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1.
Precipitation of salts in confined spaces is the key mechanism for rock weathering and damage to building materials. To date there is no comprehensive study of the parameters influencing the reduction of pore space by salt crystals and the consequences for transport and damage by crystallization pressure. A novel method is presented to quantify pore clogging (i.e., the degree to which crystallization of salts interferes with transport of solution in porous materials). After drying capillary-saturated stone specimens containing salt solutions, the rate of capillary uptake of decane into the salt-contaminated specimens is measured. By treating the salt-contaminated material as a bilayer, the width of the crystallization front and the degree of pore filling can be determined. Two model materials with different pore size distributions (Indiana and Highmoor limestone) and three salts (sodium chloride, sodium sulfate and magnesium sulfate) are selected for this study. It is shown that pore clogging results from the interplay between pore size distribution and salt properties. Different scenarios are discussed to link pore clogging with salt damage. 相似文献
2.
Accelerated weathering tests on two highly porous limestones 总被引：3，自引：0，他引：3
A major cause of weathering of building and historic monuments constructed using limestones is associated with the salt crystallization.
This may typically occur at the surface (due to efflorescence) or in subsurface layers while limestones are drying. Due to
this reason structural damage or material loss (granular disintegration, flaking, contour scaling) may occur. In this paper,
imbibition-drying cycles are carried out with pure water and solutions of NaCl with different concentrations to simulate the
weathering effect on two limestones with similar total porosity values. The imbibition kinetics of these limestones was significantly
influenced by the number of applied imbibition-drying cycles. In addition, imbibition kinetics was also dependent on the concentration
of salt solutions, the mineralogical composition as well as on the pore-size distribution of these two stones. The structural
and textural modifications that arise in the limestones due to the influence of imbibition characteristics of drying cycles
are qualitatively confirmed by scanning electronic microscope (SEM) and quantitatively with helium pycnometry measurements. 相似文献
3.
In the arid regions of Australia, fine-grained slurried wastes produced during gold mining are typically disposed of in large storages using subaerial deposition. Management of the storage is often aimed at maximising the evaporative drying that occurs, thereby maximising the density achieved. Ore processing is conducted using groundwater that can have salinities that approach solution saturation. Precipitation of salts on the tailings surfaces during evaporation leads to the development of thin salt crusts that can significantly reduce the rate of evaporation. Quantification of the actual rate of evaporation from the drying tailings surfaces is important for assessing disposal strategies. Different methods of estimating evaporation were employed at mine sites in Western Australia (WA) to provide more information on the drying behaviour of saline tailings. These techniques are described and typical results from a saline tailings storage are presented. 相似文献
4.
A common decay scenario in old and new buildings was simulated: the effects on masonry structures of salt efflorescence or subefflorescence produced by the rise of saline solution. Eight different types of masonry wall each made up of a combination of different construction materials (brick, calcarenite and four types of mortar were combined as follows: pure lime mortar, mortar + air entraining agent, mortar + pozzolana, mortar + air entraining agent + pozzolana) have been tested. These materials have different textures (strong anisotropy in brick, irregular-shaped pores in calcarenite, retraction fissures or rounded pores in mortars which also show a reduction of porosity along the contact area with the stone), different hydric behaviours (under total immersion brick + mortar specimens absorb water faster than calcarenite + mortar specimens) and different pore size distribution (brick shows unimodal pore distribution, whereas calcarenite and mortars are bimodal). In the salt weathering test, mortars interlayered with masonry blocks did not act as sacrificial layers. In fact, they allowed salts to rise through them and crystallize on the brick or calcarenite pieces causing the masonry structure to decay. Only the addition of an air-entraining agent partially hindered the capillary rise of the salt-laden solutions. 相似文献
5.
