氧化石墨烯对水泥基渗透结晶型防水材料抗渗性能的影响

研究了木质素磺酸钠(MN)对氧化石墨烯(GO)在模拟水泥水化孔隙液中的分散能力的影响,并研究了MN分散的GO对水泥基渗透结晶型防水材料(CCCW)对水泥砂浆抗渗性能的影响。通过吸光度试验、Zeta电位及原子力显微镜(AFM)研究表明,当MN与GO的质量比为3∶1时,GO在饱和氢氧化钙溶液中的分散性最佳;砂浆力学强度测试表明,当GO掺量为水泥质量的0.03%时,3天、28天的抗折抗压强度相较于不掺入MN的GO砂浆分别提高了39.13%和39.37%、33.84%和33.48%;砂浆抗渗压力和氯离子扩散系数比标准砂浆试件分别提高了160.0%和下降了50.6%;抗渗性能测试表明,当GO掺量为水泥质量的0.03%时,GO改性CCCW涂层抗渗压力比含CCCW的涂层提高了116.7%;微观测试表明,GO促进了水化反应,并在砂浆基质中发挥了填充作用和模板作用,增强了水化产物的密实度,使得砂浆和CCCW抗渗性能增加了。本文提供了一种GO改性CCCW来提升水泥砂浆的抗渗性能,在涂层防水效果和降低CCCW材料成本等应用价值得到提升。     

Combined use of waste glass powder and cullet in architectural mortar

The use of 100% waste glass cullet (WGC) as fine aggregates in architectural cement-based mortar had been proven to be feasible in previous works. This paper reports a further study on investigating the influence of using waste glass powder (WGP) as a supplementary cementitious material on the properties of glass-based architectural cement mortars. The experimental results showed a good linear relationship between the particle size of WGP and the flow values of the fresh mortar, revealing that the particle size of WGP played an important role in controlling the workability. For the hydration of white cement, the inclusion of WGP not only affected the second exothermic peak of hydration but also changed the third peak. In particular, the result indicated that the use of finer WGP had an advantage in increasing the flexural strength of the cement mortar when compared with the corresponding compressive strength, which was attributed to the morphological and pozzolanic effect of WGP. In addition, the very fine WGP could act as micro-fibers and micro-aggregates in filling the microstructure of the mortar. At 90 days of curing, the mortar prepared with finer WGP showed a distinct improvement in strength due to the improved interfacial transition zone and the pore-size refinement.     

亲水型功能化石墨烯的分散性及其对水泥基复合材料力学性能的影响

为了解决石墨烯纳米片在水泥基体中的分散问题,采用芳基重氮盐(F)对氧化石墨烯(GO)进行改性,制备了一种新型亲水型功能化石墨烯(FG).结果表明,FG在水溶剂中最大的分散浓度能够达到2.1mg/mL.FTIR、拉曼光谱和XPS结果表明F成功对石墨烯进行了表面改性.对比纯水泥基体材料,本文所制备的亲水型FG/水泥复合材料...     

Nanoindentation and SEM/EDX characterization of the geopolymer-to-steel interfacial transition zone for a reactive porcelain enamel coating

The increasing use of alternative cementitious materials such as geopolymers as an environmentally-friendly alternative to traditional cements requires an improved understanding of the interfacial transition zone (ITZ) between the matrix and reinforcing steels. In this study, nanoindentation measurements were spatially coupled to images with scanning electron microscopy and chemical composition using energy dispersive X-ray microanalysis. The study focused on the microstructure and chemical composition of the interfacial transition zone (ITZ) for reinforcing steel embedded in a geopolymer mortar. The ITZ was analyzed for uncoated steel and steel coated with a reactive porcelain enamel that improves bonding and corrosion resistance. Results indicate that a more gradual transition of mechanical properties and chemical composition for the coated steel coupled with improved integration to the mortar correlates to increased bond strength measured in macroscale experiments.     

