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1.
Jiaozhou Bay subsea tunnel is the second self built tunnel in China with the designed service life over 100 years. On the basis of service environment of subsea tunnel concrete and the durability experiments of concretes, the service life prediction model considering chloride diffusion, carbonation and bending loading was proposed. The key durability coefficient of lining concrete in subsea tunnel was investigated. And the function of chloride diffusion coefficient and rebound strength of concrete was proposed. Moreover, the chloride content in concrete varied with service time and the service life of lining concrete for subsea tunnel was predicted with the proposed service life prediction model. It was found that the value of varied cover thickness was from -4(6) to 15 mm. The chloride diffusion coefficient mean value of lining concrete in standard curing was 2.1(2.7)×10-12m2/s. And the initial chloride content in concrete was less than 0.35kg/m3. The relationship between chloride diffusion coefficient and rebound strength could be regressed to linear relationship, and the calculated chloride diffusion coefficient of lining concrete was varied from 1.5×10-12m2/s to 3.5×10-12m2/s. The predicted service life of lining concrete for Jiaozhou bay subsea tunnel was more than 100 years according to proposed model. 相似文献
2.
By adding small amount of dihydrate gypsum (CaSO4·2H2O) and silica fume in steel slag-cement system, steel slag-cement binding materials were prepared. And the dosage of CaSO4·2H2O and silica fume on the properties of steel slag-cement binding materials was studied. Hydration properties and paste structure were investigated by SEM and XRD. The results show that both CaSO4·2H2O and silica fume can improve the strength of steel slag-cement binding materials. Compared with single-doped, compound of CaSO4·2H2O and silica fume has much better effect on strength of steel slag-cement binding materials. The optimum proportion of CaSO4·2H2O and silica fume are 1% and 4%, respectively. The 3 d compressive strength is increased by 59.0%, and the 28 d compressive strength is increased by 36.5%. No matter adding CaSO4·2H2O and silica fume or not, the steel slag-cement binding materials have the same hydration products. However, the content of C-S-H gel and AFt crystals is higher, and the content of Ca(OH)2 crystals is lower in steel slag-cement binding materials containing CaSO4·2H2O and silica fume than those in steel slag-cement binding materials without CaSO4·2H2O and silica fume. 相似文献
3.
In order to discuss the deformation characteristics of rock mass under different water levels changing between 145 and 175 meter in the Three Gorges reservoir area, an experiment was carried out for the studying sandstone deformation under the conditions of three different axial stresses(σ1=55.54,34.18,12.82 MPa), two cyclic pore pressures(Pmin=2 MPa,Pmax=6 MPa) and two kinds of constant time(the upper limit time and the lower limit time(ΔT=120,240 s).With ε1-T curves and p-T curves, as well as p-ε1 hysteresis curves, it was found that the curves were continuous sine wave-shaped curves.At first, the strain decreased with loading pore pressure.And then, it decreased to valley value with pore pressure at stable upper limit.Next, it increased with unloading pore pressure and increased to peak value with pore pressure at stable lower limit.The p-ε1 hysteresis curves of the sandstone had two typical stages.And one was caused by the closure of some primary pores and crack under increasing compaction, in which the strain did not form obviously hysteresis curves, and the other was pore pressure coupling stage which showed obvious hysteresis curve in form of the anti-clockwise from the dispersed to the dense.In addition, Δε-n curves in four sections (loading, unloading, steady upper limit, steady lower limit) of p-ε1 curves were compared and respectively ananlyzed in the condition of various axial stress and different constant time . 相似文献
4.
For exploring the practicality of engineered bamboo products in timber structure, the formula of dowel bearing strength parallel to the grain was investigated. In this paper, seven groups of twenty eight specimens were tested. The effect of the thickness of engineered bamboo products, end distance and pin diameter on the maximum load, stiffness and dowel bearing strength were analyzed. It was showed the thickness of engineered bamboo products had no effect on the dowel bearing strength. The effect of end distance on the dowel bearing strength could be negligible with the end distance greater than 64mm. And the dowel bearing strength approximately linear improved with the decrease of pin diameter. The influence coefficient of pin diameter was obtained by regression analysis. Finally, a simplified theoretical calculation formula of dowel bearing strength was establishment. And the results of dowel bearing strength by the theoretical calculation formula had a good agreement with those obtained by test. 相似文献
5.
