Abstract:The time-varying properties and improvement mechanism of basalt-carbon hybrid fiber reinforced polymer(HFRP)bars in simulated seawater sea sand concrete environment are studied through tensile testing,water absorption testing and microscopic testing methods.The results demonstrate that hybrid carbon fibers significantly reduce moisture absorption in HFRP bars compared to basalt fiber reinforced polymer(BFRP)bars,attributable to the superior mechanical properties and chemical stability of carbon fiber(CF).Temperature exhibits a pronounced influence on the tensile properties of HFRP bars,and the increase in hybrid carbon fiber CF volume fraction(φ(CF))alleviates the degradation induced by high temperature and alkaline pore solution environment.When φ(CF)is 25%,the tensile strength retention exceeds 43%after 90 days of corrosion in a 55℃pore solution.The failure mode of HFRP bars is affected by φ(CF)value,and the hybrid interface of the two fibers interface is also a weak link in bars.

Abstract:The main progress including the preparation technology,hydration and hardening characteristics and mechanism,material properties of basic magnesium sulfate cement(BMSC)in the past ten years are summarized.The prospect of applying BMSC in structural reinforcement,protective coatings,military installation,waste solidification and other fields were also introduced.The discussion and outlook on the challenges faced by BMSC research and application were presented.It is believed that BMSC based materials can be used as functional materials in the engineering field,but many scientific problems still need to be solved,such as the mechanism of corrosion resistance and high durability measures of BMSC based materials.

Abstract:To achieve the efficient and resourceful utilization of sludge incineration ash(SIA),starting from the influence of SIA on the particle accumulation state,fluidity and mechanical properties of cement-based materials,the influence of SIA on the hydration process and microstructure was analyzed by hydration heat,phase composition and pore structure.The results show that the irregular morphology and high absorption characteristics of SIA reduce the fluidity of cement pastes,and the reduction increases with the increase of SIA dosage.The overall packing density of the cement-based materials can be improved by SIA for its board particle size distribution.An appropriate amount(5%mass fraction)of SIA can promote the generation of hydration products and the refinement of the pore structure through filling,nucleation,and pozzolanic reactions,thereby improving the mechanical properties of cement-based materials.A high dosage(30%mass fraction)of SIA leads to the decrease of hydration products,the increase of porosity,and the decrease of mechanical properties due to its porous characteristics and dilution effect.

Abstract:The skeleton-embedded lock continuous type dense gradation(CAC-20C)was designed,and the optimal water content and emulsified asphalt dosage of cold-mix and cold-laid asphalt mixture(CMLAM)were determined through mix proportion design.A double-layer and multi-step mixing equipment was used for production,and the plant mixing CMLAM with uniform coating was obtained.The results show that the optimal water content and emulsified asphalt dosage of CMLAM are 4.2%and 6.6%,respectively.The high-temperature performance and water stability of both the indoor mixing and plant mixing CMLAM meet the specification requirements.The compaction degree of the pavement tested on site reaches the requirements,and the void ratio is slightly higher than the design value.After curing,the dispersed structure inside CMLAM is connected into a dense whole by the asphalt membrane and cement hydration products,so that it has good mechanical strength and water stability.

Abstract:Through rapid freeze-thaw tests and tensile tests,the effects of four types freeze-thaw media(salt solutions)on the mechanical properties of basalt fiber(BF)unidirectional sheet under freeze-thaw conditions were investigated.A tensile strength degradation model for BF unidirectional sheet in salt-freezing environments was subsequently proposed.The results demonstrate that the sizing film is detached and basalt fibers are degraded by freeze-thaw cycles.The most severe erosion effect on basalt fiber filaments was observed when the specimens were exposed to the most unfavorable chloride-sulfate composite solution(SC,the mass fraction of NaCl and Na₂SO₄are 3.5%and 3.0%respectively).The tensile failure modes of specimens can be divided into four categories:middle centralized failure,middle decentralized failure,end centralized failure,and end decentralized failure.The highest reductions in tensile strength and ultimate elongation were found in specimens subjected to the SC freeze-thaw medium,whereas the elastic modulus is not significantly affected by freeze-thaw cycles.The proposed tensile strength damage model under salt-freezing environments shows good aggrement with the experimental results.

