material characterization affects the physical and mechanical properties of concrete. This characterization is determined by evaluating the physical properties and chemical composition tests of the raw materials. The physical properties are particle size distribution, density, and specific gravity. The chemical composition of materials is found by performing X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM).

2.1. Precursors

The common precursors used in alkali-activated 3D concrete are ground granulated blast furnace slag (Figure 2), fly ash (class F—Figure 3), silica fume (Figure 4) and other materials that are rich in silica (SiO2) and alumina (Al2O3) [26,27,28,29,30]. It is necessary to have in-depth knowledge about various materials used in the mix responsible for many outcomes. Such properties are grain size distribution, chemical composition, and Si/Al ratio.
Fly ash is the most widely utilized material for cement replacement because of its chemical composition. It comes in two varieties: class F fly ash and class C fly ash, with low calcium and high calcium, respectively. The bulk density of fly ash ranges from 800 to 1000 kg/m3 [30].
Another precursor used in alkali-activated concrete to change the workability and flow characteristics is GGBS. It is the byproduct obtained when iron ore [31,32,33], limestone, and coke are heated to a temperature of about 1500 °C in the furnace, with bulk density ranging between 800 and 1000 kg/m3 [30]. When slag is added to fly ash paste, it increases compressive strength, while decreasing both slump and flow value. The setting time for fly ash mortar is typically longer. However, the addition of GGBS to the mix reduces the initial and final setting times due to the pace of chemical reaction [34].
Micro silica or silica fume is used in FA and GGBS binder mix to improve the cohesive nature of alkali-activated paste. It generally comes with a specific surface area (SSA) of 15,000–30,000 m2/kg [35]. The addition of silica fume decreases the passage of electric charge into the concrete, increasing the resistance to chloride ion penetration [36]. The chemical/oxide compositions of FA, GGBS, and SF are shown in Table 1 [37].

2.2. Aggregates

In 3DCP, coarse aggregates are completely avoided in the mix. The oven-dried river sand (Figure 5) comprises three different grades, coarse, medium, and fine sand, with average particle sizes being 840 μm, 498 μm, and 176 μm, respectively [32,38]. The sand-to-binder ratio plays a major role in the mix proportion; it ranges from 1.1 to 1.9 with an interval of 0.1 [35,39].

2.3. Alkali Activation Solution

The phrase “alkali activation” (AA) refers to the reaction of a solid aluminosilicate called the “precursor” in an alkaline environment (caused by the “alkali activator”) to form a hardened paste [40]. The most commonly used alkali activators are presented in Table 2.
Among the abovementioned materials, most authors used sodium hydroxide (as pellets (Figure 6) and flakes (Figure 7)) and sodium silicate (Figure 8) as activators. As per the Indian standard code of alkali activation (IS 17452:2020) [41], the activator modulus, i.e., SiO2/Na2O,ideally ranges from 0.6 to 2. This value is dependent on the contents of GGBS and fly ash. While preparing the solution for the concrete mix, some of the following limits should be met: SiO2 = 30–35%, Na2O = 12–18%, and H2O = 40–50% of the total solution [41]. Table 3 shows the molarities utilized in earlier experiments for alkali-activated 3D-printed concrete.

2.4. Additives

To increase the rheological properties of alkali-activated paste, additives such as attapulgite nano clay (NC) (Figure 9) and polyvinyl alcohol (PVA) (Figure 10) are added. NC is used as a rheology-modifying agent, and its oxide composition is given in Table 1. In alkali-activated 3DCP,nano clay was used to increase the yield stress properties of the mix when it reacts with sodium silicate [42]. As the amount of nano clay is increased, it increases the static yield stress of the internal structure of the mix, which gives agreeable properties of 3DCP. Another additive that can be used in the mix is PVA, which is also a rheology-modifying agent and maintains the durability and mechanical performance of the printed element [48]. The properties of PVA are listed in Table 4.
In 3DCP, the peak hydration initiates the setting time of the mix. To avoid this setting of concrete in pipes and tanks, retarders are used. On the other hand, the mix has to get hard after it comes in contact with the tip of the nozzle. This is achieved by introducing accelerators to attain the yield strength, also termed set-on-demand of 3DCP. Some accelerators include the combinations of lithium hydroxide (accelerator)/sodium gluconate and sodium gluconate/sucrose [51]. The chemical admixtures used are naphthalene- based and polycarboxylate ether (PCE)-based superplasticizers (SP) [31]. These alter the printability property of the mix, which varies with the dosage. Five types of superplasticizers were evaluated for their effect on the mechanical properties of activated slag mixes: (1) melamine-based, (2) naphthalene-based, (3) vinyl copolymer type, and (4) two types of polycarboxylate-based. Trials with 1% superplasticizer by mass of binder for different mixes were performed. NaOH and slag mixes with 4% and 5% Na2O naphthalene-based superplasticizers gave better results over other types for flexural and compressive strengths at 2, 7, and 28 days [52]. A viscosity-modifying agent (VMA) is a polymeric admixture used for altering 3D printable materials. It is a key material to control the stability of the mix and fiber dispersion [44]. Typically, the VMA content is about 1% by weight of binder. Hydroxypropyl methyl cellulose-based VMA is used most frequently. The superplasticizer was used as a liquid with 34% solid content, while the VMA was used as a powder [53].

2.5. Mixing Procedure

A Hobart planetary mixer (Figure 11) can be used to make the alkali-activated 3D concrete [5,54]. The mix is prepared in three different stages. First, the dry mix is prepared from the precursors and fine sand, by feeding them into mixing bowl for about 2–3 min at 250 rpm. In the second stage, additives such as nano clay, PVA fibers, or VMA in powder form are blended with the dry mix for 3–5 min at 250 rpm. The alkali activation solution is added along with superplasticizers and mixed for 5 min at 250 rpm. Thereafter, the speed is increased gradually to 450 rpm to attain the homogeneous alkali-activated mixture [30]. The mix proportions adopted by researchers to develop alkali-activated 3D printable concrete are shown in Table 5.

2.6. Curing

The alkali-activated 3D concrete is usually cured either in heat or in ambient conditions to gain strength. Researchers have suggested curing in the oven at 60–80 °C for 24 h to gain early compressive strength. It was found that the 3 day compressive strength of alkali-activated 3D concrete is equivalent to the 28 day strength of OPC-based concrete [56,57]. Trials were conducted with a mix of fly ash, limestone, slag, and OPC. Samples were cured at 70 °C for 24 h or 48 h in moist conditions. Mixes with more slag content need moist curing to avoid micro cracks. However, oven curing gave better early strengths than moist conditions. An increase in NaOH content gave better strength for 70–85% fly ash and 15–30% limestone. It was observed that 3D printing binders gave similar strength to conventional binders [58,59].

3. Performance Evaluation of 3DCP

The onsite printing of any 3DCP building undergoes many performance evaluations at the laboratory stage. The criteria for adopting the optimum mix to execute the actual prototype structure is discussed in further sections. Figure 12 presents a graphical representation of the systematic methodology for successful 3DCP structure.

