Monument Future

Results and Discussion

Granulometry of the mortars produced in this work was compared to that of the commercial products to compare if it has an impact in the durability of the mortar. The particle diameter of all mortars ranges from 0.08 to 0.8 mm. Particle size distribution of mortar HB is a little different from the others due to the use of chamotte as aggregate. Mortar AS shows smaller particle size due to the use of air lime.

Porosity and density, water capillarity absorption and relative amount of mixing water necessary to obtain the expected workability are presented in Table 2. The mean density measured at 90 days is 1,720(109) kg/m³, HSP mortar presents the smallest value with 1534 kg/m³ and the highest value corresponds to mortar HSG with 1,873 kg/m³. These two mortars have additives, pinecone and waste glass powder respectively, which shows that the use of the correct additives is able to modify 62the density of a restoration mortar. The mean porosity at 90 days is 33.7(4) %; HSG mortar, with 29.4 %, presents the lowest value and the highest value corresponds to HSP mortar, with 40.9 %. As expected, mortar with the lowest density has the highest porosity.

Table 1: Restoration mortar formulations in weigh percentage. WGP: Waste glass powder, PN: Pine cone, PCRS (Pine Cone Resin Solution), CHAM:Chamotte (Crushed brick waste).

Figure 2: Granulometric Curves.

The mean capillarity coefficient at 180 days is 1.73(0.53) kg/m²min^½, with a minimum of 0.99 kg/ m²min^½ for mortar HSP and a maximum of 2.57 Kg/ m²min^½ for mortar HB. These results are in accord with the results obtained by Margalha et al. (2011) in mortars with hot lime mix.

Table 2: Physical characteristics of mortars. ρ: density (kg/m³), n: open porosity (%), C: Capillarity coefficient (Kg/m²min^½), W: mixing water (g water/g dry mortar).

The mean mixing water is 17(4)% in weight, the smallest value corresponds to mortar HC with 14 %, and the highest to mortar HB with 27 %.

Mechanical properties at 90 days are shown in Table 3. The mean compressive strength at 90 days is 2.36(1.3)MPa; with a minimum of 0.68 MPa (mortar HSP) and maximum of 4.30 MPa (mortar HSG). These results are in the same range than those of some commercial mortars: compression strength at 90 days, Lithomex of 8.3–9.0 MPa; Conserv, 0.97 MPa, Altarpierre, 15.6 MPa (Torney et al.2014; Lopez-Arce et al 2016). In another experimental study, comparing 160 mortars values go from 0.5 MPa to 15.20 MPa with a mean value of 3.76 MPa (Apostolopoulou et al., 2019).

The HSG mortar has the strongest mechanical properties. This mortar was fabricated with waste glass powder and the obtained results are in accord with those of Carsana et al. (2014) and Edwards et al. (2007). The mean flexural strength at 90 days for all the mortars is 0.86(.22) MPa, with a minimum value for mortar HSP and AS. Considering that AS mortar was made with aerial lime this value is in accord with the work of Margalha et al. (2011). Mortar HSG shows the highest value with 1.29 MPa.

Table 3: Mechanical properties of mortars. CS: Compressive Strength (MPa) at 90 days; FS: Flexural Strength (MPa) at 90 days; E: Young modulus (GPa), υ: Poisson coefficient.

63The use of organic additives, like resins, can improve the mechanical properties of mortars (Ordoñez et al. 2019). In our case, HSCR mortar shows only little improvement in the flexural strength compared to HSC mortar.

The mean dynamic Young’s modulus at 360 days is 7.25(2) GPa, the minimum is shown in mortar HSP with 2.58 GPa and the maximum in HSG with 11.45 GPa. These values are similar to those obtained by Nežerka et al. (2015).

The mean dynamic Poisson ratio at 360 days is 0.20(0.05), the minimum corresponds to mortar HSFD with 0.13, and the maximum to mortar HSP with 0.32. These values are similar to those of Palomar et al. (2015).

Frost Resistance results are presented in Figure 3. All mortar samples presented a slow and constant increase in weight during the thaw/frost test until the 13 cycles when the sample HFD started to lose weight. The mean mass variation per unit of mass is 0.11(0.04), with a maximum of 0.15 for the mortar HC. The mean final weight is 11(4)% higher than the initial one. This fact may indicate that mortars are still undergoing carbonation under these conditions, as carbonation produces a weight increase in mortars, clearly higher in mortars with higher amount of lime (Arizzi et al. 2012).

