Karsten Tube Research Articles

Degradation in concrete structures due to cyclic loading and its effect on transport processes—Experiments and modeling

According to the objectives of the research group 1498, this paper deals with degradation effects in concrete structures that are caused by cyclic flexural loading. The goal is to determine their influence on the fluid transport processes within the material on the basis of experimental results and numerical simulations. The overall question was, to which extent the ingress of externally supplied alkalis and subsequently an alkali‐silica reaction are affected by such modifications in the microstructure. Degradation in the concrete microstructure is characterized by ultrasonic wave measurements as well as by microscopic crack analysis. Furthermore, experiments on the penetration behavior of water into the investigated materials were performed. The penetration behavior into predamaged concrete microstructures was examined by the classical Karsten tube experiment, nuclear magnetic resonance method, and time domain reflectometry techniques. In order to create an appropriate model of the material's degradation on the water transport, the Darcy law was applied to describe the flow in partially saturated concrete. Material degradation is taken into account by an effective permeability that is dependent on the state of degradation. This effective permeability is obtained by the micromechanical homogenisation of the flow in an Representative Elementary Volume (REV) with distributed ellipsoidal microcracks embedded in a porous medium. The data gained in the microscopic crack analysis is used as input for the micromechanical model. Finite element simulations for unsaturated flow using the micromechanical model were compared with the experimental results showing good qualitative and quantitative agreement.

The influence of structural organization of epilithic and endolithic lichens on limestone weathering

AbstractHyphal penetration, mineral dissolution and neoformation at the lichen–rock interface have been widely characterized by microscopic and spectroscopic studies, and considered as proxies of lichen deterioration of stone substrates. However, these phenomena have not been clearly related to experimental data on physical properties related to stone durability, and the physical consequences of lichen removal from stone surfaces have also been overlooked. In this study, we combine microscopic and spectroscopic characterization of the structural organization of epi‐ and endolithic lichens (Caloplaca marina (Wedd.) Du Rietz, Caloplaca ochracea (Schaer.) Flagey, Bagliettoa baldensis (A.Massal.) Vězda, Porina linearis (Leight.) Zahlbr., Verrucaria nigrescens Pers.) at the interface with limestones of interest for Cultural Heritage (Portland Limestone, Botticino Limestone), with analysis of rock properties (water absorption, surface hardness) relevant for durability, before and after the removal or scraping of lichen thalli. Observations using reflected‐light and electron microscopy, and Raman analyses, showed lichen–limestone stratified interfaces, differing in the presence/absence and depth of lichen anatomical layers (lithocortex, photobiont layer, pervasive and sparse hyphal penetration component) depending on species and lithology. Specific structural organizations of lichen–rock interface were found to be associated with differential patterns of water absorption increase, evaluated by Karsten tube, in comparison with surfaces with microbial biofilms only, even more pronounced after the removal or scraping of the upper structural layers. Equotip measurements on surfaces bearing intact thalli showed lower hardness in comparison with control surfaces. By contrast, after the removal or scraping procedures, Equotip values were similar to or higher than those of controls, suggesting that the increasing open porosity may be related to a biogenic hardening process. Such counterposed patterns of porosity increase and hardening need to be considered when models relating lichen occurrence on limestones and biogeomorphological surface evolution are proposed, and to evaluate the consequences of lichen removal from stone‐built cultural heritage. Copyright © 2017 John Wiley & Sons, Ltd.

Use of zinc stearate to produce highly-hydrophobic adobe materials with extended durability to water and acid-rain

This paper presents a novel solution to increase the durability of adobe materials using zinc stearate at doses ranging from 0.25% to 2.00% w/w. Shrinkage, apparent density and ultrasonic propagation speed measurements were performed on the cured samples. In addition, water absorption and durability features were determined by capillary tests, Karsten tube measurements, immersion in water, hydrochloric acid (5% w/w) and sulphuric acid (5% w/w) solutions. The durability study was complemented by rain erosion and acid-rain erosion tests. The capillary water absorption was comparable to that of hydrophobic cement renders and the acid-rain erosion was negligible in samples containing 1.00–2.00% w/w zinc stearate. Besides, SEM examination confirmed the protective action of zinc stearate in front of acid-rain. To conclude, zinc stearate was found to be was an excellent choice to increase the durability of adobe materials.

