粉煤灰水泥压实体早期水化和孔隙结构的演变

利用压实粉体的方法制备粉煤灰水泥压实体,通过毛细吸收法、压汞法、氮吸附法、电子显微分析、非蒸发水和抗压强度的测定,研究粉煤灰水泥浆体早期水化和孔隙结构的演变。结果表明:随着水化进行,3 d龄期浆体水化显著,抗压强度迅速提高,后期水化变慢,抗压强度增长变慢。浆体孔隙率逐渐降低,3 d龄期内尤为明显;早期浆体中的大孔逐渐减少,小孔增多,最可几孔径向小孔径移动,7 d龄期后孔径变化缓慢。

流体毛细吸收法表征水泥压实体结构

通过压制干粉水泥制备压实体有助于水泥水化初始结构的可调控制备。利用乙醇毛细吸收的方法设计流体吸收量与时间平方根的线形相关系数、流体吸收系数、压实体孔隙率、流体相对吸收体积和压实体相对压缩体积等参数表征了水泥压实体结构。研究结果表明:水泥压实体在加压制备过程中实现了水泥颗粒的随机均匀分布,没有明显的颗粒团簇和粉体结拱现象,流体能在水泥压实体中均匀饱和吸收。这为水泥水化初始结构的表征和量化制备奠定了基础。

CaSO_4·2H_2O-C_3A压实体水化产生膨胀应力的机理

本工作采用自行设计的一套膨胀应力测试装置测试了在三维约束条件下CaSO_4·2H_2O-C_3A压实体在40℃的水溶液、饱和Ca(OH)_2溶液和1 mol/L NaOH溶液中水化生成钙矾石过程中产生的膨胀应力,并测试了压实体中水化生成的钙矾石的吸水肿胀应力。结果表明,CaSO_4·2H_2O-C_3A压实体在水溶液、饱和Ca(OH)_2溶液和1 mol/L NaOH溶液中水化生成钙矾石产生的最大膨胀应力为23.9 MPa、27.3 MPa和26.4 MPa,在水溶液中水化膨胀应力最小,表明Ca(OH)_2溶液和OH^-均会促进钙矾石产生的膨胀应力;生成的钙矾石45℃干燥再吸水,在约束条件下40℃的吸水肿胀应力分别为1.23 MPa、1.27 MPa和1.26 MPa,远小于钙矾石形成过程产生的膨胀应力,表明钙矾石吸水肿胀应力对CaSO_4·2H_2O-C_3A压实体水化膨胀应力的贡献很小,钙矾石形成时产生的膨胀应力主要源于结晶压力。

白云岩粉末压实体碱白云石反应的膨胀应力

采用自制膨胀应力测定仪对白云岩粉末压实体的碱白云石反应(ADR)膨胀应力进行直接测定。结果表明:白云岩粉末压实体与碱发生去白云石化反应可以产生膨胀应力,膨胀应力可以达到103 MPa。白云岩粉末压实体发生去白云石化反应产生的膨胀应力趋势相同,即变化过程可分为3个阶段:平缓阶段、缓慢增加阶段和快速增加阶段。在养护过程中,受限的白云岩粉末压实体内的白云石发生去白云石化反应,生成细小的方解石和水镁石。这些产物在受限的孔隙和间隙里沿白云石边缘生长并形成搭接框架后,继续生长引起白云岩粉末压实体缓慢产生膨胀应力。

基于系统固有频率的基层压实质量评价方法

为探讨公路基层压实过程中的压实质量评价方法,首先利用经典的振动轮-压实体力学模型,从理论上解析了系统的固有频率与刚度之间的关系,然后通过基层现场振动压实试验采集振动轮振动信号,利用信号分析与处理技术探求了系统固有频率与刚度(压实度)之间的规律。试验研究表明,系统的固有频率随压实次数的增加呈现先快速增大而后缓慢增长的趋势,这与压实度的增长规律类似。因此可以采用基于振动系统固有频率的变化来评价基层压实质量,为基层连续压实控制提供了一种技术参考。工程应用验证了该方法具有可行性与合理性。

沥青稳定碎石混合料设计方法对比试验研究

针对大粒径沥青稳定碎石基层,结合9种级配、3种沥青的沥青稳定碎石混合料,通过大马歇尔法、superpave旋转压实体积法、GTM法对大粒径沥青稳定碎石混合料材料组成设计方法进行了系统的对比试验研究;建立了3种混合料设计方法之间混合料体积及力学指标的关系;在此基础上给出了重载交通条件下大粒径沥青稳定碎石混合料组成设计方法的建议。

