Pores Of Stone Research Articles

Crystallization modifiers applied in granite desalination: The role of the stone pore structure

Soluble salts of marine origin are one of the main agents in the weathering of granitic rocks used in buildings and monuments; they cause a loss of cohesion between the mineral grains, which results in granular disintegration. This deterioration is produced by crystallization–dissolution processes of salts, mainly sodium chloride, in the interior of the rock. Desalination procedures (mainly immersion and application of adsorbent poultices) are the more usual intervention in this circumstance, but complete extraction of the salts is generally difficult to achieve. In this paper we present the results of a study of the effectiveness of two NaCl crystallization modifiers, potassium ferrocyanide and sodium ferrocyanide, in desalinating two types of granitic rock with significantly different pore structure. Evaluations have been made of how these modifiers influence, first, the transport of NaCl solution inside the rocks; second, the susceptibility of the granite to salt crystallization cycles; and third, the effectiveness of desalination by immersion in distilled water. The results obtained are that the effectiveness of the two modifiers is completely different in each of the two granites studied. In one type of rock studied, both ferrocyanides increase the evaporation rate of the saline solution inside the structure of the rock by permitting NaCl to crystallize on surfaces as efflorescences; consequently, first, the intensity of sand disaggregation during the salt crystallization test is reduced, and second, when either of the modifiers is added to distilled water, desalination is more effective than extraction with distilled water only. For the second type of granite evaluated, neither of the modifiers was found to be effective. Therefore, we conclude that the network of fissures in the rock has a significant effect on the behaviour of the solutions with modifiers, since the pore structure of the stone determines the dissolution/evaporation kinetics of the solutions of salts. Thus, generalizations about the effectiveness of specific modifiers in granites are not possible: their effectiveness must be studied for each specific stone.

Silicate Consolidants for Stone

Consolidants are sols or solutions that are used to restore the strength of weathered stone. The liquids are drawn into the pores of stone by capillary suction, then they harden by gelation and/or drying. In this chapter, we discuss the requirements that such a material must fulfill, and demonstrate the effectiveness of consolidants based on alkoxysilanes and alkylalkoxysilanes.

Stone properties and weathering induced by salt crystallization of Maltese Globigerina Limestone

Abstract Most monuments and buildings in the Maltese Islands are constructed of the local Globigerina Limestone. Today, this Globigerina Limestone shows considerable damage in many buildings, particularly through alveolar weathering, which is frequently very intense. Owing to Malta's marine environment, salt crystallization in the stone's pore spaces has been recognized as the main weathering process responsible for the deterioration of the country's monuments. In order to obtain more information on the fabric-dependent weathering processes of Globigerina Limestone, detailed analyses were carried out. Globigerina Limestone samples obtained from stone types with two different known qualities were characterized according to petrographical, geochemical and physical properties. These included porosity, pore radii distribution and tensile strength, as well as water and humidity transport properties. Investigations by means of salt crystallization tests on quarry samples of both stone types reinforced the idea that the extent of salt weathering depends on salt type and concentration and pore-space properties. Visible weathering damage was recorded and evaluated for a representative monument (the Church of Santa Marija Ta' Cwerra in Siggiewi) by means of a monument mapping method, which was carried out twice over a period of 9 years (1995 and 2004). The identified weathering forms were also correlated with a previously developed weathering model for Globigerina Limestone. According to the results of the mapping, salt analyses carried out on samples from the church and salt-loading tests on quarry samples, there exists a significant correlation between visible damage and salt load. The zoning of weathering damage is obviously related to different salt concentrations. The zone with severe weathering damage is characterized by a high concentration of halite. Consequently, salt weathering represents the main damage process for the Globigerina Limestone of Malta.

The role of saline solution properties on porous limestone salt weathering by magnesium and sodium sulfates

Saline solution properties, viscosity in particular, are shown to be critical in salt weathering associated with sodium and magnesium sulfate crystallization in porous limestone. The crystallization of sodium and magnesium sulfate within a porous limestone has been studied at a macro- and microscale using different techniques, including mercury intrusion porosimetry, environmental scanning microscopy and X-ray computed tomography. Such analysis enabled the visualization of the crystallization process in situ, and at high magnification, yielding critical information as to where and how salts crystallize. Sodium sulfate decahydrate (mirabilite) tends to crystallize in large pores as euhedral micron-sized crystals formed at low supersaturation near to the surface of the stone. In contrast, magnesium sulfate heptahydrate (epsomite) tends to precipitate as anhedral wax-like aggregates formed at high supersaturation and distributed homogeneously throughout the stone pore system filling large and small pores. While the former crystallization behavior resulted in scale formation, the latter led to crack development throughout the bulk stone. Ultimately, the contrasting weathering behavior of the two sulfates is explained by considering differences in flow dynamics of solutions within porous materials that are mainly connected with the higher viscosity of magnesium sulfate saturated solution (7.27 cP) when compared with sodium sulfate saturated solution (1.83 cP). On the basis of such results, new ways to tackle salt weathering, particularly in the field of cultural heritage conservation, are discussed.

