3D打印混凝土可塑造性能的评价方法研究

本文就3D打印混凝土的可塑造性能的评价工作展开研究,包括成型时间、承载力、变形和失稳控制.成型时间是打印混凝土试体硬化特征的判别依据,本文提出和设计了可塑造时间比的评价及测试方法;针对于打印混凝土承载力的评价,给出了统一流变模型的实验方法与参数获取手段;分析了打印混凝土材料在可塑造性能研究中的变形控制问题,提出了两项变形控制的评价方法,还给出了打印混凝土失稳破坏的控制指标;最后,通过控制打印行程时间与混凝土材料硬化强度增长关系及试体载重特征值的关系,推导出了3D打印混凝土结构总攀升高度的计算方法.     

3D打印建筑技术及其水泥基材料研究进展评述

3D打印技术具有数字化、自动化、快速高效、无模、节省材料等特点,是一种低能耗、低排放的制造技术,也是制造业升级改革的关键技术。3D打印技术在传统建筑领域具有广阔的应用前景,能够极大缩短工程建设周期、提升建筑结构可设计性,它还是一种极端环境下极具潜力的施工技术。因此,3D打印建筑技术不仅受到科研工作者的青睐,更是得到国家的大力支持。本文系统评述了国内外基于水泥基材料的3D打印建筑技术的研究进展:首先介绍了基于水泥基材料的3D打印建筑技术的起源、发展及应用;然后从可打印性能、力学性能及耐久性能三个方面对3D打印水泥基材料研究进展进行了介绍;最后提出了关于3D打印建筑技术的思考与建议,并对其发展方向进行了展望。     

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3D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,3D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可打印性的优化提升方法,并给出了标准化推广的建议,对混凝土3D打印技术的工程应用具有实践指导价值。     

3D打印混凝土材料可打印性的影响因素与测试方法

混凝土3D打印作为近年来发展出的高新技术,受到了广泛的关注,并取得了许多研究成果,但目前对材料特性的测试方法没有形成统一的认识。本文从流动性、凝结时间、流变特性、可挤出性和可建造性五个方面综述了3D打印混凝土的研究进展。流动度试验可以用来快速筛选出不适合打印的材料。从长远来看,凝结时间短的材料更有潜力。流变特性可以定量化分析材料性能,但静态屈服应力随时间的演变缺少研究。目前可挤出性仍由观察法来评判,可以使用空隙率来将可挤出性定量表示。由于坍塌方式不同,可建造性需要将打印层数与试件形变结合起来评价。本文还总结了近年来可打印性的测试方法,对其优缺点进行分析,并对可打印性的量化与评估提供了一些建议,以便研究者借鉴。     

氧化铁红颜料对白水泥基3D打印材料流变及可打印性能的影响

目前3D打印技术在建筑材料领域的研究主要集中在大型结构的建立和力学性能上,而对异形装饰及景观构件的研究还很少。本文采用白色硅酸盐水泥作为胶凝材料,并引入亚微米级粒度氧化铁红颜料来制备彩色水泥基3D打印材料,并研究氧化铁红颜料对白水泥基3D打印材料流变性能、可打印性能及力学性能的影响。结果表明,低掺量的颜料可以降低白水泥基3D打印浆体的动态流变性能,改善浆体的挤出性能。此外,颜料的掺入能够明显提高浆体的静态屈服应力,使得结构变形率从11.38%降低至4.03%。同时,颜料的掺入能够改善浆体的早期力学性能,其3 d抗压和抗折强度最高可达到48.56 MPa和5.07 MPa。总的来说,氧化铁红颜料可调控白水泥基3D打印材料流变性能和优化材料微观结构。     

