Use of a laser camera scanner to highlight the surface degradation of stone samples subjected to artificial weathering

A vision technique system was implemented in order to highlight the deterioration developing on the surfaces of stone samples during an artificial ageing test with marine spray. The system, which employs a matrix CCD camera and a laser beam, provides various kinds of information about the decay suffered by the stone samples by comparing two types of visual information at different times throughout the ageing test: the partial digital images of the sample surfaces and then the surface relief and laser light reflection obtained by casting a sheet of laser light on to the material. The accuracy of the laser camera scanner is evaluated in the first part of this paper. The methodology was successfully used to identify the degradation morphologies occurring on five types of limestone exposed to salt spray, and to quantify the deterioration using statistical parameters computed from digitised visual data.     

Rough and polished travertine building stone decay evaluated by a marine aerosol ageing test

Tablets of rough and polished travertine were aged in a sea-salt spray corrosion chamber to explore potentially contrasting stone decay behaviour due to different surface finishing processes. This paper presents a multianalytical approach to characterise the chemical, mineralogical, textural, porosimetric and colourimetric features of quarried and weathered travertine after the test. Rough and polished stone surfaces behave differently according to salt-spray absorption, newly formed pore networks, composition and habits of salts, and chromatic changes. Roughness and irregularities of the unpolished travertine favour salt inputs that in turn increase the open porosity. By contrast, the smooth finish of the polished travertine helps to protect it against salt decay, since this finishing blocks the pore system in the near-surface stone. This information is crucial to establish maintenance and conservation construction practices.     

The role of salt fog on alteration of dimension stone

Limestones and silicate rocks used as dimension stone were submitted to cycles of salt fog, totalizing 140 days in a salt spray chamber. Rock samples comprised three types of limestone, three different marbles, six types of granites, two syenites, one gabbro and one basalt. Mineral changes and variation on surface luster, weight loss and salt crystallization on rock surfaces were some of the features observed along the exposure. While losses of weight and surface luster were the most striking features observed on carbonate rocks, mineral degradation was the main modification on silicate rocks, in which biotite showed to represent a key mineral in the alteration process due to its cleavage and possibly to its composition.     

Simple durability test for cement stabilized blocks

Compressed and cement-stabilized blocks are now recognized as important walling units for building low-cost dwellings in developing countries. Although the durability of their surfaces under in-service exposure conditions in the humid tropics has become a major matter of concern, it has received little formal research. Premature deterioration - as typified by surface erosion, mass loss, pitting, cracking and crazing - is common. A weather-resistant surface is required if a block is to remain durable for its service lifetime. However, current accelerated ageing tests to predict the overall performance of blocks under conditions causing surface deterioration (wetting, abrasion and drying) are inadequate. A new method is required that can be applied to blocks immediately after curing to evaluate the likely durability of their surfaces. The present paper explores the suitability of using the slake-durability test, originally developed for argillaceous rocks, to evaluate the durability of low-cost walling materials. During the test, surface erosion leading to mass loss of between 1 and 50% is recorded within only 10 minutes, representing an acceleration of in-service ageing by a factor of around 1 million. The test method proved reliable, controllable and repeatable. More importantly, the ranking of materials via their performance in this test correlated well with a ranking of their durability in service based on long professional field experience in Uganda. It is concluded that the slake-durability test not only is robust, but also provides a quick predictive surface and quality test for cement-stabilized blocks and other like materials.     

Simple durability test for cement stabilized blocks

Compressed and cement-stabilized blocks are now recognized as important walling units for building low-cost dwellings in developing countries. Although the durability of their surfaces under in-service exposure conditions in the humid tropics has become a major matter of concern, it has received little formal research. Premature deterioration – as typified by surface erosion, mass loss, pitting, cracking and crazing – is common. A weather-resistant surface is required if a block is to remain durable for its service lifetime. However, current accelerated ageing tests to predict the overall performance of blocks under conditions causing surface deterioration (wetting, abrasion and drying) are inadequate. A new method is required that can be applied to blocks immediately after curing to evaluate the likely durability of their surfaces. The present paper explores the suitability of using the slake-durability test, originally developed for argillaceous rocks, to evaluate the durability of low-cost walling materials. During the test, surface erosion leading to mass loss of between 1 and 50% is recorded within only 10 minutes, representing an acceleration of in-service ageing by a factor of around 1 million. The test method proved reliable, controllable and repeatable. More importantly, the ranking of materials via their performance in this test correlated well with a ranking of their durability in service based on long professional field experience in Uganda. It is concluded that the slake-durability test not only is robust, but also provides a quick predictive surface and quality test for cement-stabilized blocks and other like materials.     