3.1. Rheological Properties of 3DCP

In general, 3DCP requires certain characteristics to achieve good quality in printing. These so-called rheological properties are pumpability, extrudability, printability, buildability, thixotropy open time (TOT), shape retention, and sustainability.

3.1.1. Pumpability

Pumpability is the ability to transfer the concrete mix from the tank to nozzle. Pumpability is quantified through tribometer testing, a sliding pipe rheometer, and a viscometer. After obtaining the test results, the phenomenon of pumpability can be evaluated [44]. Separation of the mixture from aggregates causes clogging of the hose. This phenomenon is mostly triggered by an excessive water-to-binder ratio or a lack of distribution of particle size [60]. The radius of the hose pipe influences the pumping of 3DCP mix. Increasing the radius and lowering the length lead to a reduction in the pumping pressure required for the material. Additional compressed air pressure is requiredto make the material move forward for printing [60].

3.1.2. Extrudability

In 3D concrete printing, extrudability is defined as the material’s ability to be pumped out smoothly through an extruder without any disruption/clogging in the pipe flow [35,61]. Many researchers have characterized this extrudability with the help of flow properties; the literature reveals that particle size, gradation, surface area, paste/aggregate volume, etc., govern the yield stress and viscosity of the material. This can be linked to flow properties inside any pipe or complex shaped channel. Test scan be conducted to check the extrudability of the mix. The mix has good extrudability if it is free from defects such as voids and discontinuity on the surface. The extrudability test is performed by extruding a single layer for 30 cm and checking every 10 cm. The test is considered satisfactory when it meets two conditions: first, it must be as per the nozzle dimension, e.g., 30 mm × 20 mm with a variation of 0.5 mm; second, the surface must be free of voids and discontinuities [61].

3.1.3. Printability

Three-dimensional concrete printability refers to the ability to create and design models concerning the designer’s blueprint. This type of printing results in the minimum usage of material that results in money and time savings. The literature reveals that, at low temperatures, concrete printing causes a printability problem in terms of stability. Thus, the rapid setting of magnesium phosphate-based cement makes it an attractive alternative to concrete printing. This greatly increases printability, design freedom, and form retention without change. However, recycled products are useful for 3DCP, where the most fundamental criterion is that the rheological characteristics and printability are met [62]. According to the researcher’s reports, flowability has the same importance when compared to printability for easy pumping. Due to the presence of fly ash in the mix and its smooth surface texture, it increases the flowability and decreases the yield shear stress [60,63]. A flow table test was conducted on 3D concrete mix according to BS EN 12350-5. The printing setup with nozzle is shown in Figure 13. The diameter of the mix before the test was calculated as 102 mm. After 25 blows, the diameter changed to 156 mm [42,64]. Another flowability test [30] was conducted according to BS EN 1015–3:1999. The mix was rested for 5, 10, and 15 min. The final diameter of the mix was measured, and the flowability was calculated in terms of percentage [65] using Equation (1).
F l o w   p e r c e n t a g e F P = D − d d × 100 ,
where D is the average diameter spread, and d is the diameter of the cone.

3.1.4. Buildability

Buildability is the ability of the printed concrete layers to support the subsequent layers on top without buckling [44]. The stability check of the mix was analyzed using the “cylinder stability test”, and it was performed as a part of evaluating this property [60]. The perfect buildability of a 3DCP mix enables the advantage of fast building. The freshly deposited mix after pumping recovers its original viscosity and yield stress before the second layer is printed over it. However, the alkali-activated concrete acts as a shear-thinning material with lower apparent viscosity. To retain this feature, researchers have advised adding attapulgite clay and some microfibers [35]. The knowledge of the effect of silicate on yield strength development within the first minutes of mixing the alkali-activated 3D concrete mix is important for the assessment of buildability. A buildability test was performed by printing 20 layers of 30 mm thickness at an interval of 1 min per layer, and the deformation was calculated for actual and theoretical height (600 mm). The errors of maximum value (2.14%) and minimum value (0.24%) were found, for which 0.2% was acceptable visually and considered as the critical value. Lastly, three possible solutions to decrease the deformation were recommended:
  • Increase the time interval from layer to layer,
  • Reduce the layer thickness,
  • Increase the rate of growth of yield stress of concrete mix [66].

3.1.5. Thixotropy Open Time (TOT)

TOT can be defined as the time interval beyond which a material loses its extrudability property; for extrusion-based concrete printing, this is always earlier than the usual setting (initial) time of the material. In other words, the open time is the time between mixing and the initial setting time of concrete [14]. Researchers used carboxyl methyl cellulose and clay to produce homogeneous flow under pressure by enhancing thixotropic accumulation in the alkali-activated mixture and preventing phase separation.
Due to the polycondensation process, some materials harden over time. In the case of 3DCP, this adversely affects the pumping and extrusion of mix through the nozzle. As TOT concerns time, many researchers have used an accelerator or retarder. The desired TOT was achieved by partially replacing 5%, 10%, and 15% FA with GGBS. This changed the yield stress over time, providing good extrudability and shape retention [35].

3.1.6. Shape Retention

Shape retention is a measure of the ability to withstand the mix in a state of ‘rest’ to retain its shape. After extruding, the material retains its shape as per the extruder dimension and is quantified by a dimensionless number called the shape retention factor (SRF). This is the ratio of the 3D concrete sample before demolding to after demolding [35]. From the literature study, it seems that the inclusion of silica fume, clarified attapulgite nano clay, and polypropylene fiber improved shape stability [54]. Pumping pressure had a significant impact on the shape retention of fresh concrete after printing. Researchers have suggested a pumping pressure range of 1–4 MPa [14,67].