Reinforcing graphene oxide/cement composite with NH<Subscript>2</Subscript> functionalizing group

In this study, pure and NH₂-functionalized graphene oxide (GO) nanosheets have been added to the cement mortar with different weight percents (0.05, 0.10, 0.15, 0.20 and 0.25 wt%). In addition, the effects of functionalizing GO on the microstructure and mechanical properties (flexural/compressive strengths) of cement composite have been investigated for the first time. Scanning electron microscopy (SEM) images showed that GO filled the pores and well dispersed in concrete matrix, whereas exceeding GO additive from 0.10 wt% caused the formation of agglomerates and microcracks. In addition, mercury intrusion porosimetry confirmed the significant effects of GO and functionalizing groups on filling the pores. NH₂-functionalizing helped to improve the cohesion between GO nanosheets and cement composite. Compressive strengths increased from 39 MPa for the sample without GO to 54.23 MPa for the cement composites containing 0.10 wt% of NH₂-functionalized GO. Moreover, the flexural strength increased to 23.4 and 38.4% by compositing the cement paste with 0.10 wt% of pure and NH₂-functionalized GO, compared to the sample without GO, respectively. It was shown that functionalizing considerably enhanced the mechanical properties of GO/cement composite due to the interfacial strength between calcium silicate hydrates (C-S-H) gel and functionalized GO nanosheets as observed in SEM images. The morphological results were in good agreement with the trend obtained in mechanical properties of GO/cement composites.     

Highly dispersed graphene oxide electrodeposited carbon fiber reinforced cement-based materials with enhanced mechanical properties

Mechanical behavior of carbon fiber (CF) reinforced cement-based materials greatly depends on the dispersion of CF and interfacial properties between the CF and cement matrix. In this study, graphene oxide (GO) was utilized to modify the surface properties of CF, including the roughness, wettability and chemical reactivity, and the graphene oxide/carbon fiber (GO/CF) hybrid fibers were fabricated by a newly designed electrophoretic depositing method. The scanning electron microscopy and contact angle measurement results indicated that GO/CF hybrid fibers not only had a rougher surface which was expected to improve the physical friction when CF was pulled out from cement matrix, but also had a higher wettability surface that made it easier to contact with cement hydrates as nucleation sites. In addition, GO/CF hybrid fibers were capable of high chemical reactivity due to the introduction of GO with many functional groups, which ensured them more likely to interact with cement hydrates due to the hydrogen bonding at interface and therefore benefited to strengthen the bonding between the CF and cement matrix. In terms of mechanical behavior, three-point bending test showed that compared with the CF reinforced cement paste, flexural strength of the GO/CF hybrid fibers reinforced cement paste was enhanced by 14.58%, and could be further improved by 10.53% when the GO/CF hybrid fibers were pre-dispersed in the GO solution and then mixed with cement powders. The larger electrostatic repulsion and steric stabilization led to the better dispersion of GO/CF hybrid fibers in GO solution, which were responsible for the further mechanical enhancement of cement paste. In conclusion, the research outcomes provided a novel way for utilizing GO as both of dispersant and surface modifier to improve the dispersion of CF in cement and strengthen its bonding with cement hydrates, consequently achieving a significant enhancement in the mechanical properties of cement paste.     

Diazonium functionalization of graphene nanosheets and impact response of aniline modified graphene/bismaleimide nanocomposites

For developing high performance of graphene-based nanocomposites, dispersibility of graphene sheets in matrices and interfacial interaction are challenging due to the strong tendency of agglomeration and surface inertia of graphene. Here we report an efficient way to functionalize graphene nanosheets with aniline groups on their surfaces, to attain the functionalized graphene nanosheets (FGS) by diazonium treatment following reduction of graphene oxide with hydrazine hydrate. Two kinds of nanocomposites based on diallyl bisphenol A modified bismaleimide (BMI-BA) resin which was filled with functionalized graphene and reduced graphene oxide nanosheets were prepared, and the FGS were linked with BMI resin by chemical bonds. The FGS/BMI-BA composite at a loading of 0.3 wt% revealed a 39% increase in impact strength and a slightly improvement in flexural strength, and the resulting composite remains stable at high temperature. This work provides more possibilities for incorporation of graphene into polymer matrices and an efficient method to toughening the BMI resin.     

