Cement & concrete composites最新文献_第3页

Electro-chemo-physical analysis for long-term reinforcement corrosion within the reactive system of concrete 混凝土反应体系中长期钢筋腐蚀的电化学物理分析

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-09 DOI: 10.1016/j.cemconcomp.2024.105846

Bin Dong , Yuguo Yu , Wei Gao , Chamila Gunasekara , Gaofeng Zhao , Arnaud Castel , Sujeeva Setunge

This paper presents an electro-chemo-physical model for analyzing long-term chloride-induced reinforcement corrosion in concrete structures. The integration of electrochemical and thermodynamic analyses enables the proposed model to capture the influence of simultaneous reactions within concrete on the corrosion process. The model is validated against experiments, where the necessity of considering the complicated reactions within concrete in long-term corrosion modeling is underscored. Building upon experimental observations and numerical explorations, a potential corrosion acceleration effect resulting from Friedel's salt dissolution in a longer term of corrosion propagation is discovered. Thereafter, a new qualitative model for describing the reinforcement depassivation process in concrete is proposed, along with discussions on governing mechanisms. From a computational perspective, the study also identifies hematite and magnetite as thermodynamically stable rusts under different concentrations of Fe²⁺ and O₂. The proposed model and discoveries are poised to contribute significantly to scientifically robust predictions of deterioration and remaining service life for aging reinforced concrete structures.

本文提出了一种电化学物理模型，用于分析混凝土结构中由氯化物引起的长期钢筋腐蚀。电化学分析和热力学分析的结合使所提出的模型能够捕捉到混凝土内部同时发生的反应对腐蚀过程的影响。该模型通过实验进行了验证，强调了在长期腐蚀建模中考虑混凝土内部复杂反应的必要性。在实验观察和数值探索的基础上，发现了弗里德尔盐溶解在长期腐蚀传播过程中可能产生的腐蚀加速效应。随后，提出了描述混凝土中钢筋去钝化过程的新定性模型，并讨论了相关机制。从计算角度来看，该研究还确定了赤铁矿和磁铁矿在不同浓度的 Fe2+ 和 O2 作用下的热力学稳定锈。所提出的模型和发现有望为科学地预测老化钢筋混凝土结构的劣化和剩余使用寿命做出重大贡献。

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引用次数: 0

Slip hardening behavior of bundled steel fibers in ultra-high performance concrete 超高性能混凝土中捆绑钢纤维的滑动硬化行为。

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-08 DOI: 10.1016/j.cemconcomp.2024.105844

Mandip Dahal, Kay Wille

This study introduces a novel steel fiber arrangement, termed “bundled fibers,” where multiple high-strength steel wires are twisted into short, discontinuous fibers. The bond behavior of these bundled fibers in ultra-high performance concrete (UHPC) was evaluated through single-fiber pullout tests. Four variations of bundled fibers, consisting of two to five wires, were tested across three embedment lengths (3.3 mm, 4.9 mm, and 6.5 mm). Results indicate that increasing embedment length and bundling more wires enhance maximum pullout load, fiber stress, pullout energy, and bond strength, although slip capacity decreases with more wires. Compared to equivalent numbers of straight fibers, bundled fibers demonstrated superior performance in all pullout parameters and outperformed five common steel fiber geometries (straight, striated, wavy, hooked, twisted) in bond strength and slip capacity. A new parameter introduced to quantify slip hardening addresses a gap in the literature, with bundled fibers showing a higher degree of slip hardening due to torsion-induced frictional bonding. Additionally, bundled fibers reduce fiber agglomeration, highlighting their potential for developing high energy-absorbing UHPC.

