水泥组成对混凝土中钢筋锈蚀的影响

本研究在人工模拟自然环境条件下加速混凝土中钢筋的锈蚀,采用电化学方法研究了水泥组成对混凝土中钢筋锈蚀的影响规律.研究结果表明,水泥组成对混凝土中钢筋的锈蚀有显著的影响作用.混合水泥配制的混凝土能有效延缓混凝土中钢筋的锈蚀,延长钢筋开始锈蚀时间;水泥混合材的密实效应及氯离子吸附效应对改善混凝土--钢筋界面区的微观孔结构和减少钢筋表面的氯离子浓度有积极作用,可以降低钢筋的锈蚀速率.     

矿物掺合料对钢筋锈蚀临界氯离子含量的影响

采用交流阻抗谱检测腐蚀电流密度并判断钢筋腐蚀开始的时间,腐蚀开始后通过化学滴定法获得自由氯离子质量分数和总氯离子质量分数,研究了粉煤灰和矿渣对砂浆中引起钢筋锈蚀的临界氯离子浓度的影响规律,探讨了钢筋腐蚀过程的电化学阻抗谱变化以及粉煤灰和矿渣对氯离子结合能力的影响。结果表明:在固定水胶比和胶凝材料用量的情况下,临界氯离子质量分数随矿物掺合料掺量的增加而降低;当粉煤灰掺量达到30%(质量分数,下同)或矿渣掺量达到50%时,临界自由氯离子质量分数由0.52%分别降低到0.33%和0.21%,临界总氯离子质量分数由0.77%分别降低到0.56%和0.38%。钢筋在腐蚀过程中阻抗谱的低频区弧线半径逐渐减小,而高频区基本没变化;掺入粉煤灰和矿渣后,基体对氯离子的结合能力增强。     

MPC粘结CFRP为阳极对锈蚀钢筋混凝土电化学除氯的研究

采用磷酸镁水泥(MPC)粘结碳纤维布(CFRP)作为电化学阳极,对锈蚀钢筋混凝土柱进行电化学除氯.研究了锈蚀钢筋混凝土柱在不同电流密度下的电化学除氯效率、距钢筋不同距离处氯离子分布.结果表明:同一电流密度下,钢筋锈蚀率15％和30％混凝土柱的除氯效率明显大于自然锈蚀和锈蚀率5％的混凝土柱;对于相同锈蚀率的钢筋混凝土,除氯效率随着电流密度的增大而增大;除氯后,混凝土中距钢筋不同位置处的残余氯离子浓度由内到外呈递增趋势,混凝土中各区域残余氯离子随电流密度的增加而降低.     

用电化学方法评价海砂超高性能混凝土中钢筋钝化行为

采用不同氯离子含量的模拟海砂制备超高性能混凝土(UHPC)及普通砂浆,通过线性极化法、交流阻抗法和循环极化法测试其内部钢筋钝化期内的电化学指标,研究了海砂UHPC中钢筋致钝演化规律,及氯离子对钢筋钝化膜生长的影响,并对比了海砂UHPC与普通海砂砂浆中钢筋钝化行为的差异性。结果表明:随着龄期增长,海砂UHPC中钢筋的锈蚀速率降低;随着海砂氯离子含量增大,锈蚀速率加快,但其影响有限,并没有对钝化膜的致密性造成影响;海砂氯离子含量在0.448%以下,钢筋均可在10 d内钝化,且钝化后锈蚀速率基本相同。     

钢筋初始锈蚀时刻的氯离子临界浓度研究综述

氯离子侵蚀是造成混凝土结构耐久性问题的罪魁祸首,当钢筋表面的氯离子浓度达到某一临界浓度时钢筋开始发生锈蚀,因此研究钢筋初始锈蚀时刻的氯离子临界浓度显得尤为重要.以钢筋初始锈蚀时刻氯离子临界浓度的表述方式、测量方法为基础,以国内外考虑不同影响因素条件下的氯离子临界浓度研究结论为载体,对当前钢筋初始锈蚀时刻的氯离子临界浓度的研究成果进行综述.总结了相关研究中的建议取值及各国国家标准中的建议取值.提出在钢筋初始锈蚀时刻锈蚀氯离子临界浓度研究领域针对临界浓度表述,影响机理,多因素耦合,数据库建立方面仍存在的问题和需要改进的方面.     

