Sandstone Decay Research Articles

Study on Changes in Physical and Mechanical Properties and Integrity Decay of Sandstone Subjected to Freeze–Thaw Cycling

To investigate the effects of long-term freeze–thaw cycles on the physical and mechanical properties as well as the attenuation trend of rocks, this study conducted saturated freeze–thaw tests on coarse sandstone and fine sandstone samples collected from the slopes of Muli Coal Mine in Qinghai Province. The samples underwent different numbers of freeze–thaw cycles, and their porosity, longitudinal wave velocity, and uniaxial compression strength were studied. The variations in the physical and mechanical properties of the two types of sandstone with respect to the number of freeze–thaw cycles were analyzed. Take uniaxial compressive strength (UCS) as the integrity index, and decay laws of rock integrity were analyzed based on the decay equation suggested in previous studies. We found that the decay index λ, which is commonly assumed to be constant, varies with the number of freeze–thaw cycles. Furthermore, the λ values varied between different rock types. For fine sandstone, the λ decreases with an increase in the number of freeze–thaw cycles, ranging from 0.00385 to 0.005. However, for coarse sandstone, the λ initially decreases and then increases with an increase in the number of freeze–thaw cycles. The range of λ for coarse sandstone is between 0.00376 and 0.00481. Finally, we established a relationship between the decay index, porosity, and longitudinal wave velocity in the fine sandstones. This relationship provides a more straightforward way to evaluate the integrity of fine sandstones subjected to different numbers of freeze–thaw cycles.

Monitoring and Evaluation of Sandstone Decay Adopting Non-Destructive Techniques: On-Site Application on Building Stones

This paper focuses on the characterization approach to evaluate the decay state of Pietra Serena of historic buildings in Florence (Italy). Pietra Serena is a Florentine sandstone largely used in the city especially during the Renaissance; it is a symbol of cultural heritage of Florence and constitutes a large part of the city center, which was named a World Heritage Site by UNESCO in 1982. Unfortunately, many environmental factors negatively affect the stone, increasing damage and the danger of falling material. Any detachment of stone fragments, in addition to constitute a loss in cultural heritage, can be dangerous for citizens and the many tourists that visit the city. The use of non-destructive techniques (NDTs) as ultrasonic and Schmidt hammer tests can quantitatively define some mechanical properties and help to monitor the decay degree of building stone. In this study, the NDTs were combined with mineralogical, petrographical, chemical and physical analyses to investigate the stone materials, in order to correlate their features with the characteristics of the different artefacts in Pietra Serena. Correlations between the NDTs results and the compositional characteristics of the on-site stone were carried out; such discussion allows to identify zones of weakness and dangerous unstable elements.

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

The weathering of rocks controls the shape of the Earth’s surface and affects their suitability as building stones. Frost weathering and crystallization of soluble salts are considered to be important factors in rock weathering. Although the crystallization of salts and ice presents obvious chemical differences, both of them produce crystallization pressure. Few studies seem to have been done on the effects of the combined action of repeated freezing–thawing and salt crystallization on the rocks. This paper studies the weathering of rocks under the combined effect of freezing–thawing cycle and salt crystallization cycle. The results show that, with the increase of freeze–thaw cycles, the samples soaked with MgSO4 solution tend to turn red and the surface particles fall off more seriously. The mass of the sandstone is increased at the beginning of the freeze–thaw cycle and then decreases. Roughness, residual moisture, and MgSO4 crystal affect the thermal conductivity. Samples soaked with 40% MgSO4 solution lost the most mass and have the lowest thermal conductivity. There are two main factors that cause damage to sandstone: (1) crystallization pressure of salt and (2) frost heave action of ice. Crystallization pressure of salt and frost heave action of ice can reduce the cohesive force between particles, making the particles fall off, which is the most important factor of sandstone damage.

