Richard Přikryl

Some microstructural aspects of strength variation in rocks

The experimental study of rock strength revealed a remarkable mechanical variation in closely related rocks. This variation is explained through a quantitative analysis of microstructures. The oriented dry rock specimens were loaded at a constant stress rate and the uniaxial compressive strength with deformation, was recorded together. Microstructures were analysed in thin sections using petrographic image analysis, making it possible to determine size, shape and the shape-preferred orientation of individual grains, grain size distribution and modal composition. The typical grain size has been found to be the main microstructural factor controlling strength variation in groups of rocks which are closely related mineralogically. The increase of strength anisotropy is connected with an increasing degree of shape-preferred orientation of rock-forming minerals.

Building Stone Decay: From Diagnosis to Conservation

Stone buildings and monuments from the cultural centres of many of the worlds urban areas. Frequently these areas are prone to high levels of atmospheric pollution that promote a variety of aggressive stone decay processes. Because of this, stone decay is now widely recognized as a severe threat to much of our cultural heritage. If this threat is to be successfully addressed it is essential that the symptoms of decay are clearly identified, that appropriate stone properties are accurately characterized and that decay processes are precisely identified. It is undoubtedly the case that successful conservation has to be underpinned by a comprehensive understanding of the causes of decay and the factors that control them. The accomplishment of these demanding goals requires an interdisciplinary approach based on co-operation between geologists, environmental scientists, chemists, material scientists, civil engineers, restorers and architects. In pursuit of this collaboration, this volume aims to strengthen the knowledge base dealing with the causes, consequences, prevention and solution of stone decay problems.

Diagnosing decay: the value of medical analogy in understanding the weathering of building stones

Abstract This paper represents the first element of the introduction to this volume, and as such investigates its principal underlying rationale; namely the importance of accurate diagnosis of stone decay in the formulation of effective conservation strategies. It does this by exploring ways in which perceived similarities between stone decay and human disease have influenced attitudes towards conservation, and how refinements within medical diagnostic strategies can inform future condition assessments of building stones. In doing so, it identifies the importance of looking beyond obvious symptoms to the isolation of the fundamental causes of decay and the factors that control them. These controls are strongly conditioned by accumulated stresses within the stonework. In many buildings these are the product of a complex history involving exposure to a variety of environmental conditions and successive human intervention. Only by understanding these memory effects is it possible to explain current decay phenomena, attempt any prediction of future behaviour or recommend appropriate intervention. The concept of appropriateness is further developed through an examination of the TNM (Tumours, Nodes and Metastases) Staging System for cancer diagnosis. This holistic scheme embodies a progressive approach to diagnosis that begins with a clinical assessment based on how the patient presents, and leads on to more detailed pathological investigations involving sampling, testing and analysis. The scheme also requires an assessment of the certainty of the diagnosis and proposed treatments must be viewed in terms of a cost benefit analysis. A modified version of this staging system has already been developed for use in the physical assessment of buildings. It is suggested that the next stage in its development, and that of any other condition assessment procedure that deals solely with the fabric of a building, is the inclusion of a value-based appraisal of its cultural significance.

Experimental weathering of marlstone from Přednı́ Kopanina (Czech Republic)—historical building stone of Prague

Abstract Romanesque builders favoured marlstones because of their easy workability. Unfortunately, this rock rapidly deteriorates when exposed to the external atmospheric conditions. Artificial weathering experiments were conducted on marlstone from Předni Kopanina quarry near Prague (Czech Republic) in order to determine: (A) which weathering factor presents major danger to this rock type, and (B) which of the test methods provide the most reliable measure of the intensity of rock disintegration. Rock specimens prepared from fresh rock were subjected to standardized freeze–thaw cycles and salt crystallization tests, and to the accelerated weathering in climatic chamber using SO 2 and a combination of freeze–thaw and SO 2 cycles. Stone properties were evaluated by non-destructive and destructive techniques including ultrasonic velocity measurements, determination of water uptake by capillary action, mechanical testing, detailed porosimetric analysis and microscopic study.

Direct measurement of 3D elastic anisotropy on rocks from the Ivrea zone (Southern Alps, NW Italy)

Abstract Lower crustal and upper mantle rocks exposed at the earths surface present direct possibility to measure their physical properties that must be, in other cases, interpreted using indirect methods. The results of these direct measurements can be then used for the corrections of models based on the indirect data. Elastic properties are among the most important parameters studied in geophysics and employed in many fields of earth sciences. In laboratory, dynamic elastic properties are commonly tested in three mutually perpendicular directions. The spatial distribution of P- and S-wave velocities are then computed using textural data, modal composition, density and elastic constants. During such computation, it is virtually impossible to involve all microfabric parameters like different types of microcracking, micropores, mineral alteration or quality of grain boundaries. In this study, complete 3D ultrasonic transmission of spherical samples in 132 independent directions at several levels of confining pressure up to 400 MPa has been employed for study of selected mafic and ultrabasic rocks sampled in and nearby Balmuccia ultrabasic massif (Ivrea zone, Southern Alps, NW Italy). This method revealed large directional variance of maximum P-wave velocity and different symmetries (orthorhombic vs. transversal isotropic) of elastic waves 3D distribution that has not been recorded on these rocks before. Moreover, one dunite sample exhibits P-wave velocity approaching to that of olivine single crystal being interpreted as influence of CPO.

