Effect of modified ethylsilicate consolidants on the mechanical properties of sandstone

Silicon alkoxides, such as silicon ethoxide or its oligomers (generally called ethylsilicates), are excellent consolidants for the weathered silicate materials. Their drawbacks, the shrinkage and cracking, can be reduced by the formation of wider pores within the gels or by the modification with particles. The sol-gel process was found to depend on the properties of particles added, especially on their size and surface properties. While the hydrophobization of the particle surface decelerated the process, the adding of hydroxylated particles had only a slight effect on the polycondensation process. In order to suppress the formation of micropores and to support the formation of more advantageous, substantially wider mesopores, organic amines are preferable as catalysts. The role of primary amines with a longer alkyl chain seems more complex than that of mere catalysts. If particles were added, no substantial effect on the character of the porosity was observed. The mechanical properties of gels modified by embedding particles or by creating mesoporosity were substantially changed. Due to the embedding of particles both the hardness and Young's modulus were increased. On the other hand, the formation of the mesoporosity within the gels had an opposite effect. The modification of consolidants by the creation of mesopores in the gels enabled to achieve an even consolidation of the stone characterized by moderate strength changes due to consolidating treatment. On the contrary, the variants with particles exhibited much higher strength increase in the surface part of stone specimens compared to inner or bottom stone areas, which is not suitable for a satisfactory consolidating intervention. (C) 2016 Published by Elsevier Ltd.