氯离子含量对混凝土硫酸盐腐蚀程度的影响研究

通过实验室完全浸泡和加大腐蚀溶液浓度的方法来加速混凝土的硫酸盐腐蚀.腐蚀溶液采用10%硫酸钠加入不同浓度的氯化钠,并以清水溶液为对比,定期测试各溶液中混凝土的立方体抗压强度,通过腐蚀后强度的变化来计算腐蚀层厚度和强度退化率,从而反映出混凝土的腐蚀程度.试验表明氯离子的存在明显的降低了混凝土硫酸盐腐蚀的程度,并且在复合溶液中随着氯离子含量的增大,混凝土受硫酸盐腐蚀程度逐渐减小.最后通过对混凝土微观结构的检测和元素分布的分析,证明了氯离子的存在影响了硫酸根离子与混凝土水化产物的反应,从而能够减轻混凝土受硫酸盐腐蚀的破坏程度.     

盐渍土环境掺粉煤灰、矿粉混凝土的硫酸盐腐蚀

不同于以往混凝土硫酸盐侵蚀研究中主要采取一定浓度的硫酸盐溶液浸泡,而改用含有一定浓度硫酸盐的土壤来模拟盐渍土环境.该文研究硫酸盐溶液干湿循环作用下半插入盐渍土中单掺粉煤灰、矿粉和对比普通混凝土试件的硫酸盐腐蚀情况,并随腐蚀发展进程对试件土上和土下区域混凝土的超声声速及宏、微观腐蚀形貌和腐蚀产物进行了检测.研究结果表明盐渍土环境混凝土土上和土下区域的硫酸盐腐蚀机理和腐蚀速度存在明显不同;遭受干湿循环的混凝土土上区以物理结晶腐蚀为主,腐蚀产物为硫酸盐晶体;埋设于盐渍土中的混凝土土下区以化学腐蚀为主,腐蚀产物为钙矾石和石膏;对应不同的混凝土硫酸盐腐蚀机理,粉煤灰和矿粉所发挥的作用各自不同,即粉煤灰的掺入不利于混凝土抗硫酸盐物理结晶腐蚀,而矿粉的掺入不利于混凝土抗硫酸盐化学腐蚀;对同一种混凝土,土上区的硫酸盐腐蚀速度明显高于土下区.     

掺石灰石粉水泥胶砂低温硫酸盐侵蚀破坏与机理

目的 研究混凝土碳硫硅酸钙侵蚀(TSA)破坏机理,以提高混凝土耐久性.方法 测试水泥胶砂在(5±1)℃,且质量分数为2%的MgSO4溶液中浸泡1a期间的外观与强度变化,利用X-射线衍射仪.傅里叶红外光谱仪,扫描电子显微镜分析了浸泡1a各砂浆的矿物成分与微观结构.结果 在低温硫酸盐环境下,少量石灰石粉的掺入可改善水泥砂浆的抗侵蚀性能,而掺量较多时反而会加速砂浆的侵蚀破坏过程.在低温硫酸盐溶液中浸泡1 a后,纯水泥砂浆的破坏形式为表面开裂、脱落,在表层砂浆中生成了大量的钙矾石和石膏晶体;掺30%石灰石粉的砂浆主要表现为表面软化、浆化,腐蚀产物以碳硫硅酸钙和石膏晶体为主,为典型的碳硫硅酸钙侵蚀(TSA)破坏.结论 使用大量石灰石填料或骨料时,水泥基材料在低温硫酸盐环境下可能发生以碳硫硅酸钙为主要腐蚀产物的TSA破坏.     

超细矿粉对混凝土界面区硫酸盐腐蚀的影响

为了研究骨料与水泥石界面区(ITZ)的组成及结构对混凝土抗硫酸盐腐蚀性能的影响,利用紫外分光光度计绘制了硫酸钠溶液浸泡混凝土试样的SO2-4浸入浓度/深度曲线,并辅以扫描电镜(SEM)和电子探针能谱(EDS)等对ITZ进行观测;同时利用XRD定量分析研究了混凝土本体相和界面相的水化产物富集的差异.结果表明:Ca(OH)2、钙矾石(AFt)等晶体富集于硫酸钠溶液浸泡后试样的ITZ,引起AFt二次结晶型的硫酸盐腐蚀破坏.在适量石膏的激发下,掺入超细矿粉(GGBS)可阻止AFt转变成单硫型水化硫铝酸钙(AFm),减少AFt二次结晶的生成,明显提高抗硫酸盐侵蚀能力,试样的同深度硫酸根浓度最低,抗硫酸盐侵蚀性能最好.     

