Abstract:The strength evolution and hydration mechanism of composite paste were explored when municipal sludge biochar(SBC)and incinerated sewage sludge ash(ISSA)were synergistically used to replace ordinary Portland cement.The results show that the synergistic replacement of 2%SBC and 10%ISSA increases the 28 d compressive strength of the composite paste by 17.5%.In terms of fresh paste hydration,SBC enhances the early hydration of ISSA at high replacement levels,while ISSA significantly improves the system's strength in the middle and late stages through pozzolanic reactions.Regarding hydration products,SBC and ISSA promotes the formation of carboaluminate phases and highly polymerizes hydrated calcium silicate(aluminate)gels in the composite paste,which effectively filles the nanopores within the matrix.

Abstract:A high early strength alkali-free and fluorine-free liquid accelerator(HEFLA)was prepared by incorporating reinforcing and stabilizing components,using polyaluminium sulfate,diethanolamine,and ethylene glycol as the main raw materials.The effects of the HEFLA on the cement hydration process and hydration products were analyzed through the tests of hydration heat,thermogravimetric analysis and X-ray diffractometer.The results show that when the dosage of the accelerator is 7%(by mass)of the cement,the initial and final setting time of the cement paste are 2.50 minutes and 7.42 minutes respectively.The compressive strength of the cement mortar at 6 hours and 1 day are 1.5 MPa and 12.4 MPa respectively.The addition of HEFLA promotes the rapid hydration of the cement to generate ettringite(AFt),increases the hydration heat release rate and the total hydration heat release,eliminates the hydration induction period,and advances the hydration acceleration period.In the formed hydration products,more AFt is contained,less monosulfate hydrate calcium sulfoaluminate(AFm)is presented,and the formation of AFm is delayed.

Abstract:In order to improve the tensile strength and anti-cracking performance of textile reinforced concrete(TRC)under the coupling effect of chloride salt corrosion and impressed current,firstly,the mechanical properties of TRC matrix fine-grained concrete mixed with carbon fiber and graphite were studied by compressive and flexural strength tests.Then,the influence of the number of textile layers and specimen thickness on the tensile and crack limiting performance of TRC was studied through uniaxial tensile testing.Finally,conduct a microscopic analysis of carbon fiber.The results indicate that the addition of carbon fiber and graphite can effectively improve the tensile strength of fine-grained concrete.Increasing the number of textile layers can significantly enhance the tensile strength of TRC and improve crack development,while increasing the specimen thickness has little effect on its tensile properties and crack morphology.The surface of the carbon fiber monofilament without direct impressed current remains smooth and intact,while the carbon fiber monofilament with direct impressed current breaks.

Abstract:To solve the problem of the poor performance and high discreteness of recycled coarse aggregate concrete(RAC),a composite modification method combining cement paste pretreatment with methyl methacrylate monomer(MMA)impregnation-polymerization was investigated.The effects of the water-cement ratio,along with the polymerization temperature,time,and environment of MMA,on the performance of MMA composite-modified recycled coarse aggregate(RCA)were investigated.The results demonstrate that optimal modification is achieved with a 0.5 water-cement ratio,24 h MMA impregnation and 24 h polymerization at 70℃in a sealed environment.After MMA composite modification,there are 70.3%reduction in water absorption,41.9%decrease in crushing index,and 83.1%reduction in porosity of the RCA.The most probable pore diameter decreases from 62.50 nm to 5.93 nm,with total harmful and multi-harmful pore content reduces by 74.9%.Compared with conventional RAC,the 28 d cube compressive strength of modified recycled coarse aggregate concrete increases by 5.9%,9.5%,and 12.7%respectively,while the axial compressive strength improves by 4.1%,9.1%,and 14.1%respectively.The mechanical properties of RAC are significantly enhanced following MMA composite modification RCA.

Abstract:When steel slag was dissolved in dilute nitric acid to quantify the Fe3O4 content,it was difficult to physically separate the amorphous phases and foreign refractory(FR)from the undissolved residue.Therefore,a new solution was proposed:completely dissolving the amorphous phase in NaOH solution at 90℃for 1 h to obtain the secondary residue S12 without the amorphous phase.There were two methods for processing S12:separating and quantifying Fe3O4 and FR by dissolution method;calculating the Fe3O4 content by measuring the Fe content.When the method of disodium ethylenediaminetetraacetate(EDTA)-triethanolamine(TEA)-diethylamine(DEA)was used to test the inert mineral content in steel slag,the residual rate of C2F in the residue was relatively high and the separation of FR was difficult.By employing the EDTA-TEA complexation method at pH value of 12.9,the residue existed no C2F retention,and the inert mineral content was quantified by subtracting the known FR content.

