Abstract:The drying shrinkage of glazed hollow beads thermal insulation mortar after two years was measured by vertical length comparator, and influences of air entraining agents of different contents (0%, 006%, 012%, 018%, 024%, by mass) on the long term drying shrinkage were investigated, water loss was measured by weighting method and pore structure was characterized by nitrogen adsorption/desorption method, the correlation among them was researched. The results show that drying shrinkage process includes three steps according to curing time extension: the acceleration period (before 7d), the deceleration period (7365d) and the metastable period (after 365d). There is no change in the development trend of drying shrinkage of mortar with addition of air entraining agents. In three steps in the curing time, the drying shrinkage at the last two stage is greatly restrained. The drying shrinkage of mortar in the first stage increases quickly owing to the fast dehydration, but its development in the last two stages is due to pore volume of mortar with radius less than 500nm, especially the increase of pore volume fraction of the pore radius within the size range of 73nm to 123nm. Effect of air entraining agents is proportional to its use level, there is no more effect with too large content of air entraining agents on drying shrinkage owing to lack of air entraining effect.

Abstract:In order to improve the bond quality of new to old concrete, a new construction process of scattering dry gravels onto the surface of self compacting concrete was put forward to replace the process of roughening the surface of old concrete. The dry gravels were considered as reinforcing particle, and rock failure process analysis (RFPA) code was used to study the failure process of slant shear specimens with different adhesion strength and reinforcing particles under static loading. The results of slant shear test of scattering dry gravels onto the surface were compared with that of the numerical simulation. The numerical simulation analyzed the failure characteristics of the specimens with different bond strength. When the adhesion strength of bonding surface is less than 30MPa, the strength of slant shear specimens of concrete with different strength grades is close, and is depended on the adhesion strength. Otherwise the strength of slant shear specimens increases with the concrete strength grades, and keeps stable around the overall axial compressive strength of the same concrete specimen at last. The size of single reinforcing particle almost has no influence on the elastic modulus and strength of slant shear specimens. The larger size of multiple reinforcing particles is better to improve the strength of slant shear specimens. The bonding surface is no longer the weakest position, and compares well with the actual experimental results. Compared with the process of roughening the surface of old concrete, the process of scattering gravels with the diameters of 520mm onto old concrete surface can improve the slant shear strength by 107%.

Abstract:Fracture properties of reactive powder concrete (RPC) which was reinforced in steel fibers，steel macro polyolefin hybrid fibers and steel polyvinyl alcohol hybrid fibers were studied by three point bending fracture test to investigate the effect of hybrid fibers on the toughness of RPC. It is found that compared to RPC specimens reinforced only by steel fibers, the crack tip of RPC specimens reinforced by hybrid fibers shows some micro cracks, their load deflection curves and load CMOD curves show an obvious secondary hardening phenomenon; compared to RPC specimens reinforced only by steel fibers, the peak load of steel macro polyolefin hybrid fibers RPC specimens and steel polyvinyl alcohol hybrid fibers RPC specimens increa ses by 544% and 854%, and fracture energy increases by 1384% and 885%, and fracture toughness improves by 1119% and 508% respectively, when steel fibers volume fraction is 15% and content of macro polyolefin fiber or polyvinyl alcohol fibers is 9kg/m3; specimens reinforced by three kinds of fibers show a perfect hybrid effect when the steel fibers volume fraction is 10%, while macro polyolefin fiber and polyvinyl alcohol fibers content is 30kg/m3 or 45kg/m3 separately; fracture properties of RPC show a significant improvement when steel fibers volume fraction is 10%15% and synthetic fibers content is 9kg/m3.

Abstract:Visual physical model experiment of aggregates motion law were carried out via transparent adhesive prepared from carbomer gel with equivalent rheological properties of fresh concrete. Based on the principle of consistency in both real time image of flow process and real aggregate distribution from fresh mortar and transparent adhesive, the mechanism of rheological deformation of mortar and aggregate settling characteristics forced vibration was analyzed. Results indicate that visual simulation method of fresh concrete based on equivalent rheological properties is unique and feasible, and from the experiments the aggregates settlement motion law i.e., displacement fields, velocity fields and other motion morphological parameters can be directly obtained，which provide vital foundation on the analysis of constitutive relationship and grain contact model of rheological concrete.

