A sensitivity study for the visualisation of bacterial weathering of concrete and stone with computerised X-ray microtomography

Geologists and engineers recently have adopted computerised X-ray microtomography (microCT), a radiological imaging technique, for geological and petrophysical applications such as the assessment of sediment characteristics, CT-measurement of compressibility and compaction, multiphase flow studies, measurement of bulk density and moisture content, and of porosity and permeability. This study focuses on another application: the monitoring of biological weathering of natural building stones and concrete. Microbial activity as a determining factor in the deterioration process of building materials has a major economic impact. Because of its non-destructive character, microCT could be the ideal monitoring technique. With this technique, three-dimensional (3D) images of the entire inner structure of the material can be obtained, together with quantitative data. In depth changes of porosity of concrete and stone specimens due to bacterial weathering were assessed in this work. Also, porosity was visualised based on 3D data with homemade software. Scanning electron microscopy (SEM) images provided additional information and supported conclusions drawn from the X-ray microCT data. Resolution improvement will make the study of petrophysical aspects of physical weathering and/or biological deterioration processes of natural building stones and concrete a promising subject for further microCT-application.     

Petrophysical properties and durability of granites employed as building stone: a comprehensive evaluation

The use of a rock as a building stone is conditioned by several factors, from its aesthetic characteristics to its petrophysical properties. Even though the latter are taken into consideration, only a few of them are usually assessed. The purpose of this study is to carry out a comprehensive evaluation of the petrophysical properties of nine Portuguese granites employed as dimension stones. Granites with different textural characteristics and degrees of weathering were selected in order to highlight the relationships between the properties, and to identify the most important ones affecting the rock behaviour. The post-tectonic granites, with low porosity and fewer fissures, show better mechanical behaviour, while the most weathered granites have poor mechanical behaviour that limits their use in some applications and/or environmental conditions.     

风化花岗岩的地质雷达波的频谱特征研究

花岗岩在我国有广阔的分布,对花岗岩的雷达波的研究可以为在花岗岩地区的工程建设施工提供有力的指导意义.通过对某隧道不同风化程度花岗岩进行地质雷达的测试,选取典型的雷达波进行频谱分析,探讨了不同风化程度花岗岩的地质雷达波的频谱特征.结果显示,全风化与强风化花岗岩的频谱能量均比较集中,但强风化花岗岩比全风化的花岗岩的频谱谱峰...     

“Plagioclase solution degree index”: a new index to evaluate the weathering degree of granite

The weathering degree of rocks has an adverse influence on their strength and deformability characteristics, which in turn influences the industrial uses of rock. The need to develop a weathering index that reveals their mechanical and engineering geological behaviors is thus pertinent to enable the building of more accurate models for forecasting geological hazards. Granite weathering in the Ma On San, Shek Kip Mei and Kwun Tong areas of Hong Kong was studied using scan electron microscope (SEM) images to observe mineral shapes for detailed identification of the weathering degree of completely decomposed granite (CDG). Plagioclase images captured from the SEM were subsequently analyzed and processed with the use of a microstructural image processing system. The results of the analyses indicate that plagioclase, though sensitive to weathering, still remains in CDG and is preserved at different weathering degrees. Hence, it provides a possibility for evaluating the weathering degree more accurately. Thus, a new index referred to as the plagioclase solution degree index is proposed to evaluate the weathering degree of granite.     

Characterization of bacterial community inhabiting the surfaces of weathered bricks of Nanjing Ming city walls

Nanjing Ming city wall, one of the important historic heritages in China, has greatly suffered weathering. Microbes play an important role in the weathering of historic buildings. However, little is known about the microbial community inhabiting naturally weathered brick minerals and their roles in the mineral weathering. To examine the associations between microorganisms and brick weathering process, we compare the phylogenetic diversity, abundance, community structure, and specific functional groups of bacteria existing in weathered bricks by using a coupled approach involving cultivation-independent analysis of denaturing gradient gel electrophoresis (DGGE) as well as cultivation-based analysis of Si-releasing bacteria. DGGE and sequence analyses show that the bacterial communities were different along a weathering gradient and the abundance of bacterial communities positively and significantly correlates with the extent of brick weathering. Laboratory brick mineral dissolution experiments indicate that bacteria isolated from the surfaces of weathered brick were very effective in enhancing brick dissolution. Phylogenetic analyses show that the weathered bricks were inhabited by specific functional groups of bacteria (Bacillus, Massillia, Brevibacillus, Glacialice, Acinetobacter, Brachysporum, and Achromobacter) that contribute to the brick weathering.     