Impact of cement repointing on rates of sandstone decay in medieval churches of the French Massif Central

Abstract Three Romanesque churches of the Bourbonnais region in the French Massif Central have been investigated. These date back to the twelfth century, and are mainly built of red and white sandstones. Their ashlar blocks were extensively repointed in the mid-twentieth century with cement-rich mortar. In order to quantitatively assess the impact of repointing on the decay rates of the sandstones, the following methods have been used: dating of reference surfaces (‘zero datum levels’) based on stone-dressing marks, stone-by-stone and terrestrial LiDAR (Light Detection And Ranging) surveys, and petrographical analyses including on-site non-destructive tests. This study reveals that, between the twelfth century and the mid-twentieth century, intrinsic geological factors have been a key control on weathering rates. Stone surface recession has proceeded, on average, 500 times faster in the poorly cemented soft white sandstone compared to the iron-cemented red sandstone (4 mm/century v. 0.008 mm/century). Since the mid-twentieth century, the replacement of the original lime mortar with a cement-rich mortar has resulted in a marked increase in weathering rates and resulting surface recession of the poorly cemented white sandstone: this increase is fivefold where cement-lime mortar (‘bastard mortar’) has been used and 10-fold where harder cement-rich mortar has been applied. By contrast, the application of cement-lime mortar between the ashlars composed of iron-cemented red sandstone had no deleterious effects. This study confirms that the use of cement-based mortar should be avoided on soft and porous masonries. It also stresses the fact that accelerated stone surface recession rates are systematically associated with heritage sites that are subject to significant anthropogenic effects caused by inappropriate interventions or excessive pressure on the monuments or their environment.

Contrasting weathering and climate regimes in forested and cleared sandstone temples of the Angkor region

ABSTRACTComparative assessment of stone weathering intensities and bioclimatic conditions was conducted at four temples located in cleared and forested sites of the Angkor Park, based on similar protocols. Four thousand sculpted lotus petals carved in the same grey sandstone were categorized by using two customized scales of weathering intensity, and climate monitoring was conducted from December 2008 to November 2009. Whereas 70% of the sandstone lotus petals are almost completely destroyed by mechanical weathering in cleared areas, 74% of petals located in forested environments appear to be totally free of mechanical weathering and are only affected by superficial biochemical weathering. Ambient conditions are also contrasting, with the magnitude of the diurnal surface temperature and relative humidity ranges being three times higher at cleared sites than in wooded areas. As wetting–drying cycles are the driving force of sandstone decay at Angkor, causal links are suggested between weathering and climate regimes. In wooded areas, the microclimate is buffered by the forest and the associated lithobionts, which maintain constant humidity levels, reduce thermal stresses at the stone surface and induce a slow biochemical weathering regime. In cleared areas, direct exposure to sunshine and monsoon rains induces pronounced wetting–drying cycles conducive to swelling–shrinking movements and other potential processes, provoking the rapid mechanical decay of the sandstone. Even if local damage can be caused by tree roots, the forest cover and the associated lithobionts obviously play an overall protective role. Additionally, microtopographical factors related to architectural designs and post‐building events probably explain intra‐site and between site minor differences in the amount of sandstone decay, by influencing key factors such as the water residence time at the stone surface. Last, the contrasting weathering regimes in forested and cleared sites are but a trend, for besides overwhelming mechanical weathering, chemical weathering is also operative at cleared sites, as indicated by salt efflorescences and ferric oxidation. Copyright © 2012 John Wiley & Sons, Ltd.

