Effect of cement type on the resistance of concrete against chloride penetration

In chloride containing environment, chloride permeability of concrete is an important parameter affecting the service life of concrete structures. The primary objective of this experimental study was to study the effect of cement types on the resistance of concrete against chloride penetration for given compressive strength classes. These cements included two different types of granulated blast-furnace slag cement (CEM III/A 32.5N and CEM III/A 42.5N), a sulfate resisting cement (SRC 32.5), and a Portland cement blended with fly ash; all of which compared to an ordinary Portland cement (CEM I 42.5R). For each binder type, four concretes at different strength classes were produced and as a result 20 mixtures were obtained. Rapid chloride ion penetration tests according to ASTM C 1202 were conducted. In addition, electrical resistivity and capillary water absorption tests were carried out. In order to characterize the concrete quality, compressive strength of the specimens were also obtained. The test results clearly demonstrated that the blast-furnace slag cements have the highest resistance against chloride penetration, while the pure Portland cement and sulfate resisting cement have the lowest resistance. Concretes produced with the sulfate resisting cement had substantially higher capillary sorption compared to other mixtures. Test results confirmed the strong relationship between the chloride permeability and electrical resistivity.     

Estimation of chloride permeability of concretes by empirical modeling: Considering effects of cement type,curing condition and age

In this study, effects of cement type, curing condition, and testing age on the chloride permeability of concrete were investigated experimentally. Chloride permeability of concrete was determined through rapid chloride permeability test (RCPT). The research variables included cement type (i.e. plain and four different blended cements), water–cement ratio (0.65 and 0.45), curing condition (uncontrolled, controlled, and wet curing), and testing age (28, 90, and 180 days). Furthermore, based on the experimental results, a neural network (NN) model-based explicit formulation was proposed to predict the chloride permeability of concrete in terms of the water–cement ratio, aggregate–cement ratio, superplasticizer–cement ratio, cement type, curing condition, and testing age. Finally, proposed NN based explicit formulation was verified by using the data gathered from the literature. The test results indicated that the selected experimental parameters had pronounced effects on the chloride permeability of concretes. Besides, it was found that the empirical model developed by using NN seemed to have a high prediction capability of the chloride permeability of concretes.     

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。     

基于电阻率静力触探的海相黏土成因特性分析

土的电阻率是表征土体导电性的基本参数,也是反映土体固有物性的一个综合性指标。众所周知,土的电阻率影响因素较多,因此电阻率随深度的变化可以反映出土体的许多性状。电阻率静力触探(RCPT)作为一种新型的原位测试技术,除可测锥尖阻力、侧壁摩阻力和孔隙水压力以外,还可以同时测试土的电阻率。首先简要介绍了RCPT测试技术,采用电阻率静力触探(RCPT)在连云港海相黏土场地进行了试验,得到土的原位电阻率测试值。结合连云港海相黏土的室内物理化学分析试验,研究了其矿物成分、沉积化学特征,分析了该海相软黏土的电阻率指标与矿物成分、离子含量、胶结特性和氧化环境间的关系。分析表明:基于RCPT测试成果是可以充分反映出连云港海相黏土的成因特性的。     

电阻率静力触探测试技术与分析

 首先,简要回顾土的电阻率理论及影响因素,介绍电阻率静力触探测试技术。然后,在归纳相关文献与基于电阻率静力触探现场试验工作的基础上,对电阻率静力触探所测电阻率与土性变化、探头参数及土的其他特性指标进行对比分析。提供的资料表明,电阻率静力触探作为一种快速、经济、可靠的原位测试工具,在评价土的工程特性和预测一些岩土参数是可行的,尤其适用于软土工程的勘察。最后,讨论应用电阻率静力触探测试技术存在的问题,展望电阻率静力触探的研究与应用前景。     

Water absorption,permeability, and resistance to chloride-ion penetration of lightweight aggregate concrete

