Intrinsic Permeability Evolution in High Temperature Concrete: An Experimental and Numerical Analysis

This paper presents an experimental and thermo-hydro-chemical-mechanical numerical analysis of concrete at high temperatures, aiming at the definition of a law describing the evolution of intrinsic permeability. The evaluation of heat and mass transfers, evolution of the phases composing the porous medium, and mechanical performances of concrete are taken into account in a full three phases coupled analysis. An experimental set-up and a numerical simulation are then presented. A hollow cylinder has been heated up to 523.15 K (250 °C) on the internal side and subjected to gas pressure/temperature measurements; the experience has been then simulated by means of a numerical code. The analysis has allowed for the definition of an original relationship describing intrinsic permeability evolution. Finally, the law has been validated measuring the actual value of intrinsic permeability on heated concrete.     

Experimental Investigation on the Permeability Evolution of Compacted Broken Coal

Given the importance of airflow seepage properties to coal self-oxidation in gob, this paper develops a method and self-designed apparatus to assess seepage properties of compacted broken coal. This study mainly focuses on the strain, porosity and permeability evolution under the different conditions of particle size, vertical stress and temperature. The studied results show: (1) The strain, porosity and permeability were enlarged when the particle size increased under the same loading stress. The porosity and permeability reduced when the vertical stress increased. (2) The non-Darcy coefficient was negative in all tests, but the absolute value of the non-Darcy coefficient generally increased when the vertical stress increased. (3) The experiment results indicated that the larger the particle was, the easier to be compacted. The larger the grain diameter was, the lower the porosity and permeability were, which shown that the void volume in broken coal with larger grain diameters could be easily compacted. (4) The permeability was reduced when the temperature increased, which indicated the permeability of the compacted broken coal decreased during low-temperature oxidation in gob. (5) By the effects of stress and the particle size diameter on the porosity and permeability, the vertical stress recovery and generally increase are advantageous to reduce the porosity and permeability in gob. It is favorable to reduce the porosity and permeability and prevent coal self-heating by reducing the degree of fragmentation and percentage of small particles or consolidate the small particles.     

芳纶纤维约束混凝土的力学性能研究

通过对比普通混凝土试件和用芳纶纤维约束混凝土试件的抗压、抗劈裂和抗折(弯拉)试验，研究了芳纶纤维约束混凝土的基本力学性能，定量地得到了芳纶纤维对混凝土试件承载力的加强效果。     

An Experimental Investigation of Permeability Measurement of Water Flow in Crushed Rocks

Due to the high permeability of water flow in crushed rocks, flow catastrophes and water inrush accidents are apt to take place in the broken zones of aquifers in coal mining engineering. The pore, crack and fracture geometries needed for water transport are strongly influenced by grains diameter size and axial displacement conditions. In order to inspect and quantify the influence, we designed and manufactured a water flow apparatus that can be connected to the electro-hydraulic servo-controlled test system MTS815.02 which provides loading pressure in the experiment. Using the apparatus and MTS system, we tested crushed mudstone, limestone and sandstone specimens and obtained the relationship between permeability and variable grain diameter of a (2.5–5 mm), b (5–10 mm), c (10–15 mm), d (15–20 mm) and e (mixed sizes) under variable axial displacement (10, 15, 20, 25, 30, 35 and 40 mm). In particular, the permeability calculation based on collection of water flow velocity and pore pressure gradient difference has involved the influence of non-Darcy flow. The results show that (1) The porosity decreases with the increase of axial displacement and decrease of bigger particle size, respectively. Particle crushing during compaction is a main cause of size 0–2.5 mm appearing, some fine particles be washed away is a main cause of weight loss because of the effect of water seepage. (2) Water flow properties of crushed rocks are found to be strongly influenced by axial displacement and grain diameter size; in general, the permeability decreases with the increase of axial displacement and the decrease of grain diameter, respectively. (3) The fluctuations of permeability–axial displacement are especially intense for mudstone and sandstone than that for limestone. The permeability of crushed rocks is not only related to loading levels but also to grain diameters, style of arrangement. (4) To each grain diameter sizes, the permeability change of sandstone has a greater value than that of mudstone and limestone. The permeability of crushed mudstone shows much less than that of limestone and sandstone.     

