Yield strength development of 3D printable concrete by the early age activation reactions plays a vital role in the printability of geopolymer concrete. This study presents a rheo-chemical approach ...to investigate the early age strength development due to alkali reactions for the formulation of suitable 3D printable one-part geopolymer concrete. The influence of design parameters, including activator content, thixotropic additive (Magnesium Alumino Silicate -MAS), and retarder (sucrose) dosage, on the rheological properties of concrete were assessed. The shear stresses of geopolymer concrete were measured with the aid of a rotational rheometer for various shearing protocols that represent the major stages of printing operation (pumping, extrusion and building). The measured rheological properties were related to reaction kinetics of geopolymer mixes using FT-IR spectroscopy and calorimetry. The results revealed that, with MAS, activator and sucrose content of 0.75 wt%, 10 wt% and 1.5 wt% of the binder respectively, the formulated one-part geopolymer showcased enhanced printing properties. This is further demonstrated by printing laboratory-scale specimens and evaluating the hardened properties.
•Rheo-chemical characterisation of printable one-part geopolymer was conducted.•Total mixing time of 15 min is necessary for complete dissolution of solid activator.•Addition of retarders showed insignificant changes in dynamic rheological properties.•Open time of the concrete was significantly extended with prolonged shearing.•Chosen one-part geopolymer mix design showed buildability of more than 120 layers.
•Paraffin/hydrophobic coated expanded perlite PCM composite was developed.•PCM leakage in the thermal energy storage system was prevented.•Microstructural and mechanical properties of PCM integrated ...concrete were investigated.•Thermal performance of PCM integrated concrete panel was studied.
In this study, a novel thermal energy storage composite was developed by impregnating paraffin into hydrophobic coated expanded perlite (EPO) granules. A paraffin/uncoated expanded perlite (EPW) phase change composite was also prepared to study and compare the stability when integrated into cementitious composites. Paraffin/EPW, containing 35% by weight of paraffin, showed significant leakage of phase change material (PCM) during integration into concrete. However, no PCM leakage was observed for novel paraffin/EPO containing 50% by weight of paraffin in the composite. Microstructural and mechanical properties were studied for the compatibility of hydrophobic coated PCM composite in concrete. The thermal behaviour of a concrete panel incorporating PCM was studied and compared with the reference panel. The results revealed that incorporation of the developed PCM composite into concrete significantly improved the thermal inertia and thermal energy storage.
This paper investigates the potential of using form-stable phase change material (FS-PCM) integrated cement mortars in building envelopes to prevent overheating and to improve summer thermal comfort. ...The FS-PCM integrated cement mortar was applied as the interior surface plastering mortar of a full-scale test hut and compared with identical test huts built on cement plasterboard (OCB) and gypsum plasterboard (GPB). The test huts were exposed to outdoor climatic conditions, and indoor thermal behaviours were continuously monitored throughout the summer period. The effects of PCM in reducing the overheating was analysed by the intensity of thermal discomfort (ITDover) and frequency of thermal discomfort (FTDover) for overheating during the summer days. The comparison between different test huts showed that the application of PCM integrated cement mortars reduced the peak indoor temperature by up to 2.4 °C, compared to GPB and OCB test rooms. More importantly, the analysis of overheating effects revealed that at lower intensive thermal discomfort levels, FS-PCM largely reduces FTDover. As the intensity of thermal discomfort increases, the reduction in ITDover becomes dominant. At highly intensive thermal discomfort levels, the reduction was neither apparent in the intensity of thermal discomfort nor the period of discomfort.
Buildability is the ability to 3D print by adding concrete layer by layer continuously to the required level without significant deformation or collapse of the freshly printed component. This paper ...presents a systematic review of the reported studies to improve the buildability of concrete. The paper also presents original concepts and some results for improving the buildability of geopolymer concrete. Two methods to enhance the buildability are discussed: (1) Additives during initial mixing of concrete (2) Buildability enhancement at the print-head by an intervention (set-on-demand). The former method is the most widely studied, however, it affects the pumpability. The latter includes mixing accelerators, heating, ultrasonication, or magnetorheological control, performed at the print-head to rapidly increase the yield strength of the material immediately prior to extrusion. This method does not affect the pumpability of the mix until it reaches the print-head. Finally, the prospects of a new set-on-demand method are presented.