3.2. Evaluation of Hardened Properties of 3DCP

Various end-product tests are conducted to assess 3D concrete mechanical properties, namely, compressive strength, flexural strength, durability, layer adhesion, and bulk density. Usually, for printed concrete, whether it is a cement-based or alkali-activated material, the cube casting procedure is the same [44]. To evaluate the hardened properties of 3D printed concrete, the below-described tests are performed.
Compressive strength: To test the compressive strength of a cast sample, 100 mm cube steel molds are used in accordance with BS EN 12390–3:2009. To test that of a printed sample, nine cubes of 100 mm size are cut from the printed samples of 350 × 350 × 500 mm slabs and tested in all directions to get an average value [19].
Flexural strength: For flexural strength, 100 × 100 × 500 mm specimens are cast in accordance with BS EN 12390–5:2009. To test the printed sample, specimens of 100 × 100 × 400 mm size are extracted from 500 × 350 × 120 mm slabs printed after 28 days of curing, before testing the four-point loading with a span of 300 mm [19].
Void measurement: Voids badly affect the hardened properties of concrete such as compressive and flexural strength. For 3D concrete, pore sizes within limits of 0.2 to 4 mm are considered [68]. These are identified using ‘image tool’ software. To investigate the void sizes, 90 × 90 mm2 surface area specimens are cast and coated with black paint. After drying, white paint is rolled on it, revealing the voids on the surface. Therefore, using image tool software, voids and their area are calculated [19]. Attapulgite nano clay and PVA fibers fill the voids effectively and help to achieve good strength [30].
Drying shrinkage: The ingredients used in the 3D concrete mix have finer particles with a maximum fine aggregate size of 2.36 mm. Regarding aggregate content, 3DCP has less than 50% of its volume compared to conventional concrete’s 70%. This means that the 3DCP mix has higher paste content, leading to larger shrinkage over drying [69]. An experiment was conducted to determine the shrinkage of 3DCP specimens in different exposure conditions; shrinkage of 0.177 mm/m when immersed in water, 0.58 mm/m in moist conditions, and 0.855 mm/m in 60% relative humidity at 200 °C was observed. These values were found to be in an acceptable range. Lastly, it was suggested that the inclusion of polypropylene (about 0.1% by volume)prevents cracking up on plastic shrinkage [19]. This technology undergoes many chemical processes, and the behavior of plastic, drying, and autogenous shrinkage differs from that of OPC concrete [70].
Interlayer bond strength: The interlayer bond strength of printed concrete was investigated with delay times of 10, 20, and 30 min. The behavior of specimens differed in terms of mechanical properties and bond strength. Delays of10 min and 30 min gave better bond strength than the 20 min delay, with the opposite trend observed for compressive and flexural strength [71]. With increased delays until printing, subsequent layers show surface moisture due to the bleeding of concrete. Hence, the relationship between bond strength and moisture content is universal.

3.3. Durability of Alkali-Activated Binders

The durability of concrete material is defined as the ability to resist any environmental exposure, with equal weightage toward mechanical properties [72,73]. Alkali-activated binders have good durability in their service period [74]. An acid attack test was conducted on both alkali-activated concrete and OPC-based concrete specimens. They were immersed in 5% concentrated hydrochloric acid and sulfuric acid for weeks, and the mass losses were evaluated [75]. The OPC binder concrete showed 78% and 95% mass losses in 5% concentrated hydrochloric acid and sulfuric acid, respectively, whereas it was less than 6% and 7%, respectively, for alkali-activated binders [76,77]. Researchers conducted an ASTM C227 mortar bar test and noticed shrinkage behavior in both types of binders, although it was greater in the OPC binder [78]. The cement concrete showed a weak performance when it came to thermal treatment and started disintegrating when the temperature rose above 300 °C. However, in the case of alkali-activated binders, stability was observed even at high temperatures [76,79]. The freezing and thawing resistance for 25 and 50 cycles was determined forecast and printed 3D concrete specimens. The same stability was revealed in cast and printed specimens, but there was spalling after 450 °C [13,72].

3.4. Microstructural Characteristics

The microstructural characteristics of 3D concrete specimens can be identified by energy-dispersive spectroscopy (EDS) combined with SEM, XRD, mercury intrusion porosimetry (MIP), and micro-computed tomography (micro-CT) tests. There are two methods to perform these analyses when observing the inside of sample, particularly with regard to pore detection: micro-CT and MIP. Arange of pore sizes and a description of how this may affect 3DCP properties are presented in Table 6 [13].
Curing temperature is critical in fly ash-based alkali-activated mortar; if the temperature is too low, SEM detects some unreacted fly ash particles at the crust. This results in poor compressive strength. Similarly, GGBS-based alkali-activated paste mixed with sodium hydroxide and silicate results in a hydrated substance known as calcium–silicate–hydrate (C–S–H) gel. SEM was used to identify the microstructural properties of GGBS-based paste. It was concluded that the fineness of GGBS was responsible for low porosity and, hence, the development of high strength [80].

4. Discussions

4.1. Environmental Footprint with 3DCP

An optimal 3D concrete mix results in low CO2 emissions and total embodied energy as compared to traditional concrete [38]. Various trials were conducted to choose the best combination with acceptable rheological characteristics, along with the carbon emissions and total embodied energy necessary to produce a unit volume of printed concrete [81]. Many assumptions were made while comparing the embodied energy of traditional OPC-based concrete versus alternative concrete. These were regarding the embodied energy required for concrete formulations, binding agents, and global potential [82]. The results show that, in a 3DCP with OPC mixture, OPC takes 74% of the total embodied energy and is responsible for 84% of carbon emissions, whereas in alkali-activated 3DCP, the activator takes 80% of the total embodied energy and is responsible for 59% of carbon emissions for the production of one unit volume of printable concrete [38], as shown in Figure 14.
In summary, alkali activation provides an option for OPC-based 3DCP to become a sustainable mix by reducing carbon emissions by 61% and total embodied energy by 14% while demonstrating equivalent mechanical capabilities [38]. Addition of insulation materials into the concrete’s mix reduces the thermal conductivity and embodied energy of the end products [83]. This further helps in reducing the energy consumption of the building and reducing the overall carbon footprint. Inclusion of these insulation materials in alkali-activated 3D printable concrete presents a challenge of making the mix energy-efficient.

4.2. Effect of Precursors on Compressive Strength

Figure 15 and Figure 16 show the behavior of compressive strength with increasing precursor content. The graph depicts the optimal concentration of fly ash and GGBS. According to the graph, the compressive strength varies with an increase in the precursor content. A content of around 1000 kg/m3 provides better strength. In terms of binder proportions, complete fly ash content did not provide the appropriate strength. Accordingly, a combination of GGBS and SF was suggested for further trials.

4.3. Effect of Alkali Activator and Water on Compressive Strength

The key component of this mixture is the alkali activator. The amount of solution mixed is critical for achieving the required strength. As the activator content increases, the mix sets more slowly and becomes uneconomical. Thus, water can be added to the mix as per the requirement. Figure 17 depicts the effect of compressive strength on the combination of AA solution and water.

4.4. Effect of Sand-to-Binder Ratio on Compressive Strength

Sand-to-binder ratio is an important element in the 3DCP mix that influences the mechanical characteristics. The fine particles fill the voids left by the absence of coarse aggregate in the 3D concrete mix, yet its volume is constrained. Figure 18 and Figure 19 depict the decreasing trend of compressive strength with the increase in sand concentration. The results predict the optimal fine particle content as varying between 600 and 800 kg/m3.

4.5. Effect of Nano Clay on Extrusion Rheology

Printability is commonly characterized as the ability to extrude the mortar mix through the nozzle. Yield stress and viscosity are key features in 3DCP. However, in the case of alkali-activated mix, the presence of silicate anions in the solution causes the mix to absorb them. This results in a reduction in low yield stress and significant double-layer repulsive interactions between slag particles. To circumvent this and sustain yield stress, nano clay can be employed to increase static yield stress. In one study, 0.4% nano clay (Figure 20) was proposed as adequate to triple the yield stress, yielding an excellent thixotropic mix for printing. A greater concentration of NC, e.g., 0.6%, resulted in discontinuous extrusion, reducing the interlayer binding strength between the layers [84].

