The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced...The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced columns and one unreinforced column.The parameters studied for the strengthened columns included axial compression ratio,reinforcement rate,defect rate,strength of SCC,and the section form of a reinforced steel tube.The results show that the steel tube SCC reinforcement method can effectively strengthen RC columns,exert the restraint effect of steel tube,and delay the development of internal concrete cracks.The method can also significantly improve the bearing capacity of RC columns.Regarding ductility,the improvement of the reinforced column is obvious,the deformation resistance of the specimen is enhanced,and the degradation of stiffness and strength is relatively slow,indicating that it has good seismic performance.展开更多
This study evaluates the performance of advanced machine learning(ML)models in predicting the mechanical properties of eco-friendly self-compacting concrete(SCC),with a focus on compressive strength,V-funnel time,Lbox...This study evaluates the performance of advanced machine learning(ML)models in predicting the mechanical properties of eco-friendly self-compacting concrete(SCC),with a focus on compressive strength,V-funnel time,Lbox ratio,and slump flow.The motivation for this study stems from the increasing need to optimize concrete mix designs while minimizing environmental impact and reducing the reliance on costly physical testing.Six ML models-backpropagation neural network(BPNN),random forest regression(RFR),K-nearest neighbors(KNN),stacking,bagging,and eXtreme gradient boosting(XGBoost)-were trained and validated using a comprehensive dataset of 239 mix design parameters.The models'predictive accuracies were assessed using the coefficient of determination,mean squared error,root mean squared error,and mean absolute error.XGBoost consistently outperformed other models,achieving the coefficient of determination values of 0.999,0.933,and 0.935 for compressive strength in the training,validation,and testing datasets,respectively.Sensitivity analysis revealed that cement,silica fume,coarse aggregate,and superplasticizer positively influenced compressive strength,while water content had a negative impact.These findings highlight the potential of ML models,particularly XGBoost and RFR,in optimizing SCC mix designs,reducing reliance on physical testing,and enhancing sustainability in construction.The application of these models can lead to more efficient and eco-friendly concrete mix designs,benefiting real-world construction projects by improving quality control and reducing costs.展开更多
Three typical toughening components(i e,emulsion asphalt,waste tire rubber particles,and polyethylene fibers)were employed to prepare self-compacting concrete(SCC).The fracture behaviors of these prepared SCC were inv...Three typical toughening components(i e,emulsion asphalt,waste tire rubber particles,and polyethylene fibers)were employed to prepare self-compacting concrete(SCC).The fracture behaviors of these prepared SCC were investigated through the three-point bending test of notched beams,in which the accompanying acoustics emissions(AE)were also recorded.The test results showed that although incorporating a single toughening component reduced the fracture strengths and fracture toughness of SCC,the combination of multiple toughening components could diminish this negative effect.In addition,introducing toughening components could enhance the fracture energy and ductility index of SCC,with an improvement up to 10 times or more when PE fibers and other toughening components were involved.Based on the results of AE characteristics,SCC exhibited a progressive damage process with mitigated crack propagation after the addition of toughening components.Overall,this study could advance the understanding of the influence mechanisms of toughening components on concrete fracture behavior and further instruct the improvement in the fracture performance of concrete.展开更多
Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of prec...Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of precast concrete slab(PCS)is vital for keeping the initial track regularity.However,the cast-in-place process of the self-compacting concrete(SCC)filling layer generally causes a large deformation of PCS due to the water-hammer effect of flowing SCC,even cracking of PCS.Currently,the buoyancy characteristic and influencing factors of PCS during the SCC casting process have not been thoroughly studied in urban rail transit.Design/methodology/approach–In this work,a Computational Fluid Dynamics(CFD)model is established to calculate the buoyancy of PCS caused by the flowing SCC.The main influencing factors,including the inlet speed and flowability of SCC,have been analyzed and discussed.A new structural optimization scheme has been proposed for PST to reduce the buoyancy caused by the flowing SCC.Findings–The simulation and field test results showed that the buoyancy and deformation of PCS decreased obviously after adopting the new scheme.Originality/value–The findings of this study can provide guidance for the control of the deformation of PCS during the SCC construction process.展开更多
Recycled large aggregate self-compacting concrete (RLA-SCC) within multiple weak areas. These weak areas have poor resistance to chloride ion erosion, which affects the service life of RLA-SCC in the marine environmen...Recycled large aggregate self-compacting concrete (RLA-SCC) within multiple weak areas. These weak areas have poor resistance to chloride ion erosion, which affects the service life of RLA-SCC in the marine environment. A three-dimensional multi-phase mesoscopic numerical model of RLA-SCC was established to simulate the chloride ions transportation in concrete. Experiments of RLA-SCC immersing in chloride solution were carried out to verify the simulation results. The effects of recycled large aggregate (RLA) content and RLA particle size on the service life of concrete were explored. The results indicate that the mesoscopic numerical simulation results are in good agreement with the experimental results. At the same depth, the closer to the surface of the RLA, the greater the chloride ion concentration. The service life of RLA-SCC in marine environment decreases with the increase of RLA content. Compared with the service life of 20% content, the service life of 25% and 30% content decreased by 20% and 42% respectively. Increasing the particle size of RLA can effectively improve the service life of RLA-SCC in chloride environment. Compared with the service life of 50 mm particle size, the service life of 70 mm and 90 mm increased by 61% and 163%, respectively. .展开更多