本研究介绍了一种新颖的钢纤维排列方式，即 "捆绑纤维"，在这种排列方式中，多根高强度钢丝被缠绕成短而不连续的纤维。通过单纤维拉拔试验评估了这些捆绑纤维在超高性能混凝土（UHPC）中的粘结行为。在三种嵌入长度（3.3 毫米、4.9 毫米和 6.5 毫米）范围内测试了四种不同的捆绑纤维，包括两到五根钢丝。结果表明，增加嵌入长度和捆绑更多钢丝可提高最大拉拔载荷、纤维应力、拉拔能量和粘结强度，但滑移能力会随着钢丝数量的增加而降低。与同等数量的直纤维相比，捆绑纤维在所有拉拔参数方面都表现出更优越的性能，在粘结强度和滑移能力方面也优于五种常见的钢纤维几何形状（直、条纹、波浪形、钩形、扭曲形）。为量化滑移硬化而引入的新参数填补了文献空白，由于扭转引起的摩擦结合，成束纤维显示出更高程度的滑移硬化。此外，成束纤维还能减少纤维结块，突出了其开发高能量吸收 UHPC 的潜力。

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引用次数: 0

Unraveling the photocatalytic and antimicrobial performance of carbon-TiO2/lignin hybrid admixtures in sustainable cement composites 揭示可持续水泥复合材料中碳-TiO2/木质素混合外加剂的光催化和抗菌性能

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-08 DOI: 10.1016/j.cemconcomp.2024.105843

Patryk Jędrzejczak , Anna Parus , Adam Kubiak , Petr Hotěk , Lukáš Fiala , Agnieszka Ślosarczyk , Teofil Jesionowski , Robert Černý , Łukasz Klapiszewski

The primary objective of this study was to develop cement composites with the ability to photocatalytically degrade contaminants and exhibit antimicrobial properties. To achieve this, titanium(IV) oxide was modified with carbon to create a photocatalyst active under both UV and visible light. The modified TiO₂ was then combined with kraft lignin, a byproduct of paper production, resulting in functional inorganic-organic hybrid systems. These hybrid materials were characterized using various research methods, including scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTG), low-temperature nitrogen sorption, and X-ray diffraction (XRD). The photocatalytic activity of these materials was evaluated under UV and visible light. The pristine components and resulting hybrid systems were incorporated into cement composites as admixtures in the amount of 1.0 wt% relative to the cement weight. The performance of both fresh and cured cement mortar was assessed, focusing on workability, compressive and flexural strength after 3 and 28 days of hydration. The compressive strength after 28 days in the case of the most favorable cement mortars improves from 54.7 MPa, as obtained for the reference sample, to values exceeding 60.0 MPa. It was established that the presence of lignin in the hybrid material introduced into the cement mortar contributes to an improvement in workability, ranging from 10 to 15 mm. Additional evaluations included pore structure parameters using mercury intrusion porosimetry, microstructural properties, photocatalytic activity as well as antimicrobial efficacy. The results indicated that the newly developed carbon-TiO₂/kraft lignin hybrid systems can be effectively utilized as functional admixtures in cement composites, enhancing their photocatalytic and antimicrobial properties.

这项研究的主要目的是开发出具有光催化降解污染物和抗菌性能的水泥复合材料。为此，用碳对氧化钛（IV）进行了改性，以产生一种在紫外线和可见光下均具有活性的光催化剂。然后，将改性后的二氧化钛与造纸副产品牛皮纸木质素结合，形成功能性无机-有机杂化系统。研究人员采用多种研究方法对这些杂化材料进行了表征，包括扫描电子显微镜（SEM）、傅立叶变换红外光谱（FTIR）、热重分析（TGA/DTG）、低温氮吸附和 X 射线衍射（XRD）。在紫外线和可见光下对这些材料的光催化活性进行了评估。原始成分和由此产生的混合系统作为外加剂掺入水泥复合材料中，掺量为水泥重量的 1.0 wt.%。对新鲜和固化水泥砂浆的性能进行了评估，重点是水化 3 天和 28 天后的可操作性、抗压强度和抗折强度。最理想的水泥砂浆在 28 天后的抗压强度从参考样本的 54.7 兆帕提高到超过 60.0 兆帕。结果表明，引入水泥砂浆的混合材料中木质素的存在有助于改善工作性，改善幅度为 10 至 15 毫米。其他评估还包括利用汞侵入孔隙测定法得出的孔隙结构参数、微观结构特性、光催化活性以及抗菌功效。结果表明，新开发的碳-二氧化钛/牛皮纸木质素杂化体系可有效用作水泥复合材料的功能掺合料，增强其光催化和抗菌性能。

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引用次数: 0

Aqueous carbonation of steel slags: A comparative study on mechanisms 钢渣的水碳化：机制比较研究