迁移性阻锈剂影响钢筋锈蚀速率的量化模型及应用

应用电化学方法测试了不同氯盐含量混凝土试件在表面涂覆迁移性阻锈剂(MCI)后不同时刻钢筋的腐蚀电流密度,应用MCI渗透模型,计算不同渗透时间钢筋界面区的阻锈剂浓度,利用统计产品与服务解决方案软件SPSS(Statistical Product and Service Solutions)进行多元非线性统计分析,得到了混凝土中钢筋腐蚀电流密度与界面区MCI浓度、水溶性氯离子含量的量化模型,应用该模型并根据Broomfield准则,计算出使不同氯盐含量混凝土中锈蚀钢筋腐蚀速率降低到钝化状态所需的临界MCI浓度,进而确定在混凝土表面MCI的涂覆量。采用Java语言进行计算机编程,根据混凝土强度(孔隙率)、混凝土水饱和度、水溶性氯离子含量、钢筋锈蚀程度及保护层厚度等参数,计算并输出使混凝土中锈蚀钢筋腐蚀速率降低到钝化状态所需的MCI涂覆量及涂覆工艺。     

钢筋在硫铝酸盐水泥砂浆中的腐蚀行为研究

为研究硫铝酸盐水泥(CSA)基材料中钢筋的腐蚀行为,将钢筋埋置在氯离子掺量不同的CSA砂浆试件中,利用电化学方法测得钢筋的腐蚀电位和腐蚀电流密度作为指标来衡量腐蚀情况,并与普通硅酸盐水泥(OPC)砂浆中的钢筋进行比较.结果表明:钢筋在CSA中的锈蚀行为与在OPC中具有明显的差异,钢筋在CSA砂浆内会发生早期腐蚀,虽然最终能够钝化,但与OPC相比,引起钢筋破钝的氯离子临界值有所降低,而且腐蚀发生后,钢筋的腐蚀速率也大幅提高.砂浆电阻测试和孔隙液化学组成分析表明CSA对钢筋腐蚀的影响机理主要与孔隙液的碱度和具有侵蚀性的硫酸根离子有关.     

钢筋在混凝土模拟孔溶液及水泥净浆中的腐蚀电化学行为

采用动电位扫描法研究钢筋在混凝土模拟孔溶液中腐蚀电化学行为，获得了不同ｐＨ值和氯离子含量对影响钢筋局部锈蚀的临界关系。采用交流阻抗技术研究了钢筋／混凝土模拟孔溶液和钢筋／水泥净浆体系的界面电化学反应机理及其电化学反应模型。结果表明，在高碱性、低氯离子含量或除氧条件下，钢筋在混凝土中将不发生严重局部腐蚀，钢筋的腐蚀电化学反应主要受扩散传质过程控制。     

氯离子含量对混凝土中钢筋锈蚀的影响

混凝土中的钢筋锈蚀破坏是混凝土结构失稳破坏的最主要原因,而导致钢筋发生锈蚀的主要原因是氯离子的存在。本文主要研究了氯离子含量对混凝土中钢筋锈蚀的影响规律。研究表明：混凝土中氯离子含量越高,钢筋开始锈蚀的时间越早;钢筋开始锈蚀后以及进入稳定锈蚀阶段时氯离子含量越高,钢筋锈蚀速率发展的速率越快,钢筋锈蚀速率越大;混凝土一旦发生开裂后,钢筋锈蚀就进入加速锈蚀阶段。试验研究进一步讨论了氯离子加速钢筋锈蚀速率的机理和出现稳定锈蚀期的原因。     

粉煤灰混凝土钢筋锈蚀影响因素研究

通过实验室加速钢筋锈蚀的方法,运用半电池电位法,研究了水胶比、粉煤灰掺量、保护层厚度和阳离子类型对混凝土钢筋锈蚀的影响。结果表明,减小水胶比,增加粉煤灰掺量(0-40%),增大保护层厚度,均可以有效提高钢筋抗锈蚀能力,但当粉煤灰掺量大于40%时,钢筋抗锈蚀能力则变差;阳离子类型对钢筋锈蚀有显著的影响,与Na Cl相比,Ca Cl2明显加快了混凝土内钢筋的锈蚀。     

Application of nanoindentation testing to study of the interfacial transition zone in steel fiber reinforced mortar