海洋环境下混凝土的硫酸盐腐蚀机理

海水中存在的硫酸根离子传输至混凝土内部将导致其腐蚀破坏。针对矿粉掺量0~65%的C40引气混凝土进行海洋潮汐区、大气区和水下区腐蚀1~2 a,测试其水溶和酸溶硫酸根离子浓度分布;分析水泥净浆中的腐蚀产物类型及含量。试验结果表明：海洋不同腐蚀区带混凝土中硫酸根离子传输量及传输深度排序为：潮汐区 > 水下区 > 大气区。混凝土中反应硫酸根离子与总硫酸根离子的关系服从线性函数分布,反应量占总硫酸根离子量的90%以上,反应的硫酸根离子量随腐蚀龄期增加而增加。海洋潮汐区和水下区生成的腐蚀产物量高于大气区,主要是钙矾石和石膏;海洋大气区暴露混凝土的腐蚀产物为钙矾石。对于P.I.52.5水泥制备的C40混凝土而言,掺加65%的矿粉有助于提升混凝土抗海洋硫酸根离子侵蚀能力。     

凝灰岩机制砂混凝土抗低温硫酸盐侵蚀性

为了研究低温环境下凝灰岩机制砂对混凝土抗硫酸盐侵蚀性的影响,结合腐蚀介质及低温环境特点,采用10±1℃的硫酸钠/硫酸镁复合溶液模拟服役环境;利用电脉冲加速腐蚀介质迁移,对比分析腐蚀前、后试样的强度变化、腐蚀产物的物相等.结果表明:凝灰岩机制砂拌制试件比河砂拌制试件更容易受到低温硫酸盐侵蚀破坏;一定掺量的氢氧化钡可改善试件的抗硫酸盐侵蚀能力,但当掺量高于4%时,改善作用开始降低;低温硫酸盐侵蚀后机制砂拌制试件的腐蚀物以碳硫硅酸钙为主,河砂拌制试件的腐蚀物以钙矾石为主.从凝灰岩石粉的物相及机制砂混凝土孔结构探讨抗低温硫酸盐侵蚀能力弱化原因.该研究可以为硫酸盐区划环境下机制砂混凝土的耐久性设计提供一定参考.     

氯盐对灌注桩混凝土硫酸盐腐蚀规律的影响

复杂盐渍环境多种离子侵蚀灌注桩混凝土等现浇混凝土结构的腐蚀规律研究较少.文中对未经标准养护的混凝土试块进行全浸泡侵蚀试验,模拟混凝土灌注桩受硫酸盐及氯盐共同作用的侵蚀过程,探讨氯盐对现浇混凝土硫酸盐腐蚀规律的影响.结果发现,混凝土试块受侵蚀的前7 d,其抗压耐蚀系数均高于1,之后呈现先增大后减小的趋势;侵入混凝土试块中的硫酸根离子随着侵入深度的增加逐渐减小,并且越向深处侵入混凝土内部的硫酸根离子含量衰减速度越快;氯离子的存在抑制了硫酸根离子在混凝土内部的扩散,且加速了硫酸根离子随深度的衰减速度.由于氯离子的先期反应阻碍了石膏型硫酸盐侵蚀发生,从而减少了硫酸盐对于混凝土侵蚀所造成的强度损失,氯盐含量低时效果最明显.     

硫酸盐腐蚀环境下CFRP-混凝土界面性能研究

通过10%硫酸钠溶液加速劣化试验,研究CFRP-混凝土粘结界面的力学性能,包括混凝土圆柱体的抗压强度、 CFRP片材的拉伸强度、混凝土的抗压强度及弹性模量.通过CFRP-混凝土粘结界面的单剪试验,研究硫酸钠溶液浸泡对CFRP与混凝土剪切粘结性能的影响,采用SEM和XRF等从微观层面探讨硫酸盐腐蚀机理.研究表明,硫酸钠溶液浸泡对CFRP的拉伸强度无影响;混凝土会受到硫酸盐的侵蚀,侵蚀程度与浸泡时间相关;因树脂的保护作用,10%硫酸盐溶液腐蚀118d对CFRP-混凝土界面的粘结性能基本无影响.     