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-06 DOI: 10.1016/j.cemconcomp.2024.105838

Nannan Zhang , Gao Deng , Wenyu Liao , Hongyan Ma , Chuanlin Hu

This study investigated the aqueous carbonation mechanisms of three typical steel slags: ladle metallurgy furnace (LMF) slag containing high Al content, electric arc furnace (EAF) slag featuring high Si content and relatively low Al content, and ladle-arc fusion (LAF) slag with medium-Al content. It was found that the carbonation kinetics of the three slags were similar and followed the surface coverage model within the first 6 h of carbonation. Initially, the carbonation process was primarily governed by the reaction product precipitation. After 3 h of carbonation, the process was dominated by mineral dissolution, controlled by the uncovered reactive sites. The carbonation-reactive Ca-bearing minerals in the slags, including silicates (CRSis) and aluminates (CRAls), sequestered CO₂ to form calcite during carbonation, accompanied by the formation of silica gel and alumina gel, respectively. CRSi, mainly larnite, was present in EAF and LAF slags, showing high reactivity, whereas mayenite (i.e., C₁₂A₇), a CRAl mineral present across all slags, exhibited high reactivity in LMF slag but lower reactivity in EAF and LAF slags. Furthermore, AFm phases and katoite (i.e., C₃AH₆) were detected in LMF slag as CRAls along with mayenite, and their carbonation reactivity decreased in the order of AFm>mayenite>katoite. As a result, low-Al steel slag tends to have higher carbonation reactivity, as manifested by the high carbonation degree of EAF slag throughout the reaction period, notably achieving a 40 % carbonation degree within 30 min and 71 % after 24 h under the studied conditions.

本研究探讨了三种典型钢渣的水碳化机理：含铝量高的钢包冶金炉（LMF）渣、含硅量高而含铝量相对较低的电弧炉（EAF）渣和含铝量中等的钢包电弧熔炼炉（LAF）渣。研究发现，三种炉渣的碳化动力学相似，在碳化的最初 6 小时内遵循表面覆盖模型。最初，碳化过程主要受反应产物沉淀的控制。碳化 3 小时后，碳化过程由矿物溶解主导，由未覆盖的反应位点控制。炉渣中具有碳化反应的含钙矿物，包括硅酸盐（CRSis）和铝酸盐（CRAls），在碳化过程中螯合二氧化碳形成方解石，同时分别形成硅胶和氧化铝胶。CRSi，主要是拉氏铝酸盐，存在于 EAF 和 LAF 炉渣中，显示出较高的反应活性，而 mayenite（即 C12A7），一种存在于所有炉渣中的 CRAl 矿物，在 LMF 炉渣中显示出较高的反应活性，但在 EAF 和 LAF 炉渣中反应活性较低。此外，在 LMF 炉渣中还检测到 AFm 相和卡托石（即 C3AH6），它们与马氏体一样都是 CRAl，其碳化反应性按照 AFmɳ马氏体ɳ卡托石的顺序依次降低。因此，低铝钢渣往往具有更高的碳化反应活性，这表现在整个反应期间 EAF 渣的碳化程度很高，尤其是在研究条件下，30 分钟内达到 40% 的碳化程度，24 小时后达到 71%。

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引用次数: 0

Effects of relative humidity on carbonation kinetics and strength development of carbonated wollastonite composites containing sodium tripolyphosphate 相对湿度对含三聚磷酸钠的碳酸硅灰石复合材料碳化动力学和强度发展的影响

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-06 DOI: 10.1016/j.cemconcomp.2024.105831

