纳米二氧化硅对丁苯共聚物/硫铝酸盐水泥复合砂浆物理力学性能的影响

为厘清纳米二氧化硅(NS)和丁苯共聚物乳液(SB)在硫铝酸盐(CSA)水泥中的协同作用，同时解决SB/CSA水泥复合砂浆凝结时间长、抗压强度低的问题，采用NS和SB对CSA水泥砂浆进行复合改性，研究改性复合砂浆物理力学性能随NS掺量的变化，并通过测定水化放热及水化产物分析NS在SB/CSA水泥复合砂浆中的作用机制。结果表明：NS可有效缩短SB/CSA水泥复合砂浆的凝结时间，提高其抗压强度，并与SB对CSA水泥砂浆抗折强度提升具有协同作用；NS最佳掺量为1.5%,此时与不加NS的纯SB改性砂浆相比，28 d抗压和抗折强度分别提高了28%、30%。同时，掺入NS会降低复合砂浆的流动度，提高表观体积密度，降低含气量和干燥收缩率，并略微降低毛细孔吸水率。NS可通过促进无水硫铝酸钙和硫酸钙反应，进一步加快SB/CSA水泥复合浆体的水化进程，提高钙矾石的含量，从而缩短凝结时间并提高力学强度。     

不同养护条件下聚合物对水泥砂浆与瓷砖粘结强度的影响

分析了聚醋酸乙烯酯与乙烯共聚物掺入水泥砂浆中的减水作用。比较了聚醋酸乙烯酯与乙烯共聚物乳液和乳胶粉对水泥砂浆与瓷砖的粘结强度；研究了聚醋酸乙烯酯与乙烯共聚物改性水泥砂浆与瓷砖粘结在不同养护条件下的粘结抗拉强度。试验结果表明，在乳液和乳胶粉掺量达8%和4%时，其减水效果分别提高36.12%和21.55%。聚合物存在形态、掺量以及养护条件对水泥砂浆与瓷砖的粘结抗拉强度有显著的影响。聚合物乳液和乳胶粉的掺入能改善砂浆与瓷砖粘结标养、高温养护和冻融循环养护时的粘结抗拉强度。比较掺乳液和乳胶粉的实验结果得知，前者除提高标养和高温养护时的粘结抗拉强度值外，还能大大改善砂浆与瓷砖粘结的耐水性。     

聚合物改性砂浆界面粘接特性的研究

根据聚合物改性砂浆不同的界面破坏形式,提出了表征界面粘接特性的内聚强度和界面结合强度概念,并通过二者的总体宏现效应-粘接强度试验探讨了乙烯-醋酸乙酸共聚物、双级配填料和水泥对砂浆内聚强度和界面结合强度的影响.试验表明,在本试验务件下乙烯-醋酸乙酸共聚物的最佳掺量范围为1.5%～3.5%.当聚合物掺量低于3.5%时,随着聚合物掺量的增加,聚合物改性砂浆的粘接强度增大,破坏形式为内聚破坏;当聚合物掺量高于3.5%时,聚合物改性砂浆界面的结合强度降低,导致粘接强度降低,破坏形式为界面破坏.具有合适配比的双级配填料可增强砂浆粘接强度,但大粒径填料的增加会降低砂浆与基材界面的结合强度,导致砂浆的粘接强度降低,在本试验条件下填料A/填料B的比例取1:2为宜.聚合物改性砂浆的粘接强度随水泥掺量的增加而增大,并在掺量为30%时出现拐点,故在本试验条件下水泥掺量取30%较佳.     

基于溶胶凝胶法改性的硅藻土对水泥基材料性能的影响

采用溶胶凝胶法对硅藻土进行改性,然后研究改性前后的硅藻土对水泥净浆(标准稠度用水量、凝结时间)及砂浆性能(力学性能、调湿性能)的影响。研究结果表明:(1)经改性后的硅藻土比表面积由初始的2.76m~2/g增大到158.52m~2/g,平均孔径由初始的3.82nm减小到1.41nm。(2)改性前后的硅藻土水泥净浆标准稠度用水量均高于纯水泥的标准稠度用水量,且随着硅藻土掺量的增加而逐渐增大;随着改性前后硅藻土掺量的增加,水泥初凝时间延长,终凝时间缩短。另外,在硅藻土掺量相同的条件下,改性硅藻土时凝结时间较原状硅藻土水泥凝结时间短。(3)改性后硅藻土的水泥砂浆强度较原状硅藻土的水泥砂浆高;随着改性前后硅藻土掺量的增加,水泥砂浆的强度均逐渐降低,而水泥砂浆吸、放湿率逐渐增大。另外,改性前后的硅藻土掺量相同时,改性后硅藻土的水泥砂浆吸、放湿率大于改性前的硅藻土水泥砂浆的吸、放湿率。(4)X射线衍射(XRD)和扫描电镜(SEM)分析结果表明,改性硅藻土的水泥砂浆较原状硅藻土的水泥砂浆有更多的水化产物,且硬化体结构更加致密。     

