Sustainable materials for 3D concrete printing
TL;DR: In this article, a prospective approach to conduct sustainability assessment based on the life cycle of 3D printed structures is presented, which also highlights the importance of considering the functional requirements of the mixes used for 3D printing.
Abstract: This paper explores the sustainability aspects of binders used in concrete 3D concrete printing. Firstly, a prospective approach to conduct sustainability-assessment based on the life cycle of 3D printed structures is presented, which also highlights the importance of considering the functional requirements of the mixes used for 3D printing. The potential of the material production phase is emphasized to enhance the sustainability potential of 3DCP by reducing the embodied impacts. The literature on the different binder systems used for producing 3D printable mixtures is reviewed. This review includes binders based on portland cement and supplementary cementing materials (SCMs) such as fly ash, silica-fume and slag. Also, alternative binders such as geopolymer, calcium sulfo-aluminate cement (CSA), limestone calcined clay cement (LC3) and reactive magnesium oxide systems are explored. Finally, sustainability assessment by quantifying the environmental impacts in terms of energy consumed and CO2 emissions of mixtures is illustrated with different binder systems. This paper underlines the effect of using SCMs and alternative binder systems for improving the sustainability of 3D printed structures.
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TL;DR: In this article , the authors present a systematic review and analysis of 3D concrete printing (3DCP) development and applications based on information from articles, patents and publicly available data.
Abstract: Since the inception of 3D concrete printing (3DCP) in the early to mid-2000's, the commercial landscape for this technology has expanded rapidly in parallel with developments of relevant materials, production technologies and knowhow. To benchmark the state-of-the-art of 3DCP technology in the construction field, this study presents a systematic review and analysis of 3DCP's development and applications based on information from articles, patents and publicly available data. An estimation of Technology Readiness Level (TRL) for 3DCP has been formulated through expert review, and the evidence suggests this is in the region of TRL6-7 similar to that reported for polymer-based fused deposition modelling processes. A new schema for the TRL assessment process is suggested and applied to two case studies: 1) the production of decorative works; 2) the fabrication of dwellings. Finally, we have identified four frontiers for research and development that should be exploited to raise the TRL of 3DCP.
48 citations
TL;DR: In this paper, the effect of using natural and recycled coarse aggregates in designing 3D printable concrete was examined using a dynamic shear rheometer, and it was observed that the addition of coarse aggregate significantly decreased the yield stress and marginally lowered the plastic viscosity.
Abstract: In the current study, we examine the effect of using natural and recycled coarse aggregates in designing 3D printable concrete. We assessed the rheological behaviourusing a dynamic shear rheometer, and it was observed that the addition of coarse aggregates significantly decreased the yield stress and marginally lowered the plastic viscosity. This was attributed to the increase in the paste and water film thickness with the addition of larger aggregates. Therefore, a reduction in the superplasticizer dosage is required to obtain coarse aggregate mixtures with similar yield stress and buildability to the control mixture. The mechanical properties were evaluated by using beam and cube samples cut out from printed wall elements. A marginal decrease in compression and flexural strength was observed for both the mixtures with natural and recycled coarse aggregates. The total and autogenous shrinkage assessment was performed using mould cast prismatic specimens, while the shrinkage cracking potential was evaluated using the restrained ring test. The coarse aggregate mixtures showed lower total and autogenous shrinkage. Notably, the addition of the saturated recycled aggregates significantly lowered the autogenous shrinkage, possibly due to internal curing. As a result, a relatively lower strain rate factor and slower development of tensile stresses occurred in the restrained shrinkage test, increasing the cracking age for the coarse aggregate mixtures. The current study, therefore, shows good potential for using natural and recycled coarse aggregates in 3D printable concrete.
39 citations
TL;DR: In this paper , the effect of using natural and recycled coarse aggregates in designing 3D printable concrete was examined using a dynamic shear rheometer, and it was observed that the addition of coarse aggregate significantly decreased the yield stress and marginally lowered the plastic viscosity.
