PSI - Issue 64

Francisco Játiva et al. / Procedia Structural Integrity 64 (2024) 1468–1475 Jativa et al./ Structural Integrity Procedia

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1. Introduction By 2050 it is expected that the amount of cement produced annually for concrete production will quadruple from 4.4 billion tons to 16 billion tons (Scrivener et al., 2018). By the same year, the global population is expected to reach 9.8 billion (United Nations, 2017); currently it is at 7.6 billion. The expected increase in demand for cement is driven by, among other factors, the population growth. At the same time, to face the challenge of climate change and resource depletion, innovative solutions for the construction sector are necessary. Construction and demolition (C&D) activities worldwide produce significant debris. As examples, in the United States alone, 600 million tons of C&D debris were produced in 2018, which is more than twice the amount of generated municipal solid waste (MSW) (U.S. Environmental Protection Agency, 2015). C&D materials account for approximately 33.5% of all debris mass in the European Union (EU) (World Cement, 2016) and in China by 2026, 4 billion tons of C&D materials are expected to be disposed (EnvGuide, 2021). Traditional concrete, on average, contains 70% aggregate by volume. Consequently, replacing virgin materials in concrete production is attractive for reducing environmental impact. Recycled aggregates in concrete production can lessen mining for virgin aggregates, but may affect compressive strength, workability, segregation, and cause adverse cement reactions (Sri Ravindrarajah et al., 1987; Sims and Brown, 2003). For that reason, the use of recycled aggregates is usually limited to 20% (De Brito and Saikia, 2012; Fiol et al., 2023). To address concrete’s brittleness, incorporating fibers can mitigate issues like plastic settlement, shrinkage, and bleeding in its fresh state, while enhancing deformation energy, reducing fatigue, and resulting in finer and better distributed cracks (Lin et al., 2023; Sasaki et al., 2023). For structural concrete applications, these properties improve the capacity in tension-drive failure modes such as shear (Lantsoght, 2019). Polypropylene and steel fibers, while widely used, are environmentally unfriendly. Natural fibers, on the other hand, could offer similar benefits and are eco-friendly and often generated as a byproduct of another industry (Hidalgo Robayo et al., 2024). This study evaluates concrete made from recycled aggregates and eco-friendly abaca (Hirondo et al., 2020; Alcivar Bastidas et al., 2023) and coconut fibers (Hussain et al., 2023; Shcherban’ et al., 2022) , and compares them with traditional polypropylene fibers, assessing aggregate characteristics (i.e. processing, aggregate characterization via sieve distribution, abrasion, alkali-silica reactivity) and mechanical performance via compressive strength, flexural performance (splitting tensile strength and toughness), and dynamic modulus of elasticity.

Nomenclature l f Ø diameter w/c L

fiber length

specimen length

resonant frequency water-cement ratio

E Young’s modulus of the material E dyn dynamic modulus of the material ≤ 1 50

a rea under the load vs net deflection curve 0 to ≤ L/ 150

2. Materials and methods 2.1. Materials 2.1.1. Recycled Aggregates

In collaboration with Holcim del Ecuador S.A., we procured 180 tons of construction and demolition debris. Given the absence of a formal categorization system at the center, extraneous materials such as plastic, steel rods, and garbage were separated from the primary material. From the initial 180 tons of material originally acquired, 67.3 tons were processed as Stone #57, 25.5 tons as Stone #7, and 69.5 tons as sand. Aggregate categorization followed ASTM C136 19 and C33-18 standards (ASTM, 2018; ASTM, 2019). Figure 1 shows the process for categorizing recycled aggregates for this case study.