Experimental Investigation on Correlation Between Permeability Variation and Pore Structure During Coal Pyrolysis

Transport in porous media with chemical and thermal effects is a common phenomenon; it is also a complicated scientific problem with applications in the field of mining engineering. In situ pyrolysis for coal gas generation is just such a problem, involving material and structural changes in the coal and surrounding rocks, with massive thermal and chemical effects. The transport properties of the coal are substantially changed, which in turn affect the thermal and chemico-mechanical reactions. A series of laboratory experiments on pore structure and permeability changes during gas coal pyrolysis were carried; the experimental procedure and results are described and analyzed in this study. The pore volume and permeability of tested specimens experienced modest changes during the heating process from 20 to 300°C, but when heated from 300 to 400°C, large pores in the specimens greatly increased and the overall porosity reached 23% at 400°C, which is larger than the percolation threshold value of the rock mass with pores and cracks. The permeability of the specimens increased exponentially with temperature, evidencing the massive structural changes that took place in the specimens during the pyrolysis process. In the high temperature range from 400 to 600°C, fewer changes in the specific surface area of microscopic and small pores in the coal took place, but the pore volume and porosity increased linearly with temperature.     

电子封装件在热-机械载荷作用下力学行为表征的实验方法综述

电子封装件在热-机械载荷作用下力学行为(尤其是热应力)的表征对于其机械可靠性的评价,失效分析和封装工艺的改进具有重要的意义.本文对目前该领域内主要的实验方法进行了简要的介绍,每项主要实验技术的优缺点、适用范围及其最新的发展及应用等都做了必要的阐述.这些实验技术与有限元方法的结合(杂交法)是探索电子封装件机械可靠性的最有效的方法并且代表着改领域的发展方向.     

钢筋再生混凝土梁徐变性能试验研究

为揭示钢筋再生混凝土梁的徐变性能,通过三种持荷水平下9根钢筋再生混凝土梁试件的徐变(徐变应变与徐变挠度)对比试验,分析了钢筋再生混凝土梁徐变与时间的相关关系,研究了加荷幅值、初始变形(初始应变、初始挠度)等因素对钢筋再生混凝土梁徐变性能的影响规律,揭示了钢筋再生混凝土梁的徐变机理。研究结果表明:在45%极限荷载水平的持续作用下,钢筋再生混凝土梁总徐变挠度值为初始挠度值的62%左右,并且在前期发展较快,7d发展至总徐变挠度值的64%左右,后期变缓;钢筋再生混凝土梁徐变随着施加荷载幅值、初始变形的升高而有所增加。经历徐变过程后的钢筋再生混凝土梁,其承载性能有所下降,变化趋势为总徐变值越大,降低的幅度也越大。     

再生碎石混凝土力学性能试验研究

针对再生粗骨料为碎石的再生混凝土,设计了99个试件,分别进行立方体抗压强度、棱柱体抗压强度、抗折强度、弹性模量和泊松比等力学性能的试验。本文研究了再生混凝土的强度指标、变形性能、损伤过程、能量耗散等特征,分析了骨料取代率对其各性能指标的影响;基于试验数据,得出各强度性能指标的换算关系;分别采用分段式本构关系模型和损伤本构关系模型对再生混凝土的应力-应变本构关系进行研究,并提出相应的本构方程。研究结果表明:与天然骨料混凝土相比,再生混凝土的各项强度指标均略为增大,但变形性能和耗能性能降低,应力-应变全曲线下降段更为陡峭;随着取代率的增大,弹性模量呈先减小后增大的变化趋势,泊松比无明显变化,与天然混凝土接近;其损伤发展过程加快,应变在ε=(3~5)×10-3时最为迅速。分段式本构方程和损伤本构方程的计算结果与试验值均能较好地吻合。     

Influence of Permeability Heterogeneity on Miscible CO<Subscript>2</Subscript> Flooding Efficiency in Sandstone Reservoirs: An Experimental Investigation

In this study, we systematically investigate the effect of core-scale heterogeneity on the performance of miscible CO₂ flooding under various injection modes (secondary and tertiary). Manufactured heterogeneous core plugs are used to simulate vertical and horizontal heterogeneity that may be present in a reservoir. A sample with vertical heterogeneity (i.e. a layered sample) is constructed using two axially cut half plugs each with a distinctly different permeability value. In these samples, the permeability ratio (PR) defines the ratio between the permeabilities of adjacent half plugs. Horizontal heterogeneity (i.e. a composite sample) is introduced by stacking two or three short cylindrical core segments each with a different permeability value. Our special sample construction techniques have also enabled us to investigate the effect of permeability ratio and crossflow in layered samples and axial arrangement of core segments in composite samples on the ultimate recovery of the floods. Core flooding experiments are conducted with an n-Decane–brine–CO₂ system at a pore pressure of 17.2 MPa and a temperature of 343 K. At this temperature, the minimum miscibility pressure of CO₂ with n-Decane is 12.6–12.7 MPa so it is expected that at 17.2 MPa CO₂ is fully miscible with n-Decane. The results obtained for both the composite and layered samples indicate that CO₂ injection would achieve the highest recovery factor (RF) when performed under the secondary mode (e.g. layered: 79.00%, composite: 89.83%) compared with the tertiary mode (e.g. layered: 73.2%, composite: 86.2%). This may be attributed to the effect of water shielding which impedes the access of the injected CO₂ to the residual oil under the tertiary injection mode. It is also found that the oil recovery from a layered sample decreases noticeably with an increase in the PR as higher PR makes the displacement more uneven due to CO₂ channelling. The RFs of 93.4, 87.89, 77.9 and 69.8% correspond to PRs of 1, 2.5, 5, and 12.5, respectively. In addition, for the layered samples, crossflow was found to have an important role during the recovery process; however, due to excessive channelling, this effect tends to diminish as PR increases. Compared with the layered heterogeneity, the effect of composite heterogeneity on the RF seems to be very subtle as the RF is found to be almost independent from the permeability sequence along the length of a composite sample. This outcome may have been caused by the small diameter of the plugs resulting in invariable 1-D floods.     

