We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research resu...We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research results show that the mechanism of nano-materials on geopolymer concrete mainly includes the filling effect,nucleation effect,and bridging effect,the appropriate amount of nano-materials can be used as fillers to reduce the porosity of geopolymer concrete,and can also react with Ca(OH)2 to produce C-S-H gel,thereby improving the mechanical properties of geopolymer concrete.The optimum content of nano-SiO_(2) is between 1.0%and 2.0%.The optimum content of nano-CaCO_(3) is between 2.0%and 3.0%.The optimum content of carbon nanotubes is between 0.1%and 0.2%.The optimum content of nano-Al_(2)O_(3) is between 1.0%and 2.0%.The main problems existing in the research and application of nanomaterial-modified geopolymer concrete are summarized,which lays a foundation for the further application of nanomaterial in geopolymer concrete.展开更多
Traditional machine learning(ML)encounters the challenge of parameter adjustment when predicting the compressive strength of reclaimed concrete.To address this issue,we introduce two optimized hybrid models:the Bayesi...Traditional machine learning(ML)encounters the challenge of parameter adjustment when predicting the compressive strength of reclaimed concrete.To address this issue,we introduce two optimized hybrid models:the Bayesian optimization model(B-RF)and the optimal model(Stacking model).These models are applied to a data set comprising 438 observations with five input variables,with the aim of predicting the compressive strength of reclaimed concrete.Furthermore,we evaluate the performance of the optimized models in comparison to traditional machine learning models,such as support vector regression(SVR),decision tree(DT),and random forest(RF).The results reveal that the Stacking model exhibits superior predictive performance,with evaluation indices including R2=0.825,MAE=2.818 and MSE=14.265,surpassing the traditional models.Moreover,we also performed a characteristic importance analysis on the input variables,and we concluded that cement had the greatest influence on the compressive strength of reclaimed concrete,followed by water.Therefore,the Stacking model can be recommended as a compressive strength prediction tool to partially replace laboratory compressive strength testing,resulting in time and cost savings.展开更多
In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand li...In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand lithology(tuff,limestone,basalt,granite),stone powder content(0,5%,10%,15%)and concrete strength grade(C60,C80,C100)as variables.The evolution of mechanical properties of HMC and the correlation between cubic compressive strength and other mechanical properties are studied.Compared to river sand,manufactured sand enhances the cubic compressive strength,axial compressive strength and elastic modulus of concrete,while its potential microcracks weaken the flexural strength and splitting tensile strength of concrete.Stone powder content displays both positive and negative effects on mechanical properties of HMC,and the stone powder content is suggested to be less than 10%.The empirical formulas between cubic compressive strength and other mechanical properties are proposed.展开更多
When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on...When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on the design of the tensioning plans and selection of control measures for the BSS.In order to accurately obtain the bending stiffness of CFST beam and clarify its impact on the mechanical properties of composite BSS during construction,the influence of some factors such as height-width ratio,wall thickness of steel tube,elasticity modulus of concrete,and friction coefficient on the bending stiffness are analyzed parametrically by the numerical simulation technology based on an actual project.The calculation formula of the equivalent bending stiffness of CFST is also established through mathematical statistical simulation.Then,the equivalent bending stiffness is introduced into the construction and use stages of the composite BSS,respectively,and the mechanical properties such as prestress-tensioning control value,structural deformation,and internal force of key members are comparatively analyzed when adopting two different construction plans.Moreover,the optimal construction plan of concrete placement first and then prestress-tensioning is proposed.展开更多
This research is an experimental study aimed at identifying and determining the physico-mechanical properties of various granular materials used in current concretes based on local aggregates (sands, gravels) from dif...This research is an experimental study aimed at identifying and determining the physico-mechanical properties of various granular materials used in current concretes based on local aggregates (sands, gravels) from different quarries, highlighting their intrinsic properties. The aim was also to test their specific influence on the cementitious matrix of hardened concrete. Several laboratory tests were conducted on samples from Brazzaville and Pointe-Noire. To develop a variety of concrete formulations meeting rheological criteria (deformability, bleeding, segregation) and create an optimal concrete formulation approach considering its microstructural and compacting matrix, a good granular distribution was planned, using two types of sand (rolled and crushed). This involved correcting the rolled sand with variable proportions (30% to 50%) of crushed sand. The results from the eight concrete formulations studied, using the Dreux-Gorisse method, showed that six formulations produced the expected results. Compressive strengths at 28 days ranged from 25 to 36.75 MPa. As a result, formulation 3 appears to be the best, with a mechanical strength of 36.75 MPa at 28 days, compared to formulation 1 (33.75 MPa), formulation 4 (27.25 MPa), and formulation 2 (26.65 MPa) for the Brazzaville locality. For the Pointe-Noire locality, formulation 8 was judged the best, with a characteristic mechanical strength of 29.70 MPa at 28 days, followed by formulation 7 (27.30 MPa), formulation 5 (22.80 MPa), and formulation 6 (18.30 MPa). In summary, the concretes formulated with raw sand showed better results than those with improved sands. The same was true for concrete formulations using rolled sand and gravel.展开更多