盐沼泽区冻融作用下桥梁桩基腐蚀损伤模拟试验

为探究高寒盐沼泽区冻融循环作用下桥梁桩基的腐蚀损伤,采用室内模拟试验,模拟在养护冻融循环条件下不同桩基混凝土配合比与不同复合盐溶液体积浓度对桩基混凝土抗侵蚀性能的影响,通过对桩基混凝土外观、质量、抗压强度、动弹性模量以及微观SEM测定的方法,分析桩基础的腐蚀损伤机理。结果表明:不同桩基混凝土配合比对桩基础的抗侵蚀性能有严重影响,当在桩基混凝土中加入粉煤灰、硅灰和膨胀剂（配比Ⅲ）时,其相对动弹性模量减小不到10%,抗侵蚀系数稳定大于0.9,质量损失小于5%,桩基混凝土表面只有轻微脱落现象,能够提升桩基础抗侵蚀性能;在不同体积浓度的复合盐溶液中浸泡,桩基混凝土在冻融循环的条件下表现出不同程度的腐蚀情况,体积浓度越大,复合盐离子相互抑制作用越明显,桩基混凝土腐蚀情况减弱,当体积浓度达到15.4%时,质量损失出现负增长。由微观SEM测试结果,钙矾石、硅灰石膏、Friedel盐是导致桩基混凝土腐蚀损伤的主要产物;建议选用桩基础的设计年限折减系数为0.6,可防止冻融循环对基准体积浓度溶液腐蚀下的桩基础设计年限的不利影响。     

掺石灰石粉混凝土的性能及其改善途径

采用不同掺量的石灰石粉取代水泥配制混凝土,同时配制复掺6%偏高岭土和20%石灰石粉的混凝土,并采用相同的胶凝材料体系制备水泥净浆,开展Na_2SO_4溶液浸泡试验。测试了混凝土抗压强度,采用RCM法和硫酸盐干湿循环侵蚀试验分别测试混凝土的氯离子扩散系数和抗硫酸盐侵蚀性,采用MIP法测试混凝土孔结构,进一步采用SEM观察浸泡后净浆试件的微观形貌。结果表明,石灰石粉对混凝土抗压强度、抗氯离子渗透性和抗硫酸盐侵蚀性均有一定的不良影响。采用偏高岭土与石灰石粉复掺可以有效提高掺偏高岭土混凝土的强度、抗氯离子渗透性和抗硫酸盐侵蚀性。其机理主要在于优化了混凝土孔结构,降低了有害离子在混凝土中的传输速度,阻止了混凝土在硫酸盐环境中钙钒石、石膏等侵蚀产物的形成。     

Deterioration mechanism of sulfate attack on concrete under freeze-thaw cycles

The experiments of concrete attacked by sulfate solution under freeze-thaw cycles were investigated. The sulfate solution includes two types of 5% Na2SO4 and 5% MgSO4. Through the experiment, microstructural analyses such as SEM, XRD and TGA measurements were performed on the selected samples after freeze-thaw cycles. The corrosion products of the concrete were distinguished and quantitatively compared by the thermal analysis. Besides, the damage mechanism considering the dynamic modulus of elastically of concrete under the coupling effect was also investigated. The experimental results show that, under the action of freeze-thaw cycles and sulfate attack, the main attack products in concrete are ettringite and gypsum. The corrosion products exposed to MgSO4 solution are more than those to Na2SO4 solution. Furthermore, the content of gypsum in concrete is less than that of ettringite in test, and some of gypsum can be observed only after a certain corrosion extent. It is also shown that MgSO4 solution has a promoting effect to the damage of concrete under freeze-thaw cycles. Whereas for Na：SO4 solution, the damage of concrete has restrained before 300 freeze-thaw cycles, but the sulfate attack accelerates the deterioration process in its further test period.     