Abstract:To clarify how coal gangue(CG)content affects the properties of geopolymer grouting materials,geopolymer grouting material prepared from coal-based solid waste such as CG was selected as the research object.The influence of CG content on the rheological and mechanical properties of coal based solid waste geopolymer grouting materials(CGGM)was systematically studied,and the microstructure of stone body was analyzed by microscopic testing methods such as mercury intrusion porosimetry(MIP),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),and scanning electron microscopy(SEM).The results indicate that the stability of CGGM slurry is improved by CG,CGGM slurry is typical viscosity time-varying power-law type fluid,and the fluidity,setting time and compressive strength of CGGM decrease with the increase of coal gangue content.When coal gangue content is 50%(accounting for the precursor),compressive strengths of stone bodies at 3 days and 28 days reaches 2.97 MPa and 8.89 MPa,respectively.CG mainly plays the role of micro aggregate and provides nucleation sites for calcium silicate hydrate(C-S-H)gel in the early stage,and polymerization occurrs in the later stage.Strength is mainly attributed to crystals and gels such as ettringite(AFt),C-S-H,and calcium(sodium)aluminosilicate hydrate(C-(N)-A-S-H).

Abstract:Basing on the dual demands of enhancing the shear bearing capacity of carbonate saline soil and improving the sustainable utilization of recycled tire polymer fiber(RTPF),a method of improving the properties of cement stabilized carbonate saline soil with RTPF was proposed.Through triaxial shear tests and microscopic inspections,the influence and mechanism of RTPF on the shear strength of cement stabilized carbonate saline soil were investigated.The results indicate that the addition of RTPF first increases and then decreases the shear strength of cement stabilized carbonate saline soil.The optimal proportion is 1.0%-2.0%for fiber bundles and 0.1%-0.2%for fibrils.RTPF can improve the cohesion and internal friction angle of cement stabilized carbonate saline soil.The toughening effect of fiber bundle is higher than that of fibrils.The piecewise function can accurately describe the stress-strain relationship of RTPF reinforced cement stabilized carbonate saline soil.

Abstract:Since the invention of Portland cement in 1824,it has rapidly replaced lime as the primary binding material in construction due to its faster setting time,higher strength,and superior durability.However,it is associated with high CO2 emissions.In recent years,to reduce the CO2 emissions from the cement industry,non-Portland cementitious materials such as alkali-activated materials,geopolymers,supersulfated cement,and all-waste binders have become hot research topics.The development history,types,properties,and application potential in low-carbon buildings of these materials are summarized,aiming to provide theoretical foundations and technical pathways for carbon reduction in China's building materials industry.

Abstract:In order to explore the quantitative relationship between pore defects and mechanical characteristics of 3D printed recycled concrete,the 3D printed recycled concrete with different recycled sand replacement rates was taked as the research object to explore its performance parameters such as compressive strength,extrusion pore defect configuration and their internal correlation.A 3D printed recycled concrete extrusion pore-stratification model was proposed.The calculation formula between compressive strength and extrusion pore defects was established.The results show that configuration characteristics such as the size,shape and distribution of the pore defects of the printed concrete in different directions are the root cause of the anisotropic forces of the 3D printed recycled concrete,and the characteristics of recycled sand directly affect the formation and development of the pore defect configuration.

Abstract:To investigate the axial compression performance of ultrahigh strength spiral stirrup confined high strength concrete columns,32 cylinder specimens were designed and manufactured with the concrete strength grade,spiral stirrup ratio and spiral stirrup yield strength as the variation parameters.The results show that the ultrahigh strength spiral stirrup has a longer elastic stress stage,which can effectively overcome the high brittleness problem of high strength concrete,and can also ensure that the plastic deformation of high strength concrete under compression is greater than 3.00%.The peak stress,peak strain and axial compressive ductility coefficient of specimen with ultrahigh strength(1 774 MPa)spiral stirrup confined concrete are 1.4,4.4 and 1.6 times to those of specimen with ordinary strength(432 MPa)spiral stirrup confined concrete,respectively.