Abstract: In the current study, we examine the effect of using natural and recycled coarse aggregates in designing 3D printable concrete. We assessed the rheological behaviourusing a dynamic shear rheometer , and it was observed that the addition of coarse aggregates significantly decreased the yield stress and marginally lowered the plastic viscosity . This was attributed to the increase in the paste and water film thickness with the addition of larger aggregates. Therefore, a reduction in the superplasticizer dosage is required to obtain coarse aggregate mixtures with similar yield stress and buildability to the control mixture. The mechanical properties were evaluated by using beam and cube samples cut out from printed wall elements. A marginal decrease in compression and flexural strength was observed for both the mixtures with natural and recycled coarse aggregates. The total and autogenous shrinkage assessment was performed using mould cast prismatic specimens, while the shrinkage cracking potential was evaluated using the restrained ring test. The coarse aggregate mixtures showed lower total and autogenous shrinkage. Notably, the addition of the saturated recycled aggregates significantly lowered the autogenous shrinkage, possibly due to internal curing. As a result, a relatively lower strain rate factor and slower development of tensile stresses occurred in the restrained shrinkage test, increasing the cracking age for the coarse aggregate mixtures. The current study, therefore, shows good potential for using natural and recycled coarse aggregates in 3D printable concrete.
35 citations
TL;DR: In this article , the effect of different molarity, Alkaline to Binder ratio (A/B), and Sodium silicate to sodium hydroxide (SS/SH) ratios on the enhancement of fresh and mechanical properties of geopolymer concrete is discussed.
Abstract: The purpose of this paper is to discuss the effect of different molarity, Alkaline to Binder ratio (A/B), and Sodium silicate to sodium hydroxide (SS/SH) ratios on the enhancement of fresh and mechanical properties of geopolymer concrete. In addition, it also reveals the investigation of recent trends and technology of developments of geopolymer concrete in recent years. The fresh and hardened properties like, slump, compressive, split tensile and flexural strength, water absorption, and bulk density of geopolymer concrete data for molarity variations ranging from 5, 8–18 M, with A/B ratios ranging from 0.30 to 0.5, and SS/SH ratios. These data further assessed using kernel density plot. Molarity and A/B ratio maximum the strength development of geopolymer concrete is computed from the graph. The various binding materials used and tests performed on geopolymer concrete by the researchers are also highlighted in this paper. Increasing the molarity and A/B ratios results in the strength development of geopolymer concrete up to a specific limit. Further increment of these parameters will not significantly affect the performance. The optimal value of molarity and A/B ratios at which give better performance is discussed in this paper. Structural performances of geopolymer concrete are higher than traditional concrete.
34 citations
TL;DR: A critical review of the state-of-the-art 3D printing geopolymers from the perspectives of production process, printability requirement, mix design, early-age material properties and sustainability, with a special focus on the effects of different factors such as matrix composition, reinforcement type, curing regime and printing configuration on the fresh and hardened properties of 3D printed geo-mers as discussed by the authors .
Abstract: Geopolymers have been considered as a promising alternative to cementitious materials for 3D printing to enhance sustainability of the construction industry. This paper presents a critical review of the state-of-the-art of 3D printing geopolymers from the perspectives of production process, printability requirement, mix design, early-age material properties and sustainability, with a special focus on the effects of different factors such as matrix composition, reinforcement type, curing regime and printing configuration on the fresh and hardened properties of 3D printed geopolymers. The relationship between key fresh properties and printability of geopolymers is discussed, based on which the potential optimal mix proportions are obtained, containing the blended precursors of fly ash, ground granulated blast-furnace slag and silica fume, liquid or solid activator, river sand with a maximum size of 2 mm, thixotropic additives (e.g., nano clay), and retarder (e.g., sucrose). This paper aims to summarise the recent advances in the development of 3D printing techniques suitable for geopolymers and geopolymers feasible for 3D printing, and to identify the knowledge gap, remaining challenges, and opportunities for future research.
31 citations
References
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TL;DR: In this paper, the authors discuss the practicality of replacing portland cements with alternative hydraulic cements that could result in lower total CO 2 emissions per unit volume of concrete of equivalent performance.
Abstract: This article discusses the practicality of replacing portland cements with alternative hydraulic cements that could result in lower total CO 2 emissions per unit volume of concrete of equivalent performance. Currently, the cement industry is responding rapidly to the perceived societal need for reduced CO 2 emissions by increasing the production of blended portland cements using supplementary cementitious materials that are principally derived from industrial by-products, such as blast-furnace slags and coal combustion fly ashes. However, the supplies of such by-products of suitable quality are limited. An alternative solution is to use natural pozzolans, although they must still be activated either by portland cement or lime or by alkali silicates or hydroxides, the production of all of which still involves significant CO 2 emissions. Moreover, concretes based on activated pozzolans often require curing at elevated temperatures, which significantly limits their field of application. The most promising alternative cementing systems for general concrete applications at ambient temperatures currently appear to be those based at least in part on calcium sulfates, the availability of which is increasing due to the widespread implementation of sulfur dioxide emission controls. These include calcium sulfoaluminate–belite–ferrite cements of the type developed in China under the generic name “Third Cement Series” (TCS) and other similar systems that make good use of the potential synergies among calcium sulfate, calcium silicate and calcium aluminate hydrates. However, a great deal more research is required to solve significant unresolved processing and reactivity questions and to establish the durability of concretes made from such cements. If we are to use these potentially more CO 2 -efficient technologies on a large enough scale to have a significant global impact, we will also have to develop the performance data needed to justify changes to construction codes and standards.
