Abstract
The decay rates of building stones and, the processes leading to their deterioration is governed by intrinsic properties such as texture, mineralogy, porosity and pore size distribution, along with other extrinsic factors related to the climate and anthropogenic activities. For urban cities such as London, the influence of extrinsic factors like temperature and rainfall, as well as the concentrations of air pollutants, such as sulphur and nitrogen oxides, along with the emissions of carbonaceous aerosols, can be particularly significant. While considering the long-term preservation of building stones used in various heritage sites in the city, it is imperative to consider how the stone could be affected by the changing air pollutant concentrations, superimposed on the effects of climate change in the region, including rising average annual temperature and precipitation with a hotter, drier summer and, warmer, wetter winter months. This paper deals with the intrinsic rock properties of the common building stones of London, including limestone, marble, granite, sandstone, slate, flint as well as bricks, building on known characteristics including strength and durability that determine how and where they are placed in a building structure. The study reviews how these stones decay due to different processes such as salt weathering in sandstone, microcracking of quartz with kaolinisation of K-feldspar and biotite in granite and dissolution of calcite and dolomite, followed by precipitation of sulphate minerals in the carbonate rocks of limestone and marble. In the urban environment of London, with progressive build up in the concentration of atmospheric nitrogen oxides leading to an increasingly acidic environment and, with predicted climate change, the diverse stone-built heritage will be affected. For example, there can be enhanced carbonate dissolution in limestone with increased annual precipitation. Due to the prolonged wetter winter, any sandstone building stone will also undergo greater damage with a deeper wetting front. On the other hand, due to predicted wetter and warmer winter months, microcracking of any plagioclase in a granite is unlikely, thereby reducing the access of fluid and air pollutants to the Ca-rich core of the zoned crystals limiting the process of sericitisation. Management of the building stones in London should include routine expert visual inspection for signs of deterioration, along with mineralogical and compositional analyses and assessment of any recession rate.
Highlights
IntroductionThe heritage buildings in any city are important as landmarks, creating a sense of identity, integrated with local history and values, often attesting to the geological substrate on which they stand
The heritage buildings in any city are important as landmarks, creating a sense of identity, integrated with local history and values, often attesting to the geological substrate on which they stand.While globally, modern buildings are predominantly composed of concrete, the building stones of the heritage sites are both compositionally and structurally distinct
In London, considering the effect of climate change (Figure 1) with predicted wetter winter months and higher annual precipitation, ion diffusion may become more pronounced as a mechanism of salt transportation and the salts are likely to stay in solution longer [63]
Summary
The heritage buildings in any city are important as landmarks, creating a sense of identity, integrated with local history and values, often attesting to the geological substrate on which they stand. The building stones undergo decay affecting their structural integrity, external fabric and the internal environment as a consequence of the natural patterns of rock weathering depending on their intrinsic properties These are superimposed by additional conditions and factors including the structure of the building and the urban climate. A significant increase and decline in predicted for London during winter and summer, respectively, towards the end of this century. As a city expands and its population grows, and if the summer temperature becomes high with low wind conditions, there could be increased concentration of air pollutants from transport emissions while, the dispersal of the pollutants will be affected by the temperature lapse rate within the planetary boundary layer The traditional pollutants, such as sulphur dioxide and smoke from coal, have decreased since the mid-20th century, with rising traffic related pollutants including nitrogen oxides and particulate matter [15]. Both intrinsic properties of the rocks, as well as the extrinsic attributes such as extreme weather events and pollution, have been considered in tandem to understand any decay of the building stones to the alteration-inducing factors
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