Abstract:To study properties of magnesium potassium phosphate cement(MKPC) containing heavy metal Pb, the fluidity, setting time, compressive strength, shrinkage deformation and leachate mass concentration of heavy metal Pb were determined. Its hydration heat, phase composition and micro structure were analyzed. The result indicates that the composite retarder and some Pb(NO3)2 are able to effectively retard setting of MKPC paste. Adding of some Pb(NO3)2 reduces the compressive strength of MKPC paste and slightly increases its shrinkage deformation, but 28d compressive strength of MKPC paste with 10% (by mass) Pb(NO3)2 is higher than 20MPa and its shrinkage deformation is almost one order of magnitude lower than that of Portland cement mortar. Pb leachate mass concentration in MKPC paste gradually increases with increase of Pb(NO3)2 content, Pb leachate mass concentration in MKPC paste with 10%Pb(NO3)2 is much lower than that set forth in the standard of ‘Identification of standard for hazardous wastes’ (GB 50853—2007).

Abstract:The chloride binding capacity of fly ash concrete was studied by wet dry alternation method, then the distributions of free chloride content and total chloride content in concrete were obtained. The effect of fly ash on chloride binding capacity was discussed, and the change rule of chloride binding capacity with depth was analyzed. The results show that content of binding chloride in concrete increases due to the addition of fly ash. But chloride binding rate and relative chloride binding coefficient of fly ash concrete are less than the ones of ordinary concrete, and tend to decrease with the increase of fly ash content. With the increase of depth, the content of binding chloride first decreases and then increases, and the chloride binding capacity increases and then basically keeps stable.

Abstract:Lightweight aggregate concrete and normal concrete were prepared, and the creep behaviors were tested by the varying stress creep test at the stress level of 30% together with the shrinkage age test at early age(028d). Results show that lightweight aggregate concrete has less shrinkage, and creep coefficient is 50% that of normal concrete with the same strength at early age. Whereas the creep strain of lightweight aggregate concrete is almost 13 times that of normal concrete at early age.

Abstract:Considering the change of water mass by convection in water mass conservation equation, a new chloride transport model was developed based on Ficks first law and mass conservation law. The solution of this new chloride transport equation was derived by alternating direction implicit (ADI) finite difference method and the results are compared with chloride transport model by Ababneh and experimental data of American Association of Roads and Transport. Capacity matrix, transfer matrix and chloride passing rate vector are associated with variables in transient heat balance equation, a numerical simulation method by ANSYS thermal analysis module for chloride transport in nonsaturated concrete is derived based on mass conservation law, and the results are compared with the new chloride transport model and experimental data. The results indicate that the new chloride transport model is more consistent with experimental data of American Association of Roads and Transport than Ababneh model. The difference of different models is very small, and considering the change of water mass by convection gives a little influence on practical engineering. The model of considering the change of water mass by convection is more consistent with chloride transport process in nonsaturated concrete, and can improve the theoretical system of chloride transport in nonsaturated concrete. The numerical simulation method based on ANSYS is less accuracy than the theoretical model but its more convenient for application in engineering practice.

Abstract:Three different types of shrinkage reducing agents(internal curing agent(SAP), expanding agent and organic shrinkage reducing agent) were introduced to the concrete with high water binder ratio,and then the effects of these shrinkage reducing agents on the compressive strength, chemical shrinkage, autogenous shrinkage, drying shrinkage and plastic cracking of concrete were studied. Reduction effects of different shrinkage reducing agents under different curing conditions of concrete were compared. Results indicate that SAP, expanding agent and organic shrinkage reducing agent all have negative effects on the 3d compressive strengths of concrete, of which the organic shrinkage reducing agent affects the most, and SAP promotes the 28d compressive strength of concrete. The SAP has better improvement effect on chemical shrinkage, autogenous shrinkage, dry shrinkage and plastic cracking because of its synergistic effect on the internal relative humidity of concrete. Expanding agent has harsh demand for the curing conditions of concrete with high water binder ratio which means that expanding agent compensates shrinkage well in seal curing conditions and defectively in dry curing conditions. As for autogenous shrinkage of concrete, organic shrinkage reducing agent performs not as well as SAP and expanding agent in seal curing condition because of the lack of “self expanding effect”. However, for drying shrinkage of concrete, the organic shrinkage reducing agent performs well in dry curing conditions, because it reduces the surface tension of pore solution in concrete and slows down the evaporation rate of internal water at the same time.