This paper presents an experimental study to evaluate effect of cumulative lightweight aggregate (LWA) content (including lightweight sand) in concrete [water/cement ratio (w/c) = 0.38] on its water absorption, water permeability, and resistance to chloride-ion penetration. Rapid chloride penetrability test (ASTM C 1202), rapid migration test (NT Build 492), and salt ponding test (AASHTO T 259) were conducted to evaluate the concrete resistance to chloride-ion penetration. The results were compared with those of a cement paste and a control normal weight aggregate concrete (NWAC) with the same w/c and a NWAC (w/c = 0.54) with 28-day compressive strength similar to some of the lightweight aggregate concrete (LWAC). Results indicate that although the total charge passed, migration coefficient, and diffusion coefficient of the LWAC were not significantly different from those of NWAC with the same w/c of 0.38, resistance of the LWAC to chloride penetration decreased with increase in the cumulative LWA content in the concretes. The water penetration depth under pressure and water sorptivity showed, in general, similar trends. The LWAC with only coarse LWA had similar water sorptivity, water permeability coefficient, and resistance to chloride-ion penetration compared to NWAC with similar w/c. The LWAC had lower water sorptivity, water permeability and higher resistance to chloride-ion penetration than the NWAC with similar 28-day strength but higher w/c. Both the NWAC and LWAC had lower sorptivity and higher resistance to chloride-ion penetration than the cement paste with similar w/c.     

Diffusion characteristics of OPC concrete of various grades under accelerated test conditions

Concrete durability mainly depends on the diffusion characteristics of concrete. Chloride ion diffusion is one of the main parameters affecting the durability of Reinforced Concrete Structures. The chloride ion penetration is determined under accelerated diffusion test condition with 12 V (Norwegian method). Depending upon the concrete quality, the diffusion test duration will vary. Generally, high grade concrete will have longer test duration as compared to lower grade concrete. In this paper, OPC concrete of M30, M40, M50, M60 and M75 grades were studied for diffusion properties under different voltages 12, 20, 30, 40, 50 and 60 V. A comparative study was made with standard Rapid Chloride Permeability Test with respective voltages. It has been observed that chloride profile and diffusion coefficient were high in low grade OPC concrete and low for high grade concrete. Minimum test duration was observed at higher voltages. With the increased voltage, the chloride profile and diffusion coefficient were found to be high.     

水压法评价混凝土渗透性的适用性研究

本文应用透水法政进快速Cl^-渗透法测定了不同强度等级、不同配合比混凝土试件的渗透性。结果表明透水法未考虑实际工程中混凝土所受的约束作用,其适用性对强度等级的依赖性很强。     

混凝土抗渗性能试验方法概述

混凝土的抗渗性能是混凝土耐久性的重要指标之一,试验主要依据普通混凝土和水工混凝土标准中的方法。本文对比分析了国内外混凝土抗渗性的试验方法,希望对相关研究中试验方法的选择、试验方法标准的修订有所帮助。     

掺粉煤灰和引气剂混凝土氯离子渗透性能研究

研究了普通混凝土、粉煤灰混凝土、引气混凝土和粉煤灰引气混凝土等四种类型混凝土的氯离子渗透性能,结果表明:混凝土的渗透系数与氯离子渗透深度有相关性,它们之间的关系可用一元幂函数表示。     

Proposed method for calculating water penetration test parameters of wall assemblies as applied to Istanbul, Turkey

