混凝土碱环境中GFRP筋耐久性能试验研究

针对玻璃纤维增强聚合物(GFRP)筋在混凝土环境中的抗拉性能进行了试验研究,通过分析侵蚀前后试件的极限抗拉强度和弹性模量等力学性能参数,研究了两种温度下碱溶液和自来水浸泡混凝土环境中GFRP筋的抗拉强度退化规律。试验结果表明,在20℃、40℃自来水环境下浸泡90d后,GFRP筋抗拉强度与对照试件相比分别下降了8.8%和12.2%,而在相同温度的碱溶液中其抗拉强度衰减量可分别达到17.5%和22.1%;随着龄期的增加,抗拉强度减小的趋势逐渐减缓;通过将GFRP筋在混凝土环境下浸泡和直接浸泡在碱溶液中抗拉强度的试验数据对比分析发现,GFRP筋在模拟碱环境中的抗拉强度退化速率约为实际混凝土环境中的2.5~3倍。     

以弹性模量为指标的CFRP网格单肢耐久性试验研究

FRP耐久性试验常以破坏性试验测量的极限强度为指标衡量FRP的性能退化,但FRP作为高分子材料,性能受到制作工艺、成分配比等诸多因素影响,材料个体差异性较大,不同阶段破坏性试验数据离散性较大;因此本文以弹性模量为指标的FRP耐久性试验,进行了水溶液、海水溶液、海水干湿循环三种工况下CFRP网格单肢耐久性破坏性试验和同体试验,利用材料腐蚀区与未腐蚀区应变一致原则建立弹性模量与抗拉强度之间的转换关系;相比传统耐久性破坏性试验方法,同体测试方法具有数据波动小、数据基准一致、试验成本低、节约材料等优点。结果表明:老化360 d,弹性模量保留率分别为96.9%、96.8%、96.1%,抗拉强度保留率分别为93.8%、89.8%、89.1%,CFRP在水浸环境中耐久性较好;采用弹性模量衡量耐久性与抗拉强度耐久性试验结果规律相似,且可以通过转化关系相互转化;用基于同体测试方法测得的弹性模量与抗拉强度关系建立的耐久性预测模型来评价FRP耐久性的方法更加合理与科学。     

混杂纤维混凝土的耐硫酸盐腐蚀性能研究

为了研究混杂纤维混凝土抗硫酸盐腐蚀性能,对聚乙烯纤维(PE)与聚丙烯粗合成纤维(HPP)混凝土进行硫酸盐干湿循环腐蚀和长期浸泡侵蚀试验,采用形貌损伤、质量损失、相对动弹性模量和抗压强度等宏观测试方法研究了混杂纤维混凝土耐硫酸盐腐蚀性能,并结合SEM微观结构测试技术分析了其腐蚀机理.结果表明:不同纤维掺量的混凝土在硫酸盐腐蚀作用下均出现了不同程度的损伤,其干湿循环的腐蚀作用较长期浸泡腐蚀混凝土的腐蚀损伤更为明显;长期浸泡腐蚀作用时,450 d素混凝土抗压强度可达到60 MPa,各纤维混凝土抗压强度均可达到70 MPa,但在干湿循环腐蚀作用下,聚乙烯纤维和聚丙烯粗合成纤维以0.8%+1.2%掺入时,混凝土抗压强度也可达到70 MPa;纤维对于混凝土内部结构应力的缓解,孔隙、通道等缺陷的分散以及纤维之间的捆绑桥联都显著的提高了混凝土抗硫酸盐腐蚀性.     

碱侵蚀环境下FRP筋的耐久性

将玻璃纤维增强塑料（GFRP）筋和碳纤维绞线（CFCC）筋在60℃碱溶液环境中进行耐久性加速实验。结果表明：GFRP筋在60℃、pH为13的碱溶液中浸泡54天后，极限拉伸强度降低了38．6％，弹性模量降低了6．6％．而在侵蚀实验经历54天后．CFCC筋试件表面未出现坑蚀现象，弹性模量提高了12．6％，说明CFCC筋的延展性有降低趋势；CFCC筋耐碱性能优于GFRP筋。     

碳化-硫酸盐-干湿循环下的项目混凝土耐久性实验研究

针对当前工程项目管理中混凝土质量控制的必要性,通过试验的方式,探讨了提高混凝土耐久性的问题。对此,在以往研究的基础上,综合考虑硫酸根离子腐蚀、碳化和干湿循环作用下,提高混凝土耐久性的最优用量。试验结果表明,在水胶比为0.5,粉煤灰掺量在30%,引气剂掺量在20%的情况下,得到的混凝土抗压强度,耐蚀系数和弹性模量最稳定。通过以上的研究,为当前工程项目施工和管理提供了科学性的参考路径。     