A commentary on climate change, stone decay dynamics and the ‘greening’ of natural stone buildings: new perspectives on ‘deep wetting’

Environmental controls on stone decay processes are rapidly changing as a result of changing climate. UKCP09 projections for the 2020s (2010–2039) indicate that over much of the UK seasonality of precipitation will increase. Summer dryness and winter wetness are both set to increase, the latter linked to projected precipitation increases in autumn and spring months. If so, this could increase the time that stone structures remain wet and possibly the depth of moisture penetration, and it appears that building stone in Northern Ireland has already responded through an increased incidence of algal ‘greening’. This paper highlights the need for understanding the effects of climate change through a series of studies of largely sandstone structures. Current and projected climatic trends are therefore considered to have aesthetic, physical and chemical implications that are not currently built into our models of sandstone decay, especially with respect to the role played by deep-seated wetness on sandstone deterioration and decay progression and the feedbacks associated with, for example surface algal growth. In particular, it is proposed that algal biofilms will aid moisture retention and further facilitate moisture and dissolved salt penetration to depth. Thus, whilst the outer surface of stone may continue to experience frequent wetting and drying associated with individual precipitation events, the latter is less likely to be complete, and the interiors of building blocks may only experience wetting/drying in response to seasonal cycling. A possible consequence of deeper salt penetration could be a delay in the onset of surface deterioration, but more rapid and effective retreat once it commences as decay mechanisms ‘tap into a reservoir of deep salt’.

Weathering rates of sandstone in a semi-arid environment (Hunter Valley, Australia)

The rate of sandstone weathering in the semi-arid climate of the Hunter Valley, New South Wales, Australia has been estimated from observations of gravestone weathering in the area. The gravestone data points to two distinct stages in the weathering process. The first stage covering the first century of exposure is characterised by a relatively low recession rate of 0.5 mm/100 years. This is followed by a second stage in which the rate of weathering increases sharply to ca 2.5 mm/100 years. The non-linear nature of the weathering trends over time suggests that during the first century of exposure, structural changes took place within the sandstone material, which lay the foundation for accelerated weathering after further exposure. Laboratory trials were also conducted to identify the effectiveness of different weathering processes in the decay of sandstone in this region. Of the four processes examined, only the freeze–thaw cycle produced a significant degree of mass loss and is therefore most likely a strong contributor to the weathering of sandstone in this region.

Geomorphology and stone conservation: sandstone decay in Stoke‐on‐Trent

Identifying stone decay forms is an essential first step in stone conservation. In this study a visually based geomorphological approach was used to provide a rapid assessment of the general weathering characteristics displayed by building sandstones in Stoke‐on‐Trent. Stone decay was found to be largely caused by the mechanical disruption of the sandstone and its occurrence was extremely variable in both space and time. The study demonstrates the close interrelationship between stone properties, environmental conditions, morphology of weathering features, and building characteristics. It is important that these close and dynamic interrelationships are recognised when seeking to explain or predict stone behaviour for management purposes.

Decay of sandstone in urban areas correlated with atmospheric aerosol

The decay of sandstone in urban areas has been investigated. Patterns and composition of the damage layers sampled on monuments and historical buildings are described. The elemental concentrations of black surface crusts are reported. Enrichment factors in relation to the sandstone and crustal rock composition have been calculated in order to point out the component due to atmospheric deposition. The presence of anthropogenic aerosol and its role in the process of damage is evidenced.

IV. The relationship of micro-organisms to the decay of stone

The first suggestion that bacteria might be agents in stone decay was probably that of Buchanan (1904) in a paper read before the Royal Philosophical Society of Glasgow in 1904. This paper contained evidence that bacteria, yeasts and moulds were associated with the decay of sandstones in the City of Glasgow, and included a brief sketch of the manner in which the autotrophic bacteria, sulphur bacteria, iron bacteria, and the nitrifying bacteria might play a part in sandstone decay. This paper was apparently unknown to later writers, Anderson (1910), Marsh (1923) and Fox and Harrison (1925), none of whom makes reference to it. In 1928 Buchanan published the results afresh with no important addition, but confirming his earlier work. Stutzer and Hartleb (1899) in an important paper, published five years before that of Buchanan, noted the solution of the lime of the cement on walls of reservoirs and dock sides. While the greater part of this solvent action was believed to be due to dissolved carbon dioxide in the water, part of it at least was attributed to the action of bacteria contained in a brown slime which covered the walls.