Monitoring of weathering and conservation of building materials through non-destructive X-ray computed microtomography

X-ray computed microtomography (µCT) is a promising non-destructive imaging technique based on measurements of the attenuation of X-rays. It provides information on the internal structure of small samples with a maximum resolution of 10 µm. For this study, two porous local natural building stones, the sandstone of Bray and the limestone of Maastricht, were selected. Possible applications of the µCT-technique for qualitative monitoring of changes comprise (1) to non-destructively determine porosity based on 3-D images, (2) to visualise weathering phenomena at the micron-scale, (3) to understand the rationale of weathering processes, (4) to visualise the presence of water repellents and consolidation products, (5) to monitor their protective effects during decay in order to understand the operating mechanisms and (6) to provide advise on the suitability of products for the treatment of a particular rock type. The µCT-technique proves to be a powerful monitoring tool for the future as the combination of 3-D visualisation and 3-D data provide new insights that could optimise conservation and restoration techniques of building materials.     

The use of neutrons and monochromatic X-rays for non-destructive testing in geological materials

In the paper we present our results for element sensitive high-energy X-ray tomography and high-speed thermal neutron tomography applied to geological samples. The tuneable monochromatic X-ray beam was used for element sensitive tomography of geological samples containing heavy elements using the K-edge dichromatic scanning technique. This type of NDT (non-destructive testing) allowed us to reveal the quantity and location of uranium, lead and mercury in Oklo samples (natural nuclear reactor) and Cinnabar stones. Fast 3-D thermal neutron imaging of dynamical processes was successfully tested at the high flux neutron tomography station of the ILL. The qualitative investigation of water repellents and consolidants applied on sandstones of Bray and limestones of Maastricht were the first samples to be studied with the new imaging technique.     

Porosity and microstructure characterization of building stones and concretes

The microstructure of building materials greatly influences engineering properties like permeability, strength and durability. To determine this microstructure, different techniques were developed, each with its own limitations. The purpose of this study on concrete and natural building stones was to compare and to combine data obtained by X-ray computed micro-tomography (micro-CT), water absorption under vacuum and mercury intrusion porosimetry (MIP). Pore-size distribution curves ranging from 10 nm to 1 mm and total porosity results were obtained. Furthermore, micro-CT revealed the presence of an interfacial transition zone (ITZ) and of micro-cracks inside the aggregates of the concrete samples after mercury intrusion. Micro-CT visualized mercury inside large air bubbles within the concrete samples. Both micro-CT and MIP were compared and their respective advantages and disadvantages discussed.     

Determination of deterioration of the main facade of the Ferit Paşa Cistern by non-destructive techniques (Konya,Turkey)

Building stones have long been one of the most widely used construction materials in the world. Building stones used in historical monuments are deteriorated partly or completely depending on the environmental and atmospheric effects. In recent years, non-destructive test methods have been used to assess deterioration of building stones used in historical monuments. Gödene stone is one of the building stones being widely used in the historical buildings in the Konya region, Central Anatolia. The most deterioration effects are observed in the Ferit Pa?a Cistern among the historical structures built with Gödene stone in the region. The aim of this study is to assess the deteriorating effects in the street façade of the Ferit Pa?a Cistern via non-destructive testing methods (Schmidt hardness rebound value, P-wave velocity, humidity measurement and thermal imaging) and create maps of deteriorated features. Turkey’s historic places are integrated to Turkish culture, efforts are made to conserve heritage through rehabilitation. Therefore, this study will help developers and federal managers during the project planning stage by providing technical data.     

Modified permeability apparatus to determine the permeability of natural building stones

Natural building stones are commonly used for a broad variety of purposes in the construction of many different types of buildings. Knowledge of the permeability of natural building stones, which are widely used in interiors, exteriors, flooring, veneering, landscaping, and walkway laying, is important for correctly determining their lifetime as well as their areas of use. The current study proposes a new test method to determine the air permeability of natural building stones, based on a previously developed method used to assess the permeability values of concrete samples. In this context, the air permeability index values of 96 natural building stone samples, belonging to 16 different types of natural stones classified into five groups, were determined using a new air permeability testing apparatus. The obtained permeability values were compared with the water absorption, open porosity, and apparent density properties of the natural building stones. Strong correlations were identified between the air permeability values of natural building stones and the open porosity and water absorption values. In contrast to other types of tests, the designed apparatus allowed information to be obtained concerning the porosity of natural building stones within a time period as short as 6 h. Based on the obtained results, the air permeability values of the natural building stones were classified into three groups as permeable, semi-permeable, and non-permeable. The study results indicated that the air permeability index can be effectively used to measure the air permeability of natural building stones within a short a period of time and by using a simple test apparatus.     

