An extensive research was undertaken in order to determine the dependence of shrinkage of high and normal strength concrete on the compressive strength and concrete composition. The part of research concerning dependence of autogenous shrinkage on compressive strength is presented in this paper. Ten groups of concrete, with the total of twenty nine mixtures, were prepared. Concrete mixtures of each individual group were made using the same quantity of water, while the quantity of cement (CEM II/A-S 42,5R) and mineral admixture (silica fume) was varied in each group. Concrete groups differed according to the quantity of water. Autogenous shrinkage of concrete was monitored together with the influence of initial curing in water on concrete shrinkage. Initial autogenous expansion was noticed during testing autogenous shrinkage, especially on normal strength concrete. Based on the analysis of experimental results, the dependence of autogenous shrinkage at one day of concrete age on compressive strength was defined. The dependence of autogenous shrinkage at later ages on compressive strength of concrete was also presented. Finally, the autogenous shrinkage components of best-known theoretical shrinkage prediction models were compared with experimental data.

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Utjecaj veličine ispitnog uzorka na mehanička svojstva mlaznog betona U radu su opisana laboratorijska ispitivanja uzoraka mlaznog betona ugrađivanog u primarni podgradni sustav tunela Sveti Ilija. Promatran je utjecaj dimenzija ispitnih uzoraka mlaznog betona na tlačnu čvrstoću i dinamički modul elastičnosti običnog i mikroarmiranog betona izrađenog in situ. Pregledom dobivenih rezultata analizirana je i opravdanost procjene tlačne čvrstoće na temelju rezultata dinamičkog modula elastičnosti. Effect of test specimen size on mechanical properties of shotcrete Laboratory testing of shotcrete installed in the primary support system of the Sveti Ilija Tunnel is described in the paper. The effect of the size of shotcrete specimens on the compressive strength and dynamic modulus of elasticity of the plain concrete and fibre reinforced concrete produced in-situ is analysed. The results are used to analyse suitability of estimating compressive strength based on the dynamic modulus of elasticity results.

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