Gioacchino Francesco Andriani

Physical properties and textural parameters of calcarenitic rocks: qualitative and quantitative evaluations

Abstract Petrophysical and mechanical properties of sedimentary rocks are influenced by size, shape, and packing of grains, porosity, cement and matrix content, all controlled strongly by depositional fabric and postdepositional processes. This paper presents a study on the textural characteristics of soft and porous calcarenites and the main methods to determine petrophysical data. The examined calcarenites, sampled from three quarry districts located in Apulia (southeastern Italy), are fine-grained and coarse-grained grainstones (“A” and “D”) and medium-grained packstones (“B”) belonging to a plio-pleistocenic formation (Calcarenite di Gravina) outcropping in the whole region. The study involved, particularly, textural analysis on thin sections using optical petrographic microscopy and evaluation of total and effective porosity by means of standard geotechnical laboratory tests, mercury intrusion porosimetry and image analysis. Grain size frequency distribution was also carried out by traditional sieve and sedimentation analysis on disaggregated materials and image analysis. Computer analysis of digital images was performed on photomicrographs applying the methods of quantitative stereology to pore size and grain size distributions. A comparison between results showed that each technique used has its limitations linked to the textural characteristics, primarily geometry and topology of the pore network, granulometry, grain shape and packing of calcarenites.

The effects of wetting and drying, and marine salt crystallization on calcarenite rocks used as building material in historic monuments

Abstract The results of a study of the effect of marine salt crystallization on the physical and mechanical properties of Plio-Pleistocene calcarenites cropping out in southern Italy are presented here. Owing to their workability, aesthetic appeal and availability, the calcarenites have been widely used as building stones in many historic monuments. Samples of medium-grained packstones and fine-grained packstones-wackestones were prepared for the salt crystallization test defined by EN 12370, using sea water instead of a 14% solution of Na2SO4 · 10H2O. To determine the effect of imbibition alone on the performance of the calcarenites, the same procedure was followed with distilled water without soluble salts. Microfabric analysis, evaluation of index parameters and grain-size distribution were carried out as well. Particular attention was given to pore-size distribution by mercury intrusion porosimetry (MIP), loss of weight and uniaxial compressive strength determined before and after the tests, and after every five cycles of complete immersion in sea water and distilled water. The results suggest that detailed information on fabric and pore network are indispensable to predicting the weatherability of rocks. Crystallization tests that involve the complete immersion of the samples in a saline solution are not effective for an understanding of the real importance of salt damage on soft and porous calcarenites owing to a significant incidence of imbibition in accelerating deterioration rates and in influencing patterns and intensity of weathering.

Petrophysical and mechanical properties of soft and porous building rocks used in Apulian monuments (south Italy)

Abstract This paper brings a comprehensive review of the main petrophysical and mechanical properties of calcarenite rocks used from time immemorial in Apulia (south Italy), with load-bearing and decorative functions both in constructions of specific historic and architectonic interest and in more common buildings. These soft and porous rocks show a reduced ability to maintain their characteristics of strength, appearance and resistance to decay over a considerable period of time. Even more than other sedimentary rocks, calcarenites belonging to the same formation can change considerably in terms of physical properties and mechanical behaviour due to the complex spatial arrangement of facies strongly conditioned by depositional fabric and diagenetic processes. A number of calcarenite varieties belonging to the Calcarenite di Gravina Fm. and Pietra Leccese Fm. was selected from different parts of Apulia and characterized according to petrographical, physical and mechanical properties. These included porosity, pore size distribution, density, water absorption, degree of saturation, permeability, thermal properties as well as compressive strength and flexural strength. Particular attention was given to the relationships between rock fabric features and physico-mechanical behaviour of the calcarenites. In addition, a comparison of data for the examined varieties was also discussed. A classification of the Apulian calcarenites based on rock fabric features and uniaxial compressive strength was proposed. Critical observations regarding the durability of the Apulian calcarenites were made, taking into account other data from literature.

Evaluating the impact of quarrying on karst aquifers of Salento (southern Italy)

Abstract This paper describes a case study in the Salento karst (Apulia, southern Italy) in a site that has been intensively used to quarry limestones in the last 30 years. After quarrying activity had stopped, the site was transformed into legal and illegal landfills where solid and liquid wastes have been repeatedly dumped, with serious consequences for the groundwater resources. In this paper, through a geological, petrographical and hydrogeological approach, we attempt to assess the consequences of the anthropogenic activities on the local hydrogeology, with particular regard to the surficial aquifer that is contained in the Plio-Quaternary calcarenites cropping out in the area. Application of some well-known methods to assess the vulnerability of aquifer systems to contamination by human activities (DRASTIC, SINTACS, LeGrand and GOD) highlights the limits of such an approach in karst environment, and the necessity to include in the methods data strictly related to the peculiarity of karst. This is further evidenced by application of the EPIK method, specifically designed for karst areas. The final part of the paper focuses on the need of a thorough understanding of the hydrogeological setting for a better management and policy action of karst environments.