•Buildability enhancement is achieved by interventions at initial mixing and at the print head.•Strength development in fresh concrete is due to re-flocculation (physical) and setting (chemical).•Enhancement at initial mixing is constrained by the pumpability limitations.•Most developed set-on-demand approach is by mixing accelerators at the print-head.•Similar approach to attain on demand setting of geopolymer concrete is discussed in detail.
•Microwaving of geopolymer is investigated as a set-on-demand technique.•At optimum residence time, interlayer bond strength showed remarkable improvement.•Buildability of concrete improved rapidly ...with microwave heating.•Duration of exposure to microwave heating is critical.
The emerging concept of 3D concrete printing (3DCP) by the laminate stacking of layers without formwork has major issues of poor interlayer bond adhesion and inadequate buildability of printed layers. This paper explores microwave heating technique as a set-on-demand method to increase the structuration rate of geopolymer concrete for 3DCP applications. The microwave heating was applied just before the placement of layers (i.e. at the nozzle head) and the effect of heating duration on the interlayer bond strength and buildability were assessed. Moreover, the loss of surface and bulk moisture and the bond strength enhancing mechanism were also investigated. The results demonstrated that the optimum microwaving duration of 10 s has increased the interlayer bond strength by 132%. The interlayer temperature and surface moisture loss has shown an increasing trend with the heating duration. Despite the increased surface moisture loss with microwave heating, the observed increment in interlayer bond strength (for up to 10 s of heating) was due to the acceleration in polycondensation reaction between the filaments having adequate stiffness for maximum mechanical interlocking with minimum deformation after stacking. On the other hand, the buildability of printed filaments, as measured from the rate of particle re-flocculation and structuration, has showed a major improvement. Findings from this study propose incorporating “set-on demand” technique using electromagnetic radiations in construction 3D printing. This initiates a new era of print heads, designed to solve problems faced by current concrete printing industry.
This study investigates alkali-activated brick waste powder as the binder for developing 3D printable geopolymer mixes. The brick waste was used as a partial replacement to fly ash in geopolymer ...binders. The effect of brick waste content on the fresh properties of printable mixes, such as flow, setting time and rheological properties were investigated. Besides, the hardened properties of 3D printed brick waste geopolymer were evaluated with the varying brick waste content in the mix. The test results demonstrated that the fresh properties of 3D printable mixes were improved with the brick waste content in the mix. Compared to the control mix, the mixes containing brick waste displayed high yield strength and apparent viscosity at an early age. On the contrary, the hardened properties of compressive strength and interlayer strength of 3D printed concrete specimens were decreased with the high brick waste content; however, the incorporation of brick waste for up to 10% has enhanced the hardened properties. Finally, the sustainability assessment of brick waste geopolymer studied with embodied energy and carbon emission calculations reveals the proposed geopolymer concrete could reduce the embodied energy and carbon emission by up to 60–80%, compared to OPC concrete.
This study investigates ground brick waste powder as a primary precursor to develop eco-friendly geopolymer foam concrete (BGFCs) using a chemical foaming method. The effect of alkali content on the ...reaction kinetics of brick powder is studied and correlated with the properties of BGFCs. The reaction rates and the formation of crystalline phases of BGFCs were identified by Fourier Transform Infrared Spectroscopy and X-Ray Diffraction test method, respectively. It is found that increasing the alkali content (Na2O) in the mix has significantly enhanced the reaction kinetics of brick powder with the rapid formation of geopolymer gel in the matrix. This has resulted in the enhancement of mechanical properties and rapid setting in BGFCs. For instance, the increase in Na2O concentration from 1:40 to 1:12 has increased the compressive strength of BGFC by 245%. The corresponding initial setting times were reduced from 315 min to 140 min. The rapid setting of geopolymer mixture has resulted in a fine, regular, and homogenous distribution of air voids in the BGFCs. Finally, carbon emission calculations were conducted to assess the environmental impacts of developed BGFCs and compared with Ordinary Portland cement (OPC) foamed concrete. It is found that the developed BGFCs could significantly reduce the carbon emission up to 60% compared to their OPC counterparts.
