## 1 Introduction  
Concrete, one of the most used construction materials, has been intensively studied due to the complex phenomena governing its behavior from an early age to the long term [1]. Despite its many uncontested advantages as a construction material, concrete also has some drawbacks that prompted an overwhelming research effort to either mitigate or eliminate them entirely. However, perhaps one of the biggest advantages of concrete is its ability to incorporate a variety of wastes from different sources: power plants [2], steel manufacturing processes [3], construction and demolition wastes, municipal wastes, etc. The latest report of ETRMA (European Tyre and Rubber Manufacturers' Association) shows that in 2019, a total of 3.55 million tons of tires reached their end of life in Europe alone. Most of them, 95%, according to the same report, were treated through either material or energy recovery (cement kilns, urban heating and power plants) techniques. The application of ELT (end of life tires) derived materials in civil engineering, public works and backfilling amounted to a total of 112 thousand tons, a significant 18% increase compared to 2018. In view of the continuously stricter regulations in terms of environmental protection and abiding by the concept of circular economy, the construction industry has looked for alternatives in terms of reducing the carbon footprint and preserving the raw materials. The use of rubber crumbs from ELTs as partial substitutes of fine and small coarse aggregates was investigated for the past 25 years. From the early works of [PERSON] and [PERSON] [4] up to the recent research of [PERSON] et al. [5], much effort was invested in understanding the behavior of this new type of concrete. From the very beginning, it was clear that adding rubber aggregates to concrete resulted in a decrease in the values of mechanical properties [6]. Since strength and elastic properties are the main parameters considered in the design process of structural elements, rubberized concrete has seen limited application in this direction unless special confining solutions were applied [7; 8; 9]. However, significant deformability was achieved for a material that is inherently brittle [10]. This fact, coupled with the proven ability of rubberized concrete to dampen vibrations, resulted in it being used for various purposes, from road crush barriers to non-structural elements designed to reduce the traffic vibrations or to have enhanced soundproofing properties. Moreover, the durability of concrete incorporating rubber aggregates was found to be higher [11], especially in the case of sulfate corrosion [12]. However, the data presented in the scientific literature focused on the short-term values of the mechanical properties of Portland cement concrete containing rubber aggregates. This is completely understandable given the fact that all design guidelines refer to the strength values and modulus of elasticity obtained by means of standardized tests at the age of 28 days. This allows for a quick and unified approach to assess whether a certain type of concrete is suitable for structural or non-structural applications. On the other hand, the long-term strength and elastic properties of concrete are rarely investigated, and it is generally assumed they increase in time, provided that there are no deleterious agents acting upon the material. Accelerated durability tests are able to offer information on the ability of concrete to keep its integrity when subjected to chemical attacks and environmental factors (freeze-thaw). The paper presents the results of a research work aimed at assessing the long-term strength and elastic properties of rubberized concrete. The parameters of the research were the rubber replacement of fine aggregates and the age of testing the specimens. Compressive and splitting tensile strength of concrete cylinders were obtained at the age of 5 years, coupled with a static and dynamic modulus of elasticity of all concrete specimens.