Abstract

Durability is one of the key functional properties of natural stones used in architecture and construction. This property is often extrapolated from index physical properties, based on the results of empirical durability tests and/or from the in situ long-term experience. In this recent study, we tested how the data obtained from common rock mechanical tests can be employed as durability estimators. Along with standard rock mechanical parameters (strength, modulus of elasticity), the stress-strain curves were evaluated to obtain crack closure, crack initiation, and crack damage thresholds of several varieties of sandstones commonly used in architectural and sculptural projects. The modulus of resilience and modulus of toughness, computed from the respective parts of the stress-strain curves, proved to have a significant correlation between resistance to weathering in the accelerated laboratory tests and/or to the known field performances of the tested stone varieties.

1 Introduction

Durability is the key functional property of natural stones used in construction and for the manufacturing of architectural elements and/or sculptures. Durability is often viewed as the resistance against various weathering processes (Frohnsdorff & Masters 1980 and Lewry & Crewdson 1994); however, in a broader sense, it covers technical serviceability. Durability is not a fundamental property, it can more likely be considered to be the long-term manifestation of repeated interactions between natural stone and the surrounding environment (Soronis 1992). The time period, during which the stone can be claimed durable, is equal to its macro- and microstructural stability, which secures fulfilments of its structural and aesthetic functions (Sims 1991 and Andrew 2002).

Assessment of durability is generally possible through one of five major approaches:

  1. practical experience,

  2. accelerated laboratory durability test,

  3. complex environmental testing,

  4. exposure site testing, and

  5. extrapolation from other physical properties (Prikryl 2013 and references therein). Each of these approaches has certain advantages and drawbacks. Although practical experience provides the most reliable results, it is highly impractical in terms of sufficient amounts of experimental materials (extensive sampling is often prohibited from heritage structures), time, and knowledge of all past weathering processes that have resulted in the observed decay pattern(s). Accelerated laboratory tests are commonly used for durability assessment because rapid standardized test procedures allow for comparisons between various stone types and/or weathering actions (e.g., freezing/thawing, wetting/drying, salt crystallization, etc.). However, several drawbacks influence their real explanatory power: the size and geometry of test specimens are far from the dimensions and geometries of the real artefacts or structural elements. Consequently, the intensity of damage might not be absolutely comparable. Oversimplification of the weathering process presents another negative factor of accelerated tests, which generally simulate only single weathering action; while during real in situ weathering, numerous actions interact. Generally speaking, most of the accelerated durability tests and post-test evaluation of variable physical properties probably rely on a partly erroneous paradigm.

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