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- Author or Editor: Ákos Török x
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The Pleistocene travertine of Buda Vár-hegy (Castle Hill) has been studied in subsurface galleries and cellars. Lithological variations, sedimentary features of the travertine and the underlying friable chalky carbonates and calcareous clays were described in the field. Four lithotypes and several microfacies types of travertine have been identified. The stratal pattern of travertine, distribution of lithotypes, the macrofauna, and the presence of microbial sediments suggests that the travertine was deposited in a shallow lake environment. The lake was fed by lukewarm springs from the central part (probably from Szentháromság-tér [Szentháromság Square] area), where the thickest travertine deposits are found. Direct evidence of cascade deposits or terraced tetarata deposits have not been found in the studied sections. The intense cementation and recrystallisation appear in the form of at least four, mostly phreatic, cement generations, including micrite envelopes, thin fibrous rims, thick radiaxial spars and pore occluding mosaics.
Abstract
A fine-grained and a medium-grained oolitic limestone of Miocene age were studied on ashlars of monuments in Budapest. The studied buildings are located in a polluted urban environment. The surface alteration is characterized by the presence of white (thin and thick) and black (laminar and framboidal) weathering crusts. Flaking, scaling and blistering are common crust detachment forms. Crust detachment is followed by rapid surface loss in the form of granular disintegration or of secondary crusts stabilizing the stone surface. Non-destructive in situ mechanical tests such as Schmidt hammer rebound and Duroscope clearly document the presence of thin and thick weathering crusts, and the degradation of underlying fine-and medium-grained limestone. Crust formation is associated with a textural change, since precipitation of pore-occluding calcite and gypsum and reduction of porosity in the crust zone has been recorded. Crust detachment is attributed to the crystallization pressure of air pollution-related gypsum, to freeze/thaw cycles, and to differences in mechanical properties of crust and host rock.
The paper provides information on the mechanical properties of granitic rocks that were subjected to heat. Two types of granitic rocks were tested under laboratory conditions at temperatures of 23 °C, 300 °C and 600 °C. The granitic rock from Bátaapáti (Mórágy Granite) is a pinkish leucocratic monzogranitic type while the second type is grey granite from Mauthausen (Austria). The samples were placed in furnace and temperature raised to 300 °C. Other set of samples were heated to 600 °C. Mechanical tests were performed on non-heated and heated samples and the test results were compared. Heating to 300 °C caused a slight increase in the uniaxial compressive strength and in indirect tensile strength, with reference to the samples kept at 23 °C. A drastic drop in both values was observed when samples were heated to 600 °C. The density of the samples did not show a major change up to 300 °C. On the contrary, a decrease in ultrasonic pulse velocity was observed, with an additional significant loss when samples subjected to 600 °C were compared to the reference samples of 23 °C. This decrease can be related to the initiation of micro-cracks. With increasing temperature the Young modulus of both granites was reduced.
Az Akadémia székházához felhasznált kőzetek
Stones at the palace of the Hungarian Academy of Sciences, Budapest
A cikk a Magyar Tudományos Akadémia Széchenyi István téri székháza ünnepélyes átadásának másfélszáz éves évfordulója alkalmából bemutatja a várostörténeti szempontból is kiemelkedő jelentőségű középület építése során alkalmazott kőanyagokat. Levéltári források és kordokumentumok alapján ismerteti az építkezés legfontosabb eseményeit, az építő- és díszítőkövek beszerzésének, felhasználásának körülményeit, az ehhez kapcsolódó költségeket, majd ezt követően a kőzetek típusait, származási helyét veszi sorra. A székház kőzeteinek kiválasztása a neoreneszánsz ízlés- és formavilágát tükrözi: az épület homlokzata uralkodóan Budapest környéki porózus mészkövekből, forrásvízi mészkőből, lábazata pedig gerecsei vörös mészkőből áll, belsejében a Habsburg Monarchia területéről származó csiszolható mészkövek és márványok láthatók.
