粉煤灰和矿渣粉对水下不分散混凝土性能的影响研究

本试验研究了粉煤灰和矿渣粉复掺时对水下不分散混凝土性能的影响,分析二者不同掺量复掺时对混凝土流动性、抗分散性、力学性能以及抗氯离子渗透性的影响规律.研究表明,与掺合料单掺相比,粉煤灰和矿渣粉复掺时混凝土流动性降低,但是抗分散性和抗氯离子渗透性明显改善,同时二者复掺时能起到“叠加效应”,使早期强度和后期强度均较高.     

高掺量低品质粉煤灰混凝土碳化性能的试验研究

进行了掺加不同品质和掺量粉煤灰、复掺矿渣粉的粉煤灰混凝土的快速碳化试验研究。结果表明,低品质粉煤灰掺量越多,越不利于混凝土抗碳化性能;20%以下掺量时,混凝土碳化深度不会显著增加;48%掺量时,混凝土抗碳化性能明显降低;在混凝土中复掺矿渣粉可以大大改善粉煤灰混凝土的抗碳化性能。提出了复掺矿渣粉的高掺量低品质粉煤灰混凝土配合比设计方法,不仅对提高粉煤灰混凝土抗压强度有利,并且可大大改善其抗碳化性能。     

早期高温养护对粉煤灰基自密实混凝土性能的影响

为研究早期养护条件对粉煤灰基自密实混凝土(SCC)性能的影响规律,采用不同掺量(30％、40％、50％、65％)的粉煤灰取代等量的水泥胶凝材料制备SCC.将其放置在标准养护箱中养护24h或在蒸养机中以60℃和90℃的温度养护24 h,之后全部取出放入自来水中养护,分析不同早期养护条件对粉煤灰基SCC力学性能的影响,探讨粉煤灰基自密实混凝土力学性能之间的关系.对不同龄期下的粉煤灰基SCC进行微观测试,包括扫描电镜(SEM)及能谱仪(EDS)测试,通过微观形貌及能谱分析解释粉煤灰基SCC的宏观工作性能和力学性能.研究表明,粉煤灰掺量增加对SCC的早期抗压强度、劈裂抗拉强度、弹性模量存在明显的负作用,而早期高温养护能够显著提高粉煤灰基SCC的早期力学性能.结合实际工程需求,粉煤灰基SCC运用于预制构件的生产具有可行性.     

矿物掺合料对低水胶比混凝土抗氯离子渗透性能的影响

采用ASTM C1202-97方法测定混凝土氯离子电通量及渗透等级,主要研究了矿渣、粉煤灰、偏高岭土在单掺及不同比例复掺时对低水胶比混凝土抗氯离子渗透性能的影响.实验结果表明:矿物掺合料能有效改善低水胶比混凝土抗氯离子渗透性能.粉煤灰与矿渣复掺时,随着矿渣所占比例增加,混凝土氯离子渗透等级逐渐降低.水胶比为0.38,偏高岭土与矿渣复掺时随着偏高岭土所占比例增大,混凝土氯离子电通量先降低后增加,与基准组相比较,掺入比例为1∶1时其28 d氯离子电通量降低了93％.偏高岭土与矿渣复掺能有效改善混凝土的孔隙结构,孔径趋于细化,提高了混凝土抗氯离子渗透性能.     

膨胀剂对碱-激发矿渣砂浆的减缩特性研究

开展了膨胀剂对碱-激发矿渣砂浆的减缩特性研究,分析了不同硫铝酸盐类膨胀剂掺量对碱-激发矿渣砂浆自收缩、干缩和抗压强度的影响,使用压汞仪研究了掺膨胀剂碱-激发矿渣砂浆的孔结构特征.结果表明,硫铝酸盐类膨胀剂对碱-激发矿渣砂浆自收缩和干缩具有一定的抑制作用,可降低收缩的增长速率,3％掺量下可分别减小自收缩35.4％和干缩29％.膨胀剂对碱-激发矿渣砂浆早期强度影响明显,但随龄期发展,其影响作用减弱,28 d时,膨胀剂组与对照组抗压强度相近.膨胀剂可增大碱-激发矿渣砂浆大于20μm的孔体积,有利于减小孔径小于20μm的孔体积,形成更为密实结构.     