Catastrophic Limestone Decay at the Central Sanctuary of Iupiter Dolichenus at Dülük Baba Tepesi in Southern Turkey: Causes and Implications for Future Conservation

Dramatic deterioration of Hellenistic-Roman limestone remains recently excavated at Dülük Baba Tepesi (Southern Turkey) has been observed following the cold, wet winter of 2011/2012. A conceptual model is presented to explain the dramatic deterioration in which case hardening develops and initially strengthens the stone against deterioration, but then makes it more prone to exfoliation and blistering. Data collected using non-destructive techniques (Equotip surface hardness tester and Karsten tube for water uptake) on Fırat and Gaziantep formation limestone time series excavated in 2005, 2007, and 2013 demonstrates the progress of case hardening and deterioration after excavation. In combination with meteorological data from Gaziantep weather station the results are used to test and revise the model taking into account non-linear and threshold effects. Future excavation and conservation efforts should take into account the often-complex interactions between post-excavation case hardening and extreme winter conditions which can cause catastrophic deterioration.

The Role of Application Techniques for High Performance Traditional Renders

Traditional renders based on lime had an aesthetic as well as a protective role for the historic masonry. They were applied in layers in order to ensure good adhesion and cohesion with the substrate but also in order to be functional. The technology of each layer was different in relation to the maximum grain size of the aggregates and the binder/aggregate ratio. Main requirements were the high water vapor permeability, the low water retention in order to avoid salt formation and the capacity of water absorption by capillarity of each layer should increase outwards. As moisture has a detrimental role in the thermal behavior of materials, an effort has been made to record the effect of layering in energy properties. Lime-based renders were tested in relation to their hybrid properties when different application techniques were followed. Two-layer renders with different technological characteristics in each layer were produced. Their behavior, in various deterioration mechanisms such as capillarity, external water uptake (measured by karsten tubes) and water vapor permeability was monitored. It seems that low porosity and adequate permeability is achieved in two-layer renders while the thermal conductivity was effective.

Bentonite as a natural additive for lime and lime–metakaolin mortars used for restoration of adobe buildings

This work estimates the behaviour of mortars based on lime, seeking their application as renders of adobe walls. Mortars with binder:aggregate 1:3 volumetric ratio were prepared as is traditionally used in old buildings in central parts of Portugal.Due to specificity of the support, two clays, natural clay bentonite (5wt.%) and artificial clay metakaolin (20wt.%) were used as additives to lime mortar to prepare 3 types of blended mortars, besides the air lime reference mortar. Mortar prisms 4×4×16cm were analysed to assess mechanical properties and salt resistance. Moreover, the mortars were placed in three ways on old adobes taken from demolished houses and their behaviour was verified by artificial accelerated ageing test. Lastly, mortars were applied on a wall made from traditional adobes, where panels were monitored and trials with adhesion strength and Karsten tubes have been conducted. The results obtained by comparison of the characteristics from all the experimental procedures reveal that mortar containing air lime and 5wt.% of bentonite fulfils in the best way the requirements in its use as render of adobe buildings.

In-situ assessment of physical performance and degradation analysis of rendering walls

The use of in-situ diagnostic techniques can lead to a more accurate evaluation of the performance level of façade claddings. The paper aims to evaluate the advantages of using visual inspection and selected in-situ techniques (infrared thermography, Karsten tubes and moisture meter) for the evaluation of the physical performance of renders and their state of deterioration. The main objective of the study is to propose a methodology for in-situ inspections with a low degree of intrusion for the evaluation of physical in-service performance of renders applied on external walls. Three experimental campaigns were performed and different types of renders were analyzed for several in-service conditions. This work enabled the identification of the various factors that affect the results of the selected in-situ techniques. Furthermore, it was made evident, that there are advantages in the cross-comparison of different results, which in certain situations can complement the visual inspection.

Radiographical investigation of fluid penetration processes in natural stones used in historical buildings