Water penetration of a building envelope assembly is typically assessed on the basis of the degree of watertightness (i.e. lack of water ingress) of the components of the assembly when subjected to simulated driving rain conditions. Test standards provide the magnitude and extent of these test conditions as suggested by the test parameters, i.e. the water spray rates and pressure differences and the dwell time over which these are to be applied. Such conditions would presume to simulate driving rain and wind conditions of locations spread over a broad geographical area. For example, the water spray rate suggested for use in watertightness performance tests in EN 12155—Curtain walling–watertightness–laboratory test under static pressure—is considered appropriate for simulating driving rain and wind conditions for locations across Europe. However, test parameters should be based on the expected driving rain intensities and wind pressures that are likely to occur for a specific climate and a given return period. It might also be based on the building type (e.g. high or low-rise building), or even on the location on the building facade. Hence, a method is required for calculating water penetration test parameters for specific buildings located in a specific climate. The purpose of this paper is to propose a method for calculating water penetration test parameters. A survey of existing methods is first provided that focuses on the quantification of driving rain on buildings and thereafter, calculation of water penetration test parameters. The merits and drawbacks of these methods are then discussed. Based on this review, a method for calculating test parameters is proposed and is applied to developing water penetration test parameters for Istanbul, Turkey. A comparison of test parameters calculated from the proposed method with those given in existing Turkish standards TS EN 12155–Curtain walling–watertightness–laboratory test under static pressure—and TS ENV 13050—Curtain walling–watertightness–laboratory test under dynamic condition of air pressure and water spray—related to Istanbul, indicated that the water spray rate given in the TS standards is higher than spray rates calculated from the proposed method for return periods of 5, 10 and 30 years.     

基于不同贯入速率砂土地基中静压敞口混凝土管桩试验研究

贯入速率对静压敞口混凝土管桩沉贯及承载力特性具有重要影响。通过砂土地基中静压敞口混凝土管桩室内模型试验，分别对不同贯入速率下模型桩土塞特性、压桩力及极限承载力变化进行研究。结果表明，模型桩贯入速率由2.0mm/min增大至3.0、4.0mm/min时，土塞高度分别降低了12.8%、27.2%，土塞率降低幅值分别为12.9%、27.2%。不同贯入速率沉桩结束后，模型桩土塞增长率分别为35.4%、23.6%及19.8%；相比于4.0mm/min贯入速率，贯入速率2.0mm/min及3.0mm/min下模型桩最终压桩力增长幅度分别为92.6%及 25.1%，极限承载力增长幅值分别为77.8%及4.5%，这主要是由于贯入过程中土塞特性差异导致的内壁摩阻力不同所引起的。研究成果可为砂土地基中敞口混凝土管桩沉桩性状及极限承载力研究提供理论依据。     

Influence of fly ash fineness on the chloride penetration of concrete

In this paper, the resistance to chloride penetration of concrete containing fly ash of various finenesses was examined. Three different fly ash finenesses viz., original fly ash, 45% fine portion and 10% fine portion fly ashes were used for the study. Chloride resistance of concretes was evaluated using the measurement of the Coulomb charge as per ASTM C1202 and by determination of chloride ingress after different periods of exposure to 3% NaCl solution in full immersion and partial immersion modes. From the tests, it is found that the resistance to chloride penetration of concrete depends on the fineness of fly ash. The rapid chloride permeability test (ASTM C1202) clearly indicates that the Coulomb charge of concrete at the age of 28 days is significantly reduced with the incorporation of fly ash. The decrease is promoted with an increase in fly ash fineness. The immersion of cut cylinders in the 3% NaCl solution for 3 and 6 months confirm that the resistance of the chloride penetration of concrete increases with an incorporation with fly ash and with an increase in the fly ash fineness.     

混凝土海洋平台氯离子侵蚀试验研究

氯离子向混凝土内部侵蚀是混凝土海洋平台结构耐久性降低的一个主要原因。而高性能混凝土特点是低水胶比及添加活性矿物集料。从而达到改善耐久性能的目的。本文对不同水胶比及掺加粉煤灰、硅灰的高性能混凝土的氯离子扩散系数进行了试验研究，分析了水胶比及粉煤灰和硅灰等活性集料对海洋混凝土结构抵抗氯离子侵蚀的耐久性能的影响，为混凝土海洋平台结构的耐久性设计与评估提供参考。     

渗透结晶材料和粉煤灰对海工混凝土氯离子渗透性能的影响研究

粉煤灰和渗透结晶材料对海工混凝土抗氯离子渗透性能有很大影响。采用了GB/T50082—2009中的快速氯离子迁移系数法和电通量法对海水环境下掺有粉煤灰和水泥基渗透结晶材料的混凝土进行测试。结果表明:在一定掺量范围内,随着粉煤灰和水泥基结晶材料掺量的增加,海水环境下混凝土抗氯离子渗透性能有显著提高。     