In recent decades,the utilization of waste tires,plastic and artificial shale ceramsite as alternative fine aggregate to make self-compacting concrete(SCC)has been recognized as an eco-friendly and sustainable method ...In recent decades,the utilization of waste tires,plastic and artificial shale ceramsite as alternative fine aggregate to make self-compacting concrete(SCC)has been recognized as an eco-friendly and sustainable method to manufacture renewable construction materials.In this study,three kinds of recycled aggregates:recycled tire rubber particles,wood-plastic particles,artificial shale ceramsite were used to replace the sand by different volume(5%,10%,20%and 30%),and their effects on the fresh and hardened properties of SCC were investigated.The slump flow and V-funnel tests were conducted to evaluate the fresh properties of modified-SCC mixtures.The hardened properties include 3,7 and 28-day compressive strengths,axial compressive strength,static elastic modulus,and compressive stress-strain behavior at 28 days.The test results showed that the incorporation of these three kinds of alternative aggregates had a negative impact on the fresh properties of SCC.Besides,the 28-day compressive strength and axial compressive strength decreased with the increase of rubber and wood-plastic particles content.In this experiment,all the three kinds of recycled aggregates can improve the ductility and deformability of SCC,and the most excellent performance comes from SCC with recycled rubber particles.展开更多
In the structures where long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Shrinkage varies with the constituent and...In the structures where long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Shrinkage varies with the constituent and mixture proportions, and depends on the curing conditions and the work environment as well. Self-compacting concrete (SCC) contains combinations of various components, such as aggregate, cement, superplasticizer, water-reducing agent and other ingredients which affect the properties of the SCC including shrinkage. Hence, the realistic prediction shrinkage strains of SCC are an important requirement of the design process for this type of concrete structures. This study reviews the accuracy of the conventional concrete (CC) shrinkage prediction models proposed by the international codes of practice, including CEB-FIP (1990), ACI 209R (1997), Eurocode 2 (2001), JSCE (2002), AASHTO (2004; 2007) and AS 3600 (2009). Also, SCC shrinkage prediction models proposed by Poppe and De Schutter (2005), Larson (2007), Cordoba (2007) and Khayat and Long (2010) are reviewed. Further, a new shrinkage prediction model based on the comprehensive analysis on both of the available models, i.e., the CC and the SCC is proposed. The predicted shrinkage strains are compared with the actual measured shrinkage strains in 165 mixtures of SCC and 21 mixtures of CC.展开更多
By the addition of superplasticizer and air entraining agent,manufactured sand selfcompacting concrete(MS SCC)with slump flow varying from 500 to 700 mm and air content varying from 2.0%to 9.0%were prepared and the pu...By the addition of superplasticizer and air entraining agent,manufactured sand selfcompacting concrete(MS SCC)with slump flow varying from 500 to 700 mm and air content varying from 2.0%to 9.0%were prepared and the pumpability of MS SCC was studied by a sliding pipe rheometer(Sliper).According to the Kaplan’s model,the initial pump pressure and the pump resistance of MS SCC were obtained.Meanwhile,rheological properties including the yield stress and the plastic viscosity of MS SCC were measured by a rheometer.The experimental results show that the increase of slump flow contributes to a higher pumpability and a proper air content,i e,6%is beneficial for the pumpability of MS SCC.Due to the existence of stone powder and stronger angularity of MS,the initial pump pressure of MS SCC is only about 60%-88%that of river sand(RS)SCC with the same slump flow and air content,indicating that MS SCC possesses a higher pumpability than RS SCC.展开更多
The aim and scope of the present study were to determine the efficacy of UFFA in evaluating the workability,static and dynamic stabilization properties,retention period,and slump loss of SCC systems in their fresh sta...The aim and scope of the present study were to determine the efficacy of UFFA in evaluating the workability,static and dynamic stabilization properties,retention period,and slump loss of SCC systems in their fresh state,as well as their compressive strength at various ages.Microstructure(SEM and XRD)of blended SCC systems were studied.Also,the thermogravimetry behavior of blended SCC specimens were researched.According to the evaluated results,incorporating up to 20%UFFA into fresh concrete improved its performance due to its engineered fine particle size and spherical geometry,both of which contribute to the enhancement of characteristics.Blends of 25%and 30%of UFFA show effect on the water-binder ratio and chemical enhancer dosage,resulting in a loss of homogeneity in fresh SCC systems.The reduced particle size,increased amorphous content,and increased surface area all contribute to the pozzolanic reactivity of the early and later ages,resulting in denser packing and thus an increase in compressive strength.The experimental results indicate that UFFA enhances the properties of SCC in both its fresh and hardened states,which can be attributed to the particles’fineness and their relative effect on SCC.展开更多
Self-compacting concrete （SCC） was used for the filling layer of CRTSⅢ plate ballastless track, which needs excellent workability. The rheological properties of SCC cement paste containing chemical admixtures （CA...Self-compacting concrete （SCC） was used for the filling layer of CRTSⅢ plate ballastless track, which needs excellent workability. The rheological properties of SCC cement paste containing chemical admixtures （CA） such as polycarboxylate-based superplasticizer （PCE）, air-entraining agent （AE） and defoamer （DF） were investigated using a Brookfield R/S SST2000 soft solid tester with a vane geometry spindle. The cementitious materials were designed as one, two and, three components systems by addition of ordinary portland cement （OPC） with these chemical admixtures. The rheological properties of one-component system （PCE paste） were improved with increasing the content of PCE. For two components systems of PCE-AE and PCE-DF, yield stress and plastic viscosity reduced firstly and increased afterward with the increasing of AE content. And the plastic viscosity reached the optimum when the content of AE is 0.004wt%. In general, the trend of yield stress and plastic viscosity decreased with the increasing of the DF content. For three components systems, PCE-AE-DF systems, the rheological properties were improved compared with the sample with AE or DF, which attributed to mixes of the active components mentioned above （CA） which could have a synergetic effect.展开更多
