纳米SiO2对钢纤维/混凝土高温后力学性能及微观结构的影响

研究了掺纳米SiO2的钢纤维混凝土(NSFC)、钢纤维混凝土(SFRC)和普通混凝土(NC)三种材料在不同加热温度后的抗压、劈裂和抗折强度等力学性能,对不同温度热处理后的微观结构进行了SEM分析,对钢纤维与过渡区界面的相结构进行了XRD分析.结果表明:在测试温度范围内,NSFC的抗压、劈裂和抗折强度均高于SFRC和NC的强度,且在400℃时达到最大值.在常温下,NSFC的抗压、劈裂和抗折强度较NC分别提高27.01％、63.28％和54.12％,400℃高温热处理后比NC分别高35.09％、84.62％和87.23％; SEM分析表明,在钢纤维与过渡区的界面处,致密度提高,显微硬度提高.由于固相反应,使界面区结构发生变化,在钢纤维表层形成扩散渗透层(白亮层),即化合物层,呈锯齿状,XRD分析证明,白亮层主要由FeSi2和复杂的水化硅酸钙组成,从而增强了钢纤维与基体的粘结力,提高了混凝土的高温力学性能.     

纳米SiO2对钢纤维/混凝土高温后力学性能及微观结构的影响

研究了掺纳米SiO₂的钢纤维混凝土(NSFC)、 钢纤维混凝土(SFRC)和普通混凝土(NC)三种材料在不同加热温度后的抗压、 劈裂和抗折强度等力学性能, 对不同温度热处理后的微观结构进行了SEM分析, 对钢纤维与过渡区界面的相结构进行了XRD分析。结果表明: 在测试温度范围内, NSFC的抗压、 劈裂和抗折强度均高于SFRC和NC的强度, 且在400 ℃时达到最大值。在常温下, NSFC的抗压、 劈裂和抗折强度较NC分别提高27.01%、 63.28%和54.12%, 400 ℃高温热处理后比NC分别高35.09%、 84.62%和87.23%; SEM分析表明, 在钢纤维与过渡区的界面处, 致密度提高, 显微硬度提高。由于固相反应, 使界面区结构发生变化, 在钢纤维表层形成扩散渗透层(白亮层), 即化合物层, 呈锯齿状, XRD分析证明, 白亮层主要由FeSi₂和复杂的水化硅酸钙组成, 从而增强了钢纤维与基体的粘结力, 提高了混凝土的高温力学性能。     

泡沫混凝土微观结构对宏观性能的影响机理

针对当前阻碍泡沫混凝土广泛应用的主要因素,即对泡沫混凝土性能的基本认知不足且技术研究尚不充分,综述泡沫混凝土在混凝土拌合至初凝、硬化过程和使用过程3个阶段中微观结构的形成及劣化机理,介绍泡沫混凝土微观结构与宏观性能之间的理论模型和模型的适用范围,证实泡沫混凝土的微观结构对自重、导热、机械强度、渗透等宏观性能的影响;从胶凝材料、集料、矿物混合材、发泡剂、外加剂、配合比以及材料制备工艺等角度分析影响泡沫混凝土微观结构的因素,探讨微观结构控制的机理和可行性,指出未来的研究方向是在当前研究的基础上对泡沫混凝土的制备条件和工艺参数控制进行进一步改进和探索。     

玄武岩纤维对喷射混凝土力学性能及微观结构的影响机制

通过力学性能实验研究了玄武岩纤维（BF）对玄武岩纤维/喷射混凝土（BF/SC）基本力学性能及韧性的影响规律,同时借助扫描SEM及核磁共振（NMR）实验对BF/SC的微观结构进行研究。结果表明:添加BF可以显著提高BF/SC的抗压强度、劈裂抗拉强度和抗弯强度;相较于素SC,掺量为3 kg/m3及7.5 kg/m3的BF/SC抗弯试块韧性较好,其能量吸收能力分别为素SC的2.42倍和2.69倍。BF在SC内部具有较好的分散性,与SC基体界面粘结性较好。适量BF有效地抑制了大体积孔隙的生成,其中掺量为3 kg/m3的BF/SC大孔径孔隙占比仅为0.25%,但过多BF掺入会导致纤维结团及孔隙率增加,因此在本文实验条件下纤维掺量为3 kg/m3时BF/SC性能最好。      

