Numerical simulation of three dimensional concrete printing based on a unified fluid and solid mechanics formulation

Deformation control constitutes one of the main technological challenges in three dimensional(3D)concrete printing,and it presents a challenge that must be addressed to achieve a precise and reliable construction process.Model-based information of the expected deformations and stresses is required to optimize the construction process in association with the specific properties of the concrete mix.In this work,a novel thermodynamically consistent finite strain constitutive model for fresh and early-age 3D-printable concrete is proposed.The model is then used to simulate the 3D concrete printing process to assess layer shapes,deformations,forces acting on substrate layers and prognoses of possible structural collapse during the layer-by-layer buildup.The constitutive formulation is based on a multiplicative split of the deformation gradient into elastic,aging and viscoplastic parts,in combination with a hyperelastic potential and considering evolving material properties to account for structural buildup or aging.One advantage of this model is the stress-update-scheme,which is similar to that of small strain plasticity and therefore enables an efficient integration with existing material routines.The constitutive model uses the particle finite element method,which serves as the simulation framework,allowing for modeling of the evolving free surfaces during the extrusion process.Computational analyses of three printed layers are used to create deformation plots,which can then be used to control the deformations during 3D concrete printing.This study offers further investigations,on the structural level,focusing on the potential structural collapse of a 3D printed concrete wall.The capability of the proposed model to simulate 3D concrete printing processes across the scales—from a few printed layers to the scale of the whole printed structure—in a unified fashion with one constitutive formulation,is demonstrated.

A Building Information Modeling-Life Cycle Cost Analysis Integrated Model to Enhance Decisions Related to the Selection of Construction Methods at the Conceptual Design Stage of Buildings

Life Cycle Cost Analysis (LCCA) provides a systematic approach to assess the total cost associated with owning, operating, and maintaining assets throughout their entire life. BIM empowers architects and designers to perform real-time evaluations to explore various design options. However, when integrated with LCCA, BIM provides a comprehensive economic perspective that helps stakeholders understand the long-term financial implications of design decisions. This study presents a methodology for developing a model that seamlessly integrates BIM and LCCA during the conceptual design stage of buildings. This integration allows for a comprehensive evaluation and analysis of the design process, ensuring that the development aligns with the principles of low carbon emissions by employing modular construction, 3D concrete printing methods, and different building design alternatives. The model considers the initial construction costs in addition to all the long-term operational, maintenance, and salvage values. It combines various tools and data through different modules, including energy analysis, Life Cycle Assessment (LCA), and Life Cycle Cost Analysis (LCCA) to execute a comprehensive assessment of the financial implications of a specific design option throughout the lifecycle of building projects. The development of the said model and its implementation involves the creation of a new plug-in for the BIM tool (i.e., Autodesk Revit) to enhance its functionalities and capabilities in forecasting the life-cycle costs of buildings in addition to generating associated cash flows, creating scenarios, and sensitivity analyses in an automatic manner. This model empowers designers to evaluate and justify their initial investments while designing and selecting potential construction methods for buildings, and enabling stakeholders to make informed decisions by assessing different design alternatives based on long-term financial considerations during the early stages of design.

Effect of Aggregate Gradation on the Properties of 3D Printed Recycled Coarse Aggregate Concrete

A simplex centroid design method was employed to design the gradation of recycled coarse aggregate.The bulk density was measured while the specific surface area and average excess paste thickness were calculated with different gradations.The fluidity,dynamic yield stress,static yield stress,printed width,printed inclination,compressive strength and ultrasonic wave velocity of 3D printed recycled aggregate concrete(3DPRAC)were further studied.The experimental results demonstrate that,with the increase of small-sized aggregate(4.75-7 mm)content,the bulk density initially increases and then decreases,and the specific surface area gradually increases.The average excess paste thickness fluctuates with both bulk density and specific surface area.The workability of 3DPRAC is closely related to the average excess paste thickness.With an increase in average paste thickness,there is a gradual decrease in dynamic yield stress,static yield stress and printed inclination,accompanied by an increase in fluidity and printed width.The mechanical performance of 3DPRAC closely correlates with the bulk density.With an increase in the bulk density,there is an increase in the ultrasonic wave velocity,accompanied by a slight increase in the compressive strength and a significant decrease in the anisotropic coefficient.Furthermore,an index for buildability failure of 3DPRAC based on the average excess paste thickness is proposed.