Lulu Cheng , Yuxuan Chen , Zhaoping Song , Qian Deng , Qingliang Yu

Assessing the impact of relative humidity (RH) on carbonation kinetics is crucial for the sustainable and high-strength advancement of CO₂-activated Ca-bearing materials incorporating phase-controlling additives. This work focuses on the carbonation kinetics, mechanical properties, and microstructure evolution of carbonated wollastonite composites containing sodium tripolyphosphate (STPP) when exposed to various RH levels. Results show that RH plays an important role during the carbonation of wollastonite, functioning both as a reaction material and accelerating role for wollastonite carbonation. The carbonation rate and the phase transition reaction of poorly crystalline CaCO₃ is accelerated at RH ranging from 70% to 95%, favouring to cementitious behaviour of CaCO₃ and results in denser microstructure, especially for 85% RH. The carbonation reaction is composed of two distinct stages, namely, wollastonite dissolution and precipitation of the stage-1 and ion-diffusion controlling of stage-2. Among them, the addition of STPP prolong the carbonation duration of stage-1. The degree of carbonation (DOC) of the internal layer sample is higher than that of the outermost layer sample. CaCO₃ and silica gel are evenly distributed indirectly, which reduces the elastic modulus at 85 % RH. However, regardless of RH, the cementitious efficiency of poorly crystalline CaCO₃ is the highest, followed by calcite and silica gel. Consequently, STPP modified carbonated wollastonite shows highest strength when exposed to 85% RH (67.3 MPa at 7 days). Our study provides a unique way toward developing the STPP-containing carbonated wollastonite system for high performance carbonated materials.

评估相对湿度（RH）对碳化动力学的影响对于含有相控添加剂的二氧化碳活化含钙材料的可持续高强度发展至关重要。本研究重点关注含有三聚磷酸钠（STPP）的碳化硅灰石复合材料在不同相对湿度下的碳化动力学、机械性能和微观结构演变。结果表明，相对湿度在硅灰石的碳化过程中起着重要作用，它既是一种反应材料，又能加速硅灰石的碳化。在相对湿度为 70% 至 95% 的条件下，结晶度较低的 CaCO3 的碳化速率和相变反应会加快，有利于 CaCO3 的胶结行为，并导致微观结构更加致密，尤其是相对湿度为 85% 时。碳化反应由两个不同的阶段组成，即第一阶段的硅灰石溶解和沉淀以及第二阶段的离子扩散控制，其中 STPP 的加入延长了第一阶段的碳化时间。内层样品的碳化程度（DOC）高于最外层样品。CaCO3 和硅胶间接均匀分布，降低了 85% 相对湿度下的弹性模量。然而，无论相对湿度如何，结晶度较低的 CaCO3 的胶结效率最高，其次是方解石和硅胶。因此，STPP 改性碳化硅灰石在暴露于 85% 相对湿度时强度最高（7 天时为 67.3 兆帕）。我们的研究为开发含 STPP 的碳酸硅灰石系统提供了一条独特的途径，可用于制造高性能碳酸材料。

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引用次数: 0

Impacts of thermal activation on lunar regolith simulant-based precursor and resulting geopolymer: Composition, structure, solubility, and reactivity 热活化对月球岩石模拟基前驱体和由此产生的土工聚合物的影响：成分、结构、溶解性和反应性

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-06 DOI: 10.1016/j.cemconcomp.2024.105840

Guangjie Xue, Guofu Qiao

Alkali activation presents a promising method for the in situ resource utilization (ISRU) of lunar regolith. Enhancing the geopolymerization reactivity of lunar regolith simulant is key in minimizing alkali activator usage and improving raw material utilization. This study investigates the impact of thermal activation on precursor materials and the resultant geopolymers. Initially, the mineralogical composition and chemical structural changes in thermally activated samples were analyzed using XRD-Rietveld, XPS, and Raman spectroscopy. Subsequently, ICP-OES was employed to measure the solubility of various thermally activated samples in NaOH solution. Finally, the physicochemical composition and microstructure of the geopolymers were evaluated using SEM-EDS, FTIR, DSC, and compressive strength tests. The results show that thermal activation enhances precursor reactivity by increasing the non-bridging oxygen (NBO) content, reducing polymerization, and altering the binding energies of Si, Al, and O. Following thermal activation, the solubility of Si and Al in the NaOH solution was significantly improved. A more comprehensive thermal activation process produces geopolymers with improved compressive strength, a higher reaction degree, and a denser microstructure, and encourages the formation of Si-rich gels. Hence, treating precursor materials via thermal activation offers vast potential for creating lunar regolith geopolymer-based building materials with excellent properties.

