K. Torfs

Origin and growth of weathering crusts on ancient marbles in industrial atmosphere

Abstract The origin and growth of weathering crusts on the ancient marbles of ruins of the Sanctuary of Demeter in the industrial atmosphere of Eleusis in Greece have been investigated. A systematic mineralogical, petrographical and chemical examination of weathered stones and crusts was performed, both in situ and in the lab, on samples taken from different parts of the monument in relation to the surface characteristics as well as to the exposure to rain, sea-salt spray and wet and dry deposition of airborne pollutants and dust. In particular, the various material–environment interactions take place, are characterized by (a) disintegrated “washed-out” surfaces, where products are taken away through dissolution, (b) rusty yellow patinas rich in Fe and Cu, (c) firmly attached black crusts in contact with percolating water, where recrystallized calcite shields amorphous deposits rich in S, Si, Fe and carbonaceous particles, (d) black loose deposits in the water sheltered areas, consisting mainly of gypsum and fly ash particles and (e) cementitious crusts, coating and pitting the horizontal surfaces. Moreover, an interconnected evolution of various physicochemical processes is shown, characteristic of the origin and growth of various crusts, which are formed and classified accordingly.

Chemical relations between atmospheric aerosols, deposition and stone decay layers on historic buildings at the mediterranean coast

To evaluate the effects of the environment on weathering of historical buildings in the Mediterranean Basin, an elaborate study has been carried out at four monuments, with specific interest directed on the action of air pollution and marine salts. The composition of the atmosphere around the monuments has been investigated by monitoring the aerosols and the total deposition. These results are combined with the stone decay phenomena to interpret the deterioration at the respective monuments. In Eleusis, Greece, a highly industrialized area, high concentrations of heavy metals and sulphate are found in the aerosols and deposition and in the decay layers of the stone, while the marine influence is obscured, in spite of its location close to the sea. In Malta and in Cadiz (Spain), the influence of the sea dominates in the stone weathering process. In Bari (Italy), next to the effects of marine aerosols on the stone decay inside and outside the building, high concentrations of sulphate are observed on the outside stones. The aerosols and depositions reflect a relatively small influence of anthropogenic derived elements; this points out the action of gaseous SO2 on the stones.

Effect of stone thickness on run-off water composition and derived damage functions in ambient exposure experiments

Abstract Field-exposure studies have been carried out to study the correlation between environmental conditions and limestone weathering, using analyses of the run-off rain water. Because no short-term correlations between environmental parameters (e.g. daily SO 2 levels) and stone decay (e.t. concomitant Ca 2+ release) have been observed until now for stone slabs with a “standard” thickness of 5 cm, stones of different thicknesses (1 and 5 cm) were exposed in parallel to check the influence of reaction product retention within the stones. It was expected that the thinner stone should retain relatively less. However, no significant differences in released ions were found. Consequently, the absence of correlations between atmospheric conditions and stone decay during short time intervals (e.g. 1 d) does not appear to be due to retention of ions in the stone. Also, it does not appear possible to correlate stone decay solely with the concentration of pollutants in the air, and other parameters have to be included. A damage function has been constructed to explain the Ca 2+ loss for both stone thicknesses as a function of rain input and environmental conditions. For the limestone of 1 cm thickness, the decay can be predicted well.

Accelerated microstructural evolution of a calcium-silicate-hydrate (C-S-H) phase in pozzolanic pastes using fine siliceous sources: Comparison with historic pozzolanic mortars

Traditional pozzolanic mortars such as those from Rhodes, Greece, or Hagia Sophia, Turkey, revealed the presence of a calcium-silicate-hydrate (C-S-H) binding phase. This phase, which is similar to that found in ordinary Portland cement (OPC), is produced under the pozzolanic reaction of slaked lime with fine reactive siliceous sources at temperatures <100 °C. The traditional siliceous sources were replaced by fumed silica or tetraethyl orthosilicate (TEOS). A microstructural analysis revealed an enhanced reaction rate but similar morphologies of the resultant C-S-H phases, confirming that the reaction-limiting factor is the dissolution of the siliceous sources.

Correlation Between Aerosols, Deposits and Weathering Crusts on Ancient Marbles

The structure and physicochemical characteristics of weathered surfaces of marble in industrial environments can be attributed to the interconnected evolution of the processes taking place at the atmospheric environment – marble interface. The present work is an attempt to correlate the aerosols of a heavily polluted atmosphere with the different weathering patterns observed on marble surfaces. Energy Dispersive X-Ray Fluorescence, X-Ray Diffraction, Porosimetry, Atomic Absorption, Atomic Emission Spectrometry, Ion Chromatography, Optical Microscopy and Scanning Electron Microscopy results were used together in principal component and discriminant analysis. These analyses were performed on forty six samples of aerosols and eighteen samples of crusts. Other parameters like orientation of the weathered surface, exposure to rainfall, presence of recrystalised calcite and gypsum were also used. The samples were collected from the archaeological site of the Sanctuary of Demeter, located near Eleusis (west of Athens, Greece), where a great number of industries (mainly metallurgical and chemical) cause several environmental problems. The results provide invaluable information on the nature of marble surface decay. The elements determining the chemical composition of the coarse airborne particles are Ca, Si, S, Br and Cl. The presence of gypsum is strongly related to black crusts or loose deposits. Y, Mn and rain exposure, are correlated with each other and related to black–gray crusts. Ca and Sr are correlated with washed-out surfaces. Finally discriminant analysis is proved to be a powerful tool in prediction of the type of decay that will be occur on a marble surface, given the composition and type of the polluted atmosphere.

DAMAGE FUNCTIONS AND MECHANISM EQUATIONS DERIVED FROM LIMESTONE WEATHERING IN FIELD EXPOSURE

In this article damage functions and mechanism equations areelaborated for Massangis limestone, exposed to ambientatmospheric conditions. Limestone slabs were placed in fivedifferent environments in Belgium and run-off water wascollected for chemical analyses, over a 3 yr period. Toelucidate the weathering mechanism and the relativecontributions of different deleterious factors, calciumconcentrations in run-off water were regressed versus thetotal (wet + dry) deposition of ions onto the stone, gaseousatmospheric pollutant concentrations and meteorological parameters. The data matrix (30 000 analytical results) was interpreted using Multiple Linear Regression (MLR) and PartialLeast Squares Regression (PLS). Mechanism equations and damagefunctions were first established for each of the five studiedsites separately and subsequently pooled regressions were calculated. A damage function is proposed and compared with limestone damage functions found in the literature, after introducing the field data presented in this work into the respective functions. Massangis limestone mass loss is bestpredicted with a PLS model. Rainwater volume is the most decisivefactor in causing mass loss at all sites, and sulphate andbicarbonate are the most important weathering products.Models established using MLR result in less reliablepredictions of mass loss compared to PLS.

Atmospheric deposition as decay factor for the Demeter sanctuary ruins in the industrial atmosphere of Eleusis, Greece

The action of air pollution and environmental conditions on the weathering of historical monuments has been investigated for the site of the Demeter Sanctuary (1500 BC) in Eleusis, Greece. Total deposition and aerosols were analysed in relation to the concentration of elements in the various types of weathered stone crusts. The objective of the study was the evaluation of the origin of the elements and ions determined in aerosols and total deposition and to relate these to possible sources (soil, underlying rock, marine spray and anthropogenic activities) using enrichment factors.