The water absorption and desorption processes of different types of lightweight aggregates were studied.Subsequently,the influences of pre-wetting lightweight aggregates on compressive strength,microhardness,phase com...The water absorption and desorption processes of different types of lightweight aggregates were studied.Subsequently,the influences of pre-wetting lightweight aggregates on compressive strength,microhardness,phase composition,hydration parameters and micromorphology of the cement pastes were investigated.The results showed that the water absorption and desorption capacities of the lightweight aggregates increased with the decrease of the densification degree.With the addition of pre-wetting lightweight aggregates,the compressive strength of the cement pastes would increase.Moreover,the enhancement effect was more obviously with the desorption capacity of pre-wetting lightweight aggregates increasing.Especially,sample S1 with pre-wetting red-mud ceramisites had the highest compressive strength,of which increased to 49.4 MPa after 28 d curing age.The reason is that mainly because the addition of pre-wetting lightweight aggregates can promote the generation of C–S–H gels in the interfacial zone,and the hydration degree of the interfacial zone increases with the water desorption of pre-wetting lightweight aggregates increasing.It is contributed to optimize the microstructure to enhance microhardness of the interfacial zone,resulting in the compressive strength of the cement-based materials improving.Therefore,the pre-wetting lightweight aggregates with high porosity and strength are the potential internal curing agents for high-strength lightweight concretes.展开更多
Three-dimensional concrete printing(3DCP)can proliferate the industrialization of the construction sector,which is notoriously conservative and indolent toward changes.However,the mechanical behavior of 3DCP should be...Three-dimensional concrete printing(3DCP)can proliferate the industrialization of the construction sector,which is notoriously conservative and indolent toward changes.However,the mechanical behavior of 3DCP should be characterized and modeled considering the interfaces when its performance is thoroughly compared to that of the existing concrete construction methods.This study presents an experimental and numerical investigation of uniaxial compression and three-point bending(TPB)tests on extruded 3DCP beams in different loading directions.The orientation of translational and depositional interfaces with respect to the direction of loading influenced the strength.Both the elastic and post-damage behavior of the 3DCP specimens were compared with those of the conventionally cast specimen under quasi-static loading conditions.Despite the higher compressive strength of the casted specimen,the flexural strength of the 3DCP specimens was higher.This study employed the finite element and cohesive zone models of the appropriate calibrated traction-separation law to model fracture in the notched TPB specimens.Furthermore,the real-time acoustic emission test revealed the nature of failure phenomenon of three-dimensional-printed specimens under flexion,and accordingly,the cohesive law was chosen.The predicted load-displacement responses are in good agreement with the experimental results.Finally,the effects of cohesive thickness and notch shape on the performance under bending were explored through parametric studies.展开更多
Constraining the processes of deformation during tectonic switching from compression to extension is difficult because of the scarcity or absence of associated sedimentary and magmatic rocks and weak metamorphism.The ...Constraining the processes of deformation during tectonic switching from compression to extension is difficult because of the scarcity or absence of associated sedimentary and magmatic rocks and weak metamorphism.The east margin of the eastern North China Craton experienced Early to Middle Jurassic compression and Early Cretaceous extension.However,the period of tectonic quiescence lasting~13 million years(between 153 and 140 Ma)during which this transition occurred is poorly understood.This paper reports the identification of small-scale N-S-trending thrust and sinistral strike-slip faults(TSS)and NWtrending thrust and dextral strike-slip faults(TDS)in the Tongyuanpu-Aiyang region,which is part of the northern Liaodong Peninsula.Calculation of the tectonic stress field using striations,fault planes and kinematics reveals a NW-SE-oriented maximum principal axis(σ1),and sub-horizontalσ2 andσ3.Assemblages of N-S-trending TSS and NW-trending TDS were arranged with right stepping and resulted in local uplift and erosion at the junctions between fault terminations,which partitioned the Early and Middle Jurassic basins into residual smaller volcanic-sedimentary basins.These basins were unconformably overlain by small Early Cretaceous volcanic-sedimentary basins,such as those at Tongyuanpu and Fangjiaweizi.Magmatic ages and the timing of basin formation constrain the initiation of tectonic switching to 156–153 Ma,and its termination to 140–139 Ma.We suggest that R-R’Riedel shears controlled the formation of the N-S-trending TSS and NW-trending TDS.The R-R’shears were produced by continued sinistral strike-slip and northward growth along the Bohai Bay segment of the Tan-Lu fault zone during the Late Jurassic to early Early Cretaceous,simultaneous with a gradual weakening in the tectonic stress field during a switch in the direction of subduction of the Palaeo-Pacific plate from NW-ward to NNW-ward.This tectonic switching might have promoted the dissolution of gold and migration of gold-bearing fluids.展开更多
基金Funded by National Natural Science Foundation of China(Nos.51878003 and 51778513)Major Special Science and Technology Project of Hubei Province(No.2018AAA001)the National Basic Research Program of China(973 Program)(No.2015CB655101).