A study of the weathering of the bukit timah granite part a: Review,field observations and geophysical survey

The Bukit Timah granite exhibits a full range of weathering grades. Examination of these exposures shows that the weathering has been rapid. Field observations and geophysical surveys show that the rock has been weathered up to 70 meters depth, and that the main mechanisms of weathering is chemical decomposition. The humid tropical condition in Singapore with high annual precipitation has produced secondary weathering of the residual soil. The weathering profiles suggest that the weathering of the Bukit Timah granite is stratified with weathered layers and a sharp boundary between the residual soil and the slightly to moderately weathered granite. This paper (Part A) is a review of current weathering classification systems for weathered rock. Some results from field observations and geophysical surveys are also presented in the paper. A weathering classification and determination method is proposed for the Bukit Timah granite. Results from field and laboratory investigations of the weathering of the granite and material properties will be presented in Part B.     

Decay of sandstone subjected to a combined action of repeated freezing–thawing and salt crystallization

Bulletin of Engineering Geology and the Environment - The weathering of rocks controls the shape of the Earth’s surface and affects their suitability as building stones. Frost weathering and...     

Characteristics of carbonate building stones that influence the dry deposition of acidic gases

The behaviour of several porous carbonate building stones used in Spanish and English monuments was compared. Stones were exposed to urban and suburban environments and subjected to simulated SO₂ atmospheres in the laboratory. Physical properties that affect the transfer of moisture were determined before and after exposure, and related to the degree of reaction of the stones. The degree of reaction was determined by analysing the reaction products. Results showed that physical properties influenced the reactivity of the stones. These characteristics also changed as the stones weathered due to the different concentrations of impurities in the material. Moreover, stones with a high specific surface area and/or a deliquescent salt content may promote more NO_x dry deposition.     

红砂岩风化机理的有机酸研究

随着工业迅猛发展,环境污染日益严重,红砂岩文物由于缺乏保护已经严重风化,在很大程度上影响了美观和研究价值。为探明有机酸在风化过程的作用,揭露红砂岩的风化机理,在广东省各地对风化红砂岩进行实地考察,用高效液相色谱仪分析风化物中有机酸,结果表明在有机酸H＋离子的攻击下,金属离子从矿物中释放出来,与酸中的-COOH基反应生成难溶性酸盐,这种有机络合物在矿物表面的化学吸附导致矿物中的电子群向边缘迁移,使之更易于发生水解,加速了岩体风化,而且岩体受污染程度与风化物中有机酸的含量、种类相关。本研究探明了有机酸在风化过程中的作用,为未风化的红砂岩文物提供一种重要的预防风化依据,为已风化的红砂岩文物修复提供理论参考,从而为石质文物的保护提供更加全面的保护策略。     

Effect of salt crystallization on stones of historical buildings and monuments,Konya, Central Turkey

In this study, we investigated the chemical and physical properties of the volcanic rocks used as building stones in historical places and monuments. The chemical weathering effect of salt crystallization on these stones was measured on the laboratory conditions (in most cases, used samples were very small). For this purpose, the dry weight loss (DWL) test was conducted. The rocks of dacite, andesite and tuffs of volcanic origin have different durability against salt crystallization. The most stable rocks are dacites (DWL 2.06%) which were used in the construction of Hittite monuments at Eflatun. The durability of the stones is closely related to their chemical, mineralogical, petrographical and mechanical properties. The stones used in the historical buildings are generally much more stable than present-day building stones.     

