ROCARE, EAP meeting Vienna, September 16th Natural cements in France

Transcription

1 ROCARE, EAP meeting Vienna, September 16th Natural cements in France Myriam Bouichou Elisabeth Marie-Victoire

2 Topics Natural cements history in France Natural cements uses in France Natural cements identification Their decays and the associated rehabilitation techniques

3 Natural cements history in France

4 Natural cements history in France 1802 : first production of natural cement, called «plastercement», using beach shingles in Boulogne-sur-mer : first natural cement factory in Pouilly, owned by Jean-Auguste Lacordaire, who had discovered a stone producing the same plaster-cement. First use of the «Roman cement» term in France : Vassy natural cement beginning.

5 Natural cements history in France From 1840 : development of numerous natural cement production sites in France and especially in the RhoneAlpes region. Rhône-Alpes region Grenoble

6 Natural cements history in France In 1891 : 16 natural cement factories in France, 5 of them in Isere (Rhone-Alpes region). In 1928 : tons of natural cement in Rhone-Alpes and tons in Vassy In 2009 : 1 natural cement production in Isere (Vicat), 19th century kiln

7 Natural cements applications in France

8 Natural cements applications in France From the first half of the 19th century : engineering applications maritime and hydraulic works harbors and docks (Normandy, Honfleur) bridges sewers (Paris) railways water and gas networks

9 Natural cements applications in France From the first half of the 19th century : architectural applications waterproofing of wet areas (terraces, basements) protection and decoration of facades (stone simulating) cast stone (concrete blocks, fake stones)

10 Natural cements applications in France Grenoble examples : façade decoration, window frames

11 Natural cements applications in France Grenoble examples : cast stones in Saint-Bruno church

12 Natural cements applications in France Marseille examples : natural cement renders, fake joints and ornaments

13 Natural cements applications in France From the first half of the 19th century : restoration of historical monuments (color close to some limestones) Saint-Eustache church in Paris Reims, Bayonne, Paris and Amiens cathedrals... Amiens cathedral Part of the western portal base was repaired using natural cement (faces, hands, feet and drapery)

14 Natural cements applications in France From the first half of the 19th century : restoration of historical monuments (color close to some limestones) Bourges cathedral sculptures especially on 3 portals of the eastern front, replacement of missing parts with Vassy cement mortar

15 Natural cements identification

16 Natural cements identification Lots of mixes quick natural cement + slow or half-slow cement natural cement + lime natural cement + portland cement... Low crystallization (burning temperature) Color can be misleading Identification uneasy

17 Natural cements identification Portland cement Natural cement Burned C< θ<1200 C C2S C3S MgO Lime Interstitial phase C3A et C4AF C2S 40µm 50µm 50µm Optic microscope after borax attack Overburned - θ>1200 C Interstitial phase : calcium alumina-silicate Optic microscope after borax attack

18 Main decays observed and current rehabilitation techniques

19 Cast stone main decays Progressive erosion of the concrete skin The aggregates get visible and the natural freestone aspect is lost

20 Cast stone main decays Black crusts and salt induced scaling 2µm Gypsum, Thenardite and Syngenite formation (2)

21 Cast stone façades current rehabilitation techniques Use of gray Portland-cement-based mortars combined with a yellow or brownish painting Initial mineral texture and ochre shades are lost

22 Renders main decays Spalling and cracking Water infiltration, mechanical and aesthetic impact

23 Renders current rehabilitation techniques Use of lime-based renders with additions of pigments Initial mineral texture and ochre shades are lost

24 Conclusion A few applications clearly identified and located, but surfaces to be repaired difficult to evaluate Initially, lack of interest and/or knowledge on natural cement cultural heritage French production of natural cements still existing, but needs of research on suitable repairing products or techniques From 2002, 2 national projects & 1 PhD

25 Conclusion Among the first main problematic accept natural cement as a cultural heritage material accept shrinkage cracking accept and appreciate a non uniform clean color Strategy : binder or ready to use mortars? Suggestion for French EAP partner : cultural heritage architects association