碱活化是一种很有前景的月球残留岩原地资源利用（ISRU）方法。提高月球碎屑模拟物的土工聚合反应活性是最大限度减少碱活化剂用量和提高原材料利用率的关键。本研究调查了热活化对前驱体材料和由此产生的土工聚合物的影响。首先，使用 XRD-Rietveld、XPS 和拉曼光谱分析了热活化样品的矿物组成和化学结构变化。随后，采用 ICP-OES 测量了各种热活化样品在 NaOH 溶液中的溶解度。最后，使用 SEM-EDS、FTIR、DSC 和抗压强度测试评估了土工聚合物的理化成分和微观结构。结果表明，热活化可通过增加非桥接氧（NBO）含量、降低聚合度以及改变硅、铝和氧的结合能来提高前驱体的反应性。更全面的热活化过程产生的土工聚合物具有更好的抗压强度、更高的反应度和更致密的微观结构，并能促进富硅凝胶的形成。因此，通过热活化处理前驱体材料为创造具有优异性能的月球碎屑土工聚合物建筑材料提供了巨大的潜力。

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引用次数: 0

An innovative method for mesoscale modelling of moisture diffusion in concrete 混凝土中水分扩散的中尺度建模创新方法

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-05 DOI: 10.1016/j.cemconcomp.2024.105836

Songsong Meng, Yifan Li, Iman Hajirasouliha, Giacomo Torelli, Maurizio Guadagnini, Kypros Pilakoutas

Moisture diffusion influences the durability and long-term performance of concrete and whilst it predominantly occurs via the cement matrix and Interfacial Transition Zone, most existing models consider concrete to be homogeneous. This paper introduces a novel micro-meso model that employs random packing and Voronoi tessellation. Rayleigh-Ritz pore distribution and Brunauer-Skalny-Bodor models are combined to determine the radius and fraction of various pores. The results indicate that relative humidity diffuses faster with increasing temperature, decreasing ambient relative humidity and tortuosity. Ambient relative humidity has a greater influence on diffusion compared to temperature and tortuosity. Numerical and experimental comparisons demonstrate that the proposed methodology effectively captures relative humidity distribution across various scenarios. Furthermore, explicit pore network modelling incorporates key parameters for a more accurate analysis. Integrating the proposed methodology into a fully coupled hygro-mechanical framework can potentially yield more accurate predictions of mechanical behaviour; enhancing the reliability of long-term performance assessments and enabling more durable concrete design.

湿气扩散会影响混凝土的耐久性和长期性能，虽然湿气扩散主要通过水泥基体和界面过渡区进行，但大多数现有模型都认为混凝土是均质的。本文介绍了一种采用随机堆积和 Voronoi 网格的新型微观渗透模型。结合 Rayleigh-Ritz 孔隙分布和 Brunauer-Skalny-Bodor 模型，确定了各种孔隙的半径和比例。结果表明，相对湿度（RH）随着温度的升高、环境相对湿度的降低和迂回度的增加而扩散得更快。与温度和迂回度相比，环境相对湿度对扩散的影响更大。数值和实验比较表明，所提出的方法能有效捕捉各种情况下的相对湿度分布。此外，显式孔隙网络建模包含了关键参数，可实现更精确的分析。将所提出的方法整合到完全耦合的湿力学框架中，有可能获得更准确的力学行为预测；提高长期性能评估的可靠性，并使混凝土设计更加耐用。

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引用次数: 0

The corrosion-inhibitory influence of graphene oxide on steel reinforcement embedded in concrete exposed to a 3.5M NaCl solution 氧化石墨烯对暴露在 3.5M NaCl 溶液中的混凝土预埋钢筋的缓蚀影响

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-05 DOI: 10.1016/j.cemconcomp.2024.105835

