Characterisation of concrete from the rupnik military line

The Rupnik military line was established in about 1935 in the Kingdom of Yugoslavia as a defence system against the Kingdom of Italy. It consists of more than 4000 reinforced concrete military bunkers positioned on the eastern part of the Rapallo border, varying in size and purpose, and was a top-secret project at the time. Different non-destructive and non-invasive techniques were used to characterise the selected bunkers and carefully conceived concrete samples to gain an insight into the concrete technology used to build these historic military infrastructures. The results of the non-destructive techniques were further compared to those of destructive techniques for a given property. It was established that very different concrete compositions were used to build the bunkers, and an extensive dispersion of the properties was confirmed for each composition. The average compressive strength of the Schmidt hammer for a given position is an acceptable estimate of the actual compressive strength of concrete without destructive intervention into a bunker. It also enables an estimation of the secant modulus of elasticity using the ModelCode2010 approach. Cylinders drilled from a bunker provided additional information about the concrete petrography, its physical and mechanical properties and the durability of reinforced concrete.