Bond strength prediction for deformed steel rebar embedded in recycled coarse aggregate concrete

This paper summarizes the results of an experimental investigation into the bond behavior between recycled aggregate concrete (RAC) and deformed steel rebars, with the main variables being the recycled coarse aggregate replacement ratio (RCAr) and water-to-cement ratio of the concrete mixture. The investigation into splitting cracking strength indicates that the degradation of the bond splitting tensile stress of the cover concrete was affected by not only the roundness of the coarse aggregate particles but also the weak interfacial transition zone (ITZ) between the cement paste and the RCA that has a more porous structure in the ITZ than normal concrete. In this study, a linear relationship between the bond strength and the density of the RCA was found, but the high compressive strength reduced the effects of the parameters. To predict the bond strength of RAC using the main parameters, a multivariable model was developed using nonlinear regression analysis. It can be inferred from this study that the degradation characteristic of the bond strength of RAC can be predicted well, whereas other empirical equations and code provisions are very conservative.     

硅源对纳米级ZSM-5分子筛结构及其对甲醇转化制丙烯与丁烯反应催化性能的影响

采用低温水热晶化法,以四丙基氢氧化铵为模板剂,分别使用98%粗孔固体硅胶和30%硅溶胶为硅源,制备不同硅铝物质的量比的纳米级ZSM-5分子筛,研究硅源对其物化结构及甲醇转化制丙烯与丁烯催化性能的影响。结果表明,硅源种类影响ZSM-5分子筛的结构及铝分布,进而影响其酸性和催化性能。固体硅胶为硅源,有利于形成弱酸性位点;硅溶胶为硅源,有利于形成强酸性位点。在相同硅铝物质的量比时,以固体硅胶为硅源的ZSM-5分子筛的总酸量小于以硅溶胶为硅源的样品。无论使用何种硅源,对ZSM-5分子筛的晶型结构影响不大,且ZSM-5分子筛颗粒形貌均呈现为由小晶粒堆积成(500~1 000)nm的类球形颗粒。以硅溶胶为硅源制备的样品颗粒尺寸大于以固体硅胶为硅源制备的样品。硅铝物质的量比为400时,两种硅源合成分子筛的丙烯与丁烯的选择性相近,但以硅溶胶为硅源的ZSM-5分子筛的寿命更长。     

干扰床分选机分选粗煤泥的规律研究

介绍了干扰床分选机的工作原理,在比较了各种粗煤泥自由沉降速度计算方法的基础上,提出了适用于粗煤泥自由沉降速度的计算公式。筹建了试验室干扰床分选机试验系统,并对新汶矿业集团汶南煤矿不同粒度级别的粗煤泥进行了干扰床分选试验,探讨了干扰床分选机分选粗煤泥的一般规律。     

高模低缩级大有光切片的质量控制

针对高模量低收缩涤纶工业丝的生产特点,推出了高模低缩级大有光切片,并制定了相应的产品质量标准,在聚酯生产中对原料使用、浆料配制工序、反应釜工艺参数调整、粒子尺寸及含水率进行了有效控制,使产品能更好地满足高模低缩级大有光切片的产品质量标准。     

提高J7/A3卷绕头丝饼外观成型质量的生产实践

探讨了J7/A3卷绕头全拉伸丝(FDY)丝饼外观成型的主要影响因素。实践表明:工艺上优化卷绕张力、卷绕成形角、松弛比、热辊温度和上油率等参数,设备上加强导丝器、J7/A3卷绕头、纸管等方面的使用管理及维修保养,能够提高丝饼外观质量,满足质量控制和客户需求。     

玻璃纤维电子布边部经纱松弛问题的分析探讨

介绍了玻璃纤维电子布织造时边部经纱松弛现象及对电子布质量的影响,分不同的工序剖析了玻璃纤维电子布织造时边纱松弛的主要原因,并针对这些原因提出了相对应的应对措施,为解决电子布生产过程中的边纱松弛提供了相关的技术解决方案。     

聚苯胺/涤纶导电纱线的制备

以涤纶纱线为基材制备涤纶/聚苯胺导电纱线。采用正交试验分析pH值、苯胺、过硫酸铵的用量对导电性能的影响。通过对比实验观察碱减量预处理的效果;利用万用表对复合纱线导电性能进行测量。结果表明:碱减量预处理非常必要,当pH值为2~3,苯胺用量为10 g,过硫酸铵质量为2g时导电纱线的电阻率最低,为96Ω·cm。     

磁纤维保健系列纱线的研制开发

利用具有独特的保健性能的磁生态保健纤维研制开发了磁纤维保健系列纱线,介绍了磁纤维保健系列纱线的纺纱工艺。     

Macroinvertebrate assemblages of littoral habitats in the Macquarie and Mersey rivers,Tasmania: Implications for the management of regulated rivers

Littoral habitats in large rivers are influenced to varying degrees by changes in discharge. Irrigation abstractions can increase the amount of habitat that would naturally be dewatered during low flow periods and therefore it is important to have some knowledge of the potential impact this may have on riverine macroinvertebrates. The macroinvertebrate assemblages of common littoral habitats in riffles, pools and runs in two reaches each of the Macquarie and Mersey Rivers, northern Tasmania, Australia were compared from samples collected during the low flow and irrigation season, between December 1991 and April 1992. The area under water of these habitats, riffle substrata, macrophyte beds and coarse woody debris, responded differently to changes in discharge. Within a reach, the same taxonomic groups often dominated the total number of macroinvertebrates for all habitats, but there were differences in the proportions contributed by these taxa to the different habitats. In general, taxa characteristic of slow-flowing or lentic habitats, such as ostracods and amphipods, were dominant in macrophyte beds in pools and runs, whereas taxa such as larval elmid beetles and hydropsychid caddisflies were dominant in riffles. A substantial component of the fauna from each habitat within a reach was unique to that habitat, but there was always a similar number of taxa common to all habitats. Classification and ordination grouped samples from both rivers firstly by habitat and secondly by month and reach. Total density and family richness of invertebrates differed by reach, habitat and month in both rivers, except for richness in the Mersey River where habitat was not significant. Differences in densities and numbers of invertebrate families among habitats were not consistent between reaches for each river. This study has highlighted the differences in macroinvertebrate assemblages of several littoral habitats in two lowland rivers in Tasmania. Differences in taxonomic composition, density and richness among habitats within reaches strongly imply the uniqueness of these habitats in terms of the invertebrate faunas that occupy them. We suggest that if maintenance of biotic diversity is an aim of instream flow management, water allocations that address low flows should place a high priority on the maintenance of a diversity of habitats.     

熔体直纺细旦涤纶FDY 44 dtex/48 f生产工艺

对熔体直纺细旦FDY 44 dtex/48 f的生产工艺进行了介绍。探讨纺丝组件、冷却条件及集束上油、缓冷区、拉伸工艺等条件对产品质量的影响。结果表明,通过侧吹风室的改造和优化工艺可以生产出优质产品。