微珠对水泥基胶凝材料性能的影响研究

对比研究了不同掺量D50为1.0μm微珠对复合水泥干粉压实体堆积密度、复合水泥浆体工作性能和力学性能的影响规律。结果表明：微珠掺量在0~40%时,复合水泥干粉压实体堆积密度与复合水泥浆体的流动度具有较好的对应关系,复合水泥干粉压实体堆积密实度越高,复合水泥浆体流动度越大;当微珠掺量30%时,复合水泥粉体堆积密度最高,空隙率最低,复合水泥浆体流动度最高,复合水泥浆体3、7 d抗压强度较低,28 d抗压强度超过纯水泥浆体,60 d抗压强度同比其他复合水泥浆体最高。

粉煤灰水泥早期水化的原位观察

将粉煤灰水泥制成尺寸为35 mm×25 mm×25 mm的压实体,采用激光共聚焦显微镜对粉煤灰水泥压实体的早期水化过程进行原位观察。结果表明:激光共聚焦显微镜可以较好地应用于原位观察粉煤灰水泥压实体的水化过程以及孔的演变过程。当粉煤灰水泥压实体与水接触8h时,水化产物围绕着水泥颗粒大量生成。随着水化时间的延长,水化产物生成量逐渐增多,水泥颗粒与粉煤灰颗粒之间的大量孔洞被水化产物填充。水化3d时,粉煤灰水泥水化达到稳定期,微结构逐渐密实。

Congenital left ventricular aneurysms and diverticula： an entity in search of an identity

Congenital left ventricular aneurysm or diverticulum are rare cardiac malformations described in 809 cases since the first description in 1816, being associated with other cardiac, vascular or thoraco-abdominal abnormalities in about 70%. It appears to be a developmental anomaly, starting in the 4th embryonic week. In an experimental study, targeted knockdown of cardiac troponin T in the chick was performed at day 3, after the heart tube has formed. Morpholino treatment of gene TNNT2 at this stage led to the development of left ventricular diver- ticula （LVD） in the primitive left ventricular wall. Diagnosis of left ventricular aneurysms （LVA）/LVD can be made after exclusion of coro- nary artery disease, local or systemic inflammation or traumatic causes as well as cardiomyopathies. Clinically, most of LVA and LVD are asymptomatic or may cause systemic embolization, congestive heart failure, valvular regurgitation, ventricular wall rupture, ventricular tachycardia or sudden cardiac death. Diagnosis is established by imaging studies （echocardiography, magnetic resonance imaging or left ventricular angiography） visualizing the structural changes and accompanying abnormalities. Mode of treatment has to be individually tai- lored and depends on clinical presentation, accompanying abnormalities and possible complications, options include surgical resection （espe- cially in symptomatic patients）, anticoagulation after systemic embolization, radiofrequency ablation or implantation of an implantable car- dioverter defibrillator （ICD） in case of symptomatic ventricular tachycardias, and occasionally combined with class I- or III-antiarrhythmic drugs. Cardiac death occurs usually in childhood, is significantly more frequent in LVA patients and caused by congestive heart failure in most of the cases, whereas patients diagnosed with LVD died more frequently from rupture of the LVD.

Experimental Study on Uniaxial Compressive Strength of Reservoir Ice

Uniaxial compression experiments on horizontal and ervoir were conducted at different temperatures and strain rates vertical samples of first-year freshwater ice in a res- with an electronic universal machine equipped with low temperature cabinet. The results show that there is no difference between the strengths of two horizontal samples with grain sizes ranging from 1 to 4 mm and 4 to 14 mm, while the strength of the 1--4 mm vertical samples is 1.4 times higher than that of the 4--14 mm vertical samples because of the change of crystal structure. For different load- ing directions, the strengths of the horizontal samples do not differ from those of the vertical samples with the same grain sizes. The relation among the uniaxial compressive strength, strain rate and temperature was established through data analysis in both the ductile and brittle regions.

Analysis of semi-solid response under rapid compression tests using multi-scale modelling and experiments

Simulating semi-solid metal forming requires modelling semi-solid behaviour.However, such modelling is difficult because semi-solid behavior is thixotropic and depends on the liquid-solid spatial distribution within the material.In order to better understand and model relationships between microstructure and behavior, a model based on micromechanical approaches and homogenisation techniques is presented.This model is an extension of a previous model established in a pure viscoplastic framework to account for elasticity.Indeed, experimental load-displacement signals reveal the presence of an elastic-type response in the earlier stages of deformation when semi-solids are loaded under rapid compression.This elastic feature of the behaviour is attributed to the response of the porous solid skeleton saturated by incompressible liquid.A good quantitative agreement is found between the elastic-viscoplastic predicted response and the experimental data.More precisely, the strong initial rising part of the load-displacement curve, the peak load and the subsequent fall in load are well captured.The effect of solid fraction on mechanical response is in qualitative agreement with experiments.