The use of recycled concrete and oyster shells as partial cement and aggregate replacements is ongoing research to solve this multifaceted problem of concrete waste in the construction industry as well as waste from o...The use of recycled concrete and oyster shells as partial cement and aggregate replacements is ongoing research to solve this multifaceted problem of concrete waste in the construction industry as well as waste from oyster shell farming. However, there is a lack of evidence on the possibility of producing a fully recycled composite consisting of recycled concrete and oyster shell without the need for new cement and natural aggregates. In this study, recycled concrete powder (RCP) and oyster shell were used to produce a green composite. Separate ground and combined ground (separate ground and co-ground) RCP and oyster shells are used to determine the effects of grinding approaches on the mechanical and chemical properties of the composite. The composite samples were molded via press molding by applying 30 MPa of pressure for 10 minutes. The results revealed that the composite prepared via the combined ground approach presented the highest flexural strength compared to the separate ground and unground samples. The FTIR and XRD characterization results revealed no chemical or phase alterations in the raw materials or the resulting composites before and after grinding. SEM analysis revealed that combined grinding reduced the particles’ size and improved the dispersion of the mixture, thereby increasing the strength.展开更多
Concrete buildings used in cold regions are prone to freeze-thaw damage, leading to internal cracking and surface peeling of the concrete. Therefore, improving the freeze-thaw resistance of concrete is of great signif...Concrete buildings used in cold regions are prone to freeze-thaw damage, leading to internal cracking and surface peeling of the concrete. Therefore, improving the freeze-thaw resistance of concrete is of great significance for the safety of hydraulic engineering. This paper explores the effect of basalt fibers on improving the frost resistance index of concrete through a series of experiments, and analyzes the influencing mechanism. The results show that adding an appropriate amount of basalt fibers can significantly improve the frost resistance of concrete and reduce the freeze-thaw damage phenomenon indicated by concrete specimens. Adding 0.1% basalt fiber can maintain the relative dynamic modulus of concrete specimens at 98% after 150 freeze-thaw cycles, while adding 0.3% basalt fiber can control the quality loss rate of concrete specimens after 150 freeze-thaw cycles at 0.87%. Taking into account both the frost resistance effect and economic factors, it is recommended that the basalt fiber content in frost resistant concrete be 0.1%. The research results can provide reference and guidance for the optimization design of the mix proportion of hydraulic concrete in cold regions.展开更多
Amidst Dhaka city’s rapidly growing urban fabric, Dhanmondi Lake is one of the few remaining natural features that directly impacts the area’s microclimate, which is especially relevant to combating the increasing u...Amidst Dhaka city’s rapidly growing urban fabric, Dhanmondi Lake is one of the few remaining natural features that directly impacts the area’s microclimate, which is especially relevant to combating the increasing urban heat island phenomenon. This research investigates the lake’s diurnal and spatial impact on local temperature and humidity variations between greenspaces and concrete landscapes. Data from 14 monitoring points, collected over two months (March-April 2024), were analyzed using descriptive statistics (mean, median, standard deviation) and inferential statistics (Pearson’s correlation coefficient), alongside spatial analysis through Inverse Distance Weighting (IDW) to visualize microclimate patterns. The results demonstrate that during the daytime, temperatures are higher in concrete areas and lower near the lake, with a strong positive correlation between distance from the lake and temperature across the lake (r = 0.933, p = 0.002). Conversely, at night, temperature decreases as the distance from the lake increases, with a strong negative correlation between them (r = −0.983, p = 0.000). The recorded nighttime temperature was relatively stable with a small variation (mean = 28.47˚C, SD = 0.21˚C) across the lake, suggesting the lake’s ability to retain heat at night. In contrast, the average temperature in the areas near the lake was relatively more stable (mean = 28.59˚C, SD = 0.06˚C). Humidity consistently showed a strong negative correlation with distance from the lake both day (r = −0.993, p = 0.000) and night (r = −0.977, p = 0.000), with higher humidity levels near the lake and lower concrete areas. These findings emphasize that distance from the lake and greenspace is a key factor influencing microclimate. The results lead to policy recommendations highlighting integrating natural elements into urban planning to mitigate urban heat island (UHI) effects and enhance thermal comfort.展开更多
When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on ...When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on the design of the tensioning plans and selection of control measures for the BSS.In order to accurately obtain the bending stiffness of CFST beam and clarify its impact on the mechanical properties of composite BSS during con-struction,the influence of some factors such as height-width ratio,wall thickness of steel tube,elasticity modulus of concrete,and friction coefficient on the bending stiffness are analyzed parametrically by the numerical simula-tion technology based on an actual project.The calculation formula of the equivalent bending stiffness of CFST is also established through mathematical statistical simulation.Then,the equivalent bending stiffness is introduced into the construction and use stages of the composite BSS,respectively,and the mechanical properties such as prestress-tensioning control value,structural deformation,and internal force of key members are comparatively analyzed when adopting two different construction plans.Moreover,the optimal construction plan of concrete placementfirst and then prestress-tensioning is proposed.展开更多
This study investigates the compressive and tensile properties of basalt fiber-reinforced concrete (BFRC) after ultra-low-temperature freeze-thaw cycles. Scanning electron microscope (SEM) analysis was conducted to ex...This study investigates the compressive and tensile properties of basalt fiber-reinforced concrete (BFRC) after ultra-low-temperature freeze-thaw cycles. Scanning electron microscope (SEM) analysis was conducted to examine the deterioration mechanisms caused by freeze-thaw cycles and sulfate erosion. The results show that compressive and tensile strengths increase with basalt fiber dosage. The optimal dosage is 0.2%. With longer exposure to sulfate erosion, both strengths decline significantly. Basalt fibers effectively bridge cracks, control expansion, enhance compactness, and improve concrete performance. Ultra-low-temperature freeze-thaw cycles and sulfate erosion cause rapid crack growth. Sulfate erosion produces crystallization products and expansive substances. These fill cracks, create pressure, and damage the internal structure. Freezing and expansion forces further enlarge voids and cracks. This provides space for expansive substances, worsening concrete deterioration and reducing its performance.展开更多
Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.Th...Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.This study designed and prepared EPS concrete materials with four levels of density.Quasi-static uniaxial compression and Split Hopkinson Pressure Bar(SHPB)impact tests were conducted to obtain stress-strain curves,elastic moduli,failure modes,energy absorptions,and strain rate effects of the EPS concrete under quasi-static and dynamic loading conditions.The influences of density on various performance indicators were analyzed.By combining the Zhu-Wang-Tang(ZWT)constitutive model with a modified elastic-brittle model,a modified dynamic constitutive model was proposed.The accuracy of the model was validated by the experimental data.The results indicate that the addition of EPS particles enhances the ductility of the EPS concrete.The EPS concrete has significant strain rate effect,which gets stronger as density increases.The modifiedconstitutive model accurately characterizes the dynamic stress-strain curves of the EPS concrete.展开更多
With the development of modern society,people put forward higher requirements for building safety,which makes the construction project face new challenges.Reinforced concrete frame structure as a common engineering ty...With the development of modern society,people put forward higher requirements for building safety,which makes the construction project face new challenges.Reinforced concrete frame structure as a common engineering type,although the construction technology has been relatively mature,but its earthquake collapse ability still needs to be strengthened.This paper analyzes the specific factors that affect the seismic collapse ability of reinforced concrete frame structure,summarizes the previous research results,and puts forward innovative application of fiber-reinforced polymer(FRP)composite materials,play the role of smart materials,improve the isolation and energy dissipation devices,etc.,to promote the continuous optimization of reinforced concrete frame structure design,and show better seismic performance.展开更多
CGCS(coal gasification coarse slag)and desert sand composite aggregate replacing river sand for the preparation of concrete(coal gasification coarse slag and desert sand composite fine aggregate concrete,abbreviated a...CGCS(coal gasification coarse slag)and desert sand composite aggregate replacing river sand for the preparation of concrete(coal gasification coarse slag and desert sand composite fine aggregate concrete,abbreviated as CDFC)were investigated to study the effect of different CGCS dosages,the sand rate of concrete,and the dosage of fly ash(FA)in cementitious material on the mechanical properties of the concrete and the excessive zone at the aggregate interface.The experimental results show that,with the increase of CGCS admixture,the CDFC water-cement ratio decreases,and the strength shows first increase and then decrease;with the increase of concrete sand rate,the CDFC strength shows first increase and then decrease,and with the increase of FA,the CDFC strength shows first increase and then decrease,when the dosage of cementitious material is 360 kg/m^(3),the composite fine aggregate dosage is 872 kg/m^(3),and the coarse aggregate dosage is 983 kg/m^(3),the maximum compressive strength of its CGCS is 47.4 MPa.The microstructures of CGCS and hydration products were analyzed by X-ray fluorescence spectrometry(XRF),X-ray diffraction(XRD),Fourier transform infrared spectrometry(FTIR),and scanning electron microscopy(SEM).It is found that the CDFC as fine aggregate can generate hydration products such as hydrated calcium silicate gel(C-S-H)in the transition zone of the concrete interface,which can greatly improve the weak zones of the concrete,and improve the strength.展开更多
To mitigate the challenges in managing the damage level of reinforced concrete(RC)pier columns subjected to cyclic reverse loading,this study conducted a series of cyclic reverse tests on RC pier columns.By analyzing ...To mitigate the challenges in managing the damage level of reinforced concrete(RC)pier columns subjected to cyclic reverse loading,this study conducted a series of cyclic reverse tests on RC pier columns.By analyzing the outcomes of destructive testing on various specimens and fine-tuning the results with the aid of the IMK(Ibarra Medina Krawinkler)recovery model,the energy dissipation capacity coefficient of the pier columns were able to be determined.Furthermore,utilizing the calibrated damage model parameters,the damage index for each specimen were calculated.Based on the obtained damage levels,three distinct pre-damage conditions were designed for the pier columns:minor damage,moderate damage,and severe damage.The study then predicted the variations in hysteresis curves and damage indices under cyclic loading conditions.The experimental findings reveal that the displacement at the top of the pier columns can serve as a reliable indicator for controlling the damage level of pier columns post-loading.Moreover,the calibrated damage index model exhibits proficiency in accurately predicting the damage level of RC pier columns under cyclic loading.展开更多
Due to the limited hydration capacity,solidification/stabilization(S/S)with waste concrete powder(WCP)has a low strength.Carbonation can reduce carbon dioxide(CO_(2))emissions and improve strength of lead-contaminated...Due to the limited hydration capacity,solidification/stabilization(S/S)with waste concrete powder(WCP)has a low strength.Carbonation can reduce carbon dioxide(CO_(2))emissions and improve strength of lead-contaminated soil,but its mechanism and environmental behaviors are unclear.In light of this,a comprehensive study was conducted on the compressive strength,lead immobilization,conductivity characteristics,and carbonation mechanism of carbonated Pb-contaminated soils stabilized with WCP compared to calcining 600℃WCP.Results indicated that with carbonation,the compressive strength of the samples was significantly improved at the early stage(1 d),resulting in increased unconfined compressive strength(UCS)by 2.5-5.2 times due to the filling of pores by calcite.It negatively affected the lead immobilization capacity of highly doped(30%)samples,while this effect reversed after 3 d of carbonating due to the reduced alkaline environment.The lead immobilization capacity decreased after 28 d of carbonating due to the cracking of samples and the influence of a lower pH on the solubility of lead-carbonated hydroxide((PbCO_(3))_(2)Pb(OH)_(2)).The water evaporation(saturation<16.8%)led to dry shrinkage cracking and decreased UCS of the samples.Based on this finding,a conductivity model was developed for carbonated and cured samples,accurately predicting changes in saturation levels(R^(2)=0.98).A relationship between conductivity and UCS or lead immobilization capacity was proposed.This research proposed an innovative method for the reduction of CO_(2)emission as well as laid down a theoretical basis for the recovery of WCP and lead-contaminated soils through carbonation.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