Aiming at the low service life and bad durability of the traditional concrete structure and concrete cover, the high dense concrete cover (HDC) was produced with the optimization of interfacial transition zone in meso scale(50 100μm) between cement mortar and aggregate of the ordinary concrete. Moreover, some properties of HDC were studied, including the impermeability, the anti corrosion behavior, anti acidic gas corrosion and freeze resistance. It was shown that the impermeability of HDC was excellent with very low permeability. Compared with ordinary concrete, the anti corrosion behavior of HDC was remarkably strengthened. And under the condition of erosion accelerated by CO2 and SO2, the freeze resistance such as the appearance after freezing and thawing, mass loss and relative dynamic modulus of HDC was better than that of ordinary concrete and neutralization depth of 90 day was less than 1 mm. On the other hand, the results of Scanning Electron Microscope (SEM) experiment indicated that the size of interfacial transition zone of HDC was effectively reduced and the microstructure compactness of concrete was increased. Therefore, it was found that the special producing technology and characteristics of HDC can improve the durability, and then the service life of structure was increased effectively. 相似文献
6.
The effects of initial high humid air curing, standard water curing and sealed curing on thaumasite form of sulfate attack (TSA) of cement based materials were studied.The Erosion products after 180 days attack in sulfate solution were analyzed by the way of X ray diffraction(XRD) and fourier transform infrared spectroscopy(FTIR).And it was found that the TSA of the cement stone was delayed in high humid air resulting from that CaCO3 generated from carbonation was filled in the pores of the specimens, forming a compacted surface and restricting SO42- intrusion.In comparison, the extent of TSA of the specimens cured in sealed condition was most severe resulting from that large amount of inter defects in specimens for the lower hydration degree, and SO42- ions could intrude into specimens more easily. 相似文献
7.
Based on monitoring data of water quality and river runoff from 2007 to 2008, the dynamics of TN and TP transported into the backwater region of the Linjiang River were investigated and fluxes of TN and TP were also estimated. It was shown that the dynamic changes of TN and TP were significant. The concentration of TP in rainy seasons was higher than that in dry seasons, while the cases for TN was contrary. The fluxes of TN and TP were significantly higher in rainy seasons than those in dry seasons. On average, there were about 4 142 t TN and 455 t TP transported into the backwater region of the Linjiang River every year. And TN flux decreased by 32.7% from 2007 to 2008, while TP flux increased by 34.3%, which was in agreement with the inter annual variation of the concentrations of TN and TP. TN flux was primarily influenced by river runoff, whereas TP flux was affected by both concentration and runoff. Further analyses indicated that TN was mainly caused by point source pollutants(dominated by NH3N, and then DON). On the contrary, TP was mainly caused by plane source pollutants(dominated by PO34P). It was also indicated that it was critical to control the point source pollution in the basin to promote the water quality of the backwater region of the Linjiang River. 相似文献
8.
A coupling modeling method with MIDAS/GTS FLAC3D was put forward aiming at the technical difficulties and deficiencies in pre processing for complex geologic body and structural engineering with FLAC3D. The coupling procedure was that, firstly, the three dimension geometry model was built with MIDAS/GTS and the model meshes were divided. And Secondly, the element and node data of the completed model built in MIDAS/GTS were exported. After data was transformed by using the interface program in MATLAB, the information was imported into FLAC3D. Thus the three dimension FLAC3D model for complex engineering was generated coupling with MIDAS/GTS. With coupling method, the complex three dimension model was built for Fanshuigou bridge Shipogou tunnel engineering above mined out region, and the results verified the feasibility and effectiveness of the proposed method. 相似文献
9.
The characteristics of recycled fine aggregate (RFA) and its concrete (RFAC) were analyzed by SEM, EDXA, XRD, Micro harness and nitrogen absorption. The results show that RFA is an artificial aggregate with complex compositions, certain hydration activity and high permeability. The mineral compositions of RFA include SiO2, CaCO3 and a small quantity of C2S, which has a certain hydration activity and can form hydration productions. The compaction rate of cement paste in RFAC is low because of pores in it. There is obvious interfacial transition zone (ITZ) between RFAC and cement paste, and its width is bigger than that in ordinary concrete. In addition, the values of micro hardness of the interfacial transition zone on both sides of RFA and cement paste are lower. The porous structure of the recycled fine aggregates and defects of ITZ are main reasons for big pores in RFAC, which has bad effect on impermeability of RFAC. 相似文献
10.