1,521 citations
TL;DR: In this article, the authors present the results of comprehensive carbon footprint estimates for both geopolymer and OPC concrete, including energy expending activities associated with mining and transport of raw materials, manufacturing and concrete construction.
Abstract: Concrete for construction has traditionally been based on an Ordinary Portland Cement (OPC) binder. Geopolymers, an alternative binder based on fly ash (a fine waste collected from the emissions liberated by coal burning power stations) that is activated by an alkaline activator, have potential to lower the significant carbon footprint of OPC concrete. This paper presents the results of comprehensive carbon footprint estimates for both geopolymer and OPC concrete, including energy expending activities associated with mining and transport of raw materials, manufacturing and concrete construction. Previous studies have shown a wide variation of reported emission estimates: the results of this study are benchmarked with data from those studies.
1,274 citations
TL;DR: In this paper, the coupled substitution of metakaolin and limestone in Portland cement (PC) was investigated and the mechanical properties were studied in mortars and the microstructural development in pastes by X-ray diffraction, thermogravimetry analysis, mercury intrusion porosimetry and isothermal calorimetry.
Abstract: This study investigates the coupled substitution of metakaolin and limestone in Portland cement (PC). The mechanical properties were studied in mortars and the microstructural development in pastes by X-ray diffraction, thermogravimetry analysis, mercury intrusion porosimetry and isothermal calorimetry. We show that 45% of substitution by 30% of metakaolin and 15% of limestone gives better mechanical properties at 7 and 28 days than the 100% PC reference. Our results show that calcium carbonate reacts with alumina from the metakaolin, forming supplementary AFm phases and stabilizing ettringite. Using simple mass balance calculations derived from thermogravimetry results, we also present the thermodynamic simulation for the system, which agrees fairly well with the experimental observations. It is shown that gypsum addition should be carefully balanced when using calcined clays because it considerably influences the early age strength by controlling the very rapid reaction of aluminates.
763 citations
TL;DR: In this article, the authors present the experimental results concerning the mix design and fresh properties of a high-performance fiber-reinforced fine-aggregate concrete for printing concrete, which has been designed to be extruded through a nozzle to build layer-by-layer structural components.
Abstract: This paper presents the experimental results concerning the mix design and fresh properties of a high-performance fibre-reinforced fine-aggregate concrete for printing concrete. This concrete has been designed to be extruded through a nozzle to build layer-by-layer structural components. The printing process is a novel digitally controlled additive manufacturing method which can build architectural and structural components without formwork, unlike conventional concrete construction methods. The most critical fresh properties are shown to be extrudability and buildability, which have mutual relationships with workability and open time. These properties are significantly influenced by the mix proportions and the presence of superplasticiser, retarder, accelerator and polypropylene fibres. An optimum mix is identified and validated by the full-scale manufacture of a bench component.
738 citations
TL;DR: In this paper, it is shown by experiment and calculation that much, if not all, of this calcite is reactive and affects the distribution of lime, alumina and sulfate and thereby alters the mineralogy of hydrated cement pastes.
Abstract: Limestone, mainly consisting of calcite, is a permitted additive to Portland cements often up to a 5 wt.% limit. It is shown by experiment and calculation that much, if not all, of this calcite is reactive and affects the distribution of lime, alumina and sulfate and thereby alters the mineralogy of hydrated cement pastes. Calcite affects the mineralogical variant of the AFm phase(s). Calcite additions affect the amount of free calcium hydroxide as well as the balance between AFm and AFt phases, although C–S–H is unaffected in much of the range of compositions. Generic data are shown in graphical form to quantify these mineralogical changes as functions of cement composition and amount of added calcite. Calculations of the specific volume of solids as a function of calcite addition suggest that the space-filling ability of the paste is optimised when the calcite content is adjusted to maximise the AFt content. However, before the calculated data can be used uncritically, certain kinetic constraints on reactivity also need to be assessed. Progress towards the quantification of paste mineralogy suggests that (i) elucidation of the mineralogy of pastes, particularly blended cement pastes, is facilitated by using both theoretical and experimental approaches and (ii) that the ultimate goal, of calculating paste mineralogy from the bulk chemistry, is attainable.
708 citations