Due to the continuously increasing building and construction industry,sand has become one of the most questioned raw materials worldwide.However,the available amount of sand suitable for concrete production is orders ...Due to the continuously increasing building and construction industry,sand has become one of the most questioned raw materials worldwide.However,the available amount of sand suitable for concrete production is orders of magnitude lower that the demand and consumption.Even though desert sand is sufficiently available,it is not usable for realizing stable concrete due to its surface shape.Against this background,the suitability of energy-efficient‘cold'dielectric barrier discharge plasma operated at atmospheric pressure for improving the properties of concrete produced from desert sand was investigated in this contribution.It is shown that such plasma treatment allows for a certain roughening and re-shaping of sand grains.As a result,the mass flow of treated sand is decreased due to an improved wedging of sand grains.This leads to a certain increase in compressive strength of concrete samples.Even though this increase is marginal,the suitability of the applied type of plasma for modification of the geometry and surface chemistry of sand grains was proven,showing its basic potential for the treatment and preconditioning of sand used for concrete,mortar or plastering.展开更多
Seven sets of concrete containing different mass ratios of nano-SiO_(2)(0%-5.0%)and nano-CaCO_(3)(0%-1.5%)were designed.A total of 28 concrete cube specimens cured for 7 and 28 days were tested for compressive strengt...Seven sets of concrete containing different mass ratios of nano-SiO_(2)(0%-5.0%)and nano-CaCO_(3)(0%-1.5%)were designed.A total of 28 concrete cube specimens cured for 7 and 28 days were tested for compressive strength(14 specimens)and split tensile strength(14 specimens),while 7 cylindrical specimens cured for 28 days were tested for impact resistance.The impact resistance of the concrete specimens was quantitatively analyzed by using impact strength(f_(a))and wear rate(L_^(a)),and the effect of dual incorporation of nano-SiO_(2)and nano-CaCO_(3)on the microstructure of concrete was further investigated by XRD and SEM.The experimental results indicate that the incorporation of 5.0%nano-SiO_(2)and 1.5%nano-CaCO_(3)improves the mechanical properties and impact resistance of concrete most significantly,and the compressive strength,split tensile strength,and impact resistance increase by around 37.80%,35.31%,and 183.36%,respectively,compared with that of ordinary concrete.At the microscopic level,nano-SiO_(2)reacts with C-H in a secondary hydration reaction to increase the number of C-S-H gels,which improves the pore structure in the matrix and favorably enhances the adhesion between aggregate and cement paste in the weakened layer,thus improving the abrasion resistance of concrete.展开更多
Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration...Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration and freeze–thaw(FT) cycles is a significant factor causing slope failure. This study aims to investigate the transmedia seepage characteristics at slope–concrete stabilizing pile interface systems by using silty clay and concrete with varying microstructure characteristics under FT cycles. To this end, a self-developed indoor test device for transmedia water migration, combined with a macro-meso-micro multiscale testing approach, was used to analyze the laws and mechanisms of transmedia seepage at the interface systems. The effect of the medium's microstructure characteristics on the transmedia seepage behavior at the interface systems under FT cycles was also assessed. Results indicated that the transmedia water migration exhibited particularity due to the migration of soil particles and the low permeability characteristics of concrete. The water content in the media increased significantly within the range of 1/3–2/3 of the height from the interface for soil and within 5 mm from the interface for concrete.FT cycles promoted the increase and penetration of cracks within the medium, enhancing the permeability of the slope-concrete stabilizing pile interface systems.With the increase in FT cycles, the porosity inside the medium first decreased and then increased, and the porosity reached the minimum after 25 FT cycles and the maximum after 75 FT cycles, and the water content of the medium after water migration was positively correlated with the porosity. FT cycles also significantly influenced the temporal variation characteristics of soil moisture and the migration path of water in concrete. The study results could serve as a reference for related research on slope stability assessment.展开更多
Concrete is one of the most important elements in building construction.However,concrete used in construction is susceptible to damage due to corrosion.The influence of corrosive substances causes changes in the reinf...Concrete is one of the most important elements in building construction.However,concrete used in construction is susceptible to damage due to corrosion.The influence of corrosive substances causes changes in the reinforcing steel and affects the strength of the structure.The repair method is one approach to overcome this problem.This research aims to determine the effect of grouting and jacketing repairs on corroded concrete.The concrete used has dimensions of 15 cm×15 cm×60 cm with planned corrosion variations of 50%,60%,and 70%.The test objects were tested using the Non-Destructive Testing(NDT)method using Ultrasonic Pulse Velocity(UPV).The test results show that the average speed of normal concrete is 5070 m/s,while the lowest average speed is 3070 m/s on the 70%planned corrosion test object.The test object was then given a load of 1600 kgf.At this stage,there is a decrease in speed and wave shape with the lowest average speed obtained at 2753 m/s.The repair method is an effort to restore concrete performance by using grouting and jacketing.Grouting is done by injecting mortar material into it.Jacketing involves adding thickness to the existing concrete layer with additional layers of concrete.After improvements were made,there was an improvement in the UPV test,with a peak speed value of 4910 m/s.Repairing concrete by filling cracks can improve concrete continuity and reduce waveform distortion,thereby increasing wave propagation speed.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.U23A20672,52171270,51879168)the PI Project of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML20240001,GML2024009)。
文摘We have described in detail the effects of nano-SiO_(2),nano-CaCO_(3),carbon nanotubes,and nano-Al_(2)O_(3) on geopolymer concrete from the perspectives of macro mechanics and microstructure.The existing research results show that the mechanism of nano-materials on geopolymer concrete mainly includes the filling effect,nucleation effect,and bridging effect,the appropriate amount of nano-materials can be used as fillers to reduce the porosity of geopolymer concrete,and can also react with Ca(OH)2 to produce C-S-H gel,thereby improving the mechanical properties of geopolymer concrete.The optimum content of nano-SiO_(2) is between 1.0%and 2.0%.The optimum content of nano-CaCO_(3) is between 2.0%and 3.0%.The optimum content of carbon nanotubes is between 0.1%and 0.2%.The optimum content of nano-Al_(2)O_(3) is between 1.0%and 2.0%.The main problems existing in the research and application of nanomaterial-modified geopolymer concrete are summarized,which lays a foundation for the further application of nanomaterial in geopolymer concrete.