复掺粉煤灰和矿渣粉大流动度混凝土的抗碳化性能

研究了复掺Ⅱ级粉煤灰和同等细底的矿渣粉，同时掺加高效减水剂配制的大流动度（180mm）混凝土的抗碳化性能。试验中改变了取代水泥量（最大80％）及掺合料中粉煤灰和矿渣粉的比例等条件。混凝土的碳化深度随时间的变化，可用幂函数d＝at^b表示，b值大多位于0．3－0．4。复掺可使取代水泥量提高。对设计寿命为50年的混凝土，在其他性能满足工程要求的条件下，从碳化性能的角度来看，混凝土中可掺加40％的粉煤灰，若采用粉煤灰与矿渣粉复掺，则在掺合料总量分别显60％、70％及80％时，相应地可掺加40％、30％及15％的粉煤灰。     

复掺偏高岭土-矿渣对轻骨料混凝土性能的影响

轻骨料混凝土具有收缩较大和渗透性较差的特性,矿物掺合料的加入可以改善轻骨料混凝土的性能.将偏高岭土(MK)和矿渣(S)以低于25％的总掺量复掺到轻骨料混凝土中,研究复掺掺合料及不同掺量对轻骨料混凝土的力学性能、氯离子扩散系数和干燥收缩的影响.利用XRD、TG、SEM等测试方法,对其影响机理进行探讨.结果表明,复掺10wt％偏高岭土与10wt％矿渣对轻骨料混凝土力学性能和抗氯离子渗透性能有显著的改善;复掺10wt％偏高岭土和15wt％偏高岭土能有效降低轻骨料混凝土干燥收缩.偏高岭土复合矿渣能优化水泥浆体的组成与结构,增强骨料与水泥浆体间的结合,降低界面过渡区的钙硅质量比,从而提高轻骨料混凝土各龄期抗压强度的抗渗性能.     

矿物掺合料对泡沫混凝土的性能影响

研究了单掺粉煤灰、矿渣粉和复掺粉煤灰与矿渣粉对干密度为400 kg/m3泡沫混凝土的抗压强度、导热系数以及吸水率的性能影响.当粉煤灰掺量为10%时,可增加抗压强度,掺量为30%时显著降低导热系数和吸水率;当矿粉掺量为20%时,可增加抗压强度和降低吸水率,但导热系数却随掺量增大而变大;当复掺粉煤灰与矿渣粉取代50%水泥,复掺比例为2:3时,能增加抗压强度和降低吸水率,导热系数随复掺比例增大而变大.在泡沫混凝土中掺加矿物掺合料,不仅可以降低水化热,还可以减少泡沫混凝土的开裂程度,该项研究成果为今后泡沫混凝土在地基保温处理、屋面保温、地暖垫层等方面提供了应用价值.     

矿物掺合料再生混凝土力学性能研究

为探究矿物掺合料对再生混凝土(RAC)力学性能的提升作用,本试验采用预湿-二次搅拌法制备再生混凝土,系统开展单、复掺矿物掺合料再生混凝土力学性能研究.试验考虑再生混凝土强度等级、再生骨料取代率、矿物掺合料种类及取代率等因素,共设计23组试验配合比,研究再生混凝土立方体抗压强度和劈裂抗拉强度经时变化规律.结果 表明,再生混凝土力学性能随强度等级升高而提升,随再生骨料取代率增大而下降.与未掺矿物掺合料的再生混凝土相比,单掺粉煤灰对再生混凝土力学性能提升效果较弱,单掺矿渣、硅灰的再生混凝土力学性能提升效果显著.养护龄期90 d时,矿渣再生混凝土劈裂抗拉强度最高提升12.7％,硅灰再生混凝土立方体抗压强度最高提升21.3％.粉煤灰-矿渣复掺对再生混凝土立方体抗压强度无提升效果,20％粉煤灰-10％矿渣复掺抗压强度甚至下降18.8％,粉煤灰-矿渣复掺对再生混凝土劈裂抗拉强度略有提升,最高为5.9％.粉煤灰-硅灰复掺对再生混凝土力学性能提升效果较好,立方体抗压强度和劈裂抗拉强度最高分别提升9.7％和18.6％.     

