Non-contact methods of measuring moisture concentration in external layers of building partitions: III—Water vapour condensation on the cementitious surfaces

This paper presents the results of the larger study into a potential application of laser radiation for the detection of phase transition processes in low temperatures occurring on the surface layers of cementitious materials. An attempt was made to identify relationships between the environmental conditions—temperature and air humidity, and the selected parameters of the reflected light. Onset of the condensation process and formation of water microdrops on the surface of the material leads to the phase displacement of individual laser rays, which are represented by different speckle images.

Although the analysis of parameters of the reflected light are very difficult in the case of porous materials because of highly developed roughness of the surface structure it has been proved that a dynamic study of the phase transition phenomena can be successfully carried out without mechanical intervention.     

基于孔隙尺度研究梯度孔隙率结构对固液相变的影响

为了进一步研究方腔内固液相变的过程,本文基于格子玻尔兹曼方法(LBM),采用两区域模型探究了方腔内填充不同方向梯度孔隙率分布的多孔骨架固液相变过程,从孔隙尺度分析了相变过程的流动和传热机理;并对梯度孔隙率多孔介质内固液相变过程中的糊状区做了详细的描述;重点研究了方腔内不同方向梯度孔隙率分布和均匀孔隙率骨架分布对相变过程的影响。研究结果表明:在填充多孔介质固液相变过程中,传热方式由热传导逐渐向自然对流换热转变,从而导致了上薄下厚的糊状区;在填充多孔介质骨架方腔内,不同方向的梯度孔隙率分布对相变过程的影响是不同的,与均匀孔隙率相比,从左到右线性减小以及从上到下线性增加和减少的多孔介质孔隙率分布,其融化率和高温壁面平均Nu数都较大,表明其孔隙率梯度分布的多孔骨架对相变换热起到了明显的促进作用;而当多孔介质孔隙率分布从左到右线性增加时,相变过程则受到明显的抑制。     

Microstructure of pre-wetted aggregate on lightweight concrete

A study was made on microstructure and water absorption rate of ‘Litcon’—a porous lightweight aggregate made from expanded clay. EDAX analysis on the aggregate particle showed different chemical compositions between the shell and the inner core of the lightweight aggregate. S.E.M. examination on the resulting concrete showed a good mechanical bonding between the cement and the aggregate interface, though traces of inter-granular cracks were observed. When the pre-wetting time of the aggregate increased, the strength and the workability of the concrete increased too. The high workability of fresh concrete was attributed to the localised high water content at the surface of the pre-wetted aggregate. The surface pores of the aggregate shell absorbed the water built-up at the cement/aggregate transition phase thus resulting with lower water content at the transition zone. EDAX analysis confirmed migration of cement phase into the aggregate shell. This loss of fluidity at the transition zone may have a significant effect on the permeability of lightweight concrete.     

聚合物改性多孔混凝土冻融特性研究

多孔混凝土路面的冻融破坏主要表现为内部冻胀及表面脱落,为研究聚合物改性多孔混凝土的冻融特性,采用快冻法对不同配比的基准混凝土、含砂混凝土及聚合物混凝土进行低温冻融循环试验,对比分析试验前后多孔混凝土试件的外观及质量损失。结果表明：基准混凝土的抗冻性主要由粗集料的冻融特性决定;而掺入机制砂或聚合物的多孔混凝土,其抗冻性由集料及胶结料的冻融特性共同决定;可通过选用抗冻性好的优质集料,增加混凝土中胶结料的含量,改善季冻地区聚合物改性多孔混凝土的抗冻性能。     

人造硅灰结构及火山灰活牲研究

以蛇纹石为原料经浓酸处理 ,其滤液用于制备轻质氧化镁 ,其残渣主要成分是二氧化硅 ,对残渣进一步超细粉磨加工制成人造硅灰。利用近代测试技术对人造硅灰的形貌、晶相、物相及孔结构和微结构形成过程进行研究 ,测试结果表明 ,人造硅灰是一种非晶态、隐晶质物质 ,具有较大的内比表面积的多孔体 ,具有较高的火山灰活性 ,是一种较为理想的替代硅灰材料。     