Abstract:Based on distributed optical fiber sensing technology and time series analysis, a method for predicting reinforced concrete expansion and cracking was proposed. The availability of this method was approved by electrical accelerated corrosion experiment. The results show that the distributed optical fiber sensing technology could acquire the concrete expansion and cracking information steadily and effectively. Moreover, the exact cracking moment and position could also be predicted precisely by using time series analysis.

Abstract:The effect of the external mechanical stress on chloride diffusivity in concrete can be equivalent to the effect of porosity change on chloride diffusivity induced by external mechanical stress. And based on this viewpoint, a meso scale model and analysis method were proposed to study the chloride diffusivity in heterogeneous concrete under compressive stress. In this approach, the mechanical simulation was performed first by using the meso scale finite element method. The outcomes of the mechanical response of concrete were then used as input data for the simulation of chloride diffusivity. The concrete at the meso scale was assumed to be a three phase composite composed of aggregate, cement paste matrix and the interfacial transition zones. The meso scopic numerical model of concrete under uniaxial compressive stress was built to investigate the chloride diffusivity behavior. The effect of compressive stress on chloride diffusivity was explored, and the quantitative relationship between effective chloride diffusion coefficient in concrete and compressive stress level was obtained.

Abstract:Influence of strain hardening cementitious composite（SHCC） as repair material, transverse reinforcement rate of repair layer and frost damage on bond slippage behavior between concrete and steel bar was investigated through pull out test. Results indicate that the ultimate bond strength decreases by about 57% for the specimens repaired by SHCC and the ultimate slip deformation increases by 34%. All of the specimens fail in pull out mode （but for ordinary concrete specimens, they fail by splitting of the concrete cover）. With the increase of transverse reinforcement rate of specimens repaired with SHCC, the ultimate bond strength increases, the crack width on the surface of specimens becomes smaller. When the specimens fail, multi crack happens on the surface of repair layer and the crack width is between 003mm to 008mm. The very good frost resistance of the matrix of SHCC and the bond performance between SHCC and existing concrete reduces the influence of frost damage on the bond performance between steel bar and concrete.

Abstract:Through three point bending tests, the ultimate load, fracture toughness, fracture energy and crack tip opening displacement（CTOD）of aligned steel fiber reinforced concrete（ASFRC） were determined and compared with those of randomly distributed steel fiber reinforced concrete（SFRC）. The results show that, compared with SFRC, the ultimate load, fracture toughness, fracture energy and CTOD of ASFRC are improved significantly. The ASFRC exhibits obvious advantages in fracture properties relative to SFRC. In ASFRC, the number of fibers bridging the two sides of cracks and the effective reinforcement of the matrix are much more than that in SFRC, which leads to the improvement in fracture property of ASFRC.

Abstract:The recycled gypsum sample with naphthalene type（FDN） superplasticizer added was prepared under the condition of laboratory simulation. The sample was dehydrated by calcination to hemihydrate and its mechanical properties were tested. The influence of FDN on the performance of recycled gypsum and its mechanism were investigated by BET, DSC/TG and SEM EDS. The results show that the mechanical performance of plaster of Paris（PONP） and its recycled plaster（R NP） with FDN are increased compared with the plaster of Paris（POP） and its recycled plaster（R P） without FDN. The strength increasing rate of R NP is much higher. The strength of R P and R NP both are decreased in comparison to POP and PONP, while the strength of R P is dropped much compared with that of R NP. The analysis results indicate that the FDN still works in R NP due to the undecomposition and adsorption of FDN during the recycled gypsum calcination, and the greater fineness of R P also contributes to the dispersion of FDN, leading to the complete development of crystals and their close overlapping, which results in the decrease of porosity and average pore size. This is the very reason that superplasticizer reinforces its hardened R NP.

