Abstract:The dynamic mechanical properties of steel fiber reinforced sulfoaluminate cement(SAC)mortars under different strain rates(80 s-1,135 s-1 and 180 s-1)were investigated by using ϕ120 separated Hopkinson pressure bar.Three-dimensional reconstruction and quantitative analysis of the microstructure of the material before and after deterioration were carried out by X-ray computed tomography(X-CT)technique.The results show that all the mortar samples show obvious strain rate effect,the addition of steel fiber significantly increases the peak stress of mortar specimen,and the optimal content is 0.3%-0.6%.With the increase of strain rate of SAC mortars,the peak stress,peak strain,elastic modulus and the area under stress-strain curve all increase.At high strain rate,the failure of mortar is mainly caused by sliding or pulling out of steel fiber.Although the steel fiber increases the porosity of SAC mortars,it formes a three-dimensional network structure,which effectively inhibites the propagation of main cracks,and the higher the steel fiber content is,the lower the proportion of micro-cracks is.

Abstract:To address the detachment of mural plaster layers induced by temperature gradients and the limitations of conventional grout in temperature control,a microencapsulated phase change material(MPCM)-modified grout was developed.Its temperature control performance and crack inhibition mechanism were systematically analyzed through experiments and numerical simulations.The results show that MPCM exhibits good thermal stability,with a mass loss rate of only 0.65%after 200 phase change cycles.When the MPCM content is 15%,the compressive strength of the MPCM-modified grout specimen reaches 1.34 MPa,demonstrating good compatibility with the strength of the mural plaster layer.MPCM improves the temperature response behavior of the grout.Compared to the unmodified specimen,the grout with 15%MPCM shows a reduction in peak temperature by 4.9℃and a decrease in the heating rate by 5.2℃/h,effectively alleviating internal gradient stresses caused by rapid temperature changes.The incorporation of 15%MPCM reduces the crack tip stress in the grout by 9.3%to 12.1%,significantly inhibiting crack extension.The research findings provide a new approach for the study of detachment grout in murals and heritage site plasters.

Abstract:To investigate the influence of recycled concrete powder(RCP)replacing fly ash on the properties of alkali-activated binder(AAB),three replacement rates of RCP,namely 10%,20%,and 30%were set up.A systematic analysis was conducted on the changing patterns of the setting time,fluidity,compressive strength,and chemical shrinkage of AAB.Moreover,microscopic testing techniques such as scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS),X-ray diffraction(XRD),and mercury intrusion porosimetry(MIP)were employed to characterize the composition of hydration products,microscopic morphology,and the evolution characteristics of pore structure.The results show that when the replacement rate of RCP is 30%,the setting time and fluidity of AAB decrease by 38.6%and 17.1%,respectively,compared with those without RCP,while the 7 d compressive strength and 3 d chemical shrinkage increase by 16.7%and 326%respectively.Microscopic analysis reveals that RCP can significantly increase the calcium-silicon ratio of AAB,promote the generation of hydrated calcium silicoaluminate(C-A-S-H)gel,and optimize the pore structure through secondary hydration reactions and physical filling effects,thereby significantly enhancing the compactness of AAB.

Abstract:The influence and mechanisms of ordinary Portland cement(OPC)dosage on the performance of full negative temperature(mold and cure at-10℃)alkali-activated slag mortar(AASM)were systematically investigated.The results demonstrate that the incorporation of OPC can enhance the full-age compressive strength of AASM cured at full negative temperature,and the optimal OPC dosage is 3%of the total binder mass.Under this dosage,the 1,7 and 28 d compressive strength of AASM are 5.0%,23.5%and 17.8%higher than that without OPC,respectively.OPC promotes the hydration degree of slag at negative temperature,leading to an increase in the hydration product amount and densification of the microstructure,thereby improving the compressive strength of AASM cured entirely at negative temperature.

Abstract:Based on the principle of synergistic utilization of industrial solid waste,an early-strength solid waste based cementitious material(SSC)was prepared using soda residue,slag,steel slag and desulfurization gypsum.The effects of soda residue on the mechanical properties,microstructure,hydrated products,pore structure,hydration kinetics and chloride ion adsorption capabilities of the SSC were investigated.The results indicate that soda residue significantly accelerates the early hydration of the SSC and enhances its early-age strength.Specifically,at an optimal mass ratio of soda residue to slag to steel slag to gypsum of 10.0∶49.5∶27.0∶13.5,the compressive strengths of the mortar specimens at 1 d and 28 d are 12.9 MPa and 44.5 MPa,respectively,with a chemical binding ratio of chlorine ion at 93%.Furthermore,the hydrated products within the hardened paste of the SSC exhibit a dense,interlocking and filling structure,with the primary hydrated products at 28 d being calcium silicate(aluminate)hydrate gel,ettringite and Friedel's salt,which form the foundational strength of the solid waste based cementitious material.

