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Research Articles

Impact of the Kinetics of Salt Crystallization on Stone Damage During Rewetting/Drying and Humidity Cycling

[+] Author and Article Information
Julie Desarnaud

Laboratoire Navier (umr8205),
6-8 ave Blaise Pascal,
77455 Marne la Vallée cedex, France;
Van der Waals-Zeeman Instituut,
University of Amsterdam, Science Park 904,
1098XH Amsterdam, Netherlands

François Bertrand

Laboratoire Navier (umr8205),
6-8 ave Blaise Pascal,
77455 Marne la Vallée cedex, France

Noushine Shahidzadeh-Bonn

Van der Waals-Zeeman Instituut,
University of Amsterdam, Science Park 904,
1098XH Amsterdam, Netherlands
e-mail: N.Shahidzadeh@uva.nl

1Corresponding author.

Manuscript received November 1, 2011; final manuscript received April 3, 2012; accepted manuscript posted October 25, 2012; published online February 7, 2013. Assoc. Editor: Younane Abousleiman.

J. Appl. Mech 80(2), 020911 (Feb 07, 2013) (7 pages) Paper No: JAM-11-1406; doi: 10.1115/1.4007924 History: Received November 01, 2011; Revised April 03, 2012

In this study, we show that the key to understand why the same salt can cause damage in some conditions and not in others is the kinetics of crystallization. We present experiments assessing the impact of the recrystallization dynamics of sodium sulfate on damage observed in sandstone after repeated cycles of rewetting/drying and humidification/drying. Macroscopic and microscopic scale experiments using magnetic resonance imaging and phase contrast microscopy demonstrate that sodium sulfate that has both hydrated and anhydrous phases can lead to severe damage in sandstone during rewetting/drying cycles, but not during humidity cycling. During rewetting (a rapid process) in regions (pores) that are highly concentrated in salt, anhydrous microcrystals dissolve only partially, giving rise to a heterogeneous salt solution that is supersaturated with respect to the hydrated phase. The remaining anhydrous crystals then act as seeds for the formation of large amounts of hydrated crystals, creating grape-like structures that expand rapidly. These clusters can generate stresses larger than the tensile strength of the stone, leading to damage. On the other hand, with humidification (a slow process) and after complete deliquescence of salt crystals, the homogeneous sodium sulfate solution can reach high concentrations during evaporation without any nucleation, favoring the formation of isolated anhydrous crystals (thenardite). The crystallization of the anhydrous salt generates only very small stresses compared to the hydrated clusters and therefore causes hardly any damage to the stone.

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References

Figures

Grahic Jump Location
Fig. 4

Rewetting/drying. Left: formation of clusters due to the growth of hydrated crystals on the remaining thenardite microcrystallites. Right: granular disintegration of the salt-contaminated sandstone (stone 2).

Grahic Jump Location
Fig. 3

Evaporation (T = 21 °C, RH ∼ 48% ± 2%) of sodium sulfate solution (S ∼ 1.1) in square microcapillaries (Cycle 1). (a) Slow growth of hydrated crystals; (b) formation of thenardite microcrystallites (dehydration) at the end of drying.

Grahic Jump Location
Fig. 2

Percentage of damage in sandstones after the second cycle (rewetting with water/drying) as a function of the supersaturation of the salt solutions used in the first cycle of wetting with salt solution followed by drying

Grahic Jump Location
Fig. 1

(a) MRI saturation profiles of the remaining water in sandstone (2.5 × 2.5 × 4 cm) during drying in C1. (b) Discrepancy between the rate of evaporation calculated by MRI profiles and weight measurements done simultaneously on the same sample due to the formation of hydrated crystals.

Grahic Jump Location
Fig. 5

Samples in contact with saturated water vapor. (a) Water uptake (weight measurements) after one month of salt-contaminated sandstones as a function of the quantity of salt in the sample. (b) Sample containing 0.25 g salt: the rate of water uptake as function of time obtained from MRI and weight measurements.

Grahic Jump Location
Fig. 6

(a) Formation of independent hydrated microcrystals during the humidification of the thenardite in microcapillary of Fig. 3(b); the liquid meniscus (in black) formed at the entrance of the capillary is visible at the right of the image. (b) Growth rate of hydrated independent crystals during humidification.

Grahic Jump Location
Fig. 7

(a) MRI saturation profiles during the second cycle of drying, after complete deliquescence. (b) Evaporation rates calculated from the MRI measurements (open symbol) and weight measurements (filled symbols). The good concordance between MRI and weight measurements reveals the formation of anhydrous crystals in the sample.

Grahic Jump Location
Fig. 8

Crystallization of thenardite (anhydrous phase) during drying of the sodium sulfate solution obtained after complete deliquescence (a) just before the nucleation and growth, (b) growth from the interface of phase III, (c) transformation to phase V (rhombohedral shape)

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