补偿收缩混凝土的自收缩特性

通过对比掺与不掺膨胀剂的混凝土的早期自收缩及其胶凝材料体系的水化热和化学结合水量发展规律,研究了膨胀剂对低水胶比混凝土自收缩的补偿作用效果。结果表明:8%掺量(质量分数)的钙矾石系膨胀剂(U型)对硅酸盐水泥混凝土和粉煤灰混凝土的自收缩有一定程度的补偿效果,而对矿渣混凝土的自收缩没有补偿。在较早期,膨胀剂促进复合胶凝材料的水化,在后期,膨胀剂也促进了矿渣–水泥体系的水化,其总放热量和化学结合水量均高于未掺膨胀剂的,但抑制了硅酸盐水泥和粉煤灰–水泥体系的正常水化,使其水化放热速率降低,总放热量和化学结合水量减小。     

Synthesis of dysprosium/Mn–Cu ferrite binary nanocomposite: Analysis of structural,morphological, dielectric,and optomagnetic properties

Manganese–copper ferrite (MCFO) and dysprosium (Dy)-doped manganese–copper ferrite nanocomposites (Mn_0.5Cu_0.5Dy_xFe_2−xO₄) (x = 0, 0.05, 0.10, and 0.15) were synthesized by sonochemical method. Crystal structure and the structural parameters of the MCFO were analyzed based on the doping concentration of Dy ion. It was observed that the average crystalline size of the synthesized nanocomposite decreases when the concentration of Dy increases. The existing spherical surface morphology of the MCFO and Dy-doped MCFO nanocomposites were obtained through scanning electron microscopy. In the UV spectrum, the pristine MCFO sample showed an absorbance peak at 743 nm whereas the absorbance values of Dy-doped ferrite nanocomposite considerably shifted (blue) toward a lower wavelength (231–222 nm). The dielectric parameters of all ferrite nanocomposites were studied in the frequency range of 100 Hz to 5 MHz. The dielectric spectrum revealed that dielectric constant and loss tangent decreased with increased doping concentration of Dy ion. The saturation magnetization also changed with Dy doping in MCFO. The impact of Dy on manganese–copper ferrite changed the optical, dielectric and magnetic properties of the prepared binary ferrite nanocomposite, which can be used for microwave-absorbing material applications.     

Mechanical Properties of Compression Molded Banana Pseudo-stem Filled Unplasticized Polyvinyl Chloride (UPVC) Composites

Mechanical strengths of a banana pseudo-stem (BPS) fiber and unplasticized polyvinyl chloride (UPVC) composite were evaluated to assess the possibility of using it as a new material in engineering applications. Samples were fabricated by the compression molding process with reference to the effect of filler loading. The samples were submitted to mechanical tests to measure tensile, flexural, and impact properties of the composites. The nature of adhesion between the matrix and the reinforcement and information relating the structure of mechanical properties can be obtained by scanning electron microscopy (SEM) assessment of the composite fracture surface. The mechanical properties show that the composites did not have good adhesion between filler and matrix; on the other hand, the filler insertion improved the flexural modulus and the material rigidity.     

单向玻璃纤维-铝合金层板的几种力学性能研究

本文用实验方法研究了单向玻璃纤维-铝合金层板的拉伸性能、疲劳性能和冲击性能。利用金属体积分数理论验证了这类层板的拉伸性能。通过对其疲劳性能的实验研究，发现裂纹扩展速率的大小及刚度的下降与加载的最大循环应力密切相关的规律。实验发现该层板具有比铝合金好得多的冲击性能。     

核壳型纳米粒子合成方法及其性能的研究进展

核壳纳米粒子作为复合纳米粒子一个重要的分支,由于其光、磁和催化等方面的优异性能,近年来引起了人们广泛的关注.本文主要介绍了核壳纳米粒子的制备方法及诸多性能,并对核壳纳米粒子的发展进行了展望.     

