Effect of cracks on hygric and thermal characteristics of concrete

Abstract

The effect of cracks on the moisture and heat transport and storage properties, basic physical properties and compressive strength of six different types of high performance concrete is analyzed in the paper. The cracks in the material specimens are randomly distributed, imposed by thermal treatment. Experimental results show that the presence of cracks affects all hygric and thermal parameters except for the specific heat capacity in quite a significant way. Also, the effects of microsilica addition and of the size and presence of aggregates are important. The liquid water transport is influenced by cracks, microsilica and aggregates in the most remarkable way, together with the compressive strength. Water vapor transport parameters, water sorption parameters, thermal conductivity and open porosity are also subject of significant changes and can indicate the damage induced by cracks with a sufficient sensitivity. Auswirkung von IntroductionProperties of concrete are mainly characterized by its compressive strength as the most representative parameter. Therefore, when first high performance concretes (HPC) appeared, they were only regarded as high strength concretes. This basic opinion has changed considerably during the last several decades. In the new HPC mixes, other properties such as moisture and salt transport and storage parameters, freeze-thaw resistance or abrasion resistance began to gain higher importance [1]- [10], and in some cases they even became decisive factors for the solutions made in the design process. In current HPC applications, compressive strength can be considered as just one among many significant parameters, and various properties related to durability issues are of equal importance.In durability assessments of concrete structures, it is essential to have wide enough information on the various properties of a particular concrete mix in order to get reliable service life estimate. During its service life, concrete can be subjected to combined effects of mechanical loads, moisture and temperature variations, chemical attacks, abrasive actions of wind-driven particles, etc. This can lead at first to surface cracking and later to crack propagation into the bulk concrete [11]- [15]. Thus, serious concrete deterioration can be induced in some cases. Crack appearance affects the concrete microstructure in a significant way, which results in changes of all material parameters which should be related to the damage of the original material. Therefore, the time factor should be taken into account when collecting the material properties as input parameters of computational models of service life.Material properties of cracked concrete were experimentally studied far less often than the respective properties of intact concrete specimens, until now. For example, mechanical properties of cracked concrete were studied in [16]-[21], water transport properties in [22]-[27], chloride transport in [28]-[34]. In addition, just one or two important parameters were determined in the majority of experimental...

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