Acoustic emission generated during the gas sorption-desorption process in coal

An experimental system for monitoring the acoustic signals generated in coal during gas sorption and/or desorption was designed and the acoustic signals were observed under different gas pressures. The experimental results show that signals generated by the coal during gas adsorption are attenuated over time. Also, the signals are not continuous but are impulsive. The intensity of the signals generated during gas desorption is far smaller than that observed during adsorption. The signal seen during desorption remains essentially stable. Cycles of sorption and desorption cause acoustic emission signals that exhibit a memory effect, which depends upon the maximum gas pressure the sample was exposed to in earlier cycles. Lower pressures in subsequent cycles, compared to the maximum adsorption pressure in previous cycles, cause both the energy and impulse frequency to be lower than previously. On the contrary, a gas adsorption pressure that exceeds the maximum pressure seen by the sample during earlier cycles causes both the energy and impulse frequency to be high.

Horizontal roof gap of backfill hydraulic support

For the backfill hydraulic support as the key equipment for achieving integration of backfilling and coal mining simultaneously in the practical process, its characteristics will directly influence the backfill body's compression ratio. Horizontal roof gap, as a key parameter of backfilling characteristics, may impact the backfilling effect from the aspects of control of roof subsidence in advance, support stress, backfilling process and the support design. Firstly, the reason why horizontal roof gap exists was analyzed and its definition, causes and connotation were introduced, then adopting the Pro/E 3D simulation software, three typical 3D entity models of backfill hydraulic supports were built, based on the influence of horizontal roof gap on backfilling effect, and influence rules of four factors, i.e. support height, suspension height, suspension angle and tamping angle, were emphatically analyzed on horizontal roof gap. The results indicate that, the four factors all have significant impacts on horizontal roof gap, but show differences in influence trend and degree, showing negative linear correlation, positive linear correlation, positive semi-parabolic correlation and negative semi-parabolic correlation, respectively. Four legs type is the most adaptive to the four factors, while six legs(II) type has the poorest adaptability, and the horizontal roof gap is small under large support height, small suspension height, small suspension angle and large tamping angle situation. By means of optimizing structure components and their positional relation and suspension height of backfill scrape conveyor in the process of support design and through controlling working face deployment, roof subsidence in advance, mining height and backfilling during engineering application, the horizontal roof gap is optimized. The research results can be served as theoretical basis for support design and guidance for backfill support to have better performance in backfilling.

Dynamic action simulation system and preliminary experiments of coal seams and gas

In order to study the dynamic action and physical effects of coal seams and gas, a simulation system for this dynamic action was developed and a physical model built in our laboratory. Using this newly built model, the volume of coal outbursts and the temperature during the outburst process were studied. The results show that： l） for coal seams with similar structure and com- ponents, two factors, i.e., gas pressure and ground stress affect the volume of coal outbursts, with gas pressure being the more im- portant of the two and 2） the changes in coal temperature, both its increase and decrease, are affected by ground stress and gas pressure, it is a process of change. Preliminary tests show that the system can simulate the dynamic interaction of coal and gas, which is helpful for studying the dynamic mechanism of solid-gas coupling of gas and coal.

Vapor Pressure Measurement and Correlation of 2-Methyl-Butanol Acetate Containing Calcium Chloride

The CaCl2 solubility in 2-methyl-butanol acetate and the vapor pressure of 2-methyl-butanol acetate containing CaCl2 were measured in the range of 90-135°C and from very low salt concentration to saturation.The experimental data were correlated with two equations,a modified Antoine equation with the dissolved salt taken into account and a nonrandom two liquid-electrolyte（e-NRTL）model.Both models are in good agreement with the experimental data.This study provides essential physical data for further investigation of vapor-liquid equilibrium system containing salt.

Effects of groove on behavior of flow between hydro-viscous drive plates

The flow between a grooved and a flat plate was presented to investigate the effects of groove on the behavior of hydro-viscous drive. The flow was solved by using computational fluid dynamics (CFD) code, Fluent. Parameters related to the flow, such as velocity, pressure, temperature, axial force and viscous torque, are obtained. The results show that pressure at the upstream notch is negative, pressure at the downstream notch is positive and pressure along the film thickness is almost the same. Dynamic pressure peak decreases as groove depth or groove number increases, but increases as output rotary speed increases. Consequently, the groove depth is suggested to be around 0.4 mm. Both the groove itself and groove parameters (i.e. groove depth, groove number) have little effect on the flow temperature. Circumferential pressure gradient induced by the groove weakens the viscous torque on the grooved plate (driven plate) greatly. It has little change as the groove depth increases. However, it decreases dramatically as the groove number increases. The experiment results show that the trend of experimental temperature and pressure are the same with numerical results. And the output rotary speed also has relationship with input flow rate and flow temperature.

