PSI - Issue 64

Pier Francesco Greco et al. / Procedia Structural Integrity 64 (2024) 1888–1895 Pier Francesco Greco/ Structural Integrity Procedia 00 (2019) 000 – 000

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1. INTRODUCTION The increasing pollution of Earth’s atmosphere has gained substantial attention within the scientific research community. A primary objective of global scientific endeavors is the mitigation and reduction of the carbon footprint. In 2015 parties of the UNFCCC (United Na tions Framework Convention on Climate Change) adopted the “Paris agreement” for reducing greenhouse gas emission of about 40% than ‘90s levels, increasing this amount of about 55% for 2030, a further objective taken by European Commission in 2020. The building construction sector poses significant challenges due to its high energy consumption and large amount of wasting materials Lavagna et al. (2018), Andrew (2018). Concrete, being one of the most used material, consumes a lot of energy during its production processes. This is primarily due to its main component, cement, needing a high cooking temperature of approximately 1400°C, compared to lime, which requires only around 1000°C Adesina (2020), Abdel-Hamid et al (2021), Librelotto et al. (2020). Additionally, the porous composition differs between the two kind of materials and the denser structure of cement avoids carbonization, leading to reduced CO2 adsorption during hardening consequently contributing to a higher amount of gas concentration in the atmosphere. When used as the matrix of composite materials for structural reinforcement, lime and cement-based mortar also exhibit varying levels of compatibility with the traditional materials used in historical buildings. The compatibility issue is particularly crucial, given that lime mortar is the main component of historical building heritage all over the world Fang et al. (2014). Since ancient Roman times, the use of lime mortar has been pivotal in various fields, leading to technological advancements through the addition of additives and alterations in composition. Vitruvio, one of the most famous architectural theorist, dedicated an entire chapter on lime and mortar, providing details on optimal composition for different applications and methods for preparation Adam (1988). Consequentely, the use of lime as a binder holds instrinsic value within our cultural heritage. Nowadays, the renewed interest in sustainability and the preservation of technical heritage has sparked a novel focus on lime mortar, suggesting its potential use as a novel material for the future with specific modifications. Enhancements in binder performance can be achieved by using different components tailored for different purposes, such as thermal insulation or structural applications. Developing an improved version of lime mortar ensures enhanced mechanical properties without compromising compatibility. The historical practice of incorporating various fiber types to enhance the mechanical properties of lime-based mortar dates back to ancient civilizations. Notably, in ancient Greece, straw and wood were commonly added to mortar for stability. Currently, substantial research efforts are directed towards investigating fiber reinforcement efficacy in mortar. Synthetic fiber-reinforced mortar is practically applied to strengthen existing constructions, using fibers like polypropylene or glass to enhance structural integrity and durability Liberotti et al. 2022, Cucuzza et al. 2023. However, escalating concerns regarding environmental sustainability and biodegradability have prompted significant exploration into natural fibers as synthetic alternatives Haily et Al. (2023). Recent literature reflects numerous contributions on the use of different natural fibers (such as hemp, flax, jute, and Spanish broom) in mortar for strengthening applications Gioffré et al. (2023), Gioffrè et al. (2024), Benfratello et al. (2013), Giglio and Savoja (2017), Juradin et al (2021), Formisano et al (2021). However, the impact of integrating natural fibers as reinforcement within mortars is marked by notable variability, with some instances demonstrating increased strength, others revealing heightened deformation, and still others exhibiting a transition in mechanical behavior from traditional brittleness to ductility. Indeed, it seems interesting to consider the development of new biocomposite materials that involve the use of nanomaterials to enhance mechanical characteristics and to reduce material variability Abbass et Al. (2023), Pepi et al (2024). This paper presents the preliminary results that will be used to assess the performance of biocomposites in structural strengthening of masonry structures, where the vegetal fibers are coated with nanomaterials. The main objective of this study is to thoroughly examine and clarify the mechanical response of mortars reinforced with natural fibers Formisano et al (2017), S. Juradin et al (2021), Greco et al (2024). Two base biocomposite materials using lime mortar as the matrix are investigated: one with hemp fibers and one with Spanish broom fibers. The reinforcing effect of these fibers is assessed through direct comparison with unreinforced specimens as reference. The mechanical behavior of the materials is analyzed using three-point bending and uniaxial compression tests, focusing on stress, strain values and Young modulus values. Furthermore, fracture energy is studied to understand the composites' ability to absorb energy before and after failure, along with the ratio between post-peak energy and total energy to quantify residual capacity.