Abstract:Through experiments such as fluidity tests,unconfined compressive strength tests,and microscopic analysis,the effects of soil sample characteristics,types of solidifying materials(SM),SM-to-soil ratio,water-to-solid ratio,and temperature on the fluidity and strength of flowable solidified soil were investigated,and its solidification mechanism was analyzed.The results show that the fluidity of flowable solidified soil(FSS)increases with a higher water-to-solid ratio,slightly decreases with a higher SM-to-soil ratio,and significantly decreases with smaller soil particle sizes.The strength of FSS increases with a higher SM-to-soil ratio.When using a solidifying agent,higher strength can be rapidly achieved under conditions of a high water-to-solid ratio,low SM-to-soil ratio,and low curing temperature compared to using cement.The solidification mechanism lies in the fact that the solidifying agent generates more ettringite(AFt)than cement.During its formation,AFt consumes a large amount of free water and effectively fills the gaps between soil particles.Together with calcium silicate hydrate gel,AFt cements the soil particles,enhancing the material's microscopic compactness and thereby improving the macroscopic strength of the FSS.

Abstract:To realize the efficient resource utilization of iron tailings,autoclaved materials were prepared by completely replacing quartz sand with iron tailings.The effects of autoclaving temperature and constant temperature duration on the mechanical properties of the materials were systematically investigated,and the phase composition and micromorphology of hydration products were analyzed by means of X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The results show that the optimal autoclaving process parameters of the material are 180℃for 5 h under constant temperature.Under these conditions,the main products are calcium silicate hydrate(C-S-H(Ⅰ)),(C-S-H(Ⅱ))and tobermorite.The phase evolution and strength development of the autoclaved material can be divided into four stages,and the content change of tobermorite is highly positively correlated with the compressive strength of the material,confirming that it is the key phase for the formation of material strength.

Abstract:An in-depth study was conducted on the compressive performance of 3D printed topology optimized concrete foundations by combining experiments and finite element analysis(FEA).The variable density method was adopted for the topology optimization design of rectangular isolated concrete foundations,foundation specimens were fabricated via 3D printing technology,and axial compression tests,eccentric compression tests,and FEA were carried out.The results show that significant differences exist in the failure crack patterns between 3D printed topology optimized concrete foundation specimens and cast-in-place foundation specimens:under axial compression,bending cracks,punching inclined cracks,and polygonal line cracks appear;under eccentric compression,only bending cracks and punching inclined cracks occur.This type of foundation exhibits excellent bearing performance:when its volume is 30%of that of the cast-in-place foundation specimen,the ultimate bearing capacity decreases by only about 25.0%;when the eccentricity increases from 1/30 to 1/5 of the foundation width,the ultimate bearing capacity decreases by approximately 31.9%.

Abstract:Complex service environments impose stringent demands on the long-term performance of concrete structures.Surface coating technology serves as a critical approach for enhancing the durability of concrete.This paper systematically summarized the technical principles and fabrication methodologies of concrete surface coatings from the perspectives of two protective mechanisms:film-forming sealing coating and penetration-enhanced coating.Subsequently,it elucidated the primary types and application performances of concrete surface coatings under three challenging service environments(severe cold,marine,and plateau).Furthermore,it discussed existing technical limitations and future development trends,aiming to furnish theoretical foundations and practical references for improving the service performance of concrete structures under complex environmental conditions.

Abstract:This study investigated the effect of CO2 curing on the carbonation performance of concrete by comparing the changes in compressive strength,carbonation rate,product composition,and micromorphology between CO2-cured and conventionally cured concrete at different carbonation ages.The results indicate that CO2 curing significantly influences the microstructural evolution of concrete.Compared with the traditional carbonation model(carbonation index λ=0.50),the relationship between carbonation depth and carbonation age for CO2-cured concrete is better described by a power function model with λ=0.21.In the early carbonation stage(<150 d),CO2-cured concrete exhibits a high carbonation rate and a fast increase in compressive strength.The high carbonation rate is mainly attributed to the partial consumption of clinker minerals during CO2 curing,which to some extent inhibits subsequent hydration and reduces the number of carbonatable substances.In the later carbonation stage(>150 d),carbonation products fill the pores,thereby reducing porosity and hindering CO2 diffusion into the matrix.At the same time,the continued hydration in the uncarbonated regions generates a large amount of hydration products,which effectively slows down the carbonation process,leading to a significant decrease in the carbonation rate.

