Abstract:Based on the life cycle assessment(LCA)methodology,this study employed three evaluation systems to analyze the impact of key mix design parameters on the carbon emissions of precast piles and explored the applicability of a load capacity-based carbon emission evaluation approach.The research results indicate that using unit load capacity as the functional unit for evaluation can effectively reveal the intrinsic relationship between carbon emissions and key mix design parameters.Under the same load capacity conditions,the use of high-strength concrete can significantly reduce the carbon emissions of a single precast pile.In building pile foundation engineering,the application of high-strength concrete precast piles can reduce the number of precast piles required,thereby substantially lowering the overall carbon emissions of the project.

Abstract:By incorporating low-viscosity chitosan-modified diatomite and palygorskite adsorbents,pervious concrete with water purification capability was prepared.After clarifying the influence of chitosan doping ratio on the Cu²⁺removal rate and unit adsorption capacity of the modified diatomite and palygorskite,further studies were conducted on the effects of adsorbent dosage on the removal rates of ammonia nitrogen(NH4-N)and Cu²⁺,water permeability and compressive strength of pervious concrete.The results show that compared to unmodified adsorbents,the Cu²⁺unit adsorption capacities of chitosan-modified diatomite and palygorskite(mass ratio is 1∶12)are increased by 1.2 times and 2.2 times,respectively.The incorporation of modified adsorbents into pervious concrete not only improves the pore structure but also significantly enhances the removal effects of NH4-N and Cu²⁺.Although the compressive strength slightly decreases with the increase of modified adsorbent dosage,it can still meet the minimum grade requirements of pervious concrete under the appropriate dosage,and can effectively improve its water permeability.

Abstract:Tension coupon tests were conducted on HRB400E steel reinforcing bars.Mechanical properties and constitutive relationship of the material were determined.Notched round bar specimens were designed according to general stress state of steel reinforcing bars.Monotonic tensile tests were conducted on the notched round bar specimens.The void growth model(VGM)was calibrated for the HRB400E steel reinforcing bars based on the test results and complementary finite element analysis.The material parameter of the VGM was determined to be η=2.03.Monotonic tensile tests were conducted on HRB400E steel reinforcing bars.Ductile fracture of the steel reinforcing bars was observed.The entire fracture processes of the steel reinforcing bars were numerically simulated with the VGM.The fracture processes obtained by the simulation are consistent with the test results.The fracture displacements predicted by the VGM agree well with the test results,with a maximum error within 10%.The applicability and accuracy of the VGM in ductile fracture analysis of steel reinforcing bars are thus verified.

Abstract:The emulsified asphalt was modified by a composite of waterborne epoxy resin,rubber latex and cement.An orthogonal experiment was conducted to analyze the significance of the effects of modifiers on the drying time and pull-off strength of the emulsified asphalt.Fluorescence microscopy,infrared spectroscopy and X-ray energy dispersive spectroscopy were used to investigate the compatibility mechanism.The results indicate that the waterborne epoxy resin has a significant impact on both drying time and pull-off strength of the emulsified asphalt.When the dosage reaches 9%,the waterborne epoxy resin begins to form a network structure.The waterborne epoxy resin,SBR and cement hydration products form a network skeleton through physical blending,which exists within the asphalt phase.Additionally,both the emulsified asphalt and the waterborne epoxy resin delay the hydration process of the cement.

Abstract:Using rubberized concrete(RC)and normal concrete(NC)as control groups,quasi-static compression tests,static flexural tests,and dynamic impact tests were conducted on polyurea particle concrete(PC)to investigate the effects of polyurea particle content and particle size on the static and dynamic mechanical properties of concrete.The results indicate that the compressive strength of PC is significantly higher than that of RC.The incorporation of polyurea particles significantly enhances the toughness of concrete.When the polyurea particle content is 10%,the peak strain of PC is concentrated between 4‰ and 6‰,at which point PC exhibits better toughness and ductility.When the polyurea particle size ranges from 1.00 to 3.00 mm,PC demonstrates relatively excellent energy dissipation characteristics.