非饱和开裂混凝土中水分运移研究

根据双重孔隙介质模型将开裂混凝土视为由完好混凝土和裂缝组成的复合孔隙材料,基于非饱和混凝土的水分运动方程和裂隙渗流的立方定律提出非饱和开裂混凝土中的水分运动方程,同时采用渗水装置对预制裂缝混凝土试块进行渗水试验,研究混凝土初始饱和度、水胶比和裂缝宽度对渗水深度的影响;采用TOUGH 2软件数值分析开裂混凝土中饱和度和水分流速的变化,根据平均流速计算渗水深度并与试验结果比较.研究发现:混凝土初始饱和度越小、裂缝宽度越大,则渗水深度越大,且渗水深度增长先快后慢,反映了混凝土基质势是开裂混凝土中水分运移的驱动因素;裂缝宽度与混凝土渗透性正相关;水分入渗开裂混凝土后流速差和平均流速随时间延长逐渐降低;采用平均流速计算的渗水深度能更好地反映渗水试验中渗水深度的变化趋势.     

环境岩土工程研究进展

该文总结了近年来国内外环境岩土工程领域的研究进展,主要包括：①环境岩土工程调查与评价方法。重点介绍了电阻率静力触探探头、与静力触探结合的传感器薄膜界面探头、光纤光学化学传感器、X荧光分析仪等在场地污染物分布和污染程度识别技术;综述了土工离心技术应用于土体及地下水中污染物运移,及污染场地修复的研究现状;总结了污染场地分类方法和风险评价模型。②城市固体废物填埋技术。介绍了固废填埋场多场相互作用的主要耦合模型理论,总结了固废生化反应-骨架变形-水气运移-溶质迁移模型及应用;提出了填埋场污防污屏障服役寿命的定量评价方法。③工业固体废弃物资源化再利用技术。介绍了废弃电石渣和木质素加固过湿土、粉土路基的性能和工程应用;总结了固化污泥和淤泥技术的研究现状。④工业污染地基处理技术。总结了工业污染场地主要修复技术;介绍了固化污染土稳定技术、新型固化剂和稳定剂的研发进展;总结了常见竖向隔离墙技术,介绍了土-膨润土系竖向隔离墙长期防渗防污性能的研究进展;介绍了曝气法处理有机污染地下水技术的研究进展。     

静力触探确定承载力在铁路地质勘察中的应用

以某铁路一段松软地基为例,讨论了在铁路工程地质勘察过程中,以静力触探数据为依据提供岩土层容许承载力及其与钻探试验统计结果的对比分析与应用,结果表明,使用静力触探方法提供的岩土层容许承载力满足设计要求。     

海底隧道非饱和混凝土中水分渗透研究

引入相对渗透率(饱和程度)kr描述非饱和与饱和状态的区别。基于Darcy定律考虑压力作用的方程,建立混凝土内各位置处压力及渗透深度随时间变化的理论模型。同时自制压力控制装置,研究压力水头下水分在非饱和混凝土中的迁移特性。对各种试验条件下的水分渗透深度进行理论分析,并同时与试验值进行比较。理论值与试验值能很好地吻合。得到渗透深度随时间的增加总是变大,且在后期的增加幅度小于前期。压力对水分渗透深度有促进作用,强度等级与水分渗透深度呈反比,而水灰比则与渗透深度呈正比。各种因素的讨论过程中,理论值与试验值都能很好的吻合。     

水泥土电阻率特性及其在粉喷桩工程中的应用研究

通过水泥土电阻率正交试验研究分析，得出影响水泥土电阻率的主要因素依次为含盐量、水泥掺入比、天然含水量、粉煤灰含量、石灰含量；同时进行了水泥土电阻率和喷粉搅拌桩身抗压强度、芯样力学性状和喷粉搅拌桩标贯击数的对比研究，探索了电阻率法在喷粉搅拌桩工程质量检测中的应用。