Experimental Investigation of the Mechanical Behavior and Permeability of 3D Printed Sandstone Analogues Under Triaxial Conditions

Transport in Porous Media - Consolidated drained triaxial tests arise as one of the most exhaustive methods to quantify the strength, volumetric behavior and failure process of rocks. Understanding...     

振动对充填裂隙渗透率影响的实验研究

为了研究振动和充填泥沙的共同作用对裂隙岩石渗透率的影响,通过对裂隙试件在充填和振动后条件下的渗流实验,得到了频率和振幅与充填裂隙岩石渗透率的关系曲线。结果表明,充填泥沙后的相对渗透率低于充填前,最小降幅为10.19%,最大降幅为59.74%。在相同的振幅下,试件的相对渗透率随频率的增加都基本呈下降趋势;振动后的渗透率低于振动前的渗透率;充填试件在较大频率振动下,渗透率减小的更为显著。在相同的频率下,充填试件振动后的渗透率基本上都减小了,最小降幅为8.90%,最大降幅为51.23%;而未充填试件振动后的渗透率与振幅存在一定关系;相对渗透率与振幅的变化之间存在拐点,相对渗透率并没有随着振幅的增加而一直减小。     

An Experimental Technique for Spalling of Concrete

The spalling strength of concrete is measured by examining the strain wave profiles in a polymer buffer bar behind the slender concrete bar specimen placed between a large diameter (Φ100 mm) Hopkinson bar and the buffer bar. The experimental results indicate that the spalling strength is related to not only the compressive strength of concrete but also the impact velocities (the loading rates). The rate effect of spalling strength mainly results from the different cracking paths in concrete under different impact velocities. However when the input compressive stress to specimen exceeds the threshold required to trigger the compressive damage, the spalling strength decreases due to the evolution and cumulation of compressive damage in concretes. The repeated impact loading experiments indicate that damage plays an important role in the spallation process of concrete. The high speed video of the spalling fracture process shows that multiple spalling fractures may occur in the scab and damage accumulation resulting from stress wave propagation in scab is the main reason for the producing of multiple spallations.     

Experimental and Numerical Analysis of Thermal Deformation of Electronic Packages,QFP and MCM

0Introduction Anelectronicpackageisgenerallyconstructedwithanactivesiliconchip,mountisland,gold wires,leadframesandsoldersasshowninFig.1(a).Toprotectfromtheenvironment,thesilicon chipisusuallyencapsulatedinresin.SincethesematerialshavedifferentCTE(coefficientofthermal expansion),stressandstrainaregeneratedbyinternalheatinginserviceoperationorthermalloading fromtheenvironment[1].Insomecases,thismaycausefailureofthewireandcrackinganddebonding insidethepackage.Thereliabilityofelectronicpackages…     

电子封装、QFP和MCM热变形的实验及数值分析

0Introduction Anelectronicpackageisgenerallyconstructedwithanactivesiliconchip,mountisland,gold wires,leadframesandsoldersasshowninFig.1(a).Toprotectfromtheenvironment,thesilicon chipisusuallyencapsulatedinresin.SincethesematerialshavedifferentCTE(coeffic…     

Permeability Impairment Study Due to Asphaltene Deposition: Experimental and Modeling Approach

This fact is well known that during any scenario of production, asphaltene deposition in porous media has a substantial effect on oil flow. But a clear understanding of asphaltene deposition mechanisms can help to minimize asphaltenic problem in oil-bearing formations. In this study, the experimental results of three dynamic CO₂ miscible injection tests were investigated. Regarding the effects of adsorption, mechanical entrapment, and sweeping mechanisms on permeability behavior, a mathematical mass and permeability variation model were developed. According to the experimental results asphaltene deposition causes a 70% loss of sand stone initial permeability while the loss is significantly low in carbonate cores, about 30%. The model validation shows that the main particulate processes of Asphaltene deposition in sandstone cores are the cake forming and adsorption while in the case of carbonate cores, are the gradual pore blocking and pore sweeping. Obtained results from mass model provide that entrainment and deposition coefficients in square mass model lead to a more flexible trend than the linear variation of general model.     