Recent progress in X-ray CT as a geosciences tool

For many years X-ray computed tomography has been widely used as a medical diagnostical tool. This non-destructive technique was soon found to be very useful in rock material research. In the 1970s CT was introduced in material research while in the 1990s, micro-CT became an important non-destructive research technique. Presently nano-CT is being developed creating even more possibilities for the 3D visualization of small objects. In this paper CT, micro-CT and nano-CT are specified and discussed. Several applications illustrate the possibilities, specific advantages and limitations of each instrument. As with every technique some restrictions occur, but X-ray CT is found to be an emerging non-destructive analytical technique with many possibilities in material research.     

Heritage stone in South Australia

South Australia has the greatest utilisation of heritage or building stone in Australia because of its lack of timber resources. Consequently, natural stone was intensively used from the beginning of European colonisation. Building stones in South Australia, notable for their variety given the State’s diverse geology, can be challenging to designate as to their international importance. However, dimension stone in South Australia can also be designated as having national, regional, local or prospective importance. Commonly, stone in South Australia is restricted in use to a specific town, or even a single construction, and has only local significance except where use involves special stone characteristics, unusual stone masonry or use in a building with significant heritage. For instance, the town of Second Valley has a localised use of marble, likely the earliest use (1849) of this rock type in the State. Another example, ‘Adelaide Black Granite’, quarried since 1958, should probably be recognised internationally as a ‘Global Heritage Stone Resource’, as it has had intensive monumental use around Australia, utilisation as cladding in modern buildings, as well as paving and walling in Australia’s National Parliament in Canberra. It has also been exported, notably used for the Australian Embassy in Japan and for a major War Memorial at Le Hamel, France. South Australian slate quarries also provide significant heritage stone. For example, the Willunga Slate quarry south of Adelaide has been sourced for roofing slate and walling since 1840 and is arguably the longest continuous mining operation in Australia; this resource has obvious national significance given a period of quarrying extending to the present, coupled with national distribution of its products. Probably the most widespread stone sourced in South Australia is the surface limestone or calcrete, quarried in the Adelaide area until the 1850s and used for general construction. The stone continues to be used in rural areas. While arguably only of local significance, it could be considered to have national importance because of its extensive use in churches, public building, hotels, houses and simple walling across a vast area of South Australia. Additional research is needed to clarify the heritage status of many building stones used in South Australia.     

Changing climate, changing process: implications for salt transportation and weathering within building sandstones in the UK

Salt weathering is a crucial process that brings about a change in stone, from the scale of landscapes to stone outcrops and natural building stone façades. It is acknowledged that salt weathering is controlled by fluctuations in temperature and moisture, where repeated oscillations in these parameters can cause re-crystallisation, hydration/de-hydration of salts, bringing about stone surface loss in the form of, for example, granular disaggregation, scaling, and multiple flaking. However, this ‘traditional’ view of how salt weathering proceeds may need to be re-evaluated in the light of current and future climatic trends. Indeed, there is considerable scope for the investigation of consequences of climate change on geomorphological processes in general. Building on contemporary research on the ‘deep wetting’ of natural building stones, it is proposed that (as stone may be wetter for longer), ion diffusion may become a more prominent mechanism for the mixing of molecular constituents, and a shift in focus from physical damage to chemical change is suggested. Data from ion diffusion cell experiments are presented for three different sandstone types, demonstrating that salts may diffuse through porous stone relatively rapidly (in comparison to, for example, dense concrete). Pore water from stones undergoing diffusion experiments was extracted and analysed. Factors controlling ion diffusion relating to ‘time of wetness’ within stones are discussed, (continued saturation, connectivity of pores, mineralogy, behaviour of salts, sedimentary structure), and potential changes in system dynamics as a result of climate change are addressed. System inputs may change in terms of increased moisture input, translating into a greater depth of wetting front. Salts are likely to be ‘stored’ differently in stones, with salt being in solution for longer periods (during prolonged winter wetness). This has myriad implications in terms of the movement of ions by diffusion and the potential for chemical change in the stone (especially in more mobile constituents), leading to a weakening of the stone matrix/grain boundary cementing. The ‘output’ may be mobilisation and precipitation of elements leading to, for example, uneven cementing in the stone. This reduced strength of the stone, or compromised ability of the stone to absorb stress, is likely to make crystallisation a more efficacious mechanism of decay when it does occur. Thus, a delay in the onset of crystallisation while stonework is wet does not preclude exaggerated or accelerated material loss when it finally happens.     