5. Conclusions

The reviewed literature discussed alkali-activated 3D printable concrete and the causes of behavior changes in the mechanical and rheological properties of 3DCP. The conclusions drawn from the review are as follows:
  • Sodium hydroxide and sodium silicate are the most used alkali activators, with fly ash, GGBS, and silica fume being the most used precursors.
  • Nano clay is an ideal ingredient as an additive for bringing yield type behavior to the mix without increasing viscosity. PVA fibers have the potential to fill tiny spaces and arrest cracking mechanisms.
  • A better 3DCP mix requires it to be printable, extrudable, and buildable, with longer TOT and better retention properties. An optimum pressure of 1–4 MPa is required for a better pumpable mix. The ideal alkali-activated 3DCP mix has a slump retention of 75 mm and a flow value of 155 to 175 mm.
  • The optimum proportions presumed foreach constituent are as follows:
  • The binder content should be around 600 to 700 kg/m3. This content is further divided into a mixture of fly ash, GGBS, and silica fume with proportions of60%, 25%, and 15% respectively. The alkali activator solution should be about 450 kg/m3. The fine particle content should range from 600 to 800 kg/m3. To modify the flow properties and mechanical properties, an optimum content of 0.4% attapulgite nano clay is ideal.
  • A higher molarity of NaOH solution (about 10 M) and Na2SiO3 (SS:SH = 2:1) gives better durability toward corrosion resistance of alkali-activated concrete. An increase in the amount of slag and alkali activator in the mix diminishes its water absorption and permeability.
  • Several studies have suggested the potential environmental improvement from alkali-activated 3DCP technology. A 30% reduction in carbon emissions has been observed in comparison with OPC-based 3DCP. However, a proper life cycle assessment of specific processes is needed in a variety of contexts to confirm environmental friendliness.

6. Future Scope

  • The 3DCP technology is a game changer in the construction industry. However, the current design standards and rules for building and construction do not apply to this technology. As a result, consistent procedures for evaluating the mechanical characteristics of conventional and 3DCP structural parts are required. The specifics concerning printer characteristics such as nozzle size, which reinforce the benefits in 3DCP for each structural part, and most importantly, interlayer bond strength have to be incorporated in standard codes.
  • In the literature, there are no studies on the inclusion of agro/industrial byproducts in alkali-activated 3D printing concrete, which offers large research potential for enhancing sustainable construction.

Author Contributions

Conceptualization, S.M., B.A.L., M.K. and R.V.R.; methodology, S.M., B.A.L., M.S., M.K. and R.C.; formal analysis, S.M., B.A.L. and R.V.R.; investigation, S.M. and B.A.L.; writing—original draft preparation, S.M., B.A.L., R.C., M.K. and R.V.R.; writing—review and editing, S.M., B.A.L. and R.V.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

List of Acronyms

AcronymMeaning
3DCPThree-dimensional concrete printing
AAAlkali activation
AAMAlkali-activated material
ASTMAmerican Society for Testing and Materials
BIMBuilding information modeling
BS ENBritish Standards European Norm
C–S–HCalcium–silicate–hydrate
CTComputed tomography
EDSEnergy-dispersive spectroscopy
FAFly ash
FPFlow percentage
GGBSGround granulated blast furnace slag
ISIndian Standard
MMolarity
MIPMercury intrusion porosimetry
NCNano clay
OPCOrdinary Portland cement
PCEPolycarboxylate ether
PVAPolyvinyl alcohol
SEMScanning electron microscopy
SFSilica fume
SHSodium hydroxide
SPSuper plasticizer
SRFShape retention factor
SSSodium silicate
SSASpecific surface area
TOTThixotropy open time
VMAViscosity-modifying agent
XRDX-ray diffraction
XRFX-ray fluorescence

