3D打印混凝土研究进展及其应用

近年来,3 D打印混凝土技术凭借着免模板、高自动化与智能化的优势,吸引了越来越多的关注,在建筑工程等领域出现了诸多的成功应用案例.但是,3 D打印工艺对混凝土的流变性能提出了更高的要求,而当前的混凝土相关标准与规范无法指导3 D打印混凝土的设计.同时,受打印工艺的影响,3 D打印混凝土的硬化性能和配筋技术也与传统混凝土...     

3D打印混凝土技术在澳大利亚的最近研究进展

3D打印,又被称为增材制造,是通过逐层累积叠加制造三维物体的一种技术手段。过去几年中,这种技术吸引了越来越多来自建筑业的关注。与传统混凝土浇筑技术相比,3D打印混凝土的应用可以实现更加高效的自由建筑制造,同时减小对人工劳动力的依赖。在全球范围内,由于相关高校和科研单位的积极参与,关于3D打印混凝土的研究工作取得了巨大的进展,其中包括澳大利亚的相关研究。本文主要对澳大利亚在3D打印混凝土研究方面有代表性的两所高校的最新进展进行介绍,两所学校分别是皇家墨尔本理工大学(RMIT大学)和斯威本科技大学。本文首先介绍了两所高校的打印设备及其特点,随后讨论了具体研究领域和近期发表的相关文章。RMIT大学主要侧重于研究纤维增强对3D打印混凝土力学性能方面的影响,而斯威本科技大学则着重研究3D打印地聚物混凝土的性能。本文旨在促进相关领域研究人员对澳大利亚3D打印混凝土研究团队和研究进展的理解。     

Effect of partial replacement of geopolymer binder materials on the fresh and mechanical properties: A review

The growth of demand for concrete raises concerns about the consumption of natural resources and ordinary Portland cement. Geopolymer composites show promise as a sustainable alternative for conventional cement concrete. Considering the wide range of potential geopolymer composites applications (including suitability for transportation infrastructure, underwater applications, repair and rehabilitation of structures as well as recent developments in 3D printing), the desired fresh and mechanical properties of the geopolymer composite may vary between applications: for example, rapid setting can be a merit for certain applications and a demerit for others. Therefore, the desired fresh and mechanical properties (e.g., workability, setting time, compressive strength, etc.) can be controlled for a given geopolymer source material through its partial substitution by natural or by-product materials. Recognizing the critical role of various replacement materials in enhancing the potential applications of geopolymer composites, the present review was undertaken to quantify and understand the effect of partial replacement by fly ash, metakaolin, kaolin, red mud, slag, ordinary Portland cement, and silica fume on the setting time, workability, compressive strength and flexural strength of various source materials addressed in the literature. The review also provides insights into research gaps in the field to promote future research.     

混凝土3D打印材料及3D打印模板技术应用进展

混凝土3D打印是现代数字化制造的典型代表,因其智能化、个性化、绿色建造的工艺优势受到广泛关注。作为一种新型建造方式,3D打印为建筑业带来了颠覆性的影响,并对传统混凝土材料提出了全新的挑战。如何提升混凝土材料与3D打印技术的适应性,实现3D打印技术在建筑中的广泛应用是人们普遍关注的焦点。本文概述了混凝土3D打印技术的发展历程,系统论述了混凝土3D打印材料在流变性、可挤出性、可建造性以及力学性能方面的研究现状,同时,介绍了3D打印模板技术在装饰及异型构筑物上的典型应用,以期为混凝土3D打印的研究与未来工程发展提供一定的参考与借鉴。     

水泥基复合材料3D可打印性的量化、优化及标准化

水泥基复合材料的3 D可打印性与打印工艺的协调兼容是无模快速建造成型的关键.然而,3 D打印原材料和配合比多样,打印设备不同,成型工艺各异,且3D可打印性的量化与评估尚未形成统一标准,为该技术的工程应用和推广带来不便.本文分析了3D可打印性的影响因素,综述了混凝土3D可打印性的量化评价方法,总结分析了六种3D可打印性的...     