Abstract:Glazed hollow beads, cement, fly ash, polypropylene（PP） fibers and carbon nanotubes were used to prepare composite thermal insulation materials.The surface microstructure of unmodified and modified PP fibers, the fracture profile of samples and the active functional group of PP fibers were analyzed by SEM and IR to study the effects of modified PP fibers on mechanical property of the composite thermal insulation materials. The SEM was adopted to analyze the fracture profile of composite thermal insulation materials, to study the effects of carbon nanotubes on strength and electromagnetic shielding effectiveness of the composite thermal insulation materials. The results show that active functional group —OH and—COOH are introduced into modified PP fibers. Compared to the samples mixed with unmodified PP fibers, the flexural and compressive strength of samples mixed with modified PP fibers increase by 2069% and 1176%, respectively. After adding carbon nanotubes, the flexural and compressive strength of composite thermal insulation materials are improved significantly, the electromagnetic shielding effectiveness of materials is also improved significantly when electromagnetic radiation frequencies are between 515 GHz.

Abstract:The surface of wood/polyethylene composites was coated with isocyanate to improve its adhesion properties. Contact angle test, scanning electron microscope （SEM）, Fourier transform infrared spectroscopy （FTIR）, X ray photoelectron spectroscopy （XPS） and bonding strength test were used to study the effect of surface treatment with isocyanate on the surface properties and bonding properties of wood/polyethylene composites. The results show that, after surface treatment of sanding and isocyanate coating, the surface roughness for the sample increases, and the surface wettability is improved. The results of FTIR and XPS analysis show that the content of oxygen element increases, and the —OH, —CO and —O—C groups are formed on the surface of the treated composites. After surface treatment of sanding and isocyanate coating, the NCOgroup is introduced on the surface of the composites, which would be of great benefit to the adhesion between acrylate adhesive and wood/polyethylene composites, and to the achievement of fast bonding for wood/polyethylene composites.

Abstract:A series of repeated shear tests of asphalt mortars was conducted by using dynamic shear rheometer（DSR） at different temperatures and stress levels. The correlation of three fatigue life criteria （NP20，Nfm，Nf50） and the effects of filler bitumen ratio（by mass）, temperature and stress level on fatigue life of asphalt mortar were studied. Fatigue life prediction equations of asphalt mortars considering influence of temperature were established by fitting test data. The results show that there are good linear relationships between Nfm and Nf50, Np20 and Nf50. Nf50 is recommended as a simple and effective fatigue life criteria of asphalt mortars. At the same temperature and stress level, the fatigue life of asphalt mortar increases with the increase of filler bitumen ratio. At the same stress level, the fatigue life of asphalt mortar（filler bitumen ratio 08） decreases with the increase of temperature. The fatigue lives of asphalt mortars at different temperatures and stress levels could be well predicted by the established fatigue life prediction equation.

Abstract:In order to study pavement performance deterioration law of asphalt mixture after ultraviolet（UV） aging, the nonlinear equation of road performance of asphalt mixture was established by Verhulst model, and the parameters in the nonlinear equation were estimated by Levenberg Marquardt（LM） algorithm and the least square method. The reliability of the nonlinear equation was verified through the pavement performance tests of AC 13 and AC 16 asphalt mixture at the different times of UV aging in lab. The results show that the LM algorithm is more reliable than the least square method to estimate the parameters in the nonlinear equation, the nonlinear equation can accurately predict the low temperature splitting strength and dynamic stability of asphalt mixture, the maximum errors between the calculated values and experimental values are 035%, 764%（AC 13 asphalt mixture）and -081%, -1145%（AC 16 asphalt mixture）. The reduction of UV aging rate and UV aging residual index for road performance of asphalt mixture are remarkable after 194h UV aging in lab （28712 h UV aging outside）,and with the increase of UV aging time in lab, the UV aging rate and UV aging residual index tend to stable.