In order to ensure sustainability if historic buildings their technical state has to be inspected on regular basis. Damage assessment has to be preferably carried out using non-destructive methods otherwise damage accumulation may occur during life-cycle of the constructions. According to character of detected damage appropriate intervention measures (i.e. strengthening, consolidation, etc.) have to be then efficiently applied. Among other factors significantly influencing life span of constructions weathering agents (rain, erosion, dissolution, etc.) may cause rapid degradation of mechanical properties.In this paper X-ray radiograhical imaging was used to describe fluid penetration process in porous Maastricht limestone that is commonly used for restoration purposes. The imaging was performed in custom radiography device simulating practical in-situ measurements using microtube device. This device is a modified Karsten tube capable of determining absorbed volume and its speed even on inclined surfaces. However actual fluid penetration process in terms of saturation depth/volume ratio and shape of fluid wave propagating through microstructure is indeterminable using microtube. For this purpose real-time radiography imaging of fluid saturation process was performed to investigate behaviour of fluid in the material. Furthermore X-ray computed microtomography was performed to develop finite element model for simulation of fluid flow in the porous microstructure.Using the real-time imaging relations between penetration speed, penetration depth and penetrated volume were assessed. These results can be used to validate results from microtube measurements including nonlinear regions present when semi-spherical wave propagates through the material. Using a set of finite element simulations of the microtube experiment fluid velocity distribution in the material together with effective Darcy's flux were calculated and results were compared to those from real-time imaging.

Air lime–metakaolin–sepiolite mortars for earth based walls

The present study aims to evaluate the behaviour of mortars based on lime, with the addition of metakaolin and sepiolite, seeking their application as renders on adobe walls. Since the renders used in traditional adobe buildings are mortars whose binder is lime, three mortars were formulated based on lime. An air lime mortar with sand and two other mortars, also based on air lime, but with the addition of metakaolin or metakaolin and sepiolite were tested. The mortar prisms 4×4×16cm were analysed in the laboratory conditions in view of mechanical properties. In parallel, the mortars were placed on old adobes, taken from demolished houses and their behaviour was verified with artificial accelerated ageing tests. Finally, mortars were placed on a wall made from traditional adobes, where panels were monitored and trials with Karsten tubes and Schmidt hammer have been conducted. The results obtained by comparison of the characteristics of mortars studied as prisms in laboratory conditions, applied on adobes and the adobe wall provided an extended study which is necessary to assess the suitability of mortars for use in the rehabilitation of adobe buildings.

Validation of in situ Applicable Measuring Techniques for Analysis of the Water Adsorption by Stone

As the water adsorbing behaviour (WAB) of stone is a key factor for most degradation processes, its analysis is a decisive aspect when monitoring deterioration and past conservation treatments, or when selecting a proper conservation treatment. In this study the performance of various non-destructive methods for measuring the WAB are compared, with the focus on the effect of the variable factors of the methods caused by their specific design. The methods under study are the contact-sponge method (CSM), the Karsten tube (KT) and the Mirowski pipe (MIR). Their performance is compared with the standardized capillary rise method (CR) and the results are analysed in relation to the open porosity of different lithotypes. Furthermore the effect of practical encumbrances which could limit the application of these methods was valuated. It was found that KT and CSM have complementary fields of investigation, where CSM is capable of measuring the initial water uptake of less porous materials with a high precision, while KT was found commodious for measuring longer contact times for more porous lithotypes. MIR showed too many discommodities, leading to unreliable results. To adequately compare the results of the different methods, the size of the contact area appears to be the most influential factor, whereas the contact material and pressure on the surface do not indicate a significant influence on the results. The study of these factors is currently being extended by visualization of the water adsorption process via X-ray and neutron radiography in combination with physico-mathematical models describing the WAB.

Using the Karsten tube to estimate water transport parameters of porous building materials

Over the last decades the Karsten tube has been used as a versatile testing device to measure the water absorption of porous walls. It is non-destructive and it can give reproducible results when used accurately. A major drawback however is the lack of a physical interpretation of the results. This paper uses analytical models and a numerical simulation in 3D to allow a more fundamental and general interpretation of the test results. A relatively simple model for a soil infiltrometer test was proven to give a good fit to experimental field data and to lab test results. 3D numerical simulations, performed with Delphin 5 software, provide extra insight about the correctness of the model assumptions of a sharp front process and a simplified shape of the wetting front. A supplementary measurement of the increase of the diameter of the wetted zone during the test allows a straightforward calculation of the capillary saturated moisture content and the sorptivity of the material. Moreover an analytical relation is presented between the results of the Karsten test as described in the old standards and the sorptivity.

Pore-structure and water transport properties of surfacetreated building stones

This paper describes the details of a laboratory investigation aimed at ascertaining the effect of penetrating surface treatments on the micro-porosity and water transport properties of three building stones used in the construction of historic buildings and monuments within Europe. The pore-structure and morphology of treated and untreated stone specimens were assessed using a combination of helium autopycnometry, mercury intrusion porosimetry and scanning electron microscopy techniques. Water repellence and transport properties were evaluated using the Karsten tube and magnetic resonance imaging techniques respectively.