Abstract:The interfacial bonding properties of coating/steel substrate system with different graphene oxide(GO)content in marine environment were studied by experimental and finite element simulation methods.The fracture strength,fracture toughness and interfacial shear strength of the graphene oxide coating were calculated through the tensile test combined with the results obtained from digital image correlation method(DIC).The finite element method was used to simulate the surface and interface cracking processes of the coating/steel substrate system.The results show that the enhancement effect of GO on the interfacial bonding properties of coating/steel substrate system increases first and subsequently decreases with the increased addition amount of GO.Coating with 0.3%GO has the best interfacial bonding property after corrosion,and the addition of GO has the most significant improvement on the fracture toughness of the coating.

Abstract:In order to improve the low-temperature performance and self-healing performance of pyrolytic carbon black(PCB)and C9 petroleum resin(C9PR)modified asphalt,a composite modified asphalt with PCB from waste tire and C9PR was prepared.Complex modulus,phase angle,rutting factor,and fatigue factor were used to analyse the high and low temperature rheological properties of the modified asphalt samples.Response surface method was used to optimize the parameters of self-healing factors affecting the modified asphalt.The results show that the addition of PCB and C9PR enhances the high-temperature performance of asphalt.And the rheological properties at high temperatures increases gradually with the increase of C9PR dosage.The low-temperature rheological properties of PCB/C9PR-modified asphalt show a trend of increasing and then decreasing with the increase of C9PR dosage.And the best low-temperature rheological performance is achieved with the addition of 2%of C9PR.The optimum self-healing parameters are 65.49%of the damage degree,47.64℃of the healing temperature and 44.6 min of the healing time.

Abstract:The effects of the maximum particle size of coral sand,water-to-binder ratio,and microbead content on the performance of high strength coral sand cementitious grout(HSCSCG)were investigated.Additionally,the influence of early strength agent,and plastic expansion agent on the complete vertical expansion rate curve of HSCSCG within 48 hours was explored.The results show that the strength of HSCSCG first increases and then decreases as the maximum particle size of coral sand decreases,with a noticeable ultra-early retardation phenomenon.The combination of early strength agent and plastic expansion agent enables controllable development of ultra-early vertical expansion.Within the scope of this study,HSCSCG exhibites relatively optimal performance when the maximum coral sand particle size is 1.25 mm,the water-to-binder ratio is 0.24,the microbead content is 30.00%,and the dosages of early strength agent and plastic expansion agent are 1.00%,0.06%,and 4.00%,respectively.

Abstract:Through a synchronized printing method,3D printing mortar(3DPM)specimens with interlayer reinforcement were prepared.X-ray computed tomography(X-CT)technology was used to analyze the impact of reinforcement materials,interface types(ordinary interface,reinforced interface,serrated interface,and reinforced-serrated interface),and printing time intervals on interlayer structure and pore distribution.The results demonstrate that the composite reinforcement effect of introducing self-compacting grouting material and increasing serrated interfaces is the most significant,which can effectively reduce interlayer porosity and printing cold joints of 3DPM,enhancing the uniformity of 3DPM.

Abstract:The effects of acrylate monomer ratios and functional groups on the performance of acrylic coatings and their protective effectiveness on cement-based materials were investigated using an orthogonal experiment.Characterization techniques such as Fourier-transform infrared spectroscopy(FTIR)and Raman spectroscopy were employed,along with measurements of contact angle,adhesion strength,and chloride ion penetration resistance to evaluate the overall performance of different acrylic coating formulations.The results show that the introduction of urea groups enables the formation of hydrogen bonds between the acrylic coating and the mortar surface,thereby enhancing adhesion and imparting self-healing capability to the coating.After drying at 50℃for 20 min,scratches on the acrylic coating samples are completely healed,with the highest contact angle reaching 106.3° and a maximum adhesion strength of 4.4 MPa.The synergistic effect of 2-(2-oxo-1-imidazolidinyl)ethyl methacrylate and methyl methacrylate effectively reduce chloride ion penetration.