References

  1. 3DCP Database. Available online: https://3dconcreteprinting.info/ (accessed on 2 February 2023).
  2. Rael, R.; San Fratello, V. Developing Concrete Polymer Building Components for 3D Printing. In Proceedings of the 31st Annual Conference of the Association for Computer Aided Design in Architecture (ACADIA), Banff, AB, Canada, 13–16 October 2011; pp. 152–157. [Google Scholar] [CrossRef]
  3. Khoshnevis, B.; Zahiri, B.; Yuan, X.; Xi, B. Deformation Analysis of Sulfur Concrete Structures Made by Contour Crafting. In Proceedings of the AIAA SPACE 2015 Conference and Exposition, Pasadena, CA, USA, 31 August–2 September 2015. [Google Scholar] [CrossRef]
  4. Allouzi, R.; Al-Azhari, W.; Allouzi, R. Conventional Construction and 3D Printing: A Comparison Study on Material Cost in Jordan. J. Eng. 2020, 2020, 1424682. [Google Scholar] [CrossRef]
  5. Nematollahi, B.; Xia, M.; Sanjayan, J.; Vijay, P. Effect of Type of Fiber on Inter-Layer Bond and Flexural Strengths of Extrusion-Based 3D Printed Geopolymer. Mater. Sci. Forum 2018, 939, 155–162. [Google Scholar] [CrossRef]
  6. Kirkpatrick, K. The Construction Industry in the 21 St Century. Commun. ACM 2018, 61, 18–20. [Google Scholar] [CrossRef]
  7. Horta, I.M.; Camanho, A.S.; Johnes, J.; Johnes, G. Performance Trends in the Construction Industry Worldwide: An Overview of the Turn of the Century. J. Product. Anal. 2013, 39, 89–99. [Google Scholar] [CrossRef]
  8. Hossain, M.A.; Zhumabekova, A.; Paul, S.C.; Kim, J.R. A Review of 3D Printing in Construction and Its Impact on the Labor Market. Sustainability 2020, 12, 8492. [Google Scholar] [CrossRef]
  9. Kondepudi, K.; Subramaniam, K.V.L. Formulation of Alkali-Activated Fly Ash-Slag Binders for 3D Concrete Printing. Cem. Concr. Compos. 2021, 119, 103983. [Google Scholar] [CrossRef]
  10. Panda, B.; Tay, Y.W.D.; Paul, S.C.; Tan, M.J. Current Challenges and Future Potential of 3D Concrete Printing. Materwiss. Werksttech. 2018, 49, 666–673. [Google Scholar] [CrossRef]
  11. Nadu, T. Potential Technology—Incubation: Ghtc-INDIA 3D Printed Houses Technology. pp. 261–264. Available online: https://ghtc-india.gov.in/IHTM/Content/img/company-logos/pdf/54.pdf (accessed on 11 January 2023).
  12. Panda, B.; Singh, G.B.; Unluer, C.; Tan, M.J. Synthesis and Characterization of One-Part Geopolymers for Extrusion Based 3D Concrete Printing. J. Clean. Prod. 2019, 220, 610–619. [Google Scholar] [CrossRef]
  13. Sikora, P.; Techman, M.; Federowicz, K.; El-Khayatt, A.M.; Saudi, H.A.; Abd Elrahman, M.; Hoffmann, M.; Stephan, D.; Chung, S.Y. Insight into the Microstructural and Durability Characteristics of 3D Printed Concrete: Cast versus Printed Specimens. Case Stud. Constr. Mater. 2022, 17, e01320. [Google Scholar] [CrossRef]
  14. Paul, S.C.; van Zijl, G.P.A.G.; Gibson, I. A Review of 3D Concrete Printing Systems and Materials Properties: Current Status and Future Research Prospects. Rapid Prototyp. J. 2018, 24, 784–798. [Google Scholar] [CrossRef]
  15. De Schutter, G.; Lesage, K.; Mechtcherine, V.; Nerella, V.N.; Habert, G.; Agusti-Juan, I. Vision of 3D Printing with Concrete—Technical, Economic and Environmental Potentials. Cem. Concr. Res. 2018, 112, 25–36. [Google Scholar] [CrossRef]
  16. Bos, F.; Wolfs, R.; Ahmed, Z.; Salet, T. Additive Manufacturing of Concrete in Construction: Potentials and Challenges of 3D Concrete Printing. Virtual Phys. Prototyp. 2016, 11, 209–225. [Google Scholar] [CrossRef]
  17. Federowicz, K.; Kaszyńska, M.; Zieliński, A.; Hoffmann, M. Effect of Curing Methods on Shrinkage Development in 3D-Printed Concrete. Materials 2020, 13, 2590. [Google Scholar] [CrossRef] [PubMed]
  18. Park, K.M.; Min, K.S.; Lee, B.C.; Roh, Y.S. Proposal for Enhancing the Compressive Strength of Alkali-Activated Materials-Based Binder Jetting 3D Printed Outputs. Constr. Build. Mater. 2021, 303, 124377. [Google Scholar] [CrossRef]
  19. Le, T.T.; Austin, S.A.; Lim, S.; Buswell, R.A.; Law, R.; Gibb, A.G.F.; Thorpe, T. Hardened Properties of High-Performance Printing Concrete. Cem. Concr. Res. 2012, 42, 558–566. [Google Scholar] [CrossRef]
  20. Hajimohammadi, A.; van Deventer, J.S.J. Characterisation of One-Part Geopolymer Binders Made from Fly Ash. Waste Biomass Valorization 2017, 8, 225–233. [Google Scholar] [CrossRef]
  21. Flower, D.J.M.; Sanjayan, J.G. Green House Gas Emissions Due to Concrete Manufacture. Int. J. Life Cycle Assess. 2007, 12, 282–288. [Google Scholar] [CrossRef]
  22. He, Y.; Zhang, Y.; Zhang, C.; Zhou, H. Energy-Saving Potential of 3D Printed Concrete Building with Integrated Living Wall. Energy Build. 2020, 222, 110110. [Google Scholar] [CrossRef]
  23. Xu, H.; Van Deventer, J.S.J. The Geopolymerisation of Alumino-Silicate Minerals. Int. J. Miner. Process. 2000, 59, 247–266. [Google Scholar] [CrossRef]
  24. Panda, B.; Paul, S.C.; Mohamed, N.A.N.; Tay, Y.W.D.; Tan, M.J. Measurement of Tensile Bond Strength of 3D Printed Geopolymer Mortar. Meas. J. Int. Meas. Confed. 2018, 113, 108–116. [Google Scholar] [CrossRef]
  25. Sandanayake, M.; Gunasekara, C.; Law, D.; Zhang, G.; Setunge, S. Greenhouse Gas Emissions of Different Fly Ash Based Geopolymer Concretes in Building Construction. J. Clean. Prod. 2018, 204, 399–408. [Google Scholar] [CrossRef]
  26. Abhishek, H.S.; Prashant, S.; Kamath, M.V.; Kumar, M. Fresh Mechanical and Durability Properties of Alkali-Activated Fly Ash-Slag Concrete: A Review. Innov. Infrastruct. Solut. 2022, 7, 1–14. [Google Scholar] [CrossRef]
  27. Kamath, M.; Prashant, S.; Kumar, M. Micro-Characterisation of Alkali Activated Paste with Fly Ash-GGBS-Metakaolin Binder System with Ambient Setting Characteristics. Constr. Build. Mater. 2021, 277, 122323. [Google Scholar] [CrossRef]
  28. Lanjewar, B.A.; Chippagiri, R.; Dakwale, V.A.; Ralegaonkar, R.V. Application of Alkali-Activated Sustainable Materials: A Step towards Net Zero Binder. Energies 2023, 16, 969. [Google Scholar] [CrossRef]
  29. Nodehi, M.; Taghvaee, V.M. Alkali-Activated Materials and Geopolymer: A Review of Common Precursors and Activators Addressing Circular Economy. Circ. Econ. Sustain. 2022, 2, 165–196. [Google Scholar] [CrossRef]
