Pitting corrosion resistance of a novel duplex alloy steel in alkali-activated slag extract in the presence of chloride ions

In this study, two types of reinforcing steels(conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions(ordinary Portland cement(OPC) extract and alkali-activated slag(AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various Na Cl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.

Experimental Study on Chloride Ion Penetration Resistance of Coal Gangue Concrete under Multi-Factor Comprehensive Action

In order to investigate the chloride ion penetration resistance of coal gangue concrete under multi-factor comprehensive action, the non-steady-state accelerated chloride ion migration test was used to test the chloride diffusion law of coal gangue concrete specimens by crack width, curing temperature and water-cement ratio. Three groups of crack width (0 mm, 0.05 - 0.12 mm, 0.12 - 0.2 mm), three curing temperatures (high temperature 45, medium temperature 25, low temperature 10), three water cement ratios (0.3, 0.4, 0.5) were set in the experiment. The results show that when the curing temperature and water cement ratio are constant, the crack width less than 0.12 mm has little effect on the chloride content and chloride diffusion coefficient. When the crack width is larger than 0.12 mm, the chloride penetration depth increases with the crack width. The resistance to chloride ion penetration of gangue concrete is greatly influenced by the water cement ratio. The influ-ence degree of three factors on chloride ion migration coefficient of gangue concrete is as follows: water cement ratio > crack width > curing temperature.

Negative effect improvement of accelerated curing on chloride penetration resistance of ordinary concrete

Four mineral admixture concrete specimens werefabricated to study the negative effect improvements ofaccelerated curing on the chloride penetration resistance ofordinary concrete. After reaching different initial strengths, the specimens were placed in 40, 60, or 80 t water tanks foraccelerated curing. The Coulomb values of the specimens weemeasured with ASTM C1202 experiment at 28, 100, 200, ad300 d. Partial specimens were also selected for rapid chlorideion migration coefficient and mercury intrusion porosimetryexperiments. The experimental results show that theaccelerated curing for ordinary concrete linealy deterioratesthe chloride penetration resistance, whereas the incorporationof mineral admixtures improves the concrete microscopic pore-structures and negative effects. An upper temperature limit of60 t of the accelerated curing is suitable for obtainingsuperior chloride penetration resistance for the mineraladmixture concrete. Pre-curing at a normal temperature of 20t is beneficial for improving the negative effect, which isalso aieviated with increasing testing age as a result of thesuccessive hydration of binder materials in concrete.

The Influence of Mineral Functional Materials on Chloride Ion Penetration of Concrete

The mechanism of chloride ion penetration in high performance concrete was analy zed. The experimental results indicate that there are two important reasons that influence the anti-chloride penetration of high performance concrete. One is the function effect of mineral functional material, so that it increases conc rete's capability to resist chloride ion penetration. The other is combined acti on of mineral functional material's original capability of binding the chloride ion (physical adsorption) and physicochemical adsorption after hydration.

Chloride ion penetration into concrete under hydraulic pressure

The lining concrete of subsea tunnel services under combined hydraulic pressure, mechanical and environmental loads. The chloride ion and water penetrations into concrete under hydraulic pressure were investigated. The experimental results indicate that the water penetration depth, chloride ion transportation depth, and the concentration of chloride ion ingression into concrete increase with raised hydraulic pressure and hold press period. But the chloride ion transportation velocity is only 53% of that of water when concrete specimens are under hydraulic pressure. The chloride transportation coefficient of concrete decreases with hold press period as power function. And that would increase 500% 600% in chloride transportation coefficient when the hydraulic pressure increases from 0 to 1.2 MPa. The hydraulic pressure also decreases the bound chloride ion of concrete to about zero. Besides, the low water-cementitions materials and suitable content of mineral admixture(including fly ash and slag) improve the resistance capacity of chloride penetration, and binding capacity of concrete under hydraulic pressure.

