Céline Thomachot-Schneider

Assessment of new protective treatments for porous limestone combining water-repellency and anti-colonization properties

Water is known to be the main deteriorating agent of building geomaterials. Owing to the presence of water, the alteration phenomena observed particularly on limestones are transportation of soluble salts, dissolution of calcite and development of micro-organisms. In restoration works, several chemical treatments can be used, such as biocides to remove existing biofouling and water-repellents to prevent the ingress of water and its deteriorating effects. The aim here was to combine these two properties in one treatment that could be applied at the end of the restoration work and to develop treatments based on natural products and that are safer for the users and the environment. Products with water-repellent and/or anti-colonization properties were developed and tested on a bioclastic limestone both in laboratory and outdoor conditions. They were compared with commercial water-repellents and a preventive anti-colonization treatment. Samples were exposed for 2 years in a forest environment, where the hydrophobicity and the colonization were evaluated every 6 months. In the laboratory, anti-colonization effects were determined through algae growth measurements. The product that confirmed an efficient hydrophobicity and anti-colonization effect will be applied on a restored site to test it under real conditions.

Comparison between petrophysical properties, durability and use of two limestones of the Paris region

Abstract Most buildings of architectural heritage in Paris and its surroundings are built with Lutetian limestone. Several historic buildings of the ‘Vexin Normand’ region show Lutetian limestone in the upper parts of their walls, while the lower parts are built with a chalk known as ‘Pierre de Vernon’. The ‘Pierre de Vernon’ appears up to the first metre, although in exceptional cases it can reach the middle height of a building. Commonly, chalks exhibit low durability due to their high porosity. However, ‘Pierre de Vernon’ is supposed to have greater durability than other chalks because of its historic use for basement construction. The objective of this research was to understand the use of the ‘Pierre de Vernon’ in the lower part of the constructions. A petrophysical characterization of Vernon chalk and Lutetian limestone was carried out, focusing mainly on the differences in porosity and water uptake. Salt crystallization tests were done to contrast their response to decay. Colour and roughness measurements and scanning electron microscope observations were performed. Results show that the different porous networks of these two limestones lead to a high contrast in their hydric properties and responses to decay, and the use of Vernon chalk in the lower sections of buildings has been found to be appropriate.

Stone uses in Reims Cathedral: provenance, physical properties and restoration phases

Abstract Reims Cathedral is a major monument in the NE of France originally built with local Lutetian limestone. The recent closure of the last quarries has made restoration using the same stone more complicated. The restoration stones used currently are Lutetian limestones from the centre of the Paris Basin (Saint-Pierre-Aigle and Saint-Maximin stones). Mapping of the Cathedrals façades confirmed the data from ancient manuscripts: Courville stone was the original building stone, but several other local stones from various quarries and beds were also used. As a follow-up to this mapping, Lutetian limestones from five disused quarries were sampled for petrophysical characterization tests: thin section analyses, porosimetry, capillary and drying kinetics. The petrophysical properties of the limestones showed differences between the two main local stone types (Ditrupa limestone and miliolids limestone) and also between the quarries. This study addresses the difficulty of selecting new stone for restoration. Should ancient quarries be re-opened? If so, which ones?

GIS-based variability of building materials towards the Île-de-France cuesta (Paris Basin, France): inventory, distribution, uses and relationship with the environment

Abstract The Pays rémois in the eastern Paris Basin is an administrative area of 1394 km2; in the surroundings of Reims (France). Two main geological substrata are separated by the Île-de-France cuesta: the Tertiary substratum in the western part is composed of various types of geomaterials (clay, sandstone, limestone, burrstone), whereas the substratum in the eastern part is composed only of Cretaceous Chalk. A field survey in each commune of the Pays rémois identified 26 building materials documented in a Geographic Information System database (GIS-database) that includes information about them (lithology, petrographical and petrophysical data, weathering) and the corresponding buildings (e.g. town, georeferenced data, building type, position on the façade). The spatial analysis of the building materials’ distribution (Standard Deviational Ellipse) with GIS identifies their uses and the criteria established for the selection of the materials: availability, efficiency, workability and durability. Some lithologies were preferred for particular buildings or selected for their efficiency in specific positions. The study also defines the relation between the stones’ origin (local and non-local stones) and their application. This database is useful to establish stone replacement strategies in the Pays rémois.