  30. Chougan, M.; Ghaffar, S.H.; Sikora, P.; Chung, S.Y.; Rucinska, T.; Stephan, D.; Albar, A.; Swash, M.R. Investigation of Additive Incorporation on Rheological, Microstructural and Mechanical Properties of 3D Printable Alkali-Activated Materials. Mater. Des. 2021, 202, 109574. [Google Scholar] [CrossRef]
  31. Chen, Y.; Jia, L.; Liu, C.; Zhang, Z.; Ma, L.; Chen, C.; Banthia, N.; Zhang, Y. Mechanical Anisotropy Evolution of 3D-Printed Alkali-Activated Materials with Different GGBFS/FA Combinations. J. Build. Eng. 2022, 50, 104126. [Google Scholar] [CrossRef]
  32. Muthukrishnan, S.; Ramakrishnan, S.; Sanjayan, J. Effect of Alkali Reactions on the Rheology of One-Part 3D Printable Geopolymer Concrete. Cem. Concr. Compos. 2021, 116, 103899. [Google Scholar] [CrossRef]
  33. Bong, S.H.; Nematollahi, B.; Nazari, A.; Xia, M.; Sanjayan, J. Method of Optimisation for Ambient Temperature Cured Sustainable Geopolymers for 3D Printing Construction Applications. Materials 2019, 16, 902. [Google Scholar] [CrossRef]
  34. Nath, P.; Sarker, P.K. Effect of GGBFS on Setting, Workability and Early Strength Properties of Fly Ash Geopolymer Concrete Cured in Ambient Condition. Constr. Build. Mater. 2014, 66, 163–171. [Google Scholar] [CrossRef]
  35. Panda, B.; Tan, M.J. Experimental Study on Mix Proportion and Fresh Properties of Fly Ash Based Geopolymer for 3D Concrete Printing. Ceram. Int. 2018, 44, 10258–10265. [Google Scholar] [CrossRef]
  36. Rostami, M.; Behfarnia, K. The Effect of Silica Fume on Durability of Alkali Activated Slag Concrete. Constr. Build. Mater. 2017, 134, 262–268. [Google Scholar] [CrossRef]
  37. Amran, M.; Murali, G.; Hafizah, N.; Khalid, A.; Fediuk, R.; Ozbakkaloglu, T.; Huei, Y.; Haruna, S.; Yong, Y. Slag Uses in Making an Ecofriendly and Sustainable Concrete: A Review. Constr. Build. Mater. 2021, 272, 121942. [Google Scholar] [CrossRef]
  38. Bong, S.H.; Xia, M.; Nematollahi, B.; Shi, C. Ambient Temperature Cured ‘Just-Add-Water’ Geopolymer for 3D Concrete Printing Applications. Cem. Concr. Compos. 2021, 121, 104060. [Google Scholar] [CrossRef]
  39. Zhang, C.; Hou, Z.; Chen, C.; Zhang, Y.; Mechtcherine, V.; Sun, Z. Design of 3D Printable Concrete Based on the Relationship between Flowability of Cement Paste and Optimum Aggregate Content. Cem. Concr. Compos. 2019, 104, 103406. [Google Scholar] [CrossRef]
  40. Provis, J.L. Alkali-Activated Materials. Cem. Concr. Res. 2018, 114, 40–48. [Google Scholar] [CrossRef]
  41. IS:17452-2020; Use of Alkali Activated Concrete for Precast Products—Guidelines. Bureau of Indian Standards: New Delhi, India, 2020.
  42. Kondepudi, K.; Subramaniam, K.V.L.; Nematollahi, B.; Bong, S.H.; Sanjayan, J. Study of Particle Packing and Paste Rheology in Alkali Activated Mixtures to Meet the Rheology Demands of 3D Concrete Printing. Cem. Concr. Compos. 2022, 131, 104581. [Google Scholar] [CrossRef]
  43. Gavali, H.R.; Bras, A.; Faria, P.; Ralegaonkar, R.V. Development of Sustainable Alkali-Activated Bricks Using Industrial Wastes. Constr. Build. Mater. 2019, 215, 180–191. [Google Scholar] [CrossRef]
  44. Sikora, P.; Chougan, M.; Cuevas, K.; Liebscher, M.; Mechtcherine, V.; Ghaffar, S.H.; Liard, M.; Lootens, D.; Krivenko, P.; Sanytsky, M.; et al. The Effects of Nano- and Micro-Sized Additives on 3D Printable Cementitious and Alkali-Activated Composites: A Review. Appl. Nanosci. 2022, 12, 805–823. [Google Scholar] [CrossRef]
  45. Dai, X.; Aydin, S.; Yardimci, M.Y.; De Schutter, G. Rheology and Structural Build-up of Sodium Silicate- and Sodium Hydroxide-Activated GGBFS Mixtures. Cem. Concr. Compos. 2022, 131, 104570. [Google Scholar] [CrossRef]
  46. Bong, S.H.; Nematollahi, B.; Nazari, A.; Xia, M.; Sanjayan, J.G. Fresh and Hardened Properties of 3D Printable Geopolymer Cured in Ambient Temperature. In RILEM Bookseries; Springer: Cham, Switzerland, 2019; Volume 19, pp. 3–11. [Google Scholar]
  47. Vijai, K.; Kumutha, R.; Vishnuram, B.G. Effect of Types of Curing on Strength of Geopolymer Concrete. Int. J. Phys. Sci. 2010, 5, 1419–1423. [Google Scholar]
  48. Muthukrishnan, S.; Ramakrishnan, S.; Sanjayan, J. Effect of Microwave Heating on Interlayer Bonding and Buildability of Geopolymer 3D Concrete Printing. Constr. Build. Mater. 2020, 265, 120786. [Google Scholar] [CrossRef]
  49. Panda, B.; Ruan, S.; Unluer, C.; Tan, M.J. Improving the 3D Printability of High Volume Fly Ash Mixtures via the Use of Nano Attapulgite Clay. Compos. Part B Eng. 2019, 165, 75–83. [Google Scholar] [CrossRef]
  50. Pva Fibers. Available online: https://www.indiamart.com/proddetail/hthm-pva-fibre-for-concrete-cement-sheets-and-construction-industry-24691447933.html (accessed on 21 March 2023).
  51. Muthukrishnan, S.; Ramakrishnan, S.; Sanjayan, J. Technologies for Improving Buildability in 3D Concrete Printing. Cem. Concr. Compos. 2021, 122, 104144. [Google Scholar] [CrossRef]
  52. Palacios, M.; Puertas, F. Effect of Superplasticizer and Shrinkage-Reducing Admixtures on Alkali-Activated Slag Pastes and Mortars. Cem. Concr. Res. 2005, 35, 1358–1367. [Google Scholar] [CrossRef]
  53. Mohan, M.K.; Rahul, A.V.; Van Tittelboom, K.; De Schutter, G. Rheological and Pumping Behaviour of 3D Printable Cementitious Materials with Varying Aggregate Content. Cem. Concr. Res. 2021, 139, 106258. [Google Scholar] [CrossRef]
  54. Rahul, A.V.; Santhanam, M.; Meena, H.; Ghani, Z. 3D Printable Concrete: Mixture Design and Test Methods. Cem. Concr. Compos. 2019, 97, 13–23. [Google Scholar] [CrossRef]
  55. Muthukrishnan, S.; Ramakrishnan, S.; Sanjayan, J. Set on Demand Geopolymer Using Print Head Mixing for 3D Concrete Printing. Cem. Concr. Compos. 2022, 128, 104451. [Google Scholar] [CrossRef]
  56. Kong, D.L.Y.; Sanjayan, J.G. Effect of Elevated Temperatures on Geopolymer Paste, Mortar and Concrete. Cem. Concr. Res. 2010, 40, 334–339. [Google Scholar] [CrossRef]