Effects of Silica Fume and Steel Fiber on Chloride Ion Penetration and Corrosion Behavior of Cement-based Composites

This project was aimed to evaluate the chloride permeability and corrosion behavior of cement-based composites which comprised fibers and silica fume in the mixes~ Resistivity, polarization resistance, ponding and rapid chloride penetration results of specimens were obtained through tests. Test results indicate that resistivity, open circuit potentials and direct current polarization of specimens with w/b ratio of 0.35 are higher than those of specimens with w/b ratio of 0.55. For length-diameter ratio of 65, resistivity and direct current polarization of specimens with fiber length of 35 mm were similar to those of 60 mm. In addition the open circuit potentials of specimens with fiber length of 60 mm were slightly higher that those of 35 mm. The resistivity decreased with increasing steel fiber content, and the open circuit potential and direct current polarization increased with increasing steel fiber content. The specimens containing silica fume were found to provide higher resistivity, open circuit potentials and direct current polarization than the control specimens. The incorporation of steel fiber and silica fume in composites achieved more significantly decreases in resistivity and increases in direct current polarization than steel fiber composites or silica fume composites. The penetration depth and six-hour total charge passed of specimens for w/b ratio of 0.35 were lower than those for w/b ratio of 0.55. For length-diameter ratio of 65, the penetration depth of specimens for fiber length of 35 mm was similar to that of 60 mm. The penetration depth decreased with increased steel fiber content in the composites. By regression analysis, a good correlation between open circuit potential and direct current polarization, and chloride penetration depth and direct current polarization.

Porosity,Pore Size Distribution and Chloride Permeability of Shotcrete Modified with Nano Particles at Early Age

Nano particles have been found to be effective in enhancing many properties of regular concretes. However, there is little information on the effect of nano particles on shotcrete. In fact, if similar positive effect of nano particles can also appear in shotcrete, they will greatly benefit the wide application of shotcrete in more and more repair and strengthening of structures in civil engineering, especially in corrosive environments. In this study, through experiments on 70 specimens, the effects of nano SiO2, CaCO3 and Al2O3 particles on the early-age porosity, pore size distribution, compressive strength and chloride permeability of shotcrete were investigated.Test results indicated that nano SiO2 particles significantly increased the compressive strength and chloride penetration resistance; nano Al2O3 and CaCO3 particles had slight enhancing effect on the compressive strength; nano CaCO3 particles were most effective in promoting the chloride penetration resistance of shotcrete. As a conclusion, nano SiO2 particles were recommended when both early age compressive strength and chloride penetration resistance were crucial, and nano CaCO3 particles were recommended when only chloride penetration resistance was concerned for their high cost-effectiveness.

纤维-地聚物混凝土力学性能及耐久性能研究

为改善地聚物混凝土的力学性能和耐久性,通过掺入不同长度和掺量的聚丙烯纤维,对地聚物混凝土的力学性能、抗冻性、抗氯离子侵蚀性及抗裂性进行了研究,并基于SEM试验,从微观角度进一步解释聚丙烯纤维的作用机理.结果表明:聚丙烯纤维的掺入能够提高地聚物混凝土的力学性能和耐久性能,当纤维掺量为0%~0.6%时,随着纤维掺量的增加,地聚物混凝土的改善效果越明显.当掺量超过0.6%时,其力学性能和耐久性开始下降.通过SEM分析也表明,聚丙烯纤维能够提高基体内部的整体性和密实性,从而显著改善地聚物混凝土的力学性能和耐久性.最终推荐掺量0.6%长度为12 mm的聚丙烯纤维为最佳掺量.

改性硫铝酸盐水泥砂浆力学性能及耐久性能研究

过快的流动度损失和后期不稳定的强度发展限制了硫铝酸盐水泥工程中的进一步应用。因此以葡萄糖酸钠作为缓凝剂,掺入硅灰制备成改性硫铝酸盐水泥砂浆,并对其工作性能、力学性能和抗氯离子渗透性能开展了系统研究。研究结果表明:葡萄糖酸钠掺量0.4%可有效延长硫铝酸盐水泥砂浆凝结时间,提高砂浆流动性和抗氯离子渗透性能;硫铝酸盐砂浆工作性能、力学性能和抗氯离子渗透性能均随硅灰掺量的增加先提高后降低,硅灰最优掺量为20%。

含氯再生骨料混凝土中钢筋抗锈蚀性能试验研究

沿海地区废弃混凝土受氯离子侵蚀,为使其更好地再生利用,探究含氯再生骨料混凝土的改性方法及钢筋抗锈蚀性能,以矿物掺合料种类及掺量、再生骨料强化为变量,设计15组混凝土,对混凝土中钢筋通电加速锈蚀,并通过电化学工作站的线性极化法和电化学阻抗谱法测试其钢筋电化学指标。结果表明:含氯再生骨料混凝土中钢筋锈蚀进程快于普通不含氯再生骨料混凝土;纳米SiO_(2)溶液强化含氯再生骨料,以及在混凝土中复掺矿物掺合料均可提高含氯再生骨料混凝土钢筋抗锈蚀性能;通过强化改性的含氯再生骨料混凝土的钢筋抗锈蚀性能不低于普通再生骨料混凝土。

