Properties of Czech WW2 Concrete Fortifications after 80 Years

Abstract

This paper deals with the investigation of properties of Czech fortification concrete bunkers built before Second World War (WWII). The Czech defense system consisted mainly of light bunkers type No. 37. The vast numbers of these bunkers have been preserved in various conditions to nowadays. The light bunkers type No. 37 were designed to last limited lifetime of decades. According to the preserved test protocols, strength of used concrete varied from 40 to 50 MPa, measured on cube specimens with dimensions 200×200×200 mm. There is an information, in general public, about high quality and strength of used concrete. The non-destructive analysis of compressive strength, determined by Schmidt hammer was performed. This method was used to maintain a historical value of the structures. Three were analyzed different bunkers type No. 37 located in Western Bohemia - Pilsner region. Tested bunkers are preserved in various conditions with various quality of concrete. The measurements by Schmidt hammer took place in several locations especially in the interior part. The exterior was also investigated but only in the locations of surface which were not covered with camouflage plaster. Non-destructive testing had shown high quality of concrete older than 80 years old concrete, with compressive strength between 50 to 60 MPa. On the other hand, based on the visual assessment, the concrete showed very different characteristics, especially in compactness and the quality of surface layer. We can find places with insufficiently compacted concrete with exposed steel reinforcement.

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