海洋环境下CFRP筋与混凝土长期粘结性能研究

对3类碳纤维浸胶纱试件的拉伸力学性能进行了比较分析,优选后制备了碳纤维复合材料(CFRP)筋,并对海洋海水条件下CFPR筋与混凝土粘结性能的耐久性进行了加速腐蚀试验研究,对极限粘结强度和自由端发生0.05、0.10和0.25 mm滑移值时的设计粘结强度进行了比较分析。结果表明,国产T700级碳纤维浸胶纱的极限抗拉强度略低于东丽T700碳纤维,但其弹性模量高于后者;在加速腐蚀试验周期内,CFRP筋与混凝土的极限粘结强度和设计粘结强度都得到了明显的提高。     

GFRP筋拉伸力学性能与破坏形态试验分析

对不同尺寸和纤维含量条件下的螺纹纤维筋进行研究,利用一次性拉伸和循环拉伸试验,观察筋体在受力中表观特征和应力的对应关系,对比分析玻璃纤维增强复合材料（GFRP）筋体1/2和1/4处的应力应变关系。结果表明,GFRP筋达到一定的应力时筋体出现裂纹,裂纹开展从筋体套筒附近开始,并随着应力增加而向中间扩展,在破坏前随应力减小而逐渐闭合;裂纹在筋体破坏前纵向发展,在达到破坏荷载时裂纹呈现横向参差不齐的断裂破坏特征;材料的弹性模量稳定,泊松比受加载循环影响而减小;不同纤维含量的GFRP筋会有不同的破坏荷载和破坏形态;筋体的破坏性质介于脆性破坏和塑性破坏之间;直径为20mm和直径为25mm筋体利用效率最高,是较为优化的筋体尺寸类型。     

长期腐蚀环境影响下GFRP筋混凝土构件的老化机理及抗弯性能研究

为了研究长期腐蚀环境影响下GFRP筋混凝土构件的老化机理以及抗弯性能,分别分析了水分、温度、碱性环境等因素对GFRP筋抗拉强度、有效受拉面积和粘结强度等性能方面的影响。基于GFRP筋材料老化后与混凝土协同工作关系的变化,通过构造新的几何条件,推导了老化GFRP筋正截面抗弯承载力计算公式,利用推导的公式分析了不同GFRP筋老化率对构件承载力的影响。研究表明:GFRP筋混凝土构件在腐蚀环境长期作用下,GFRP筋不断老化,其抗拉强度、有效受拉面积以及粘结性能都有不同程度的降低;随着GFRP筋材料老化率的不断增加,构件抗弯承载力损失率也不断增加,当老化率达到27%时,构件抗弯承载力也相应损失了25.97%。     

碱液下GFRP筋力学性能劣化模型研究

为研究碱液下玻璃纤维增强复合材料（GFRP）筋力学性能劣化规律,对直径为20 mm和25 mm的GFRP筋进行碱溶液分别浸泡30、90 d和180 d后的拉伸试验,得到筋体在碱液不同腐蚀时间后筋体的极限拉伸强度及弹性模量等力学性能指标;对比研究了相同直径筋体在盐溶液浸泡180 d后的力学性能变化;建立了碱液下GFRP筋剩余强度衰减模型。结果表明,相同的腐蚀龄期,碱性环境对GFRP筋力学性能劣化影响高于盐环境;碱液下GFRP筋拉伸强度随浸泡时间的增长呈下降趋势,GFRP筋前期被腐蚀速率高于后期;分析修正后的碱液下筋体剩余强度衰减模型与试验结果吻合度较高。     

碱溶液、紫外线及其交叉环境下BFRP筋耐久性能试验研究

为研究直径和腐蚀环境对BFRP筋拉伸力学性能影响,开展了三种直径(6 mm、8 mm、10 mm)BFRP筋试件在自然环境、碱溶液环境(pH=10)、紫外线照射环境(辐照度为550W/m~2)及两种腐蚀环境交叉作用下拉伸试验,采用扫描电子显微镜(SEM)对BFRP筋拉伸断裂进行了分析,并对试验结果进行了研究。主要结论如下:三种不同环境作用下,随着腐蚀时间延长,BFRP筋抗拉强度减小且强度退化率逐渐下降,BFRP筋弹性模量上下波动均不超过5%,且无明显规律,断裂伸长率变化趋势与拉伸强度基本相同;紫外线环境下BFRP筋抗拉强度有退化和不完全恢复现象;交叉环境下直径分别为6 mm和8 mm BFRP筋抗拉强度也有退化和不完全恢复现象,10 mm BFRP筋则没有。基于本文所定义的耐久性衰减速率,对直径分别为6mm和8 mm BFRP筋耐久性的影响,碱环境最大,交叉环境居中,紫外线环境最小;对10 mm BFRP筋耐久性的影响,交叉环境最大,碱环境居中,紫外线环境最小。三种不同环境作用下,直径为6 mm BFRP筋耐久性衰减平均速率均最大,直径为10 mm的测试结果均最小。     

