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The present work investigates the feasibility of producing boards, with unconventional materials, namely hazelnut shells as a high-mass bio-aggregate and a sodium silicate solution as a no-toxic adhesive, and discusses possible applications based on an extensive characterization. The aim is to define a feasible reuse of a largely produced agro-industrial by-product to reduce the high environmental impact caused by both the construction and the agriculture sectors, by proposing a building composite that improves indoor comfort. The presented combination of aggregate-adhesive generated a product with characteristics interesting to explore. The thermal conductivity is moderated, and the composite achieved values of σ max = 0.39 N/mm² for flexural strength and σ max = 2.1 N/mm² for compressive strength, but it showed high sorption capacity with a moisture buffering value of about 3.45 g/(m² %RH), and a peak of sound absorption between 700 and 900 Hz. Therefore, the boards' most promising performance parameters seem to be their high hygroscopicity and acoustic absorption behaviour, namely in the frequency range of the human voice. Hence, the proposed composite could improve indoor comfort if applied as an internal coating board. • Hazelnut shells are an agro-industry waste largely available and suitable to produce boards. • Hazelnut shells, sodium silicate, and composite boards using both are highly hygroscopic. • Applied in buildings as indoor coating boards they could act passively as moisture buffers. • The hazelnut shells-based board shows positive, uncommon acoustic absorption performance. • The composite board can avoid the indoor acoustic discomfort caused by people's speech. [ABSTRACT FROM AUTHOR]

• Agro-industrial wastes are feasible to produce bio-composite boards and panels with different adhesives. • The properties of the bio-composites widely depend on the selected adhesives. • Sodium silicate-based bio-composites have high hygroscopicity and good resistance to mould growth. • Starch-based bio-composites are easily affected by mould at high relative humidity. • Citric acid and sodium silicate solution can improve bio-composites biological resistance. Laboratory tests were carried out to evaluate the feasibility of producing boards or coating panels with good hygrothermal performance by using different agro-industrial wastes (grape and olive press wastes, hazelnut shells, spent coffee and pine) and adhesives (gypsum-based binder, sodium silicate solution and starch-based glue). Hygrothermal properties and resistance to mould growth, including the effect of citric acid, were evaluated. The results highlighted the benefits and drawbacks of each adhesive: the binder seems more adequate to produce bio-based plastering mortars than boards; the other adhesives seem efficient solutions to produce boards with good hygrothermal properties; for the natural glue the bio-susceptibility needs improvement. [ABSTRACT FROM AUTHOR]

• Lignocellulosic bio-wastes from forest management and agro-industry as building materials are reviewed. • Some bio-wastes produced in Euro-Mediterranean countries are selected. • Studies on eco-efficient boards made of natural fibers and other bio-wastes are analysed. • Further studies on properties of bio-wastes and eco-efficient boards are needed. This study investigates the possibility of using agro-industrial wastes for building products, mainly focusing on their insulation properties. A classification of bio-wastes is provided, namely of the lignocellulosic ones and their features and properties are described. Information about three main topics is collected: world production and consumption of some crops already used as building materials, their chemical composition and their most studied properties. Since the considered materials are lignocellulosic and they have many common features, a comparison is made. The aim is to have comparable information to support future research related to the production of eco-efficient indoor insulation boards. The result of this research is the choice of four different agro-industrial wastes produced in the Euro-Mediterranean Countries. This area was chosen as buildings typically have little or no insulation due to the regional mild climate; however, particularly with climate change, indoor hygrothermal comfort is poor. The collection of information allows some conclusions to be reached about the different bio-wastes already studied and identify gaps in the literature. [ABSTRACT FROM AUTHOR]