Zuzana Slížková

Standardization of peeling tests for assessing the cohesion and consolidation characteristics of historic stone surfaces

A peeling test known as the “Scotch Tape test” has been used for more than 40 years in conservation practice for assessing the consolidation efficiency of degraded stone. However, the method has not been supported by any standard or reliably verified recommendations for its application. Its applicability is overestimated, and its unrestricted use without adequate knowledge and sufficient understanding can lead to non-comparable, non-reproducible and, in many cases, incorrect and severely biased results and assessments. This paper presents the results of a recent study focused on establishing limits for application, reliable procedures and a “standard” protocol for testing the cohesion characteristics of brittle and quasi-brittle materials, mainly mortars and stones. The main application strategy exploits repeated peeling in the same place on a surface in order to eliminate the effect of the natural decrease in the detached material from the subsurface layers, which might be incorrectly interpreted as a consolidation effect. There is a discussion of factors influencing the performance of the peeling test method, and examples of peeling measurements on various natural and artificial stones are presented.

Α Nano Approach to Consolidation of Degraded Historic Lime Mortars

This paper presents a comparative study of the effects of calcium hydroxide based agents on consolidating a lean lime mortar. In the first part, it describes the properties and characteristics of CaLoSiL® – a new stone strengthener based on colloidal suspensions of lime nanoparticles in various solvents. It further summarizes the results of recent tests on the influence of applying nano-agents based on colloidal calcium hydroxide dispersed in ethanol or isopropyl alcohol (CaLoSiL®), and compares them with the effects of lime water and with a traditional barium hydroxide treatment. The tests were carried out on non-standard test specimens fabricated from a lean mortar (1:9) and developed specially for the purpose of testing the relatively low strengthening effects that are typical for lime water consolidation. The comparison presented in this paper is based on the mechanical characteristics of consolidated lime mortar.

In situ peeling tests for assessing the cohesion and consolidation characteristics of historic plaster and render surfaces

Abstract Standard application principles for the peeling test, also known as the scotch tape test, for assessing the surface cohesion characteristics of materials have been presented by the authors in earlier papers on laboratory testing of stone and mortar consolidation effects. The method has been in use for a long time for evaluating the strengthening of surface layers of mortars, but there have been no standards or reliably verified recommendations on how the test should be applied. Nevertheless, the method has been attracting continuing research, because it is a simple and quite reliable method for in situ testing of consolidation effects, if it is applied correctly. Our paper summarizes the basic principles, and presents illustrative results of an investigation of important historic buildings. It goes on to suggest some practical approaches and designs that are useful for in situ applications. We present a mathematical procedure suitable for evaluating the results that are obtained. We recommend repeated peeling on exactly the same place on the surface in order to compensate for and eliminate the effect of the natural decrease in the material detached from the subsurface layers, which might be incorrectly interpreted as a consolidation effect. The examples and validation measurements presented here include in situ measurements.

Characteristics of Mortars from Ancient Bridges

Mortars from two medieval bridges (Charles Bridge in Prague and a bridge in Roudnice) and two Roman bridges (Ponte di Augusto in Narni and a bridge in Sardinia) were analysed using various techniques to obtain their chemical and physical characteristics. The analysis of binder quality was based on thermogravimetric analysis, using a methodology which enables the hydraulicity of the mortar to be expressed by the CO2/H2O ratio. The mechanical tests were performed on non-standard mortar specimens. The ratio binder/aggregate was determined dissolving the binder by an acid, and a sieving analysis was applied to the separated aggregate. The material characteristics of mortars from historic bridges were compared with each other, taking into account the requirements for mortar strength according to construction function and degree of exposure.

Flexural Tests on Consolidation Effects on Stone

This paper describes laboratory verification tests for determining the efficiency of various consolidation treatments on Czech quartz sandstone. It compares material data acquired using circular discs and rectangular plates. While the application of rectangular plates enables the testing not only of strength but also of other material characteristics – e.g., moisture, water saturation or temperature dilation parameters – on identical specimens, the biaxial bending easily applicable only for mechanical testing gives data better describing material unisotropy. At the same time the influence of two different modes of consolidation agent application was taken into account – namely, capillary rise and brushing, which is typically used in conservation practice. Furthermore, cylinders and cubes were treated with the consolidation agents in order to determine their depth penetration ability. After maturing, the cylinders and cubes were cut into thin slices after being tested with ultrasonic measurements to determine differences in wave velocity across the specimen along the depth profile of the treated bulk. The experimental data were compared to ultrasonic tests as well as theoretically computed strength, for which a FEM model was used in the case of biaxial bending. Differences in consolidation effects are also discussed in relation to the chemical characteristics of the applied consolidation agents which were based in the case under study on ethylsilicate compounds and thus produced various amount of acting SiO2 gel inside the porous system. Both techniques were found to be useful in the testing of consolidation agents being developed before their introduction into conservation practice.