试析PP膜对表层混凝土微观结构的影响

借助PP膜,将其制作成透水模板开展混凝土性能实验,对实验的混凝土进行表层取样,进行扫描电镜研究。研究发现,随着养护时间推移,水泥水化会更加完美。本文分析了pp膜对表层混凝土微观结构影响。     

聚氨酯对环氧树脂涂料力学性能和微观结构的影响

通过聚氨酯增韧环氧树脂制备一种强度高、附着力大、耐水性好、耐化学稳定性强的涂料.通过正交实验法,确定了涂料的最佳工艺条件,进行了拉伸强度、冲击强度、吸水率、附着力、红外光谱和扫描电镜等测试.实验结果表明:聚氨酯含量15％(质量分数,下同),固化剂含量15％,反应温度70℃,反应时间60min时,涂料的力学性能最佳;制备...     

Si含量对(AlCrTiZrHf)-Six-N高熵薄膜微观结构和力学性能的影响

采用自制的复合靶材,通过直流磁控溅射技术,在单晶Si基片上沉积一系列不同Si含量的(AlCrTiZrHf)-Si_x-N高熵薄膜,并依次采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、高透射电子显微镜(HRTEM)和纳米压痕仪对薄膜进行表征和测试,研究Si含量对其微观结构和力学性能的影响。实验结果显示,(AlCrTiZrHf)N薄膜成柱状晶生长,并具有(111)晶面的择优取向。Si元素的掺入,使得原薄膜的(111)峰消失,(AlCrTiZrHf)-Si_x-N薄膜晶粒得到细化,同时生成网状非晶相,从而形成非晶包裹纳米晶的纳米复合结构。随着Si含量的增加,薄膜力学性能先上升后下降,这种趋势归因于所形成的纳米复合结构,并且当Si含量为8%(体积比)时,薄膜的硬度和弹性模量最高,分别为26.6和250.9 GPa。     

冻融循环作用下玄武岩纤维-矿渣粉-粉煤灰混凝土压拉强度试验与细观结构

对玄武岩纤维-矿渣粉-粉煤灰混凝土(BF-SP-FAC)进行了单轴抗压试验、劈裂抗拉试验、冻融循环试验、气孔结构测试试验和SEM分析.研究了不同冻融次数下BF-SP-FAC冻融损伤量、抗压强度、抗拉强度的变化,分析了气孔结构参数(含气量、气孔比表面积、气泡间距系数和气泡平均弦长)与BF-SP-FAC抗压强度、抗拉强度、...     

粉体表面包碳对3Y-TZP陶瓷烧结性能及微观结构的影响

采用对纳米氧化锆陶瓷粉体表面包碳,研究了在不同烧结工艺下,碳含量(0%～7.0%(wt))的变化对纳米氧化锆陶瓷烧结性能及微观结构的影响.分析结果表明:包裹少量碳能明显提高烧结活性,增大烧结坯密度.在本实验条件下,碳含量为1.5wt%的纳米氧化锆陶瓷在1250℃低温氧化气氛中烧结,可得到相对密度约为96%、晶粒尺寸约为85m的陶瓷体,此后随着碳含量的增加,致密度减小;采用真空烧结,由于碳没有被氧化,包裹层的存在阻止了晶界的扩散,延缓了陶瓷体烧结的致密化过程,烧结性能较差;同时碳的加入有效地抑制了晶粒的长大.     