Hygrothermal performance of various Typha–clay composite:

This article deals with the influence of both morphology and amount of Typha on hygrothermal behavior of a Typha–clay composite for building application. An agromaterial containing the fiber mix of Typha Australis and clay was made in three samples: three fiber mixtures were prepared with different amounts Typha and cut type (transversal or longitudinal). The physical properties of these materials were studied in terms of porosity, apparent and absolute density, thermal conductivity, and hygric properties. Results show a real impact of the Typha fraction type and its volume content on hygrothermal properties of the studied material due to the porosity. The transversal fraction of Typha (80% in volume weight) seems to be the optimal composition for a better hygrothermal behavior.

Chlorophyll Fluorescence and Colorimetric Analysis for Monitoring the Algal Development on Biocide-Treated Stone

The present study used two non destructive technics, chlorophyll fluorescence and colorimetry to assess the Chlorella vulgaris growth on stone surface treated by experimental treatments for preventing biofouling. A protocol for laboratory tests was set up, consisting of inoculating treated slabs stone with a suspension of an algae culture (Chlorella vulgaris), that is a well known monument colonizing organism. The biofouling test was carried out under fluorescent lights for four weeks at room temperature which was 20°C and monitored by chlorophyll a fluorescence and colorimetry analysis. These techniques are rapid, non-invasive, and reliable. Treatments were introduced by mixing a tetraethoxysilane base with different ingredients: chitosan and/or silver nitrate for biocide effect and/or hydrophobic silica for water repellency. Results revealed four different patterns of algal development. The stones treated with the product containing chitosan and silver nitrate did not show any difference in their fluorescence signal as compared with the untreated stones (control). The stones treated with the product containing only silver nitrate showed biocide effect two weeks after the start of the experiment. The product containing silver nitrate, chitosan and hydrophobic silica at low concentrations completely inhibited algal development in the long term, the similar product with the same compounds at a higher concentration only delayed algal development by 1-2 weeks. This suggests that low concentrations of the products have a synergistic effect, that is lost if they occur in excess. In the present study, chlorophyll a fluorescence proved to be a valuable tool in detecting damage in the photosynthetic system of organisms and as a useful complement to other conventional measurements such as colorimetry.

Simulation of acid weathering on natural and artificial building stones according to the current atmospheric SO 2 /NO x rate

The building stones are affected by pollution. Since 1980s, the actions to reduce the greenhouse gas emissions led to the inversion of the SO2/NOx proportions in the atmosphere. This study aims at estimating the effects of nitrogen and sulfur compounds on stones by assessing the changes of three building limestones and one reconstituted stone submitted to acid attacks. Two of these stones were already contaminated with sulfates, while the two others were fresh quarried. Two different types of accelerated aging tests were used: (1) the exposition to two mixed acid and saturated atmospheres (HNO3 and H2SO3) to simulate the ancient and current pollutants ratio and (2) the immersion in a mixed acid solution (HNO3 and H2SO4) and in rainwater (pH 5 and 5.9), with and without agitation to simulate stagnant water and storm runoff water. Macroscopic, binocular and SEM observations, variations of color, weight, porosity, salt content and dissolved calcium were assessed over time. The sulfur amount influences the esthetic alterations such as color changes due to the salt precipitation and the oxidation of metallic compounds. During the immersion tests, the dissolution in the acid solution was more efficient than in the rainwater, due to the combination of the acidity and the karst effects. In the mixed acid atmospheres, the behavior of the porous network depends on the pore size distribution while in the immersion tests it is the open porosity. The high initial sulfur content of the contaminated stones increases the dissolution rate and limits the crystallization.