基金Funded by China National Key Research and Development Program for Application and Verification of Typical Groundwater Contaminated Sites(No.2019YFC1804805)Shenyang Key Laboratory of Safety Evaluation and Disaster Prevention of Engineering Structures(No.S230184)the Funding Project of Northeast Geological S&T Innovation Center of China Geological Survey(No.QCJJ2023-39)。
文摘Traditional machine learning(ML)encounters the challenge of parameter adjustment when predicting the compressive strength of reclaimed concrete.To address this issue,we introduce two optimized hybrid models:the Bayesian optimization model(B-RF)and the optimal model(Stacking model).These models are applied to a data set comprising 438 observations with five input variables,with the aim of predicting the compressive strength of reclaimed concrete.Furthermore,we evaluate the performance of the optimized models in comparison to traditional machine learning models,such as support vector regression(SVR),decision tree(DT),and random forest(RF).The results reveal that the Stacking model exhibits superior predictive performance,with evaluation indices including R2=0.825,MAE=2.818 and MSE=14.265,surpassing the traditional models.Moreover,we also performed a characteristic importance analysis on the input variables,and we concluded that cement had the greatest influence on the compressive strength of reclaimed concrete,followed by water.Therefore,the Stacking model can be recommended as a compressive strength prediction tool to partially replace laboratory compressive strength testing,resulting in time and cost savings.
基金Funded by the National Natural Science Foundation of China(Nos.U1934206,52108260)China Academy of Railway Sciences Fund(No.2021YJ078)+1 种基金Railway Engineering Construction Standard Project(No.2023-BZWW-006)New Cornerstone Science Foundation through the XPLORER PRIZE。
文摘In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand lithology(tuff,limestone,basalt,granite),stone powder content(0,5%,10%,15%)and concrete strength grade(C60,C80,C100)as variables.The evolution of mechanical properties of HMC and the correlation between cubic compressive strength and other mechanical properties are studied.Compared to river sand,manufactured sand enhances the cubic compressive strength,axial compressive strength and elastic modulus of concrete,while its potential microcracks weaken the flexural strength and splitting tensile strength of concrete.Stone powder content displays both positive and negative effects on mechanical properties of HMC,and the stone powder content is suggested to be less than 10%.The empirical formulas between cubic compressive strength and other mechanical properties are proposed.
文摘When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on the design of the tensioning plans and selection of control measures for the BSS.In order to accurately obtain the bending stiffness of CFST beam and clarify its impact on the mechanical properties of composite BSS during construction,the influence of some factors such as height-width ratio,wall thickness of steel tube,elasticity modulus of concrete,and friction coefficient on the bending stiffness are analyzed parametrically by the numerical simulation technology based on an actual project.The calculation formula of the equivalent bending stiffness of CFST is also established through mathematical statistical simulation.Then,the equivalent bending stiffness is introduced into the construction and use stages of the composite BSS,respectively,and the mechanical properties such as prestress-tensioning control value,structural deformation,and internal force of key members are comparatively analyzed when adopting two different construction plans.Moreover,the optimal construction plan of concrete placement first and then prestress-tensioning is proposed.
文摘This research is an experimental study aimed at identifying and determining the physico-mechanical properties of various granular materials used in current concretes based on local aggregates (sands, gravels) from different quarries, highlighting their intrinsic properties. The aim was also to test their specific influence on the cementitious matrix of hardened concrete. Several laboratory tests were conducted on samples from Brazzaville and Pointe-Noire. To develop a variety of concrete formulations meeting rheological criteria (deformability, bleeding, segregation) and create an optimal concrete formulation approach considering its microstructural and compacting matrix, a good granular distribution was planned, using two types of sand (rolled and crushed). This involved correcting the rolled sand with variable proportions (30% to 50%) of crushed sand. The results from the eight concrete formulations studied, using the Dreux-Gorisse method, showed that six formulations produced the expected results. Compressive strengths at 28 days ranged from 25 to 36.75 MPa. As a result, formulation 3 appears to be the best, with a mechanical strength of 36.75 MPa at 28 days, compared to formulation 1 (33.75 MPa), formulation 4 (27.25 MPa), and formulation 2 (26.65 MPa) for the Brazzaville locality. For the Pointe-Noire locality, formulation 8 was judged the best, with a characteristic mechanical strength of 29.70 MPa at 28 days, followed by formulation 7 (27.30 MPa), formulation 5 (22.80 MPa), and formulation 6 (18.30 MPa). In summary, the concretes formulated with raw sand showed better results than those with improved sands. The same was true for concrete formulations using rolled sand and gravel.
