CZECH WW2 CONCRETE FORTIFICATIONS: CORROSION PROCESSES AND REMEDIATION METHOD BASED ON CRYSTALLIZING COATING

Concrete is a relatively new structural material, hence the remediation of concrete structures is very rare. There are a lot of concrete fortifications in the Czech Republic, which were built just before WW2. These bunkers formed a long defensive line along the Czechoslovak borders as a protection against Hitler’s army. Today, after 80 years, many of the bunkers are listed as Czech national technical monuments with a strict protection of their historical authenticity. The article describes the technical survey and the possible conservation method of a selected concrete fortification, which exhibits a number of moisture related problems. The studied two-storey, heavily fortified bunker is situated close to the northern border of the Czech Republic, former Czechoslovakia. A detailed survey of the building includes the analysis of the interior environment parameters and laboratory testing of the used concrete. A long-term diagnosis identified the main problem, which lies in the inhomogeneity of the used concrete and the relating massive water ingress. However, the monitored bunker currently does not serve as a military structure and, therefore, a simple solution to improve the internal environment was suggested on the basis of the conducted measurements. With respect to the main causes of failures, the authors suggested a conservation method based on using a crystallizing coating. The suitability of the method was first verified under laboratory conditions and then also on the real bunker

CRYSTALLINE ADMIXTURES AND THEIR EFFECT ON SELECTED PROPERTIES OF CONCRETE

There have been many experimental measurements of the waterproofing ability and durability of concrete with a crystalline admixture, but some other important properties have not been reliably tested yet. The results of the tests, carried out by the authors, showed that crystalline admixtures reduce the water vapor permeability of concrete by 16-20 %. The authors also carried out the water pressure test in different time intervals, during the initial phase of cement hydration. The test results have shown that the full waterproofing effect of concrete with a crystalline admixture is available approximately on the 12th day after the concrete creation. The crystalline admixture effect on the compressive strength of concrete was also the subject of the testing. The results have shown that the compressive strength of the concrete with a crystalline admixture (added in an amount of 2 %) and the compressive strength of the specimens from concrete without admixture were almost identical after 28 days

Parapet structure from special shaped TRC blocks

The paper describes innovative parapet solution based on special shaped blocks made form textile-reinforced concrete - TRC. The blocks are designed for a placement at the parapet of building with a flat roof. The solution is appropriate for buildings with precast-concrete bearing structure by following the principle of precast technology (short construction time, minimal technological pauses). However, presented parapet TRC blocks can be used for energy efficient buildings as well in combination with thick layers of thermal insulation. The technical solution was registered as utility model no. CZ27642(U1)

EFFECT OF BACTERIA BACILLUS PSEUDOFIRMUS AND FUNGUS TRICHODERMA REESEI ON SELF-HEALING ABILITY OF CONCRETE

There are usually used inorganic substances for the strengthening of self-healing ability of concrete but some specific types of bacteria or fungi may also be considered for use. The bacteria’s ability to fill pores and micro-cracks was investigated on cylindrical concrete specimens with the diameter 55 mm and height 5 mm. Bacteria Bacillus pseudofirmus and fungus Trichoderma reesei was used for the experiment. The main objective of the experiment was to investigate, if it is possible to use Bacillus pseudofirmus and Trichoderma reesei for self-healing concrete. The results show, that it is more advantageous to use Bacillus pseudofirmus than Trichoderma reesei in alkaline environment. It is desirable to create the most ideal conditions for microorganism’s growth, as possible. Bacteria should have positive effect on self-healing ability of concrete. Any effect of fungus on self-healing ability of concrete wasn’t confirmed

Properties of Czech WW2 Concrete Fortifications after 80 Years

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

REMEDIATION TECHNOLOGY OF CLOCHE REPLACEMENT FOR WW2 FORTIFICATION IN THE CZECH REPUBLIC

Nowadays many parts of the Czechoslovak border fortification built in 1935 – 1938 have been sold to the private owners who want to reconstruct it. One of the biggest problems while reconstructing these objects is missing cloches. The aim of this study is to find solution of this problem. Authors wanted to offer the owners (usually clubs of military history) authentic design of the cloche for low cost, high durability and full functionality of the cloche that enables installation of original weapons.A result of the work was a development of a technical solution of the cloche consisting of a replica of the upper part made of reinforced concrete in combination with lower part made of concrete. This unique technical solution was confirmed as an utility model CZ32920(U1). Remediation measure was approved by the team at the pillbox T-S 20 in Červený Kostelec in 2019

UNDERGROUND AIR DUCT TO CONTROL RISING MOISTURE IN HISTORIC BUILDINGS: IMPROVED DESIGN AND ITS DRYING EFFICIENCY

The underground air ducts along peripheral walls of a building are a remediation method, which principle is to enable an air flow along the moist building structure’s surface to allow a sufficient evaporation of moisture from the structure. This measure reduces the water transport (rising moisture) into the higher parts of the wall where the high water content in masonry is undesirable. Presently, underground air ducts are designed as masonry structures, which durability in contact with ground moisture is limited. The article describes a new design of an underground air duct, which is based on specially shaped concrete blocks (without wet processes, because the blocks are completely precast). The air duct from concrete blocks is situated completely below the ground surface (exterior) or below the floor (interior). Thanks to this, the system is invisible and does not disturb the authentic look of rehabilitated historic buildings. The efficiency of the air duct technical solution was verified by the results of tests (based on the measured moisture values) conducted on a laboratory model. The experimental study showed that the moisture in the masonry equipped with the presented underground air duct had decreased considerably compared to the reference sample, namely by 43 % on average. The experimental study was numerically validated through numerical simulations performed with the program WUFI 2D

EFFECT OF BACTERIA <em>BACILLUS PSEUDOFIRMUS</em> AND FUNGUS <em>TRICHODERMA REESEI</em> ON SELF-HEALING ABILITY OF CONCRETE

There are usually used inorganic substances for the strengthening of self-healing ability of concrete but some specific types of bacteria or fungi may also be considered for use. The bacteria’s ability to fill pores and micro-cracks was investigated on cylindrical concrete specimens with the diameter 55 mm and height 5 mm. Bacteria Bacillus pseudofirmus and fungus Trichoderma reesei was used for the experiment. The main objective of the experiment was to investigate, if it is possible to use Bacillus pseudofirmus and Trichoderma reesei for self-healing concrete. The results show, that it is more advantageous to use Bacillus pseudofirmus than Trichoderma reesei in alkaline environment. It is desirable to create the most ideal conditions for microorganism’s growth, as possible. Bacteria should have positive effect on self-healing ability of concrete. Any effect of fungus on self-healing ability of concrete wasn’t confirmed