# Influence of Concrete Strength Class on the Long-Term Static and Dynamic Elastic Moduli of Concrete
###### Abstract  
Construction materials, among which concrete is by far the most used, have followed a trend of continuously increasing demand in real estate. A relatively small number of research works have been published on the long-term material properties of concrete in comparison to studies reporting their findings at standard curing ages of 28 days. This is due, in part, to the length of time one must wait until the intended age of concrete is reached. The present paper contributes to filling this gap of information in terms of the strength and dynamic elastic properties of concrete. The dynamic modulus of elasticity may be used to assess the static modulus of elasticity (Young's modulus), a key property used during the design stage of a structure, in a non-destructive manner. This paper presents the results obtained from laboratory tests on the long-term (6 years) characterization of concrete from the point of view of dynamic shear and longitudinal moduli of elasticity, dynamic Poisson's ratio, static modulus of elasticity, compressive and tensile splitting strengths, and their change depending on the concrete strength class. long-term mechanical properties; dynamic modulus of elasticity; dynamic shear modulus; concrete strength class +
Footnote †: journal: Applied  
19 November 2021  
6 December 2021  
Published: 9 December 2021  
**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. **Published:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. life under severe environmental conditions [3; 4]. However, given that some of the building stock is fast approaching its designed lifetime, coupled with a growing awareness of the need to understand what happens to concrete in the long run, an increased number of research works dedicated to investigating the long-term properties of concrete and concrete structural elements have been published. Recent studies have revealed the effect of metakaolin and silica fume on the long-term strength and durability properties of concrete [5]. Both supplementary cementitious materials have an influence on either the compressive strength or internal structure of concrete, but their synergistic long-term effect does not produce significantly improved mechanical properties. However, using metakaolin in combination with polymer admixture has resulted in improving the long-term strength and durability of concrete [6]. Using wastewater as mixing water in concrete was found to have adverse effects on the mechanical properties and durability of concrete in the long run, but the use of industrial treated wastewater had minor negative effects on the abovementioned properties [1]. This represents a significant step forward in reducing the amount of fresh water used in the construction industry. The effect of curing conditions has also been investigated from the point of view of the long-term properties of concrete. Steam curing is a technique used in the production of prefabricated/precast elements to ensure a higher early-age performance. Several curing procedures have been investigated: steam curing, step-curing and variable-rate curing, each of which was found to have a direct influence on the heat damage effect in concrete, with consequences for its long-term properties [7]. Material properties have a direct effect on the behavior of structural elements in buildings. It was reported that long-term concrete shrinkage results in a decreased magnitude of the load, causing the occurrence of the first crack in reinforced concrete elements and reducing the tension stiffening mechanism for lower longitudinal reinforcement ratios [8]. Some of the concrete poles supporting power lines are made using spun-concrete technology. They are subjected to repeated freeze-thaw cycles during their lifetime in conjunction with various other environmental factors and chemical attacks.