不同厚度二维VN插入层对TiSiN纳米复合膜微观结构和力学性能的影响

采用TiSi复合靶与V靶, 用射频磁控溅射工艺在TiSiN纳米复合膜中插入不同厚度的VN纳米层, 采用X射线衍射仪(XRD)、高分辨透射电子显微镜(HRTEM)和纳米压痕仪研究了VN插入层厚度对TiSiN纳米复合膜的微观结构和力学性能的影响。结果表明: 当TiSiN纳米复合膜中插入VN纳米层厚度较小时, 薄膜由纳米复合结构转变成纳米多层结构, 薄膜硬度降低。继续增加VN层厚度, 薄膜硬度随之升高, 在VN沉积层厚为0.5 nm时薄膜出现连续贯穿多层纳米层、结晶度良好的柱状晶, TiSiN层与VN层呈共格外延生长的结构, 薄膜硬度达到37.2 GPa。随着VN层厚的继续增加, 薄膜的共格外延生长结构消失, 硬度下降。     

Effect of sludge water from ready-mixed concrete plant on properties and durability of concrete

Besides the increasing disposal cost, sludge water, a wastewater washout from ready-mixed concrete plant, has caused environmental impact problems. This paper investigates the utilization and recycling of sludge water as mixing water for concrete production. The basic properties of sludge water were obtained according to ASTM standards. The properties of dry sludge powder such as chemical compositions and physical properties were investigated. The properties of fresh concrete studied were unit weight, slump, and temperature rise. The mechanical properties of concrete, such as compressive strength and modulus of elasticity, were studied. The durability aspects, such as drying shrinkage and weight loss due to acid attack, were investigated. For parametric study, sludge water was used as a replacement of tap water varying from 0% to 100% by weight. The water-to-cement ratios were 0.5, 0.6, and 0.7, respectively. In this study the sludge water tested has a high alkalinity and the total solids content exceeding the limit of ASTM C94, contributing to the more porous and weaker matrix. As a result, when increasing the percentage of sludge water in mixing water, the drying shrinkage and weight loss due to acid attacks increased, and the slump and strength decreased. However, the unit weight and temperature of fresh concrete were not affected by the use of sludge water.     

Effect of further water curing on compressive strength and microstructure of CO2-cured concrete

This study aims to investigate the effects of further water curing on the compressive strength and microstructure of CO₂-cured concrete. The results showed that concrete with a residual w/c ratio of 0.25 showed the most rapid strength development rate upon further water curing due to hydration of uncarbonated cement particles. Thermogravimetric, IR-spectrophotometric and scanning electron microscope examinations indicated that further hydration of the cement particles could form C-S-H gel and ettringite crystals. The results showed that the calcite formed during the initial CO₂ curing was consumed during the further hydration of C₃A, and produced calcium monocarbonaluminate hydrate. Also, Ca(OH)₂ was not detected due to its reaction with the formed silica gel. Mercury intrusion porosimetry test results indicated that the porosity and pore size of the CO₂ cured mortar decreased further after water curing.     

Interdependence of microstructure and strength of structural lightweight aggregate concrete

The demand for lightweight concrete is steadily increasing because of economic and practical considerations. Hence, the inherent internal and external features of lightweight aggregates have been a subject of intense research in recent years. This study provides new insight into the micro-structural and chemical factors which influence the strength properties of structural lightweight aggregate concrete. These are described with respect to four expanded clay lightweight aggregates used in nine concrete compositions containing various types and proportions of dispersing agents such as water-reducing admixtures and superplasticizers, with silica fume and ground granulated blast-furnace slag as optional mineral admixtures. The microstructural characteristics of the paste-aggregate interface and the paste porosity of these concretes are discussed. The methods used include scanning electron microscopy-energy-dispersive X-ray analysis, X-ray diffraction analysis, optical microscopy and compressive strength testing.     

Influence of confinement on high strength concrete behavior

An experimental program has been made in order to study the confined concrete behavior when its strength changes from traditional values to high strength values and with confinement levels ranging from 0% to values higher than 4%. The specimen shape and size have also been included as variables. With the data experimentally achieved, the parameters that define the stress-strain curve for concrete were adjusted using a statistical methodology that gives us suitable approximation levels. A stress-strain curve model is proposed, which lets us know precisely the confined concrete behavior up to high strain levels and analyze the material ductility. The achieved improvement, thanks to the confinement, was quantified regarding the parameters that define the concrete behavior, particularly the maximum strength, the strain at the peak and the ductility.