Abstract:Based on a multi-scale framework encompassing the nanoscale-microscale-macroscale,the asphalt-tuff aggregate interface was investigated by molecular dynamics simulations.Six types of interface models were constructed while tensile simulations were conducted.The effects and mechanisms of anti-stripping agents and aggregate modifiers on interface adhesion property were explored.The results indicate that the distribution of asphalt components is regulated by anti-stripping agents through polar groups.The enrichment of asphaltenes at the interface is driven by the depolymerization of the polyoxyethylene ether chains in Xintuo anti-stripping agent(XT).Interfacial adhesion is synergistically enhanced by silane coupling agents(Si)together with Luyou anti-stripping agent(LY).The phenol hydroxyl-amino hydrogen bonds and aromatic ring-alkyl chain π-interlocking interactions improve the interfacial adhesion property by 87.36%.Performance trade-offs can be balanced by the proposed combined treatment strategy.For the model LY-Si,not only is interface adhesion property improved,but also a 300%increase in the diffusion coefficient is realized,and a simultaneous enhancement in interfacial toughness and relaxation capability is accomplished.The adhesion behavior of materials can be effectively predicted by the nanoscale model.

Abstract:To explore the relationship between the internal pore structure and shear strength of cemented sand and gravel(CSG)under different surface treatment methods.Python was used to preprocess and perform 3D reconstruction of X-ray computer tomography images of CSG under three different surface treatment methods,achieving 3D visualization and quantitative characterization of the internal pore structure.Combined with indoor direct shear test,the XGBoost algorithm was used to establish the relationship between 3D pore structure parameters and macroscopic mechanical properties.The results indicate that the surface treatment method significantly affects the 3D pore structure and mechanical properties of CSG.Untreated surfaces have irregular pore distributions,which can lead to stress concentration.In contrast,applying mortar or grout on the surface can effectively improve the pore structure,with grout being the most effective,significantly enhancing the uniformity and complexity of the pores in CSG.The relationship between pore sphericity and pore size distribution follows a double exponential decay,and more spherical pores help to improve friction performance.The research results can provide valuable insights for optimizing the construction process of cemented sand and gravel layers and improving their mechanical properties.

Abstract:To investigate the fire resistance performance of inorganic-banded bamboo composite(InorgBam)beams,standard fire tests were conducted on two full-scale InorgBam beams.The results show that the high-temperature resistance characteristics of the inorganic adhesive effectively delay the inward development of surface charring in the InorgBam beams.Under standard fire exposure,the surface charring of the InorgBam beams is uniform.At load ratios of 0.3 and 0.4,the average charring rates of the InorgBam beams are approximately 0.35 and 0.38 mm/min,respectively,with fire resistance limits exceeding 2.0 hours in both cases.The established thermo-mechanical coupled finite element model effectively simulates the fire resistance performance of the InorgBam beams.The fire resistance limit of the InorgBam beams exhibits a negative power-exponential relationship with the load ratio,a linear negative correlation with the span-to-depth ratio,and a linear positive correlation with the section height.

Abstract:To further clarify the influence of anti-corrosion coating thickness on the protective effect of cement-based materials,the variation regularity of flexural strength of cement mortars with different thicknesses under sulfate attack was investigated.The attack state of the cement mortars was analyzed by nuclear magnetic resonance,scanning electron microscopy,and X-Ray diffraction.Combined with impermeability and bond strength of the coatings,the influence mechanism of coating thickness on the sulfate attack resistance of cement mortars was elucidated.The results reveal that the sulfate attack resistance of coated cement mortars first increases and then decreases as the coating thickness increases.Under the experimental conditions of this study,the lowest flexural strength loss rate,surface damage grade,and pore deterioration degree are exhibited by the cement mortar with a coating thickness of 90 μm.The optimal protective effect is achieved by the anti-corrosion coating with a thickness of 90 μm.

Abstract:A chemical thermodynamic model to predict the mineral composition of stabilized soil under varying water contents,stabilizer dosages,and incorporation methods(internal and external mixing)was established.Based on the simulation results,key mix proportion parameters were identified and used to prepare representative samples.The macroscopic compressive strength,XRD patterns,and 29Si NMR spectra were analyzed to investigate the response mechanisms of the mix proportion parameters.The results demonstrate that the thermodynamic model reliably predicts the evolution of mineral phases in stabilized soil.The stabilizer dosage significantly influences the formation of reaction products,while water content has a relatively minor effect.The strength development is primarily governed by the total amount of reaction products,the n(Al)/n(Si)ratio,the proportion of hydrated aluminosilicate gel in the cementitious system,and the mean chain length of all gel phases.These factors should be incorporated into thermodynamic simulations to improve the accuracy of mix proportion design.

