再生集料掺量对混凝土碳化性能研究

在同一水灰比条件下,研究了再生集料0、30％、50％、70％和100％5种掺量下的再生混凝土在3d、7d、28d 3个龄期下的抗压强度和3d、7d、14 d、28 d和56d5个龄期下的碳化性能.结果表明:低替代量的再生集料对于混凝土的抗压强度影响不大,当替代量＞50％时会较大地降低混凝土的抗压强度.再生集料的掺量与碳化之间并没有明显的线性关系.当再生集料掺量100％时,再生混凝土的碳化最低,而再生集料掺量为30％和70％时,其碳化深度最大,再生集料掺量50％与普通混凝土碳化深度大致相当.     

温度匹配养护对大掺量矿物掺合料混凝土抗压强度及早期水化性能的影响

大体积混凝土由于胶凝材料水化放热,其内部温升对混凝土强度发展规律有很大影响.采用温度匹配养护和标准养护两种不同的养护方式,研究了单掺40％粉煤灰、单掺50％矿粉以及复掺30％粉煤灰和20％矿粉三种大掺量矿物掺合料混凝土与纯水泥、单掺20％粉煤灰两种普通混凝土在不同温度养护条件下的抗压强度差异,并对胶凝材料水化早期的浆体进行了扫描电镜和化学结合水测试.结果 表明:与纯水泥混凝土相比,温度匹配养护对大掺量矿物掺合料混凝土早期强度发展的促进作用要显著得多,且大掺量矿物掺合料混凝土温度匹配养护方式下的各龄期强度均比标准养护方式下的要高,然而纯水泥混凝土温度匹配养护条件下的后期强度却要低于标准养护条件下的后期强度.温度匹配养护方式下较高的早期水化温度显著加速了大掺量矿物掺合料混凝土的水化反应进程,从而使大掺量矿物掺合料混凝土的早期强度提高.     

白糖和葡萄糖酸钠二元复合对长螺旋咬合桩用超缓凝混凝土性能的影响

为解决咬合桩施工现场超缓凝混凝土的制备问题,探究缓凝剂的作用机理,采用白糖和葡萄糖酸钠按质量比7∶3配制复合缓凝剂,对比一次搅拌和二次搅拌工艺,制备超缓凝混凝土。采用抗压抗折一体化试验机、环境扫描电子显微镜(ESEM)、总有机碳分析仪和等温量热仪测试分析超缓凝混凝土的力学性能、微观形貌、吸附量和水化性能。结果表明,混凝土的凝结时间随着缓凝剂掺量的增加而延长。当缓凝剂掺量为0.38%(质量分数)时,一次搅拌组初、终凝时间分别为31 h和46 h,二次搅拌组初、终凝时间分别为34 h和50 h;当缓凝剂掺量为0.50%(质量分数)时,一次搅拌组初、终凝时间分别为61 h和78 h,二次搅拌组初、终凝时间分别为65 h和84 h。两种掺量下,混凝土56 d抗压强度均达到40 MPa以上,满足两种工况的施工要求。采用二次搅拌工艺制备超缓凝混凝土有助于进一步延长混凝土的凝结时间,改善混凝土拌合物的流动性,但会略微降低混凝土的抗压强度。不同缓凝剂在水泥颗粒表面的吸附能力强弱顺序为:葡萄糖酸钠>白糖-葡萄糖酸钠>白糖>白糖-葡萄糖酸钠后掺。缓凝剂的掺入起到降低水化放热,抑制水泥水化的作用,从而延长混凝土的凝结时间。     

煅烧煤矸石再生细骨料混凝土徐变性能

为研究不同煅烧温度、煤矸石掺量、粉煤灰掺量及水胶比对再生细骨料混凝土抗徐变性能的影响,采用4因素3水平的正交原理,对不同试验条件下再生细骨料混凝土进行120 d的干缩和徐变性能研究.结果 表明:对于养护28 d后的试件,影响其抗压强度最大的因素是煤矸石掺量的不同;干缩变形量从基础养护起第80 d为分界线,分快速干缩和稳定干缩两阶段,同时受煅烧温度和水胶比影响较大,但适当的粉煤灰掺量和煅烧温度不仅能抑制干缩,而且能致密空隙并降低水化热;持续荷载120 d时,构件整体徐变变形增大,分为快速、慢速和稳定3个阶段,受煅烧温度和煤矸石掺量影响较大,同时徐变变形与时间存在相对较高的相关性.     