界面区结构对水泥砂浆强度的影响

在研究具有水硬性表面层和惰性内核复合结构的深加工处理石英集料对砂浆界面区结构的改进效果，比较深加工处理石英砂浆（ＭＴＱＳ）、普通石英砂浆（ＭＱＳ）和硬化水泥浆体（ＨＣＰ）等３种试样强度随养护时间变化的基础上，研究了界面区结构对水泥砂浆强度的影响．结果表明：使用深加工处理石英集料能有效地改进界面区薄弱结构；界面区结构对水泥砂浆的早期强度影响较小，但对后期强度影响较大；改进界面区结构能大幅度提高水泥砂浆的抗压强度和抗折强度．     

氧化石墨烯纳米片层对水泥基复合材料的增韧效果及作用机制

通过氧化和超声波分散制备了氧化石墨烯（GO）纳米片层分散体系,研究了GO纳米片层对水泥基复合材料的增韧效果及作用机制。用EDS、FTIR、XRD、SEM和AFM对GO纳米片层的结构进行了表征。研究结果表明：所得GO含氧量为32.3wt%,GO纳米片层的厚度为6 nm左右,在GO片层表面含有羟基、羧基和磺酸基等活性基团。水泥基复合材料的SEM形貌及力学性能测定结果表明：当GO掺量为0.03wt%时,GO能够使水泥水化产物形成花朵状晶体,并使水泥基复合材料的拉伸强度、抗折强度和压缩强度比对照样品分别提高了65.5%、60.7%和38.9%。提出了GO纳米片层对水泥水化产物的模板调控机制,揭示了花状晶体的形成过程。     

Improving the thermal and mechanical properties of silicone polymer by incorporating functionalized graphene oxide

Functionalized graphene oxide (FGO) was produced by reacting graphene oxide nanosheets with vinyl trimethoxy silane (VTMS). The results confirmed the attachment of VTMS molecules to the surface of GO sheets by Si–O–C bonding. The introduction of VTMS molecules led to an excellent dispersibility in tetrahydrofuran and to the complete exfoliation of FGO with a thickness of about 1.19 nm. Meanwhile, FGO/silicone polymer composites were prepared by solution blending method. The incorporation of 0.5 wt% of FGO in silicone polymer improved remarkably the thermal stability, tensile strength, and thermal conductivity of the silicone polymer composite, due to the homogeneous dispersion of FGO in the composites as well as to the strong interfacial adhesion with silicone polymer matrix. Tensile strength and thermal conductivity of the FGO/silicone polymer composite were increased by 95.6 and 78.3 %, respectively, with the addition of 0.5 wt% FGO. The 5 % weight loss temperature of the composite at 0.5 wt% FGO loading was detected 26.1 °C higher than that of silicone polymer.     

Multi-scale investigation of microstructure,fiber pullout behavior,and mechanical properties of ultra-high performance concrete with nano-CaCO3 particles

The mechanical properties of a fiber-reinforced concrete are closely related to the properties of the matrix, fiber, and fiber-matrix interface. The fiber-matrix bond property is mainly governed by the adhesion between the fiber and surrounding cement materials, as well as the strength of materials at the interfacial transition zone. In this paper, the effect of nano-CaCO₃ content, varying between 0 and 6.4%, by mass of cementitious materials, on microstructure development, fiber-matrix interfacial bond properties, and mechanical properties of ultra-high performance concrete (UHPC) reinforced with 2% steel fibers were investigated. The bond properties, including bond strength and pullout energy, were evaluated. Mercury intrusion porosimetry (MIP), backscattered electron microscopy (BSEM), optical microscopy, and micro-hardness testing were used to characterize the microstructure of matrix and/or interfacial transition zone (ITZ) around an embedded steel fiber. Test results indicated that the incorporation of 3.2% nano-CaCO₃ significantly improved the fiber-matrix bond properties and the flexural properties of UHPC. This was attributed to densification and strength enhancement of ITZ as observed from micro-structural analyses. Beyond the nano-CaCO₃ content of 3.2%, the fiber bond and mechanical properties of UHPC decreased due to increased porosity associated with agglomeration of the nano-CaCO₃.     