Evaluation of moisture susceptibility of porous asphalt concrete using water submersion fatigue tests

Porous asphalt concrete due to its open structure is exposed to water and therefore susceptible to water damage. Effect of water, temperature and frequency on mechanical properties of porous asphalt concrete was investigated. An innovative test method developed in Switzerland is used to mechanically test 150 mm diameter cylindrical cores from eight materials in dry state and while being submerged under water. Although the conventional indirect tensile strength ratio delivers useful data about the water sensitivity of porous asphalt specimen, the coaxial shear test provides vital information about the development of fatigue damage in the material. Application of coaxial shear test (CAST) for a twin lay porous asphalt as well as conventional porous asphalt shows a reduction in complex modulus due to fatigue loading after each thermal cycle and due to detrimental effects of water submersion. Moisture susceptibility results using CAST reflected the field inspections of surface degradation. In addition, investigation of the microstructure has given insight into the mechanical behavior of selected materials.     

地下洞穴对表面波表观相速度影响的数值分析

通过有限元数值模拟，得到了含洞穴固体介质在动荷载下表面质点的速度响应。根据表面质点响应中瑞利波和反射体波能量分配分析表观相速度扰动机制，讨论振源、测点、洞穴三者相对位置及频率对表面波表观相速度影响。表观相速度扰动程度随频率减小而增加，商至出现大扰动。大扰动峰值频率与反射波基频有关，基频随振源、测点及洞穴间相对位置变化。最后讨论由大扰动峰值波长与洞穴埋深关系，并给出洞穴埋深估算方法。     

定形PEG/SiO2/石墨复合相变蓄热混凝土制备及性能研究

为制备性能优异的相变蓄热混凝土,试验确定了定形PEG/SiO2/石墨复合相变蓄热骨料中相变材料的组成比例和制备工艺,并研究了相变蓄热骨料对混凝土力学性能和热工性能的影响。结果表明,相变材料中PEG含量为80%,石墨掺量为6%时,相变材料在具有合适相变温度和相变焓的同时,有良好的导热性能;相变蓄热骨料的合适吸附时间和温度分别为3 h和80℃,经表面封装后的相变蓄热骨料具有优异的稳定性。相变蓄热骨料虽然降低了混凝土的抗压强度和导热系数,但延缓了水泥水化热造成的温度升高,延缓了放热速率,能防止温度应力造成的混凝土开裂,且能明显改善混凝土的储热性能,综合考虑相变蓄热骨料替代率不宜大于80%。     

Between suburbanisation and re-urbanisation: revisiting the urban life cycle in a Mediterranean compact city

The redistribution of population over larger regions progressively further away from the dense core seems to be the new feature of the (originally compact) Mediterranean cities. With the aim of better understanding the nature of the urban transition taking place in these cities, we studied the phenomenon of population redistribution in Athens Metropolitan Area (AMA) in light of the city’s Urban Life Cycle (ULC). The research was carried out for a time frame of 60 years (1951–2011) using spatial analysis, correlation and multivariate statistics. Results reveal a phase of compact urban expansion occurring in the AMA until 1991, reflected in suburbanisation processes in the immediate proximity of the urban agglomeration. In the following period, the analysis showed signs of a period of transition difficult to interpret within the approach adopted by the ULC theory. A number of municipalities of the urban area experienced positive rates of population growth after decades of decline, while municipalities of the agglomeration and ring remain relatively stable. Altogether, these results can be interpreted as signs of a potential future re-urbanisation. The analysis performed provides insights on the debate over the future of Mediterranean cities, while demonstrating the advantages of adopting a multi-scale assessment methodology for identifying urban transitions.     