文摘The use of recycled concrete and oyster shells as partial cement and aggregate replacements is ongoing research to solve this multifaceted problem of concrete waste in the construction industry as well as waste from oyster shell farming. However, there is a lack of evidence on the possibility of producing a fully recycled composite consisting of recycled concrete and oyster shell without the need for new cement and natural aggregates. In this study, recycled concrete powder (RCP) and oyster shell were used to produce a green composite. Separate ground and combined ground (separate ground and co-ground) RCP and oyster shells are used to determine the effects of grinding approaches on the mechanical and chemical properties of the composite. The composite samples were molded via press molding by applying 30 MPa of pressure for 10 minutes. The results revealed that the composite prepared via the combined ground approach presented the highest flexural strength compared to the separate ground and unground samples. The FTIR and XRD characterization results revealed no chemical or phase alterations in the raw materials or the resulting composites before and after grinding. SEM analysis revealed that combined grinding reduced the particles’ size and improved the dispersion of the mixture, thereby increasing the strength.
文摘Concrete buildings used in cold regions are prone to freeze-thaw damage, leading to internal cracking and surface peeling of the concrete. Therefore, improving the freeze-thaw resistance of concrete is of great significance for the safety of hydraulic engineering. This paper explores the effect of basalt fibers on improving the frost resistance index of concrete through a series of experiments, and analyzes the influencing mechanism. The results show that adding an appropriate amount of basalt fibers can significantly improve the frost resistance of concrete and reduce the freeze-thaw damage phenomenon indicated by concrete specimens. Adding 0.1% basalt fiber can maintain the relative dynamic modulus of concrete specimens at 98% after 150 freeze-thaw cycles, while adding 0.3% basalt fiber can control the quality loss rate of concrete specimens after 150 freeze-thaw cycles at 0.87%. Taking into account both the frost resistance effect and economic factors, it is recommended that the basalt fiber content in frost resistant concrete be 0.1%. The research results can provide reference and guidance for the optimization design of the mix proportion of hydraulic concrete in cold regions.
文摘Amidst Dhaka city’s rapidly growing urban fabric, Dhanmondi Lake is one of the few remaining natural features that directly impacts the area’s microclimate, which is especially relevant to combating the increasing urban heat island phenomenon. This research investigates the lake’s diurnal and spatial impact on local temperature and humidity variations between greenspaces and concrete landscapes. Data from 14 monitoring points, collected over two months (March-April 2024), were analyzed using descriptive statistics (mean, median, standard deviation) and inferential statistics (Pearson’s correlation coefficient), alongside spatial analysis through Inverse Distance Weighting (IDW) to visualize microclimate patterns. The results demonstrate that during the daytime, temperatures are higher in concrete areas and lower near the lake, with a strong positive correlation between distance from the lake and temperature across the lake (r = 0.933, p = 0.002). Conversely, at night, temperature decreases as the distance from the lake increases, with a strong negative correlation between them (r = −0.983, p = 0.000). The recorded nighttime temperature was relatively stable with a small variation (mean = 28.47˚C, SD = 0.21˚C) across the lake, suggesting the lake’s ability to retain heat at night. In contrast, the average temperature in the areas near the lake was relatively more stable (mean = 28.59˚C, SD = 0.06˚C). Humidity consistently showed a strong negative correlation with distance from the lake both day (r = −0.993, p = 0.000) and night (r = −0.977, p = 0.000), with higher humidity levels near the lake and lower concrete areas. These findings emphasize that distance from the lake and greenspace is a key factor influencing microclimate. The results lead to policy recommendations highlighting integrating natural elements into urban planning to mitigate urban heat island (UHI) effects and enhance thermal comfort.
基金supported by the Project on Excellent Post-Graduate Dissertation of Hohai University,Nanjing,China(422003508)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(SJCX23_0187+2 种基金422003287)the National Natural Science Foundation of China(52250410359)Young Elite Scientists Sponsorship Program by Jiangsu Provincial Association for Science and Technology(TJ-2023-043).
文摘When the upper chord beam of the beam-string structure(BSS)is made of concrete-filled steel tube(CFST),its overall stiffness will change greatly with the construction of concrete placement,which will have an impact on the design of the tensioning plans and selection of control measures for the BSS.In order to accurately obtain the bending stiffness of CFST beam and clarify its impact on the mechanical properties of composite BSS during con-struction,the influence of some factors such as height-width ratio,wall thickness of steel tube,elasticity modulus of concrete,and friction coefficient on the bending stiffness are analyzed parametrically by the numerical simula-tion technology based on an actual project.The calculation formula of the equivalent bending stiffness of CFST is also established through mathematical statistical simulation.Then,the equivalent bending stiffness is introduced into the construction and use stages of the composite BSS,respectively,and the mechanical properties such as prestress-tensioning control value,structural deformation,and internal force of key members are comparatively analyzed when adopting two different construction plans.Moreover,the optimal construction plan of concrete placementfirst and then prestress-tensioning is proposed.
文摘This study investigates the compressive and tensile properties of basalt fiber-reinforced concrete (BFRC) after ultra-low-temperature freeze-thaw cycles. Scanning electron microscope (SEM) analysis was conducted to examine the deterioration mechanisms caused by freeze-thaw cycles and sulfate erosion. The results show that compressive and tensile strengths increase with basalt fiber dosage. The optimal dosage is 0.2%. With longer exposure to sulfate erosion, both strengths decline significantly. Basalt fibers effectively bridge cracks, control expansion, enhance compactness, and improve concrete performance. Ultra-low-temperature freeze-thaw cycles and sulfate erosion cause rapid crack growth. Sulfate erosion produces crystallization products and expansive substances. These fill cracks, create pressure, and damage the internal structure. Freezing and expansion forces further enlarge voids and cracks. This provides space for expansive substances, worsening concrete deterioration and reducing its performance.