In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires,a SiO_(2) aerogel-cement mortar coating was prepared.Based on the HC curve,a self compacting concrete cube spec...In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires,a SiO_(2) aerogel-cement mortar coating was prepared.Based on the HC curve,a self compacting concrete cube specimens coated and uncoated with SiO_(2) aerogel-cement mortar(SiO_(2)-ACM)were heated to simulate tunnel fire for 0.5,1,1.5,2,2.5,3 and 4 h,respectively.The residual compressive strength was tested after the specimens were cooled to room temperature by natural cooling and water cooling.The results show that,the damages of specimens become more serious as fire time goes on,but the residual strength of specimens coated with SiO_(2)-ACM is always higher than that of uncoated with SiO_(2)-ACM.In addition,the residual strength of specimens cooled by water cooling is lower than that of natural cooling.However,for the specimens coated with SiO_(2)-ACM,the adverse effects of water cooling are lessened.With the increase of fire time,the protective effect of SiO_(2)-ACM is still gradually improved.Finally,a formula was established to predict the residual 150 mm cube compressive strength of specimens protected by SiO_(2)-ACM after a simulated tunnel fire.展开更多
Requirements of self-compacting concrete （SCC） applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be s...Requirements of self-compacting concrete （SCC） applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash （FA） substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC （with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation （Vs.~0 mm： V10-16 ram： V16.20 mm= 30%： 30%：40%）） with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d.展开更多
To study the relationship between acoustic emission characteristic parameters of self-compacting concrete(SCC)and its destruction evolution,under uniaxial compression,acoustic emission(AE)tests are performed on C30 se...To study the relationship between acoustic emission characteristic parameters of self-compacting concrete(SCC)and its destruction evolution,under uniaxial compression,acoustic emission(AE)tests are performed on C30 selfcompacting concrete test blocks that are preserved for 7 days and 28 days,the corresponding relationship among energy,amplitude,ring count and different failure stages of the specimens are analyzed by AE experiment,and the spatial distribution of AE in each stage is described by introducing location map.The test shows that there are two rules for the failure of SCC specimens cured for 7 days and 28 days:(1)The first failure law is divided into four stages according to the percentage of the stress value reaching the limit stress:Initial stage:above 10%,the compaction time of test block cured for 28 days is relatively low;Elastic failure stage:30%–35%,the cumulative value of each parameter increases linearly,and the cumulative value of the amplitude is the largest;Crack stable propagation stage:35%–90%,there is a moment that causes local stress concentration in both test blocks;Active stage:above 90%,the cumulative value of the parameter rises sharply,then continues to load the test block instability and damage.(2)The second failure law is divided into five stages according to the percentage of the stress value reaching the limit stress:Initial stage:15%–20%,the cumulative value of each parameter increases with time;Elastic failure stage:20%–40%,the cumulative value of the parameter continues to grow,but the growth curve is approximately parallel;Crack stable propagation stage:40%–60%,all parameters increased sharply and the increase reached the peak of the whole process;A stable state:60–80%,the emission characteristic parameter will become zero,and the stable state of the 28 days curing test block is lagging;Active stage:above 90%,the number of signals increased sharply,but the energy and amplitude are low,and the later test block is completely fractured.(3)In the process of failure,the test block of SCC will form an inverted triangle or landslide failure surface,and the part above the failure surface is prone to failure,and there is a tendency to leave the test block.(4)Under uniaxial compression,the penetration of SCC cracks is mostly shear penetration.展开更多
For the sake of expounding the relationship between coarse/fine aggregate volume content and properties of self-compacting concrete(SCC),a parameter of aggregate space coefficient is proposed to study systematically t...For the sake of expounding the relationship between coarse/fine aggregate volume content and properties of self-compacting concrete(SCC),a parameter of aggregate space coefficient is proposed to study systematically the effects of fine/ coarse aggregates on workability,strength and volume stability of SCC by experiments. The optimized coarse/fine aggregates volume content of SCC was discussed with regard to specified properties. Results indicate there is a close relationship between aggregate space coefficient and properties of SCC not only in fresh state but also in hardened state. With the increasing coarse/fine aggregate space coefficients,workability of fresh SCC will be improved,the compressive strength decreases slightly and shrinkage of SCC however increases. When coarse aggregate space coefficient ranges from 1.2 to 1.7 and the fine aggregate space coefficients is from 0.6 to 1.0,SCC can meet self-compactability requirements in fresh state and have a good volume stability and appropriate strength in hardened state. The results will benefits for developing a new mixing design method for SCC.展开更多
To meet the requirements of construction of concretes filled in the steel tube arches,a C60 grade micro-expansive self-compacting concrete （SCC） was prepared from manufactured sand （MS）.The utilization of MS with ...To meet the requirements of construction of concretes filled in the steel tube arches,a C60 grade micro-expansive self-compacting concrete （SCC） was prepared from manufactured sand （MS）.The utilization of MS with a high content of quarry limestone fines was dealed for SCC applications.The workability,compressive and splitting strength,modulus of elasticity,restrained expansion and chloride ion permeability as well as freeze-thaw resistance of three MS-SCC mixes with fines content of 3%,7% and 10% were tested and compared with those of the natural sand （NS）-SCC mix.The experimental results indicate that the performances of the C60 MS-SCC with fines content of 7% are excellent and compared favorably with those of C60 NS-SCC.展开更多