Abstract:Laboratory test was utilized to evaluate the effect of the proportion of rock asphalt and SBS on the performance of Terminal Blend asphalt （TB asphalt）. Based on the fluorescence microscopy and the surface energy test, the enhancement effect and strengthening mechanism of rock asphalt and SBS on TB asphalt were investigated. The results show that both rock asphalt and SBS can improve the high temperature property of TB asphalt without affecting its outstanding low temperature performance notably. The grade of TB blended with 20%（by mass, the same as below）rock asphalt and 20% crumb rubber can reach PG 7628. Besides, the rutting test results indicate that the high temperature performance of TB/rock asphalt （10% rock asphalt+10% crumb rubber） compounded with 2%（by mass）SBS is better than that of 45% SBS modified asphalt （PG 7622）, which means a remarkable reduction of the use level of SBS and thus the production cost. The results by the surface energy test and TSR show that the adhesion of TB asphalt shows increase at first and then decrease with the increase of rock asphalt and SBS content, and rock asphalt and SBS can generally improve the adhesion of TB asphalt. The observed results of fluorescence microscopy further confirm that SBS and TB/rock compound asphalt is homogeneous and stabilized internally.

Abstract:The casting molding with a small dish container was used which for prepare the softening point test disk used as the microscopic observation sample. Then the effects of the samples flatness and magnification on obtaining a good and true microscopic phase image of the modifier were investigated. Based on this， the microscopic phases of both bitumen samples modified by SBS with different storage durations as designed in the experiments and samples produced by different manufacturers were observed. In addition， the macroscopic properties of modified bitumen were also tested. The results show that the samples without cover glass are not influenced by the external perturbation so that the microscopic images are more realistic; there is an interpenetrating and stable network structure formed like ‘lizard skin’ in the sample with 45%（by mass） SBS modifier after swelling for two months. This indicates an excellent macroeconomic performance. ‘Segregation’ phenomena were found in the asphalt samples produced by manufacturers, and a wide variety of ‘coalescence’ was found in microscopic phase. Therefore, the correlation between phase microstructure and macroeconomic performance of SBS modified bitumen is significant. Fluorescence microscopic technique has a great advantage in the detection of modified asphalt performance indicators for a simple preparation and convenient testing method.

Abstract:To make clear of the developing process of rutting, the accumulated plastic deformation of three types of asphalt pavement structure with semi rigid base was studied based on mechanistic empirical method. Three modules were included in the analysis process that were temperature field, dynamic modulus and dynamic creep model of asphalt mixture. Among them, dynamic modulus and dynamic creep model of asphalt mixture were obtained by laboratory tests. Firstly, temperature field module was used to get the temperature values of different points in asphalt layer and the dynamic moduli corresponding to the temperatures with different loading frequencies were input into mechanical model as parameters to get the stress status of asphalt pavement. Then, plastic strains of asphalt layers were analyzed by the dynamic creep model and the total rutting was calculated. The results show that surface and middle AC layers have the most contribution to rutting in the AC+AC+AC structure. If the surface AC layer is substituted with surface SMA layer, the rutting in asphalt pavement will be reduced significantly and the rutting in middle AC layer will be the most. So, to reduce the rutting in asphalt pavement, SMA+AC+AC structure and SMA+AC+LSPM（large stone porous asphalt mixture） structure should be recommended and meanwhile, the high temperature stability of materials used in middle layer should be paid much attention in the design.

Abstract:In order to study the effect of freeze thaw cycles on the compression performance, 24 recycled concrete brick masonry specimens were tested in the laboratory with climate simulation. The changing rule of compressive strength, elastic modulus and the constitutive relation curve along with the increase of the number of freeze thaw cycle was established, and the degradation relationship of the average compressive strength of brick masonry structure with the number of freeze thaw cycle was also established. Based on the fitting of the measured stress strain curve of masonry, the masonry compressive constitutive relation curves with different cycles was obtained, which will provide theoretical basis for active masonry structure durability and seismic performance evaluation under the freeze thaw cycle.