基金Supports from National Natural Science Foundation of China(U20A20286 and 12372135)。
文摘Expanded polystyrene(EPS)concrete,known for its environmental friendliness,energy absorption capacity,and low impedance,has significant potential application in the fields of wave absorption and vibration reduction.This study designed and prepared EPS concrete materials with four levels of density.Quasi-static uniaxial compression and Split Hopkinson Pressure Bar(SHPB)impact tests were conducted to obtain stress-strain curves,elastic moduli,failure modes,energy absorptions,and strain rate effects of the EPS concrete under quasi-static and dynamic loading conditions.The influences of density on various performance indicators were analyzed.By combining the Zhu-Wang-Tang(ZWT)constitutive model with a modified elastic-brittle model,a modified dynamic constitutive model was proposed.The accuracy of the model was validated by the experimental data.The results indicate that the addition of EPS particles enhances the ductility of the EPS concrete.The EPS concrete has significant strain rate effect,which gets stronger as density increases.The modifiedconstitutive model accurately characterizes the dynamic stress-strain curves of the EPS concrete.
文摘With the development of modern society,people put forward higher requirements for building safety,which makes the construction project face new challenges.Reinforced concrete frame structure as a common engineering type,although the construction technology has been relatively mature,but its earthquake collapse ability still needs to be strengthened.This paper analyzes the specific factors that affect the seismic collapse ability of reinforced concrete frame structure,summarizes the previous research results,and puts forward innovative application of fiber-reinforced polymer(FRP)composite materials,play the role of smart materials,improve the isolation and energy dissipation devices,etc.,to promote the continuous optimization of reinforced concrete frame structure design,and show better seismic performance.
基金Funded by the Scientific Research Program of Jilin Provincial Department of Education(No.JJKH20250981KJ)。
文摘CGCS(coal gasification coarse slag)and desert sand composite aggregate replacing river sand for the preparation of concrete(coal gasification coarse slag and desert sand composite fine aggregate concrete,abbreviated as CDFC)were investigated to study the effect of different CGCS dosages,the sand rate of concrete,and the dosage of fly ash(FA)in cementitious material on the mechanical properties of the concrete and the excessive zone at the aggregate interface.The experimental results show that,with the increase of CGCS admixture,the CDFC water-cement ratio decreases,and the strength shows first increase and then decrease;with the increase of concrete sand rate,the CDFC strength shows first increase and then decrease,and with the increase of FA,the CDFC strength shows first increase and then decrease,when the dosage of cementitious material is 360 kg/m^(3),the composite fine aggregate dosage is 872 kg/m^(3),and the coarse aggregate dosage is 983 kg/m^(3),the maximum compressive strength of its CGCS is 47.4 MPa.The microstructures of CGCS and hydration products were analyzed by X-ray fluorescence spectrometry(XRF),X-ray diffraction(XRD),Fourier transform infrared spectrometry(FTIR),and scanning electron microscopy(SEM).It is found that the CDFC as fine aggregate can generate hydration products such as hydrated calcium silicate gel(C-S-H)in the transition zone of the concrete interface,which can greatly improve the weak zones of the concrete,and improve the strength.
基金supported by National Natural Science Foundation of China(Project No.51878156)EPC Innovation Consulting Project for Longkou Nanshan LNG Phase I Receiving Terminal(Z2000LGENT0399).
文摘To mitigate the challenges in managing the damage level of reinforced concrete(RC)pier columns subjected to cyclic reverse loading,this study conducted a series of cyclic reverse tests on RC pier columns.By analyzing the outcomes of destructive testing on various specimens and fine-tuning the results with the aid of the IMK(Ibarra Medina Krawinkler)recovery model,the energy dissipation capacity coefficient of the pier columns were able to be determined.Furthermore,utilizing the calibrated damage model parameters,the damage index for each specimen were calculated.Based on the obtained damage levels,three distinct pre-damage conditions were designed for the pier columns:minor damage,moderate damage,and severe damage.The study then predicted the variations in hysteresis curves and damage indices under cyclic loading conditions.The experimental findings reveal that the displacement at the top of the pier columns can serve as a reliable indicator for controlling the damage level of pier columns post-loading.Moreover,the calibrated damage index model exhibits proficiency in accurately predicting the damage level of RC pier columns under cyclic loading.
基金the National Natural Science Foundation of China(Grant Nos.42177163 and 42071080)the China Postdoctoral Science Foundation(Grant No.2022M723347).
文摘Due to the limited hydration capacity,solidification/stabilization(S/S)with waste concrete powder(WCP)has a low strength.Carbonation can reduce carbon dioxide(CO_(2))emissions and improve strength of lead-contaminated soil,but its mechanism and environmental behaviors are unclear.In light of this,a comprehensive study was conducted on the compressive strength,lead immobilization,conductivity characteristics,and carbonation mechanism of carbonated Pb-contaminated soils stabilized with WCP compared to calcining 600℃WCP.Results indicated that with carbonation,the compressive strength of the samples was significantly improved at the early stage(1 d),resulting in increased unconfined compressive strength(UCS)by 2.5-5.2 times due to the filling of pores by calcite.It negatively affected the lead immobilization capacity of highly doped(30%)samples,while this effect reversed after 3 d of carbonating due to the reduced alkaline environment.The lead immobilization capacity decreased after 28 d of carbonating due to the cracking of samples and the influence of a lower pH on the solubility of lead-carbonated hydroxide((PbCO_(3))_(2)Pb(OH)_(2)).The water evaporation(saturation<16.8%)led to dry shrinkage cracking and decreased UCS of the samples.Based on this finding,a conductivity model was developed for carbonated and cured samples,accurately predicting changes in saturation levels(R^(2)=0.98).A relationship between conductivity and UCS or lead immobilization capacity was proposed.This research proposed an innovative method for the reduction of CO_(2)emission as well as laid down a theoretical basis for the recovery of WCP and lead-contaminated soils through carbonation.