Simulation and experimental study of high pressure switching expansion reduction considering real gas effect

Switching expansion reduction(SER)uses a switch valve instead of the throttle valve to realize electronically controlled pressure reduction for high pressure pneumatics.A comprehensive and interactive pneumatic simulation model according to the experimental setup of SER has been built.The mathematical model considers heat exchanges,source air pressure and temperature,environmental temperatures and heat transfer coefficients variations.In addition,the compensation for real gas effect is used in the model building.The comparison between experiments and simulations of SER indicates that,to compensate the real gas effect in high pressure discharging process,the thermal capacity of air supply container in simulation should be less than the actual value.The higher the pressure range,the greater the deviation.Simulated and experimental results are highly consistent within pressure reduction ratios ranging from 1.4 to 20 and output air mass flow rates ranging from 3.5 to 132 g/s,which verifies the high adaptability of SER and the validity of the mathematic model and the compensation method.

Experimental investigation of axially loaded steel fiber reinforced high strength concrete-filled steel tube columns

An experimental study on the compressive behavior of steel fiber reinforced concrete-filled steel tube columns is presented. Specimens were tested to investigate the effects of the concrete strength, the thickness of steel tube and the steel fiber volume fraction on the ultimate strength and the ductility. The experimental results indicate that the addition of steel fibers in concrete can significantly improve the ductility and the energy dissipation capacity of the concrete-filled steel tube columns and delay the local buckling of the steel tube, but has no obvious effect on the failure mode. It has also been found that the addition of steel fibers is a more effective method than using thicker steel tube in enhancing the ductility, and more advantageous in the case of higher strength concrete. An analytical model to estimate the load capacity is proposed for steel tube columns filled with both plain concrete and steel fiber reinforced concrete. The predicted results are in good agreement with the experimental ones obtained in this work and literatures.

Numerical Investigation of Pressure Distribution in a Low Specific Speed Centrifugal Pump

To study the pressure distribution of the volute casing, front casing and back casing in a prototype centrifugal pump, the pressure experiments and numerical simulations are carried out at six working conditions in this paper. The experimental results shows that the asymmetry of static pressure distribution on volute casing and front cavity is caused by the tongue of the volute and it may result in high radial and axial resultant force which can cause vibration and noise in the centrifugal pump. With the increasing of flow rote, the asymmetry of static pressure distribution and the magnitude of static pressure values reduce. The numerical results indicate that the pressure fluctuation near the tongue is strongest and it becomes slighter at point away from the tongue. With the increasing of flow rote, the local high=pressure region in impeller passage reduces and the flow becomes smoother accordingly, whereas the fluid speed becomes much higher which may cause further flow losses. The results predicted by numcrical simulation are in coincident with the experimental ones. It shows that the turbulence model for simulating the flow field in centrifugal pumps is feasible.

In situ observations of tungsten speciation and partitioning behavior during fluid exsolution from granitic melt

Most economically important tungsten(W)deposits are of magmatic-hydrothermal origin.The species and partitioning of W during fluid exsolution,considered to be the controlling factors for the formation of ore deposits,are thus of great significance to investigate.However,this issue has not been well addressed mainly due to the significant difference in reported partition coefficients(e.g.,from strongly incompatible to strongly compatible)between fluid and melt(D_(W)^(fluid/melt)).Here,we used an in situ Raman spectroscopic approach to describe the W speciation,and to quantitatively determine the Dfluid/melt of individual and total W species in granite melts and coexisting Na2WO4 solutions at elevated temperatures(T;700–800C)and pressures(P;0.35–1.08 GPa).Results show that WO_(4)^(2-)and HWO4are predominant W species,and the fractions of these two species are similar in melt and coexisting fluid.The partitioning behaviors of WO_(4)^(2-)and HWO4are comparable,exhibiting strong enrichment in the fluid.The total DW fluid/melt ranges from 8.6 to 37.1.Specifically,DW fluid/melt decreases with rising T–P,indicating that shallow exsolution favors enrichment of W in evolved fluids.Furthermore,Rayleigh fractionation modeling based on the obtained D_(W)^(fluid/melt)data was used to describe the fluid exsolution processes.Our results strongly support that fluid exsolution can serve as an important mechanism to generate W-rich oreforming fluids.This study also indicates that in situ approach can be used to further investigate the geochemical behavior of ore-forming elements during the magmatic-hydrothermal transition,especially for rare metals associated with granite and pegmatite.