Emil Soból

Deformation Behavior of Recycled Concrete Aggregate during Cyclic and Dynamic Loading Laboratory Tests

Recycled concrete aggregate (RCA) is a relatively new construction material, whose applications can replace natural aggregates. To do so, extensive studies on its mechanical behavior and deformation characteristics are still necessary. RCA is currently used as a subbase material in the construction of roads, which are subject to high settlements due to traffic loading. The deformation characteristics of RCA must, therefore, be established to find the possible fatigue and damage behavior for this new material. In this article, a series of triaxial cyclic loading and resonant column tests is used to characterize fatigue in RCA as a function of applied deviator stress after long-term cyclic loading. A description of the shakedown phenomenon occurring in the RCA and calculations of its resilient modulus (Mr) as a function of fatigue are also presented. Test result analysis with the stress-life method on the Wohler S-N diagram shows the RCA behavior in accordance with the Basquin law.

Scale Effect in Direct Shear Tests on Recycled Concrete Aggregate

Abstract The depletion of natural resources is forcing researchers to explore the possibilities of new aggregates, such as recycled concrete aggregate (RCA). In this article, the mechanical properties and the influence of the size of the direct shear box on the obtained parameters were examined. The study was conducted in two apparatus: medium (120 × 120 mm) and large (250 × 250 mm). In each of these devices, a total of 6 tests were performed: 3 for dry sample and 3 at optimum moisture content. From the results, the conclusions described below have been drawn

Material damping ratio from free-vibration method

Abstract One important aspect of soil dynamics is attenuation or energy loses. This inherent dynamic property is essential in the analysis of soil behavior subjected to a dynamic load. Energy absorption in soils leads to the definition of an equivalent viscous damping ratio (D). In resonant column testing there are commonly two different approaches in measuring material damping: during a steady-state vibration (SSV), when the specimen is vibrated at its first mode; and during free-vibration decay (FVD). The study reports results associated with the small to medium strain range material damping from FVD method, i.e. there is a cut off the constant vibration of the specimen at resonance and the specimen is allowed to free-vibration mode while the decay strain amplitude during free-vibration is calculated. The experiments were conducted on cohesive soils (sasiCl, Cl, clSa) from various test sites located in Warsaw, Poland. All the specimens were subjected to torsional mode of vibration at their first natural frequency, at different mean effective stress. The authors paid particular attention to the number of successive cycles after the free-vibration of the material is initiated. They examined various propositions from the literature and compare the received damping values using different number of cycles of vibration. The results showed that the most stable values of material damping ratio can be obtained by selecting each time a line of best fit on the authors’ choice of number of free-vibration cycles. However, the number of these cycles should not exceed 10.

Nonlinear dynamic properties of silty clay from Warsaw area

Abstract In this work, the small-strain and nonlinear dynamic properties of silty clay samples were studied by means of the low- and high-amplitude resonant column (RC) tests at various mean effective stresses (p’). The tested specimens were collected from the centre of Warsaw, district Śródmieście. Initially, the low-amplitude tests (below 0.001%) were conducted. Subsequently, the nonlinear testing was performed, at shearing strains greater than 0.001%. These tests were carried out in order to receive the dynamic properties of silty clay specimens in the nonlinear shear strain range. The small-strain material damping ratios (Dmin) of silty clay samples were also measured during the low-amplitude resonant column testing. The results show that increasing shear strain (γ) above the elastic threshold (γte) causes a decrease of the shear modulus (G) and normalized shear modulus (G/Gmax) of analyzed soil samples. Simultaneously, it is observed a increase of its damping ratio (D) and normalized damping (D/Dmin) with increasing shear strain (γ). Predictive equations for estimating normalized shear modulus and material damping of silty clay soils were presented here as well. The equations are based on a modified hyperbolic model and a statistical analysis of the RC tests results. The influence of unloading process on dynamic properties of the tested material was also discussed in the paper.