High-Performance Repair Mortars for Application in Severe Weathering Environments: Frost Resistance Assessment

Frost is one of the main degradation processes affecting historic buildings in cold environments. Lime mortar is particularly sensitive to degradation by freeze-thaw cycles due to its high porosity and low mechanical resistance. The aim of the present research is to assess the frost resistance of seven lime-based mortars to be used in repairs. Mortars with different binder composition and a traditional hydrophobic additive were tested. Specimens with three months of age were subjected to freeze-thaw cycles and the ageing action was evaluated by means of mechanical and physical measurements. Improved durability of lime-based mortars with hydraulic binders and linseed oil additive has been confirmed and the different mortar formulas may be promising for repairs according to specific environmental conditions.

Comparative Tests of Strengthening Effects on Weak Mortars Consolidated with Various Agents

The capacity of various consolidating liquids to strengthen weak mortars is reported in this paper. Commercial products (CaLoSiL IP 15, KSE 100) and liquids prepared in laboratory by dissolving chemicals in water (barium hydroxide, ammonium oxalate, ammonium phosphate) or by dilution more concentrated products (Syton X 30) were used for the experiment. In order to study the influence of the mineralogical composition of the mortar, various sorts of sand were alternatively used in the experiment for the mortar preparation. The efficiency of the treatment was evaluated as mechanical strength change measured on different shape specimens - on tubes for compression strength, on thin plates for tension test and on beams for flexural strength. All the tested consolidation agents showed positive strengthening effect when they were used for consolidation of the poor lime mortar, with the exception of the influence of lime water on the flexural strength. Very different results were achieved on soil-based mortar.

Soils and Earthen Building Materials Used for the Buddhist Temple Complex

ABSTRACT This article presents a comprehensive study of the local soils and historic earthen building materials used in Nako temple complex in Western Himalayas. On-site and laboratory investigations followed a holistic approach to characterize materials and identify historic manufacturing formulas. The interdisciplinary and novel methodology used for analysis of the earthen building materials combine geological, chemical, mineralogical, geotechnical, and mechanical approach. The results presented in this article enable a better understanding of material culture and advance the study of damage and decay processes found in the temple buildings. In addition, a suitable conservation and preservation strategy is presented.

Failure and Repair in Cultural Heritage Conservation

Architectural heritage objects exhibit a vast variety of damage and failures which is difficult to categorize for the sake of designing general preventive or repair and conservation measures. The authors studied sensitivity of historic structures and elements to weather and disasters within several international research projects using their personal experience and research as well as records of damage and failures gathered in literature and special databases. It should be emphasized that any historic structure or element cannot be dealt with unless its material characteristics and a general environmental situation, (e.g. hydro-geological conditions), have been taken into account, which must be reflected in evaluating results and designing mitigation strategies. This paper presents selected examples from a developed information system containing data on typical damage and failures related to weathering effects and disasters action, namely wind, floods and landslides. In specific cases, not the historic structure but its surroundings and supporting structure are prone to failure, which can adversely affect their behaviour and response and cause damage to cultural heritage objects. The approach is documented by preventive strategies and measures and accompanied with life expectancy and repair cost estimates.

Restoration of Outdoor Plaster Pavement Floors in a Medieval Czech Castle

Abstract Substantial tests and analyses of an ancient exterior plaster floor at Karlštejn Castle in Bohemia have led to the design of a new material for replacing and repairing a historic mortar floor. The replacement material has a reasonably high degree of similarity and compatibility with an acceptable level of safety and reliability. The floor was cast in situ during extensive restoration works at the end of the nineteenth century and exhibits surprisingly high durability and strength. The investigation used some non-standard testing methods developed for small-size specimens. In designing the new material, attention was paid to lime mortars with hydraulic admixtures. A metakaoline-modified mortar was finally recommended as the repair and replacement material for restoring the rampart outdoor pavement of Karlštejn Castle.