Boundary Element Method for Time-dependent Chloride Diffusion and the Chloride Distribution in Concrete

The process of chloride diffusion in concrete is time-dependent.The boundary element method (BEM) with a time-dependent diffusion coefficient is presented for chloride diffusion in concrete based on the suitable transformation of variables.The fundamental solution of the partial differential equation for time-dependent chloride diffusion in concrete is developed,and the compensation length of the diffusion field is defined as well as the compensation coefficient.The scheme of BEM with a time-dependent diffusion coefficient is developed.Two examples are given to demonstrate the accuracy and efficiency of the presented method and the rationality and the importance of the compensation length for the method.     

Study on Influence of Mineral Admixture on Chloride Ion Penetration and Diffusion in Concrete

In this paper, the influences of different kinds and different amount of mineral admixture to Cl-penetration and diffusion in concrete are studied. The results of experiment show that separate addition of mineral admixture (ground fly ash, slag fines, silica fume) into concrete can improve its resistance to chloride ion penetration and diffusion. Furthermore,the effect of silica fume is the best, fly ash second, and then follows slag fines. Mechanism analysis shows that the pozzolanic effect of mineral admixture improves the interface between the cement and aggregate in concrete, reduces the total porosity, makes pores more smaller, on the other hand it increases the Cl-consolidation capability of concrete with low alkaline C-S-H gel produced. So the resistance to chloride ion penetration of concrete is improved.     

Diffusion Behavior of Chloride Ions in Concrete Pipe Piles

Concrete pipe piles, whose internal surface is usually closed and external one is exposed to chloride environment, are widely used in marine environment. Based on Fick second law and the boundary condition of pipe pile, the analytical solution to chloride diffusion equation was deduced with the method of separation of variables. The solution comprises two parts: a stationary solution consisting of Bessel functions, and a transient solution. This is different from the traditional analytical solution that is based on semi-infinite boundary condition. Applying this result to a typical PHC pipe pile, the diffusion of chloride concentration was analyzed. Furthermore, the effects of the ratio of outer radius and inner radius, diffusion coefficient and protective concrete cover thickness on diffusion of chloride concentration were also discussed. When the ratio of outer radius and inner radius equals 1.5, the decay rate of secondary segment of transient solution is 4 times larger than that of the primary part. This example provides a computational basis for the corrosion of steel bar and some reference for durability design of pipe piles as well.     

Chloride Ion Diffusion Coefficient Model of R.C. Elements under Multiple Factors

Based on the analysis of chloride ion-induced erosion mechanism of reinforced concrete and the Fick’s second law, a multi-factor model of the chloride ion erosion is established. In this model, the influences of water-cement ratio, humidity, time, temperature, and chloride ion binding capacity of concrete are taken into consideration, and the mathematic solution to the new model is provided by considering the boundary conditions. The new model is verified by analyzing the long-term exposed experiment data. Compared with the traditional model of Fick's second law, the model can indicate the development trend of the structure eroded by chloride and the chloride ion concentration in different depth, and at the same time, it can predicate the chlorine ion concentration on rebar surface in different corrosion periods and the initiation corrosion time of reinforcement.     

Influence of Transverse Flexural Crack on Chloride Penetration in Concrete

The mechanism for chloride penetration in cracked concrete and its major impact factors were analyzed. As a result, a revised chloride diffusion model based on Fick's Law was built by dual porous medium model. Then several cracked reinforced concrete beams self-anchored with sustained flexural loads were immersed in the 5% NaCl solution with the condition of dry-wet cycles. After 15 times of dry-wet cycles, the rapid chloride testing (RCT) was used for the determination of chloride ion content of the powder at each cracked sections. The test results show that: 1) with the condition of dry-wet cycles, the chloride content will occur a peak in the surface 20mm concrete, so the depth for surface convection zone can be assumed to be 15~20 mm; 2) when the crack width is less than 0.3mm, the equivalent chloride diffusion coefficient increases steadily, which agrees well with model's prediction; when the crack width is larger than 0.3mm, the equivalent chloride diffusion coefficient augments rapidly and influence of convection on chloride penetration becomes more significant; 3) the deterioration factor for equivalent chloride diffusion coefficient in flexural cracked concrete is directly correlative with crack width, which can be expressed by second order power function or separate function.     

孔隙分形修正的混凝土中氯离子扩散系数

在已有的氯离子扩散理论和孔隙分形理论的基础上,提出小孔的孔轴线分形维数表征氯离子扩散的曲折度、大孔的孔表面分形维数修正孔隙率,并推导得到基于孔隙分形修正的氯离子扩散系数模型。通过分析龄期为14 d和28 d不同配比混凝土的基于孔隙分形的氯离子扩散系数模型的计算结果和快速氯离子扩散试验(ASTM C1202)电通量,发现两者之间有良好的线性关系。采用基于孔隙分形修正的氯离子扩散系数代入Fick第二定律的解析解,对试验后各组混凝土中不同扩散深度的氯离子浓度进行拟合,计算结果与实测值吻合情况较好。     

Influence of Shrinkage Cracks on Chloride Penetration and Crabonation of Concrete

The influence of shrinkage crack on chloride ion penetration and carbonation of concrete is investigated. The concrete samples with shrinkage crack of 0.07 mm,0.1 mm,0.2 mm,0.4 mm and 0.62 mm are prepared, and both an accelerated carbonation test and Qingdao sea water corrosion test are conducted on sound concrete and cracked concretes. The depths of carbonation, the content of free chloride and total chloride in crack zone and perimeter zone of concrete are analyzed. The enperimental result shows that both free chloride and total chloride content in cracked concrete increase with the rise of the shrinkage crack width, and they are related in quadratic function. The chloride penetration velocity in crack zone is higher than that in perimeter zone of concrete. However, the increased specific surface in shrinkage crack tip improves chloride binding capacity and decreases the free chloride content in this zone. When the shrinkage crack is less than 0.07mm, the carbonation depth in crack zone is same as that of sound concrete. The chloride diffusion coefficient and the carbonation depth of cracked concrete increase limited as the shrinkage crack is less than 0.1mm, and then increase significantly with the increasing of shrinkage cracked width. Moreover, the carbonation depth in crack zone is increased by 3mm in comparison with that in perimeter zone of cracked concrete.     

Mechanical and Chloride Diffusion Behavior of Kaolinite Clay Modified Cement-Based Material

The effects of kaolinite clay on the microstructure (pore structure, internal structure) and mechanical properties (workability, early-age and long-term flexural strength, chloride diffusion property) of the cementitious composites were tested. It is shown that the addition of clay improves the micro-pore structure in the cement paste and limits the introduction of chloride ions. As a result, it is suggested that the kaolinite clay would act as both filler and accelerator of cement hydration. Compared with the control specimen, the flexural strength of cement paste with 1% kaolinite clay increased by 30.41%, 39.04%, 36.27% and 38.32% at 1, 3, 7 and 90 curing ages, respectively. The 28-day flexural strength increased slightly. It is observed that the clay modified cement mortar has lower chloride diffusion coefficient values compared to the plain mortar, and the 28-day DCl of cement mortar decreased by 53.03% with 5% clay. Compared with the controlled sample, the increase in compressive strength and the reduction in chloride diffusion coefficient of the concrete with 5% clay addition is 28.4% and 18.87% respectively. The chloride diffusion coefficient of concrete decreases with the amount of clay addition exponentially. The 28-day compressive strength increases linearly with the chloride diffusion coefficient of the concrete.     

Chloride Transport in Splitting Cracked Concrete at Marine Tidal Zone

The chloride ion transport in concretes with different size of splitting cracks at marine tidal zone is investigated. The splitting crack widths of concrete are about 003 mm, 005 mm, 010 mm, 015 mm and 030 mm. The cracked concrete and sound concrete are placed at marine tidal zone for 30 d, and the chloride ion content in crack zone and perimeter zone of concrete, chloride ion penetration depth and steel bar corrosion area are quantitatively determined. It is shown that splitting crack will be recovered when the concrete is unloaded in split test. And the splitting crack width of concrete should be characterized by the value of displacement sensor when the concrete is unloaded in split test. The chloride ion content of cracked concrete decreases with increased depth, and then gets to remain steady from 10 mm to the inner. The relationship between chloride ion content and crack width in the steady zone can be regressed as the exponential function and the linear function for the crack zone and the perimeter zone of concrete, respectively. Due to away from the crack zone, the influence of splitting crack width on accelerated chloride ion ingression in the perimeter zone is less than that in the crack zone. When the splitting crack width is more than 005 mm, the chloride ion penetration depth in crack plane and in vertical crack plane of concrete is 50 mm and 20 mm, respectively. And the steel corrosion area enlarges with the increasing crack width. And the chloride diffusion coefficient of cracked concrete is closely related to the resistance capacity to chloride penetration of concrete, crack density (matrix width, crack width), and chloride binding capacity of concrete. When the crack density of concrete is less than 70, the chloride diffusion coefficient of cracked concrete increases with decreased crack density linearly. The chloride penetration will accelerate near the crack zone. And the raised splitting crack width will lead to its influence area in concrete increased quickly.     

Microcracking and Chloride Penetration of Concrete under Uniaxial Compression

A non-destructive method of evaluation of specific crack area was used to characterise microcracking in concrete prisms during uniaxial compression loading and unloading. Chloride profiles were also measured after the same concretes were exposed to chloride environment. The relation among microcracking, stress-strength ratio and chloride penetration of concrete were analysed based on the experimental results. Under compressive load, the apparent chloride diffusion coefficient decreases until about one third of the ultimate load. Further increase of compressive load improves the chloride diffusion coefficient again. There is a close link between microcracking and stress-strength ratio. The index of specific crack area can be used to indicate the microcracking and study chloride transport behaviour into concrete under the influence of microcracking.     

Service Life Prediction of Concrete Structures under Chloride Environment

The problems rendered from the conventional time marching, referring to stepwise time marching scheme (STMS) adopted in boundary element method (BEM) for chloride diffusion in concrete structures, were investigated, and a new time marching, referring to initial time marching scheme (ITMS) in BEM, was developed for evaluation of service life of the concrete structures under chloride environment. Results of the numerical examples show that the ITMS-BEM proposed can eliminate domain integral and simplify the computational model, so that the stability in iteration process can be improved, resulting in better efficiency and accuracy, compared with the STMS-BEM. It can also be concluded that the dimensions of the diffusion of chloride can affect the service life of the concrete structure significantly, which should be taken into account in structural design.     

氯离子和盐基阳离子对蔬菜种子萌发及其幼苗生长的影响

为研究蔬菜种子对不同盐基离子胁迫的响应问题,以空心菜、辣椒和菜心种子为实验材料,NaCl、KCl、CaCl₂和MgCl₂4种盐分作为胁迫因子,探究Cl^-及盐基阳离子对蔬菜种子萌发及其幼苗生长的影响。结果表明:(1)在设置的Cl^-浓度范围内,低浓度Cl^-促进空心菜和辣椒种子萌发及其幼苗生长;而高浓度Cl^-却显著抑制空心菜和辣椒种子萌发及其幼苗的生长。菜心种子的萌发及其幼苗生长受盐胁迫的影响表现为,随Cl^-浓度升高抑制作用逐渐增强。说明空心菜和辣椒具有一定的适应盐渍土壤环境的能力,而菜心不适应盐渍土壤环境。(2)相同Cl^-浓度下,不同盐基阳离子对空心菜和辣椒种子萌发的影响差异不显著;对菜心种子萌发的抑制作用表现为K⁺最强,Na⁺最弱。不同盐基阳离子对空心菜幼苗胚根和株高的抑制作用均表现为K+最强,Ca²⁺最弱;对菜心幼苗胚根和株高的抑制作用表现为Mg<...     

带裂缝混凝土氯离子扩散作用试验研究及数值模拟

为了准确评估带裂缝工作混凝土结构的耐久性能,针对氯离子在带裂缝混凝土中的扩散过程进行研究。提出了无损制备裂缝的方法,可高效易行地在混凝土侧面及内部产生裂缝。对带裂缝的水泥砂浆试件进行氯盐溶液浸泡试验,深入研究了单缝和双缝试件中氯离子的扩散作用,修正了氯离子的扩散系数,并对带裂缝混凝土的氯离子扩散过程进行了数值模拟。研究结果表明：氯离子会沿裂缝发展方向及垂直于裂缝发展方向扩散,随着水灰比的减小,砂浆试件的抗氯离子扩散性能明显提高,在一定范围内,当裂缝间距增大,双缝间的氯离子扩散交互影响作用明显减小,ANSYS软件的模拟结果与试验数据吻合良好。     

Influence of Electrochemical Chloride Extraction on the Microstructure of Desalinated Pastes of Concrete

A set of installation is designed for electrochemical chloride extracting circularly on reinforced concrete.The removal efficiency is discussed using saturated Ca(OH)2 solution,saturated Ca(OH)2 0.001 mol/L Li2B4O7 solution and distilled water as electrolyte,respectively.And the microstructure of cement paste is analyzed by scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDS).The results prove that using saturated Ca(OH)2 0.001 mol/L Li2B4O7 solution as electrolyte is more favorable to removing chloride in concrete.Treated by electrochemical desalination,the hydrated product C-S-H resolves and Ca(OH)2 in the concrete increases,too.It deposites on the wall of pores and fills in pores,and then causes the porosity to decrease,while the ratio of Ca /Si of C-S-H increases in the interface between the steel and the concrete.     

Service Life Prediction of Lining Concrete for Jiaozhou Bay Subsea Tunnel

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-12m2/s. And the initial chloride content in concrete was less than 0.35kg/m3. 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-12m2/s to 3.5×10-12m2/s. The predicted service life of lining concrete for Jiaozhou bay subsea tunnel was more than 100 years according to proposed model.     

Study on Mechanism of Diffusion Enhancement of Ions on Surface by Negative Bias

In the paper, the enhancing process of diamond nucleation by negative substrate bias in hot filament CVD system was analyzed. Combining theory related to plasma and collision, the effects of bias on enhancing diffusion of active ions on substrate surface were primarily investigated theoretically, and the relative formulas of diffusion coefficient and diffusive distance with bias were given. The results showed that diffusion coefficient and diffusive distance increased with raising of negative substrate bias.     

柑橘黄龙病入侵与疫情扩散模型研究

为了提示柑橘黄龙病入侵发病扩散规律,评估防控成效,有效控制疫情,2002—2007年在柑橘黄龙病初发生区采用设立自然条件、治虫防病和综合防控三处理类型,监测柑橘黄龙病发生扩散动态,结合面上疫情普查资料,创建柑橘黄龙病自然条件下、治虫防病条件下以及综合防控条件下的疫情扩散模型,分别为：P₁=12.9690N₁-18.10（n=6,r=0.9945**）或P₁=0.2293N12+11.135N₁-14.89（n=6,r=0.9948**）,P₂=7.8857N₂-10.2667（n=6,r=0.9675**）或P2=1.4107N²₂-1.9893N2+2.90（n=7,r=0.9996**）和P3=-0.1398x N₃²+1.1248N3-1.141(n=6,r=0.8396*),结果表明柑橘黄龙病在自然条件下从发病到毁园需要9a时间,单一治虫防病措施难以达到持续控制效果,只有采取综合防控措施,才能达到可持续控制,保障柑橘优势产业持续健康发展。     

Strength-permeability Model of Pervious Cement Concrete

High permeability is an important characteristic of pervious concrete. For the existing permeability testing devices of pervious concrete, the specimen sidewall leakage is serious due to the large numbers of open pores on the surface of specimens. To solve the problem, a new permeability testing method for pervious concrete was developed and a composite sidewall structure with waterproof daub, flexible rubber cushion and rigid sleeve sidewall was proposed. Meanwhile, the strength and permeability of pervious cement concrete are incompatible with a reciprocal relationship. However, limited research has been conducted on the relationship between them. Effects of water-cement ratio (W/C), aggregate-cement ratio and porosity on the properties of pervious concrete, including strength and permeability, were studied. Furthermore, strength-porosity model, permeability-porosity model and strength-permeability model were established. Tests reveal that: a) There is an optimum W/C of pervious concrete, at which strength reaches the maximum; b) The relationship between the strength and W/C shows a downward quadratic curve, and the permeability is proportional to porosity and aggregate-cement ratio; c) The relationship between strength and permeability of pervious cement concrete can be well fitted with the Lorentzian function, and the strength decreases when the permeability increases, but the rate of reduction decreases gradually. The optimum combination of strength and permeability should be determined based on the specific engineering requirements in design.     

Probing and Analysis of Diffusion Model for Technology Creating Something New

Technology Creating something new is spring of technology progress,and diffusion of trasfer of technology is a key stage or symbol of technology progress.Raz Baruch,Liu Wenge and Zhu Jiaxing,respectively,had given or modified receiver state model of technology transfer.This paper firstly explains that S-type model is a model of simple,applicable and higher guasi-degree for technology transfer as well.Next,a long-time model of receiver state of technology(development) in technology diffusion is obtained and Zhu's model is revised.     

A Time-effect Model for Concrete Compressive Strength under Sustained Load

Based on the existed stress-strain curve of concrete prism under one-off short-term load and the concrete creep model, a new time-effect model for evaluation of concrete compressive strength is established through the synthesis of the concrete creep attenuating effect under sustained load and the concrete strength enhancing effect by age, a corresponding computer program has been developed. The computation of related indices and their change rules of several different-grade concrete materials with the program was carried out and the results were compared with experimental data and finite element numerical results reported in the literature, the reasonableness and practicality of the proposed new model have been verified.