PSI - Issue 64

Salvatore Benfratello et al. / Procedia Structural Integrity 64 (2024) 1935–1942 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The preservation, the protection and the renovation of this heritage represent a very challenging task for architects, engineers and restorers. Very often the interventions required involve the adaptation of the structure to standards and, consequently, the strengthening of its elements. The improvement of the structural behaviour can be usually achieved by three different standard approaches: a) thickness swelling with the same material constituting the masonry, realizing suitable connections between the original and the new masonry (both the stiffness and the strength of the masonry are increased); b) reinforced plaster of suitable thickness on both the faces of the panel (the stiffness increment is negligible with respect to that of the strength); c) introducing suitably designed steel frame (both the stiffness and the strength of the masonry are increased). Clearly, the materials to be adopted should possess many different peculiar characteristics, ranging from the mechanical to the insulation ones, ensuring a compatibility with masonry. With the developments of the research in new materials as well as in theoretical and numerical modelling of the mechanical behaviour, the above-described approaches have been improved and new ones have been proposed. For example, the reinforcement of the plaster can be obtained by natural or artificial fibres (the so called carbon fiber-reinforced polymer (CFRP) or other fibres); an improvement of the mechanical behaviour of steel frame has been recently proposed in Benfratello et al (2021) taking into account the development of new beam column moment resisting connections (see Benfratello and Palizzolo (2017), Benfratello et al. (2017), Benfratello et al. (2019) a,b, Benfratello et al. (2020)). Among the new approaches to increase the structural performance of buildings the use of stainless-steel ribbon (Colajanni et al. (2016), Colajanni et al. (2017)) is worth of noting. In the last decades the increasing problem of waste management all over the world has led to the definition and implementation of different strategies to achieve sustainable environments in the framework of the so-called circular economy. Especially in the construction industry this aspect, together with the increasing attention to both thermal and acoustical insulation, led the researchers to focus on new eco-friendly materials obtained by recycling wastes and utilizing natural materials (see e.g. Badagliacco et al. (2021)). In last years, a growing attention was addressed to alkali-activated binders, widely known as geopolymers (see Davidovits (1989)), as possible substitute of ordinary Portland cement (OPC) as construction materials (Zhang et al. (2018)). Considering that geopolymers are developed starting from aluminosilicate-based raw materials (i.e. precursors), alkaline activators, water and other ingredients, they can be considered as “cement - free” materials and can be produced by using industrial waste residues or by products, such as construction wastes and so on (Alhawat et al. (2022), Lazorenko et al. (2022)). Due to this reason, to the reduced CO2 emissions and improved energy savings required by the manufacturing of geopolymer concretes than for OPCs, these materials are nowadays considered as eco-friendly construction materials. Further, their good mechanical properties and durability have attracted the interest of civil engineering industries (Das et al. (2014)). Despite all the advantages reported above, geopolymers evidence brittle behavior similarly to OPC. To overcome this drawback enhancing the ductility of geopolymers, one of the most investigated approaches consists in their reinforcement with synthetic fibers (see, e.g., Bai et al. (2020)) or mineral fibers such as basalt (Wang et al. (2022)). On the other hand, plant-based natural fibers attracted great interest due to their mechanical properties, sound and thermal insulation, low raw material cost and processing, large availability and lightweight. Furthermore, these fibers are renewable, biodegradable also showing a carbon dioxide neutral life cycle (Fiore and Calabrese (2019)). For all these reasons, several authors have recently addressed their efforts towards the utilization of natural fibers as reinforcement of geopolymer based materials. Aim of the paper is a first approach to evaluate the chance of adopting geopolymer plaster reinforced by natural fibers to improve the structural response of masonry structures. This goal is achieved by focusing the attention to sisal fibers as reinforcement, by performing suitable experimental tests to characterize the mechanical response of the reinforced geopolymer, by obtaining a numerical model of this material and by performing a structural analysis of a masonry panel with and without the sisal reinforced geopolymer plaster. The obtained results about the masonry panel are compared with those arising from a standard approach as reinforced plaster and confirm the effectiveness of the sisal reinforced plaster for increasing the structural response of masonry. Nomenclature Young’s modulus of the masonry F horizontal applied force bending test strength