水工结构高强钢筋混凝土梁受剪性能试验研究

通过对12根配置高强箍筋的混凝土梁在集中荷载作用下的受剪试验,研究梁的挠度、箍筋应变、斜裂缝扩展规律及破坏形态。依据现行《水工混凝土结构设计规范》,对比分析试验梁斜截面承载力及考虑荷载长期作用的正常使用阶段斜裂缝宽度。研究结果表明,配置高强箍筋的混凝土梁斜向开裂规律和受力特征与普通钢筋混凝土梁基本相同,受剪承载力可按现行《水工混凝土结构设计规范》公式计算,且有较高安全储备。当考虑荷载长期作用,HRBF500钢筋在水工结构中抗拉强度设计值取360MPa时,斜裂缝宽度满足正常使用极限状态要求。     

Gas Sorption and the Consequent Volumetric and Permeability Change of Coal I: Experimental

Experimental and numerical investigations were conducted to study adsorption and desorption of pure and multicomponent gas on coal, and the sorption-induced volumetric strain and permeability change of the coal. This paper presents the experimental work. Using CO \(_2\) , N \(_2\) , and CO \(_2\) and N \(_2\) binary mixtures of different composition as injection gases, the measurements were conducted on a cylindrical composite coal core at varying pore pressures and constant effective confining pressure. Sorption was measured using a volumetric method. The initial and equilibrium system pressure and gas phase composition were measured. The total amount of adsorption and the composition of the adsorbed phase (for adsorption of binary gas mixtures) were calculated based on material balance. During the process of sorption, the volume of the core was monitored by recording the volume of the water in the confining pressure vessel. Sorption-induced strain was calculated as the ratio of the sorption-induced volumetric change to the initial volume of the core. After adsorption equilibrium was reached, the permeability of the core was measured based on the Darcy equation for gas flow. Sorption and permeability measurements were conducted for each test gas at first increasing and then decreasing pressures. Volumetric strain was only measured while pore pressure increased. To our knowledge, this is the first study measuring adsorption, volumetric strain, and permeability on the same piece of core with the same apparatus.     

化学腐蚀对混凝土材料力学特性影响的试验研究

对不同水化学环境腐蚀过程中砂浆试样物理力学性质进行了试验研究,分析了溶液pH值、浓度及水化学成分对砂浆的腐蚀程度,探讨了砂浆试样的化学腐蚀机制。试验结果表明:在相对封闭的环境条件下,无论是哪种水化学溶液,随着化学侵蚀时间的加长,溶液的pH值均趋于碱性;同时,溶出的Ca2+、Mg2+离子具有累积性特点。在其他条件相同的情况下,水化学溶液的离子成分对砂浆试样的腐蚀程度各不相同。酸性条件下,Na2SO4溶液砂浆试样物理化学性质的影响要比NaHCO3溶液大;中性条件下,与纯净的蒸馏水相比,Na2SO4溶液对砂浆试样的腐蚀作用要强一些。     

Experimental Study of Bacterial Penetration into Chalk Rock: Mechanisms and Effect on Permeability

Bacterial selective plugging is one of the mechanisms through which microorganisms can be applied for enhanced oil recovery, as bacteria can plug the water-swept zones of a reservoir, thus altering the flow paths and improving sweep efficiency. However, complete understanding of the penetration behavior of bacteria is lacking, especially in chalk formations where characteristic pore throat sizes are comparable with the sizes of bacterial cells. In this study, two bacterial strains, Bacillus licheniformis 421 (spore-forming) and Pseudomonas putida K12 (non-spore forming) were used to investigate the penetration of bacteria into chalk and its effect on permeability reduction. The core plugs were produced from Stevns Klint outcrop with low permeability (2–4 mD) and with pore sizes comparable to bacterial sizes. Both types of bacteria were able to penetrate and to be transported through the cores to some extent. A significantly higher number of B. licheniformis 421 was detected in the effluents as compared to P. putida K12. It was demonstrated that the spore-forming B. licheniformis 421 penetrates in the form of spores. P. putida K12 is found to penetrate the core, however, in smaller numbers compared to B. licheniformis. It was shown that both bacteria, under different injection concentrations, were capable of plugging the porous rock, as indicated by reduction of the core permeability. An incubation period of 12 days did not allow the permeability to return to initial condition. Based on the results it can be concluded that, when injected into chalk, spore forming bacteria have higher chance to survive and penetrate into deeper formation; and both types of bacteria may cause permeability reduction.