Texture Analysis of Grey-Tone Images by Mathematical Morphology: A Nondestructive Tool for the Quantitative Assessment of Stone Decay

Both a low-cost and easily handled nondestructive methodology and its validation criterion are proposed. The methodology is based on image analysis by mathematical morphology for the assessment of decayed stone surfaces in historic limestone buildings. It is adapted to follow the evolution, at macroscopic time and space scales, of stone materials used in art pieces and monument building stones. This methodology is applied to the quantitative analysis of textures of static grey-tone CCD video camera images representative of flat stone structures that cannot be handled. These structures line the walls inside an important church, Basílica da Estrela, built in the 18th century and located in the city of Lisbon. Detailed visual/tactile observation shows that these flat vertical structures are more or less damaged depending on their position inside the church. The damage is possibly associated with different environment conditions both from the atmosphere inside the church and from contact with the walls of the church. The presence of these pathologies breaks down the order and organization of sound rock textures introducing changes in the topographical and optical characteristics of the texture of the surfaces. This new methodology is based on the granulometry and covariance analysis of grey-tone images corresponding to the structures studied. The validation criterion allows the results of the proposed methodology to be compared to the results of a previous qualitative study made by experts in the field using visual assessment and monument mapping as a valid methodology to assess the degree of decay. This procedure is based on optical and topographical characteristics and type of decay of the stone surface, and the quantity of material lost from the surface of the panels during the year. As discussed in this paper, in the context of cultural heritage, the proposed methodology was validated and its results can be considered an improvement on and complementary to expert visual analysis and also to other nondestructive techniques.     

Volcanic tuffs from Hesse (Germany) and their weathering behaviour

In the Hessian region of Germany numerous deposits of tuffs are known from which natural building stones were extracted. Many buildings show examples of the use of this material in the past. In contrast to their attractive appearance and ease of extraction from quarries, tuffs are liable to destruction by weathering. Most common damages are disintegration, crumbling, cracking, scaling and flaking. In this paper, the causes of damage of selected varieties have been analysed using petrographical and petrophysical methods. The measured values are disadvantageous in comparison to other natural building stones. Large amounts of swellable clay minerals, mostly forming the cementing material, cause scaling due to repeated humidification. High porosity including negative pore structures and high adsorption effects results in structural damages while freezing. Consequently, most varieties of the described tuffs possess a limited usage as an outdoor building material.     

A comparison of the properties and salt weathering susceptibility of natural and reconstituted stones of the Orval Abbey (Belgium)

The Orval Abbey, a major monument of southern Wallonia, Belgium, was partly destroyed and rebuilt several times between the Middle Ages and the present time. The oldest parts are made of natural stones of local origin (Bajocian and Sinemurian limestones) and the most recent parts are mostly made of reconstituted stone. The process of reconstituted stone making is not known. Although confronting the same environmental conditions, the reconstituted stone is much more susceptible to weathering than the natural limestones, especially to salt crystallisation. The present study compared the mineralogical and petrophysical properties of these building materials to gather information on the making of the reconstituted stone and to understand the difference in salt susceptibility between natural and reconstituted stones. Microscopic observations and petrophysical measurements showed that the reconstituted stone is composed of debris of Sinemurian and Bajocian limestone and cement, and the salt efflorescences were thenardite. Within the cement, amorphous grains were found that may correspond to grains of clinker, which have not reacted during stone making. Although its porosity and water transfer properties were close to that of the Bajocian limestone, its pore access distribution was centred around 0.1 μm. Furthermore, the details of the pore size distribution allowed calculating salt susceptibility indices that were very high in the case of the reconstituted stone. Thus, the composition of the cement and the pore size distribution are likely the two factors explaining a high susceptibility of the reconstituted stone to salt weathering.     

某厂房地基处理失误的岩土工程分析

招商局漳州开发区某工厂2#厂房采用独立基础,以强夯压实填土为基础持力层,厂房建成后就产生严重不均匀沉降,无法正常使用。本文对产生严重不均匀沉降的原因进行了分析:先围堰后抛石填海导致围堰角点内侧淤泥富集且厚薄不一,高夯能强夯引起富集的淤泥产生扰动强度大幅降低,潮间带采用高压旋喷加固填石不但不成桩、还扰动填石并导致填石中的细颗粒松动随落潮流失等,是地基产生不均匀沉降的主要原因。     

Engineering properties of Hınıs ignimbrites and their usability as a building stone (Erzurum, Turkey)

The survival of several ancient monuments made of ignimbrites in Hınıs town (Erzurum-Anatolia), which has suffered from intense annual temperature fluctuations and strong seismic activity, can mainly be attributed to use of suitable building stones. This paper examines the usability as building stones of Middle Miocene Hınıs ignimbrites that widely outcrop in and around Hınıs town. The petrographical, geochemical, mechanical, and physical properties determined lead to categorization of the ignimbrites as four different types. The Hınıs ignimbrites contain dasite–trachy–andesite and rhyolite. Rhyolite is the strongest material whereas the other types, being more porous, are weaker, lighter, and have good heat-insulation properties. Being light (easily transportable, machinable, and workable), good heat insulators, environmentally friendly (because of natural ventilation), sufficiently elastic to sustain seismic loading in the area under study, and more cost-effective than artificial stones, Hınıs ignimbrites are certainly a preferable option for use as light building stone. These ignimbrites are not suitable for use as floor covering, however, (because of rapid abrasion) or for building structural columns (because of low strength).     

