镍铁粉对水泥水化性能的影响

采用镍铁渣制成粒径小于0.075 mm的粉体,作为矿物掺合料取代部分水泥,研究镍铁粉不同掺量对水泥水化性能以及强度的影响。XRF分析发现,镍铁粉中含有较多的SiO_(2)、MgO、FeO,具有较高的火山灰活性。镍铁粉的掺入可以较大程度上延缓水泥水化时间,相较空白组,掺30%镍铁粉时,第2个水化放热峰的出现时间延缓8 h左右;降低体系的水化放热量,相较空白组,当镍铁粉掺量为10%、20%、30%时,体系的累计放热量依次下降33%、46%、63%;掺入镍铁粉明显降低试块的抗压强度,但镍铁粉具有二次水化作用,可以使试块后期抗压强度增幅较大,掺20%镍铁粉试块的28 d抗压强度可达到空白组的86%。

粉煤灰/矿粉-水泥胶凝体系的水化放热性能

利用等温量热仪,研究粉煤灰/矿粉-水泥胶凝体系3 d内水化放热性能,借助X射线衍射仪与热分析仪分析不同胶凝体系的水化产物。结果表明:掺量质量分数为45%时,粉煤灰-水泥胶凝体系3 d的水化放热量为175.4J/g,矿粉-水泥胶凝体系为205.4 J/g;矿粉-水泥胶凝体系水化速率峰值出现时间为15.3 h,大于粉煤灰-水泥胶凝体系的10.22 h;双掺粉煤灰和矿粉等量取代质量分数为50%水泥时,随粉煤灰掺入比例的增大,水化放热量减小的程度增大,但粉煤灰或矿粉的掺入比例与水化热峰值及其出现时间关系不大;掺入粉煤灰和矿粉后,可以明显降低早期水化产物中钙钒石(AFt)和氢氧化钙(CH)的生成量。

粉煤灰粒径分布对硅酸盐水泥水化性能的影响

为研究粉煤灰粒径对硅酸盐凝胶材料水化性能的影响,经球磨仪研磨得到3种不同粒径的粉煤灰,探讨其对硅酸盐水泥水化放热速率、水化放热总量、水化反应程度和粉煤灰自身水化反应程度的影响。结果表明:随粉煤灰粒径的减小,粉煤灰的水化活性明显增大,水化反应程度增大,养护龄期为7 d时,水化程度增加20.7%;粉煤灰粒径分布对硅酸盐水泥水化放热总量的影响较小,主要影响其水化放热速率、水化反应程度,养护龄期为28 d时,胶凝材料水化程度增加3%。

粉煤灰混合水泥体系的水化放热模型

通过调整粉煤灰-水泥体系中的粉煤灰掺量,参照国家标准GB/T12959-2008《水泥水化热测定方法》中的溶解热法测试体系在恒温(20±1℃)条件下各龄期的水化放热量。分析粉煤灰对体系水化放热量的影响表明,粉煤灰-水泥体及系水化放热模型可以采用统一表达式:粉煤灰的水化放热量,等于某时刻粉煤灰与水泥水化放热量的比值系数乘以粉煤灰的掺量再乘以水泥恒温水化放热统一表达式。

基于ARIMA模型的硅钙渣水泥复合胶凝材料水化热预测

预测硅钙渣水泥复合胶凝材料水化过程中产生的热量,对于这种材料在混凝土结构中的应用具有现实意义。本文基于ARIMA模型基本理论,建立了硅钙渣掺量分别为0%、10%、30%(质量分数,下同)下硅钙渣水泥复合胶凝材料的水化放热量预测模型,通过与试验数据的对比,验证了模型的准确性与可靠性;基于0%、10%、30%这三种硅钙渣掺量下复合胶凝材料的水化放热量试验数据,建立不同龄期下复合胶凝材料的水化放热量预测模型,并对其他硅钙渣掺量下复合胶凝材料的水化放热量进行预测。结果表明:0%、10%、30%这三种硅钙渣掺量下水化放热量预测值与试验值的相对误差均值均小于5%,这说明运用ARIMA模型预测硅钙渣水泥复合胶凝材料的水化放热量具有较高准确性和可靠性;其他硅钙渣掺量下复合胶凝材料水化放热量的预测结果符合实际变化趋势,进一步证明了ARIMA模型在水化热预测方面的可行性,这为定量研究与预测不同类型胶凝材料的水化放热量提供了一种有效方法。

