Synthesis of calcium based nano powders for application in conservation and restoration of heritage mortar

Abstract

In recent years, nano calcium hydroxide (NCH) finds its potential applications in conservation and restoration of heritage structures due to its improved surface treatment. In the present study hexagonal NCH powders were synthesized for surface treatment of heritage mortar. Lime is usually adopted for the conservation of surface treatment due to quick transformation of lime into calcium carbonate. However the incomplete lime carbonation process and reduced penetration depth are the undesired limits for the surface treatment. Present work will report the chemical stability and mechanical behavior before and after surface treatment using this synthesized NCH powder in heritage mortar. For this purpose, morphologically tuned Calcium hydroxide nono powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy and energy dispersive X-ray analysis (EDAX). For the restoration purpose mortar samples of the heritage building were collected and treated with synthesized NCH powder. The untreated and treated mortar samples were again characterized by XRD, FESEM, EDAX, nano indentation techniques, mercury intrusion porosimetry and thermal expansion coefficient (TEC). The results showed regular hexagonal shaped layered nanoparticles with dimensions about 100–200 nm. These nano particles have pure crystalline features and a high reactivity in terms of the carbonation process. FESEM and EDAX line mapping were performed on the treated mortar sample to evaluate penetration depth and grain adhesion of the nanopowders with treated sample. It was also observed that TEC was decreasing after treatment of synthesized NCH powder which revealed that the mortar under goes shrinkage due to volume decrease of the nano Ca(OH)2 phase.