A comprehensive study on development of a small-sized self-propelled robot for bridge inspection

Application of maintenance to ensure the safety, extend the service life and reduce the life-cycle cost of civil structures is important. In this paper, a new inspection method is proposed using a robot which can effectively approach target sections of structures, such as areas that are either too narrow or too dangerous to approach and perform both visual and detailed inspection with various devices. The small-sized self-propelled robot was initially developed. The test model can freely move on the surfaces of various types of structures. Next, the function to detect the deterioration of concrete or steel surfaces by attached cameras to the robot was examined. Moreover, a function was installed to identify the location of the robot automatically using a phase-only correlation method and to determine structural behaviours using an accelerometer. Finally, the applicability of robotic movement and all installed functions was tested on an existing bridge.     

Dry deposition effect of marine aerosol to the building stone of the medieval city of Rhodes,Greece

Continuous exposure to marine aerosol of the historic buildings of the medieval city of Rhodes (Greece) has produced severe weathering of the building stone (biocalcarenite). The aim of the research was to investigate the effect of marine aerosol dry deposition on the architectural surfaces. Particles were collected in a cascade impactor, on stone samples collected at the buildings and on fresh quarry samples exposed at the monitoring positions. Meteorological conditions were constantly monitored in situ. Collected samples were analysed by SEM/EDX and chemical techniques to acquire information on their morphology and chemical composition. According to their morphology and composition, collected particles were classified into four major groups. Deposited and suspended particles were compared to determine their possible sources. The production of marine aerosol is favoured when north, high-speed winds prevail. Sea-salt is deposited having different morphologies. The zone mostly influenced by the deposition of sea-salt lies within 100 m from the northern fortification wall of the city. Stone mass loss was determined for different monitoring positions and was found to be proportional to sea-salt concentrations. Relative humidity fluctuations permit NaCl deliquescence/crystallisation cycles. Macroscopic examination of the buildings confirmed that the positions with the highest chloride concentrations present severe damage.     

基于透明土的管桩贯入特性模型试验研究

由于受土塞效应等因素影响,开口管桩和闭口管桩在贯入过程中的挤土效应存在明显的差异;然而针对该两者贯入特性的研究相对较少。基于透明土和PIV（Particle Image Velocimetry）技术,开发了相应的桩基贯入模型试验系统,用于桩基贯入过程中桩周土体变形的非插入式测量。试验选用的透明土由玻璃砂和具有相同折射率的孔隙液体制成。该试验系统主要包括：线性激光光源、CCD（Charge-Coupled Device）相机、自动沉桩加载仪和计算机控制系统等。激光射入透明土,和透明土之间的相互作用产生了独特的散斑场,通过CCD相机摄取贯入过程中各个时刻散斑场变形的图片,然后通过PIV技术对这些变形前后的图片进行处理,即可得到整个土体位移场。分别进行了开口管桩和闭口管桩的桩基贯入试验,得到了对应的土体位移场,并对桩基贯入引起的桩周土体径向位移试验结果与圆孔扩张法、应变路径法等理论计算结果进行对比分析;研究结果表明,对于闭口管桩,由于竖向位移的影响,试验值比圆孔扩张法结果小,其与应变路径法更为接近;对于开口管桩,由于沉桩过程中土塞作用,试验值比圆孔扩张法大,其影响不可忽略。     

Characterization of building stones from the ancient Tyana aqueducts,Central Anatolia,Turkey: implications on the factors of deterioration processes

Many archaeological and historical monuments constructed by different civilizations over the last 5500 years can be observed in the Ni?de region located in central Anatolia. The Tyana aqueduct as a continuation of the Roman Pool is one such important historical monument. The aqueducts that carried the water of the Roman Pool to the ancient city of Tyana were constructed during the time of the Roman emperors Trajan, Hadrian and Marcus Aurelius Antoninus. Half of the total length of the aqueducts (3 km) is on the surface and the rest is buried. The engineering properties of the rocks used in such archaeological and historical buildings are very important in terms of conserving these structures for future generations. In this study, the geomechanical and geotechnical features of the Tyana aqueducts were investigated to understand the rock types, deterioration in the stones over time and problems originating from these features. Also, for restoration purposes, the ancient stone quarry areas for the aqueducts were identified, and the chemical, petrographical and geomechanical properties of fresh travertine blocks from these quarries were determined. The main rock type used as building stones in the aqueducts is Mio-Pliocene travertine. Laboratory studies were performed to determine the mineralogical, petrographic and petrophysical properties of the building stone samples. Fresh and used travertine samples were composed exclusively of calcite crystal. The results of chemical analyses were similar for fresh and used travertine samples. To determine the geomechanical properties of the travertines, dry unit weight, water absorption, effective porosity, P-wave velocity, Böhme abrasion test, capillary water absorption and uniaxial compressive strength experiments were conducted. In addition, Schmidt hammer hardness measurements were performed on site for the different levels and different textural characteristics of the belts on the travertines. According to the experimental data obtained, higher strength was displayed by samples with fine grains, massive texture and low porosity. The deterioration effects in most of the travertines used in the original structure are very low. In addition to human effects, the use of small stone dimensions (especially the stones used in belts as keystones) and the use of stone from the same quarry but with features that differ or are inferior are thought to be factors in the destruction of the Tyana aqueducts.     