Abstract:The quantitative characterization methods of free water and its action mechanism were studied by relating rheological properties of fresh cement paste to the packing density of cement partials. The results show that free water in cement paste can be classified by the plastic limit and liquid limit. Type 1 free water that is the water exceeding plastic limit can separate cement particles. Type 2 free water that is the water exceeding liquid limit will cause the flow of cement paste under gravity. The improvement of flowability by adding superplasticizer is not only due to the increase of dispersion of cement particles, but also mainly because of lower adsorption force of cement particles to water, lower loose bound water amount of cement particles, and higher free water amount of cement paste. The flowability of cement paste can be accurately and effectively controlled when it is associated with the free water amount.

Abstract:Influence laws of failure shape, stress strain curve, peak stress and secant modulus affected by size and spatial location of aggregate in concrete were studied under same condition based on particle flow concrete. Through analyzing the results of uniaxial compression simulation experiment of the concrete with different mortar and aggregate mass ratios(5∶5,4∶6,3∶7,2∶8) and different gradations(gradation 1, gradation 2, gradation 3 and gradation 4), it is found that aggregate has the effect of preventing crack propagation, the larger the aggregate, the greater the effect of preventing crack propagation, micro cracks was found to occur at around the aggregate and propagate. It is proved in many micro tests, that adding aggregate in mortar can greatly improve concrete strength and deformation characteristics. Comparing to peak stress 52MPa and secant modulus 307GPa of mortar, the peak stress of different gradations with 5∶5 and 4∶6 of mass ratio increases by 22%48% and secant modulus inereses by -8%99% with average value being 65MPa and 72MPa, 374GPa and 426GPa, the peak stress of different gradations with 3∶7 and 2∶8 of mass ratio sharply increases by 40%228% and secant modulus dramatically decreases by 79%92% with average value being 92MPa and 154MPa, 158GPa and 44GPa, which proves that under the same mass ratio, the higher the aggregate gradations, the easier it is to form structure built on stilts, causing local instability and affecting the enhancement effect; under the same grading, the strength of concrete increases with the increase of the mass ratio, and the stress strain curve firstly changes from unimodal to bimodal and then back to unimodal, which suggests that the stability of aggregate spatial structure determines change of stress strain curve.

Abstract:In order to study the mechanical behavior of recycled aggregate concrete(RAC) under triaxial compression, 24 cylinder specimens were tested by considering the parameters of concrete strength, lateral confinement and recycled coarse aggregate(RCA) replacement ratio. The failure patterns of the specimens were observed in the tests. The stress strain curves, peak stress and peak strain were obtained. The formulas for calculating the strength, elastic modulus and peak strain were put forward. The test results show that the failure pattern of RAC is the shear failure. The elastic modulus, the peak stress and the corresponding peak strain are enlarged with the increase of lateral confinement, and after the peak point in the stress strain curve, the descending branch is gentle and the ductility is better. Finally, based on the Mohr Coulomb failure criterion the strength criterion of recycled concrete is discussed.

Abstract:The effects of Na bentonite and Ca bentonite on resistance of cementitious materials to sulfate attack at low temperature were studied. The paste samples made from cement and limestone powder were immersed in 5%(by mass) Na2S04 solution at 5℃ and the corrosion products were analyzed by IR and XRD. It is indicated that the degree of corrosion of cement limestone powder specimens aggravated with immersion time. The specimens without bentonite fell off at edges and corners notably, and thaumastie was the main component of corrosion products. In corrosion products of specimens, the content of thaumasite generation decreases with the increase of bentonite content, and the corrosion degree of specimens decreases as well. When the use level of bentonite is the same, the effect of Na bentonite to improve resistance of the cement limestone powder cementitious material to sulfate attack at low temperature is greater than that of Ca bentonite.

