Effects of SA surface treatment on the properties of CaCO3 used as filler in construction composites

Abstract

Calcium carbonate (CaCO3 ) is mineral filler that has been most extensively used in the construction composites as well as in the polymer industry. Coarse CaCO 3 grains can be easily incorporated into the composite material, but the smaller-sized particles tend to agglomerate due to the enhanced particle-to-particle interactions, which leads to serious performance problems. The most efficient way of surpassing this problem is to enhance the final composite properties by surface treatment of the filler with a surfactant. Following such procedure a water-repellent construction composites are obtained (i.e. reparation mortars, mortars for the exterior works, thin coatings for concrete walls, etc.). The stearic acid is a universal and economical surfactant which is often used to improve CaCO3 hydrophobic properties. This study investigates and subsequently compares the surface and mechanical properties of untreated ground calcium carbonate powder and treated powder with stearic acid using a dry process coating system. The CaCO 3 powder (grain size class: -200 + 63 μm) was pulverized in a laboratory Retsch-ZM-1 mill with a 250 μm mesh size sieve and a peripheral comminuting path. The surface of CaCO3 powder is generally hydrophilic, but it was changed to a hydrophobic surface when coated with SA. The coating procedure was conducted in following manner: 1% of SA was added to the CaCO3 powder which was previously thermally treated at 120°C for 2 hours, and the mixture was stirred in a laboratory mixer with 1500 rpm. The surface treatment decreases the intensity of particle-to-particle interaction and increase adhesion of filler. There has been extensive research reporting about the effects of stearic acid surface treatment on the physical properties and thermal behavior as well as mechanical properties of CaCO3 composites. The contact angle of water on the coated calcium carbonate powder surface and hydrophobicity are increased with increasing concentration of SA. As a result, thermal stability and mechanical properties of the composite were increased compared to untreated CaCO3 composites. The influence of surface treatment of the particles, with and without stearic acid on the mechanical, thermal and structural properties was studied. The experiments included mechanical and physical testing; differential thermal analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The composite systems containing coated CaCO3 were found to exhibit better mechanical properties as compared to composite systems containing uncoated CaCO3 .