Influence of curing conditions on the shrinkage behavior of three-dimensional printed concrete formwork

The use of three-dimensional(3D)printed concrete as formwork is becoming more widely applied within the industry.However,the technology is still not optimized and there are many reports of preliminary cracking during the curing of cast concrete.This is believed to result from differential shrinkage between the printed and cast concrete.These cracks(in the printed concrete or at the interface between the infill and printed concrete)form a preferential path for aggressive substances and can reduce the durability of the combined concrete element.To ensure the desired service life of the structure,it is important that the differential shrinkage between cast and printed concrete is understood.This study investigated the effect of curing conditions on the differential shrinkage behavior of 3D and cast concrete.The influence of prewetting of the dry-cured 3D printed formwork was also determined.In the experimental program,a vibrated and self-compacting concrete were used as cast material.Linear 3D printed formwork was produced and combined with cast concrete to simulate a concrete structure.Printed formwork was cured for 1,7,or 28 d exposed to the air(relative humidity:60%or 95%)or submerged in water.The length change of the combined elements was observed over 56 d after concrete casting and throughout the thickness of the materials.Results show that increasing the curing period in dry conditions of the printed concrete leads to an expansion of the formwork on the first day after casting.The expansion leads to a non-uniform strain evolution throughout the curing period of the combined element.Printed concrete formwork stored in wet conditions does not expand after the casting process but tends to show a decreasing linear deformation within the whole elements.

Geometric quality evaluation of three-dimensional printable concrete using computational fluid dynamics

The importance of geometrical control of three dimensional(3D)printable concrete without the support of formwork is widely acknowledged.In this study,a numerical model based on computational fluid dynamics was developed to evaluate the geometrical quality of a 3D printed layer.The numerical results were compared,using image analysis,with physical cross-sectional sawn samples.The influence of printing parameters(printing speed,nozzle height,and nozzle diameter)and the rheological behavior of printed materials(yield stress),on the geometrical quality of one printed layer was investigated.In addition,the yield zone of the printed layer was analyzed,giving insights on the critical factors for geometrical control in 3D concrete printing.Results indicated that the developed model can precisely describe the extrusion process,as well as the cross-sectional quality.

The impacts of fabrication systems on 3D concrete printing building forms

Recently,3D concrete printing(3DCP)technology starts entering the market from factories and laboratories,contributing to the creation of new construction methods and architectural forms.However,since the technologies of most 3DCP institutions are independently developed,there is a lack of consensus in terms of construction methods and development approaches in the industry.In this paper,based on 423DCP architectural works completed in last five years,a quantitative analysis was made to evaluate the impacts of the fabrication system on 3DCP building forms.The paper introduced three criteria,including Workspace Index,Geometric Complexity Index,and Tectonic Prospect Index,analyzing and answering the discussions about"adopting in-situ printing or prefabrication","using gantry printers or robotic arms"from the perspective of architectural form.By analyzing specific construction methods and design strategies in these projects,the research summarized three development trends,"mobile equipment,algorithmic structure,and intelligent construction",which will affect the future development of 3DCP building forms.Finally,the paper discussed the advantages,limitations,and potential of four different 3DCP fabrication systems,expecting to point out the directions to further optimize each system and realize more diverse 3DCP buildings.

Selection of digital fabrication technique in the construction industry--A multi-criteria decision-making approach

Digital fabrication techniques,in recent decades,have provided the basis of a sustainable revolution in the construction industry.However,selecting the digital fabrication method in terms of manufacturability and functionality requirements is a complex problem.This paper presents alternatives and criteria for selection of digital fabrication techniques by adopting the multi-criteria decision-making technique.The alternatives considered in the study are concrete three-dimensional(3D)printing,shotcrete,smart dynamic casting,material intrusion,mesh molding,injection concrete 3D printing,and thin forming techniques.The criteria include formwork utilization,reinforcement incorporation,geometrical complexity,material enhancement,assembly complexity,surface finish,and build area.It demonstrates different multi-criteria decision-making techniques,with both subjective and objective weighting methods.The given ranking is based on the current condition of digital fabrication in the construction industry.The study reveals that in the selection of digital fabrication techniques,the criteria including reinforcement incorporation,build area,and geometrical complexity play a pivotal role,collectively accounting for nearly 70% of the overall weighting.Among the evaluated techniques,concrete 3D printing emerged as the best performer,however the shotcrete and mesh molding techniques in the second and third positions.