Abstract:The influence of multi factors(admixture, water cement ratio, curing age, accelerated corrosion regimes) on the bond strength between the steel and concrete was researched. The influence degree of each factor on the bond strength between steel and concrete was determined. Besides, the multiple nonlinear regression model was proposed. The experiment results show that the maximum bond strength between the steel and concrete is obtained for the specific factors. The influence of different factors on the bond strength of reinforced concrete is different. The influence of water cement ratio and admixture are most remarkable, while the influence of accelerated corrosion regime is not notable. The multi nonlinear regression model is established to describe the influence of multi factors on the bond strength between the steel and concrete effectively. The bond strength of reinforced concrete decreases with the increase of water cement ratio and increases with the increase of curing age. Besides, change of bond strength of reinforced concrete is different for different admixtures and different accelerated corrosion systems.

Abstract:In order to monitor the corrosion of reinforcement in reinforced concrete structures, a monitoring method based on wave propagation method with piezoelectric ceramic(PZT) was proposed. Firstly, based on PZT wave propagation, experiments and numerical simulation were conducted to investigate and identify the stress wave propagation attenuation law in absence of the corrosion of reinforcement. Secondly, eighteen reinforced concrete specimens were prepared, and PZT actuators/sensors were attached at the same position on the surface of each embedded reinforcement. Finally, fast electrochemical corrosion was applied to these specimens, and the PZT test was carried out to enable the specimen corrosion process to trace the influence of corrosion on the wave propagation characteristics. The results show that the corrosion of reinforcement affects the stress wave propagation attenuation law seriously, and it shows a quadratic function between the amplitude of the wave propagation and the corrosion rate of reinforcement.

Abstract:In order to evaluate the mechanical properties of high strength Q460 steel after cooling from high temperature, high strength Q460 steel was heated by electric furnace and cooled down with natural cooling or water cooling, then the tensile test was carried out. The strain stress curve, yield strength, ultimate strength, elastic modulus and ultimate elongation of high strength Q460 steel after cooling from high temperature were determined. The yield strength, ultimate strength and elastic modulus of high strength Q460 steel after cooling from high temperature were compared with that of ordinary Q235 steel. The results show that the mechanical properties of high strength Q460 steel change after high temperature compared with that at room temperature, especially when the temperature exceeds 700℃. When the temperature exceeds 700℃, cooling method has great influence on ultimate strength and ultimate elongation of high strength Q460 steel, the ultimate strength of high strength Q460 steel under water cooling is much higher than that under natural cooling, the ultimate elongation of high strength Q460 steel under water cooling is much lower than that under natural cooling. The influence of cooling method on yield strength and elastic modulus is not notable. The reduction factors of yield strength, tensile strength and elastic modulus of high strength Q460 steel after cooling from high temperature are different from those of ordinary Q235 steel.

Abstract:To solve the problem that the dry film thickness of the concrete coatings was difficult to be tested nondestructively, ultrasonic coating thickness gauge was adopted to measure the dry film thickness of coating on the surface of concrete in different strength grades. Uncertainty evaluation and quality judgment of the measurement results were conducted. The results show that the degree of reliability of the measurement results could be found by the uncertainty evaluation, which is the important basis for quality judgment whether the measurement result satisfies the requirements or not. The higher the strength grade of concrete is, the smaller the uncertainty of the dry film thickness of concrete coatings is, and vice versa.

Abstract:Using the porous graphite as an inorganic carrier, through the physical adsorption in high temperature, two fatty acids, lauric acid and myristic acid, were adsorbed into porous graphite. According to the temperature sensibility and long term stability detected by hot and cold durability test, the proper firing technology, the adsorption content of fatty acids, and the adsorption temperature were determined. The results show that when the firing temperature is 800℃, the porous graphite can adsorb 700%(by mass) fatty acids phase change materials into the internal pores under 70℃ water bath.This kind of composite phase change product achieves less than 3% mass loss after thermal cooling cycling. The phase transformation point is not changed and the loss of enthalpy of transformation is 1014% after being immersed into alkaline environment.