Abstract:The coral coarse aggregate(CCA)was strengthened by cement based materials(cement paste and cement dry-powder).The influences of strengthening methods and factors on the microstructure of strengthened CCA and the properties of SCAC were studied by means of macroscopic and microscopic mechanisms investigations.Based on the digital image correlation method,the deformation field distribution and damage process of SCAC were also systematically analyzed to obtain its mechanism.The results show that the microstructure of CCA is improved,the dense aggregates coating and the high-strength composite CCA are formed by strengthening cementitious materials.Compared with coral aggregates concrete(CAC),the prism compressive strength of SCAC is significantly enhanced and an average 18.54%increase is observed.The deformability and energy dissipation are also greatly improved(average growth 11.19%and 56.56%).Furthermore,the characteristics of the stress-strain curve of SCAC is changed.Finally,an analytical constitutive model of SCAC considering the effects of the strengthening variables is established.

Abstract:The biaxial tensile tests of nine types of domestic G-type membrane materials were carried out.The correlation among the biaxial tensile elastic modulus and the uniaxial ultimate tensile strength and various technical parameters was studied.The results show that the warp elastic modulus of all nine membranes is greater than the weft elastic modulus,and the Poisson's ratio exceeds 0.5.Tensile strength,weave count,fabric areal density,membrane areal density and thickness are positively correlates with the elastic modulus,and the fiber diameter is negatively correlated.The elastic modulus is not determined by a single factor but is the result of the interaction of multiple factors,providing a scientific basis for the multi-scale analysis and parametric design of the membranes.

Abstract:To investigate the diffusion behavior of ultraviolet-aged asphalt,component analysis,Fourier-transform infrared spectroscopy,atomic force microscopy and fluorescence microscopy were employed on 90#asphalt sliced at various depths,dark temperature,and dark time.The content of light and heavy components,the absorption peak intensity of carbonyl and sulfoxide groups,the surface microstructure and the fluorescence micrograph of asphalt were compared and analyzed.The results show that diffusion occurs between the surface and interior of ultraviolet-aged asphalt,with functional groups and components diffusing along concentration gradient.The content change rate of carbonyl and sulfoxide functional groups effectively reflects the diffusion extent of aged asphalt,which correlates positively with dark temperature and dark time,among which dark temperature has the greatest impact on diffusion behavior of aged asphalt.

Abstract:The effect of ultrafine phosphorus slag powder on the performance of concrete was discussed and its internal mechanism was analyzed from a microscopic point of view.The results show that ultrafine phosphorus slag has a significant retarding effect and lower early compressive strength,then the compressive strength and resistance to chloride penetration of the concrete are both enhanced at 28 d.This is because the ultrafine phosphorus slag,through grinding treatment,increases the pozzolanic activity and improves the physical filling effect,leading to a denser microstructure in the hardened paste.This phenomena indicates that ultrafine phosphorus slag is suitable for concrete projects that require special retarding or high resistance to chloride penetration,helping to reduce cement usage and decrease CO2 emissions,and shows promising application prospects.

Abstract:To quantitatively analyze the compressive strain characteristics of asphalt mixtures with different structures under viscoelastic state at normal temperature,the digital speckle correlation method was used to obtain the entire loading process images of asphalt mixtures under uniaxial compression mode.The strain field of asphalt mixtures under load was calculated and visualized,and indicators such as mean strain,probability of relative strain strength,and proportion of high strain were proposed.The relationship between the structural characteristics and the evolution of the strain distribution was established.The results indicate that under the viscoelastic state at normal temperature,the role of the skeleton is limited,and the failure mode of uniaxial compression is shear failure.The stress transmission capacity of asphalt mixtures can be characterized by the mean strain.Both the evolution amplitude and rate of the vertical strain are greater than those of the horizontal strain.The proportion of high strain can reflect the degree and extent of damage,and the structural design of the asphalt mixtures can be optimized by means of the strain characteristics.