•Ground brick waste as a primary precursor in geopolymer foam concrete was investigated.•Alkali content significantly affects the reaction kinetics and hardened properties.•High alkali content mix showed fine and regular pore size distribution.•Geopolymer foam concrete reduced carbon emissions by up to 88%.
•Effect of EP lightweight aggregates on the properties of GFC is studied.•EP reduces the amount of foam to achieve low density.•Fine and homogenous distribution of air voids attained by using EP ...additive.•Mechanical and thermal performance of EP integrated GFC is significantly enhanced.
This study demonstrates the development of geopolymer foamed concrete (GFC) by introducing a double hierarchical porous structure using premade foam and lightweight porous aggregates. Hydrophobic expanded perlite (EP) was used as porous aggregate and the addition of 10% and 20% of the binder (by eliminating corresponding volumes of sand) were investigated. It was observed that the incorporation of EP has brought obvious benefits in improving the mechanical and thermal properties of GFC. The amount of foam required to achieve a similar density of GFC was reduced by 19% and 53% for 10% and 20% of EP respectively, due to the presence of the large amount of open pores in EP. The compressive strength of cube specimens has increased by 75% and 180% at 7 days and 65% and 188% at 28 days, respectively. The reaction kinetics of geopolymers studied using FT-IR reveals that the reaction rates of geopolymer binders increase with the amount of EP. It is also shown that the increase in the amount of geopolymer gel particulates surrounding bubbles is the major reason for attaining fine air voids and strong binding skeleton in GFC-20EP, compared to the other two groups. Consequently, the pore homogeneity index, as measured from the ultrasonic velocity at different directions, was improved from 50% to 90%. The thermal performance tests conducted using prototype test cells reveals that the indoor thermal conditions will significantly improve when the GFC-20EP is used as building elements. This is particularly demonstrated by the reduction in peak indoor temperature of 1.8 °C and an increase in thermal inertia of 1.7 °C with GFC-20EP, compared to GFC-s.
Geopolymer foam concrete (GFC) has attracted significant research interest in various fields, thanks to their porous structure which brings the inherent merits of lightweight, acoustic and thermal ...insulation, and fire resistance. This review is focussed on three primary functional properties of GFC, namely mechanical properties (compression and flexural strengths), serviceability (thermal conductivity, sound absorption, and fire resistance), and durability. The functional properties depend on the fundamental fresh and hardened properties (rheology, stability, density, porosity and pore morphology), and all these properties are decided by the materials, foaming methods, curing conditions, and additives. A clear insight to these relationships and the ways of optimising the performance as a construction material are therefore presented. Also, the challenges towards the large-scale production and real-world application of GFC are discussed. The identified research needs include studies on fresh properties, durability, processing techniques to attract industrial applications, and developing 3D printable GFC.
•Materials and processing techniques in geopolymer foam concrete are reviewed.•Insight to the engineering properties of geopolymer foam concrete is presented.•Discussion on the rheology and the stability of fresh geopolymer foam concrete.•Challenges towards large-scale production and real-world applications are addressed.
The lightweight concrete (density <1000 kg/m3) is generally attained by introducing a large amount of air voids into fresh concrete for making so-called foam concrete. Such foam concrete is quite ...challenging in 3D concrete printing due to the high flowability of fresh mixes affecting the printability and foam stability during extrusion process. To overcome these limitations, this study investigates a combination of lightweight aggregates and premade foam in foam concrete to attain a density below 1000 kg/m3 for 3D printing applications. The expanded perlite (EP) aggregate was used as a replacement for fine sand that substantially reduced the foam content in the mix. The effect of EP on the fresh state properties such as rheology and printability as well as hardened properties including, mechanical properties, porosity and pore size distribution were investigated. It was demonstrated that the introduction of combined lightweight aggregate and foam has significantly improved the fresh and hardened properties of produced lightweight concrete. For instance, fresh foam concrete containing EP aggregate displayed high yield strength and apparent viscosity compared to the foam concrete without EP at similar densities. The compressive strength of 3D printed specimens containing EP was determined as 12.95 MPa, 15.5 MPa and 10.6 MPa in the perpendicular, longitudinal, and lateral directions respectively, compared to 5.5 MPa, 8.4 MPa and 4.2 MPa for the sand group at the similar density. Moreover, fine and regular pore size distribution was observed for 3D printed foam concrete with EP aggregate.
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