Abstract:Honeycomb paperboards after dipping in acetylene carbon black were introduced to gypsum based microwave absorbing materials. Gypsum boards with single layer and double layer honeycomb structure were prepared and the microwave absorbing properties in the range of 218GHz were studied using N5234A PNA L microwave network analyzer. The results indicate that microwave absorbing properties of the specimens with single layer honeycomb structure are mainly affected by the size of each unit cell, including the side length and the height. The reflection loss of the gypsum board is below -10dB in the whole range of 818GHz when the side length and the height are 6mm and 8mm, respectively. For gypsum boards with double layer honeycomb structure, the microwave absorbing property is further improved due to the impedance gradient structure formed by different layers, including matching layer and absorbing layer. Different unit cell sizes are designed for two layers based on the impedance match principle. The optimal reflection loss obtained in the double layer gypsum boards is below -8dB in the frequency range of 218GHz and the lowest peak value could reach -203dB.

Abstract:The hollow polymer latex particles with uniform size and good monodispersity were made by in situ polymerization with the non solvent method of encapsulation with cross linking modification, and the effect of cross linking monomer(DVB) use level in the shell on the synthesis process, morphology and opacity of the hollow polymer latex particles and its dry film was investigated by particle size analyzer, viscometer, acid value analysis, SEM, TEM and UV Vis spectrophotometer, differential scanning calorimetry. Test results show that when the cross linking monomer content(by mass) in the shell is less than 15% of the total monomer used, because the reduction of the cross linking monomer contents in the shell, the strength of the shell of the hollow polymer latex particles decreases, which causes the hollow polymer latex particles to be easily collapsed as well as a wider particle size distribution when the pore was swelling. When the content is greater than 20%, with the increase of the cross linking monomer use level in the shell, the strength of the shell increases and the particle size of polymer latex particles decreases, which makes the swelling become difficult. When the content is between 15%20%, the particle size distribution is uniform, shell strength is moderate with better swelling property, the film obtained from the dried emulsion which contained the hollow polymer latex particles show the optimal opacity performance.

Abstract:In order to improve electromagnetic wave absorbing properties of asphalt pavement, the asphalt mixture samples were prepared using natural magnetite powder as absorber. The electromagnetic parameters such as complex dielectric constant and complex magnetic permeability of samples with different replacement rates of natural magnetite powder were tested by the method of rectangular waveguide. Reflection loss of samples were calculated based on the transmission line and impedance theory. Results show that with addition of natural magnetite powder, electromagnetic parameters of asphalt mixture are improved significantly. With the increasing grade and increasing replacement rate of natural magnetite powder, the real part of the complex dielectric constant is significantly increased while the imaginary part has little change. Both the real and imaginary parts of complex magnetic permeability are increased with the increasing grade and increasing replacement rate of natural magnetite powder. Asphalt pavement with reflection loss of less than -10dB can be prepared by adding natural magnetite powder in grade of 60 and above. There are three kinds of matching thickness (3,5,7cm) of electromagnetic wave absorbing asphalt pavement during 211cm. The recommended design value of asphalt pavement thickness is 3cm. When the designed thickness of pavement layer is higher than 3cm, the lower replacement rate of natural magnetite powder should be selected.

Abstract:Through indoor experiments, rutting resistance, low temperature performance, moisture sensitivity and fatigue resistance of WMA containing different RAP contents ranging from 0% to 50% were researched. The results show that, the RAP mass content in asphalt mixture could increase to 50% when Evotherm WMA technology is introduced; for WMA containing RAP, the rutting resistance, moisture sensitivity and low temperature performance are improved when the RAP mass content increases to 30%40% and then degrades; the fatigue resistance is degraded gradually when RAP content increases, and the performance is degraded much more seriously under higher strain.The rutting resistance and moisture sensitivity of WMA mixtures containing RAP are inferior to HMA containing RAP, the fatigue resistance of WMA containing RAP is superior to HMA containing RAP, and the low temperature performance of WMA and HMA under same RAP mass content is relatively close.