Gypsum is one of the most universally distributed salts in weathered materials but little is known about the influence of environmental conditions on the damage generated by gypsum in stones. To quantify the damage induced by gypsum crystallization acoustic emission techniques are employed to record the elastic energy released during salt crystallization cycles in a limestone. Different environmental conditions have been established during the cooling and drying periods in traditional salt crystallization cycles. During drying two different temperatures (50 and 25 °C) and relative humidity (low, 25 % at 50 °C and 65 % at 25 °C, and high, 99 %) have been applied. The acoustic emission signals are filtered by a frequency analysis in order to eliminate signals corresponding to external noise or artifacts. Our experimental results show that acoustic emission activity is higher under high relative humidity conditions than under low relative humidity conditions, and also higher when drying at 50 °C than at room temperature. Microscopic observations on the weathered samples indicated that under high relative humidity conditions and at room temperature, gypsum crystallizes not on the sample surface, like in the other samples, but deeper in the inner part of the sample, in good agreement with previously published data. We show that using acoustic emissions as usually done in rock mechanics is also very useful in the study of stone decay and weathering processes in the laboratory. 相似文献
6.
In lagoonal and marine environments, both historic monuments and recent buildings suffer from severe salt damage caused by sea flooding, sea-level rise and frequent storm events. Salt-water contamination of groundwater systems, a widespread phenomenon typical of coastal areas, can lead to a deterioration not only of the quality of fresh groundwater resources, but also of building materials in urban settlements. A general overview is given of the hydrogeological configuration of the subsoil of Venice (Italy), with particular reference to the shallow groundwater circulation. The relationship between the seawater in the subsoil and salt decay processes, due to salt crystallization, is highlighted. These processes affect civil constructions in Venice??s historic center. Perched aquifers, influenced by tide variations and characterized by salt-water intrusion, favor the transport of salts within masonry walls through the action of rising damp. In fact, foundations, in direct contact with the aquifers, may become a preferential vehicle for the transportation of salt within buildings. Decay patterns of different building materials can be detected through non-destructive techniques, which can identify sea-salt damage and therefore assist in the preservation of cultural heritage in coastal areas. 相似文献
7.
We report on the crystallization behavior and the salt weathering potential of Na2SO4, MgSO4 and an equimolar mixture of these salts in natural rock and porous stone. Geochemical modeling of the phase diagram of the ternary Na2SO4–MgSO4–H2O system was used to determine the equilibrium pathways during wetting (or deliquescence) of incongruently soluble minerals and evaporation of mixed electrolyte solutions. Model calculations include stable and metastable solubilities of the various hydrated states of the single salts and the double salts Na2Mg(SO4)2·4H2O (bloedite), Na2Mg(SO4)2·5H2O (konyaite), Na12Mg7(SO4)13·15H2O (loeweite) and Na6Mg(SO4)4 (vanthoffite). In situ Raman spectroscopy was used to study the phase transformations during wetting of pure MgSO4·H2O (kieserite) and of the incongruently soluble salts bloedite and konyaite. Dissolution of kieserite leads to high supersaturation resulting in crystallization of higher hydrated phases, i.e. MgSO4·7H2O (epsomite) and MgSO4·6H2O (hexahydrite). This confirms the high damage potential of magnesium sulfate in salt damage of building materials. The dissolution of the incongruently soluble double salts leads to supersaturation with respect to Na2SO4·10H2O (mirabilite). However, the supersaturation was insufficient for mirabilite nucleation. The damage potential of the two single salts and an equimolar salt mixture was tested in wetting–drying experiments with porous sandstone. While the high damage potential of the single salts is confirmed, it appears that the supersaturation achieved during wetting of the double salts at room temperature is not sufficient to generate high crystallization pressures. In contrast, very high damage potentials of the double salts were found in experiments at low temperature under high salt load.1 相似文献
8.