两种乳胶粉对三元胶凝体系饰面砂浆性能的影响

研究了乙烯-醋酸乙烯共聚物(乳胶粉A)及乙烯-醋酸乙烯-丙烯酸酯三元共聚物(乳胶粉B)对铝酸盐水泥-硅酸盐水泥-半水石膏三元体系饰面砂浆抗泛白性、耐沾污性、吸水性及力学性能的影响。结果表明,乳胶粉B对各项性能的作用效果均优于乳胶粉A。乳胶粉B掺量为0~6%时砂浆7d泛白等级为0级;适当掺量的乳胶粉B能改善砂浆的耐沾污性,在其掺量大于等于12%时,砂浆的耐沾污性优于未掺乳胶粉的砂浆;乳胶粉A的掺量为3%~9%时,乳胶粉B掺量为3%~15%时可改善砂浆的吸水性;乳胶粉A能提高砂浆抗折强度及拉伸粘结强度,但会降低砂浆的抗压强度,而乳胶粉B能同时提高砂浆的抗折强度、抗压强度及拉伸粘结强度。     

丁苯乳液改性水泥砂浆的物理性能

本文研究了丁苯乳液SD622S改性水泥砂浆的物理性能,包括新拌砂浆的减水率、保水率、体积密度、凝结时间,硬化砂浆的体积密度、孔隙率、毛细孔吸水率等.实验结果表明:丁苯乳液可提高砂浆的减水率和保水率,使砂浆的凝结时间延长.随着丁苯乳液掺量的增加,硬化砂浆的毛细孔吸水率降低.丁苯乳液使新拌砂浆和硬化砂浆的体积密度减小,但随聚合物掺量的增加有所回升.硬化砂浆的孔隙率随聚合物掺量的变化趋势正好相反.     

橡胶微粉对无机聚合物胶凝材料力学性能的影响

主要研究了橡胶微粉对无机聚合物砂浆和水泥砂浆力学性能的影响.实验结果表明,随着橡胶微粉掺量的增加,无机聚合物砂浆和水泥砂浆的抗压强度、抗折强度均有所下降,其中无机聚合物砂浆弹性模量降低、变形能力增强、弯曲韧性系数稍有降低;水泥砂浆弹性模量升高、变形能力下降、弯曲韧性系数下降.分析材料微观破坏形貌后发现,与水泥砂浆相比,橡胶微粉与无机聚合物砂浆界面粘结较好,粘结强度高,从而造成无机聚合物砂浆和水泥砂浆这两种材料体系在橡胶微粉掺杂后力学性能的差异.     

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。     

硅烷复合乳液对水泥砂浆干燥收缩性能及力学性能的影响

将氧化石墨烯/异丁基三乙氧基硅烷复合乳液(GO/lBTS复合乳液)和正硅酸四乙酯/异丁基三乙氧基硅烷复合乳液(TEOS/lBTS复合乳液)分别内掺到水泥砂浆中,研究了两种硅烷复合乳液在不同掺量下对砂浆在养护过程中的干燥收缩性能、水分散失和力学性能的影响.研究结果表明:GO/lBTS复合乳液能有效抑制砂浆的干燥收缩和水分散失,当掺量为2％时,砂浆干燥收缩量和水分散失量达到最小,而且力学强度达到平均最高;TEOS/lBTS复合乳液对砂浆干燥收缩和水分散失的抑制作用不明显,但是当掺量为2％时,力学性能达到最大,抗压强度和抗折强度分别提高了5％和17％;但两种硅烷复合乳液掺量不宜超过水泥质量的3％.通过SEM、EDS测试发现,GO/lBTS复合乳液会在砂浆内部形成一层分散均匀的絮状结构.另外,红外光谱测试结果表明,硅烷复合乳液通过化学键与水泥基材料相结合.     