多孔轻瓷规整填料在焦炉煤气脱萘净化中的应用

文章阐述了老式脱萘填料比较容易堵塞，新型多孔轻瓷填料有着木格栅填料所无法比拟的优点，能够在相同的重量下扩大四倍的吸附面积，提高了脱萘液的脱萘效果和洗萘塔的净化效率，确保了民用焦炉煤气的质量。     

NaCl溶液运移过程的电容成像法室内监测研究

电容成像法是根据被测物质各相具有不同的介电常数,当各相组分分布或浓度发生变化时,将引起被测介质介电常数发生变化,从而使测量电极对间的电容值发生变化。以这些电容测量值作为投影数据,通过一定的图像重建算法,便可以获得介电常数分布,从而获得物质分布的图像。本研究运用电容成像法对NaCl溶液运移过程进行了实时监测,首先通过小砂盒进行了用不同浓度NaCl溶液饱和的多孔介质测定,得到了电容标定曲线,从而说明了电容成像法的有效性,然后通过砂槽进行了非饱和带中NaCl溶液的运移试验,并利用电容成像法进行了同步的动态监测,得到横纵向电容时间变化曲线,以及影像图,并通过三维电容相对值变化明显的看出NaCl溶液运移过程。这说明利用电容成像法对非饱和多孔介质中NaCl溶液的空间分布范围进行圈定并监测其迁移过程是完全可行的。     

基于孔隙率的多孔轻集料植被混凝土配合比研究

根据陶粒形态、成分较均一,呈球体或椭球体的特点,推导出多孔轻集料植被混凝土理论计算公式,并提出一种新的多孔轻集料植被混凝土配合比设计方法,即以孔隙率为主要设计参数,通过公式计算出包裹轻集料的水泥浆厚度和质量,调整水泥浆的水灰比,配置具有一定强度且不流淌的多孔轻集料植被混凝土。     

Photocatalytic degradation of Acid Red 4 using a titanium dioxide membrane supported on a porous ceramic tube

A photocatalytic membrane supported on a porous ceramic tube was described, in which permeation of solutes through the membrane and tube and photocatalytic reaction occur simultaneously. In this photocatalytic membrane reactor, TiO(2) catalyst was coated on the surface of a porous ceramic tube and all experiments were conducted in one pass dead-end system. The objectives of this study are to demonstrate the predominance of dead-end operation and to determine the reaction kinetics model of the photocatalytic reaction. Acid Red 4 (AR 4) dye was used as a model pollutant. A detailed study of physical parameters including flow configurations (dead-end and cross-flow), flow rate, initial dye concentration, light intensity and catalyst loading has been performed to obtain the reaction kinetics. The simultaneous effect of light intensity and catalyst loading was also determined experimentally. Experiments were also conducted to compare the photocatalytic degradation of AR 4 in the dead-end and cross-flow system. The major findings of this study are: (1) the decomposition ratios for dead-end system were three and five times higher than cross-flow system at flow rates of 6.67x10(-8) and 4.00x10(-7)m(3)/s, respectively. (2) The decomposition ratio increased with increasing catalyst loading and light intensity, but remained constant at higher catalyst loading. (3) The decomposition ratio was found to be decreased with increasing flow rate.     

Thermal performance of diesel engine exhaust heat recovery system using concentric tube heat exchanger inserts with different porous materials

This paper aims to analyse and improve the thermal performance of a concentric tube heat exchanger using porous material inserts. In this method, two different types of porous materials such as cast iron and mild steel were introduced on the outer surface of the inner tube wall of a concentric tube exchanger. The porous particle improves the convective heat transfer co-efficient between the tube wall and fluid flow surface. Experimentally, it was found that the inserted porous material enhances the heat exchanger effectiveness by 76% for cast iron and 77% for mild steel. The effect of inserting porous particles on the waste heat recovered from the engine exhaust was also investigated in the present study.     

Loss of infectivity of poliovirus 1 in river water under simulated field conditions

The effects of light, virus concentration, and turbidity on the rate of loss of infectivity (LOI) of poliovirus 1 were investigated in two test systems, which utilized flowing river water. Two levels of each variable were used in a 2³ confounded factorial design. The seeded systems were sampled at regular intervals to establish LOI rates. Virus infectivity was measured by plaque assay. Loss of infectivity followed a two-component curve; an initial, rapid phase followed by a second, slower component. The slopes of the two components were examined by the analysis of variance to determine the potential influence of each variable. Both light and turbidity exerted a significant influence on the LOI rate in the second component of the LOI curve and also in the transition period between the two components; however, during the initial, rapid phase none of the variables influenced the LOI rate (at the 0.05 significance level). This research demonstrates the significance of light as a virucidal component in the aquatic environment.     