  57. Nematollahi, B.; Sanjayan, J.; Shaikh, F.U.A. Synthesis of Heat and Ambient Cured One-Part Geopolymer Mixes with Different Grades of Sodium Silicate. Ceram. Int. 2015, 41, 5696–5704. [Google Scholar] [CrossRef]
  58. Alghamdi, H.; Nair, S.A.O.; Neithalath, N. Insights into Material Design, Extrusion Rheology, and Properties of 3D-Printable Alkali-Activated Fly Ash-Based Binders. Mater. Des. 2019, 167, 107634. [Google Scholar] [CrossRef]
  59. Bakharev, T. Thermal Behaviour of Geopolymers Prepared Using Class F Fly Ash and Elevated Temperature Curing. Cem. Concr. Res. 2006, 36, 1134–1147. [Google Scholar] [CrossRef]
  60. Amran, M.; Abdelgader, H.S.; Onaizi, A.M.; Fediuk, R.; Ozbakkaloglu, T.; Rashid, R.S.M.; Murali, G. 3D-Printable Alkali-Activated Concretes for Building Applications: A Critical Review. Constr. Build. Mater. 2022, 319, 126126. [Google Scholar] [CrossRef]
  61. Nerella, V.N.; Gmbh, P.E. 3D-Printing Technology for on-Site Construction. 2017. Available online: www.cpi-worldwide.com (accessed on 12 January 2023).
  62. Xia, M.; Nematollahi, B.; Sanjayan, J. Printability, Accuracy and Strength of Geopolymer Made Using Powder-Based 3D Printing for Construction Applications. Autom. Constr. 2019, 101, 179–189. [Google Scholar] [CrossRef]
  63. Tay, Y.W.D.; Qian, Y.; Tan, M.J. Printability Region for 3D Concrete Printing Using Slump and Slump Flow Test. Compos. Part B Eng. 2019, 174, 106968. [Google Scholar] [CrossRef]
  64. ASTM C1437-01; Standard Test Method for Flow of Hydraulic Cement Mortar. ASTM: West Conshohocken, PA, USA, 2001; pp. 7–8.
  65. Ma, G.; Li, Z.; Wang, L. Printable Properties of Cementitious Material Containing Copper Tailings for Extrusion Based 3D Printing. Constr. Build. Mater. 2018, 162, 613–627. [Google Scholar] [CrossRef]
  66. Yuan, Q.; Li, Z.; Zhou, D.; Huang, T.; Huang, H.; Jiao, D.; Shi, C. A Feasible Method for Measuring the Buildability of Fresh 3D Printing Mortar. Constr. Build. Mater. 2019, 227, 116600. [Google Scholar] [CrossRef]
  67. Secrieru, E.; Mechtcherine, V.; Schröfl, C.; Borin, D. Rheological Characterisation and Prediction of Pumpability of Strain-Hardening Cement-Based-Composites (SHCC) with and without Addition of Superabsorbent Polymers (SAP) at Various Temperatures. Constr. Build. Mater. 2016, 112, 581–594. [Google Scholar] [CrossRef]
  68. Ma, L.; Zhang, Q.; Jia, Z.; Liu, C.; Deng, Z.; Zhang, Y. Effect of Drying Environment on Mechanical Properties, Internal RH and Pore Structure of 3D Printed Concrete. Constr. Build. Mater. 2022, 315, 125731. [Google Scholar] [CrossRef]
  69. Salet, T.A.M.; Ahmed, Z.Y.; Bos, F.P.; Laagland, H.L.M. Design of a 3D Printed Concrete Bridge by Testing. Virtual Phys. Prototyp. 2018, 13, 222–236. [Google Scholar] [CrossRef]
  70. Binders, A. Long-Term Strength Development of Fly Ash-Based One-Part Alkali-Activated Binders. Materials 2021, 14, 4160. [Google Scholar]
  71. Sanjayan, J.G.; Nematollahi, B.; Xia, M.; Marchment, T. Effect of Surface Moisture on Inter-Layer Strength of 3D Printed Concrete. Constr. Build. Mater. 2018, 172, 468–475. [Google Scholar] [CrossRef]
  72. Nodehi, M.; Aguayo, F.; Nodehi, S.E.; Gholampour, A.; Ozbakkaloglu, T.; Gencel, O. Durability Properties of 3D Printed Concrete (3DPC). Autom. Constr. 2022, 142, 104479. [Google Scholar] [CrossRef]
  73. Baz, B.; Aouad, G.; Kleib, J.; Bulteel, D.; Remond, S. Durability Assessment and Microstructural Analysis of 3D Printed Concrete Exposed to Sulfuric Acid Environments. Constr. Build. Mater. 2021, 290, 123220. [Google Scholar] [CrossRef]
  74. Bernal, S.A.; Provis, J.L. Durability of Alkali-Activated Materials: Progress and Perspectives. J. Am. Ceram. Soc. 2014, 97, 997–1008. [Google Scholar] [CrossRef]
  75. Davidovits, J.; Comrie, D.C.; Paterson, J.H.; Ritcey, D.J. Geopolymeric Concretes for Environmental Protection. Concr. Int. 1990, 12, 30–39. [Google Scholar]
  76. Pacheco-Torgal, F.; Abdollahnejad, Z.; Camões, A.F.; Jamshidi, M.; Ding, Y. Durability of Alkali-Activated Binders: A Clear Advantage over Portland Cement or an Unproven Issue? Constr. Build. Mater. 2012, 30, 400–405. [Google Scholar] [CrossRef]
  77. Rangan, B.V. Geopolymer Concrete for Environmental Protection. Indian Concr. J. 2014, 88, 41–59. [Google Scholar]
  78. Fernández-Jiménez, A.; Puertas, F. The Alkali-Silica Reaction in Alkali-Activated Granulated Slag Mortars with Reactive Aggregate. Cem. Concr. Res. 2002, 32, 1019–1024. [Google Scholar] [CrossRef]
  79. Ponomar, V.; Adesanya, E.; Ohenoja, K.; Illikainen, M. High-Temperature Performance of Slag-Based Fe-Rich Alkali-Activated Materials. Cem. Concr. Res. 2022, 161, 106960. [Google Scholar] [CrossRef]
  80. Yang, K.-H.; Song, J.-K. Workability Loss and Compressive Strength Development of Cementless Mortars Activated by Combination of Sodium Silicate and Sodium Hydroxide. J. Mater. Civ. Eng. 2009, 21, 119–127. [Google Scholar] [CrossRef]
  81. Han, Y.; Yang, Z.; Ding, T.; Xiao, J. Environmental and Economic Assessment on 3D Printed Buildings with Recycled Concrete. J. Clean. Prod. 2021, 278, 123884. [Google Scholar] [CrossRef]
  82. Jamieson, E.; McLellan, B.; Van Riessen, A.; Nikraz, H. Comparison of Embodied Energies of Ordinary Portland Cement with Bayer-Derived Geopolymer Products. J. Clean. Prod. 2015, 99, 112–118. [Google Scholar] [CrossRef]
  83. Chippagiri, R.; Bras, A.; Sharma, D.; Ralegaonkar, R.V. Technological and Sustainable Perception on the Advancements of Prefabrication in Construction Industry. Energies 2022, 15, 7548. [Google Scholar] [CrossRef]
  84. Panda, B.; Ruan, S.; Unluer, C.; Tan, M.J. Investigation of the Properties of Alkali-Activated Slag Mixes Involving the Use of Nanoclay and Nucleation Seeds for 3D Printing. Compos. Part B Eng. 2020, 186, 107826. [Google Scholar] [CrossRef]
Energies 16 04181 g001 550
Figure 1. Schematic diagram of difference between conventional concreting and 3DCP.
Figure 1. Schematic diagram of difference between conventional concreting and 3DCP.
Energies 16 04181 g001
Energies 16 04181 g002 550
Figure 2. Ground granulated blast furnace slag (GGBS).