The present paper focuses on the re-evaluation of archive engineering geological data of sic core drillings at one of the new metro stations of Budapest (Kálvin square, metro line 4). More than 1000 data of total coring length of more than 210 meters were used for statistical calculations. The data set includes index of plasticity, skewness, void ratio, water content, dry and water saturated bulk density, relative humidity, angle of friction, cohesion and compressive strength. Based on the data set the engineering geological description of sediments was reevaluated, and sand, clay, silt and bentonite-rich horizons were identified. Three new crosssections were prepared. Statistical analyses proved that there is an increase in cohesion and density of clays and silts with depth, indicating the role of consolidation.
The Micro-Deval test method is used for testing of aggregate durability. The present paper focuses on two Hungarian andesites obtained from the quarries of Recsk (Mátra Mountains, Hungary) and of Nógrádkövesd (Cserhát Mountains, Hungary). The aim of this study is to find a simple test method based on the original Micro-Deval test method to assess the long-term durability of aggregates. An additional part of the research was to develop suitable mathematical models that can describe the behavior of the andesite aggregates under continuous abrasive impact. The relevant standard (EN 1097-1:2012) recommends 12,000 rotations to determine the Micro-Deval coefficient required for classification of the aggregates. Within the framework of this research, a modified Micro-Deval test was applied: the number of rotations was increased in several steps and the degree of abrasion was measured afterwards. Regression analyses were used to outline mathematical forms which characterize the dependence between the number of rotations and the degree of abrasion. According to the results, the long-term Micro-Deval tests significantly modify the assessed durability and thus provide information on the long-term abrasive impact. The degree of change depends on the studied material: the ratio of the long-term Micro-Deval coefficients of the two studied andesite types is larger than 3. The regression analyses of the measured Micro-Deval coefficients revealed that quadratic curves are suitable to describe these tendencies for both andesite aggregates.
Abstract
Three types of porous limestone from Sóskút quarry and two limestone types obtained directly from Matthias Church of Budapest (both in Hungary) were used to test the performance of five stone consolidants. The quarry specimens were treated under laboratory conditions by saturation. Three types of silicic acid ester, an aliphatic uretan resin and a polymethyl methacrylate were applied to the stone. Physical parameters such as density, porosity, ultrasonic sound velocity and Duroscope rebound value were measured on untreated and treated samples. The absorption rate of different consolidants was also detected. The physical properties of untreated and treated specimens were compared in order to analyze the performance of the consolidants. Duroscope tests have shown that after consolidation there is an increase in surface strength.
Abstract
Miocene siltstone with variable sand content and bentonitic clay is the most abundant sediments encountered at the metro construction site at Rákóczi Square (Budapest). Core logs, drilling reports and records of laboratory analyses were studied to better understand the local geology and to prepare a database on engineering geologic properties of the materials. Using this database, geologic sections were prepared and geomathematical methods were used to obtain a better correlation of the strata in the area and a reconstruction of the geologic evolution of the area. The samples were divided into five groups based on physical properties. These five parameters allowed the use of multivariate statistical methods as cluster and discriminant analysis. As a result it was possible to identify several types of lithotypes, including two bentonitic clays with substantially different properties, one fat clay, one medium clay and one sandy, lean clay and siltstone group.
Abstract
Porosity and water absorption of different binder/aggregate ratios of repair mortar and porous limestone were studied that were used in many Hungarian monuments. Different types of mortars were analyzed by using mercury intrusion porosimetry (MIP) and the water saturation method (WSM). Test results showed that there was a strong correlation between the absorption mechanism and the porosimetric characteristics. Mechanical properties of the tested mortars were observed earlier. Pore size distribution confirms that the total porosity increases with increasing aggregate content. Natural stones mainly have medium and large pore radii (1–100 μm) while repair mortars, even with increased aggregate ratio, have smaller pore radii (0.01–0.1 μm). The comparison of different data allows us to state that pore characteristics such as pore volume, pore geometry, pore size distribution and network connectivity are the key control factors of stone and mortar deterioration.
