Modified Ethylsilicates as Efficient Innovative Consolidants for Sedimentary Rock

Abstract

Although silicon alkoxides (especially ethylsilicates) have long been used as consolidants of weathered stone monuments, their physical properties are not ideal. In this study, an innovative procedure for the consolidation of sedimentary rocks was developed that combines the use of organometallic and alkylamine catalysts with the addition of well-defined nanoparticles exhibiting a narrow size distribution centered at ca. 10 nm. As a suitable test material, Pietra di Lecce limestone was selected because of its color and problematic physico-chemical properties, such as rather low hardness. Using the developed procedure, the mechanical and surface properties of the limestone were improved without the unwanted over-consolidation of the surface layers of the stone, and any significant deterioration in the pore size distribution, water vapor permeability, or the stone’s appearance. The developed modified ethylsilicates penetrated deeper into the pore structure of the stone than the unmodified ones and increased the hardness of the treated material. The formed xerogels within the stone pores did not crack. Importantly, they did not significantly alter the natural characteristics of the stone.

Potential of Advanced Consolidants for the Application on Sandstone

“…The self-developed alkoxide-based consolidants were prepared by adding the nanoparticles (3 wt.%) to Dynasylan ® 40 [11,13,14]. Afterwards, catalyst n-octylamine (0.18 wt.%) (Alfa Aesar) was added.…”

“…Another strategy involves the incorporation of elastic segments, such as hydroxyl-terminated polydimethylsiloxane (PDMS), into the xerogel structure; these segments effectively removed the stress caused by capillary pressure [5][6][7][8][9]. Another more general approach is based on the incorporation of various oxide nanoparticles, such as SiO 2 , TiO 2 , Al 2 O 3 and ZnO (so-called particle-modified consolidants, PMC) [3,8,[10][11][12][13][14][15]. Due to the increase in the pore size of PMC-based xerogel and the improvement of its mechanical properties, cracking was reduced, and the consolidation effect enhanced.…”

“…The Czech Republic is particularly suitable in this respect because it is rich in sandstone quarries, meaning that a wide range of samples differing in texture and mechanical properties are available. Our previous studies have shown that sandstone from the Msene quarry in Central Bohemia is suitable for the evaluation of consolidation performance because it is characterized by high-porosity and relatively low mechanical strength [11,13,14]. This sandstone is characterized by high-purity (over 95% of quartz and a small amount of binder), homogeneity and a well-defined monomodal porous system with a narrow pore-size distribution.…”