Enrico Sassoni

ABSTRACT The issue of developing new sustainable building materials, having a reduced impact on the environment, has become a very important task, as the building sector is responsible for huge natural resources consumption and waste production. In the case of composite materials for building thermal insulation, the use of natural fibers, obtained from vegetable renewable resources and/or from agricultural wastes, in order to replace inorganic mineral fibers, has been investigated in recent years. Among other fibers, hemp-based composites, bonded by Portland cement, slaked lime or organic polymers, have been extensively studied because of hemp good thermal and acoustic insulating properties, low density, good specific tensile properties, rapid growing and high dry biomass production. In this study, novel hemp-based composites, obtained by using alternative binders with very reduced environmental impact, were produced and characterized in terms of physical, thermal and mechanical properties. Four types of panels were produced for different applications: two panel types, having a relatively low density, were investigated as possible composites for building thermal insulation; for the other two types, having a relatively high density, the possible use in the building/furniture industry, as substitutes for high density formaldehyde-bonded wood particles boards, was investigated. The results of the study show that the novel composite materials have very promising properties. Low density panels (ρ = 600-650 kg/m3) exhibited thermal conductivity values (λ = 0.087-0.138 W/mK) in good agreement with those reported in the literature for composite materials from natural resources with a similar bulk density, but, at the same time, they exhibited significantly higher mechanical properties. High density panels (ρ = 1250-1300 kg/m3) exhibited very good mechanical properties (flexural strength up to 17.5 MPa), which makes these panels very promising composite materials. Further tests are in progress to evaluate additional physical-mechanical properties, as well as reaction to fire and physical-mechanical durability.

ABSTRACT The goal of our work is to develop two classes of treatment for marble and limestone: 1) corrosion-resistant coatings and 2) consolidants for weathered stone. HAP has the same crystal structure as calcite and a small lattice mismatch (~5%), but is orders of magnitude less soluble. A layer of HAP can be deposited on the internal surface area of damaged limestone by exposing it to an aqueous solution of diammonium hydrogen phosphate (DAP) at room temperature and neutral pH. The treatment was applied to samples that were artificially “weathered” by heating in air, which is shown to produce a highly reproducible degree of damage for both limestone and marble. Limestone samples were treated with a 1 molar DAP solution by capillary absorption or by brushing until apparent refusal and sealing for 48 hours; they were then washed in deionized water and dried at room temperature. The dynamic elastic modulus was restored to its original value and the tensile strength (measured by the Brazilian test) rose about 25%. To protect marble from corrosion, the HAP deposit should ideally be nonporous, so it is necessary to achieve control over the nucleation and growth of the phosphate layer. Preliminary results indicate that dense layers can be produced at room temperature and neutral pH by controlling the calcium concentration in solution.

ABSTRACT The effectiveness of using hydroxyapatite (HAP) as a consolidant for carbonate stones was evaluated. HAP was chosen as a consolidating agent since it is notably less soluble than calcite and has a similar crystal structure and a close lattice match to it. Among possible methods for forming HAP, the reaction between the calcite of the stone and a solution of diammonium hydrogen phosphate (DAP) in mild conditions was chosen. Indiana Limestone samples, artificially damaged by heating to 300°C for 1 hour, were treated with a 1 molar DAP solution by partial immersion and capillary absorption for 48 hours or by brushing until apparent refusal and wrapping with a plastic film for 48 hours. After washing in deionized water for 3 days and drying under a fan at room temperature until constant weight, the improvements in dynamic elastic modulus and tensile strength were evaluated. The formation of calcium phosphate phases was observed by scanning electron microscopy (SEM) and the phase characterization performed by energy dispersive X-ray spectroscopy (EDS) and electron back-scattered diffraction (EBSD). The water absorption modification after the consolidating treatment was then assessed. Results show that treated samples experienced significant increases in dynamic elastic modulus and tensile strength, as a consequence of crack reduction and pore filling consequent to HAP deposition at grain boundaries. The sorptivity of the treated samples is reduced by 26-44% (based on treatment technique), so that water and water vapor exchanges with the environment are not blocked.