Abstract:Based on backscattered electron(BSE)images,the performances of the frequency-grayscale histogram method,cumulative frequency-grayscale histogram method,and Gaussian mixture model(GMM)method in phase analysis of cement-based repair materials(CRM)were compared,and phase proportion in the repaired interfacial transition zones were studied based on the method with the optimal performance.The results indicate that the GMM method exhibits the best stability and consistency and is recommended for use in grayscale threshold segmentation for quantitative phase analysis.The pores and unreacted particles are densely distributed in repaired interfacial transition zones,with a higher content of unreacted particles in modified Portland cement-based repair materials and a greater proportion of pores in phosphate cement-based repair materials,so the appropriate treatment should be applied in repair work to enhance the effectiveness of the repair.

Abstract:To evaluate the durability of magnesium phosphate cement under dry-wet cycles and reveal its deterioration mechanism,20,40,and 60 dry-wet cycles were conducted on magnesium phosphate cement specimens.The degradation process of macroscopic strength and deformation parameters as well as the crack propagation law were analyzed through uniaxial compression tests and X-ray computed tomography(X-CT).The changes in phase composition,content and morphology of hydration products were characterized by X-ray diffraction(XRD),thermogravimetry(TG),and scanning electron microscopy(SEM).The results show that in the early stage of dry-wet cycles,the secondary hydration effect increases the compressive strength and elastic modulus of magnesium phosphate cement,but then gradually decreases with the increase of dry-wet cycles,and the failure mode changes from brittle to plastic.Due to the increase in crack and pore connectivity induced by dry-wet cycles,the fracture mode changes from tensile failure to tensile-shear failure.The deterioration mechanism of magnesium phosphate cement is mainly controlled by the dissolution of K-struvite,thermal expansion and dry-wet shrinkage caused by moisture.

Abstract:Porous aggregates were prepared by coal gangue and fly ash.The evolution of the phase composition,microscopic structure and pore structure of the aggregates during the sintering process were analyzed by X-ray diffraction,scanning electron microscope and mercury intrusion porosimeter.The results show that under the process conditions of preheating temperature of 500℃,preheating time of 20 min,sintering temperature of 1 000℃,and sintering time of 10 min,the coal gangue-fly ash porous aggregates prepared have a cylinder pressure strength of 2.50 MPa and a thermal conductivity of 0.141 6 W/(m·K).When the sintering temperature increases form 1 000℃to 1 200℃,mullite accumulates to form pores with a pore diameter d<1 000 nm,and the medium pores and large pores are covered by a liquid phase with an average thickness of approximately 0.466 µm.The volume fraction of large pores decreases by 34.49%,and the cylinder pressure strength increases.The high thermal conductivity of mullite and the decrease in the average pore diameter lead to an increase in the thermal conductivity of the porous aggregates.The carbon total emission of the porous aggregates in 1 m3 concrete is 140.200 kg CO₂ eq.,which is 56.2%and 56.3%lower than that of Stalite aggregates and fly ash lightweight aggregates respectively,indicating that it has greater green potential.

Abstract:By changing the bubble structure parameters of 3D printing cement mortar(3DPCM)through air entraining agent,the evolution law of bubble structure in 3DPCM was studied,and the influence of bubble structure on the microstructure and macroscopic properties of 3DPCM was revealed.The results show that due to the high viscosity of the slurry and the influence of the vibration-free process in 3DPCM,bubbles can stably exist in the high viscosity slurry and are difficult to discharge.The strength of 3DPCM is generally lower than that of the cast mortars.As the amount of the air entraining agent increases,the strength anisotropy becomes more significant,and the coefficient of variation of strength also increases accordingly.Meanwhile,the porosity of 3DPCM is higher than that of cast mortars.Affected by lateral traction and vertical compression,the bubbles mostly take on irregular elongated shapes and tend to accumulate at the printing interface,leading to slippage at the interface and accelerate the failure of the specimens.

Abstract:Five machine learning algorithms were employed to predict the workability and mechanical properties of manufactured sand concrete and a strategy for mix design was proposed using gradient boosting decision tree(GBDT)and XGBoost.Under specific performance requirements,iterative optimization through error analysis yields recommended mix for manufactured sand concrete.The results show that the for manufactured sand concrete produced using the machine-learning-recommended mix has an error of within 10%of the target values,confirming the feasibility of mix design for manufactured sand concrete under specific performance requirements.