We point out the weak points of oxidation ditch excess activated sludge thickening by cavitation air floatation process. out in this paper and the reasons for such weak points are analyzed, and some advanced measures are put forward and. a mModified cavitation air flotation (MCAF) equipment MCAF 10 for oxidation ditch sludge thickening has been developed. The flocculant FO4440SH with 1.0 kg/tDS was added with 1.0 kg/tDS and the 0.2kg/tDS of the surfactant 1227 were adopted with addition of 0.2kg/tDS. When the CAF 5 was employed to thicken oxidation ditch excess sludge, the optimal solid loading was 230kgMLSS/m3·d, and the hydraulic loading was 90 m2/m3·d, and the SS in the effluent was 200～250mg/L;. When the MCAF 10 was used to thicken oxidation ditch excess activated sludge, the optimal solid loading was 270kgMLSS/m3·d, hydraulic loading was 110 m2/m3·d, and the SS of the effluent was 100～150mg/L. The experimental results indicate that the modified cavitation air flotation (MCAF) equipment is more suitable for sludge thickening. 相似文献
11.
Collapsible loess was collected from a suburban district of Shanxi, China. Dynamic model experiments of different hammer blows were designed to simulate the in-situ test on collapsible loess. The model experiments results showed that the density and shear strength parameters of the soil specimens increased with the increase of blows while the collapsible coefficient of the loess decreased with the increase of blows. However, after eight blows, the vertical displacement, the density, the internal friction angle and the cohesion of the loess were tend to be constant, and the collapsible coefficient was less than 0.015 that means the loess is stable. Furthermore, scanning electron microscope was used and SEM image analysis program was established to study the micro-structure of the specimens. The analysis of results showed that small pores in the soil increased with the increase of the blows; before compaction the content of pores with an equivalent pore diameter under 16 μm was 92.6%, the content of pores with an equivalent pore diameter larger than 16 μm was 7.4% and the content of pores with an equivalent pore diameter less than 4 μm was 66.9%. After ten blows, there were nearly no pores with an equivalent pore diameter larger than 16 μm, while the content of the pores with an equivalent pore diameter less than 4 μm was 81.8%. According to quantitative analysis, the relations between the blows and the plane void ratio, and the equivalent pore diameter were established. Meanwhile, the relations between the collapsible coefficient and the plane void ratio, the equivalent pore diameter were established. 相似文献
12.
Manganese alloy slag is an industrial waste produced from manufacture of manganese alloy. Recent years environment pollution of manganese slag has been becoming heavier and heavier with the development of manganese industry. Aiming to sort out this problem, combination of manganese slag and ground granulated blastfurnace slag (GGBS) were applied to prepare alkali activated cementitious material. Compressive strength and flexural strength of cementitious material prepared with combination of alkali slag manganese slag were measured. And micro structure of hydration production was investigated by scanning electro microscope (SEM). It was shown that the flexural and compressive strength of cementitious material with alkali GGBS manganese slag system were decreased with the increase of replacement of GGBS by manganese slag. The increase of the fineness of manganese slag was favorable for strength improvement of the alkali GGBS manganese slag material. It was concluded that ground manganese slag had hydraulic activity in alkali activated cementitious material and the activity was lower than that of GGBS. 相似文献
13.
Deng Chuanbin Qian Zhenming 《保鲜与加工》1995,(5):13-19
The paper presented a new micomechanics load-transfer model for single-fibre fragmentation test. The interfacial shear streength and the crack will develop along the interface. The fibre stochastic strength distribution was modelled by a two-parameter Wibull distribution. The influence of the interfacial bonding strength and fibre axial-tensile strength on stress states in components of composites was discussed. The interfacial state during the fragmentation process may be one of following three states: 1) fully bonding; 2) partial bonding; 3) fully debonding; according to the fibre axialtensile strength and interfacial properties (including interfacial bounding shear strength, interfacial friction coefficient and matrix radial pressure) after elastic constants and geometrical parameters of composites phases are given. The necessary conditions for these three states were discussed- Finally, a suitable definition of the critical fibre length was given and the critical length was constrouted by two parts :debonding fibre length and bonding fibre length. 相似文献
14.
The high grade gray water was pre treated by biologic contact oxidation on load of 0.72 KgBOD5·m-3·d-1, and then post treated by constructed wetland. On the basis of experiment, it was found that: Totle nitrogen (TN) was the restrictive index of the combinational technique. To meet the reclaimed water quality standard and reuse for waterscape, the peak hydraulic load of constructed wetland was 0.50 m·d-1 in summer (30~36 ℃), and 0.33 m·d-1 in winter (8~12 ℃). And the load ratio of the peak hydraulic under the summer and winter conditions was 3:2. With the experimental results and reclaimed water quantity requirements in different seasons of buildings, treatment scale can be determined. 相似文献
15.
According to the characteristics of interfacial stress between surrounding rock and shotcrete support, mechanical model of composite curved beame for support system of tunnel surrounding rock and shotcrete lining was established, considering the interfacial deformation coordination and the effects of bearing arch of surrounding rock. Then from static equilibrium of two differential elements, the differential equations for the radial displacement of composite curved beam were obtained. All analytic formulas of both interfacial stress and internal forces between surrounding rock and shotcrete lining by arbitrary distribution load were derived. And thus the mechanical condition of interface zone and the stress concentration position were obtained, which is convenient to assess the stability of surrounding rock and predict the safety. Finally, the analysis of tunnel project excavated by bench method showed that shotcrete lining made the formation of compressive stress zone in surrounding rock by transferring stress from the interface between surrounding rock and shotcrete, which is beneficial to improve the stability of surrounding rock. 相似文献
16.
The first degree second order moment method (JC method) recommended in Unified Standard for Reliability Design of Building Structures (GB500682001) was applied to analyze the reliability of steel reinforced high strength concrete filled steel tubular slender columns. Several performances were studies, which were the influences of different load combinations, specific values of loads, strength grades of concrete, thickness of steel tube, area of cross section of structural steel, steel yield strength and slenderness ratio on the reliability of the composite column. It was found that, when the slenderness ratios were within common range, the reliability indexes of the proposed formulae satisfied the demand of GB500682001 for plastic material on the whole. And it was concluded that the reliability index varied with the load combination and specific value of loads. The reliability index increased with the increase of concrete strength grade and decreased with the increase of steel tube thickness. Furthermore, steel yield strength and slenderness ratio had different influences on the reliability indexes. 相似文献
17.
Kinetics of phosphates removal by Municipal Solid Waste Incineration(MSWI) fly ash were investigated with the tests of EDS, XRF and TEM. It was shown that 95% of phosphates was removed by MSWI fly ash in 30min under 303 K. The process was heat in taking process whereas the heat amount required was small. Heavy metals were stabilized during the process and no heavy metals were detected in solution after reaction. Chemical precipitation was the main way of phosphates removal. Ca、Fe、Zn etc. can provide cations for phosphates removal reaction. The macro kinetics of phosphates removal by MSWI fly ash can be represented by the model of sphere internal diffusion control. And internal diffusion process of PO34 and soluble products were the controlling step. The relation between reaction rate of phosphate (X) and reaction time (t) can be represented as 13(1X)2/3+2X=kt; the apparent activation energy was about 10.06kJ / mol . 相似文献
18.
The mechanical properties, hydration products, and pore structure of SSC(super sulphated cement) were tested with universal test machine,XRD(X-ray diffraction), SEM(scanning electron microscope) and MIP(mercury intrusion porosimetry), which were compared with P·O 42.5 and slag cement. Results show that the main hydration products of SSC are ettringite, C-S-H gel and little gypsum crystals, while without calcium hydroxide; SSC hardened paste has smaller threshold pore diameter, the most probable pore diameter, middle pore diameter and average pore diameter, and has lower porosity and higher density, which can effectively promote the 90-day strength increase of SSC paste. 相似文献
19.
Because of the existence of initial hydraulic gradient in clay, non Darcy equation with initial hydraulic gradient was modified with classical consolidation theories of sand drained ground.And the approximate solution in the instance of vacuum preloading was presented.Based on this, the effect of initial hydraulic gradient on the seepage front, the pore water pressure and the average degree of consolidation were investigated.It was found that the spread of vacuum pressure was delayed because of initial hydraulic gradient, resulting in the dissipation of pore water pressure and the speed of soil layer consolidation.The hysteresis became more and more evident with the increase of initial hydraulic gradient.In addition, initial hydraulic gradient also caused some residual pore water pressure which could not reach vacuum pressure.Thus, the ultimate average degree of consolidation was less than 100%, which decreased with the increase of initial hydraulic gradient. 相似文献
20.
In order to achieve the comprehensive utilization of iron slag and steel slag, foamed concrete were prepared by adding small amount of gypsum, lime and clinker in steel slag-iron slag system and using aluminum powder as foaming agent,. The three-day, seven-day and twenty-eight-day bulk density and compressive strength of foamed concrete with the different ratio of the main raw materials were researched. Furthermore, in order to research the hydration mechanism and microstructure of foamed concrete, the XRD and SEM images of the three productions of foamed concrete were analyzed. The results showed that the coordination of the dosage of steel slag and iron slag was better when the former was 30% and the latter was 45%, Meanwhile, the compressive strength was 5.1 MPa, the bulk density was 625 kg/m 3; Ettringite and C-S-H gel synergies generated in steel slag-iron slag system. Besides, hydration activity of steel slag was obviously lower than that of iron slag. 相似文献