西藏扎布耶碳酸盐型盐湖卤水相化学研究 总被引：12，自引：0，他引：12
中国盐湖资源丰富,且水化学类型齐全。西藏扎布耶盐湖位于西藏高原腹地,该湖卤水水化学类型为碳酸盐型,已处于盐湖演化晚期,是一个固液共存的盐湖矿床,具有很好的工业开发价值。笔者分别在15℃、25℃下对该卤水进行了等温蒸发实验,研究了在此两个温度下卤水中各元素富集行为和盐类矿物析出规律。并通过讨论其与国内外碳酸盐型和硫酸盐型锂盐湖的卤水蒸发路径和矿物析出异同,指出扎布耶盐湖具有其独特的卤水蒸发析盐路径。在本实验中低温有利于卤水中锂的富集,而高温有利于硼的富集,碳酸锂和钾盐交叉析出,低温时钾的矿物主要为钾石盐,高温时主要为钾芒硝,高温有利于获得高品位的碳酸锂混盐。 相似文献
9.
为了研究地下盐穴开挖扰动区（EDZ）损伤盐岩在盐穴综合利用过程中的自恢复特性,设计了损伤盐岩在卤水温度作用下的自恢复试验。结果表明：损伤盐岩经过卤水浸泡后在不同温度下烘干时力学性质可以得到恢复,在试验温度范围35～80 ℃内,其恢复效果随着温度的增加而增强。经过恢复处理的损伤盐岩试件二次加载时的声发射特征显示,其Felicity比低于0.1,Kaiser效应基本不成立,说明损伤盐岩在自恢复处理过程中其内部损伤在细观尺度上发生愈合。根据损伤盐岩试件自恢复处理后的细观形貌特征,总结出盐岩损伤恢复3种不同的细观机制：基于扩散作用的损伤微裂纹愈合,基于NaCl晶体重结晶作用的微裂隙充填以及破碎区NaCl晶体颗粒的愈合黏结。盐岩损伤恢复过程中,裂纹中充填的饱和卤水为裂纹中的物质传递提供了通道,同时提供了大量的结晶基础物质,为盐岩损伤愈合奠定了基础。温度的升高为盐岩损伤恢复提供了更高的能量,提升了损伤愈合速度,同时使氯化钠重结晶密度增加,从而提高了损伤恢复程度。 相似文献
10.
11.
The paper principally focuses on the durability assessment of various stratigraphic levels of Ahlat ignimbrites collected from the eastern region of Turkey. A total of four different ignimbrite types with dissimilar color, texture and particularly welding degree were tested in laboratory. The laboratory tests performed on the ignimbrite specimens indicate that the welding degree as well as the lithic material content mainly controls the strength and capillarity properties of the ignimbrites. In addition, the durability of highly porous ignimbrites strongly depends upon the degree of welding. The effect of several weathering agents on the ignimbrites was evaluated on the basis of decay constant parameter. Accordingly, salt and ice crystallization pressures are a couple of major destructive agents acting within the micropores of the ignimbrites. Conversely, the investigated specimens are relatively durable against cyclic wetting–drying. Statistical evaluations reveal that the pore diameter is the major controlling factor on the deterioration rate of the ignimbrites after specifically recurrent freeze–thaw cycles. Moreover, the dry unit weight of the ignimbrites is more significant than the uniaxial compressive strength considering the deterioration rates during wetting–drying and salt crystallization. A less significant relationship was obtained between pore diameter and salt crystallization decay constant. 相似文献
12.
Xunming Wang Ting Hua Caixia Zhang Guangqiang Qian Wanyin Luo 《Environmental Earth Sciences》2013,68(3):623-631
In China’s arid regions, aeolian salts are transported along with dust aerosols, but their contents and the emission rates are poorly understood. Using samples with undisturbed surfaces and artificially disrupted surfaces (to simulate human disturbances such as reclamation, planting, trampling by animals, and other activities), the transport rates for windblown material and the salt contents of clay playa surfaces were investigated in a wind tunnel. The results showed that under wind velocities ranging from 8 to 22 m/s, wind erosion rates ranged between 0.009 and 0.066 g/m2/s for the undisturbed surfaces and between 0.011 and 0.048 g/m2/s for the artificially disrupted playa surfaces. Although the amount of wind-transported material that was captured was too small to allow an analysis of individual salt contents using the available equipment, electrical conductivity measurements and correlation analysis revealed mean total salt contents of 9.59 g/kg in the transported materials collected above the sealed playa surfaces versus 3.38 g/kg in materials from the same surfaces that were artificially cracked after testing the sealed surfaces. Given the large areas containing clay playas in China’s arid regions, these results will improve our understanding of aeolian salt transport in arid China and will facilitate interpretation of the sources of aeolian salts. 相似文献
13.