Monoclinic-celsian ceramics formation: Through thermal treatment of ion-exchanged 3D printing geopolymer precursor

Based on conventional ion exchange method from zeolite materials, we herein report a facile synthetic procedure to prepare monoclinic celsian ceramics through thermal treatment of ion-exchanged 3D printing geopolymer precursors. In this contribution, both ion exchange process and thermal evolution of celsian precursors were systematically investigated. The results proved 3D printing Na- and K- based geopolymer were ideal precursors with low residual Na⁺ content (0.10 meq/g) and K⁺ content (0.05 meq/g) and translated into monoclinic celsian after being heated at 1400 °C. With increasing Sr²⁺ doping concentration from 20% (mole ratio) to 30% (mole ratio), more significant phase transition results (hexagonal → monoclinic) were observed. All 3D printing geopolymer precursors kept fine integrity and stable 3D structure upon ion exchange process and heating, indicating the combination of geopolymer technique and 3D printing opens up a versatile and robust way to yield monoclinic celsian ceramics and related components of complex shapes.     

Lightweight geopolymer concrete: A critical review on the feasibility,mixture design,durability properties,and microstructure

Lightweight geopolymer concretes have gained attention because of their superior durability, lower environmental impact and sustainable characteristics. They are the product of natural or artificial aggregates with low specific gravities mixed with aluminosilicate binders, and an alkaline solution. In this study, different aspects of lightweight geopolymer concretes and mortars such as environmental and economic considerations, materials and mixture, durability-related properties like permeability, chloride attacks and performance at high temperatures, thermal conductivity, and the microstructure are reviewed. This study also discusses the effect of different geopolymer binders and various alkaline activators and additives with focus on lightweight geopolymer concrete made with different lightweight aggregates. The key results from previous studies in literature pertaining mix proportions, chemical composition and properties of lightweight geopolymers are summarized and presented. The main aim is to provide an informed outlook on the advantages and drawbacks of lightweight geopolymer concretes and present a comprehensive review of the studies performed in this area.     

3D printing of cordierite honeycomb structures and evaluation of compressive strength under quasi-static condition

Ceramic honeycombs exhibit unique mechanical properties based on engineered formulations and geometry of cells. Extrusion of formable paste through a complex honeycomb die is the commonly practiced technique for the manufacturing of honeycombs globally. Extrusion die fabrication is a complex process which necessitates sophisticated infrastructure facilities that provide high geometrical accuracy and finish to produce defect free honeycombs. Furthermore, every configuration of honeycomb requires a specific tool. Additive manufacturing (AM)/ 3D printing is a rapid prototyping technique which offers flexibility in fabrication of honeycombs with desired geometries from a virtual model directly. Further, this does not require complicated dies. In this study, viscoplastic printable cordierite raw mix paste with a shear rate exponent of 0.87 was printed into honeycombs with hexagonal, square, and triangular cells using a ram type 3D printer. The printed honeycomb samples are found to possess good integrity and near net shape after drying. Sintered 3D-printed honeycomb samples of all configurations have exhibited cordierite as a major phase along with minor phases of magnesium aluminate (MgAl₂O₄) spinel, clinoenstatite (MgSiO₃), and corundum (Al₂O₃) with sintered density of 2.41-2.48 g/cc. The samples are also subjected to compression testing under quasi-static condition. The study demonstrates 3D printing as a viable and flexible technique for rapid prototyping of honeycombs with desired configurations and engineered properties.     