文摘The water absorption and desorption processes of different types of lightweight aggregates were studied.Subsequently,the influences of pre-wetting lightweight aggregates on compressive strength,microhardness,phase composition,hydration parameters and micromorphology of the cement pastes were investigated.The results showed that the water absorption and desorption capacities of the lightweight aggregates increased with the decrease of the densification degree.With the addition of pre-wetting lightweight aggregates,the compressive strength of the cement pastes would increase.Moreover,the enhancement effect was more obviously with the desorption capacity of pre-wetting lightweight aggregates increasing.Especially,sample S1 with pre-wetting red-mud ceramisites had the highest compressive strength,of which increased to 49.4 MPa after 28 d curing age.The reason is that mainly because the addition of pre-wetting lightweight aggregates can promote the generation of C–S–H gels in the interfacial zone,and the hydration degree of the interfacial zone increases with the water desorption of pre-wetting lightweight aggregates increasing.It is contributed to optimize the microstructure to enhance microhardness of the interfacial zone,resulting in the compressive strength of the cement-based materials improving.Therefore,the pre-wetting lightweight aggregates with high porosity and strength are the potential internal curing agents for high-strength lightweight concretes.
基金the Science and Engineering Research Board,India,under the scheme"Early Career Research Award(No.ECR/2018/001638)"DST-SERB and VSSC,and ISRO of the project titled"Functionality Enhancement Through Design and Development of Advanced Finite Element Algorithms for STR Tools"under the IMPRINT.IIC(IMP/2019/000276)schemeThe authors acknowledge the Smart Materials and Structure Laboratory for facilitating the AE sensor test and DST-FIST funded facility,SHIMADZU AGS-X 100-kN universal testing machine,at the Department of Mechanical Engineering,Indian Institute of Technology Guwahati.Biranchi Panda would like to thank the Science and Engineering Research Board(SERB),India,for the start-up grant(No.SRG/2021/000052).
文摘Three-dimensional concrete printing(3DCP)can proliferate the industrialization of the construction sector,which is notoriously conservative and indolent toward changes.However,the mechanical behavior of 3DCP should be characterized and modeled considering the interfaces when its performance is thoroughly compared to that of the existing concrete construction methods.This study presents an experimental and numerical investigation of uniaxial compression and three-point bending(TPB)tests on extruded 3DCP beams in different loading directions.The orientation of translational and depositional interfaces with respect to the direction of loading influenced the strength.Both the elastic and post-damage behavior of the 3DCP specimens were compared with those of the conventionally cast specimen under quasi-static loading conditions.Despite the higher compressive strength of the casted specimen,the flexural strength of the 3DCP specimens was higher.This study employed the finite element and cohesive zone models of the appropriate calibrated traction-separation law to model fracture in the notched TPB specimens.Furthermore,the real-time acoustic emission test revealed the nature of failure phenomenon of three-dimensional-printed specimens under flexion,and accordingly,the cohesive law was chosen.The predicted load-displacement responses are in good agreement with the experimental results.Finally,the effects of cohesive thickness and notch shape on the performance under bending were explored through parametric studies.
基金supported by the National Key R&D Program of China(Grant No.2016YFC0600102)the National Natural Science Foundation of China(Grant No.42030306)the 111 Project of the Ministry of Science and Technology,China(Grant No.BP0719021)。
文摘Constraining the processes of deformation during tectonic switching from compression to extension is difficult because of the scarcity or absence of associated sedimentary and magmatic rocks and weak metamorphism.The east margin of the eastern North China Craton experienced Early to Middle Jurassic compression and Early Cretaceous extension.However,the period of tectonic quiescence lasting~13 million years(between 153 and 140 Ma)during which this transition occurred is poorly understood.This paper reports the identification of small-scale N-S-trending thrust and sinistral strike-slip faults(TSS)and NWtrending thrust and dextral strike-slip faults(TDS)in the Tongyuanpu-Aiyang region,which is part of the northern Liaodong Peninsula.Calculation of the tectonic stress field using striations,fault planes and kinematics reveals a NW-SE-oriented maximum principal axis(σ1),and sub-horizontalσ2 andσ3.Assemblages of N-S-trending TSS and NW-trending TDS were arranged with right stepping and resulted in local uplift and erosion at the junctions between fault terminations,which partitioned the Early and Middle Jurassic basins into residual smaller volcanic-sedimentary basins.These basins were unconformably overlain by small Early Cretaceous volcanic-sedimentary basins,such as those at Tongyuanpu and Fangjiaweizi.Magmatic ages and the timing of basin formation constrain the initiation of tectonic switching to 156–153 Ma,and its termination to 140–139 Ma.We suggest that R-R’Riedel shears controlled the formation of the N-S-trending TSS and NW-trending TDS.The R-R’shears were produced by continued sinistral strike-slip and northward growth along the Bohai Bay segment of the Tan-Lu fault zone during the Late Jurassic to early Early Cretaceous,simultaneous with a gradual weakening in the tectonic stress field during a switch in the direction of subduction of the Palaeo-Pacific plate from NW-ward to NNW-ward.This tectonic switching might have promoted the dissolution of gold and migration of gold-bearing fluids.
