Ornamental stone sludge recovery as thermo-eco mortar for plaster.

Ornamental stone sludge deriving from cutting processes is a topical issue at National and International level. The primary objective of the European Directive 2006/21/EC is to minimize the production of waste, generated by mining industry and encourage its recovery by means of recycling, reuse or recovery operations. The identification of best practices for the recovery of raw materials is one of the goal for circular economy concept. The main problems of ornamental stone sludge are related to physical and chemical characteristics: heavy metals concentration, due to cutting tools wear, very fine particle size distribution, and huge volume in limited areas. The research aims to exploit the physical and chemical characteristics of the sludge for their proper recovery, thus minimizing waste and bringing economic and environmental benefits to the companies that produce this waste. From literature few studies were carried out on reuse of sawing sludge as a plaster. Husam D. Al- Hamaiedeh and Waleed H. Khushefati, in 2013, have studied the reuse of sludge deriving from the cutting of granites as an additive for mortars and concrete cement. Pierucci A. et al, in 2007, investigated the reuse of sludge deriving from the processing of marble in mortars and plasters for the restoration of buildings. In this context the sludge deriving from the cutting of Piedmont silicate rocks is to be reused in substitution of the sands and fine particle normally used to produce plasters. For this purpose the Luserna stone sludge processed with diamond blade and diamond wire, with a low concentration of metals, and Luserna stone sand deriving from flaming process, was chosen. What we want to achieve is a lightened thermal eco-plaster. The first step concern the sludge characterization: particle size distribution, specific gravity, chemical analysis, leaching test, SEM and XPRD analysis and magnetic separation to identify the metals concentration. The second step foresees the development of the eco-mortar for plaster mix design and its characterization by means of different tests carried out according to UNI EN 988-1 (Technical specifications for mortar for masonry work. Part 1: Mortars for internal and external plasters). The performed test are as follow: bulk density of fresh mortar, spreading test, dry bulk density, flexural and compressive strength before and after freeze and thaw cycle, definition of compressive strength class and category, adhesive strength (pull out),thermal conductivity at 15 and 68 days of maturation and in dry condition, resistance to salts crystallization cycle, water absorption before and after freeze and thaw cycle and salt crystallization cycle, chemical analysis and leaching test and SEM analysis on final product. Sawing sludge deriving from the processing of Luserna stone has improved the rheological, thermal and physical performance of the environmentally friendly plaster, conferring a light macroporous cellular structure by means adding organic foam, thus facilitating its installation even for high thicknesses

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Silicate Sawing Sludge Recovery in Thermo Eco-Mortar for Macroporous Plaster

The aim of this research was to develop a new eco-product to find a correct recovery of silicate sawing sludge by means of waste management according to European criteria. To reach this goal, a thermal eco-mortar for a macroporous plaster was developed. The main characteristics of a plaster that influence the correct choice of the mortar are good adherence with underlying support, impermeability, thermal and acoustic insulation, mechanical resistance and ability to allow transpiration processes through the wall’s perimeters. Plaster is a mortar composed of a binding part that incorporates sand with a selected particle size distribution, not greater than 2 mm. The sludge, to be used as plaster, must satisfy requirements related to thermal insulation, resistance to moisture, mechanical resistance and good injection. For this purpose, low-content metals sludge, derived from the Luserna stone flaming and cutting slabs, are to be reused as a substitute for the sands and fine particles, respectively, that are normally used to produce plasters. The laboratory tests carried out on the finished product, in accordance with European standards, are as follows: water absorption, specific density, flexural and compressive strength, before and after freeze and thaw cycles, pull out, salt crystallisation cycle resistance and thermal conductivity. Chemical and leaching tests were carried out to verify the possible release of heavy metals into the environment after installation. The product quality was demonstrated as the cement mortars, incorporating the metals, did not allow their release in nature. A sludge recovery, in an unaltered state, was provided to reduce any costs connected to a pre-treatment and to make recovery economically advantageous for the stone sector

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