The Role of Calcite Dissolution and Halite Thermal Expansion as Secondary Salt Weathering Mechanisms of Calcite-Bearing Rocks in Marine Environments

This research focuses on the analysis of the influence of two secondary salt weathering processes on the durability of rocks exposed to marine environments: chemical dissolution of rock forming minerals and differential thermal expansion between halite and the hosting rock. These processes are scarcely treated in research compared to salt crystallisation. The methodology followed in this paper includes both in situ rock weathering monitoring and laboratory simulations. Four different calcite-bearing rocks (a marble, a microcrystalline limestone and two different calcarenites) were exposed during a year to a marine semiarid environment. Exposed samples show grain detachment, crystal edge corrosion, halite efflorescences and microfissuring. Crystal edge corrosion was also observed after the laboratory simulation during a brine immersion test. Calcite chemical dissolution causes a negligible porosity increase in all the studied rocks, but a significant modification of their pore size distribution. Laboratory simulations also demonstrate the deterioration of salt-saturated rocks during thermal cycles in climatic cabinet. Sharp differences between the linear thermal expansion of both a pure halite crystal and the different studied rocks justify the registered weight loss during the thermal cycles. The feedback between the chemical dissolution and differential thermal expansion, and the salt crystallisation of halite, contribute actively to the rock decay in marine environments.

The effects of climate change on the Pleistocene rock art of Sulawesi

The equatorial tropics house some of the earliest rock art yet known, and it is weathering at an alarming rate. Here we present evidence for haloclasty (salt crystallisation) from Pleistocene-aged rock art panels at 11 sites in the Maros-Pangkep limestone karsts of southern Sulawesi. We show how quickly rock art panels have degraded in recent decades, contending that climate-catalysed salt efflorescence is responsible for increasing exfoliation of the limestone cave surfaces that house the ~ 45 to 20-thousand-year-old paintings. These artworks are located in the world’s most atmospherically dynamic region, the Australasian monsoon domain. The rising frequency and severity of El Niño-induced droughts from anthropogenic climate change (that is, higher ambient temperatures and more consecutive dry days), combined with seasonal moisture injected via monsoonal rains retained as standing water in the rice fields and aquaculture ponds of the region, increasingly provide ideal conditions for evaporation and haloclasty, accelerating rock art deterioration.

Influence of wall composition on moisture related degradation of the wall surfaces in Hagia Sophia, Istanbul

Over the past 10 years, our research team has holistically studied the environmental aspects of the conservation and restoration of the Hagia Sophia, which is suffering from severe degradation of its wall paintings, including the exfoliation of wall paintings and inner finishing materials, mainly due to salt crystallisation. In the present study, we investigated the influence of environmental factors and wall composition on the hygrothermal behaviour in the structure, such as moisture accumulation and evaporation within the walls, which significantly affect salt crystallisation. The differences in distribution of high moisture content at second cornice are depending on the azimuth, and the high correlation between high moisture content and deterioration severity is significant. A two-dimensional numerical model of the simultaneous transfer of heat and moisture considering the measured material physical properties and wall composition of the exedra wall is developed to quantitatively investigate the influence of environmental factors on moisture accumulation. Numerical results show that infiltrated rainwater tends to accumulate because the original builders used connection mortar, which has a much larger moisture diffusivity than that of modern mortar, and the accumulated water at the bottom of the wall is difficult to drain owing to the shape of the wall. In the northwest exedra, the influence of wind-driven rain on water accumulation is similar to that of runoff rainwater from the upper roofs, which probably causes deterioration over a wide area. In addition, the effect of the deterioration suppression measure by the re-covering of the outer surfaces of the west wall in 2013 is verified, and an appropriate suppression measure against water permeation is examined using a numerical model.

Direct observation of pore collapse and tensile stress generation on pore walls due to salt crystallization in a PDMS channel

In contrast with the classical picture where the generation of stress on pore walls due to salt crystallisation is analysed by a compressive stress using the concept of crystallization pressure, we report a mechanism leading to the generation of a local tensile stress.

Spatially isolating salt crystallisation from water evaporation for continuous solar steam generation and salt harvesting

Efficient solar steam generation and concurrent salt harvesting from saline water were achieved with both continuous operation and long-term stability.