多孔介质孔隙结构重构及水蒸气传递特性

采用随机生长法分别构造了各向同性、各向异性的孔隙率相同,孔径分布和孔隙表面分形维数不同的多孔介质,探索了在多孔介质孔隙率相同的情况下,微观孔隙结构对孔隙内湿传递过程的影响。结果表明:决定多孔介质内部输运特性的孔隙结构参数,除孔隙率以外,孔径分布和孔隙表面分形维数等参数对多孔介质孔隙中水蒸气扩散过程的影响显著;孔隙率相同,孔径分布和孔隙表面分形维数不同的3种各向同性和3种各向异性多孔介质的水蒸气扩散浓度最大差别分别为30.6%和23.3%;各向同性多孔介质的小孔分布率越大,孔隙表面分形维数越大,说明孔隙的连通性和水蒸气在多孔介质孔隙中的扩散性能越好;各向异性多孔介质(水蒸气扩散的方向垂直于其生长率较大的方向)的大孔分布率越大,孔隙表面分形维数越小,水蒸气在多孔介质孔隙中的传递性能越好。     

饱和土沉积谷场地对平面P波的散射

把沉积谷软土场地用饱和多孔介质的Biot动力学理论模拟 ,周围的场地用单相介质弹性动力理论模拟 ,利用波函数展开法 ,在频域内给出了不同土层界面条件 (透水条件和不透水条件 )下具有饱和土沉积层的圆弧形沉积河谷场地对平面P波散射问题的解析解。利用该解分析了不同土层界面条件 ,以及饱和土层的孔隙率和饱和度在不同入射角下对地面运动的影响     

Fractal diffusion of VOCs in dry porous building materials

For the purpose of clarifying the influence of microscopic structural characteristics on the diffusive transport of volatile organic compounds (VOCs) in building materials, many researchers have proposed different models to predict the diffusion process based on the micro-structure analysis. In this study a fractal model was developed and analyzed to investigate the mass transfer characteristics of VOCs’ diffusive transport in dry porous building materials. The classical Fick’s diffusion law was extended to a fractal diffusion model. Using the method of separation of variables, the theoretical solution to a fractal diffusion model of VOCs in a porous structure was obtained. Combined with microscopic pore structure characteristics, the surface fractal dimensions of medium density fiberboards (MDFs) used for building decoration were evaluated by using the experimental results of mercury intrusion porosimetry (MIP). The diffusion process of VOCs in dry porous building materials was simulated by using different surface fractal dimensions and fracton spectral dimensions. Simulated results showed that the surface fractal dimensions and fracton spectral dimensions exhibit different effects on the migration process of VOCs in dry porous building materials. Both the surface fractal dimensions and fracton spectral dimensions reflect the influence of fractal structures on diffusive transport of VOCs. Combining the surface fractal dimensions with fracton spectral dimensions provides a novel interpretation for the diffusion process of VOCs in dry porous building materials.     

多孔介质中沉积颗粒脱离特性试验研究

开展沉积颗粒在多孔介质中脱离过程试验对研究地下水源热泵回灌堵塞过程有重要意义。利用自主研发的砂层沉积–脱离模拟试验系统,研究增加渗流速度和改变渗流方向对多孔介质中已沉积颗粒脱离特性的影响。结果表明:在改变渗流速度大小条件下,渗流速度越大,已沉积的颗粒越容易发生脱离,到达悬浮颗粒相对浓度第二次峰值所需的时间越短,而达到二次峰值时所注入的水量接近;与改变渗流速度大小相比,用改变渗流方向的方式进行沉积颗粒脱离效果更为明显,到达二次峰值所需时间更短、水量更少,但随着时间增加,多孔介质中又会出现类似渗流方向改变前的堵塞现象;渗流条件变化后的初始阶段是已沉积颗粒脱离的主要时期。研究结果为水源热泵回灌过程中悬浮颗粒在地层中的沉积-脱离特性进一步研究奠定了基础。