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。     

纤维对3D打印混凝土打印性能与力学性能的影响

为了研究纤维掺入对3D打印混凝土(3DPC)性能的影响,通过掺入聚乙烯醇(PVA)、聚丙烯(PP)纤维以及剑麻纤维,探究了纤维对3DPC流变性能、打印性能、力学性能以及孔结构的影响规律。流变性能测试结果表明,3DPC的静态屈服应力与三种纤维的掺量均呈线性上升关系,但纤维对3DPC流变性能的影响程度有所差异。打印性能测试结果表明PVA纤维的掺入会降低3DPC的可挤出性,但能明显提高挤出后混凝土的尺寸均匀性。力学性能与孔结构的测试结果表明,PP纤维对3DPC抗压强度有明显的提升效果,剑麻纤维对3DPC抗折强度有最显著的增强效果,而纤维掺量提高会降低3DPC表观密度,使内部孔隙率增加,从而导致高掺量纤维的增强效果弱于低掺量纤维。     

3D打印技术在塑料工业中的应用

首先对3D打印技术进行讲解分析,并综合讲述其工业原理,分析3D打印技术在塑料行业各个方面的应用案例。通过将3D打印技术引入塑料工业,完善了产品开发的新程序及制造工艺,并能切实解决以往设计与制造方法中存在的资源浪费和能源消耗过度的问题,旨在通过本研究总结对实际生产制造提供一定的理论依据,并对3D打印技术的发展起到有益的促进作用。     

3D打印技术在现代服饰创新设计中的应用

论述了3D打印技术的基本原理、特征、材料、加工工艺、应用领域,并结合具体案例分析3D打印服装的审美价值及艺术性。3D打印技术突破了传统服装设计的多种限制,在满足个性化需求、革新服装产业生产方式、加快智能化应用等方面均具有重要价值。随着对3D打印技术研究的逐渐深入,其可应用于服装设计的材料及工艺更加多样化,有助于推动服装产业的创新发展。     

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。     

Experimental study on mix proportion and fresh properties of fly ash based geopolymer for 3D concrete printing

This paper presents the material design and fresh properties of geopolymer mortar developed for 3D concrete printing application. Unlike traditional casting, in 3D printing, extruded materials are deposited layer-by-layer to build complex architectural and structural components without the need of any formwork and human intervention. Extrudability, shape retention, buildability and thixotropic open time (TOT) are identified as critical early-age properties to characterize the 3D printable geopolymer material. Five different mix designs of geopolymer are tested in a systematic experimental approach to obtain a best printable mix and later it is used to print a 60-centimeter-tall freeform structure using a concrete gantry printer to validate the formulation.     

绿色再生轻骨料混凝土短肢剪力墙抗震性能的研究

分析绿色再生轻骨料混凝土不同取代率"L"形截面短肢剪力墙力学性能,研究普通混凝土和最优配合比剪力墙试件抗震性能。试验结果表明:最优配合比试件比废砖掺量为0和100%的试件墙体达到屈服的时间较晚;竖向钢筋配置较多的会使钢筋较晚的进入屈服状态,能承受水平往复荷载的能力更强;较高的竖向钢筋配筋率能提高试件的耗能能力。最优配合比能提高试件耗能能力、承载能力、延性系数、结构耗能能力。研究的成果可为绿色再生轻骨料混凝土短肢剪力墙构件的设计和实际工程应用提供参考,同时为该类构件的深入研究打下基础。     

自密实混凝土研究进展

评述了自密实混凝土在其设计方法与制备技术领域的研究进展.深入调查了自密实混凝土拌合物工作性的测试与评价方法及其应用技术等方面的最新动态.综合分析了自密实混凝土拌合物的流变特性、硬化后的性能及其微观结构特征.对自密实混凝土的设计原理、工作性测试评价方法及其工程应用的发展前景进行了展望,指出了加强自密实混凝土施工质量控制措施及其质量保证体系研究的重要性.     