Linking fresh paste microstructure,rheology and extrusion characteristics of cementitious binders for 3D printing

Cementitious binders amenable to extrusion-based 3D printing are formulated by tailoring the fresh microstructure through the use of fine limestone powder or a combination of limestone powder and microsilica or metakaolin. Mixtures are proportioned with and without a superplasticizer to enable different particle packings at similar printability levels. A simple microstructural parameter, which implicitly accounts for the solid volume and inverse square dependence of particle size on yield stress can be used to select preliminary material combinations for printable binders. The influence of composition/microstructure on the response of pastes to extension or squeezing are also brought out. Extrusion rheology is used in conjunction with a phenomenological model to better understand the properties of significance in extrusion-based printing of cementitious materials. The extrusion yield stress and die wall slip shear stress extracted from the model enables an understanding of their relationships with the fresh paste microstructure, which are crucial in selecting binders, extrusion geometry, and processing parameters for 3D printing.     

高强石膏3D打印浆体材料的制备与性能研究

使用预先混合的高强石膏浆体材料进行3D打印的工艺具有制品强度高、打印周期短等优点,但仍存在石膏初凝时间过短、浆体可堆叠性不足等问题。在此基础上研究了植物蛋白类缓凝剂和多聚磷酸盐缓凝剂对材料抗压强度、流动性和可打印时间的影响,并研究了增塑剂羟丙基甲基纤维素醚(HPMC)对浆体流变性能和3D打印构件体积稳定性的影响。结果表明,两种缓凝剂对石膏水化的延缓机理不同,植物蛋白类缓凝剂可以延长流动度的稳定时期,多聚磷酸盐缓凝剂则不能很好地增加可打印时间,浆体在初凝前8~12 min就已失去流动性。HPMC的加入可显著提升浆体材料的表观粘度和屈服应力并消除缓凝剂造成的泌水现象,但对塑性粘度增幅不大,且会降低材料的抗压强度。高HPMC掺量下的高强石膏3D打印构件的体积稳定性较好,在0.020%(质量分数)植物蛋白类缓凝剂和0.60%(质量分数)HPMC掺量下3D打印构件的体积变形率为0.09。     

Development of enhanced three-dimensional printed packings for scale-up of distillation columns: A successful case study

This publication presents a general approach for the enhancement of packings regarding scalability, separation efficiency, and fluid dynamic properties using three-dimensional (3D) printing. The methodology is used to develop miniaturized, scalable packings for process development, and scale-up applications. For this purpose, a 3D printable computer-aided design version of the Rombopak 9M industrial packing (RP9M-3D), which is known for its positive scalability properties, was created. An initial characterization by means of computational fluid dynamics simulations and mass transfer measurements reveals positive but also negative design properties. These findings are used to create a more advanced, miniaturized packing structure, the XW-Pak. The evolved structure is compared to the RP9M-3D. The simulation and experimental results show that the enhanced packing, which is still in the early stages of development, exhibits higher separation efficiencies with improved scalability properties at the same void fraction and surface area than the RP9M-3D.     

3D printing of SiC ceramic: Direct ink writing with a solution of preceramic polymers

3D structured SiC ceramics with varying feature sizes (100–400?μm) were achieved by direct ink writing of polycarbosilane (PCS)/n-hexane solution. The rheological properties of the PCS solution and printing parameters were tailored for optimum writing behaviour. The integrity and clear surface of the filaments indicated the printing ability of forming the self-supporting features along with the rapid evaporation of solvent. As-printed 3D structured PCS was processed by oxidative crosslinking and pyrolysis and converted to SiC ceramic. Although strong shrinkage occurred during the pyrolysis, SiC ceramic maintained the original 3D structure. Both proper viscoelasticity of printable solutions and the homogeneous shrinkage in the pyrolysis determine the integrity and feature characteristic of 3D structured SiC using direct ink writing preceramic polymer.     