The results of salt crystallization tests are presented in figure 4. Weight decreases for all the samples during 16 cycles. Mortars AS and HSP collapse prematurely, with partial destruction at cycle 8. Mortar HSC shows the same partial destruction at cycle 13. In contrast, all the other mortars resist 16 cycles. In mortars HC, HB and HS, deterioration occurred at a much slower rate. These values are within normal boundaries according to Klisińska-Kopacza et al. (2013). Low weathering rate is related to the presence of hydraulic lime and hard minerals, such as silicates. Mineral additives can improve the durability of the mortars according to Theodoridou et al. (2014). The Mortar HSPR showed better durability in comparison with the mortar HSP. We can say that the addition of pinecone resin solution seems to be adequate to increase the durability of mortars.

Figure 3: Frost Resistance test. ΔM/M(%) vs number of cycles.

Figure 4: Salt Crystallization test. ΔM/M(%) vs number of cycles.

Conclusions

Correlations were established between mortars properties and the use of different additives. It can be concluded that employed recyclable additives will improve some mortars properties.

Pinecone fragments reduce significantly the capillarity coefficient but also its mechanical properties. The waste glass powder improves the compressive strength of materials and decreases porosity. Mortars with crushed brick waste as aggregate absorb almost twice more water than mortars with sand, this additive can be used as a red dye and has a high resistance in durability tests.

The Pinecone Resin shows an improvement in the durability of the mortars as well as a slight improvement in mechanical properties.

Future works will seek to combine different additives in order to obtain better mortars.

New methods to calculate the life cycle analysis are available with Open LCA methods, We plan to use design models and economic models in order to select the composition of new mortars we want to develop.

Acknowledgements

We thank the programs “Make Our Planet Great Again” and “Initiative d’excellence Paris Seine” for 64providing economic support for the development of this research; and the companies Socly, Rocamat, Briqueterie d’Allone and Fédération du Verre for providing the materials for this work.

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COMPARISON OF PHYSICO-CHEMICAL PROPERTIES BETWEEN ANCIENT AND RESTORATION RENDERS IN THE VEXIN FRANÇAIS AREA (NW OF PARIS)

Claire Noël, Beatriz Menéndez

IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

– PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

Laboratoire Géosciences et Environnement Cergy, Université de Cergy Pontoise, 95000 Neuville-sur-Oise, France

Abstract

In the Paris area there are important gypsum resources which results in an extended use of gypsum in traditional architecture as façade renders. Traditional renders are still visible today in urban areas and in the surrounding countryside. This study concerns renders of the vernacular architecture of the Vexin Français, few tens of kilometres North-West of Paris and is based on the work carried out by Tiffanie Le Dantec in her PhD thesis. We focus our research on the analysis of ancient and new renders in order to propose suitable conservation or restoration solutions. This preliminary study compares several physical, chemical and mineralogical properties of ancient render samples and modern renders formulations used for façade restoration, in order to find possible relationships between the characteristics of studied formulations and their physical properties. The final goal is to estimate physical properties of ancient renders from their mineralogical composition.

Keywords: Traditional gypsum renders, renders conservation, renders restoration, mechanical properties, chemical analysis, hydric properties

Introduction

In the Vexin Français area, 40 to 70 km NW from Paris, two principal construction techniques are found: important buildings (churches, chateaux or big houses) are built in ashlar masonry, whereas smaller ones (farms, houses and other vernacular buildings) are made on random rubble masonry covered by renders. Nowadays many new owners of traditional buildings want to remove renders in order to show the stone masonry. This new tendency has two major disadvantages: it alters region landscape and it exposes masonry to weathering and decay induced by environmental conditions.

The long-term goal of the study is to provide proofs that traditional renders are much more adequate and durable when repairing stone façades than new cement base renders. Most of the façades in the Vexin area are made of rubble stones with a lime mortar and covered by a plaster of Paris, lime or plaster of Paris-lime render. The use of this kind of render has aesthetic purposes, helps to evacuate the humidity and has a protection role.

Our study focused on comparisons between ancient renders sampled in façades of the Vexin area and new formulations of renders supplied by Plâtrière Vieujot. This society has been producing plaster of Paris renders since 1880. One of its renders, “plâtre Briard” is used in rural areas of Paris region as external render 66because of its non-uniform aspect due to the presence of impurities like charcoal and small pieces of gypsum stone.