岩石风化程度特征指标的分析研究

岩石风化程度的划分及工程特性研究，对于工程基础面高程的选择以及工程环境或工程材料的利用具有重要意义。关于岩石风化程度划分目前多是采用工程地质定性评价方法，依赖定性的不确定判据进行岩石风化程度划分带有很大随意性。因此，研究和发展定量分析评价方法是必要的。岩石经过风化作用，形成的风化裂隙具有无方向性、不规则发育等特点，与构造作用形成的微裂隙有着本质区别；风化作用改变了岩石的矿物成分，岩石在风化过程中表现出来的阶段性，反映了岩石的不同风化程度。基于对风化岩石显微裂隙的发育状况及其次生充填特点、长石蚀变性质、粘土矿物成分变化等定性资料的分析研究，给出了定量化的统计，建立了岩石风化程度划分的判据。给出的定量指标很好地反映了风化岩石质量，且与反映岩石风化程度的一些物理力学指标存在良好相关性。     

Chromatic weathering of black limestone quarried in Varenna (Lake Como,Italy)

The causes of chromatic weathering in black limestone have been investigated on samples from the main quarry of Varenna (Lake Como, Italy), which provided building stones for Lombard architecture. Our studies have been carried out combing colorimetric, mineralogical, chemical, microstructural and geochemical observations. The results suggest that the chromatic weathering affecting the surfaces of black limestone is not due to oxidation of the original organic matter present in the bulk, as believed. Chemical and mechanical weathering associated with the deposition of new organic matter are the most important phenomena occurring on the surface, leading to a diffuse roughness of surface and de-cohesion.     

云母石英片岩片理面力学特征试验研究

云母石英片岩的矿物成分和微观结构决定了其各向异性特征,通过铸体磨片和电镜扫描试验,获得了云母石英片岩的矿物组成和微观结构特征;通过三轴剪切试验,获得了微风化岩样片理面力学参数;通过强风化和中风化岩块的点荷载试验,结合强风化岩样的片理面剪切试验,得出了强风化和中风化岩样的片理面力学参数;按照材料力学理论,采用片理面力学参数计算得出岩样的最小单轴抗压强度,进而计算得出岩样的各向异性系数;以垂直片理面的抗压强度作为计算依据,计算得出岩样的风化系数,进而总结出岩样的各向异性系数与风化系数的关系,揭示了风化过程中片理面力学特征的变化规律。     

风化岩石的破碎分形及其工程地质意义

利用分形统计的方法,对风化花岗岩矿物成分的粒度分布特征进行了分析和统计,并根据分析的结果指出,岩石的风化破碎过程具有分形特征。其粒度分布的双对数曲线为多段折线,不同斜率的折线段对应不同的分形维。因此,分形维至少有2个数值,一为结晶颗粒粒度分形维,一为碎裂颗粒粒度分形维。同时,根据试验结果和理论分析得到,碎裂粒子的累积频率分布也符合指数分布,并给出了用指数分布系数求解碎块的碎裂概率的理论计算公式。随后,讨论了碎裂分形维和岩石强度与颗粒结构的关系,并以岩石的降维碎裂演化,得到以分形维描述的岩石风化速率。     

Effect of Weathering of Coal and Organic Dusts on Their Spontaneous Ignition

Weathering of coal and other cellulosic dusts occur due to the process of wetting and subsequent drying, or by subjecting them to a temperature higher than the ambient temperature for prolonged time periods. The first type of weathering occurs in a wetted storage. The second type of weathering occurs when a dust processing unit stores and maintains the dust deposit at an elevated temperature. As a result of weathering, the physical and thermal properties of the dust may change. Therefore, the weathered dust sample is expected to ignite at a different hot plate temperature as compared to that of a fresh sample, when tested in a standard test method (ASTM E 2021). In this study, three dust samples namely, wheat flour, Pittsburgh seam coal and powder river basin coal, are tested. These dust samples are subjected to one or both types of weathering. Thermogravimetric analysis and standard ignition tests are carried out with both fresh and weathered dust samples. Estimation of the activation energies and reactivity, and measurement of the minimum surface temperature for the onset of ignition have been carried out for all the cases. The implications of the observed results on industrial safety related to combustible dust layers are discussed.     