PVA纤维改性地坪修补砂浆性能研究

以PVA纤维作为外掺物质,研究了其掺量对水泥砂浆流动度、力学性能以及耐磨性能的影响规律,并对其改性机理进行了分析。结果表明,随着PVA纤维掺量的增加,复合砂浆试样流动度逐渐下降,各龄期复合砂浆试样抗折强度均表现为先增加后降低,PVA纤维复合砂浆试样各龄期单位面积磨损量均表现为先减小后增大。     

Prediction of bending strength of long corrugated boxes

Long corrugated boxes were supported at both ends and bent by a concentrated force applied at the middle. Boxes with different lengths, cross‐sectional shapes, flute directions and board strengths were tested, using a standard compression tester with a fixed platen in accordance with ASTM D‐642. An equation was developed to relate compression strength to the various properties of the box. The correlation coefficient R² for the fit to actual data was about 0.4. Boxes having the flutes run around the box had a 20% higher compression strength than with horizontal flutes. The most significant factor was found to be the board edge crush strength. The results suggest that failure of boxes in bending is due to localized crushing at the point of application of the load, rather than whole‐box collapse. Copyright © 2001 John Wiley & Sons, Ltd.     

The effect of adding nano-SiO2 and nano-Al2O3 on properties of high calcium fly ash geopolymer cured at ambient temperature

This article presents the effect of adding nano-SiO₂ and nano-Al₂O₃ on the properties of high calcium fly ash geopolymer pastes. Nano-particles were added to fly ash at the dosages of 0%, 1%, 2%, and 3% by weight. The sodium hydroxide concentration of 10 molars, sodium silicate to sodium hydroxide weight ratio of 2.0, the alkaline liquid/binder ratio of 0.60 and curing at ambient temperature of 23 °C were used in all mixtures. The results showed that the use of nano-SiO₂ as additive to fly ash results in the decrease of the setting time, while the addition of nano-Al₂O₃ results in only a slight reduction in setting time. Adding 1–2% nano-particles could improve compressive strength, flexural strength, and elastic modulus of pastes due to the formation of additional calcium silicate hydrate (CSH) or calcium aluminosilicate hydrate (CASH) and sodium aluminosilicate hydrate (NASH) or geopolymer gel in geopolymer matrix. In addition, the additions of both nano-SiO₂ and nano-Al₂O₃ enhances the shear bond strength between concrete substrate and geopolymer.     

新型4层瓦楞纸板的性能分析

研究了一种新型的4层瓦楞纸板结构,并将4层瓦楞纸板和3层、5层瓦楞纸板的平压强度、边压强度、戳穿强度和耐破度性能进行比较,最后得到新型4层瓦楞纸板的主要优点是:厚度比5层瓦楞纸板要薄,节省了夹芯纸的用量,降低瓦楞纸板的成本,而且强度高,在一定情况下可以代替5层瓦楞纸板达到抗压、防震、缓冲的目的。     

The role of 0–2 mm fine recycled concrete aggregate on the compressive and splitting tensile strengths of recycled concrete aggregate concrete

The aim of this study is to investigate the role of 0–2 mm fine aggregate on the compressive and splitting tensile strengths of recycled concrete aggregate (RCA) concrete with normal and high strengths. Normal coarse and fine aggregates were substituted with the same grading of RCAs in two normal and high strength concrete mixtures. In addition, to keep the same slump value for all mixes, additional water or superplasticizer were used in the RCA concretes. The compressive and splitting tensile strengths were measured at 3, 7 and 28 days. Test results show that coarse and fine RCAs, which were achieved from a parent concrete with 30 MPa compressive strength, have about 11.5 and 3.5 times higher water absorption than normal coarse and fine aggregates, respectively. The density of RCAs was about 20% less than normal aggregates, and, hence, the density of RCA concrete was about 8–13.5% less than normal aggregate concrete. The use of RCA instead of normal aggregates reduced the compressive and splitting tensile strengths in both normal and high strength concrete. The reduction in the splitting tensile strength was more pronounced than for the compressive strength. However, both strengths could be improved by incorporating silica fume and/or normal fine aggregates of 0–2 mm size in the RCA concrete mixture. The positive effect of the contribution of normal sand of 0–2 mm in RCA concrete is more pronounced in the compressive strength of a normal strength concrete and in the splitting tensile strength of high strength concrete. In addition, some equation predictions of the splitting tensile strength from compressive strength are recommended for both normal and RCA concretes.     