The characteristics of the profiles of elastic modulus and hardness of the steel fiber-matrix and fiber-matrix-aggregate interfacial zones in steel fiber reinforced mortars have been investigated by using nanoindentation and Scanning Electron Microscopy (SEM), where two sets of parameters, i.e. water/binder ratio and content of silica fume were considered. Different interfacial bond conditions in the interfacial transition zones (ITZ) are discussed. For sample without silica fume, efficient interfacial bonds across the steel fiber-matrix and fiber-matrix-aggregate interfaces are shown in low water/binder ratio mortar; while in high water/binder ratio mortar, due to the discontinuous bleeding voids underneath the fiber, the fiber-matrix bond is not very good. On the other hand, for sample with silica fume, the addition of 10% silica fume leads to no distinct presence of weak ITZ in the steel fiber-matrix interface; but the effect of the silica fume on the steel fiber-matrix-aggregate interfacial zone is not obvious due to voids in the vicinity of steel fiber.     

10℃下不同水灰比水泥基材料抗硫酸盐侵蚀性能试验研究

研究了不同水灰比对水泥砂浆试件在10℃下抗硫酸盐侵蚀的性能的影响,采用0.36与0.5两种水灰比的普通硅酸盐水泥、中抗硫水泥以及加入矿粉与硅灰的水泥砂浆试件,测试各试样在(10±1)℃的3％Na2SO4溶液中浸泡后的强度变化情况,综合考虑强度与抗蚀系数对砂浆抗硫酸盐侵蚀性能进行评价.结果表明:在10℃下0.36水灰比试件强度高于0.5水灰比试件,抗硫酸盐侵蚀性能随着水灰比的降低而提高;加入矿物掺合料明显改善了水泥砂浆抗硫酸盐侵蚀性能,并且硅灰的含量越高效果越明显.砂浆抗硫酸盐侵蚀性能15％矿粉+3％硅灰>15％矿粉+1％硅灰>中抗硫水泥>普通硅酸盐水泥.     

Effect of carbon fibres on the mechanical properties and corrosion levels of reinforced portland cement mortars

The changes in mechanical properties of portland cement mortars due to the addition of carbon fibres (CF) to the mix have been studied. Compression and flexural strengths have been determined in relation to the amount of fibres added to the mix, water/binder ratio, curing time and porosity. Additionally, the corrosion level of reinforcing steel bars embedded in portland cement mortars containing CF and silica fume (SF) have also been investigated and reinforcing steel corrosion rates have been determined. As a consequence of the large concentration of oxygen groups in CF surface, a good interaction between the CF and the water of the mortar paste is to be expected. A CF content of 0.5% of cement weight implies an optimum increase in flexural strength and an increase in embedded steel corrosion.     

5℃环境下水泥砂浆抗硫酸盐侵蚀性能试验研究

研究了不同水泥品种、矿物掺合料对水泥基材料在5℃下抗硫酸盐侵蚀的性能的影响,分别采用普通硅酸盐水泥、中抗硫水泥以及加入矿粉与硅灰的水泥砂浆试件,测试各试样在(5±1)℃的3%Na2 SO4溶液浸泡后的强度变化情况,综合考虑砂浆强度与抗蚀系数对砂浆抗硫酸盐侵蚀性能进行评价,并运用SEM、EDS、XRD分析方法对腐蚀机理进行了分析.结果表明:在5℃环境下,砂浆试样的强度普遍低于常温环境下,砂浆抗硫酸盐侵蚀能力15%矿粉+3%硅灰>中抗硫水泥>15%矿粉+1%硅灰>普通硅酸盐水泥;加入矿物掺合料明显改善了水泥砂浆抗硫酸盐侵蚀性能,并且硅灰的含量越高效果越明显;低温下腐蚀产物不仅有石膏,还有碳硫硅钙石的生成.     

Corrosion monitoring of reinforcing steel in cement mortar by EIS and ENA

Health degradation by corrosion of steel in civil engineering, especially in rough environment, is a persistent problem. Environment pollution and global warming will exacerbate this problem. The assessment of whole-life costing and residual service life prediction of structures is very important. Pitting corrosion is the most important factor which influences the service life of the reinforced concrete structures in many chloride included environments. Electrochemical impedance spectroscopy (EIS) method is used to study the corrosion process of reinforcing steel in cement mortar. According to the results of the experiments, dispersion and diffusing effect control the electrochemical process of carbon steel corrosion in the cement mortar. By fitting the results with EC, the parameters about CPE and Warburg impedance are calculated. The pitting corrosion behavior of reinforcing steel in cement mortar has been studied by electrochemical noise analysis (ENA) method, the wavelet transform has been employed to analyze the EN data of reinforcing steel in mortar, and the energy distribution plot (EDP) is plotted. The experimental results show that the change of EDP during the corrosion process can qualitatively reveal useful information on corrosion mechanisms.     