矿物掺合料及高吸水树脂对高强混凝土水化及收缩性能的研究

针对公路桥涵高强混凝土巨型墩柱早期收缩开裂严重影响混凝土耐久性的问题,研究了矿物掺合料及高吸水树脂掺量对混凝土水化放热量、自收缩、干燥收缩、相对温湿度及强度的影响。研究结果表明,粉煤灰和矿粉均可降低水化放热量,并抑制混凝土自收缩和干燥收缩,且粉煤灰的抑制效果优于矿粉,但活性低于矿粉;随着掺量的增大粉煤灰降低水化放热量和抑制收缩作用越大,但矿粉掺量提高作用恰相反;高吸水树脂具有保湿自养护作用,随着掺量增加,保湿越明显,但掺量过高影响混凝土抗压强度;高吸水树脂抑制混凝土自收缩和干燥收缩效果比矿物掺合料更为显著,且随掺量提高收缩降低,此外,混凝土其内部湿度大小与收缩有一定相关性,湿度越小收缩越大,湿度降低速率与收缩增大速率一致。

活化金尾矿掺量对混凝土力学性能与微观结构性能的影响

这是一篇陶瓷及复合材料领域的论文。为了研究活性金尾矿掺量对混凝土力学性能、微观结构性能和水化性能的影响,开展了不同掺量金尾矿混凝土的力学性能、XRD、TG-DTG和水化特性实验。结果表明:在粉磨时间为30 min时,金尾矿的比表面积达到了极大值以及其晶体结晶化度达到了极小值。而在金尾矿掺量为30%时,混凝土的基本力学和物理性能达到较佳状态;且掺入活性金尾矿混凝土的微观结构性能、水化放热速率和放热量均优于掺入非活性金尾矿混凝土的微观结构性能、水化放热速率和放热量。随着金尾矿粉磨时间的不断增大,金尾矿粒度累积曲线的变化规律都呈现先增大后趋于稳定的趋势,且随着粉磨时间的不断增大,金尾矿粒度累积越来越大。

蓄热法在砼结构冬季施工中的应用

在我国三北地区 (东北、华北、西北 ) ,为加快工程进度 ,往往要进行砼结构的冬季施工 ,其冬季施工工程措施和方法很多 ,但最简单、最经济的方法是蓄热法 .本文简述砼结构蓄热法冬季施工的特点、施工方法、要求及注意事项 。

硫铁矿尾矿矿渣改良混凝土力学性质与耐久性

为了研究黔北地区的硫铁矿矿渣在代替混凝土骨料后混凝土的力学性能,采用X衍射仪对黔北地区的硫铁矿尾矿进行物相和矿物成分的分析,用硫铁矿尾矿矿渣来制备硫铁矿尾矿矿渣改良混凝土,并对其力学性质和冻融特性进行研究。结果表明:硫铁矿尾矿矿渣掺量的增大可以延长了改良混凝土的凝结时间,而在硫铁尾矿矿渣掺量为20%以及混凝土的水灰比为0.40时,改良混凝土的7 d抗压强度和28 d抗压强度较大。在同一水化时间下,混凝土的水化放热速率、水化放热量以及DTA值随着硫铁尾矿矿渣掺量的增大不断降低。同时,随着冻融次数的不断增大,混凝土的抗压强度不断减小,且抗冻性指标也不断减小,这说明了冻融循环作用可以削弱水泥固化土抵抗变形能力和降低承载力的作用。

A facile one-pot hydrothermal synthesis as an efficient method to modulate the potassium content of cryptomelane and its effects on the redox and catalytic properties

Cryptomelane has been widely applied as catalyst in oxidation reactions due to its excellent redox properties and low cost.Here,a novel one-pot hydrothermal synthesis using a potassium permanganate aqueous solution as precursor and ethanol as reducing agent has successfully been developed to obtain cryptomelane nano-oxides.This synthetic route makes it possible to control the amount of potassium incorporated into the structure of the cryptomelane by selecting the appropriate synthesis temperature and ethanol initial concentration.Taking advantage of this approach,the effect of potassium concentration on the structural stability and reducibility of the cryptomelane,which are poorly discussed in the literature,has been studied.We have observed that samples with low content of potassium(~11%)show high conversions of CO to CO2 especially at low temperatures.The lower activity of the samples with high K contents(~16%)can be ascribed to the beneficial effect of K on the structural stability of cryptomelane in detriment of labile oxygen on cryptomelane surface.