Yield strength in submicrovolumes of single crystals

The specificity of the transition from elastic to elastoplastic deformation in defect-free single crystals during the localization of the deformation in a submicron region has been studied by nanoindentation. A sharp transition from elastic to elastoplastic deformation has been observed in tested single crystals at depths of about 20–50 nm. To define the yield strength using the nanoindentation data, the stressed-strained state in the contact region has been analyzed. It has been shown that the yield strength in submicrovolumes of single crystals is tens-hundreds times higher than that at the macroscopic level and approaches the value of the theoretical shear strength. A mechanism of the transition from elastic to elastoplastic deformation has been discussed in the framework of the phenomenological model of the nucleation of dislocations. The transition has been induced by the homogeneous nucleation of dislocations in a contact.     

A practical model for efficient anti-fatigue design and selection of metallic materials:Ⅰ.Model building and fatigue strength prediction

The high cost and low efficiency of fatigue tests are bottleneck problem for the anti-fatigue design of metallic materials.For this problem,a theoretical fatigue model is proposed in this study,the possible applications have also been discussed.Specific results would be introduced in two serial papers,in which the first paper focuses on the model building and the applications on fatigue strength prediction;the second paper put emphasis on the influencing factors of the model parameters and the applications on fatigue strength improvement.In this first paper,a theoretical model is proposed considering both the strength and plastic restrictions of fatigue strength.As the model builds up a brief relationship among yield strength(Y),tensile strength(T)and fatigue strength(F),it is named as the Y-T-F model.Through the verification with fatigue strength data covering various kinds of metallic materials and loading condi-tions,this Y-T-F model exhibits both generality and accuracy.With the Y-T-F model,the efficient fatigue strength prediction could be conducted by brief linear fitting and calculation,just through yield strength,tensile strength and several known fatigue strength data.Moreover,through its deduced Y-F model,the analytical formula of fatigue strength continuously changing with materials strengthening can be obtained,as well as the maximum value of fatigue strength and corresponding critical yield strength.In summary,the Y-T-F model would be useful for reducing the fatigue tests,thus providing new possibilities on the efficient anti-fatigue design and selection of metallic materials.     

Concrete with ceramic waste aggregate

Use of hazardous industrial wastes in concrete-making will lead to greener environment. In ceramic industry about 30% production goes as waste, which is not recycled at present. In this study an attempt has been made to find the suitability of the ceramic industrial wastes as a possible substitute for conventional crushed stone coarse aggregate. Experiments were carried out to determine the compressive, splitting tensile and flexural strengths and the modulus of elasticity of concrete with ceramic waste coarse aggregate and to compare them with those of conventional concrete made with crushed stone coarse aggregate. The properties of the aggregates were also compared. Test results indicate that the workability of ceramic waste coarse aggregate concrete is good and the strength characteristics are comparable to those of the conventional concrete.     

碳/铝复合材料界面结合强度对拉伸性能的影响

本文主要研究C/Al复合材料先驱丝的界面结合强度的表征方法以及界面结合状态对复合材料拉伸性能的影响.用自行研制的小型剪切试验机测定复合材料先驱丝的纵向剪切强度,通过计算得到复合材料界面处的剪切强度以此作为界面结合强度的定量表征方法.实验证明,不同界面结合强度的复合丝在宏观上表现出有不同纵向剪切强度值,复合材料的界面结合强度可以用界面剪切强度值定量描述.复合材料拉伸强度随界面强度提高而减少,在满足复合材料横向强度要求前提下,降低复合材料界面结合有利于提高拉伸强度.     

High-Cycle Fatigue of Materials and Parts of Gas-Turbine Engines

We present a historical survey of the development of the scientific direction called “Structural Strength” at the Central Institute of Airplane Engine Manufacturing (CIAEM) for the last 30 years in connection with the 100th birthday of Academician S. V. Serensen, founder of this direction in the USSR, and the 75th anniversary of foundation of the CIAEM. We present the principal results obtained by the scientific staff of the Sector of Fatigue Strength of Materials of Gas-Turbine Engines at the CIAEM.__________Translated from Problemy Prochnosti, No. 3, pp. 5 – 21, May – June, 2005.     

膨胀螺栓与混凝土拉拔力的测试和分析

叙述了膨胀螺栓与混凝土拉拔力的设计准则和试验方法,并对影响拉拔性能的因素进行了分析和评价。