It has become a research hotspot to explore raw material substitutes of concrete.It is important to research the mechanical properties of self-compacting concrete(SCC)with slag powder(SP)and rubber particle(RP)replaci...It has become a research hotspot to explore raw material substitutes of concrete.It is important to research the mechanical properties of self-compacting concrete(SCC)with slag powder(SP)and rubber particle(RP)replacing cement and coarse aggregate,respectively.12 kinds of composite modified self-compacting concrete(CMSCC)specimens were prepared by using 10%,20%and 30%SP and 30%,40%,50%and 60%RP.The rheological properties,mechanical properties and microstructure of the CMSCC were investigated.Results indicate that the workability,compressive strength,splitting tensile strength and flexural strength of CMSCC prepared by 20%SP and less than 40%RP are improved.In order to maximize the utilization of waste materials,20%SP and 40%RP can be used as the optimal ratio of the combined modifier.The microstructure shows that the addition of proper amount of SP is conducive to the formation of increasingly more uniform C-S-H gel.C-SH gel can fill the internal pores of the sample and enhance the adhesion between the aggregate,thus improving the mechanical properties of CMSCC.RP has a rougher surface and lower density and stiffness,which inhibits the workability and mechanical properties of CMSCC.The above research results have important theoretical and practical significance for the selection of raw materials of self-compacting concrete and the rational use of industrial wastes.展开更多
Combining with the technology of self-compacting concrete, self-stressing concrete and concrete-filled steel tube, we can get self-compacting and self-stressing concrete-filled steel tube. In order to study the expans...Combining with the technology of self-compacting concrete, self-stressing concrete and concrete-filled steel tube, we can get self-compacting and self-stressing concrete-filled steel tube. In order to study the expansive mechanism of self-stressing concrete, the continuous observation of 47 days on six specimens was carried on. The specimens have different steel area to concrete area ratio. The expansive process in hoop and axial direction were studied, and the expansive mechanism was discussed too. The experimental results identify that the creep and elastic deformation take a large proportion in effective free expansion. The calculating formulas of self-stress in hoop and axial directions were presented here.展开更多
Based on the investigation of fiber influence on workability of self-compacting concrete (SCC), tests were carried out on two series of SCC rectangular simply supported beams, which were made of hooked steel fibers re...Based on the investigation of fiber influence on workability of self-compacting concrete (SCC), tests were carried out on two series of SCC rectangular simply supported beams, which were made of hooked steel fibers reinforced concrete with or without stirrups, subjected to four-point symmetrically placed vertical loads. The major test variables are steel fiber contents and stirrup ratios. The results indicate that the ultimate load significantly increases with the increase of fiber content; the addition of ...展开更多
A novel ellipsis-ring cracking apparatus with an automatic monitoring system was used to measure the restrained shrinkage and initial cracking time of self-compacting concrete (SCC). The free shrinkage, restrained shr...A novel ellipsis-ring cracking apparatus with an automatic monitoring system was used to measure the restrained shrinkage and initial cracking time of self-compacting concrete (SCC). The free shrinkage, restrained shrinkage and strength were integrated to evaluate the effect of the mineral admixtures and content of cementitious materials on shrinkage of SCC. The experimental results show that the initial cracking time of SCC incorporating fly ash was delayed, the shrinkage value and rate was reduced. The hydration achievement of silica fume increased free shrinkage and reduced initial cracking time of FA-SCC comparing to control sample, but silica fume improved the mechanical properties of FA-SCC in early age. As same strength, with the reducing the content of cementitious materials, the initial cracking time of SCC delayed and cracking sensitivity decreased markedly, especially when the content of cementitious materials achieve 450 kg/m3.展开更多
This study focuses on the workability and compressive strength of ceramsite self-compacting concrete with fine aggregate partially substituted by steel slag sand(CSLSCC)to prevent the pollution of steel slag in the en...This study focuses on the workability and compressive strength of ceramsite self-compacting concrete with fine aggregate partially substituted by steel slag sand(CSLSCC)to prevent the pollution of steel slag in the environment.The SF,J-ring,visual stability index,and sieve analysis tests are primarily employed in this research to investigate the workability of freshly mixed self-compacting concrete containing steel slag at various steel slag sand replacement rates.The experiment results indicate that CSLSCC with the 20%volume percentage of steel slag(VPS)performs better workability,higher strength,and higher specific strength.The 7-day compressive strength of CSLSCC with the 0.4 of the water-binder ratio(W/B),decreases with the increase of steel slag content,while the 28-day compressive strength increases significantly.The ceramsite self-compacting concrete with good comprehensive performance can be obtained when the substitution rate of steel slag sand for fine aggregate is less than 20%(volume percentage).展开更多
基金Natural Science Foundation of Sichuan Province under Grant Nos.2022NSFSC0319 and 2022NSFSC0095the Science and Technology Research Projects of Mianyang,China under Grant No.15S-02-3。
文摘The behavior of reinforced concrete(RC)square columns strengthened with self-compacting concrete(SCC)-filled steel tubes under cyclic loading was experimentally investigated.Tests were carried out on eleven reinforced columns and one unreinforced column.The parameters studied for the strengthened columns included axial compression ratio,reinforcement rate,defect rate,strength of SCC,and the section form of a reinforced steel tube.The results show that the steel tube SCC reinforcement method can effectively strengthen RC columns,exert the restraint effect of steel tube,and delay the development of internal concrete cracks.The method can also significantly improve the bearing capacity of RC columns.Regarding ductility,the improvement of the reinforced column is obvious,the deformation resistance of the specimen is enhanced,and the degradation of stiffness and strength is relatively slow,indicating that it has good seismic performance.