缓凝剂和早强剂对混凝土性能的影响试验研究

针对混凝土抗压强度和凝结时间等性能要求,在混凝土制备中掺入不同量的缓凝剂或早强剂,并对不同掺量下的缓凝剂和早强剂对混凝土性能的影响进行研究。结果表明,掺入0.06%的葡萄糖酸钠缓凝剂后,混凝土在凝结时间、抗压强度和坍落度等方面都有所提高;掺入硫酸钠后,混凝土凝结时间、坍落度有所下降,但抗压强度有所提高。     

粉煤灰对混凝土抗冻临界强度的影响研究

为研究粉煤灰对混凝土抗冻临界强度的影响规律,制备了不同预养护时间、抗冻温度粉煤灰掺量的混凝土试验样品,测试其抗冻4 d后60 d抗压强度,分析了粉煤灰掺量对混凝土抗压强度的影响规律,找出了不同粉煤灰掺量混凝土的抗冻临界强度。研究结果表明:粉煤灰混凝土的60d抗压强度随抗冻温度的降低而减小;混凝土保证最终强度的预养护时间随粉煤灰掺量的增大而增长;粉煤灰混凝土的抗冻临界强度随受冻温度的减低而增大。     

再流化混凝土的性能试验研究

混凝土搅拌站对失去工作性能的混凝土处理方式往往是再流化之后降低标号使用,该方法往往缺乏对再流化混凝土工作性能,硬化性能的定量分析,容易造成资源浪费,导致经济方面的损失,本文为了研究这一问题,使用葡萄糖酸钠作为缓凝剂,配合少量减水剂和水,将混凝土再流化,测定再流化混凝土初始工作性能,120分钟工作性能,凝结时间以及各龄期的抗压强度,并且测定了使用葡萄糖酸钠作为缓凝剂时的混凝土的绝热温升曲线,结果表明:葡萄糖酸钠的二次加入能够明显延长混凝土的凝结时间,明显降低再流化混凝土3天抗压强度,但是并不影响再流化混凝土的7天和28天抗压强度,二次掺加葡萄糖酸钠的量为胶凝材料总量的百分之0.04到百分之0.06之间时,再流化混凝土各方面工作性能最理想。在绝热情况下,葡萄糖酸钠的加入明显提高混凝土内部的温度,而且随缓凝剂量的增加绝热温度增加。葡萄糖酸钠的掺量达到胶凝材料总量的百分之0.1情况下,混凝土内部绝热温度最高,可以达到44.8摄氏度。     

风积沙混凝土的碳化试验研究与预测

用风积沙(沙漠沙)部分或全部替代普通河砂拌制混凝土具有重大的社会与经济效益.沙漠地区环境气候条件十分恶劣,研究风积沙混凝土在复杂环境下的耐久性能意义重大.设计制作了不同风积沙掺量(0、20％、40％、60％、80％、100％)的混凝土试块,并标准养护28 d,研究在实验室加速碳化3 d、7 d、14 d、21 d和28 d后的碳化规律.运用MATLAB拟合得到了风积沙混凝土的CO2扩散系数随风积沙掺量变化的数学表达式,并建立了以风积沙掺量为主要参数的碳化深度预测模型.模型的建立为风积沙混凝土在沙漠及周边区域的推广应用提供重要的参考.     

负10℃条件下缓凝剂对快硬硫铝酸盐水泥水化及强度的影响

研究了–10℃环境中氯化钙溶液拌合冷物料条件下,硼砂、葡萄糖酸钠、L(+)-酒石酸对快硬硫铝酸盐水泥凝结硬化行为、强度发展的影响,分析了缓凝剂对水化产物的影响。结果表明:–10℃条件下采用氯化钙溶液拌合时,0.6%掺量硼砂可使初凝时间延长至25 min、终凝时间延长至28 min,而葡萄糖酸钠和L(+)-酒石酸对初终凝时间影响不显著。随着硼砂、葡萄糖酸钠掺量的增加,不同龄期强度均逐渐下降,28 d最大降低值可达到25.5 MPa;L(+)-酒石酸会使得强度下降得更为明显,0.3%(质量分数)掺量时便会使得1 d抗压强度下降10.9 MPa,0.6%掺量时28 d抗压强度下降27.3 MPa。掺0.6%硼砂的1 d试样中钙矾石的形貌未发生明显变化,但生成量减少5.31%;葡萄糖酸钠使钙矾石呈短柱状,生成量几乎不变;L(+)-酒石酸使得钙矾石呈针状,生成量无明显变化。–10℃条件下硼砂可显著延长快硬硫铝酸盐水泥的凝结时间,且适当掺量时强度损失可接受,是适宜的缓凝剂;葡萄糖酸钠、L(+)-酒石酸的缓凝效果不明显,且会改变钙矾石的形态与分布,并会使强度显著下降。     

