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- 2025 (2)
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- Englisch (2)
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- Lightweight aggregates (1)
- Lime mortar (1)
- Protective system (1)
- Recycling (1)
- Repair mortar (1)
- Rock powder (1)
- Sandstone (1)
- Silica sol (1)
- Stone conservation (1)
- Stone preservation (1)
Organisationseinheit der BAM
This paper deals with the study of different lime-based repair mortars for the conservation of sandstone objects in the context of monument preservation. New types of lightweight aggregates, which were manufactured from masonry rubble, were used to develop these repair mortars. This allows for recycling of construction and demolition waste while helping to conserve natural resources. As part of this work, the mortars were comprehensively characterised in terms of their chemical, physical, mechanical and hygric properties, such as bulk density, pore structure, strength, water absorption, shrinkage and carbonation. All mortars are lightweight mortars with bulk densities of about 1300 kg/m³. They achieve high porosities of around 50 %. At the same time, the mortars exhibit sufficient compressive strengths ranging from 1.8 to 11.3 MPa. The compressive strength depends on the degree of carbonation of the mortars and increases with sample age. The analysis of the pore structure shows that the mortars mainly contain macropores. The large number of capillary pores, with sizes ranging from 0.1 to 1000 μm, results in a good water absorption behaviour. The evaluation of the results proves that the repair mortars are compatible with Cotta sandstone.
A silica-based protective system modified with rock powder for the preservation of tuff stone
(2025)
Tuffs are lightweight and porous pyroclastic rocks composed of a volcanic ash matrix containing pumice and rock fragments, quartz, sanidine and other individual crystals, zeolites, and clay minerals. Due to their low density and high porosity, tuff stones are easy to work with and transport. They have been used as construction material in many historical buildings in Germany. However, most tuff stones exhibit poor resistance to weathering due to their morphology and porosity. If the physico-chemical degradation of the stones is already well advanced, ensuring the safety of the buildings often requires extensive stone replacement. However, this contradicts the fundamental principle of conservation, which prioritises the preservation of the original material. In a recently completed research project, a silica-based protective system modified with rock powder was developed for the preservation of tuff stone. Suitable colloidal silica dispersions and modified rock powders customised produced from tuff waste were used. The protective system was optimised to reduce the capillary water absorption of tuff while maintaining its water vapour diffusion properties, to build a durable protective system-tuff bond, and to achieve a visual and tactile resemblance to tuff. The protective system was developed at laboratory scale. It was subsequently applied to a test area at a restoration site in Berlin-Zehlendorf, Germany, to assess its performance under outdoor conditions. By applying the new protective system, the historic building structure is better preserved, tuff stone resources are saved, and tuff waste is effectively recycled.