The Influence of the Material Structure on the Mechanical Properties of Geopolymer Composites Reinforced with Short Fibers Obtained with Additive Technologies

Additive manufacturing technologies have a lot of potential advantages for construction application, including increasing geometrical construction flexibility, reducing labor costs, and improving efficiency and safety, and they are in line with the sustainable development policy. However, the full exploitation of additive manufacturing technology for ceramic materials is currently limited. A promising solution in these ranges seems to be geopolymers reinforced by short fibers, but their application requires a better understanding of the behavior of this group of materials. The main objective of the article is to investigate the influence of the microstructure of the material on the mechanical properties of the two types of geopolymer composites (flax and carbon-reinforced) and to compare two methods of production of geopolymer composites (casting and 3D printing). As raw material for the matrix, fly ash from the Skawina coal power plant (located at: Skawina, Lesser Poland, Poland) was used. The provided research includes mechanical properties, microstructure investigations with the use of scanning electron microscope (SEM), confocal microscopy, and atomic force microscope (AFM), chemical and mineralogical (XRD-X-ray diffraction, and XRF-X-ray fluorescence), analysis of bonding in the materials (FT-IR), and nuclear magnetic resonance spectroscopy analysis (NMR). The best mechanical properties were reached for the sample made by simulating 3D printing process for the composite reinforced by flax fibers (48.7 MPa for the compressive strength and 9.4 MPa for flexural strength). The FT-IR, XRF and XRD results show similar composition of all investigated materials. NMR confirms the presence of SiO₄ and AlO₄ tetrahedrons in a three-dimensional structure that is crucial for geopolymer structure. The microscopy observations show a better coherence of the geopolymer made in additive technology to the reinforcement and equal fiber distribution for all investigated materials. The results show the samples made by the additive technology had comparable, or better, properties with those made by a traditional casting method.     

Influence of Aluminosilicate for the Prediction of Mechanical Properties of Geopolymer Concrete – Artificial Neural Network

In this paper, details and results of experimental and predictive studies carried out to determine the mechanical properties of Aluminosilicate materials like Ground Granulated Blast furnace Slag (GGBS) and Fly Ash (FA) based geopolymer concrete specimens are presented and discussed. The major parameters considered in the experimental study are the percentages of GGBS and Fly ash and the percentage of manufactured sand (m-sand) used to replace conventional river sand used in the production of geopolymer concrete. Sodium hydroxide and sodium silicate solutions were used as the activator in the production of geopolymer concrete. The mechanical properties of the geopolymer concrete determined were the compressive strength, split-tensile strength and flexural strength. The test results showed that the mechanical properties of geopolymer concrete improved with increase in the percentage use of GGBS. Also, it was observed from the test results that increase in the percentage use of m-sand increased the mechanical properties of the geopolymer concrete up to an optimum dosage beyond which reduction in the mechanical properties was observed. The predicted mechanical properties of the geopolymer concrete using Artificial Neural Network (ANN) was found to be in good agreement with the test results.

     

Influence of steel and PP fibers on mechanical and microstructural properties of fly ash-GGBFS based geopolymer composites

In this study, experimental investigations were carried out to estimate the mechanical and microstructural properties of polypropylene (PP) and steel fiber reinforced geopolymer mortar. Two industrial by-products are used as binders to produce the geopolymer composites, i.e., fly ash (FA) and ground granulated blast furnace slag (GGBFS). Different percentages of PP and steel fibers are used in geopolymer mortars to find the mechanical properties such as compressive, splitting tensile and flexural strengths were investigated to understand the strength behavior. However, the compressive elastic modulus values were estimated through the proposed equation based on the compressive strength of the fiber reinforced geopolymer composite samples. Moreover, to understand the geopolymeic reaction, microstructural studies, i.e., scanning electron microscopy (SEM), were conducted. The experimental results revealed that the addition of PP fibers up to 2.0% (volume fraction) enhanced the flexural properties of geopolymer mortar samples. The compressive strength of the steel fiber-reinforced geopolymer composite reached a maximum of 2.5% volume fraction, being a 13.26% improvement over the control mix. The flexural toughness index of the PP and steel fiber reinforced composites improved with increasing the fraction. However, steel fiber reinforced geopolymer samples are shown better flexural toughness compared to PP fibers. The SEM analysis of the geopolymer control mix achieved a good degree of geopolymerization and both the fibers yielded a considerable interfacial bonding with the geopolymer paste.     