On the applicability of geomechanical models for carbonate rock masses interested by karst processes

Rock mass classification and geomechanical models have a particular importance for carbonate rocks, due to their peculiar fabric, variability of the main features, and scarce availability of experimental data. Carbonates are particularly sensitive to syn-depositional and post-depositional diagenesis, including dissolution and karstification processes, cementation, recrystallisation, dolomitisation and replacement by other minerals. At the same time, as most of sedimentary rocks, they are typically stratified, laminated, folded, faulted and fractured. The strength and deformability of carbonate rock masses are, therefore, significantly affected by the discontinuities, as well as by their pattern and orientation with respect to the in situ stresses. Further, discontinuities generally cause a distribution of stresses in the rock mass remarkably different from those determined by the classical elastic or elasto-plastic theories for homogeneous continua. Goal of this work is the description of the difficulties in elaborating geomechanical models to depict the stress–strain behavior of karstified carbonate rock masses. Due to such difficulties, a high degree of uncertainty is also present in the selection of the most proper approach, the discontinuum one or the equivalent continuum, and in the numerical model to be used within a specific engineering application as well. The high uncertainty might cause wrong assessments as concerns the geological hazards, the design costs, and the most proper remediation works. Even though recent developments in the application of numerical modeling methods allow to simulate quite well several types of jointed rock masses, as concerns carbonate rock masses many problems in representing their complex geometry in the simulation models still remain, due to peculiarity of the structural elements, and the presence of karst features. In the common practice, the improper use of the geomechanical models comes from a superficial geological study, or from the lack of reliable geological and structural data that, as a consequence, bring to erroneous evaluations of the influence of the geological-structural features on the in situ stress state and the stress–strain rock mass behavior.

Ultrasonic wave velocity measurements for detecting decay in carbonate rocks

Ultrasonic testing is a non-destructive technique commonly employed for assessing indirectly some geomechanical parameters of natural building stones. Pulse wave propagation in rock materials depends not only on physical properties, e.g. density, elasticity, porosity and water content, but also on fabric elements and their arrangements, spatial distributions and preferred orientations. In contrast, ultrasonic velocity can reflect the state of conservation of stone by comparing data from fresh material with those obtained from tests made on decayed material. The ‘Avorio’ limestone is a valuable building and ornamental material, quarried in the Trani stone basin (Apulia, southern Italy), which is very popular in Italy and abroad where it is used in modern and historic buildings. The stone response to decay processes is not fully understood simply because this material has not yet been well studied. To better understand how durable this material is in terms of physical resistance to change with respect to salt and thermal deterioration mechanisms, selected samples of the ‘Avorio’ limestone were submitted to artificial ageing processes by thermal stresses and by stresses due to salt crystallization, performed independently. The artificial ageing processes involved thermal cycles at temperatures between 200 and 600°C, based on an experimental procedure, and a standardized salt crystallization test in sodium sulphate solution. Repeated measurements of pulse velocity, before, during and after every accelerated ageing cycle, were compared with mass loss and porosity changes, the latter by water imbibition and capillarity testing. Very statistically significant relationships between physical response and rates and patterns of the stone decay were illustrated. The experimental results showed that the ultrasonic pulse velocity decreases as deterioration of the stone increases under accelerated ageing: a strong negative correlation exists between P-wave velocity and porosity. This study confirmed that ultrasonic pulse velocity is a good indicator of damage for carbonate stones, particularly for varieties without clear anisotropies, in terms of structure and texture.

On the technical properties of the Carovigno stone from Apulia (Italy): physical characterization and decay effects by means of experimental ageing tests

Apulia (southern Italy) is typified by widespread outcrops of rocks exploited in the last centuries in historical architectures and religious constructions, as building and decorative stone. Today, as in the past, these stones represent an important source for region economy and prestige, due to their uses for modern works, restoration of local medieval churches and also exporting abroad. Among these, a noteworthy and still poorly known material is the Carovigno stone. In this paper, firstly an overall view on the, mineralogical and petrophysical features of the stone was reached through a multianalytical approach based on several investigation procedures and techniques, including ultrasonic test, X-ray diffractometry, scanning electron microscopy, optical microscopy, mercury intrusion porosimetry. In order to simulate decay phenomena, the Carovigno stone samples were processed to three different ageing tests: cycles of thermal treatments at different high temperatures, cycles of heating–cooling and cycles of exposure to decahydrate sodium sulphate and sodium chloride saline solutions. During and after each ageing processes, mineralogical transformations and petrophysical changes were evaluated. Results suggested that the Carovigno stone is a fine-grained calcarenite, pure or nearly pure, characterized by high porosity and, consequently, very notable thermal stress resistance. Conversely, the type and amount of porosity causes stone predisposition to salt crystallization decay.