不同粉煤灰掺量混凝土的早期抗压与抗渗性能

试验研究了不同粉煤灰掺量混凝土的早期抗压强度和抗渗性能,结果表明,不同粉煤灰掺量的混凝土,其早期强度随粉煤灰掺量的增加降低越显著,28d时粉煤灰的掺量对混凝土强度的影响作用逐渐减弱;不同粉煤灰掺量混凝土的早期抗渗性能随粉煤灰掺量的增加降低也越明显,7d以后粉煤灰对混凝土抗渗性能的改善随粉煤灰掺量的增加而增强。     

不同产地不同部位巫山淫羊藿中黄酮的HPLC分析

建立HPLC梯度洗脱法同时测定巫山淫羊藿中3种黄酮:淫羊藿次苷Ⅰ,朝藿定C和淫羊藿苷质量分数的方法。采用HPLC法,色谱柱为phenomenex C18分析柱(5μm,4.6 mm×250 mm);流动相为(A)水,(B)乙腈;柱温35℃;流速1.0 mL/min;检测波长270 nm;线性梯度洗脱条件:B∶15%(5 min),B∶30%(10 min),B∶50%(30 min)。本方法测定淫羊藿次苷Ⅰ,朝藿定C和淫羊藿苷的线形范围在0.20—1.80μg,r=0.999 3,r=0.999 9和r=0.999 7;平均回收率分别为98.43%,97.58%和97.91%,RSD(n=3)分别为2.16%,1.77%和1.90%。该方法简便、准确、重现性好,可作为同时测定淫羊藿次苷Ⅰ,朝藿定C和淫羊藿苷质量分数的方法。     

Unperturbed chain dimensions of polyisobutylene in different solvents and at different temperatures

Summary Intrinsic viscosity of polyisobutylene is determined in different solvents and at different temperatures. The intrinsic viscosity is found to increase with the increase in temperature. These variations are explained in terms of variation in thermodynamic quality of the solvent. From these data, the upertubed parameter (k₀) is determined. It is observed that it firstly increases with temperature and then seems to level off and is found to be different for different solvents. k₀ is also correlated with different thermodynamic parameters like H, A, and .     

Low temperature oxidation of coals of different rank and different sulphur content

Five coals of different rank and of different content of sulphur were subjected to oxidation by peroxyacetic acid (PAA), 5% nitric acid, by oxygen in 0.5N Na₂CO₃ aqueous solution and the air oxidation for 7 days at 125 °C. The processes of oxidation were carried out for coal samples demineralised by the Radmacher method, and additionally for the pyrite-free coal samples. Proximate, elemental and spectral analyses of the initial coals and the products obtained from them were made. The most effective oxidising agents were 5% HNO₃ and PAA. As a result of oxidation, a significant part of the organic components of coal is converted into acid soluble products. Depending on the oxidising agent, the loss of sulphur in the solid oxidation products was different and the highest for the coal samples oxidised with HNO₃ and PAA. Formation of oxidised sulphur species (SO and -SO₂) was detected by IR spectroscopy. FTIR data also provide useful information on evolution of the molecular structure of different rank coals on oxidation, in particular in the carbonyl and aliphatic ranges (1800-1500 and 3500-2800 cm⁻¹).     

咪鲜胺在不同pH溶液及3种水体中的光解

以高压汞灯为光源，研究了咪鲜胺在不同pH和不同水体中的光化学降解情况。结果表明：咪鲜胺的光化学降解速率随着pH的增大而减慢；咪鲜胺在供试的3种水体中的光化学降解速率大小为：稻田水〉河水〉纯水。     

Stereospecificity of different lipases

The stereospecificity of 4 lipases towards enantiomeric alkyldiacylglycerols and alkylmonoacylglycerols was investigated. No stereospecific breakdown of the former substrate was observed for lipases from pancreas,Rhizopus arrhizus, Pseudomonas fluorescens, or bile salt-stimulated lipase from human milk. All lipases degraded 2-oleoyl-3-tetradecyl-sn-glycerol faster than 1-tetradecyl-2-oleoyl-sn-glycerol. Among X-1-acyl-3-alkylglycerol isomers, 1-acyl-3-alkyl-sn-glycerol was preferentially attacked by the 3 first mentioned lipases. Possible mechanisms and metabolic implications for these stereospecificities are discussed. A preliminary account of this work was given in Abstract 457 of the ISF/AOCS World Congress, New York, 1980.     