喷射3D打印磷酸镁水泥与混凝土界面粘结性能研究

本文结合喷射3D打印全角度智能建造与磷酸镁水泥(MPC)快硬早强、高粘结性能,研究喷射3D打印MPC与混凝土界面粘结性能。通过掺加偏高岭土(MK)和粉煤灰(FA)调控MPC凝结时间、流变和力学性能,研发可喷射3D打印MPC,分析喷射3D打印MPC与混凝土界面粘结强度和微观结构变化规律。结果表明:MK通过降低MPC水化放热速率可明显提高MPC凝结时间,FA可缩短MPC初凝与终凝时间差,进而提高喷射3D打印MPC稳定性;MPC抗折强度随MK掺量先增大后降低,FA可进一步提高MPC抗折强度;随MK掺量增加,MPC静态屈服应力逐渐提高,FA对MPC屈服应力作用不明显,但可显著降低MPC塑性粘度,当掺加30%MK和15%FA时,可保证MPC良好可喷射3D打印建造性和泵送性;喷射3D打印通过高速喷射挤压作用,提高MPC与混凝土界面以及MPC层间粘结强度,使喷射3D打印MPC层间及其与混凝土微观界面粘结密实。     

4D printing of polyurethane paint-based composites

ABSTRACT

In recent studies, polyurethane has shown multiple properties that make it an excellent candidate material in 4D printing. In this study, we present a simple and inexpensive additive method to print waterborne polyurethane paint-based composites by adding carboxymethyl cellulose (CMC) and silicon oxide (SiO₂) nanoparticles to the paint. The first function of CMC and SiO₂ is to improve rheological properties of the polyurethane paint for making a printable precursor, which improves the printing resolution and enhances additive manufacturability. Second, the composite precursors improve the curing rate of the polyurethane paint without changing its inherited shape memory properties. Third, the printed composite parts shown enhanced mechanical strength compared with that of the parts printed with pure polyurethane. Finally, the 3D printed polyurethane-CMC and SiO₂ parts exhibit time-resolved shape transformation upon heat stimulation. To the best of our knowledge, this is the first study of using the polyurethane paint as the precursor for 4D printing, which would open new possibilities in future applications in biomedical engineering, soft robotics and so on.     

Mechanochemical fabrication of geopolymer composites based on the reinforcement effect of microfibrillated cellulose

In this study, microfibrillated cellulose-reinforced geopolymer organic/inorganic hybrid materials, were prepared via a simple green mechanochemical method. The interaction between microfibrillated nanocellulose and geopolymer was further investigated by molecular dynamics simulation. The study established that mechanical ball milling could effectively promote the microfibrillation of bamboo pulp fibers to form reinforced geopolymer composites with a uniformly distributed cellulose skeleton network. The compressive strength of geopolymer blended with 2% microfibrillated cellulose was shown to be 85.1% higher than that of the pristine geopolymer after 30 days. In addition, the hybrid system was found to maintain excellent thermal stability due to the effective protection of the biomass components by the inorganic matrix. This one-step mechanochemical process provided an efficient approach for preparing geopolymer composites, which offers significant application potential for use in road repairs, high-temperature-resistant materials, and additive manufacturing via 3D printing.     

螺杆挤出式3D打印机结构设计与仿真分析

分析了传统桌面级FDM型3D打印机与螺杆挤出式3D打印机的挤出原理,为提升桌面级FDM型3D打印机对打印材料的兼容性并降低打印材料的制作成本,设计了螺杆挤出式3D打印机新结构,具有螺杆与机筒便捷拆换功能.结合设计计算获得了适用于打印丙烯腈?丁二烯?苯乙烯共聚物(ABS)材料的螺杆计量段结构,在螺杆低转速与小型化的要求下...