Deteriorating effects of lichen and microbial colonization of carbonate building rocks in the Romanesque churches of Segovia, Spain

In this study, the deterioration effects of lichens and other lithobionts in a temperate mesothermal climate were explored. We examined samples of dolostone and limestone rocks with visible signs of biodeterioration taken from the exterior wall surfaces of four Romanesque churches in Segovia (Spain): San Lorenzo, San Martín, San Millán and La Vera Cruz. Biofilms developing on the lithic substrate were analyzed by scanning electron microscopy. The most common lichen species found in the samples were recorded. Fungal cultures were then obtained from these carbonate rocks and characterized by sequencing Internal Transcribed Spacers (ITS). Through scanning electron microscopy in back-scattered electron mode, fungi (lichenized and non-lichenized) were observed as the most frequent microorganisms occurring at sites showing signs of biodeterioration. The colonization process was especially conditioned by the porosity characteristics of the stone used in these buildings. While in dolostones, microorganisms mainly occupied spaces comprising the rock's intercrystalline porosity, in bioclastic dolomitized limestones, fungal colonization seemed to be more associated with moldic porosity. Microbial biofilms make close contact with the substrate, and thus probably cause significant deterioration of the underlying materials. We describe the different processes of stone alteration induced by fungal colonization and discuss the implications of these processes for the design of treatments to prevent biodeterioration.     

基于透明土材料的沉桩过程土体三维变形模型试验研究

为了对沉桩过程中桩周土体内部的变形特性进行非插入式测量,利用正十二烷、十五号白油混合液和玻璃砂合成透明土,并在此基础上设计了沉桩模型试验系统；该系统包括激光器、线性发生器、CCD（charge-coupled device）相机、沉桩加载仪和计算机等。激光经线性发生器转化后将透明土样切分,形成土体内部颗粒切面,CCD相机连续拍摄沉桩过程中该切面的图像,并通过计算机中图像处理软件进行分析,得到该切面变形前后的变形位移场。通过与数值模型的对比分析,验证模型试验结果的可靠性。对多个切面变形前后的位移场进行分析,从而得到沉桩过程中土体变形的完整三维变形场。试验结果表明,试验条件下沉桩水平挤土位移影响范围为8R；与常规模型试验方法相比,方法实现了土体内部变形的三维测量,有助于了解土体在各种荷载条件下的变形机理。     

结构性能退化的评估和贝叶斯动态预测

结构性能的退化影响因素复杂、时间跨度长、不确定性大,其预测不可避免地要考虑具体结构的实际情况,即在一般规律认识的基础上,不断利用在具体结构生命周期中得到的新信息,更新对结构未来性能退化的预测,进而得到更确切合理的可靠度分析和决策。基于这一思路,引入贝叶斯动态模型理论,设计模型结构,用于结构性能退化的预测。同时,根据结构性能退化的多阶段特点和目前工程实践可获取的结构检测信息的实际情况,提出状态指标的概念,用于描述结构性能退化。计算实例验证贝叶斯动态预测的优越性及信息更新对结构性能退化预测和寿命评估的影响,同时说明状态指标具有简便实用的特点。     

结构性能退化的评估和贝叶斯动态预测

 结构性能的退化影响因素复杂、时间跨度长、不确定性大，其预测不可避免地要考虑具体结构的实际情况，即在一般规律认识的基础上，不断利用在具体结构生命周期中得到的新信息，更新对结构未来性能退化的预测，进而得到更确切合理的可靠度分析和决策。基于这一思路，引入贝叶斯动态模型理论，设计模型结构，用于结构性能退化的预测。同时，根据结构性能退化的多阶段特点和目前工程实践可获取的结构检测信息的实际情况，提出状态指标的概念，用于描述结构性能退化。计算实例验证贝叶斯动态预测的优越性及信息更新对结构性能退化预测和寿命评估的影响，同时说明状态指标具有简便实用的特点。     

Evaluation and Bayesian dynamic prediction of deterioration of structural performance