Figure 2. Ground granulated blast furnace slag (GGBS).
Energies 16 04181 g002
Energies 16 04181 g003 550
Figure 3. Fly ash (FA).
Figure 3. Fly ash (FA).
Energies 16 04181 g003
Energies 16 04181 g004 550
Figure 4. Silica fume (SF).
Figure 4. Silica fume (SF).
Energies 16 04181 g004
Energies 16 04181 g005 550
Figure 5. Fine sand.
Figure 5. Fine sand.
Energies 16 04181 g005
Energies 16 04181 g006 550
Figure 6. Sodium hydroxide (SH) pellets.
Figure 6. Sodium hydroxide (SH) pellets.
Energies 16 04181 g006
Energies 16 04181 g007 550
Figure 7. Sodium hydroxide flakes.
Figure 7. Sodium hydroxide flakes.
Energies 16 04181 g007
Energies 16 04181 g008 550
Figure 8. Sodium silicate (SS) solution.
Figure 8. Sodium silicate (SS) solution.
Energies 16 04181 g008
Energies 16 04181 g009 550
Figure 9. Attapulgite nano clay [49].
Figure 9. Attapulgite nano clay [49].
Energies 16 04181 g009
Energies 16 04181 g010 550
Figure 10. Polyvinyl alcohol fibers [50].
Figure 10. Polyvinyl alcohol fibers [50].
Energies 16 04181 g010
Energies 16 04181 g011 550
Figure 11. Planetary mixer [50].
Figure 11. Planetary mixer [50].
Energies 16 04181 g011
Energies 16 04181 g012 550
Figure 12. Graphical representation of methodology of 3DCP.
Figure 12. Graphical representation of methodology of 3DCP.
Energies 16 04181 g012
Energies 16 04181 g013 550
Figure 13. Printing setup with nozzle [55].
Figure 13. Printing setup with nozzle [55].
Energies 16 04181 g013
Energies 16 04181 g014a 550Energies 16 04181 g014b 550
Figure 14. Alkali-activated 3D concrete vs. OPC conventional concrete.
Figure 14. Alkali-activated 3D concrete vs. OPC conventional concrete.
Energies 16 04181 g014aEnergies 16 04181 g014b
Energies 16 04181 g015 550
Figure 15. Effect of FA and GGBS as binders on compressive strength.
Figure 15. Effect of FA and GGBS as binders on compressive strength.
Energies 16 04181 g015
Energies 16 04181 g016 550
Figure 16. Trend of compressive strength with binder content.
Figure 16. Trend of compressive strength with binder content.
Energies 16 04181 g016
Energies 16 04181 g017 550
Figure 17. Effect of alkali activator solution on compressive strength.
Figure 17. Effect of alkali activator solution on compressive strength.
Energies 16 04181 g017
Energies 16 04181 g018 550
Figure 18. Variation in compressive strength with sand/binder ratio changes.
Figure 18. Variation in compressive strength with sand/binder ratio changes.
Energies 16 04181 g018
Energies 16 04181 g019 550
Figure 19. Trend of compressive strength with sand content.
Figure 19. Trend of compressive strength with sand content.
Energies 16 04181 g019
Energies 16 04181 g020 550
Figure 20. Effect of nano clay on development of static yield stress.
Figure 20. Effect of nano clay on development of static yield stress.
Energies 16 04181 g020
Table
Table 1. Chemical compositions of GGBS, fly ash, and micro silica.
Table 1. Chemical compositions of GGBS, fly ash, and micro silica.
Oxide [Reference]Fly Ash
[9]		GGBS
[9,34]		Silica Fume
[30]		Nano Clay
[9]
CaO4.3044.600.641.98
SiO251.132.8085.1055.20
Al2O325.612.40.2912.20
Fe2O312.50.542.534.05
MgO12.54.732.258.56
Na2O1.450.220.970.53
K2O0.700.336.070.68
SO30.244.260.99-
TiO21.320.510.100.49
P2O50.010.880.210.65
MnO0.370.150.19-
Loss on Ignition0.570.093.60-
Table
Table 2. Types of alkali activator solutions.
Table 2. Types of alkali activator solutions.
Alkali Activator MaterialIS Code
Sodium hydroxide (NaOH)IS 252:2013
Potassium hydroxide (KOH)IS 6831:1992
Sodium silicate (alkaline grade)IS 381:1995
Potassium silicateIS 8813:1995
Sodium carbonateIS 251:1998
Potassium carbonateIS 7129:1992
Table
Table 3. Molarity of sodium hydroxide solution used in the literature.
Table 3. Molarity of sodium hydroxide solution used in the literature.
SS:SHMolarity (M)Reference
-3[9]
1:0.183[42]
2:1, 3:15[18]
2:110[43,44]
2:110.50[45]
1.5:1, 3:18[46]
2.5:18[47]
Table
Table 4. Properties of poly-vinyl fibers.
Table 4. Properties of poly-vinyl fibers.
FiberDiameter
(μm)		Length
(mm)		Aspect RatioYoung’s Modulus
(GPa)		Elongation at Rupture
(%)		Density
(kg/m3)		Nominal Strength
(MPa)		Reference
PVA150128025–41613001000[30]
Table
Table 5. Mix proportions from the literature study.
Table 5. Mix proportions from the literature study.
Fly ash
(kg/m3)		GGBS
(kg/m3)		Silica Fume
(kg/m3)		Aggregate
(kg/m3)		Molarity of NaOHSS:SHAA Solution
(kg/m3)		Water
(kg/m3)		Fibers
(kg/m3)		Nano Clay
(kg/m3)		Strength
(MPa)		Reference
661.5275.6165.3606.410M2:1441.1---58[30]
661.5275.6165.3606.410M2:1441.3-1.1-70
661.5275.6165.3606.410M2:1441.3-2.2-55
661.5275.6165.3606.410M2:1441.3--4.4163
661.5275.6165.3606.410M2:1441.3-1.14.4165
353.5353.5-1060.416M2:1247.499.0--15[55]
351.6351.6-1054.816M2:1246.1105.5--25
350.3350.3-1050.916M2:1245.2112.1--55
349.0349.0-1046.116M2:1244.3118.7--60
348.4348.4-1045.216M2:1243.9122.0--65
671.6118.565.8869.210M2:1355.565.8--25[35]
635.2112.062.2971.510M2:1336.362.2--25
602.5106.359.01063.210M2:1318.959.1--25
573.0101.1`56.11146.010M2:1303.356.2--25
546.396.453.51221.110M2:1289.253.5--25
Table
Table 6. Pore size description from micro-CT test.
Table 6. Pore size description from micro-CT test.
Diameter (µm)Inference
>0.1More harmful
0.05–0.10Harmful
0.0045–0.05Less harmful
<0.05Harmless
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Mujeeb, S.; Samudrala, M.; Lanjewar, B.A.; Chippagiri, R.; Kamath, M.; Ralegaonkar, R.V. Development of Alkali-Activated 3D Printable Concrete: A Review. Energies 2023, 16, 4181. https://doi.org/10.3390/en16104181

AMA Style

Mujeeb S, Samudrala M, Lanjewar BA, Chippagiri R, Kamath M, Ralegaonkar RV. Development of Alkali-Activated 3D Printable Concrete: A Review. Energies. 2023; 16(10):4181. https://doi.org/10.3390/en16104181

Chicago/Turabian Style

Mujeeb, Syed, Manideep Samudrala, Bhagyashri A. Lanjewar, Ravijanya Chippagiri, Muralidhar Kamath, and Rahul V. Ralegaonkar. 2023. "Development of Alkali-Activated 3D Printable Concrete: A Review" Energies 16, no. 10: 4181. https://doi.org/10.3390/en16104181

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop