Effect of Curing Age on Chloride Diffusion Coefficient of Recycled Aggregate Concrete Subjected to Compressive Stresses

The effect of curing age on chloride diffusion coefficient of recycled aggregate concrete subjected to different compressive stresses was investigated.A compression loading setup was both designed and fabricated.The chloride diffusion coefficients of recycled aggregate concrete under compressive stresses were measured by the rapid chloride ion migration(RCM)method.The experimental results show that the chloride diffusion coefficients of recycled aggregate concrete(RAC)under different compressive stress ratios generally decrease with the increase of curing age.For RAC subjected to the same compressive stress ratios,the chloride diffusion coefficients approximately have power functions with curing ages and the relationship models are proposed.Moreover,the influence of curing age on chloride diffusion coefficient firstly decreases and then increases as the compressive stress ratio increases.

M-T Scheme for Predicting Effective Diffusion Coefficient of Chloride Ions in Cement-based Materials

To investigate the transport characteristics of chloride ions in cement-based materials, the Mori-Tanaka (M-T) prediction scheme of the effective diffusion coefficient in composites containing single-phase and multi-phase inclusions is systematically deduced based on the theory of composite mechanics and porous medium. The volume fraction, morphology and distribution of aggregates, as well as the interfacial transition zone (ITZ) are fully taken into consideration in this proposed model. The results show that the algorithm of M-T prediction scheme with high accuracy is relatively simple.

Convolutional Neural Network-Based Regression for Predicting the Chloride Ion Diffusion Coefficient of Concrete

The durability performance of reinforced concrete(RC)building structures is significantly affected by the corrosion of the steel reinforcement due to chloride penetration,thus,the chloride ion diffusion coefficient should be investigated through experiments or theoretical equations to assess the durability of an RC structure.This study aims to predict the chloride ion diffusion coefficient of concrete,a heterogeneous material.A convolutional neural network(CNN)-based regression model that learns the condition of the concrete surface through deep learning,is developed to efficiently obtain the chloride ion diffusion coefficient.For the model implementation to determine the chloride ion diffusion coefficient,concrete mixes with w/c ratios of 0.33,0.40,0.46,0.50,0.62,and 0.68,are cured for 28 days;subsequently,the surface image data of the specimens are collected.Finally,the proposed model predicts the chloride ion diffusion coefficient using the concrete surface image data and exhibits an error of approximately 1.5E−12 m^(2)/s.The results suggest the applicability of proposed model to the field of facility maintenance for estimating the chloride ion diffusion coefficient of concrete using images.

Calculation of ion diffusion coefficient related to concrete deterioration based on Debye-Hückel-Onsager theory

This paper applies the Debye-Hückel-Onsager electrolyte solution theory to investigate the diffusivity of ions in concrete pore solutions.First,a model of the diffusion coefficient associated with the ionic species,solution concentration and ambient temperature is proposed in the saturated concrete.Secondly,as an example,the effects of sodium chloride solution concentration,which are associated with influencing factors such as the ionic cloud radius,electrophoresis and relaxation,on the chloride diffusion coefficient are analyzed.It is found that the diffusion coefficient decreases with the increase in solution concentration,and the electrophoresis and ionic cloud radius are two important factors influencing the ionic diffusivity.Finally,the experiments,in which the chloride diffusion coefficients in specimens under different water-cement ratios are measured by the rapid chloride migration（RCM）method,are carried out to validate the effectiveness of the proposed model,and the results indicate that there is a generally reasonable agreement between the experimental and the proposed model results.

Effect of Fly Ash on Frost-Resistance and Chloride Ions Diffusion Properties of Marine Concrete

It is necessary to pay more attention to the durability of concrete undergoing freeze-thaw cycles and seawater attack simultaneously.Investigated are the effects of water-binder ratio,fly ash（FA）contents and air-entraining agent on resistance to frost and chloride diffusion of marine concrete blended with FA in natural seawater.The results show that fly ash does not improve the frost resistance of concrete but can improve its resistance to chloride diffusion by addition of less than 30%.The resistance to frost and chloride diffusion of FA concrete can be improved with the decrease of water-binder ratio,and FA may improve both of them simultaneously only being mixed with air-entraining agent.A ratio（named as R）of the frost-resisting durability factor to chloride diffusion coefficient can be used to evaluate the durability of marine concrete.Scanning electron microscope（SEM）analyses are consistent with the evaluations by the value of R.

Diffusion of Chloride Ions in Soils:I.Influences of Soil Moisture, Bulk Density and Temperature

Diffusion coefficients of chloride ions in four soils of different texture with varying effective moisture content and varying bulk density from 1.1 to 1.6 g cm3 under three different temperatures were determined by the diffusion-cell method using 36Cl-labelled CaCl2 solution. The results showed that activation energy decreased with water content, which indicated that the threshold for diffusion was lower at a higher soil moisture rate. Therefore, the diffusion coefficient (D) of chloride ions in soil increased consistently with soil moisture. Although a near linear increase in the diffusion coefficient with increasing soil moisture or bulk density in all the soils was observed, the increase rate in different soils was not the same. The D value increased with temperature, and with temperature increased by 10℃ in the range from 5 "C to 45℃ theD valve increased by 10%～30%, averaging about 20%.

Durability of sea-sand containing concrete:Effects of chloride ion penetration

This paper describes an orthogonal experiment on the effect of water/cement ratio,water consumption per cubic meter,curing time,and type of sand on the response＂resistance to chloride ion penetration＂.A sea-sand containing concrete was used for the trials.An analysis of chloride ion diffusion coefficients at different factor levels was performed.A predictive model of chloride ion diffusion in concrete is developed through regression analysis.The experimental results show that when the water/cement ratio varies from 0.45 to 0.60,and the water consumption per cubic meter varies from 185 to 215 kg,and the curing time varies from 30 to 180 d then the size of the effects fall in the order（most significant first）： curing time,type of sand,water consumption per cubic meter,and water/cement ratio.Chloride ion penetration is reduced,and better durability of the concrete is observed,with longer curing times,less water consumption per cubic meter,and a smaller water/cement ratio.

混凝土暴露试验的稳定时长与试验分析方法

混凝土自然暴露试验通常用于研究混凝土的氯离子扩散系数,但需要选择合适的分析方法,并确定稳定暴露时长。为此,首先系统研究混凝土的氯离子瞬时扩散和平均扩散理论,明确扩散方程中不同参数的时变特性,揭示了瞬时扩散解析解在分析混凝土中氯离子扩散过程和浓度分布时与平均扩散解析解等价。然后,引入随机数模拟混凝土取样误差,利用蒙特卡洛法分析氯盐环境下混凝土暴露时长、取样误差以及不同回归分析方法对扩散系数计算结果的影响,研究表明瞬时扩散解用于混凝土自然暴露试验分析时容易受到参数迭代初值的影响,导致初始扩散系数计算结果不稳定,而平均扩散解可以避免该问题,因而平均扩散解更适合于混凝土自然暴露试验数据的回归分析。在此基础上,研究确定了不同取样误差下的混凝土稳定暴露时长。最后,通过工程实例分析验证了回归分析方法以及稳定暴露时长在氯盐环境下混凝土自然暴露试验数据分析中的合理性和必要性。

开裂混凝土中氯离子等效扩散系数计算方法

氯离子侵蚀对钢筋混凝土结构有严重的劣化作用,混凝土中的裂缝为氯离子的快速扩散提供了通道,进而加快了结构力学性能的失效速度。现有研究多集中于单一裂缝特征因素对氯离子扩散系数的影响,根据试验结果给出的拟合公式具有局限性。结合机器视觉技术提取和量化多个裂缝特征因素,构建考虑裂缝密度、裂缝内界面粗糙度和裂缝取向度叠加影响的代表性单元体积(REV)模型,并计算其等效扩散系数,将已有研究的试验结果与基于REV模型的计算结果进行对比。结果表明:不同盐冻条件下的平均相对误差为1.6%,完成28次盐冻后不同初始裂缝条件下的平均相对误差为2.9%,计算结果与试验结果较为吻合,表明提出的开裂混凝土中氯离子等效扩散系数具有较好的可靠性。

钢纤维和碳纳米管对超高性能混凝土抗氯离子渗透性能的影响

碳纳米管的掺入对超高性能混凝土(UHPC)的抗氯离子渗透性能的影响尚不清晰,且很少有涉及加载对UHPC抗氯离子渗透性能影响的研究。因此,通过氯离子扩散系数测试法测定氯离子扩散系数,盐溶液浸泡下测定不同深度处氯离子浓度,观察微观结构等试验方法来探究碳纳米管和加载对UHPC抗氯离子渗透性能的影响。结果表明:加载造成的损伤会降低UHPC的抗氯离子渗透性能;在不同的加载程度下,不同浓度的碳纳米管对UHPC的抗氯离子渗透性能的影响是有区别的;碳纳米管既起到了填充孔隙的作用,又起到了促进钢纤维电化学腐蚀的作用。

磷酸钒锂/碳复合材料在锂离子电池中的电化学性能及电极反应动力学研究

相比于溶胶-凝胶法制备的Li_(3)V_(2)(PO_(4))_(3)/C(LVP/C-S),采用水热超声辅助流变相法结合溶液沉积法制备的Li_(3)V_(2)(PO_(4))_(3)/C(LVP/C-R)复合正极材料具有更优异的电化学性能。通过XRD、SEM和Raman光谱仪等对合成材料进行表征。将合成材料作为锂离子电池正极组装半电池进行倍率和循环性能测试,同时通过循环伏安法、电化学阻抗以及恒流间歇滴定技术分析电极反应动力学。结果表明,水热超声辅助流变相法合成的Li_(3)V_(2)(PO_(4))_(3)(LVP-R)通过溶液沉积法包覆碳层后,晶面间距增大,粒径更小,导电性、振实密度增大,分散性明显提升。这有利于Li^(+)在正极材料中嵌入/脱出,以及缩短Li^(+)的扩散路径,从而促使锂离子电池的倍率性能、库仑效率和循环稳定性提高。LVP/C-R作为锂离子电池正极材料,在0.1 C电流密度下表现出较高的初始放电比容量(160.12 mA·h/g),且在1 C倍率下循环200圈后放电容量保持率为89.16%,远高于LVP/C-S。此外,相比于LVP/C-S和LVP-R,LVP/C-R在锂离子电池中具有更大的Li^(+)表观扩散系数且动力学性能更优。

玄武岩纤维混凝土力学性能及氯盐侵蚀行为

为探究氯盐侵蚀对玄武岩纤维混凝土力学性能的影响及氯盐在混凝土中的侵蚀行为,以抗压强度、劈裂抗拉强度、氯离子沉积量为表征手段进行盐雾侵蚀试验,并根据Fick第二定律计算得到不同侵蚀龄期下氯离子扩散系数。结果表明:混凝土强度在氯盐侵蚀过程中呈现先上升后下降的趋势;通过氯盐侵蚀的玄武岩纤维与普通混凝土相比,能有效提高混凝土的抗压及劈裂抗拉强度,降低混凝土劣化速率;在相同深度及侵蚀龄期下玄武岩纤维混凝土氯离子含量均低于普通混凝土;此外,氯离子扩散系数随着侵蚀龄期的增加而降低,且相同龄期下玄武岩纤维混凝土氯离子扩散系数均低于普通混凝土。

粉煤灰基地聚物混凝土的抗氯盐侵蚀性能研究

对比研究了氯盐侵蚀0~360 d内,粉煤灰基地聚物混凝土(以下简称FABGC)与普通混凝土(以下简称OPC)的抗压强度、质量损失率、氯离子含量、氯离子扩散系数、微观结构。结果表明:各侵蚀龄期下,OPC的抗压强度、质量损失率、氯离子含量基本均高于FABGC;随着侵蚀龄期的增加,FABGC和OPC的抗压强度、氯离子扩散系数基本呈下降趋势,质量损失率、氯离子含量呈增大趋势;当侵蚀龄期达到60 d后,OPC的抗压强度损失率、质量损失率和氯离子扩散系数均明显高于FABGC;随着侵蚀深度的增加,FABGC与OPC氯离子含量逐渐降低;与FABGC相比,未受氯盐侵蚀时,OPC的微观结构更致密,但受氯盐侵蚀后,OPC的微观结构劣化速率较快。

成型方式对RCM法氯离子扩散系数的影响

为降低标准试模对水泥混凝土抗氯离子渗透试验方法(RCM法)氯离子扩散系数的影响,更有效、真实地反映工程实体耐久性,确保混凝土质量及其耐久性在整个结构服役期内的性能,本文基于不同成型方式对比试验,推荐使用水泥混凝土立方体试模(150 mm×150 mm×150 mm)成型抗氯离子扩散系数试件,以降低成型方式对RCM法氯离子扩散系数的影响。

西北地区强腐蚀环境高耐久性纤维增强混凝土技术研究

针对西北地区核电工程恶劣环境,采用镁质抗蚀增强剂、水化热抑制剂、高性能复合矿物掺合料等制备了聚丙烯纤维增强C40高性能混凝土,研究了镁质抗蚀增强剂和水化热抑制剂对混凝土的工作性、力学性能和耐久性能的影响,并基于试验结果对纤维的最佳掺量进行了优选。结果表明:掺加水化热抑制剂和镁质抗蚀增强剂的混凝土具有良好的工作性,掺入不同掺量的纤维,混凝土的出机坍落度仍保持在160 mm以上,含气量在2.7%~4.2%之间;掺加水化热抑制剂和镁质抗蚀增强剂,混凝土的3 d抗压强度降低,7 d、28 d抗压强度提高,而随着纤维掺量的增加,混凝土的抗压强度提高;水化热抑制剂和镁质抗蚀增强剂的掺入可有效提高混凝土的抗氯离子渗透性能,掺入适量纤维可显著提高混凝土的抗氯离子渗透性能;水化热抑制剂和镁质抗蚀增强剂的掺入可提高混凝土的抗硫酸盐侵蚀性能,适量纤维的掺入也可提高混凝土的抗硫酸盐侵蚀性能;综合考虑工作性、力学性能和耐久性能,纤维推荐掺量为1.0 kg/m^(3)。

再生微粉对混凝土抗氯离子渗透性能的影响

研究了分别单掺与复掺再生混凝土粉(RCP)、再生砖粉(RBP)对混凝土抗氯离子渗透性能的影响,并建立了氯离子扩散系数和电通量之间的关系式。结果表明:单掺RCP或RBP时,随着其掺量从0增至30%,试件的电通量和氯离子扩散系数均先减小后增大,说明抗氯离子渗透性能先增强后减弱,RCP和RBP的最佳掺量均为10%;复掺RCP和RBP时,随着RBP占比的增加,试件的电通量和氯离子扩散系数均先减小后增大,最佳m_(RBP)∶m_(RCP)为1∶1;掺再生微粉混凝土的氯离子扩散系数和电通量之间具有良好的线性关系。

基于包覆性钡盐的混凝土防腐剂性能研究

采用碱性纳米二氧化硅分散液对钡盐进行包覆性处理,基于三种钡盐(氢氧化钡、碳酸钡、硝酸钡)配制盐卤腐蚀抑制剂,与未包覆钡盐类盐卤腐蚀抑制剂进行对比,研究包覆性钡盐盐卤腐蚀抑制剂的抗蚀系数、28d抗压强度比和氯离子扩散系数。结果表明,包覆性钡盐盐卤腐蚀抑制剂可显著提高混凝土的耐蚀性能,其90d抗蚀系数高达1.189,28d抗压强度比高达111.11%,氯离子扩散系数低至2.50×10^(-12)m^(2)/s。

氯盐全浸泡下水泥基复合材料的抗腐蚀性能

为研究工程水泥基复合材料(ECC)的抗氯离子腐蚀性能,设计了ECC和海工混凝土(MC)的氯盐全浸泡腐蚀试验,分析了腐蚀龄期对ECC的氯离子扩散深度、浓度和扩散系数的影响。研究发现ECC的氯盐腐蚀主要发生在早期;腐蚀20 d后的ECC氯离子侵蚀深度趋于稳定,MC的氯离子侵蚀深度随着腐蚀龄期的增长而持续增加。采用Matlab和Origin软件对试验结果进行拟合,得到腐蚀环境下的ECC表层氯离子浓度边界条件和等效表观氯离子扩散系数计算模型,为预测氯离子腐蚀下的ECC寿命提供了理论依据。

基于改进点源扩散模型的电极极差电位研究

本文建立点源扩散模型,研究了电极电位的变化规律,将圆柱体Ag/AgCl电极等效为点源模型,通过Fick定律建立Cl-浓度扩散方程,利用0阶贝塞尔函数得到了浓度与时间、距离的函数关系,通过浓度依赖动力学方程建立浓度、温度与电极电位的表达式,利用数值计算分析了不同浓度、温度、时间对电极电位的影响,并与传统的互补误差函数模型作对比,在点源扩散模型的基础上,将氯离子扩散系数视为变量的同时,引入其对时间、温度的影响。利用数值计算分析了不同浓度、温度、时间对电极电位的影响,结果表明:改进的点源模型所推导的极差电位精度更高。

Corrosion life of artificial reef under natural seawater conditions

Corrosion of steel bars with chloride salt erosion is one of the main reasons for the deterioration of the performance of reinforced concrete structures.The key to the service life of concrete members is the transport rate of chloride ions and the time for rusting of steel bars.In this paper,the artificial reef concrete member is taken as the research object,and the diffusion coefficient of seawater chloride ion in C30,C35 and steel slag composite artificial reef concrete is analyzed.The critical chloride ion concentration of steel corrosion in concrete is used as the boundary condition for life prediction.The chloride ion diffusion model predicts the corrosion life of C30,C35 and steel slag composite artificial reefs in seawater.The results show that the diffusion law of chloride ions in concrete artificial reefs basically meets Fick's second law.The corrosion life of C30,C35 and steel slag composite concrete reefs was calculated by the model to be 51.6,54.8 and 56.8 years,respectively.