文摘This study evaluates the performance of advanced machine learning(ML)models in predicting the mechanical properties of eco-friendly self-compacting concrete(SCC),with a focus on compressive strength,V-funnel time,Lbox ratio,and slump flow.The motivation for this study stems from the increasing need to optimize concrete mix designs while minimizing environmental impact and reducing the reliance on costly physical testing.Six ML models-backpropagation neural network(BPNN),random forest regression(RFR),K-nearest neighbors(KNN),stacking,bagging,and eXtreme gradient boosting(XGBoost)-were trained and validated using a comprehensive dataset of 239 mix design parameters.The models'predictive accuracies were assessed using the coefficient of determination,mean squared error,root mean squared error,and mean absolute error.XGBoost consistently outperformed other models,achieving the coefficient of determination values of 0.999,0.933,and 0.935 for compressive strength in the training,validation,and testing datasets,respectively.Sensitivity analysis revealed that cement,silica fume,coarse aggregate,and superplasticizer positively influenced compressive strength,while water content had a negative impact.These findings highlight the potential of ML models,particularly XGBoost and RFR,in optimizing SCC mix designs,reducing reliance on physical testing,and enhancing sustainability in construction.The application of these models can lead to more efficient and eco-friendly concrete mix designs,benefiting real-world construction projects by improving quality control and reducing costs.
基金Funded by Yunnan Provincial Science and Technology Project(No.202004AR040022)National Natural Science Foundation of China(No.52178261)+1 种基金Natural Science Foundation of Hunan Province(No.2022JJ40615)Changsha Municipal Natural Science Foundation(No.kq2202099)。
文摘Three typical toughening components(i e,emulsion asphalt,waste tire rubber particles,and polyethylene fibers)were employed to prepare self-compacting concrete(SCC).The fracture behaviors of these prepared SCC were investigated through the three-point bending test of notched beams,in which the accompanying acoustics emissions(AE)were also recorded.The test results showed that although incorporating a single toughening component reduced the fracture strengths and fracture toughness of SCC,the combination of multiple toughening components could diminish this negative effect.In addition,introducing toughening components could enhance the fracture energy and ductility index of SCC,with an improvement up to 10 times or more when PE fibers and other toughening components were involved.Based on the results of AE characteristics,SCC exhibited a progressive damage process with mitigated crack propagation after the addition of toughening components.Overall,this study could advance the understanding of the influence mechanisms of toughening components on concrete fracture behavior and further instruct the improvement in the fracture performance of concrete.
文摘Purpose–The precast concrete slab track(PST)has advantages of fewer maintenance frequencies,better smooth rides and structural stability,which has been widely applied in urban rail transit.Precise positioning of precast concrete slab(PCS)is vital for keeping the initial track regularity.However,the cast-in-place process of the self-compacting concrete(SCC)filling layer generally causes a large deformation of PCS due to the water-hammer effect of flowing SCC,even cracking of PCS.Currently,the buoyancy characteristic and influencing factors of PCS during the SCC casting process have not been thoroughly studied in urban rail transit.Design/methodology/approach–In this work,a Computational Fluid Dynamics(CFD)model is established to calculate the buoyancy of PCS caused by the flowing SCC.The main influencing factors,including the inlet speed and flowability of SCC,have been analyzed and discussed.A new structural optimization scheme has been proposed for PST to reduce the buoyancy caused by the flowing SCC.Findings–The simulation and field test results showed that the buoyancy and deformation of PCS decreased obviously after adopting the new scheme.Originality/value–The findings of this study can provide guidance for the control of the deformation of PCS during the SCC construction process.
文摘Recycled large aggregate self-compacting concrete (RLA-SCC) within multiple weak areas. These weak areas have poor resistance to chloride ion erosion, which affects the service life of RLA-SCC in the marine environment. A three-dimensional multi-phase mesoscopic numerical model of RLA-SCC was established to simulate the chloride ions transportation in concrete. Experiments of RLA-SCC immersing in chloride solution were carried out to verify the simulation results. The effects of recycled large aggregate (RLA) content and RLA particle size on the service life of concrete were explored. The results indicate that the mesoscopic numerical simulation results are in good agreement with the experimental results. At the same depth, the closer to the surface of the RLA, the greater the chloride ion concentration. The service life of RLA-SCC in marine environment decreases with the increase of RLA content. Compared with the service life of 20% content, the service life of 25% and 30% content decreased by 20% and 42% respectively. Increasing the particle size of RLA can effectively improve the service life of RLA-SCC in chloride environment. Compared with the service life of 50 mm particle size, the service life of 70 mm and 90 mm increased by 61% and 163%, respectively. .