A new measurement method of crack propagation rate for brittle rock under THMC coupling condition

A new electrical method of conductive carbon-film(with waterproof and anticorrosion ability)was proposed to continuously measure crack propagation rate of brittle rock under THMC coupling condition.A self-designed coupling testing system was used to conduct THMC coupling fracture tests of the pre-cracked red sandstone specimens(where the temperature is only changed)by this new electrical method of conductive carbon-film.Calculation results obtained by the energy method coincide well with the test results.And the higher the temperature is,the earlier the crack is initiated and the larger the crack propagation rate and accelerated velocity are,which can prove the validity of the new electrical method.This new electrical method has advantages of continuously measuring crack propagation rate over the conventional electrical,optical and acoustic methods,and can provide important basis for safety assessment and cracking-arrest design of deep rock mass engineering.

Measurements of Hydrate Equilibrium Conditions for CH4, CO2, and CH4＋C2H6＋C3H8 in Various Systems by Step-heating Method

Phase equilibrium conditions of gas hydrate in several systems were measured by the step-heating method using the cylindrical transparent sapphire cell device.The experimental data for pure CH4 or CO2+deionized water systems showed good agreement with those in the literatures.This kind of method was then applied to CH4/CO2+sodium dodecyl sulfate(SDS)aqueous solution,CH4/CO2+SDS aqueous solution+silica sand,and(CH4+C2H6+C3H8)gas mixture+SDS aqueous solution systems,where SDS was added to increase the hydrate formation rate without evident influence on the equilibrium conditions.The feasibility and reliability of the step-heating method,especially for porous media systems and gas mixtures systems were determined.The experimental data for CO2+silica sand data shows that the equilibrium pressure will change significantly when the particle size of silica sand is less than 96μm.The formation equilibrium pressure was also measured by the reformation of hydrate.

Physicochemical properties of aqueous solutions of sodium glycinate in the non-precipitation regime from 298.15 to 343.15 K

The physicochemical properties,including the density,viscosity,and refractive index of aqueous solutions of sodium glycinate as a solvent for CO_2 absorption in the non-precipitation regime were measured under the wide temperature range of 298.15 to 343.15 K.The concentration of the sodium glycinate in an aqueous form in the non-precipitation regime was identified up to 2.0 mol ? L^(-1).The coefficients of thermal expansion values were estimated from measured density data.It was found that,the densities,viscosities and refractive indices of the aqueous sodium glycinate decrease with an increase in temperature,whereas with increasing sodium glycinate concentration in the solution,all three properties increase.Thermal expansion coefficients slightly increase with rising temperature and concentration.The measured values of density,viscosity and refractive index were correlated as a function of temperature by using the least squares method.The predicted data obtained from correlation equations for all measured properties were in fairly good agreement with the experimental data.

Condensing Heat Exchanger

The paper shows a method of designing a heat exchanger recovering heat from the condensation of water vapour contained in flue gases. A heat exchanger condenses water vapour and SO2 （sulphur dioxide） in the presence of inert gases （CO2, CO, N2, O2） contained in flue gases. A mathematical model and a sample design of a heat exchanger were presented. The heat exchange is capable of recovering from a dozen or so to several dozen percent of heat from flue gases escaping into the atmosphere. A second advantage of the heat exchanger is the possibility to reduce the emissions of SO2 considerably. Depending on the parameters, it can be even a sevenfold reduction in the emissions. The main mathematical tool used for designing the condensing heat exchanger is the Colburn-Hougen method. The authors omitted that part of the method which requires iterative calculations. The Mollier diagram was used instead.

Reduced CoNi2S4 nanosheets decorated by sulfur vacancies with enhanced electrochemical performance for asymmetric supercapacitors

Nowadays,it is a matter of great concern to design electrode materials with excellent electrochemical performance for supercapacitors by a safe,efficient and simple method.And these characteristics are usually related to the vacancies and impurities in the electrode.To investigate the effect of the vacancies on the electrochemical properties of the supercapacitor cathode material,the uniform reduced CoNi2S4(r-CoNi2S4)nanosheets with sulfur vacancies have been successfully prepared by a one-step hydrothermal method.And the formation of sulfur vacancies are characterized by Raman,X-ray photoelectron spectroscopy and other means.As the electrode for supercapacitor,the r-CoNi2S4 nanosheet electrode delivers a high capacity of 1918.9 Fg-1 at a current density of 1 A g-1,superior rate capability(87.9%retention at a current density of 20 A g-1)and extraordinary cycling stability.Compared with the original CoNi2S4 nanosheet electrode(1226 F g-1at current density of 1 A g-1),the r-CoNi2S4 nanosheet electrode shows a great improvement.The asymmetric supercapacitor based on the r-CoNi2S4 positive electrode and activated carbon negative electrode exhibits a high energy density of 30.3 Wh kg-1 at a power density of 802.1 W kg-1,as well as excellent long-term cycling stability.The feasibility and great potential of the device in practical applications have been successfully proved by lightening the light emitting diodes of three different colors.