Push-out bonding strengths of four different dowel systems luted with two different adhesive systems

This in vitro study investigates the bonding capacity of resin cements to dowels, using the push-out bonding strength of four different dowel systems, namely, stainless steel dowels (SSD), resin-supported polyethylene fiber dowels (RSPFD), zirconia dowels (ZD), and superpost glass fiber dowels (GFD), luted in root canals, using two different resin cements, namely, Multilink Automix Cement and Clearfil Esthetic Cement. Ninety-six maxillary central incisor teeth were sectioned below the cementoenamel junction, and the roots were treated endodontically. Then the roots were placed into four groups, based on the dowel systems used. The roots were further placed into two subgroups, based on the cement type used as subgroup A and subgroup B. Push-out bonding tests were performed on the bonded specimens, which were cut into 1 mm thick sections. A two-way ANOVA test and Tukey’s HSD tests were performed. The push-out bonding strength values for SSD, ZD, and RSPFD were not significantly different (p > 0.05). The means for GFD were significantly higher than the means for ZD (p < 0.05) when Multilink Automix Cement was used. However, when Clearfil Esthetic Cement was used, the means for RSPFD were significantly higher (p < 0.001) than the means for the other systems. When Clearfil Esthetic Cement was used, the RSPF dowel system provided significantly higher bonding strength values than the other systems.     

Grindability of different alumina grades

Conclusions Comparative investigations were made of alumina grades G-2, GK, and G-0. It was established that for the production of mullite-corundum chamotte it is best to use alumina G-0 because of its better grindability, compared with G-2, ensuring a higher quality of chamotte during firing in rotary kilns.Translated from Ogneupory, No. 6, pp. 9–12, June, 1981.     

Calculation of excess molar volumes with different cubic equations of state and different mixing rules

The effects of the simple composition-dependent combining rules (conventional, Adachi-Sugie and van Laar-Stryjek-Vera-type) and Huron-Vidal-NRTL mixing rules and different cubic equations of state (Redlich-Kwong, Soave-Redlich-Kwong, Peng-Robinson and Peng-Robinson-Stryjek-Vera) on excess molar volume correlation are examined. The results obtained for some asymmetric non-ideal mixtures indicate very good agreement between correlated and experimental data in all cases when Huron-Vidal-NRTL mixing rules are coupled with the Peng-Robinson-Stryjek-Vera equation of state.     

Synthesis of different magnetic carbon nanostructures by the pyrolysis of ferrocene at different sublimation temperatures

Various magnetic nanostructures such as Fe nanoparticles (Fe-NPs) adhering to single-walled carbon nanotubes, carbon-encapsulated Fe-NPs, Fe-NP decorated multi-walled carbon nanotubes (MWCNTs), and Fe-filled MWCNTs have been synthesized by the pyrolysis of pure ferrocene. It is found that the formation of the nanostructures can be selectively controlled by simply adjusting the sublimation temperature of ferrocene, while keeping all other experimental parameters unchanged. Magnetic characterization reveals that these nanostructures have an enhanced coercivity, higher than that of bulk Fe at room temperature. Based on the experimental results, the formation mechanism of the nanostructures is discussed in detail.     

Comparison of different heterogeneous catalysts and different alcohols for the esterification reaction of oleic acid

Oils with high amount of free fatty acid (FFA) are becoming one of the most promising alternatives to produced biodiesel; due, principally, to it low cost. However, because of the presence of FFA, the conventional basic homogenous catalyst should not be used with the aim to avoid the production of soaps.In this work, different catalysts, such as solid resins, zeolite and enzymes, as well as different alcohols: ethanol anhydrous, ethanol 96°, 1-propanol, 2-propanol and butanol, were tested for the direct esterification reaction of pure oleic acid.The influence of several variables, such as alcohol’s carbon chain length, the presence of water, which has a negative effect on the final conversion shifting the final conversion to a lower level, and the location of the OH group were studied.The enzymatic catalyst, Lipozyme CALB, turned out to be the best one, achieving a final conversion of 98% after three days reaction.