Abstract:Aiming at the corrosion problem of concrete in saline soil area of Qarhan Salt Lake in Qinghai,by measuring the dynamic elastic modulus and compressive strength of high performance concrete(HPC)exposed for 8 years,the relationship between relative dynamic elastic modulus,compressive corrosion coefficient and 28 d compressive strength was studied,and the binary correlation analysis of HPC's brine resistance was made by combining water-binder ratio and slag content.Finally,the correlation between carbonation depth and 28 d compressive strength was analyzed.The results show that the corrosion resistance of HPC decreases with the decrease of 28 d compressive strength in brine environments.The critical value of relative dynamic elastic modulus for HPC corrosion damage is 0.80,contrary to the traditional theoretical threshold of 0.60.When the water-binder ratio is lower than 0.33,the slag content is more than 26%,and the carbonation depth is controlled below 20 mm,HPC achieves high brine corrosion resistance.

Abstract:The simplex centroid mixture design method was employed to investigate the effects of CO2 mixing on the properties of steel slag(SS)-fly ash(FA)concrete.The results indicate that while CO2 mixing significantly reduces the slump of concrete,incorporating appropriate contents of SS and FA improved its flowability.During early hydration,CO2 mixing intensify the adverse effects of FA while mitigating the negative effect of SS.In later stages,increasing FA content leads to continuous strength reduction.Microstructural analysis reveals that systems with high SS content form high-density calcite,improving structural density,while systems with high FA content produce low-density aragonite.

Abstract:The static and dynamic mechanical properties of basalt fiber-reinforced concrete(BFRC)and polyethylene fiber-reinforced concrete(PEFRC)with different fiber volume fractions were investigated.The results indicate that the static mechanical properties of PEFRC are better than those of BFRC with in the test parameter.The static mechanical properties of the corresponding fiber-reinforced concrete(FRC)are significantly improved when the volume fractions of basalt fiber(BF)and polyethylene fiber(PEF)were 0.10%and 0.20%,respectively.The dynamic compressive strength of concrete is optimized at a BF and PEF volume fraction of 0.20%,while PEFRC exhibits the best dynamic compression toughness at a PEF volume fraction of 0.15%.The dynamic viscoelastic damage constitutive models for BFRC developed based on the ZWT(Zhu-Wang-Tang)constitutive model,can accurately predict the dynamic mechanical properties of FRC under impact load.

Abstract:The effects of two early-strength components,MgSO4 and triethanolamine(TEA),on the storage stability of Al2(SO4)3 solutions containing diethanolamine(DEA)were investigated,and the influences of DEA-Al2(SO4)3 solution(herein after referred to as Al2(SO4)3 solution)incorporating different early-strength components on the setting time of cement paste and the strength of cement mortar were also studied.A fluorine-free,chlorine-free,and alkali-free liquid accelerator(LA)was prepared by combining Al2(SO4)3 solution with MgSO4 and TEA,and its comprehensive performance was tested.Hydration heat analysis,hydrogen proton low-field nuclear magnetic resonance analysis,X-ray diffraction,thermogravimetric analysis,and scanning electron microscopy were employed to elucidate the mechanism of LA.The results show that at low LA content,both MgSO4 and TEA can enhance the early-strength effect of Al2(SO4)3 solution.The incorporation of LA significantly shortens the setting time of cement paste and improves the early compressive strength of cement mortar.LA promotes the formation of early ettringite crystals in hardened paste,accelerates the development of a skeletal framework in the liquid phase,and thereby achieves rapid setting,hardening,and early strength development of the cementitious system.

Abstract:A synchronized printing process for interlayer reinforcement of 3D printing mortar has been proposed.As the printing mortar was extruded,the reinforcement material could automatically flow and level along the zigzag grooves formed on the surface of the previous layer of filaments,wetting the interface and filling the pore defects.The effects of reinforcement material,interface types(ordinary interface,reinforced interface,zigzag interface,and reinforced-zigzag interface),and time intervals on interlayer bonding performance and porosity were compared.The results indicate that the composite reinforcement is the most significant,with a 72%increase in 3D interlayer bonding strength relative to the baseline sample and an 61%reduction in average porosity,while still demonstrating excellent bonding strength after long time intervals.