A simple, inexpensive and large volume pore water sampler for sandy and muddy substrates

The construction and testing of a low cost, simple, intertidal and sub-tidal pore water sampler for use in sandy and muddy substrates are described in this note. The sampler, “porextractor”, is made of polyvinyl chloride (PVC) plumbing materials that can be readily sourced at any local hardware shop and costs AU $ 15.00 to build. The only mechanical component of the porextractor is a plunger that is used only once at the time of deployment. The porextractor has been designed for use on seagrass beds to collect pore water samples with minimal disturbance to the substratum for nutrient flux studies. The relative efficiency of the porextractor was tested against the widely used “Winger and Lasier” sampler, a vacuum operated diffuser stone pore water sampler. The two samplers were compared for the volume of pore water collected in sandy and muddy substrates in the laboratory, and the concentrations of total nitrogen and total phosphorus in samples collected from a sandy substrate in Amphibolis and Posidonia seagrass meadows off the Adelaide coast. While the porextractor and the Winger and Lasier samplers worked equally well in the sandy sediments, the porextractor was more efficient than the latter in muddy sediments, where clogging was a major problem. In addition, there were no significant differences ( p ≤ 0.05) in the concentrations of total nitrogen and total phosphorus measured from the pore water samples collected by the two samplers in situ from the seagrass bed. The simplicity, ease of construction, non-substrate specificity, and large sample volume yield are some of the major merits of the porextractor over other conventional techniques used for pore water sampling.

Fractal geometry and mercury porosimetry: Comparison and application of proposed models on building stones

Different fractal models of porous solid are described and compared. Fractal dimension, following the different methodologies proposed to evaluate fractal dimensions, of different unweathered stones and building stones were measured using mercury porosimetry in a pore diameter range between 100 and 0.0065 μm. In all cases, fractal behaviour expands more than 1.5 orders of magnitude. In general, fractal dimension values calculated from the different models are consistent between them. Fractal dimension can be used as stone pore system descriptor and, in addition, allows the differentiation between weathered and unweathered stones.

Multiple spin echoes technique as a tool for the evaluation of stone pore size

Multiple spin echoes technique as a tool for the evaluation of stone pore size

The fractal dimension of stone pore surface as weathering descriptor

Pore surface fractal dimension of building stones were measured using mercury porosimetry in a pore diameter range from 100 to 0.012 μm. Surface fractal dimension can be used as descriptor of the stone pore surface, allowing an easier differentiation between weathered and unweathered stone than the pore size distribution. For the studied materials, weathering processes cause an increase in the surface fractal dimension.

The application of the acoustic emission technique to stone decay by sodium sulphate in laboratory tests

Acoustic emission was monitored during salt crystallisation cycles in order to study the mechanisms of rock deterioration by sodium sulphate in laboratory tests. Some porous carbonate stones used in Spanish monuments (Cathedral of Oviedo, Murcia and Seo Vella of Lerida) were selected for this study. The acoustic emission detected during the different stages of the cycles (immersion, drying and cooling) was interpreted to be the result of the salt behaviour inside the stone. The use of this technique has confirmed that this behaviour depends on salt characteristics (solubility, hydration state and polymorphism of anhydrous sodium sulphate) and stone porosity and pore network.

Development of organosilicone‐polyurethanes as stone preservation and consolidation materials

Two organosilicone-modified polyurethanes are investigated as potential materials for the conservation and consolidation of natural stones. The materials are low molecular weight oligomers at the application stage and react with the humidity of the air to give polymers, forming continuous microlayers. The two differ in the length of the organosilicone chain, resulting in pronounced differences in their physical state: one forms a brittle glassy material (Tg ≈ 70°C). and the other, a soft rubbery material (Tg ≈ −100°C). The rate of the polymerization of the prepolymers was investigated at different conditions, showing a strong dependence on the presence of a catalyst and air humidity. Both these favorable conditions exist probably in the natural stone pores, enhancing the formation of the protective hydrophobic internal microlayer. © 1996 John Wiley & Sons, Inc.

Development of organosilicone-polyurethanes as stone preservation and consolidation materials

Two organosilicone-modified polyurethanes are investigated as potential materials for the conservation and consolidation of natural stones. The materials are low molecular weight oligomers at the application stage and react with the humidity of the air to give polymers, forming continuous microlayers. The two differ in the length of the organosilicone chain, resulting in pronounced differences in their physical state : one forms a brittle glassy material (T g 70°C), and the other, a soft rubbery material (T g -100°C). The rate of the polymerization of the prepolymers was investigated at different conditions, showing a strong dependence on the presence of a catalyst and air humidity. Both these favorable conditions exist probably in the natural stone pores, enhancing the formation of the protective hydrophobic internal microlayer.

