3D concrete printing has the potential to replace shotcrete for construction of linings of tunnels in hard rock.The shear strength of the interface between rock and printed concrete is vital,especially at super-early ...3D concrete printing has the potential to replace shotcrete for construction of linings of tunnels in hard rock.The shear strength of the interface between rock and printed concrete is vital,especially at super-early ages.However,traditional methods for testing the shear strength of the interface,e.g.,the direct shear test,are time-consuming and result in a high variability for fast-hardening printed concrete.In this paper,a new fast bond shear test is proposed.Each test can be completed in 1 min,with another 2 min for preparing the next test.The influence of the matrix composition,the age of the printed matrices,and the interface roughness of the artificial rock substrate on the shear strength of the interface was experimentally studied.The tests were conducted at the age of the matrices at the 1st,the 4th,the 8th,the 16th,the 32nd,and the 64th min after its final setting.A dimensionless formula was established to calculate the shear strength,accounting for the age of the printed matrices,the interface roughness,and the shear failure modes.It was validated by comparing the calculated results and the experimental results of one group of samples.展开更多
Robotic-based technologies such as automated spraying or extrusion-based 3-dimensional(3D)concrete printing can be used to build tunnel linings,aiming at reducing labor and mitigating the associated safety issues,espe...Robotic-based technologies such as automated spraying or extrusion-based 3-dimensional(3D)concrete printing can be used to build tunnel linings,aiming at reducing labor and mitigating the associated safety issues,especially in the high-geothermal environment.Extrusion-based 3D concrete printing(3DCP)has additional advantages over automated sprayings,such as improved surface quality and no rebound.However,the effect of different temperatures on the adhesion performance of 3D-printed materials for tunnel linings has not been investigated.This study developed several alkali-activated slag mixtures with different activator modulus ratios to avoid the excessive use of Portland cement and enhance sustainability of 3D printable materials.The thermal responses of the mixtures at different temperatures of 20 and 40℃ were studied.The adhesion strength of the alkali-activated material was evaluated for both early and later ages.Furthermore,the structural evolution of the material exposed to different temperatures was measured.This was followed by microstructure characterization.Results indicate that elevated temperatures accelerate material reactions,resulting in improved early-age adhesion performance.Moreover,higher temperatures contribute to the development of a denser microstructure and enhanced mechanical strength in the hardened stage,particularly in mixtures with higher silicate content.展开更多
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 develop...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.展开更多
基金Financial support by the Ministry of Science and Technology of China(No.2021YFE0114100)by the Federal Ministry of Education,Science and Research(BMBWF)of Austria(No.CN11/2021)+5 种基金jointly provided for the project‘Intense Upgrades of the New Austrian Tunnelling Method(NATM)and Demonstration of its Applicability to High-Quality Urban Development’,is gratefully acknowledgedsupported by the Science and Technology Commission of Shanghai Municipality(No.21DZ1203505)the National Natural Science Foundation of China(Grant Nos.51908424 and U1934210)Shanghai Rising-Star Program(No.22QB1405000)Jiangxi Province Department of Transportation Key Engineering Project(No.2021C0008)the financial support provided by the Chinese Scholarship Council(CSC,No.202006260198).
文摘3D concrete printing has the potential to replace shotcrete for construction of linings of tunnels in hard rock.The shear strength of the interface between rock and printed concrete is vital,especially at super-early ages.However,traditional methods for testing the shear strength of the interface,e.g.,the direct shear test,are time-consuming and result in a high variability for fast-hardening printed concrete.In this paper,a new fast bond shear test is proposed.Each test can be completed in 1 min,with another 2 min for preparing the next test.The influence of the matrix composition,the age of the printed matrices,and the interface roughness of the artificial rock substrate on the shear strength of the interface was experimentally studied.The tests were conducted at the age of the matrices at the 1st,the 4th,the 8th,the 16th,the 32nd,and the 64th min after its final setting.A dimensionless formula was established to calculate the shear strength,accounting for the age of the printed matrices,the interface roughness,and the shear failure modes.It was validated by comparing the calculated results and the experimental results of one group of samples.
基金the Industrial Research Fund(No.IOF.PRO.2022.0010.01).
文摘Robotic-based technologies such as automated spraying or extrusion-based 3-dimensional(3D)concrete printing can be used to build tunnel linings,aiming at reducing labor and mitigating the associated safety issues,especially in the high-geothermal environment.Extrusion-based 3D concrete printing(3DCP)has additional advantages over automated sprayings,such as improved surface quality and no rebound.However,the effect of different temperatures on the adhesion performance of 3D-printed materials for tunnel linings has not been investigated.This study developed several alkali-activated slag mixtures with different activator modulus ratios to avoid the excessive use of Portland cement and enhance sustainability of 3D printable materials.The thermal responses of the mixtures at different temperatures of 20 and 40℃ were studied.The adhesion strength of the alkali-activated material was evaluated for both early and later ages.Furthermore,the structural evolution of the material exposed to different temperatures was measured.This was followed by microstructure characterization.Results indicate that elevated temperatures accelerate material reactions,resulting in improved early-age adhesion performance.Moreover,higher temperatures contribute to the development of a denser microstructure and enhanced mechanical strength in the hardened stage,particularly in mixtures with higher silicate content.
基金the National Natural Science Foundation of China(Grant No.52008224)the Open Fund of innovation institute for Sustainable Maritime Architecture Research and Technology(iSMART),Qingdao University of Technology(No.2020-031)+1 种基金the Key Technology Research and Development Program of Shandong(No.2019GSF110004)the financial support received from the Industrial Research Fund(IOF.PRO.2022.0010.01)from Ghent University.
文摘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.