氯盐结晶作用下掺合料对海工HPC性能的影响

通过6 mol/L的NaCl溶液半浸泡和干湿循环实验,对海洋环境氯盐结晶作用进行模拟,研究了氯盐结晶作用下矿物掺合料对海工HPC(高性能混凝土)性能的影响。结果表明:混凝土在氯盐结晶作用下,相对动弹模量和抗压强度后期均呈现下降趋势,其中干湿循环的盐结晶破坏作用最为严重;由于盐溶液毛细上升原因,混凝土在泛霜结晶区也产生明显的氯离子渗透。在28 d等抗压强度下,掺矿物掺合料明显有助于提高混凝土抗盐结晶破坏和抗氯离子渗透性能,其中干湿循环90次后的混凝土,氯离子渗透深度仅约为空白混凝土的2/5。通过微观分析发现,盐结晶破坏主要与混凝土中存在的大孔和毛细孔有关。

含氯再生骨料混凝土抗氯离子渗透性能的研究

采用纳米SiO_(2)溶液浸泡含氯再生骨料以降低骨料含氯量,并在此基础上考虑复掺矿物掺合料,设计16组配合比以制备C40再生骨料混凝土,测定其7 d、28 d的抗压强度与28 d的电通量、Cl^(-)扩散系数。结果表明:再生骨料中的Cl^(-)可提高混凝土7 d的抗压强度,少量降低其28 d的强度,但会大幅度破坏混凝土抗Cl^(-)渗透性能;纳米SiO_(2)溶液改性后骨料含氯量显著降低,与矿物掺合料联合作用将有效提升再生混凝土力学性能与抗Cl^(-)渗透性能;其中,30%粉煤灰与8%硅灰复掺优化效果最佳,Cl^(-)渗透系数较未掺掺合料组降低85.6%。基于含氯再生骨料多重界面与Cl^(-)扩散机理,推导“内渗型”Cl^(-)扩散模型,并将其用于含氯再生骨料混凝土构件服役任意龄期的Cl^(-)含量预测。

粉煤灰和表面防护剂对混凝土抗氯离子渗透性能的影响

提升混凝土耐久性能的关键在于提高其抗渗性能,涂抹表面防护材料和掺加粉煤灰是两种常用的技术手段,为研究两种技术对混凝土抗氯离子渗透性能的协同提升效果,设计了不同掺量粉煤灰混凝土,对部分试件进行了无机表面防护材料喷涂,研究其对立方体抗压强度和抗氯离子渗透性的影响。试验结果表明:混凝土的抗压强度受粉煤灰掺量的显著影响,而受表面防护剂的影响不大;涂抹防护剂对无掺加粉煤灰或掺加少量(9.5%)粉煤灰混凝土的抗氯离子渗透性能提升效果更为明显;对掺量较大(19%)的粉煤灰混凝土,测试其抗氯离子渗透性能时,建议以长龄期的结果为主为宜。

铁尾矿混凝土力学性质及耐久性

这是一篇陶瓷及复合材料领域的论文。为了研究铁尾矿混凝土在受硫酸钠溶液干湿循环作用后的力学特性和耐久性,开展了受硫酸钠溶液侵蚀混凝土的抗压实验、抗氯离子侵蚀实验、抗冻实验和水化特性实验,分析不同铁尾矿掺量、干湿循环次数、溶液浓度对混凝土力学性质和耐久性的影响。结果表明:在铁尾矿掺量为30%、干湿循环次数为60次和硫酸钠浓度为5%时,混凝土的质量损失率较小而抗压强度耐腐蚀系数较大。随着铁尾矿掺量的不断增大,混凝土的抗氯离子侵蚀性能、抗冻性能越好,水化反应放热量不断减小。

