The development of concrete technology results in a new generation of cement-based concrete such as high-performance concrete, self-compacting concrete and high-performance, self-compacting concrete. These concretes are characterised by better parameters not only in terms of strength and durability but also rheology of the mixtures. Obtaining such properties requires the adoption of a different composition and proportion of ingredients than ordinary concrete. The greater share of cement in these concretes causes an increase in the energy consumption and emissions (per unit of concrete volume) at the production stage. However, use of new generation concrete allows for a reduction of overall dimensions of a structural element, due to the increased strength parameters. Such a solution may finally result in lower consumption of resources and energy, as well as a decrease of gas emissions. The article presents the results of a comparative environmental analysis of ordinary and new generation concrete structures.

This paper provides an analysis of the development of bond strength in composite members of the concrete-to-concrete type. The experimental study was performed to evaluate the development of the bond strength between two concrete layers. In the study, two different types of concrete were used-normal concrete (NC) and high-performance concrete (HPC). Composite specimens of the substrate and overlay were of the NC-HPC and HPC-HPC types and reference NC-NC specimens were also made. The analysis of the bond strength was performed on composite cubes of size 150x150x150 mm which were subjected to splitting tension tests after 3, 7, 14 and 28 days of curing of the concrete overlay. The results of the study show that the basic phenomenon which affects bond strength is adhesion between concrete layers which develops with curing of the concrete overlay. The highest increase in the value of tensile bond strength was observed in the first 3 days of curing of the composite specimens. In this period the NC-NC composite reaches 53% of its 28-day tensile bond strength, the NC-HPC specimen-67% and the HPC-HPC-74%. The experiments showed different modes of interface failure depending on the configuration type of concrete in composite specimens. In the case of composite specimens NC-NC and HPC-HPC the observed dominant interface failure mode occurred within the overlay transition zone. For the NC-HPC specimens, the interface failure mode was observed both in the overlay transition zone and in substrate made of NC. No changes in the modes of bond mechanism failure were observed during curing of the composite specimens. The results obtained were compared with the existing studies in the literature on bond strength in composite concrete members.

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