Abstract:The material addition process has a crucial effect on the performance of modified asphalt.A series of high content SBS modified asphalt(HCBMA)was prepared by using four addition process,including the oil-filled premixing,granulating premixing,simultaneous addition and subsequent addition,and a multi-angle evaluation method was adopted for the research.The results show that the addition process can significantly affect the performance of HCBMA.The absorption of rubber oil by high content SBS and base asphalt has a competitive relationship.HCBMA prepared by oil-filled premixing has the best high temperature rheological properties,the simultaneous addition process shows the best fatigue resistance,but the fatigue performance of the granulation premixing process(two-screw extrusion granulation)is the weakest.High temperature performance of the subsequent addition process is the lowest,while the low temperature performance indicators are the best.Compared with the oil-filled premixing/simultaneous premixing/subsequent addition process,HCBMA prepared by the granulation premixing process shows the smallest molecular weight,polydispersity index and aging index,which means the degradation degree of SBS is relatively deep during the preparation process.Asphalt mixture is prepared by the oil-filled premixing process has the high temperature rutting and low temperature cracking resistance,while the simultaneous addition process shows the opposite phenomenon.Considering the performance of asphalt and mixtures,it is recommended to adopt the oil-filled premixing process.It is also necessary to combine rheological properties and asphalt mixture performance due to the conventional performance evaluation method of HCBMA is insufficient.

Abstract:The effects of the silica-aluminum molar ratio of the raw materials on the compressive strength,sodium(calcium)silicate aluminate hydrate(N(C)-A-S-H)gel content and microstructural aspects of iron tailings geopolymer(IOTG)were investigated by means of regulating the silica-aluminum molar ratio of the raw materials by blending bauxite(BX)and silica fume(SF)into iron tailings(IOT)for improving the mechanical properties of IOTG.The results show that the silica-aluminum molar ratio of the raw materials significantly affects both compressive strength and gel content of IOTG.When n(Si)/n(Al)is 2.0,the 28 d compressive strength and N(C)-A-S-H gel content of IOTG reach the maximum value synchronously with 32.13 MPa and 59.75%,respectively.The silica-aluminum molar ratio of the raw materials plays a stabilizing role in the formation of chain structures such as Si—O—T inside the gel product,effectively promoting the internal microstructure of IOTG towards densification and enhancing its mechanical properties.

Abstract:Based on the engineering performance requirements of prefabricated vertical drains(PVDs),the base material for preparing degradable prefabricated vertical drain(DPVD)core that can replace PVD core and its related properties were studied through the blending of polylactic acid(PLA)and polybutylene adipate-co-terephthalate(PBAT).The results indicate that the PLA/PBAT composite with 30%PBAT content is the optimal base material for manufacturing DPVD core.The DPVD developed exhibits a tensile strength of 2.82 kN/dm,a compressive yield strength of 3.35 MPa,and a longitudinal flow capacity of 84.0 cm³/s under a confining pressure of 350 kPa.

Abstract:The effects of different fiber types,fiber impregnation treatments,and fiber reinforcement ratios on the flexural tensile strength of cast mortar were compared.Fibers with superior performance and good compatibility for 3D printing were selected and validated through printing tests.The results indicate that ultra-high molecular weight polyethylene(UHMWPE)fibers provide the most significant improvement in the flexural tensile strength of mortar.Mineral fibers,due to their poor abrasion resistance,offer limited enhancement and even reduce the flexural strength of mortar;however,after impregnation treatment,they significantly improve the flexural tensile strength.Impregnated carbon fibers outperform UHMWPE fibers in enhancing the flexural tensile strength.As the reinforcement ratio of UHMWPE fibers increases,the flexural strength and deflection of mortar are substantially improved.The failure mode of 3D-printed flexural specimens with a 0.3%reinforcement ratio is characterized as under-reinforced failure,exhibiting multiple cracking and high ductility.Appropriately increasing the reinforcement ratio helps restrain crack propagation.

Abstract:To investigate the workability and mechanical properties of cemented sand,gravel and rock(CSGR)under different two-grade aggregate conditions,both single-factor experiments and multifactorial experiments based on response surface methodology were conducted.The effects of sand ratio,water-binder ratio,and two-grade aggregate both individually and interactively,on the performance of CSGR,were thoroughly analyzed.A second-order polynomial regression model was established,and multi-objective optimization was performed using the non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ).The results show that the water-binder ratio has a significant influence on the vibratery compaction(VC)value,compressive strength,splitting tensile strength,and tensile-compressive strength ratio of CSGR.Additionally,the interaction between two-grade aggregate and the water-binder ratio has a significant effect on compressive strength.The NSGA-Ⅱ successfully achieves multi-objective optimization of"VC value-compressive strength-splitting tensile strength",providing reliable and diversified mix design solutions for CSGR.This study offers valuable insights for the practical construction and broad application of CSGR dams.