不同尺度纤维复合增强水泥基材料的抗氯离子渗透性能

为研究不同尺度纤维复合增强水泥基材料的抗氯离子渗透性能,对单掺和复掺碳酸钙晶须、聚乙烯醇(PVA)纤维的水泥基材料分别进行电通量试验、电镜扫描观测及基本力学性能试验,分析不同纤维尺度、掺量及复合比例对水泥基材料抗氯离子渗透性能和基本力学性能的影响规律,并基于试验结果给出了多纤维复合增强水泥基材料的氯离子侵蚀深度计算模型。结果表明,不同尺度纤维可在不同结构层次上发挥对水泥基材料的增强作用,使得多纤维复合增强水泥基材料的抗氯离子渗透性能明显优于单一纤维增强水泥基材料;多纤维复合材料的抗压强度与氯离子侵蚀深度及电通量大致呈反比例关系;当复合材料的抗压强度提高13.6%时,其氯离子侵蚀深度和总电通量则分别降低39.1%和44.7%;建立的氯离子侵蚀深度计算模型,可用于多纤维复合增强水泥基材料的抗氯离子渗透和侵蚀性能评估。

聚乙烯醇纤维改性混凝土及抗盐蚀研究

针对普通混凝土耐久性和抵抗恶劣环境差的问题,提出通过聚乙烯醇纤维对混凝土进行改性,并研究了纤维对混凝土的改性效果。试验结果表明,当聚乙烯醇纤维掺量为12%时(PVA12样品),混凝土坍落度较基础混凝土下降了约45%。在28 d龄期,PVA12混凝土抗压强度约为65 MPa,较基础混凝土抗压强度提升了约28%;抗折强度达到了8.5 MPa,较基础混凝土提升了约55%;剩余强度较PVA6混凝土剩余强度增加了约210%;电阻率较基础混凝土大18.6Ω·cm;氯离子迁移系数与基础混凝土较为接近,满足抗氯离子渗透能力极高的标准要求。改性混凝土表现出良好的工作性能、力学性能和抗氯离子渗透能力。

橡胶混凝土掺杂玄武岩纤维的抗氯离子渗透性能研究

为研究掺杂玄武岩纤维的橡胶混凝土的抗氯离子渗透性能并得出最佳配合比,本文确定橡胶颗粒掺量、玄武岩纤维掺量和玄武岩纤维长度三个因素,进行6 h电通量试验,通过比较电通量的大小对9组混凝土试件的进行研究。实验结果表明:试件电通量随着橡胶颗粒掺量的增加表现出先减小后增大的趋势,且掺量从15%到20%时的增大幅度明显大于掺量从10%到15%时的减小幅度;随着玄武岩纤维掺量的增加,电通量亦先减小后增大,且变化幅度较为平均;随着玄武岩纤维长度的增加电通量持续减小且幅度由小变大。推荐配合比为:橡胶颗粒体积取代率15%、玄武岩纤维掺量0.10%、玄武岩纤维长度18mm。

掺硅粉对普通硅酸盐水泥-硫铝酸盐水泥复合胶凝体系混凝土耐久性的影响研究

通过在m(普通硅酸盐水泥)∶m(硫铝酸盐水泥)=3∶7的复合胶凝体系(P·O-SAC)中掺入不同比例的硅粉,对复合胶凝体系的水化过程和混凝土的抗压强度、抗劈裂强度以及抗氯离子侵蚀进行试验,改善多元复合胶凝体系混凝土的耐久性能。研究表明:硅粉的掺入量越多,复合水泥的初凝和终凝时间越长;掺入适量的硅粉能有效提高P·O-SAC混凝土的抗压强度,改善P·O-SAC混凝土后期强度的发展;硅粉能提升P·O-SAC混凝土抗氯盐侵蚀的能力。

新型玄武岩纤维束混凝土耐久性能试验

为研究新型玄武岩纤维束混凝土的耐久性能,研究了玄武岩纤维束掺量和长度对混凝土抗氯离子渗透性能、抗冻性方面的影响.结果表明:加入玄武岩纤维束后导致混凝土抗氯离子渗透性能降低,纤维束的掺量越大,氯离子扩散系数越大;玄武岩纤维束掺量相同时,短纤维束混凝土抗氯离子的渗透性优于长纤维束混凝土;掺入玄武岩纤维束有利于提高混凝土的抗冻性能,当掺量达到7.96 kg/m^(3)后,随纤维掺量继续增多,混凝土相对动弹性模量的降幅差别不大,掺量为11.94 kg/m^(3)时,抗压强度损失率最低,为11.4%;玄武岩纤维束掺量相同时,不同长度的玄武岩纤维束对混凝土的相对动弹性模量排序为30 mm>20 mm>40 mm,抗压强度损失率排序为30 mm<20 mm<40 mm.