掺PVA纤维的抗裂改性水泥的性能与应用研究

抗裂性差是水泥基材料存在的主要问题之一,严重影响水泥基材料物理力学性能和耐久性。本文对掺PVA纤维的抗裂改性水泥的性能与应用进行了研究。结果表明,与普通水泥砂浆相比,掺PVA纤维的抗裂砂浆的强度、变形性能、抗裂性和耐久性均具有明显改善。PVA纤维增强抗裂砂浆技术在工程中得到了实际的应用。     

新型聚合物水泥胶浆界面剂粘结性能及作用机理研究

采用新型聚合物水泥胶浆作为界面剂以提高新旧混凝土之间的粘结性能,通过拉拔粘结强度与劈裂抗拉粘结强度实验对5种不同类型的聚合物水泥胶浆界面剂的粘结性能进行了测试,并利用扫描电镜(SEM)分析研究了丁苯聚合物水泥胶浆的界面增强机理。实验结果表明,5种聚合物乳液中,丁苯聚合物水泥胶浆具有较好的拉拔粘结性能,当优选m(水泥)∶m(DB-1乳液)=3∶2时,其7d、28d拉拔粘结强度分别达到1.83MPa、2.41MPa,相比水泥净浆空白样分别提高了144%、96%;在劈裂抗拉粘结强度方面,水平方向浇筑时劈裂抗拉粘结强度相对较高,当聚合物水泥胶浆的优选m(水泥)∶m(DB-1乳液)=3∶2,水平浇筑时其28d劈拉粘结强度达到2.96MPa,明显高于不掺界面剂的试样以及掺加其它配比界面剂的混凝土试样;经过微观测试分析,丁苯DB-1聚合物水泥砂浆内部界面过渡区(ITZ)相比空白样明显致密,表明丁苯聚合物的加入有效填充了水泥基材料内部的宏观与微观缺陷,提高了界面过渡区的密实程度。     

石墨烯表面性质对水泥砂浆复合材料力学性能和微观结构的影响

近年来,利用石墨烯及其衍生物改善水泥基复合材料性能受到了广泛关注。但是,关于石墨烯表面性质对水泥基材料的性能影响却鲜有报道。为此,采用不同浓度的L-抗坏血酸(10wt%、20wt%、30wt%、50wt%和70wt%)和还原时间(15 min、30 min、45 min和60 min)将氧化石墨烯(GO)转化为还原氧化石墨烯(rGO),然后以相同剂量(水泥质量的0.05%)加入到水泥砂浆复合材料中,研究了不同还原程度的rGO对水泥砂浆力学性能的影响。测试结果表明,通过50wt%L-抗坏血酸还原30 min制备的rGO的加入使水泥砂浆28天抗压强度和抗折强度相比于普通试样分别提高了36.84%和43.24%。SEM等分析表明,GO和不同还原程度的rGO均可促进Ca(OH)₂的结晶和水化硅酸钙凝胶(C-S-H)中二氧化硅四面体的形成,形成致密的微观结构。但存在一个最佳阈值(即通过50wt%的L-抗坏血酸还原30 min),在该阈值下,有利于rGO表面官能团与水化产物的结合。      

Simulation of single fiber pullout response with account of fiber morphology

A finite element model was developed at the single fiber length scale to predict the quasi-static pullout response of individual fibers from cementitious composites. The model accounts for energy dissipation through granular flow of the interfacial transition zone (ITZ) and matrix, plastic work in the fiber, and frictional dissipation at the fiber–ITZ interface. The considered fiber morphology was a triangular cross section that had been uniformly twisted along the fiber length. The model was calibrated to published experimental data for fiber pitches of 12.7 and 38.1 mm/revolution pulled from cement mortar with a 44-MPa unconfined compressive strength. The model was used to investigate slip-hardening behavior, tunneling of the cement mortar, in situ pullout behavior of helically twisted fibers at a crack plane, and provide an alternate explanation for the pullout response of twisted fibers from a 84-MPa unconfined compressive strength matrix containing silica fume. Calculations show that twisted fibers can provide up to 5 times the peak pullout force and 10 times the total work compared with straight fibers and infer work-hardening behavior during fiber pullout. The findings indicate that the tailoring of fiber morphology and control of constituent properties are important avenues for achieving significant improvements in the performance of fiber-reinforced cementitious composites.     