硅灰对钢纤维混凝土耐久性能的影响研究

为提高钢纤维混凝土耐久性能,采用复掺的方式,选择高品质的硅灰掺入到钢纤维的混凝土结构中。在保证基准配合比相同的情况下,通过不同的硅灰与钢纤维配合比,探讨硅灰对钢纤维混凝土耐久性能的影响。通过实验结果表明,随着硅灰掺入钢纤维混凝土量的增加,混凝土的抗折强度、抗压强度和劈裂强度、抗冻性能都明显提高,并在12%硅灰+1.2%钢纤维时达到最大。     

活性掺合料对环氧树脂修补砂浆综合性能的影响

为了探究活性掺合料对环氧树脂修补砂浆的改性效果,为修补工程应用提供依据。研究硅灰和粉煤灰对环氧树脂修补砂浆力学性能、粘结强度、尺寸稳定性和抗冻性的影响,并采用扫描电子显微镜(SEM)和压汞法探究和分析影响机理。结果表明:环氧树脂使砂浆抗压强度降低,掺入硅灰可补偿强度损失,掺粉煤灰砂浆的强度随龄期增加而增加,但其中28 d和56 d强度低于对照组;硅灰和低掺量(≤10%,质量分数)粉煤灰可以提高修补砂浆粘结强度;硅灰对修补砂浆尺寸稳定性有不利影响,粉煤灰则相反;砂浆的抗冻性随着硅灰掺量增加先增加后降低,随着粉煤灰掺量增加而降低。     

Study on the corrosion behavior of reinforcing steel in cement mortar by electrochemical noise measurements

The corrosion behavior of reinforcing steel in cement mortar has been studied by electrochemical noise (EN) compared with the electrochemical impedance spectroscopy (EIS). The wavelet transform, as well as the statistical methods including the standard deviation of current noise (σ_I) and noise resistance (R_n), has been employed to analyze the EN data of reinforcing steel in mortar. It is revealed that there exist three different corrosion stages of reinforcing steel in cement mortar, including a competition process between breakdown and repassivation of passive film, a pitting development and an active corrosion during the 20 cyclic immersion and drying tests. The energy distribution plot (EDP) is able to provide useful information about the dominant process for the different corrosion stages.     

硅灰改性水泥/石灰砂浆微观结构的研究

以水泥和石灰为胶凝材料,中细砂为集料,再掺加有机聚合物流化剂制成水泥/石灰砂浆,水泥/石灰砂浆中添加外加剂的文献资料很少,通常是有关水泥砂浆的研究.本实验用硅灰取代10%(质量分数)的普通硅酸盐水泥,水泥、石灰和砂子的质量比为3:1:12,外加有机聚合物对砂浆改性,利用扫描电子显微镜、能谱仪和压汞仪对浆体进行微观分析.分析结果显示,由于硅灰的加入,浆体内部水化产物在早期先以Ⅲ型C-S-H凝胶的形式出现,随后,Ⅲ型和I型的C-S-H凝胶以并存的形式在水化后期出现;正如预期的那样,试样的总的孔隙率也比没加硅灰前有了大幅度的下降,而抗压强度的提高在水化后期才表现出来.     

Effect of steel microfibers on corrosion of steel reinforcing bars

Steel microfiber reinforcement was previously found to be successful in mitigating alkali silica reaction in concrete, an expansive phenomenon. The use of steel microfibers to mitigate rebar corrosion, another expansive reaction, was investigated. Mortar specimens with and without steel microfiber reinforcement were exposed to a corrosive environment. All specimens were prepared with water/cement ratios of both 0.40 and 0.55, cured for 28 days, and then submerged in aerated 3.5% NaCl solution. The corrosion behavior of the specimens was monitored via electrochemical measurements. Three types of electrochemical tests were performed: corrosion potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Chloride concentration measurements and microscopic analysis were performed as well. The polarization curves, Tafel, and polarization resistance measurements indicate that the steel rebar in the microfiber-reinforced mortars are more resistant to corrosion than the rebar in the control mortars, despite higher chloride concentrations. Furthermore, the steel microfiber-reinforced cement based materials have a lower electrolytic resistance. This is not indicative of a higher corrosion rate, which would be the case if it had been observed in standard mortar specimens.