PSI - Issue 81

Nazar Sydor et al. / Procedia Structural Integrity 81 (2026) 360–366

361

high strength of concrete leads to a predominance of brittle failure, which is related to the development and propagation of cracks within the material. Sustainable development is one of the most important aspects of the modern world in every industry. In construction, this strategy includes increasing the durability of materials, products, and structures, as well as designing and using low-energy environmentally friendly materials. Reducing carbon emissions is crucial to reducing global warming and climate change trends. Since the production of cement, the main component in cementitious materials, generates about 9.5% of total CO2 emissions in the world (Ho and Huynh (2023)), replacing cement with alternative materials, in particular additional cementitious materials SCM, can significantly reduce the carbon footprint of the industry (Mehta and Walters (2008). Due to improvements in the mechanical properties and durability of concrete, the trend of using mineral additives continues to grow (Malik et al (2025)). Mineral additives can be divided into two groups: chemically active mineral additives (highly reactive pozzolans) and microfiller mineral additives (low- and moderately reactive pozzolans). The type of additive is determined by its physical properties (particle size, particle shape, specific surface area, etc.) and chemical properties (chemical and phase composition, ratio of hydraulic oxides) ( Sicáková and Špak (2018) ). The main functions of supplementary cementitious materials are to densify the particle packing during the preparation of the concrete mix, improve the microstructure of the concrete by minimizing its porosity, and enhance its resistance to aggressive environments due to their pozzolanic activity (Khan et al. (2025); Malik et al. (2025)). Standard EN 206 specifies three kinds of Type II additives (fly ash, blast furnace slag (GGBS), and silica fume) and defines the conditions for their use in concrete. Additionally, studies have been conducted on the use of zeolites as a partial replacement for cement, confirming their long-term potential for increasing concrete strength ( Sicáková et al. (2017); Markiv et al. (2020)). The study by Suda and Srinivasa Rao (2020) shows that using an optimal combination of microsilica and GGBS can improve the durability characteristics of concrete compared to using these supplementary cementitious materials individually. In the study by Rocha et al. (2025), the properties of ternary mixtures containing Portland cement, recycled concrete powder, and metakaolin were evaluated to produce HSC with a compressive strength of 60 MPa. Recently, researchers such as Amsalu Fode et al. (2023); He et al. (2021); Hakeem et al. (2022); Li et al. (2022), Marushchak et al. (2025); Pozniak et al. (2024); Topylko et al. (2025) have focused on waste materials (ash, ground brick, glass powder, etc.) as mineral additives for eco-friendly HSCs. On one hand, the adding of mineral additives aims to reduce the carbon footprint of concrete; on the other hand, it must ensure the necessary strength performance. Therefore, a main characteristic of mineral additives determining their effectiveness is their pozzolanic reactivity, which arises from their interaction with Ca(OH) 2 , a product of cement hydration. From this perspective, a promising additive for HSCs is microsilica, which is characterized by a high specific surface area and high reactivity ( Dybeł and Furtak (2017);Malik et al. (2025)). Modern modifiers of the microstructure of HSCs are nanomaterials (Sanytskyi 2 et al. (2024); Sikora et al. (2022); Marushchak 1 et al. (2018)). The high strength of concrete leads to a predominance of brittle failure, which negatively affects its durability. The most effective solution to this problem lies in the use of dispersed reinforcement, which can provide three-dimensional reinforcement and enhance the mechanical properties of concrete (strength, crack resistance, impact resistance, etc.) as well as the operational reliability of structures. In this context, fiber-reinforced concrete (FRC), high-performance fiber-reinforced concrete (HPFRC), and engineering cementitious composites have been developed (Al-Ameri et al. (2022); Ruiz et al. (2023); Sydor et al. (2021). Composites with additives of materials characterized by high elastic properties demonstrate increased impact resistance; however, they sharply reduce compressive strength (Abdelmonem et al. (2019); Marushchak et al. (2024); Yu et al. (2016)) FRC is known for its impressive properties, including a high strength to density ratio, increased tensile and flexural strength, as well as outstanding compressive and tensile strength under both static and dynamic impact loads (Mousavi et al. (2019); Marushchak 2 et al. (2018)). These characteristics, particularly the high strength-to-weight ratio observed in ultrahigh performance mixtures, enable the design of tall and architecturally complex structures while optimizing material usage (Ou et al. (2012)). Commonly used fibers in cementitious fiber-reinforced composites include polypropylene, glass, basalt, and steel fibers (Hassan et al. (2024); Sanytskyi 1 et al. (2024); Ou et al. (2012)). The main structural characteristic of both conventional and HSC is compressive strength, which is a dynamic property and depends on time, volume changes and internal stresses in the concrete even before mechanical loading. Concrete testing methods are focused on properties tested after 28 days. However, pozzolanic additives require a longer time to develop their properties due to the slower progress of pozzolanic interaction. Therefore, short-term property values may not be relevant for HSC. For structural applications and durability, it is important to understand the development of concrete strength over time, which usually increases with age. However, studies by Lantsoght et al. (2018) reported a temporary decrease in tensile strength over time for HSC with strength class C55/67. Awasthy et al. (2023) showed that in the case of direct tension and flexural tests after 28 days of wet curing, there is a temporary decrease (about 20 – 25%) for both normal strength and HSC specimens. Ho and Huynh (2023) showed that when Portland cement was replaced by 10 – 50% fly ash, the strength of HSC increased at the ages of 28, 56, and 120 days. Chen et al. (2020) noted that with increasing compressive strength, HSC containing silica fume and slag exhibits a decrease in specific creep and creep coefficient. The compressive strength of concrete prepared with 30% fly ash and 30% slag gradually increases with time (from 14 to 900 days) compared to the control concrete. With increasing age of the concrete, a decrease in porosity and capillary water absorption was observed (up to 900 days) (Miah et al. (2023)). Considering the contradictory results of previous studies, the aim of this research is to evaluate the mechanical properties of high strength fiber-reinforced concrete during long-term curing in order to understand its long-term performance.