Abstract:Based on the viscoplastic theory in the effective stress space,this study establishes a theoretical correlation between the uniaxial dynamic and static tensile behaviors of ultra-high performance concrete(UHPC).The rate sensitivity effects on plastic evolution and damage evolution were investigated,and the criteria for plastic evolution and damage accumulation under dynamic tensile conditions were elucidated.A uniaxial tensile viscoplastic damage constitutive model for UHPC was developed,accompanied by a proposed expression for the dynamic increase factor of tensile strength.In addition,the model was validated against experimental data from both static and dynamic uniaxial tensile tests.The results demonstrate that the proposed constitutive model effectively reproduces the plastic evolution,damage evolution,and stress-strain relationships of UHPC under uniaxial tension,thereby providing a valuable reference for nonlinear analysis of UHPC structures.

Abstract:To investigate the protective effect of embedded anode cathodic protection on steel corrosion in sea sand concrete,the evolution of interfacial bond performance after anode consumption was studied through bond-slip tests and backscattered analysis.A bond-slip constitutive model was developed based on experimental data,and a long-term usable embedded zinc alloy anode protection scheme was proposed.The results show that after 360 days of seawater immersion,the bond strength between steel bars and sea sand concrete decreases by 30%due to steel corrosion.The bond strength between steel bars and concrete remains unchanged after applying the embedded zinc alloy anode cathodic protection system.The bond strength increases slightly after corrosion of the embedded zinc alloy anode,and the generated calcium zincate corrosion products show almost no expansion.

Abstract:Salt spray and dry-wet cycle accelerated corrosion tests were employed to simulate the marine atmospheric corrosion environment,and high-cycle fatigue tests were conducted on Q690D steel unequal thickness butt joint specimens with different corrosion cycles to systematically investigate the effect of corrosion damage on fatigue properties.The parameters of the fatigue damage evolution equation based on continuum damage mechanics were calibrated.The results show that with the increase in the corrosion cycle,the mass loss rates of specimens rise,the corrosion rate decreases,and the maximum depth of surface pits increases.Surface corrosion damage forms stress concentration sources,induces micro-crack initiation,and significantly reduces the fatigue properties of the joints.The fatigue fracture of the corroded specimens exhibits multi-source characteristics.The greater the initial damage degree,the faster the fatigue damage growth rate.

Abstract:Through partition treatment,the porosity,pore size distribution,ion content distribution and microscopic products were studied to reveal the evolution mechanism of pore structure in the immersion zone,crystallization zone and drying zone of semi-immersed concrete under sulphate attack.The results show that the immersion zone is affected by chemical erosion products such as ettringite,with large expansion force,enhanced pore connectivity,and the most serious damage.The crystallization zone is mainly affected by the physical crystallization expansion of Na2SO4 and water evaporation,with more micropores and weaker connectivity.The drying zone has the most micropores and the weakest connectivity.

Abstract:To prevent cracking in clay anti-seepage layers,which poses a threat to engineering safety,palm fibers were added to improve the cracking resistance of clay.Evaporation cracking tests were conducted under dry-wet cycles.The cracking characteristics,failure mechanism and microscopic mechanism of the modified clay with different reinforcement ratios(0%,0.2%,0.4%,0.6%,0.8%)were systematically investigated.The results show that the increase of dry-wet cycles can significantly accelerate water evaporation.Palm fibers effectively slow down water evaporation and decrease water content.When the reinforcement ratio increases from 0.2%to 0.8%,the effect of suppressing water evaporation does not improve significantly.Palm fibers can significantly decrease the cracking width of clay and promote the formation of fine cracks,leading to improved soil stability.The water content and cracking characteristics of clay are mainly influenced by the dry-wet cycles,and the reinforcement ratio has a significant impact on the change amplitude,but little impact on the change trend.