玄武岩石材矿尾砂应用实验研究

针对玄武岩质建筑石材矿山产生的废弃物（碎石和尾砂）,依据环氧树脂有机胶黏剂的热固成型原理,使用环氧树脂乳液、有机固化剂和无机胶黏剂对废弃物进行复合石材试验.经物料均匀搅拌、模具成型、热压机施压和样品干燥、抛光、切边、修整等工序试制复合石材.通过测试复合样品的物理性能参数,其抗折强度超过天然石材商品,其他指标也基本达到相应建筑石材产品的质量标准.这种矿山废料的再利用方法,对减少矿山尾砂、治理环境污染、变废为宝以及增加企业经济收益有一定的作用.     

微波等离子体炬质谱技术快速鉴别天然石材与人造石材

天然石材主要有大理石、花岗岩等;人造石材多以不饱和聚酯树脂为基料,添加适量的无机物粉料和添加剂固化制成。由于石材种类繁多,并且各种石材的岩体所含矿物成分也有差异,当前很少应用化学成分分析方法准确、快速鉴别天然和人造石材,仅有的红外光谱法由于对待测物纯度的要求较高而具局限性。本文基于微波等离子体炬源(MPT)同时具有热解吸与强电离能力,能在短时间内离子化待测物的特点,采用微波等离子体炬质谱(MPT-MS)技术,无需样品复杂预处理直接对天然与人造石材进行分析,获得正离子检测模式下在m/z 50~1000之间的石材的指纹谱图,并运用化学计量学的主成分分析(PCA)方法处理所获取的数据,实现了不同建筑石材的区分。结果表明,MPT-MS能够获得石材丰富的指纹谱图,结合PCA方法能够快速鉴别天然石材与人造石材,天然石材中解吸出的物质主要为CO₂和H₂O的团簇分子;而人造石材中解吸出的主要成分为有机物(人为添加的黏合剂等)。本研究采用的MPT-MS技术无需采用喷雾、激光、基质和加热等方法辅助,并且无需对石材进行任何复杂的处理即可进行质谱分析,从而获取石材表面及内部物质的质谱信息,为快速直接鉴定石材样品提供了一种新的质谱分析方法。     

青田石的矿物组成特征研究

采用偏光薄片观察、X射线粉晶衍射仪、扫描电镜/能谱分析等测试方法对浙江青田县青田石进行了研究,结果表明,所选青田石样品中的封门黄、黄金耀、灯光冻、红花冻4个品种的主要矿物成分为叶蜡石;封门黑、紫檀冻这两个品种主要由叶蜡石和绢云母组成;蓝星、猪油冻、酱油冻这3个品种的主要组成矿物为叶蜡石和伊利石;珍珠冻的主要组成矿物是红柱石和叶蜡石;山炮绿的主要组成矿物为绢云母。     

观赏石及其分类

本文首先介绍了观赏石的概念,然后提出了观赏石的命名原则,进而按矿物的化学成分和晶形、岩石的成因、化石种类、陨石的化学和矿物成分、天然造型、用途等方面对观赏石进行了分类。最后阐明了观赏石是重要的自然资源。     

Durability of carbonate rock as building stone with comments on its preservation

Carbonate rocks have been extensively used as building stones because of their availability, workability, and attractiveness. Unfortunately, however, some stones suffer from chemical attack or freeze-thaw activity. The environmental affects, especially those due to pollution of the atmosphere, are discussed in terms of weathering processes, salt crystallization, and acid deposition. A review of some recent research in relation to deterioration of stone in urban environments is given and carbonate rocks are classified in relation to position within a building, geographical location, and degree of pollution. Some comments on stone preservation are provided, especially in terms of the properties a preservative should possess.     

Moisture content of natural stone: static and dynamic equilibrium with atmospheric humidity

Among hygric properties of stone material, the sorption behaviour is of essential importance because of the permanence of the processes involved. New results from static sorption experiments performed by standard techniques and by a new tool are reported for six different building stones. Furthermore, an example of dynamic sorption behaviour under continuously changing humidity is presented. For the static equilibrium sorption measurements a close relation to the stone type, its pore properties, such as specific inner surface, pore volume, pore size distribution as well as capillary water uptake and water saturation, is drawn. The comparison of the different data allows us to retrieve correlations between material features that are crucial for weathering processes. The sorption–desorption processes respond spontaneously on even small humidity changes as shown by the dynamic sorption experiment. A permanent breathing-process of the material is imposed.