Klára Kroftová

The application of carbon composites in the rehabilitation of historic baroque vaults

The stabilization and reinforcement of damaged barrel vaults with lunettes over an arcaded walk, applying composite strips based on high-strength carbon fibers and epoxy resin, was performed during the restoration of a historic monastery. The application of reinforcing composite strips in the soffit of damaged barrel vaults was preceded by relatively extensive experimental research and theoretical analyses. This method significantly reduces the interventions into and the degradation of the original historic structure (surface application) and is reversible.

THE EFFECT OF DEGRADATION PROCESSES ON THE SERVICEABILITY OF BUILDING MATERIALS OF HISTORIC BUILDINGS

The article presents an analysis of degradation processes and partial results of an experimental research into materials and structures exposed to the effects of external environments with an emphasis on the effects of moisture and chemical degradation processes on major mechanical properties of sandstone.

Stabilization, Conversation and Strenghthening of Historic Plaster Using Nanofibres

The paper deals with the stabilization, conservation and strengthening of historic plaster fabrics based on nanofibers. As a result of degradation processes, especially of a chemical nature, accompanied by increased humidity of historic masonry, there is a loss of cohesion and a disturbance of the surface finish and plaster. Traditional remediation techniques and methods normally lead to a reduction of diffuse permeability in the multiphase structure and create different expansion properties under the plaster. The undesirable feature of this method is its irreversible character. Currently there are a number of primarily preferred procedures that stabilize the structure of the external finish, yet at the same time preserve the original features of the historical plasters. This paper will list the partial results of the ongoing in-situ and laboratory research applications of fabric based on nanofibers formed by the supporting layer and spinning polymer.

The Application of Nanomaterials in Restoring Historic Structures

The current approach to the restoration of listed buildings emphasizes the minimization of interference and the maintenance of authenticity and historical value as a whole, alongside detail. This opens a wide field of applications for composite materials and nanomaterials. The use of nanotechnology is currently one of the most reviewed areas of research in various technical disciplines. The extraordinary properties of nanomaterials allow their successful use in the restoration of listed buildings.

Comparison of the Degree of Consolidation of Historic Plaster Layers by Means of Lime Hydrate Nanosuspensions

Historic masonry is usually coated with multiple plaster layers, exposed to long-term extreme loading (climatic effects, elevated moisture levels, salt crystallization and recrystallization, biological effects, etc.). As a consequence of the above negative cyclic effects, degradation processes are triggered off leading to a loss in plaster cohesion with the substrate masonry and successive falling-off of surface layers. The strengthening and rehabilitation of plasters with degraded binder components, impaired structure, insufficient adhesion of individual layers of plaster to the masonry surface, with elevated salt contents in the pore system and surface crusts represent a demanding task in terms of the stabilization of such degraded plasters and coatings. Consolidation (i.e. enhancement of mechanical characteristics) belongs to the basic objectives of the restoration of historic plasters, its principle is to return binder into the material structure, fill in existing hollow spaces, heal cracks, etc. Degraded lime plasters are strengthened with consolidating agents applied in the form of solutions, e.g. lime water, organosilicates or lime nanosuspensions, etc. The lime nanosuspension is composed of lime hydrate nanoparticles, dispersed in an alcoholic medium. Due to the deposition of calcium carbonate in the degraded material, the bonds are re-strengthened and the material consolidated. The article presents partial results of theoretical and experimental research addressing potential consolidation of historic plaster layers with lime nanosuspensions prepared by the synthesis of Ca(OH)2, which were successively modified and enriched with other components.

NANOTECHNOLOGY IN THE CULTURAL HERITAGE - INFLUENCE OF NANOSPENSIONS ADOPTED BY NANOPARTICLES OF TiO2 FOR CLEANING THE SURFACE OF HISTORICAL PLASTERS

The continuous development of nanostructure and the study of physico chemical processes in the nanometer range lead to new methods that can slow down the degradation processes of a work of art, or even restore damage caused, for example, by an inappropriate restoration process. The use of nanosuspensions based on calcium hydroxide is probably the most widespread application of nanomaterials in heritage care, especially in the field of hardening of lime building materials (plaster, limestone, etc.). In combination with titanium dioxide, it should be a successful suspension in the fight against biological agents, surface contamination or in the protection of UVresistant building materials.

Physical and mechanical characteristics of building materials of historic buildings

The article presents partial results of laboratory research into physical and mechanical characteristics of materials most commonly used as walling units in masonry structures of historic and heritage buildings. Core boreholes and specimens for the laboratory research of selected characteristics were sampled from accessible places of historic buildings, which had not been restored or reconstructed. The results of the research brought new knowledge about the unreliability (variance) of the properties of historical, mainly natural building materials, and, at the same time, pointed out the need for further research and extension of knowledge necessary for the assessment of residual physical and mechanical characteristics of historic masonry structures.

EXPERIMENTAL RESEARCH INTO DYNAMIC PROPERTIES OF MASONRY BARREL VAULTS NON-REINFORCED AND REINFORCED WITH CARBON COMPOSITE STRIPS

The study of dynamic behaviour of vaults of historic buildings reveals new knowledge which can be used for the local analysis and stabilisation and rehabilitation designs of damaged vaulted structures. The analysis of the results of dynamic loading brings objective background material for the identification and localisation of failures according to MAC or COMAC criteria (1, 2) and the assessment of serviceability and structural reliability of vaulted structures of historic buildings.

GROUTING METHODS FOR THE REHABILITATION AND REINFORCEMENT OF MASONRY STRUCTURES DAMAGED BY CRACKS

The article sums up the requirements for historic masonry structures whose reinforcement is based on the grouting technology application, the grouting implementation procedure in relation to the extent, type and size of masonry damage. Special focus is put on grouting agents and requirements for their characteristics.

Discoloration of Historic Wood after the Application of Nanotextiles

The article addresses the discoloration of historic wood after application of nanotextiles. The nanofiber fabrics used for experimental testing were made of the PVB polymer and the Paraloid B72 acrylic resin. For the verification of the possibility to increase the biocidal efficiency of historic wood have also been made nanotextile with dopants Ag ant TiO2. Discoloration of historic wood after the application of selected nanotextiles were tested on the wood samples, which were removed from historic building Hájčí Dvůr, Praha 5. The article was written with support from the research project NAKI DF12P01OVV37: Progressive Non-Invasive Methods for the Stabilization, Conservation and Strengthening of Historic Structures and their Parts with Fiber – and Nanofiber – based Composite Materials.