Abstract:To reduce the cracking risk of the flexural composite interface in solid waste coarse aggregate composite beams,hybrid solid waste coarse aggregates(HWCA)were prepared by combining high-stiffness iron ore waste coarse aggregates(IRCA)and low-stiffness spontaneous combustion coal gangue coarse aggregates(SGCA),and the corresponding HWCA concretes were made.The mechanical properties of HWCA concretes and flexural performance of composite beams were investigated,and the elastic ratio of aggregate to mortar was proposed as a criterion for determining the extreme values in the elastic modulus and Poisson's ratio of concretes.The results indicate that when the volume fraction of IRCA is 60%,the stiffness of HWCA is equivalent to that of natural coarse aggregate(NCA),and the difference in the elastic modulus of HWCA concretes decreases from 28.03%to 2.44%.When the volume fraction of IRCA is 68%and 92%,the compressive strength and elastic modulus of HWCA concretes begin to decrease from the peak values,respectively.The composite beams prepared with HWCA concretes can effectively mitigate the stress concentration at the composite interface and improve the crack resistance of the composite interface.

Abstract:Soil site,as a representative building type in China,have been in urgent need of repair due to climate change and human damage in recent years,with consequent disease problems.Reinforcement-modified materials have been practically applied in many years of research as materials for the restoration of earthen ruins.Nevertheless,how to apply modern modified materials to different types of soil sites and improve their performance is still the focus of current research.The new research progress based on the formation mechanism and causes of soil site diseases and the use of different modified materials are summarized,and look forward to the future development direction of soil site modification and conservation research,so as to provide a reference basis for the research of soil site conservation and other earth engineering practices.

Abstract:The effects of sulfate attack on the mechanical properties,phase compositions,and pore structure of cement-based materials were investigated using X-ray diffraction,mercury intrusion porosimetry,and thermodynamic simulation.The results indicate that after 120 d of sulfate attack,the formation of expansive corrosion products such as ettringite is accelerated,leading to significant changes in both macro-and micro-properties.The compressive strength coefficient under erosion shifts from an increasing trend to a decreasing one,accompanied by aggravated mass loss.A higher water-to-cement ratio results in more corrosion products,primarily accumulating in the 10-100 nm transitional pores.The expansion of these corrosion products damages the pore structure,reducing the number of transitional pores while increasing the average pore size from 45.31 nm at 120 d to 78.79 nm at 180 d,ultimately causing severe deterioration of the cement-based materials after 180 d.

Abstract:Through experiments such as unconfined compressive strength tests,phase composition and microstructure analysis,and heavy metal content determination,the effect and mechanism of organic matter content and the type of solidification materials on the performance of solidified sludge backfill materials were investigated.The results show that organic matter has a significant inhibitory effect on the solidification effects of cement and sludge solidifier.The unconfined compressive strength of sludge solidifier solidified sludge at 7 days and 28 days are 3.0-4.2 times and 3.1-4.5 times that of cement solidified sludge.Compared with the cement solidified sludge,the sludge solidifier solidified sludge generates more ettringite crystals,which compactly fill the gaps between sludge particles.Combined with the cementing effect of calcium silicate hydrate gel on sludge particles,the compactness of the solidified sludge is significantly improved,and a better stabilization effect on the heavy metals in sludge is demonstrated.The strength of the solidified sludge as a subgrade backfill material meets the requirements of the specification,and the pollution risk is low.

Abstract:The deterioration mechanisms of modified rubber-toughened recycled aggregate concrete(MRRAC)subjected to elevated temperatures ranging from 25℃to 600℃were investigated,with particular focus on mass loss,compressive strength degradation,and toughness evolution.The thermal damage mechanisms at the microscale were comprehensively characterized through scanning electron microscopy(SEM)analysis.The results demonstrates that pretreatment of rubber particles with 10%sodium hydroxide solution significantly enhances the high temperature compressive strenghth and toughness of recycled aggregate concrete after heated at 450℃,with a 58%improvement in compressive strength compared to untreated specimens.A predictive model for the residual compressive strength ratio of MRRAC is developed by incorporating key parameters including the replacement rate of recycled aggregates and rubber content.The fundamental mechanism underlying the improved high temperature resistance is revealed.The softening and decomposition of rubber particles create pore structures within the concrete matrix,which effectively expandes the release channels for internal free water and bound water,thereby reducing the internal-external pressure gradient and mitigating thermal damage.