Damage Evolution of Concrete under the Actions of Stray Current and Sulphate

Based on the mechanism of stray current generation in underground structures,the concrete durability test device for stray current and sulphate in typical soil environment was designed to study the damage of concrete under the action of stray current and sulphate.The deterioration law of concrete under the action of stray current and sulphate was studied by microscopic techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XRD).The microstructure of corroded concrete was observed to determine the phase composition of erosion products.The damage performances such as quality,strength,and dynamic elastic mode of corroded concrete were performed.The experimental results show that,under the action of stray current,the products of sulfate-eroded concrete are mainly gypsum,ettringite,and thaumasite;the stray current accelerates the hydration process of cement and the erosion of concrete by sulfate;when the concrete pores are filled with the erosion product,there is an increase of approximately 10% in the concrete compressive strength and dynamic elastic modulus;and the concrete compressive strength is more sensitive to the stray current electrification period than the current intensity.     

干湿交替环境下混凝土受硫酸盐侵蚀劣化机理

通过试验模拟干湿循环作用下混凝土受不同质量分数硫酸钠的侵蚀特点,从不同侵蚀时间后混凝土的表观特征、质量经时变化规律、混凝土中硫酸根离子分布、侵蚀深度、混凝土轴心抗压强度、劈裂抗拉强度经时退化规律、变形经时变化规律等方面全面衡量混凝土的硫酸盐侵蚀损伤特征;讨论硫酸盐溶液质量分数、侵蚀龄期对混凝土损伤累积规律的影响;根据SEM图像分析受蚀混凝土的微观结构特征,揭示了干湿循环和硫酸盐侵蚀共同作用下,不同侵蚀时期后混凝土损伤的演变机理.试验结果表明,在干湿循环作用下硫酸钠对混凝土的侵蚀损伤是侵蚀产物与硫酸盐结晶膨胀共同作用的结果;在侵蚀初期由于晶体的填充密实作用,使得受蚀混凝土的质量、强度与延性增大;随着侵蚀时间的延长,混凝土不仅受到钙矾石、石膏等侵蚀产物的膨胀损伤作用,而且叠加了干湿循环过程中Na2SO4·10H2O的结晶膨胀作用,使得混凝土损伤反复进行并不断累积,加速了混凝土的受蚀劣化速度,质量、强度逐渐降低,脆性变大;由于拉应力的叠加效应,混凝土劈裂抗拉强度对硫酸盐侵蚀损伤更敏感.     

硫酸盐渍土中灌注桩竖向承载力演变规律

盐渍土中硫酸盐含量极高,对灌注桩具有极强的腐蚀作用从而影响其承载特性,为明确和分析混凝土灌注桩在硫酸盐盐渍土腐蚀下竖向承载力的演变规律,以及桩径、桩长对灌注桩腐蚀后承载力变化规律的影响,根据硫酸盐环境下混凝土劣化的腐蚀反应和机理,建立了硫酸盐渍土腐蚀环境下单桩承载力的评价模型;结合案例对硫酸盐渍土地区混凝土灌注桩的侧阻力、端阻力及桩体强度进行研究,分析和对比了桩长及桩径对硫酸盐腐蚀下灌注桩的承载特性演变规律的影响.结果表明:硫酸盐渍土腐蚀作用下灌注桩的侧阻力、端阻力及桩体强度均发生变化;桩侧阻力受到腐蚀产物积累、膨胀引起的桩周混凝土劣化和桩侧应力重分布的影响,同时也依赖于桩长及桩径变化;端阻力则由于单桩竖向有效面积的减小而降低;硫酸盐腐蚀作用下桩体强度降低幅度较大.由此可知,相同腐蚀条件下,增加桩径可有效提高抵抗硫酸盐腐蚀引起的承载力损失;实际设计中应考虑增加桩径的方法抵抗硫酸盐腐蚀引起的承载力损失.     

Influence of Thermally Treated Flue Gas Desulfurization （FGD） Gypsum on Performance of the Slag Powder Concrete

The feasibility of flue gas desulphurization （FGD） as concrete admixture was studied. A combined concrete admixture of the thermally-treated FGD gypsum and slag powder was explored. The FGD gypsum was roasted at 200℃ for 60 min and then mixed with the slag powder to form FGD gypsum-slag powder combined admixture in which the SO3 content was 3.5wt%. Cement was partially and equivalently replaced by slag powder alone or FGD gypsum-slag powder, at concentration of 25wt%, 40wt%, and 50wt%, respectively. The setting times, hydration products, total porosity and pore size distributions of the paste were determined. The compressive strength and drying shrinkage of cement mortar and concrete were also tested. The experimental results show that, in the presence of FGD gypsum, the setting times are much slower than those of pastes in the absence of FGD gypsum. The combination of FGD gypsum and slag powder provides synergistic benefits above that of slag powder alone. The addition of FGD gypsum provides benefit by promoting ettringite formation and forms a compact microstructure, increasing the compressive strength and reduces the drying shrinkage of cement mortar and concrete.     