L. Djenaoucine , C. Argiz , Á. Picazo , A. Moragues , J.C. Gálvez

Steel reinforcement corrosion significantly reduces the durability and service life of concrete structures, particularly in chloride-rich environments such as marine and coastal areas. This study aims to reduce the corrosion rate using graphene oxide (GO) as a corrosion inhibitor. Two GO dosages (0.0005 and 0.005 wt%) were evaluated for their effectiveness in mitigating corrosion in reinforced concrete exposed to a 3.5M NaCl solution. To assess the corrosion behavior of the steel reinforcement, Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy (EIS), and Linear Polarization Resistance (LPR) were evaluated over one year by wetting/drying cycles. Oxygen permeability and electrical resistivity tests were also conducted to evaluate the concrete's susceptibility to corrosion. Both GO content demonstrated significant corrosion inhibition, with the 0.005 wt% dosage providing the most effective protection. This was evidenced by the lowest i_corr values recorded during the final cycle (52), larger capacitive loops, and higher impedance in EIS results, indicating enhanced corrosion resistance. Visual inspection of steel bars further confirmed these findings, showing no signs of deterioration or discoloration in GO-modified concrete compared to steel bars extracted from reference concrete. SEM-EDS analysis revealed higher carbon content on the steel surface, suggesting GO adsorption and the formation of a protective passive layer. These results suggest that GO is a promising nanomaterial for inhibiting corrosion in steel-reinforced concrete exposed to aggressive environmental conditions.

钢筋锈蚀会大大降低混凝土结构的耐久性和使用寿命，尤其是在海洋和沿海地区等氯离子含量较高的环境中。本研究旨在使用氧化石墨烯（GO）作为缓蚀剂来降低腐蚀速率。研究评估了两种石墨烯剂量（0.0005 和 0.005 wt.%）在减轻暴露于 3.5M NaCl 溶液中的钢筋混凝土腐蚀方面的效果。为了评估钢筋的腐蚀行为，对开路电位 (OCP)、电化学阻抗谱 (EIS) 和线性极化电阻 (LPR) 进行了评估，以监测一年内湿润/干燥循环的腐蚀情况。此外，还进行了透氧性和电阻率测试，以评估混凝土的易腐蚀性。两种 GO 含量都有明显的缓蚀效果，其中 0.005 wt.% 的剂量提供了最有效的保护。这表现在最后一个循环中记录的 icorr 值最低（52），电容环较大，EIS 结果的阻抗较高，表明抗腐蚀能力增强。对钢筋的目测进一步证实了这些发现，与从参照混凝土中提取的钢筋相比，GO 改性混凝土中的钢筋没有劣化或变色的迹象。扫描电子显微镜-电子显微镜分析（SEM-EDS）显示，钢材表面的碳含量更高，这表明 GO 被吸附并形成了一个被动保护层。这些结果表明，GO 是一种很有前途的纳米材料，可用于抑制暴露在侵蚀性环境条件下的钢筋混凝土的腐蚀。

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引用次数: 0

Experiment and simulation on the coupled effects of calcium leaching and chloride transport in concrete under hydraulic pressure 水压作用下混凝土中钙浸出和氯离子迁移耦合效应的实验与模拟

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-03 DOI: 10.1016/j.cemconcomp.2024.105834

Jie-jing Chen , Qing-feng Liu , Wei-liang Jin , Jin Xia

This study investigated the coupled effect of calcium leaching and chloride erosion on concrete subjected to hydraulic pressure by combining experiments and numerical simulations. Several tests including titration, pH, XRD, TG, MIP, and SEM-EDS were employed to analyze chloride concentration, pH value, solid phase compositions, and microstructure of concrete under hydraulic pressure. Concurrently, a model based on the physicochemical interactions between the pore solution and the hydration products was constructed to elucidate the process of calcium leaching and multi-ion transport. The experimental and simulation results reveal that hydraulic pressure accelerates calcium leaching in concrete, leading to a maximum porosity that reaches 1.5 times the initial porosity after a year. In addition, both the pH value and chloride binding capacity in the zone close to the exposure surface decrease. The enrichment of Ca²⁺ and OH⁻ occurs at a specific depth within concrete during the calcium leaching process, and over time, this enrichment effect grows increasingly significant. Along the depth within the concrete, a transient increase in chloride binding capacity can be observed, which can be attributed to OH⁻ and Ca²⁺ enrichment.