考虑过渡区界面影响的混凝土宏观力学性质研究

混凝土材料的宏观力学特性及破坏机理由其细观组分来决定,界面过渡区是影响混凝土断裂破坏路径及宏观力学特性的重要因素。认为界面过渡区是区别于远处砂浆基质的一层含较高孔隙率的近场砂浆材料,采用“两步等效法”得到了混凝土细观单元的等效本构关系模型。最后基于细观单元等效化方法分析了在单轴拉伸、单轴压缩及弯拉载荷条件下混凝土试件的破坏过程及宏观力学性质,探讨了界面过渡区对混凝土力学特性的影响,并与随机骨料模型分析结果进行了对比。结果表明:界面相的存在对混凝土的弹性模量、强度及残余强度等力学性质有很大影响,在对混凝土宏观力学特性及细观断裂破坏过程进行研究时不可忽略其影响。     

Diffusivity evolution under decalcification: influence of aggregate natures and cement type

Since the decalcification of cement paste has been largely reviewed, we focus our studies on the influence of aggregate nature on this phenomenon in relation to the type of cement used, Ordinary Portland Cement or blended cement with fly ash and slag. Some characteristics of similar mortar mixtures where only aggregate nature differs (lime and siliceous sand) are therefore compared for the two types of cement before and after chemical decalcification induced by ammonium nitrate attack: mechanical strength, microstructure (porosity observed by mercury intrusion and profiles of oxide content trough degraded and sound zones determined by electronic microprobe analysis), transport properties (chloride ions diffusivity, gas and water permeabilities). The characterization of sound mortars underlines that siliceous aggregates promote less porous cementitious matrix. The duplication of ammonium nitrate attacks on same material allows testing the experimental parameters governing the degradation. The flows of calcium leached, the microstructure and the evolution of transport properties with decalcification suggest that limestone aggregates are not inert material. Consequently, for the mortars incorporating siliceous sand, the cementitious matrix is more decalcified and this leads to an amplification of ionic transports, especially through blended cement paste.     

Effects of light crude oil contamination on the physical and mechanical properties of geopolymer cement mortar

Fly ash and oil contaminated sand are considered as the two waste materials that may affect environment. This paper investigated the suitability of producing geopolymer cement mortar using oil contaminated sand. A comparison between physical and mechanical properties of mortar produced using geopolymer and Ordinary Portland Cement (OPC), in terms of porosity, hydration and compressive strength, was conducted. The results showed that heat curing can increase the compressive strength of geopolymer mortar up to 54% compared to ambient curing situation. The geopolymer mortar with 1% of light crude oil contamination yielded a 20% higher compressive strength than OPC mortar containing sand with a saturated surface dry condition. Furthermore, the formation of efflorescence decreased as the level of oil contamination decreased. Moreover, the heat curing method increased the kinetic energy and degree of reaction for geopolymer cement mortar, which cause an increment of the density of the pore system and improving the mechanical properties of the resulting composites. From the results of this study, it was demonstrated that geopolymer mortar has the potential of utilizing oil contaminated sand, and reducing its environmental impacts.     

Recent progress in the development and properties of novel metal matrix nanocomposites reinforced with carbon nanotubes and graphene nanosheets

One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.     

相变储能混凝土的制备与性能

膨胀珍珠岩吸附硬脂酸丁酯后用石灰石粉末改性制成相变储能骨料（PCESA）,用其等体积部分取代砂制备相变储能混凝土。测试相变储能混凝土的抗压强度和劈裂抗拉强度,通过SEM图像分析相变储能混凝土的微观形貌,用DSC测试PCESA的相变特征及相变储能混凝土的比热容。试验结果表明：相变储能混凝土中PCESA结构保持完整且其与水泥石的界面过渡区密实,相对提高了相变储能混凝土的强度;PCESA具有较好的热物理性能,添加在混凝土中增强了混凝土的储能能力;当PCESA的掺量为20vol%时,相变储能混凝土具有较好的力学性能和热物理性能,在建筑结构中使用既可以起到承重的作用又能实现节能的目的。