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.
基金funded by the Bundesministerium für Bildung und Forschung(Nos.13FH6I06IA and 13FH6I08IA)。
文摘Due to the continuously increasing building and construction industry,sand has become one of the most questioned raw materials worldwide.However,the available amount of sand suitable for concrete production is orders of magnitude lower that the demand and consumption.Even though desert sand is sufficiently available,it is not usable for realizing stable concrete due to its surface shape.Against this background,the suitability of energy-efficient‘cold'dielectric barrier discharge plasma operated at atmospheric pressure for improving the properties of concrete produced from desert sand was investigated in this contribution.It is shown that such plasma treatment allows for a certain roughening and re-shaping of sand grains.As a result,the mass flow of treated sand is decreased due to an improved wedging of sand grains.This leads to a certain increase in compressive strength of concrete samples.Even though this increase is marginal,the suitability of the applied type of plasma for modification of the geometry and surface chemistry of sand grains was proven,showing its basic potential for the treatment and preconditioning of sand used for concrete,mortar or plastering.
基金Funded by the National Natural Science Foundation of China(No.51579195)。
文摘Seven sets of concrete containing different mass ratios of nano-SiO_(2)(0%-5.0%)and nano-CaCO_(3)(0%-1.5%)were designed.A total of 28 concrete cube specimens cured for 7 and 28 days were tested for compressive strength(14 specimens)and split tensile strength(14 specimens),while 7 cylindrical specimens cured for 28 days were tested for impact resistance.The impact resistance of the concrete specimens was quantitatively analyzed by using impact strength(f_(a))and wear rate(L_^(a)),and the effect of dual incorporation of nano-SiO_(2)and nano-CaCO_(3)on the microstructure of concrete was further investigated by XRD and SEM.The experimental results indicate that the incorporation of 5.0%nano-SiO_(2)and 1.5%nano-CaCO_(3)improves the mechanical properties and impact resistance of concrete most significantly,and the compressive strength,split tensile strength,and impact resistance increase by around 37.80%,35.31%,and 183.36%,respectively,compared with that of ordinary concrete.At the microscopic level,nano-SiO_(2)reacts with C-H in a secondary hydration reaction to increase the number of C-S-H gels,which improves the pore structure in the matrix and favorably enhances the adhesion between aggregate and cement paste in the weakened layer,thus improving the abrasion resistance of concrete.
基金financially supported by Jilin Provincial Natural Science Foundation (No.20220101164JC)。
文摘Understanding the factors triggering slope failure is essential to ensure the safety of buildings and transportation infrastructure on slopes. Specifically,the failure of stabilizing piles due to groundwater migration and freeze–thaw(FT) cycles is a significant factor causing slope failure. This study aims to investigate the transmedia seepage characteristics at slope–concrete stabilizing pile interface systems by using silty clay and concrete with varying microstructure characteristics under FT cycles. To this end, a self-developed indoor test device for transmedia water migration, combined with a macro-meso-micro multiscale testing approach, was used to analyze the laws and mechanisms of transmedia seepage at the interface systems. The effect of the medium's microstructure characteristics on the transmedia seepage behavior at the interface systems under FT cycles was also assessed. Results indicated that the transmedia water migration exhibited particularity due to the migration of soil particles and the low permeability characteristics of concrete. The water content in the media increased significantly within the range of 1/3–2/3 of the height from the interface for soil and within 5 mm from the interface for concrete.FT cycles promoted the increase and penetration of cracks within the medium, enhancing the permeability of the slope-concrete stabilizing pile interface systems.With the increase in FT cycles, the porosity inside the medium first decreased and then increased, and the porosity reached the minimum after 25 FT cycles and the maximum after 75 FT cycles, and the water content of the medium after water migration was positively correlated with the porosity. FT cycles also significantly influenced the temporal variation characteristics of soil moisture and the migration path of water in concrete. The study results could serve as a reference for related research on slope stability assessment.
基金supported by the Ministry of Education,Culture,Research,and Technology(Indonesia),Grant number 107/E5/PG.02.00.PL/2024,AZ.
文摘Concrete is one of the most important elements in building construction.However,concrete used in construction is susceptible to damage due to corrosion.The influence of corrosive substances causes changes in the reinforcing steel and affects the strength of the structure.The repair method is one approach to overcome this problem.This research aims to determine the effect of grouting and jacketing repairs on corroded concrete.The concrete used has dimensions of 15 cm×15 cm×60 cm with planned corrosion variations of 50%,60%,and 70%.The test objects were tested using the Non-Destructive Testing(NDT)method using Ultrasonic Pulse Velocity(UPV).The test results show that the average speed of normal concrete is 5070 m/s,while the lowest average speed is 3070 m/s on the 70%planned corrosion test object.The test object was then given a load of 1600 kgf.At this stage,there is a decrease in speed and wave shape with the lowest average speed obtained at 2753 m/s.The repair method is an effort to restore concrete performance by using grouting and jacketing.Grouting is done by injecting mortar material into it.Jacketing involves adding thickness to the existing concrete layer with additional layers of concrete.After improvements were made,there was an improvement in the UPV test,with a peak speed value of 4910 m/s.Repairing concrete by filling cracks can improve concrete continuity and reduce waveform distortion,thereby increasing wave propagation speed.