本研究通过实验和数值模拟相结合的方法，研究了水压作用下钙浸出和氯侵蚀对混凝土的耦合效应。通过滴定、pH 值、XRD、TG、MIP 和 SEM-EDS 等试验分析了水压作用下混凝土的氯离子浓度、pH 值、固相组成和微观结构。同时，构建了基于孔隙溶液与水化产物之间物理化学相互作用的模型，以阐明钙浸出和多离子迁移的过程。实验和模拟结果表明，水压加速了混凝土中的钙浸出，导致最大孔隙率在一年后达到初始孔隙率的 1.5 倍。此外，靠近暴露面区域的 pH 值和氯化物结合能力都有所下降。在钙沥滤过程中，Ca2+ 和 OH- 在混凝土内部特定深度发生富集，随着时间的推移，这种富集效应越来越显著。沿着混凝土内部的深度，可以观察到氯化物结合能力的瞬时增加，这可以归因于 OH- 和 Ca2+ 的富集。

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引用次数: 0

Experiment and modelling of degradation mechanism of cement mortar with graphene oxide nanosheets under sulfate attack 硫酸盐侵蚀下氧化石墨烯纳米片水泥砂浆降解机理的实验与建模

IF 10.8 1区工程技术 Q1 CONSTRUCTION & BUILDING TECHNOLOGY

Cement & concrete composites

Pub Date : 2024-11-02 DOI: 10.1016/j.cemconcomp.2024.105833

Hongyan Zeng , Ruichen Zhou , Jing Yu , Yunjin Hu , Shen Qu , Junbin Chen , Shaodan Hou

Degradation of cementitious materials caused by sulfate attack poses a significantly challenge to their durability. Using nano-additives to enhance the mechanical and durability properties of cementitious materials is a promising solution; however, the impact of graphene oxide (GO) on the sulfate resistance is not yet fully understood. While efforts have been made to study the degradation mechanism through accelerated indoor tests with high sulfate concentrations, these methods fail to accurately replicate real-world field exposure conditions. To better understand the degradation mechanism of GO-modified mortars under actual field conditions, this study examines the long-term degradation (over 24 months) of GO-modified mortars exposed to sulfate solutions with varying concentrations: 0 % (reference), 2.1 % (field condition), 5 % (laboratory condition), and 15 % (high-concentration condition). Additionally, a comprehensive chemo-mechanical model that considers multiple factors and time-varying boundary conditions was proposed. The study thoroughly discusses the effects of GO dosage, sulfate concentration, and exposure time on the degradation mechanism. Comparison with experimental data revealed that cement mortar degradation under sulfate attack is primarily driven by the crystallization pressure related to ettringite formation in diluted sulfate solutions, while the precipitation of alkali ions from mortar pore solutions occurs in concentrated sulfate solutions. In real-field conditions, cement mortar degradation primarily involves gypsum precipitation rather than ettringite formation. This study demonstrates that well-dispersed GO nanosheets can significantly enhance durability of cementitious materials against sulfate attack, offering valuable insights for strategic applications of GO nanosheets in cementitious materials.

硫酸盐侵蚀导致的混凝土降解严重影响了混凝土的耐久性。利用纳米添加剂来提高混凝土（包括砂浆）的机械和耐久性能是一种很有前景的解决方案，但氧化石墨烯（GO）对耐硫酸盐性能的影响仍未得到充分了解。虽然人们一直在努力通过高浓度硫酸盐的室内加速试验来了解降解机理，但这些方法无法准确复制现场暴露条件。为了更好地了解 GO 改性砂浆在实际现场条件下的降解机理，本研究对暴露在不同浓度硫酸盐溶液中的 GO 改性砂浆的长期降解（24 个月）进行了深入研究：0%（参考值）、2.1%（现场条件）、5%（实验室条件）和 15%（高浓度条件）。此外，还提出了一个具有时变边界条件的多因素耦合化学机械模型，并深入讨论了 GO 用量、硫酸盐浓度和暴露时间对降解机制的影响。根据实验数据进行验证后发现，在稀释的硫酸盐溶液中，砂浆在硫酸盐侵蚀下的降解主要是由与乙曲石形成有关的结晶压力驱动的，而在浓硫酸盐溶液中，砂浆孔隙溶液中的碱离子会发生沉淀。在实际现场条件下，砂浆降解主要涉及石膏的沉淀，而不是乙长石。研究表明，分布均匀的 GO 纳米片可以在硫酸盐侵蚀下显著提高混凝土的耐久性。这些发现为利用 GO 纳米片提高混凝土耐久性提供了宝贵的见解。

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