Materials Science Forum Vol. 1148

Abstract: This paper deals with the experimental determination of the freezing and thawing resistance of concrete using an innovative approach to evaluating the signal obtained by the ultrasonic pulse velocity test. Test specimens made of two types of concrete were used for the experiment. They were concrete mixtures of similar composition - the same components were used for their production. The only major difference was their level of resistance to freezing and thawing. The test specimens were prisms produced in the laboratory using plastic moulds and cylinders obtained by core drilling from the experimental pillar. The core-drilled test specimens were exposed to 100 freeze-thaw cycles and the test prisms with as many as 200 freeze-thaw cycles. After every 25th cycle, the non-destructive parameters were determined using the ultrasonic pulse velocity test as well as the resonance method. It was found that more advanced parameters of the ultrasonic signal than just its velocity were useful for evaluating the freezing and thawing resistance of concrete.

Abstract: It is increasingly evident that the construction industry must undergo a thorough transformation. Globally, the construction sector is responsible for up to 50% of carbon emissions and approximately 50% of resource consumption. This high resource consumption correlates with substantial waste generation. To reduce the environmental impact of civil engineering, priority should be given to preserving existing structures, even if they require repair or significant retrofitting, or at least reusing their components.. However, practical implementation is challenging, primarily due to the lack of proper assessment of existing structures, which is crucial for making decisions regarding liability. Currently, there are no well-established rules for determining the design life and safety of structures incorporating elements derived from dismantled ones. This paper identifies, based on the report prepared for the European Commission [1], best practices in the construction industry and the most promising measures to reduce its climate impact in the future. From the structural engineer's perspective, these measures would certainly involve substituting carbon-intensive materials with low-carbon alternatives and embracing adaptive, modular, and reversible designs supported by data-driven models. Reuse and disassembly are crucial for circular systems in the construction industry, particularly in designing connections and ensuring the transfer of information about structural elements throughout their lifecycle, including the concept of creating 'smart elements' equipped with Structural Health Monitoring (SHM) systems. The possibilities for implementing the concept of reuse of building structures is also discussed in the paper.

Abstract: Creep and shrinkage of concrete are important parameters for verification of ultimate and serviceability limit states. The prediction models which can be found in design codes, are applicable for ordinary concrete types. Unusual concrete types, like e.g., white concrete can be used, but their properties should be investigated by experimental testing. The paper is focused on measurement of shrinkage and creep of white and grey concrete of the same strength class. The experiments showed that both, creep and shrinkage of white concrete are higher than those of ordinary grey concrete. The measured shrinkage strains were compared with predicted shrinkage strains using various prediction models.

Abstract: Research in the field of recycled aggregate reuse in load-bearing structures is essential, as is the increase in awareness of the impact of construction on the environment. Using secondary raw materials also reduces landfilling and rock mining, and, from a practical point of view, this practice provides new materials for concrete. In this paper, the effect of using recycled aggregate concrete (RAC) on the basic properties of standard concrete is studied. Three types of concrete were studied: natural aggregate concrete (NAC) and two mixtures with 50 % and 75% replacement of natural coarse aggregates by recycled concrete aggregate. Results showed that using recycled aggregates reduces the mechanical properties of hardened concrete. The different properties of hardened concrete with a rate of recycled aggregate also impact the design process of the load-bearing structures of the buildings. The standard regulations in Slovakia allow using recycled concrete aggregate for up to 55% of all aggregates, but many designers do not trust this material. However, we cannot avoid using secondary raw materials in designing new structures in the future. The knowledge of recycled aggregate concrete presented in this paper provides directions for research and the concrete industry to focus on sustainable concrete products systematically.