Kirsten Linnow Michael Steiger Christine Lemster Hilde De Clercq Maja Jovanović 《Environmental Earth Sciences》2013,69(5):1609-1620
Several double salts have been detected in building materials and most of these salts are incongruently soluble compounds. In contrast to single salts, however, no systematic investigations of the crystallization behavior and deleterious effects of incongruently soluble double salts exist. To assess the damage potential of these salts, a systematic investigation of their highly complex behavior is desirable. This paper deals with the crystallization behavior of various solids in the ternary mixed NaNO3–Na2SO4 system including the formation of the double salt darapskite, Na3NO3SO4·H2O. The crystallization sequence during droplet evaporation experiments at room conditions was determined using Raman and polarization microscopy. The basic idea of this research is to use deviations of the crystallization sequence of a salt or a mixed salt solution from the equilibrium pathway as an indicator to detect the degree of supersaturation. The observed crystallization pathway includes the formation of the metastable phases Na2SO4(III), Na2SO4(V) and darapskite. The experimental observations are discussed on the basis of the NaNO3–Na2SO4–H2O phase diagram and the results provide evidence for crystal growth from highly supersaturated solutions in both systems. If the crystals growing under these conditions are confined, these supersaturations result in substantial crystallization pressures. 相似文献
14.
Enrica Balboni Rosa M. Espinosa-Marzal Eric Doehne George W. Scherer 《Environmental Earth Sciences》2011,63(7-8):1463-1473
Magnesium sulfate salts have been linked to the decay of stone in the field and in laboratory experiments, but the mechanism of damage is still poorly understood. Thermomechanical analysis shows that expansion of stone contaminated with magnesium sulfate salts occurs during drying, followed by relaxation of the stress during dehydration of the precipitated salts. We applied thermogravimetric analysis and X-ray diffractometry to identify the salt phases that precipitate during drying of bulk solutions. The results show the formation of 11 different crystal phases. A novel experiment in which a plate of salt-laden stone is bonded to a glass plate is used to demonstrate the existence of crystallization pressure: warping of the composite reveals significant deformation of the stone during re-wetting of lower hydrates of magnesium sulfate. Environmental scanning electronic microscope (ESEM)/STEM experiments show that hydration of single crystals of the lower hydrates of magnesium sulfate is a through-solution crystallization process that is only visible at a small scale (~μm). It is followed by growth of the crystal prior to deliquescence. This demonstrates that crystallization pressure is the main cause of the stress induced by salt hydration. In addition, we found that drying-induced crystallization is kinetically hindered at high concentration, which we attribute to the low nucleation rate in a highly viscous magnesium sulfate solution. 相似文献
15.
P. López-Arce R. Fort M. Gómez-Heras E. Pérez-Monserrat M. J. Varas-Muriel 《Environmental Earth Sciences》2011,63(7-8):1487-1509
El Paular Monastery (eleventh century) is one of the most important Carthusian monasteries in Spain and is highly affected by crystallisation of Mg-sulphates, together with chlorides and nitrates. Urgent remediation of the decay process is needed to guarantee the stability of the building materials from the cloister and to make their hallways suitable for the exhibition of an important collection of seventeenth century paintings. This paper aims to characterise the building materials, salts and their interaction to suggest preservation strategies to minimise the impact of salts both in the short and the long term. These strategies include architectural solutions (such as a ventilation system to avoid increasing dampness and hence the dissolution, mobilisation and crystallisation of salts), petrophysical-based solutions (i.e. exploiting the porosity differences between building materials and poultices to maximise salt reduction) and strategies based on the physicochemical behaviour of salts and relative humidity transfer through the stone (to determine the most suitable environmental conditions to prevent crystallisation of the most harmful salt species). This research represents both a practical and experimental exercise that is useful for conservation scientists and restorers involved in the field of preservation of monuments, and for environmental control to avoid salt crystallisation. 相似文献
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17.