Abstract:The effects of the content of square and flat rubber particles on the shear characteristics of rubber-sand mixtures were investigated through indoor direct shear tests.A discrete element method(DEM)model was established to reveal the macro-meso mechanical responses of rubber-sand mixtures,in which real river sand scanning data files and a particle clustering method were used to simulate sand particles and rubber particles,respectively.The results indicate that the internal friction angles of both types of rubber-sand mixtures decrease with the increase of rubber particle content,reaching a maximum value when the rubber particle content is 5%.Under the same rubber particle content,square rubber-sand mixture has higher shear strength,while flat rubber-sand mixture has a more significant dilatancy inhibition effect.The force chain network of rubber-sand mixture is dominated by"sand-sand"contacts,which bear the main stress.Compared to flat rubber-sand mixture,the square rubber-sand mixture has a higher proportion of"sand-sand"contacts,which is macroscopically manifested as higher shear strength.

Abstract:Macroscopic and microscopic creep tests were conducted,combined with low-field nuclear magnetic resonance 1H-NMR and nitrogen adsorption tests,to systematically investigate the creep characteristics and humidity response mechanisms of hardened cement paste under different internal relative humidity conditions(10%-98%).The results indicate that as the internal relative humidity decreases,the creep deformation of hardened cement paste gradually decreases,the creep modulus significantly increases,and the characteristic time shortens accordingly.Within the relative humidity range of 10%-98%,the relationship between creep modulus and relative humidity conforms to a parabolic function.Based on this,a creep modulus-relative humidity dependency model was established,demonstrating good predictive capability.With decreasing internal relative humidity,both the pore volume and water saturation of gel pores and transition pores show a declining trend.The creep modulus exhibits a strong negative linear correlation with the water saturation of gel pores,while its relationship with the water saturation of transition pores follows a parabolic pattern.

Abstract:Coated treatment was conducted on sludge gasification slag using a blended mixture of cement and fly ash,and the treated slag was utilized as coarse aggregate for lightweight aggregate concrete.The influences of coarse aggregate type and volume fraction on the performance of concrete were systematically investigated.A two-dimensional finite element model of concrete was established to simulate the damage distribution and stress-strain curve during concrete failure under uniaxial compressive conditions.The results show that the sludge gasification slag retains its lightweight characteristics after being coated with the cement and fly ash,while its cylinder compressive strength significantly increases from 2.5 MPa to 6.1 MPa.When the volume fraction of coarse aggregate is 40%,the concrete with coated sludge gasification slag aggregate exhibits the smallest damage area and the optimal compressive performance.

Abstract:The effects of thermal cycling on the compressive strength,splitting tensile strength,water absorption and pore structure of C45,C60 and C90 concrete under 40-90℃and 40-200℃were investigated.The mechanisms by which thermal cycling affects the mechanical properties and microstructure of concrete were elucidated.The results demonstrate that under 40-90℃thermal cycling,the hydration process of concrete is accelerated,leading to a significant enhancement in mechanical properties.After 90 cycles,the compressive strength of C45 concrete increases by up to 41.5%.Under 40-200℃thermal cycling,the quantity of certain hydration products decreases,and the strength initially improves but then declines with increasing cycles.Due to lower hydration degrees and a more porous internal structure,the mechanical property of low-strength-grade concrete is more significantly affected by thermal cycling.As the number of thermal cycles increases,the concrete structure becomes looser,the number of internal pores rises,and the proportion of harmful and multi-harmful pores within the pore structure increases.

Abstract:Based on 687 sets of concrete compressive strength data,the standard uncertainty and expanded uncertainty were evaluated using the measurement uncertainty assessment method.By integrating the conversion results of the expanded uncertainty interval,the characteristics of strength distribution,the determination of single value eligibility,and the comprehensive assessment method were systematically analyzed.The results indicate that the compressive strength interval can effectively quantify the impact of uncertain factors,and there is a significant correlation between the average strength interval and the probability interval of the normal distribution.The method for determining single value eligibility can provide a quantitative basis for the uncertainty in critical value determination.The comprehensive assessment method can account for the differences between the specimens submitted for inspection and the actual testing conditions,providing an important basis for enhancing the rigor and applicability of engineering quality assessment.