Elastic Parameters of West Bohemian Granites under Hydrostatic Pressure

The West Bohemian seismoactive region is situated near the contact of the Moldanubian, Bohemian and Saxothuringian units in which a large volume is occupied by granitoid massifs. The spatial distribution of P-wave velocities and the rock fabric of five representative samples from these massifs were studied. The P-wave velocities were measured on spherical samples in 132 independent directions under hydrostatic pressure up to 400 MPa, using the pulse-transmission method. The pressure of 400 MPa corresponds to a depth of about 15 km in the area under study. The changes of P-wave velocity were correlated with the preferred orientations of the main rock fabric elements, i.e., rock forming minerals and microcracks. The values of the P-wave velocity from laboratory measurements on granite samples fit the velocity model used by seismologists in the West Bohemian seismoactive region.

Understanding the Earth scientist's role in the pre-restoration research of monuments: an overview

Abstract To understand the role of the earth scientist in the pre-restoration research of stone monuments, it is necessary to summarize the tasks that he/she can fulfil. Pre-restoration research into building materials is generally conducted to provide information on types of material, their damage and repair. Although the technologist and restorer must manage the practical aspects of repair, the earth scientist can make a significant contribution in terms of material research. First, he or she can answer questions on the nature of the stone(s) used, their provenance (location of the quarry), and their weathering characteristics in terms of the deterioration of physical and mechanical properties and destruction of rock fabric. Second, the earth scientist can research the physical and mechanical properties of new stone proposed for as a replacement for decayed stonework, including recommendations for alternative materials where stone from the original quarry is no longer available.

Microstructures and physical properties of “backfill” clays: comparison of residual and sedimentary montmorillonite clays

Hydrophysical behaviour of a backfill material produced as a mixture of montmorillonite-rich clays (fine-grained fraction) and ballast material (coarse-grained fraction) is studied. Two different genetic types of clays are evaluated—bentonite, representing the residual weathering type, and sedimentary montmorillonite-rich clay. Hydrophysical properties (liquid and plastic limits, permeability and swelling pressure) were determined for mixtures of mixing ratios from 0% to 100% by weight. The microstructural study focused mainly on pore space and specific surface determination that were employed for the interpretation of the hydrophysical properties. The most favourable results were obtained for activated Ca-bentonite but sedimentary montmorillonite-rich clays yielded good quality backfilling mixtures as well. The transition from fine to coarse-fraction dominated behaviour was established for mixtures containing about 20% of clayey admixture.

Durability assessment of natural stone

Durability is one of the most significant aspects of the behaviours of natural stone in the real environment. As it is not a fundamental property, it cannot be measured in situ or by using any simple laboratory test. Therefore, durability is assessed by using several approaches such as (1) accelerated laboratory durability tests (freeze–thaw cycling, wetting–drying, salt crystallization resistance), (2) complex environmental testing in test cabinets, and (3) exposure site testing. In this review paper, the advantages and drawbacks of these approaches are discussed and compared with other approaches such as practical experience and/or indirect assessments of selected physical properties, which have been found empirically to have a strong influence upon the durability of materials. Based on current information, accelerated laboratory durability tests (although the most widespread type of tests) exhibit serious limitations in terms of oversimplified test methods. Complex environmental testing provides more reliable results, but is less accessible for common testing owing to experiments’ long duration and high operational costs. Similar drawbacks are applicable for in situ testing. Practical experience combines the value of the material’s exposure in real-life conditions and the duration of interactions; but it is highly impractical when the sampling of experimental materials is required. Extrapolation of the durability of natural stone from the results of some common laboratory tests (porosimetry approach for complex evaluation of pore space; mechanical properties under various degrees of saturation; response of a natural stone exposed to water (i.e. swelling behaviour)) seems to be an appropriate alternative to previous approaches.

Geological features, technological characterization and weathering phenomena of the Miocene Bryozoan and Lithothamnion limestones (central-southern Italy)

Bryozoan and Lithothamnion limestones (BLL) from centralsouthern Italy, commercially known as Perlato Royal Coreno, were used for a long time in the monumental architecture of the Campania and Lazio regions. In this paper, new mineralogical-petrographical and engineering geological data about BLL are reported and the relations between the lithofacial and technical features of this stone are investigated. A field survey of the main limestone outcrops allowed a lithostratigraphic reconstruction of this formation to be drawn and the eight main lithotypes presently used as dimension stones to be recognized. Mineralogical and petrographical characterization was performed by means of X-ray powder diffraction and optical microscopy observation of thin sections (under transmitted, UV-reflected light and cold cathodoluminescence). Petrophysical characterization enabled to compare some engineering-geological properties and to evaluate the influences of rock fabric, chemical composition, fractures and stylolithes on the technical features of the stone. Ageing tests were also performed. Finally the main weathering phenomena affecting the stone were recognised through a detailed study on the facades of the bell tower of the Santa Chiara monastery in Naples