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Résumé Un programme expérimental a été développé pour étudier le comportement du béton confiné avec une teneur en armature transversale de 0% à 4%. L'étude analyse des bétons de résistance entre 25 MPa et 100 MPa. D'autres variables ont été la forme et la dimension des éprouvettes. Avec les résultats expérimentaux obtenus on a réalisé une analyse statistique pour définir les paramètres de la courbe Contrainte-déformation avec une bonne corrélation. On a proposé un modèle de courbe Contrainte-déformation qui montre le comportement du béton à hautes performances confiné jusqu'à des niveaux de déformation très élevés, et qui permet l'analyse de la ductilité du matériau. Les performances obtenues grace au confinement ont été quantifiées d'après les paramètres qui définissent le comportement du béton, en particulier de sa résistance, de la déformation au pic et sa ductilité.

     

Management of arsenic-laden water plant sludge by stabilization

When arsenic is co-precipitated with iron hydroxide in an arsenic-removal water plant, a large quantity of sludge is generated which contains a good amount (an average of 6.1 kg As/m³ of sludge) of arsenic. The present paper attempts to find some suitable solutions to disposal of this arsenic-bearing sludge. As a safe means of disposal, stabilization processes such as briquette production, cement mortar and concrete making have been attempted in the present investigation. It has been found that in the preparation of briquette, cement–sand mortar and concrete, mixing up to 10, 18 and 40% of arsenic-bearing sludge by volume, respectively with the other common ingredients did not produce a TCLP leachate beyond its permissible direct inland water discharge standards of 0.2 g/m³ as stipulated by the Ministry of Environment & Forest, Government of India. Also, it was noted that 25% (by volume) of cement could be replaced by fly ash to stabilize arsenic-laden sludge to the tune of 11% by volume of cement–sand (1 : 3) mortar.     

Influence of pressure-assisted polymerization on the microstructure and strength of polymer-infiltrated ceramics

A method of manufacturing polymer-infiltrated ceramics (PICs) is to pre-infiltrate a porous ceramic with a liquid monomer and subsequently polymerize the organic component inside the ceramic structure. The volume reduction during polymerization leads to the formation of pores (defects), which has a detrimental effect on the mechanical properties of PICs. To avoid the generation of defects, a new polymerization method that uses pressure during polymerization was developed. To investigate the influences of pressure and heating rate on strength and microstructure, both parameters were varied. The influences of both parameters on the strength of PICs were studied using a biaxial test. The influence on the microstructure was investigated through microscopy. Fracture toughness and R-curve behavior of the manufactured PICs were determined with the SEVNB method. The process parameters have a strong influence on strength and microstructure of PICs. Defect-free PICs with improved strength could be manufactured using elevated pressure during polymerization. As expected, a distinct R-curve behavior and enhanced fracture toughness relative to composites manufactured using conventional methods was found. The developed manufacturing method leads to defectless PICs with increased mechanic behaviors.     

Influence of powder characteristics and powder processing routes on microstructure and properties of hot pressed silicon nitride materials

Four different commercial Si₃N₄ powders were hot pressed with the addition of La₂O₃ and Y₂O₃ as sintering aids. Two powder processing routes were set up: addition of sintering aid powders by ultrasonic dispersion, addition of nanodispersed amorphous additive species by chemical coprecipitation. The following aspects were analyzed: characteristics of starting powders and powder mixtures, with reference to surface modification (electrokinetic behaviour and surface properties) induced by the powder treatment; sintering behaviour of the powder mixtures; influence of raw powders characteristics and processing route on microstructure and properties of dense materials. The microstructural characteristics of hot pressed materials (grain size, aspect ratio, grain boundary phases) were found to be dependent on powder characteristics and its process history. Significant variation of the mechanical properties (Young modulus, hardness, toughness and strength) were related to microstructural features. Strength, for example, ranges from 600 to 1200 MPa at room temperature and from 400 to 1000 MPa at 1200°C; toughness ranges from about 4 to about 6 MPam^1/2.