Preizkušanje betona za sanacijo objektov Rupnikove linije

Rupnikova linija je sistem vojaških utrdb, postavljenih na Rapalski meji, ki naj bi pred drugo svetovno vojno takratno Jugoslavijo varovala pred vdorom Italijanskih sil. Sestavlja jo več kot 4000 armiranobetonskih vojaških objektov, zgrajenih med letoma 1935 in 1940. Delimo jo na (visoko ležečo) zgornjo in (nizko ležečo) spodnjo linijo. Ker bunkerji v svoji življenjski dobi še niso bili sanirani in so nekateri v slabem stanju, smo za izbrane bunkerje na podlagi predhodnih raziskav v okviru magistrske naloge sprojektirali beton, ki naj bi bil primeren za njihovo sanacijo. V okviru raziskave smo preverjali, če so mehanske lastnosti replik betona primerljive z mehanskimi lastnostmi historičnega betona. Vzorce historičnega betona smo izvrtali iz izbranih bunkerjev Rupnikove linije in jih narezali na valje premera 95 mm in višine 100 mm. V raziskavi smo uporabili 9 vzorcev zgornje in 6 vzorcev spodnje linije. Za primerjavo smo v laboratoriju pripravili dve mešanici, repliki historičnega betona. V prvo mešanico, ki naj bi bila namenjena sanaciji izbranih bunkerjev zgornje linije, je bil vgrajen apnenčev agregat, v drugo, ki naj bi bila namenjena sanaciji izbranih bunkerjev spodnje linije, pa smo vgradili dolomitni agregat. Iz vsake mešanice smo pripravili 6 kock dimenzij 100 × 100 × 100 mm in 6 kock dimenzij 150 × 150 × 150 mm, skupaj 24 vzorcev. Vzorcem smo na podlagi meritev s hidravlično stiskalnico najprej določili izhodiščne vrednosti tlačne trdnosti in statičnega modula elastičnosti. Po tem smo vzorce izpostavili 30 ciklom zmrzovanja in tajanja s prisotnostjo talilnih soli. Med ciklanjem smo z ultrazvokom spremljali spremembo tlačne trdnosti in dinamičnega modula elastičnosti, hkrati pa smo jim merili izgubo mase. Na podlagi rezultatov smo se opredelili glede ustreznosti betonskih mešanic za sanacijo z vidika tlačne trdnosti, modula elastičnosti in zmrzlinske odpornosti. Rupnik fortification line is a system of military fortifications on the Rapallo border, built just before the second world war. Its purpose was to defend the Kingdom of Yugoslavia from an attack by Italian forces. The fortification line consists of about 4000 military structures built between 1935 and 1940. Most of the structures were made with reinforced concrete and were split between the upper line (high positions) and the lower line (low positions) made of different concrete mixtures. Some of the structures are in a terrible state and in need of restoration, so we designed a concrete mix suitable for their restoration based on the research included in this thesis. The study compared the mechanical and physical properties of the replicated concrete samples to the samples of historic concrete gained from the structures on the fortification line. Samples of concrete were taken from selected fortifications and shaped into cylinders measuring 95 mm in diameter and 100 mm in height. Of all the samples 9 were taken from the bunkers of the upper line and 6 were taken from those of the lower line. Two different mixtures of concrete were prepared. For the restoration of the upper line, limestone aggregate was used, and for the restoration of bunkers of the lower line, dolomite aggregate was used. Each mixture was used to produce six 100 × 100 × 100 mm cubes and six 150 × 150 × 150 mm cubes, 24 in total. Using a hydraulic press, we set a base value for the concrete specimens' compressive strength and modulus of elasticity. The samples were then exposed to 30 freeze-thaw cycles, with the presence of chlorides, where compressive strength and dynamic modulus of elasticity were measured using ultrasound. Loss of mass was also measured at the same time. The results were used as the basis for determining the suitability of the concrete mixtures for the restoration of the structures on the Rupnik military line.