Enhanced Roadway Inventory Using a 2-D Sign Video Image Recognition Algorithm

Abstract:   This article presents a two-dimensional (2-D) color, shape, and texture-based stop sign recognition algorithm. The theoretical base of establishing a suitable 2-D correlation coefficient threshold value that can both eliminate nonstop sign objects and minimize the possibility of false-positive identifications is presented. Both the one-dimensional (1-D) algorithm, which has been developed by the authors, and the 2-D algorithm provide a simple and feasible means to automatically extract stop signs from roadway inventory video images with a very competitive computation speed of less than 25 ms for processing a 400 × 300 pixel image. The 2-D algorithm was able to correctly detect all of the images that were correctly detected by the 1-D algorithm. In addition, the 2-D algorithm could correctly detect two of the remaining five images that could not be correctly detected by the 1-D algorithm. The type of images that can be correctly detected by the 2-D algorithm but not the 1-D algorithm is significant because there is a need to recognize the tilted stop signs. The 2-D algorithm can detect stop signs tilted up to 35°. Similarly, the 2-D algorithm can detect a stop sign with its surface being blocked up to 20%. The improved detectability, with only a marginally increased time in the image processing, suggests that the 2-D algorithm is a better algorithm than the 1-D algorithm for processing stop sign images from video logging of roadway inventory. This algorithm can be extended to recognize other signs, such as yield signs, with a slight modification.     

柏叶口水库坝址基岩风化的综合判定

通过勘察研究,阐述了工程场区岩体风化类型及岩体强风化带、弱风化带、微风化带在空间上的分布及其规律,分析了岩体风化波速比Kw、岩体完整性系数KV和RQD值之间的相关性,确定了综合划分工程场区岩体风化带的定性和定量指标。     

峨眉山玄武岩岸坡深部差异风化岩体特征及成因

西南地区某水电工程的峨眉山玄武岩,其岩体风化具有特殊性,存在岸坡内部（或深部）岩体风化局部加强的特殊现象（称为差异风化）。该差异风化岩体在表观特征、分布特征、化学特征及形成环境上具有与岸坡表部一般风化岩体不同的显著特征。以该处差异风化岩体发育分布规律为基础,结合其化学特征、河谷演化过程及浅生改造理论分析其成因机制。研究表明：差异风化不具随水平深度增大风化逐渐减弱特征,分布受长大张性结构面控制,表现为局部的裂隙式风化加剧,张性结构面两侧 5 ～ 15 cm 范围内岩体红度增加;差异风化岩体发生了化学风化,但并未发生明显的脱硅富铝与盐类淋失迁移,仅表现为二价铁减少、三价铁富集;控制性结构面具浅生改造特征,差异风化岩体赋存于浅生结构所形成的相对封闭空间;浅生改造正是导致差异风化岩体形成的根本原因。     

On the anisotropy of the athenian schist and its relation to weathering

The influence of schistosity on the strength of the “Athenian schist” when considering the anisotropy index as derived from point load testing, is examined. Furthermore, the influence of the degree of weathering upon the anisotropic characteristics of the schist is also investigated. Anisotropy index values are found to range between just below 1 and 3 approximately. Low anisotropy values correspond to rock in its very weathered state, higher values are related to less weathered material and there is also a trend for anisotropy to decrease towards sound rock conditions. Point load testing proved a reasonable means for assessing those rock characteristics associated with strength, anisotropy and weathering state, while slake durability testing showed considerable insensitivity towards the latter.     

A study of the weathering of the Bukit Timah granite Part B: Field and laboratory investigations

Field investigations consisting of surface seismic refraction and electrical resistivity surveys, drilling and downhole geophysical logging of the rock mass and of the residual soil indicate that the weathering of the Bukit Timah granite has been rapid and is primarily caused by chemical decomposition due to the tropical climate in Singapore. The granite is usually overlain by a thick layer of residual soil. Laboratory tests indicated a large reductions of the material strength, the modulus of elasticity, the rock mass quality and other mechanical properties of the weathered granite. Apart from the mechanical properties of the residual material and/or of the weathered granite rock, physical properties including density, water content, Atterberg's limits, grain size distribution, permeability, sonic velocity and electrical resistivity were also studied in order to assess the weathering grade and the weathering processes.