The deterioration of structural performance is a time-variant process with a large amount of uncertainties and incompleteness of load and environmental effects. It seems inevitable that the prediction of structural deterioration should be based on a philosophy of information updating. In the present paper, a new model system for structural performance prediction is introduced based on Bayesian dynamic linear model (DLM) theory. The system can implement Bayesian updating on the prediction of the time series process of structural deterioration. It can effectively incorporate useful information through the deterioration process of structures to update the prediction. Intervention and monitoring techniques are also designed to ensure the stability of the model system. This paper also defines an indicator of the so-called ‘condition index’ to evaluate the structural performance. Using condition indexes, the qualitative condition rating of structural performance based on visual inspection in current engineering practice can be integrated into the Bayesian DLMs. Case studies validate the advantages of Bayesian DLMs. The information updating has a favourable effect on reliability analysis and life prediction. The condition indexes are simple and convenient used in practice.     

气力输送水泥粉体装置灭木垛火试验研究

为了研究水泥粉体扑灭木垛火灾的可行性,通过自行设计的气力输送水泥粉体装置开展木垛火的灭火试验研究,利用温度采集装置和摄像机等仪器测试水泥粉体灭火前后木垛火的变化规律.结果表明,气力输送水泥粉体能有效抑制木垛表面明火,显著降低木垛火的燃烧温度,其中水泥粉体主要通过堆积覆盖作用进行灭火,而过大的木垛高度和孔隙率对水泥粉体灭...     

Comparison of accelerated climate ageing methods of polymer building materials by attenuated total reflectance Fourier transform infrared radiation spectroscopy

The degradation of the polymer building materials polypropylene (PP) and high density polyethylene (HDPE) intended for application as water barriers/repellants around building foundation walls have been studied. The PP and HDPE samples have been subjected to various accelerated climate ageing methods for comparison, including exposure to ultraviolet and infrared radiation, heated air, water spray and freezing. The climate ageing processes have been qualitatively and quantitatively investigated by attenuated total reflectance (ATR) Fourier transform infrared (FTIR) radiation spectroscopy.     

Water absorption and dehydration of natural stones versus time

Physical, chemical and mechanical properties of natural stones play an important role on deciding their application area as a building stone. In this study, water absorption and dehydration time of five different types of natural stones (marble, limestone, travertine, onyx and granite) were comparatively examined. Porosity, dry unit weight, wet unit weight, water absorption ratio and chemical analyses of the rock samples were also determined. In the light of the obtained experimental results, it was found that MgO content as the chemical property, and porosity as the physical property played a major role in the water absorption capacity and dehydration time of the studied natural stones. Basing on some observations made in this study, it was also emphasized that common standards involving the determination of water absorption coefficient by the capillarity test in rocks should be re-evaluated.     

采用VC＋＋编程对石材大板表面轮廓提取的研究

本文采用CCD摄像机、图像采集卡和计算机来实现非接触测量系统的硬件搭建,构成了基于CCD技术的石材大板在线测量系统,解决了天然石材传统接触式尺寸测量方法的缺陷。由CCD采集的彩色石材大板图像通过图像处理技术并结合vc＋＋编程实现了图像灰度变换、平滑处理、图像分割和数学形态学处理过程,快速完成了石材大板表面轮廓提取,为进一步对石材大板表面尺寸在线测量提供了理论和实践基础。     

机制砂钢纤维喷射混凝土在铁路隧道中的应用

通过对喷射工艺以及机制砂和钢纤维喷射混凝土特点的分析,直接采用增加水泥用量和保持机制砂中石粉含量和合理的喷射工艺,设计机制砂钢纤维喷射混凝土,在施工中能取得好的效果.     

高庙子膨润土膨胀力时效性试验研究

针对高庙子膨润土在不同含水率和不同干密度条件下膨胀力时效性进行了试验研究。首先采用静力压实法将3种不同含水率的高庙子膨润土粉末压实为两种不同密实状态的试样,随后在保持压实试样的体积和含水率不变的条件下,分别静置0,1,7,15,30和90 d,最后采用膨胀仪对完成静置试样的膨胀力进行量测;同时结合静置过程,完成了部分试样的扫描电镜（SEM）试验。试验结果表明：高庙子膨润土的膨胀力随静置时间的增长不断减小,且前期减小明显,后期逐渐趋于稳定;膨胀力的时效性与试样初始条件有关,试样含水率和干密度越大,膨胀力随静置时间的衰减越明显,即时效性越强。SEM试验结果表明,静置90 d后,高庙子膨润土内的蒙脱石发生了水化,集合体分解,颗粒相互黏结,微观孔隙结构趋于均质化,呈现点阵式的絮状结构;试样静置过程中不同微观结构层次之间的水分重分布导致的蒙脱石水化是高庙子膨润土静置过程中膨胀力降低的主要内在原因。