Modeling Damage to Limestone Exposed to Atmospheric Pollutants

ABSTRACTPreservation of building and monument stone exposed to acidic environments relies on the understanding of acidic precipitation deposition processes and damage mechanisms. Presented here is a model which predicts sulfur accumulation in porous limestone subjected to dry deposition of SO2. The model assumes deposition and reaction of SO2 to form a thin gypsum crust on the moist surface of the stone, and subsequent sulfur (as aqueous sulfate) transport and accumulation in the stone interior driven by diurnal wetting and drying of the stone surface. Characterization of the limestone pore structure contributes significantly to the evaluation and interpretation of modeled sulfate transport and accumulation in porous building materials. Predicted sulfur accumulation in the stone interior is dependent on the surface boundary conditions, the stone pore geometry and structure, and the rates and mechanisms of aqueous/solid sulfur partitioning (i.e. adsorption, precipitation and dissolution). Model results are compared to moisture content and sulfur accumulation measured in limestone briquettes exposed to a natural dry deposition environment. The model successfully predicts moisture transport in field-exposed limestone, but overestimates the rate of sulfur accumulation. The model may be improved by quantification of the time dependence of the surface sulfate concentration and better understanding of the sulfate partitioning mechanisms.

Real time measurements of sandstone deterioration: a microcatchment study : D. P. Halsey, S. J. Dews, D. J. Mitchell & F. C. Harris, Building & Environment, 30(3), 1995, pp 411–417

Abstract In order to gain a greater insight into the mechanisms responsible for the deterioration of sandstone buildings, chemical analysis of runoff water from sandstone and glass (control) surfaces has been carried out. Results indicate that the blocking of the stone's pores by atmospheric particulates, soluble salts and algae may be involved in this decay. Evidence is presented which indicates that pressures created by salts and trapped moisture may cause the detachment of surface layers of sandstone from buildings. Weakening by kaolinite formation is identified as a potential factor in sandstone weathering.

Real time measurements of sandstone deterioration: a microcatchment study

In order to gain a greater insight into the mechanisms responsible for the deterioration of sandstone buildings, chemical analysis of runoff water from sandstone and glass (control) surfaces has been carried out. Results indicate that the blocking of the stone's pores by atmospheric particulates, soluble salts and algae may be involved in this decay. Evidence is presented which indicates that pressures created by salts and trapped moisture may cause the detachment of surface layers of sandstone from buildings. Weakening by kaolinite formation is identified as a potential factor in sandstone weathering.

Bubble size distribution in a bubble column applied to aquaculture systems

Bubble size distribution affects the gas-liquid mass transfer rates during aeration and foam fractionation processes employed in recirculating aquacultural systems. The effects of air flow rate, protein concentration and air stone pore size on bubble characterization were investigated. Bubble size was measured photographically in conjunction with image-processing techniques. The study indicated that bubble size increased with air flow rate and air stone pore size, but decreased with protein concentration. Within the tested range of these variables, the geometric diameters of the majority of the bubbles (90%) were within the range of 0·5–3·0 mm, and the bubble sizes followed a normal distribution.

いおう含浸における砥石気孔の等価モデルと最適含浸条

In the sulfur treatment, commonly immersing a heated stone in molten sulfur, stone's pores are filled by the capillary force. So, an equivalent model, assuming pores to be straight capillaries, is proposed, and the equation giving move of liquid up in the tube is derived. This equation contains variables of contact angle, surface tension, viscosity, specific gravity and penetrating height of the liquid, and tube diameter. The equivalent tube diameter determined from the experimental results naturally includes intricacy of a pore pipe, and is almost dependent only on the given stone structure, particularly grain size, and unconcerned with the liquid nature. In sulfur treatment, required impregnation time takes a minimum value near 150°C where liquid's viscosity comes to the smallest, especially for the stone pre-heated over 250°C, because of an elimination of adsorbed substances from atmosphere through the pre-heating. As it is seen that adsorbed substances are not water, this heating may be replaced with isolating the stone to be treated from air by means of keeping it in water.

Salt Burst by Hydration Pressures in Architectural Stone in Urban Atmosphere

Research Article| February 01, 1970 Salt Burst by Hydration Pressures in Architectural Stone in Urban Atmosphere E. M WINKLER; E. M WINKLER Department of Geology, University of Notre Dame, Notre Dame, Indiana 46556 Search for other works by this author on: GSW Google Scholar E. J WILHELM E. J WILHELM Department of Chemical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1970) 81 (2): 567–572. https://doi.org/10.1130/0016-7606(1970)81[567:SBBHPI]2.0.CO;2 Article history received: 07 Jul 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation E. M WINKLER, E. J WILHELM; Salt Burst by Hydration Pressures in Architectural Stone in Urban Atmosphere. GSA Bulletin 1970;; 81 (2): 567–572. doi: https://doi.org/10.1130/0016-7606(1970)81[567:SBBHPI]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Salt bursts can cause extensive spalling in stone structures. Water-soluble salts and their hydrates Na2CO3 H2O (Na2CO3-7H2O, Na2CO3 10H2O), Na2SO4 (Na2SO4 10H2O), and MgSO4-H2O (MgSO4 7H2O) are trapped in pores of stone and concrete by both infiltration upward from the ground and by the reaction of carbonate and silicate rocks with sulfuric and carbonic acids from polluted urban atmospheres. The crystallization of the salts and their recrystalhzation from a lower to a higher hydrate within the range of mineral stability may develop stresses of high magnitude. Theoretical bursting pressures were calculated thcrmo-dynamically from vapor pressures of the hydrates and from humidities of the air for several air temperatures. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.