A new mix design concept for earth-moist concrete: A theoretical and experimental study

This paper addresses experiments on earth-moist concrete (EMC) based on the ideas of a new mix design concept. First, a brief introduction into particle packing and relevant packing theories is given. Based on packing theories for geometric packing, a new concept for the mix design of earth-moist concrete will be introduced and discussed in detail. Within the new mix design concept, the original grading line of Andreasen and Andersen [Andreasen, A.H.M. and Andersen, J., 1930, Ueber die Beziehungen zwischen Kornabstufungen und Zwischenraum in Produkten aus losen Körnern (mit einigen Experimenten). Kolloid-Zeitschrift 50, p. 217-228 (in German).], modified by Funk and Dinger [Funk, J.E. and Dinger, D.R., 1994, Predictive Process Control of Crowded Particulate Suspensions, Applied to Ceramic Manufacturing. Kluwer Academic Press, Boston.], will be used for the mix proportioning of the concrete mixtures.Mixes consisting of a blend of slag cement and Portland cement, gravel (4-16), granite (2-8), three types of sand (0-1, 0-2 and 0-4) and a polycarboxylic ether type superplasticizer are designed using the new mix design concept. The designed concrete mixes are tested in the lab, both in fresh and hardened states, to show the suitability of the ideas of the new mix design concept. The tested concrete mixes meet the requirements on the mechanical and durability properties.Furthermore, the application of fine stone waste materials in the form of premixed sand (Premix 0-4) is presented. By means of an optimized particle packing, stone waste materials can be used to reduce the amount of the most cost intensive materials in earth-moist concrete mixes, viz. binder and filler. The results of tests carried out on mortar samples as well as on paving blocks produced on a laboratory paving stone machine will be discussed. The application of fine stone waste materials in earth-moist concrete mixes does not only meet the current trends in raw materials use, but also fulfill the technical requirements of the concrete in fresh and hardened state.     

Properties of fresh and hardened concrete

The present paper reviews the literature related to the properties of fresh and hardened concrete published after the previous (12th) International Congress on the Chemistry of Cement held in Montreal in 2007.Workability and fundamental rheological properties, reversible and non-reversible evolution, thixotropy, slump loss, setting time, bleeding, segregation and practical issues related to formwork filling and pressure, are addressed among the properties of fresh concrete.Among hardened concrete properties compressive strength and other mechanical and physical properties of hardened concrete, such as tensile strength, elastic properties, shrinkage, creep, cracking resistance, electrical, thermal, transport and other properties are covered. Testing, interpretation, modeling and prediction of properties are addressed, as well as correlation with properties of fresh concrete and durability, effects of special binders, recycled and natural aggregates, fiber reinforcement, mineral and chemical admixtures. Special attention is given to the properties of hardened lightweight and self-compacting concrete.     

A review: 3D printing of microwave absorption ceramics

Along with extensive research on the 3D printing and microwave absorption ceramics, 3D printing technology provides a great possibility for microwave absorption ceramics with arbitrary shapes in a faster, cheaper and more flexible way. This review focuses on the latest evolution in the raw materials, the structure design and the advanced additive manufacturing technologies of 3D printing microwave absorption ceramics. Firstly, the representative raw materials are divided into three categories, including ceramic powder, cermet powder and precursor resin. In addition, additives give rise to improvement of microwave absorption properties of ceramics. Secondly, based on two attenuation theories, structure design makes further efforts to enhance the microwave absorption performance of ceramics. Finally, comparisons are made between diversified manufacturing technologies to facilitate the selection of the best ones for different application in practical use. This study presents a summary of research that has been conducted to produce microwave absorption ceramics by additive manufacturing.     

A method for mix-design of fiber-reinforced self-compacting concrete

The addition of fibers to self-compacting concrete (SCC) may take advantage of its superior performance in the fresh state to achieve a more uniform dispersion of fibers, which is critical for a wider structural use of fiber-reinforced concrete. Some useful, mainly empirical, guidelines are available for mix design of fiber-reinforced SCC. In this work a “rheology of paste model” is applied to the mix design of Steel Fiber Reinforced SCC (SFRSCC). Fibers are included in the particle size distribution of the solid skeleton through the concept of an equivalent diameter, defined on the basis of the specific surface. The influence of fibers (type and quantity) on the grading of solid skeleton, minimum content and rheological properties of the paste required to achieve the required self-compactability and rheological stability were studied. Tests were conducted on both plain and fiber-reinforced concrete made with a variety of mix compositions. In addition, rheological tests were made with corresponding cement pastes.