Deterioration mechanisms of sulfate attack on concrete under alternate action

By micro- and macro-observations, the deterioration mechanisms of concrete under alternate action between repeated sub-high temperature/cooling by water and sodium sulfate solution attack (TW-SA) were studied; meanwhile, the single sodium sulfate solution attack (SA) was also done as comparison. Micro-observations included the analysis of attack products by thermal analysis method and the determination of sulfate-ion content from surface to interior by chemical titrating method (modified barium sulfate gravimetric method). Macro-observations mainly included the mechanical behaviors such as compressive strength, splitting strength. The experimental results indicate, in both cases, the main attack product is ettringite, only in the first layer of case SA some gypsum is checked; in case SA, the sulfate ions mainly concentrate in the surface layer, so the attack is relatively mild; but in case TW-SA, the repeated sub-high temperature/cooling by water promotes the sulfate ions diffusing inwards, which leads to obvious strength degradation.     

Mechanical property and microstructure of alkali-activated Yellow River sediment-coal slime ash composites

This work focuses on the production of a new composite material using Yellow River sediment and coal slime ash via alkali-activating method. XRD, FTIR and SEM/EDS were used to characterize the alkali-activated products and microstructure of the composite material. Compressive strength was tested to characterize the mechanical property of the composite material. It is found that the compressive strength of the Yellow River sediment-coal slime ash composites increases as the added Ca(OH)₂ content grows. The compressive strength increases fast in the early stage but slowly after 28 days. The strength of the composites can be significantly improved via the addition of small amount of NaOH and gypsum. The products (C-S-H, ettringite and CaCO₃), especially C-S-H, make much contribution to the enhancement of strength. The highest strength of the composites can reach 14.4 MPa after 90 days curing with 5% Ca(OH)₂, 0.2% NaOH and 7.5% gypsum. The improved properties of the composites show great potential of utilizing Yellow River sediment for inexpensive construction materials.     

高渗透压-硫酸盐侵蚀下混凝土时空劣化

为了模拟研究混凝土海水环境下的侵蚀损伤及劣化规律,采用质量分数10% Na₂SO₄溶液对混凝土试样进行不同渗透压和不同时长下的室内侵蚀试验. 结合微米压痕试验、CT扫描试验和电子显微镜扫描试验,对高渗透压-硫酸盐耦合侵蚀作用下混凝土的侵蚀损伤及微观力学性能进行研究. 试验结果显示,渗透压加速了离子迁移,主要起到了促进化学侵蚀作用. 渗透压越大,混凝土化学损伤速率越快,侵蚀深度越深;骨料与砂浆胶结处是易侵蚀、易破坏的薄弱点;混凝土内部孔隙易生成水化产物,高渗透压下容易生成大量短柱状石膏晶体及细密的针状钙矾石晶体.     

硫酸盐侵蚀环境因素对混凝土性能退化的影响

考虑硫酸盐侵蚀的阳离子类型、侵蚀溶液浓度、侵蚀溶液的PH值等环境因素影响，研究了环境因素对受硫酸盐腐蚀的混凝土性能退化的影响，对在不同侵蚀环境下受腐蚀混凝土试件的抗压强度、抗折强度进行了测试，实验结果表明，在腐蚀后期硫酸钠溶液中混凝土强度降低幅度比在硫酸镁溶液中混凝土强度降低幅度大；随腐蚀溶液浓度的增大和pH值的降低，混凝土强度衰减率增大，对各种环境条件下不同腐蚀阶段的混凝土进行了超声声速测试，测试结果表明：随混凝土强度的降低，超声波在混凝土中的传播速度降低，两的变化规律具有一致性，超声声速的变化可以反映不同腐蚀程度混凝土强度的变化情况。