The effects of silica fume and hydrophobic materials on mechanical and physical properties of clay plasters

The structures constructed by using earth materials have been used since ancient times. These structures are widely used due to their energy saving, environmental pollution reduction, easy to find and reusable properties and researches are continuing to improve some of these properties. Clay can be defined as fine-grained material found in earth. Today, with the more widespread use of technology and current researches, clay and clay products are used in many industry areas. Plaster production is one of these industrial areas. Plasters are applications for the protection of the inner and outer walls and aesthetic appearance. Clay plasters contain clay as binders. These plasters give important functions to the structures due to their clay properties. Due to the water absorption properties of clays, their structural forms may deteriorate from the moment water enters between the grains. To prevent this undesirable situation, water repellent materials can be added to the structure of the clay plaster mixtures. Water repellent (hydrophobic) materials increase the resistance of clay plasters and many other building materials to moisture. In this study, silica fume, zinc stearate and calcium stearate were preferred in order to increase the moisture resistance of conventional clay plasters. The aim of this study is to investigate the strength performance and durability of clay plasters by adding hydrophobic materials to the mixtures of clay plasters. Mixtures to be used in the study; clay-sand mixture, clay-sand-lime mixture, clay-sand-cement mixture and clay-sand-lime-cement mixtures. 0.5%, 1%, 1.5% and 2% by mass of silica fume, zinc stearate and calcium stearate were added to each of these mixtures. In this study, destructive and non-destructive tests were performed on the samples to determine the physical, chemical, mechanical and durability properties of clay plasters. As a result of the tests, it was observed that the silica fume used in this study did not show a good hydrophobic property. Additionally, the zinc stearate and calcium stearate did not show a good mechanical behavior, but it was observed that silica fume contributed to the strength of the plaster samples and the zinc stearate and calcium stearate contributed to their strength. It has been observed that by increasing the hydrophobic properties of the samples, waterproof surfaces are obtained and thus the durability properties are improved. Keywords: Clay plaster, Plasticity, Compressive strength, Hydrophobic materials, Durability