在自然营力和人为作用下,平遥古城墙和民居的青砖产生了严重的风化病害,亟须保护和修复。通过现场调查,发现风化病害发生部位都在毛细水上升高度范围内（距地面1~3m）,主要风化形式为等厚状剥落、鳞片状剥落、颗粒脱落、盐分结晶。通过室内测试和实验,得到了古砖的矿物、化学成分,物理、力学性质以及耐盐、耐冻性能。本文认为毛细水在墙体中上升时携带的盐分是古砖风化的主要原因,冻融循环则加剧了风化的进程。由于水分减少和/或温度降低,古砖孔隙中的可溶盐会“捕获”自由水使其变成带有若干结晶水的结晶盐。盐分结晶后体积增大在古砖孔隙中产生的膨胀力致使古砖破坏。根据古砖的风化机理,提出了“阻水、脱盐、强砖”的防风化方法。本文提出的古砖风化机理和防风化方法的技术流程和分析方法,可以为相关砖石文物的保护和修复提供参考。 相似文献
18.
Potash in salt extruded at Sar Pohl diapir, Southern Iran 总被引：2，自引：0，他引：2
Recent progress in the search for potassium salts in Iran is outlined. After reviewing how most potassium ores form by the evaporation of seawater ± hydrothermal brines, we focus on how most ores are deformed within salt diapirs. We summarise the history of the 150 or so diapirs of Hormoz salt emergent in the Zagros Mountains of Iran and then consider in detail the nature of potash at Sar Pohl, 60 km west of Bandar Abbas. These deposits are unique in that they occur in salt that extruded sub-aerially and spread over the surrounding ground surface via gravity-driven collapse. Mapping and drilling of the complex structural geology of Sar Pohl found the potash beds to be dispersed in distal salt but concentrated in piles of recumbent folds with axes circumferential to the mountain over lows in the vent rim.Equivalents of the curtain folds surviving in the stems of German diapirs presumably still exist beneath Sar Pohl and would be safer to mine than the recumbent folds in this soluble mountain. However, it should be possible to continuously pump water onto the exposed salt and guide the resulting brines through evaporation ponds and then a crystallization plant on the adjacent plains. This approach would accelerate natural degradation processes but harvest potash currently draining into the gulf. 相似文献
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20.
We report on the crystallization behavior and the salt weathering potential in natural rock and porous stone of single salts (NaNO3, Na2SO4) and salt mixtures in the ternary NaNO3–Na2SO4–H2O system. Geochemical modeling of the phase diagram of the ternary NaNO3–Na2SO4–H2O system was used to determine the equilibrium pathways during wetting (or deliquescence) of incongruently soluble minerals and evaporation of mixed electrolyte solutions. Experiments were carried out in order to study the phase changes during dissolution either induced by deliquescence or by the addition of liquid water. In situ Raman spectroscopy was used to study the phase transformations during wetting of pure Na2SO4 (thenardite) and of Na3NO3SO4·H2O (darapskite). In both experiments crystallization of Na2SO4·10H2O (mirabilite) from highly supersaturated solutions is demonstrated confirming the high salt weathering potential of thenardite and darapskite wetting. In order to study the damage potential of darapskite experimentally, wetting–drying experiments with porous sandstone with the two single salts (Na2SO4, NaNO3) and two NaNO3–Na2SO4 salt mixtures were carried out. Different destructive and non-destructive techniques were tested for damage monitoring. NaNO3 was found to be the least damaging salt and Na2SO4 is the most damaging one. The classification of the two salt mixtures was less obvious. 相似文献