Abstract:A method for accurately measuring concrete shrinkage and crack development is proposed based on optical frequency domain reflectometry(OFDR)technology using a distributed optical fiber strain analyzer.Laboratory experiments were conducted to investigate the effects of single and hybrid additions of 0.2%polypropylene fiber(PPF)or 1%steel fiber(SF)by volume on shrinkage behavior and crack morphology of self-compacting concrete(SCC),with 30%cement replaced by fly ash(FA).The results show that this method effectively identifies,locates,tracks,and quantifies crack evolution by analyzing strain fields induced by shrinkage and crack formation/propagation.Compared to the control mix with 30%FA,the addition of 1%SF alone reduces the drying shrinkage strain of SCC from 725 μm/m to 314 μm/m,while the hybrid addition of 1%SF and 0.2%PPF decreases the crack width from 2.10 mm to 0.07 mm.

Abstract:Nuclear magnetic resonance(NMR)technology was used to study the early deterioration behavior of tuff manufactured aggregate concrete under sulfate environment,with the influences of water-binder ratio and sulfate environment being systematically investigated.The results demonstrate that sulfate chemical corrosion and dissolution of hydration products are identified as the primary causes of early performance degradation in tuff manufactured aggregate concrete,with ettringite and gypsum being predominantly formed as corrosion products during the initial stage.It is revealed that the reduction of initial porosity in tuff manufactured aggregate concrete can effectively inhibit the penetration and transportation of sulfate ions.After 270 days of corrosion,the volume proportions of multi-harmful pores and harmful pores in concrete exposed to sulfate solution environment are observed to increase by 2.42%and 5.17%respectively,compared with those in sulfate saline soil environment.

Abstract:Triethoxysilane and isocyanate were added to reduce the polarity of oxygen-containing functional groups in the aged asphalt,and bio-oil regenerator was added to replenish the light components lost in the aged process of asphalt,therefore,the performance of the aged asphalt was restored from the perspective of physical blending and hydrogenation reduction.Then,the improvement effect of its performance was evaluated systematically,and the improvement mechanism was analyzed.The results show that the appropriate amount of bio-oil has a significant physical blending effect on the aged asphalt,and can effectively reduce the dynamic viscosity of the aged asphalt,but has little effect on the fatigue resistance,aging resistance of the aged asphalt and the adhesion to the aggregate.While hydrogenation reduction can significantly improve the fatigue resistance,low temperature crack resistance and adhesion to aggregates of the aged asphalt by reducing the polarity of aged asphalt.The mechanism of physical blending and hydrogenation reduction is different,but their synergistic effect is better.

Abstract:A water-purifying pervious concrete was prepared using brick-concrete recycled powder and recycled brick aggregate to realize the resource utilization of brick-concrete construction waste.The effects of recycled powder and chitosan content on the mechanical and adsorption properties of paste were studied.The effect of volumetric structure parameters on the mechanical and water permeability properties of pervious concrete was studied,and the adsorption capacity of pervious concrete for Pb2+was discussed.The results show that the introduction of recycled powder or chitosan can improve the mechanical and adsorption properties of the paste,but the mechanical properties are weakened when the content is too high.As the ratio of paste to aggregate increases,the mechanical properties of the water-purifying pervious concrete improve,but water permeability decreases.Conversely,as the design porosity increases,its mechanical properties decline,but water permeability improves.The Pb2+removal rate of prepared concrete can increase 43.11%and the effect of brick recycled aggregate on improving water purification function is better than that of prepared paste.

Abstract:Nano-CaCO3 and nano-SiO2 were incorporated into recycled aggregate self-compacting concrete(RASCC)to investigate the multiple interfacial performance by nanoindentation technique and to explore the relationship between the microscopic properties and macroscopic mechanical properties of RASCC.The results show that the incorporation of nano-CaCO3 and nano-SiO2 can effectively improve the microstructure and interfacial modulus of the old aggregate-new mortar interfacial transition zone(ITZ2)and the old mortar-new mortar interfacial transition zone(ITZ3),and increase the compressive strength and modulus of elasticity of RASCC,with the modification effect of nano-SiO2 being more significant.The mechanical properties of RASCC are maximized at a doping level of 1.0%for nano-SiO2 or nano-CaCO3,and decrease due to the agglomeration of the particles when the doping level is further increased.After nano-SiO2 modification.The macroscopic mechanical properties show a significant correlation with ITZ3 interfacial modulus,and increase and then decrease with the increase of interfacial modulus RASCC.