基金the financial support from the National Natural Science Foundation of China,grant number 11772351Double Shield TBM Material Optimization and Supporting Technology Research-TBM Segment Rapid Support Scientific Research Project[contract NO:PM2017/D02]the National Key R&D Program of China(No.2018YFC0406604).
文摘In recent decades,the utilization of waste tires,plastic and artificial shale ceramsite as alternative fine aggregate to make self-compacting concrete(SCC)has been recognized as an eco-friendly and sustainable method to manufacture renewable construction materials.In this study,three kinds of recycled aggregates:recycled tire rubber particles,wood-plastic particles,artificial shale ceramsite were used to replace the sand by different volume(5%,10%,20%and 30%),and their effects on the fresh and hardened properties of SCC were investigated.The slump flow and V-funnel tests were conducted to evaluate the fresh properties of modified-SCC mixtures.The hardened properties include 3,7 and 28-day compressive strengths,axial compressive strength,static elastic modulus,and compressive stress-strain behavior at 28 days.The test results showed that the incorporation of these three kinds of alternative aggregates had a negative impact on the fresh properties of SCC.Besides,the 28-day compressive strength and axial compressive strength decreased with the increase of rubber and wood-plastic particles content.In this experiment,all the three kinds of recycled aggregates can improve the ductility and deformability of SCC,and the most excellent performance comes from SCC with recycled rubber particles.
文摘In the structures where long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Shrinkage varies with the constituent and mixture proportions, and depends on the curing conditions and the work environment as well. Self-compacting concrete (SCC) contains combinations of various components, such as aggregate, cement, superplasticizer, water-reducing agent and other ingredients which affect the properties of the SCC including shrinkage. Hence, the realistic prediction shrinkage strains of SCC are an important requirement of the design process for this type of concrete structures. This study reviews the accuracy of the conventional concrete (CC) shrinkage prediction models proposed by the international codes of practice, including CEB-FIP (1990), ACI 209R (1997), Eurocode 2 (2001), JSCE (2002), AASHTO (2004; 2007) and AS 3600 (2009). Also, SCC shrinkage prediction models proposed by Poppe and De Schutter (2005), Larson (2007), Cordoba (2007) and Khayat and Long (2010) are reviewed. Further, a new shrinkage prediction model based on the comprehensive analysis on both of the available models, i.e., the CC and the SCC is proposed. The predicted shrinkage strains are compared with the actual measured shrinkage strains in 165 mixtures of SCC and 21 mixtures of CC.
基金Funded by the National Natural Science Foundation of China(Nos.U1934206 and 52108260)the Foundation of China Academy of Railway Science Corporation Limited(No.2020YJ049)。
文摘By the addition of superplasticizer and air entraining agent,manufactured sand selfcompacting concrete(MS SCC)with slump flow varying from 500 to 700 mm and air content varying from 2.0%to 9.0%were prepared and the pumpability of MS SCC was studied by a sliding pipe rheometer(Sliper).According to the Kaplan’s model,the initial pump pressure and the pump resistance of MS SCC were obtained.Meanwhile,rheological properties including the yield stress and the plastic viscosity of MS SCC were measured by a rheometer.The experimental results show that the increase of slump flow contributes to a higher pumpability and a proper air content,i e,6%is beneficial for the pumpability of MS SCC.Due to the existence of stone powder and stronger angularity of MS,the initial pump pressure of MS SCC is only about 60%-88%that of river sand(RS)SCC with the same slump flow and air content,indicating that MS SCC possesses a higher pumpability than RS SCC.
文摘The aim and scope of the present study were to determine the efficacy of UFFA in evaluating the workability,static and dynamic stabilization properties,retention period,and slump loss of SCC systems in their fresh state,as well as their compressive strength at various ages.Microstructure(SEM and XRD)of blended SCC systems were studied.Also,the thermogravimetry behavior of blended SCC specimens were researched.According to the evaluated results,incorporating up to 20%UFFA into fresh concrete improved its performance due to its engineered fine particle size and spherical geometry,both of which contribute to the enhancement of characteristics.Blends of 25%and 30%of UFFA show effect on the water-binder ratio and chemical enhancer dosage,resulting in a loss of homogeneity in fresh SCC systems.The reduced particle size,increased amorphous content,and increased surface area all contribute to the pozzolanic reactivity of the early and later ages,resulting in denser packing and thus an increase in compressive strength.The experimental results indicate that UFFA enhances the properties of SCC in both its fresh and hardened states,which can be attributed to the particles’fineness and their relative effect on SCC.
基金Funded by the National Natural Science Foundation of China(No.51178363)
文摘Self-compacting concrete （SCC） was used for the filling layer of CRTSⅢ plate ballastless track, which needs excellent workability. The rheological properties of SCC cement paste containing chemical admixtures （CA） such as polycarboxylate-based superplasticizer （PCE）, air-entraining agent （AE） and defoamer （DF） were investigated using a Brookfield R/S SST2000 soft solid tester with a vane geometry spindle. The cementitious materials were designed as one, two and, three components systems by addition of ordinary portland cement （OPC） with these chemical admixtures. The rheological properties of one-component system （PCE paste） were improved with increasing the content of PCE. For two components systems of PCE-AE and PCE-DF, yield stress and plastic viscosity reduced firstly and increased afterward with the increasing of AE content. And the plastic viscosity reached the optimum when the content of AE is 0.004wt%. In general, the trend of yield stress and plastic viscosity decreased with the increasing of the DF content. For three components systems, PCE-AE-DF systems, the rheological properties were improved compared with the sample with AE or DF, which attributed to mixes of the active components mentioned above （CA） which could have a synergetic effect.