Influence of the Manufacturing Process on Corrosion Behavior of Soda-Lime-Silicate Glassware

The reaction of soda-lime-silicate glassware with model cleaning solutions gives rise to a systematic pattern of inhomogeneous corrosion. This corrosion is not uniform on the entire surface, but is localized only to certain regions of the glassware. The surface composition, as determined by X-ray photoelectron spectroscopy, and the microstructure, as characterized by optical and scanning electron microscopy, vary considerably in different regions of the glassware. The visibly heterogeneous corrosion pattern, which correlates with the compositional and structural inhomogeneities, is explained in terms of surface conditions that exist during different stages of glass manufacturing. The role of sodium disilicate in solution is also explored for promoting inhomogeneous glass corrosion.     

Chromium-Free Corrosion Resistance of Metals by Ceramic Coating

Metal surfaces can be improved in terms of thermal, mechanical, and chemical properties by a ceramic coating. The chromium-free corrosion resistance of stainless steel was achieved using a chemical solution method. Precursor solutions were prepared from metal alkoxides and were deposited on stainless-steel surfaces by dip coating and heat-treating at temperatures <500°C. The stainless steel was coated by silica, zirconia, and titania single-layer coating films, and/or coated by silica/zirconia and silica/titania double-layer coating films. The corrosion resistance was improved remarkably by a submicrometer silica-based coating on the stainless steel.     

Influence of Grain Phase on Slag Corrosion of Low-Cement Castable Refractories

The grain phase has a significant influence on the extent and mechanism of attack of low-cement castables with similar bond systems in a crucible corrosion test. The general corrosion mechanism, as determined by post mortem scanning electron microscopic examination of corroded samples and thermodynamic calculations for all four grain types examined (white-fused alumina (WFA), tabular alumina (TA), brown-fused alumina (BFA), and alumina-rich spinel (S)), involves initial reaction of the most penetrating slag (enriched in calcium, manganese, and iron, because these elements diffuse rapidly) with the fine alumina and calcium aluminates of the matrix. This reaction gives a CaO-rich local liquid, which can then react with each grain predominantly to form calcium hexaluminate (CA₆) and hercynitic spinel. In the WFA system, a complete CA₆ layer forms around the grain, whereas in the TA system, this layer is incomplete. In both systems, extensive penetration occurs, although corrosion is low. In the BFA system, titanates are released from the grain into the bond, leading to increased densification of the refractory, via liquid-phase sintering, and consequent low penetration. However, the resulting fluid liquid dissolves easily in the slag, so that corrosive wear is high, even though a CA₆ layer forms around the grain. In the S grain system, uptake of the rapidly diffusing cations into the spinel crystal structure leads to silica-rich and viscous local liquid, which leads to low penetration and corrosion.     

Dissolution of silica component of glass network at early stage of corrosion in initially silica-saturated solution

Corrosion of glass in silica-saturated solution has been performed with the assumption that dissolution of silicate species from the glass network would not occur. Using surface-sensitive analytical techniques, we report experimental evidence suggesting the dissolution of silicate network species from a model nuclear waste glass, called international simple glass (ISG), in an aqueous solution initially saturated with soluble silica species. Results from low energy ion scattering and X-ray photoelectron spectroscopy reveal a complete depletion of mobile element species (B, Na) from the ISG surface and an enrichment of Zr on the outmost surface. In support of spectroscopic analyses, results from topographic imaging with atomic force microscopy show a stochastic dissolution of glass surface resulting in a higher surface roughness with increasing corrosion time in aqueous solution. This study shows that a true equilibrium between soluble silica species in the solution phase and silicate species in the glass network could not be warranted by performing corrosion experiments in the solution where dissolved silica species are initially equilibrated with amorphous silica in the presence of KOH. The leaching of mobile species (B, Na) could affect the saturation level of aqueous solution and induce further dissolution of the glass surface.     

Hydrothermal Corrosion and Strength Degradation of Aluminum Nitride Ceramics

The hydrothermal corrosion and strength degradation of aluminum nitride (AlN) ceramics were investigated. The weight gain in AlN ceramics after corrosion occurred because of the formation of boehmite. The reaction kinetics of AlN with water were diffusion controlled through the boehmite product layer. At 180°C, immersion in water caused no strength degradation, and water vapor caused a 20% strength degradation. At 300°C, immersion in water caused a 20% strength degradation, and water vapor caused a 30% strength degradation.     