TMPTMA在硅橡胶中的应用研究

研究了助交联剂三羟甲基丙烷三甲基丙烯酸酯(TMPTMA)对硅橡胶硫化性能、力学性能、低温性能和粘接性能的影响。结果表明,加入少量TMPTMA能改善硅橡胶的硫化特性和工艺性,提高硫化胶的硬度,降低硅橡胶的结晶温度,并有效提高硅橡胶与金属的粘接强度;但TMPTMA用量超过一定数值后,由于TMPTMA部分自聚合,在硅橡胶内形成一定的交联网络,造成两相界面粘接力变差,致使硅橡胶的拉伸强度降低。当TMPTMA用量为1份时,硅橡胶具有最佳的综合性能。     

聚氨酯种类对机械性能以及阻尼性能影响研究

分别以聚四氢呋喃醚二醇(PTMEG)、聚氧化丙烯二醇(PPG-1000)为软段,以二苯基甲烷二异氰酸酯(MDI-50、MDI-100LL),以及扩链剂1,4-丁二醇(BDO)、三羟甲基丙烷(TMP)为硬段,采用预聚体法制备了聚氨酯弹性体。并系统研究了聚氨酯体系中各组分的种类对材料机械性能和阻尼性能的影响。     

A new precursor to lightweight porous Si–Al–O–B ceramics with enhanced microwave transmissivity

Nowadays, complicated preparation processes and harsh sintering conditions wave transparent ceramics limit its further development. To solve this problem, we explore a promising precursor by adopting a polymerization-pyrolysis method to prepare porous Si–Al–O–B ceramics at a mild sintering condition (1000 °C). The porous Si–Al–O–B ceramics exhibits enhanced wave transparency at 10–16 GHz with a low dielectric constant (<3), a low loss angle tangent value (<0.01), and simultaneously, a relative high flexible strength of 82 MPa. According to the results of the XRD and FTIR analysis, porous Al₄B₂O₉ crystallization dispersed in the amorphous SiO₂ matrix constructs the main phases of the products. The changes of Al and B elements are confirmed to have an effect on the phase compositions and micro structure of the composite ceramics, which obviously affect the mechanical and dielectric properties of the derived ceramics. The as-prepared porous Si–Al–O–B ceramics could be a potential candidate for next generation electronic window materials due to its low dielectric constant and loss angle tangent value, as well as high flexible strength.     

Effects of support and additive on oxidation state and activity of Pt catalyst in propane combustion

The effects of support and additive on the oxidation state and catalytic activity of Pt catalyst in the low temperature propane combustion were systematically investigated on Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂–Al₂O₃. The catalytic activity varied much with both support materials and additives. The catalyst on the more acidic support showed higher activity, and the catalytic activity on every support materials increased as the electronegativity of additives increased, while some additives decreased the activity. The oxidation state of platinum, estimated by white line intensity of Pt L_III-edge XANES spectrum, also varied with the support and additives, and additives with higher electronegativity greatly prevented the platinum from its oxidation under oxidising atmosphere. Among almost all the catalysts with various supports and various additives, a clear relationship was observed between the oxidation state of platinum and the catalytic activity; the more metallic platinum showed higher activity. Thus, it was concluded that the total electrophilic/electrophobic property derived from those of the support and additive controls the oxidation state of platinum, which intensively affects the catalytic activity; i.e. higher electrophilic property provides less oxidised platinum, resulting in high catalytic activity. The mechanism of this effect was also discussed on the basis of thermochemical data, and it was proposed that the electrophobic materials promote the noble metal oxidation since the noble metal oxo-anion such as PtO^δ− is more stabilised with electrophobic cation.     

聚丙烯基抗菌塑料的制备与性能研究

利用熔融挤出共混技术制备了聚丙烯(PP)基抗菌塑料。研究了抗菌母料Antim-PP对PP的抗菌性能和力学性能的影响。结果表明,当抗菌母料与PP的质量比为4:100时,抗菌PP塑料对大肠杆菌的抗菌率大于99%,抗菌母料的加入使共混物的冲击性能有明显改善,其他力学性能基本不受影响。