基金Funded by the National Natural Science Foundation of China(No.51678081)Natural Science Foundation of the Jiangsu Higher Education Institution of China(No.18KJB560001)。
文摘In order to facilitate self-compacting concrete to be better used in tunnel linings that can resist fires,a SiO_(2) aerogel-cement mortar coating was prepared.Based on the HC curve,a self compacting concrete cube specimens coated and uncoated with SiO_(2) aerogel-cement mortar(SiO_(2)-ACM)were heated to simulate tunnel fire for 0.5,1,1.5,2,2.5,3 and 4 h,respectively.The residual compressive strength was tested after the specimens were cooled to room temperature by natural cooling and water cooling.The results show that,the damages of specimens become more serious as fire time goes on,but the residual strength of specimens coated with SiO_(2)-ACM is always higher than that of uncoated with SiO_(2)-ACM.In addition,the residual strength of specimens cooled by water cooling is lower than that of natural cooling.However,for the specimens coated with SiO_(2)-ACM,the adverse effects of water cooling are lessened.With the increase of fire time,the protective effect of SiO_(2)-ACM is still gradually improved.Finally,a formula was established to predict the residual 150 mm cube compressive strength of specimens protected by SiO_(2)-ACM after a simulated tunnel fire.
基金Funded by National Natural Science Foundation of China(Nos.U1134008 and 51302090)the Fundamental Research Funds for the Central Universities(No.2015ZJ0005)
文摘Requirements of self-compacting concrete （SCC） applied in pre-stressed mass concrete structures include high fluidity, high elastic modulus, low adiabatic temperature rise and low drying shrinkage, which cannot be satisfied by ordinary SCC. In this study, in order to solve the problem, a few principles of SCC design were proposed and the effects of binder amount, fly ash （FA） substitution, aggregate content and gradation on the workability, temperature rise, drying shrinkage and elastic modulus of SCC were investigated. The results and analysis indicate that the primary factor influencing the fluidity was paste content, and the main methods improving the elastic modulusof SCC were a lower sand ratio and an optimized coarse aggregate gradation. Lower adiabatic temperature rise and drying shrinkage were beneficial for decreasing the cement content. Further, based on the optimization of mixture, a C50 grade SCC （with binder amount of only 480 kg/ m3, fly ash substitution of 40%, sand ratio of 51% and proper coarse aggregate gradation （Vs.~0 mm： V10-16 ram： V16.20 mm= 30%： 30%：40%）） with superior workability was successfully prepared. The temperature rise and drying shrinkage of the prepared SCC were significantly reduced, and the elastic modulus reached 37.6 GPa at 28 d.
基金Beijing Natural Science Foundation(8214060)National Natural Science Foundation of China(42107164).
文摘To study the relationship between acoustic emission characteristic parameters of self-compacting concrete(SCC)and its destruction evolution,under uniaxial compression,acoustic emission(AE)tests are performed on C30 selfcompacting concrete test blocks that are preserved for 7 days and 28 days,the corresponding relationship among energy,amplitude,ring count and different failure stages of the specimens are analyzed by AE experiment,and the spatial distribution of AE in each stage is described by introducing location map.The test shows that there are two rules for the failure of SCC specimens cured for 7 days and 28 days:(1)The first failure law is divided into four stages according to the percentage of the stress value reaching the limit stress:Initial stage:above 10%,the compaction time of test block cured for 28 days is relatively low;Elastic failure stage:30%–35%,the cumulative value of each parameter increases linearly,and the cumulative value of the amplitude is the largest;Crack stable propagation stage:35%–90%,there is a moment that causes local stress concentration in both test blocks;Active stage:above 90%,the cumulative value of the parameter rises sharply,then continues to load the test block instability and damage.(2)The second failure law is divided into five stages according to the percentage of the stress value reaching the limit stress:Initial stage:15%–20%,the cumulative value of each parameter increases with time;Elastic failure stage:20%–40%,the cumulative value of the parameter continues to grow,but the growth curve is approximately parallel;Crack stable propagation stage:40%–60%,all parameters increased sharply and the increase reached the peak of the whole process;A stable state:60–80%,the emission characteristic parameter will become zero,and the stable state of the 28 days curing test block is lagging;Active stage:above 90%,the number of signals increased sharply,but the energy and amplitude are low,and the later test block is completely fractured.(3)In the process of failure,the test block of SCC will form an inverted triangle or landslide failure surface,and the part above the failure surface is prone to failure,and there is a tendency to leave the test block.(4)Under uniaxial compression,the penetration of SCC cracks is mostly shear penetration.
文摘For the sake of expounding the relationship between coarse/fine aggregate volume content and properties of self-compacting concrete(SCC),a parameter of aggregate space coefficient is proposed to study systematically the effects of fine/ coarse aggregates on workability,strength and volume stability of SCC by experiments. The optimized coarse/fine aggregates volume content of SCC was discussed with regard to specified properties. Results indicate there is a close relationship between aggregate space coefficient and properties of SCC not only in fresh state but also in hardened state. With the increasing coarse/fine aggregate space coefficients,workability of fresh SCC will be improved,the compressive strength decreases slightly and shrinkage of SCC however increases. When coarse aggregate space coefficient ranges from 1.2 to 1.7 and the fine aggregate space coefficients is from 0.6 to 1.0,SCC can meet self-compactability requirements in fresh state and have a good volume stability and appropriate strength in hardened state. The results will benefits for developing a new mixing design method for SCC.