Corrosion of Aluminum Nitride (AlN) in Aqueous Cleaning Solutions

The corrosion of aluminum nitride (AlN) in aqueous solutions has been evaluated in situ , using an ammonium/ammonia ion-selective electrode. The corrosion behavior of AlN over a pH range of 5.5–12 indicates that the corrosion products that are formed act as a protective barrier layer in the pH regime where they have the lowest stability. An insoluble barrier layer is formed via the oxidation of the AlN surface in air at a temperature of 750°C for 10 min. This oxynitride layer, which is 200 Å thick, prevents the corrosion of the AlN in a pH 9.5 aqueous solution; however, the thermal conductivity is reduced by 6.6%.     

Observed volatilization behavior of silicon carbide in flowing hydrogen above 2000 K

The intrinsic compatibility of silicon carbide (SiC) and hydrogen (H₂) at high temperatures (2000-2473 K) and pressure near one atmosphere was evaluated through a combination of thermodynamic calculations and hot hydrogen exposure testing. Thermodynamic calculations predict the decomposition of SiC in a hydrogen environment to form free silicon (Si) and free carbon (C). Free Si is predicted to vaporize from the surface as a volatile species, while free C may interact with H₂ to form the hydrocarbons CH₄ (T < 2100 K) or C₂H₂ (T > 2100 K). Coupons of high purity chemical vapor deposition (CVD) β-SiC were exposed to slowly flowing hydrogen at temperatures ranging between 2000 and 2473 K. SiC experienced active attack as the result of H₂ exposure, exhibiting linear weight loss kinetics and an Arrhenius dependence of weight loss on exposure temperature. The linear volatilization constant was experimentally evaluated to correspond with an activation energy of 370 ± 18 kJ/mol. Due to the dependence of observed corrosion rates on gas velocity, corrosion of SiC in flowing H₂ was determined to be governed by external mass transfer of volatile Si species through the boundary layer. Experimentally derived mass losses were in good agreement with mass losses predicted by a boundary layer limited gas diffusion model.     

Effect of submicron spinel powders on the microstructure evolution and properties of alumina‐based refractory castables

The physical properties, including flow value, apparent porosity, and mechanical strength, increased significantly with submicron spinel contents in this study. The excellent physical properties can be attributed to the close‐packed microstructure and high bonding strength between spinel and aggregates/matrix. Additionally, the submicron spinel powders promoted the formation of tabular CA₆ grains that generated a cross‐linked structure and enhanced the mechanical properties. The microstructures of corroded castables suggested that submicron spinel powders contributed to the formation of a continuous and thick spinel layer at the slag–refractory interface and subsequently improved the slag resistance of the castables.     

Translucent Polycrystalline Alumina with Improved Resistance to Sodium Attack

Reaction of sodium with polycrystalline alumina (PCA) arc tubes in high-pressure sodium lamps can limit lamp performance. The rate of degradation depends on the grain-boundary diffusion of a reaction product, aluminum, through the PCA wall. The effects of sintering aids and other dopants on the sodium resistance of PCA are investigated via accelerated lamp tests and microstructural analyses. Key material parameters for sodium resistance are the spinel (MgAl₂O₄) second phase and the grain-boundary MgO level. Eliminating spinel in the sintered body, doping with tetravalent cations to charge-compensate the Mg²⁺ solutes, and creating a second phase to absorb MgO in situ , significantly improve the resistance of PCA to sodium attack.     

Ablation resistance of SiC‐modified ZrC coating prepared by SAPS for SiC‐coated carbon/carbon composites

This study evaluated the ablation resistance of ZrC/SiC coating for carbon/carbon (C/C) composites at different temperatures and heat fluxes, which improved the researches on ultra‐high temperature oxidation of ZrC/SiC system. Results showed that the protection of coating depended on temperature and heat flux. Ablation test for 120 seconds under heat flux of 2.4 MW/m² at 2270°C revealed a good ablation resistance, with the linear ablation rate reduced by 96.4% and the mass gain rate increased by 383.3% compared with those of pure ZrC coating. The good ablation resistance was attributed to the formation of dense oxide scale surface. SiC could improve the compactness of the oxide scale at this temperature by forming SiO₂. A dense scale could not form at 2105°C after ablation for 120 seconds, resulting in a dissatisfactory ablation resistance of the coating. After ablation for 120 seconds at 1738°C, the coating was integrated due to the protection of glassy SiO₂ encapsulated ZrO₂. The coating could not resist the strong shear force from the flame at heat flux of 4.2 MW/m² and was severely damaged after ablation for 60 seconds.