基金Funded by the Science and Technology Item of Communication Construction for West China (No.2009318811082)
文摘To meet the requirements of construction of concretes filled in the steel tube arches,a C60 grade micro-expansive self-compacting concrete （SCC） was prepared from manufactured sand （MS）.The utilization of MS with a high content of quarry limestone fines was dealed for SCC applications.The workability,compressive and splitting strength,modulus of elasticity,restrained expansion and chloride ion permeability as well as freeze-thaw resistance of three MS-SCC mixes with fines content of 3%,7% and 10% were tested and compared with those of the natural sand （NS）-SCC mix.The experimental results indicate that the performances of the C60 MS-SCC with fines content of 7% are excellent and compared favorably with those of C60 NS-SCC.
基金This research was supported by the Key Science and Technology Projects in Transportation Industry(2018-MS2-051).
文摘It has become a research hotspot to explore raw material substitutes of concrete.It is important to research the mechanical properties of self-compacting concrete(SCC)with slag powder(SP)and rubber particle(RP)replacing cement and coarse aggregate,respectively.12 kinds of composite modified self-compacting concrete(CMSCC)specimens were prepared by using 10%,20%and 30%SP and 30%,40%,50%and 60%RP.The rheological properties,mechanical properties and microstructure of the CMSCC were investigated.Results indicate that the workability,compressive strength,splitting tensile strength and flexural strength of CMSCC prepared by 20%SP and less than 40%RP are improved.In order to maximize the utilization of waste materials,20%SP and 40%RP can be used as the optimal ratio of the combined modifier.The microstructure shows that the addition of proper amount of SP is conducive to the formation of increasingly more uniform C-S-H gel.C-SH gel can fill the internal pores of the sample and enhance the adhesion between the aggregate,thus improving the mechanical properties of CMSCC.RP has a rougher surface and lower density and stiffness,which inhibits the workability and mechanical properties of CMSCC.The above research results have important theoretical and practical significance for the selection of raw materials of self-compacting concrete and the rational use of industrial wastes.
基金the National Natural Science Foundation of China (50578027)
文摘Combining with the technology of self-compacting concrete, self-stressing concrete and concrete-filled steel tube, we can get self-compacting and self-stressing concrete-filled steel tube. In order to study the expansive mechanism of self-stressing concrete, the continuous observation of 47 days on six specimens was carried on. The specimens have different steel area to concrete area ratio. The expansive process in hoop and axial direction were studied, and the expansive mechanism was discussed too. The experimental results identify that the creep and elastic deformation take a large proportion in effective free expansion. The calculating formulas of self-stress in hoop and axial directions were presented here.
基金Supported by National Natural Science Foundation of China (No. 50578026)
文摘Based on the investigation of fiber influence on workability of self-compacting concrete (SCC), tests were carried out on two series of SCC rectangular simply supported beams, which were made of hooked steel fibers reinforced concrete with or without stirrups, subjected to four-point symmetrically placed vertical loads. The major test variables are steel fiber contents and stirrup ratios. The results indicate that the ultimate load significantly increases with the increase of fiber content; the addition of ...
基金Funded by the National Natural Science Foundation of China (50539010) Nation High Technic R&D Program "863 Program" of China (No. 2005AA332010)
文摘A novel ellipsis-ring cracking apparatus with an automatic monitoring system was used to measure the restrained shrinkage and initial cracking time of self-compacting concrete (SCC). The free shrinkage, restrained shrinkage and strength were integrated to evaluate the effect of the mineral admixtures and content of cementitious materials on shrinkage of SCC. The experimental results show that the initial cracking time of SCC incorporating fly ash was delayed, the shrinkage value and rate was reduced. The hydration achievement of silica fume increased free shrinkage and reduced initial cracking time of FA-SCC comparing to control sample, but silica fume improved the mechanical properties of FA-SCC in early age. As same strength, with the reducing the content of cementitious materials, the initial cracking time of SCC delayed and cracking sensitivity decreased markedly, especially when the content of cementitious materials achieve 450 kg/m3.
基金supported by the National Key Research and Development Program of China(No.2021YFB3802005)the National Natural Science Foundation of China(Grant No.51978002)+1 种基金the Natural Science Foundation for the Higher Education Institutions in Anhui Province of China(Grant No.KJ2020A0845)the Housing and Urban-Rural Construction Science and Technology Plan in Anhui Province of China(Grant No.2021-YF69).
文摘This study focuses on the workability and compressive strength of ceramsite self-compacting concrete with fine aggregate partially substituted by steel slag sand(CSLSCC)to prevent the pollution of steel slag in the environment.The SF,J-ring,visual stability index,and sieve analysis tests are primarily employed in this research to investigate the workability of freshly mixed self-compacting concrete containing steel slag at various steel slag sand replacement rates.The experiment results indicate that CSLSCC with the 20%volume percentage of steel slag(VPS)performs better workability,higher strength,and higher specific strength.The 7-day compressive strength of CSLSCC with the 0.4 of the water-binder ratio(W/B),decreases with the increase of steel slag content,while the 28-day compressive strength increases significantly.The ceramsite self-compacting concrete with good comprehensive performance can be obtained when the substitution rate of steel slag sand for fine aggregate is less than 20%(volume percentage).
