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The volume changes of cement based composites are significantly exhibited in the hardening process. Initial phases of the hardening are complemented by the expansion due to the heat evolution that is subsequently alternated by the shrinkage. Both could cause a crack initiation. It is evident that ultimate volume changes of cement based composites are a complex process, because the final shrinkage is determined by the binder used, exposition and also by the previous history. The paper focuses on the evaluation of the main types of cements based on the Portland clinker by using a conventional procedure for the determination of the shrinkage on the standard cements mortars. These mortars were exposed to drying after 1 and 3 days of curing, related to the actual degree of hydration, which was estimated on the basis of compressive strength development. The hydration process was additionally monitored using thermogravimetry on the accompanying paste specimens during one year. The performed experimental program confirmed the essential sense of the curing regime especially for blended cement systems, which exhibited very low values of the hydration degree at applied curing intervals. Despite the slightly higher values of shrinkage of blended cements, the obtained results signalize the crucial effect of prolonged curing for these types of binders. The conclusion highlighted the necessity of taking into consideration the hydration degree during cement testing by using the conventional contact method. Otherwise, the simple interpretation leads to an overestimation of the less-suitable material solution.

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.

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.

This article deals with the long-term durability of a relatively new composite – textile reinforced concrete (TRC). The studied composite material introduces a modern and favourite solution in contemporary architecture and structural engineering. It could also be used in renovation and monument restoration due to its high utility properties. The experimental program was focused on the determination of the resistance of the TRC in an aggressive environment using durability accelerated tests. The high performance concrete (HPC), which we used in our study, exhibited a compressive strength exceeding 100MPa after 28 days. Specimens were subjected to a 10% solution of H2SO4, 10% solution of NaOH, and freeze-thaw cycling respectively. All these environments can occur in real conditions in the TRC practical utilization. The testing was carried out on "dog-bone" shaped specimens, specially designed for the tensile strength measurement. Studied TRC specimens were reinforced by textiles of three different square weight that were applied in one or two layers, which led to the expected increase of tensile strength The freeze-thaw cycling had the biggest influence on the tensile properties, because it causes micro-cracks formation. The specimens exposed to the chemically aggressive environment deteriorated mostly on the surface, because of the high density of the concrete and generally low penetration of the media used. The resistance of the studied TRC to the aggressive environment increased with the applied reinforcement rate. The performed experimental programme highlighted the necessity of including the durability properties in the design of structural elements.

The main objective of this article is to present the influence of high temperatures on mechanical properties of advanced refractory cement composite reinforced with carbon fibres. The presented material is suitable for industrial applications and can withstand elevated temperatures up to 1000 °C. The action of high temperatures was investigated on two temperature levels 600 °C and 1000 °C and was compared to reference specimens dried at 105 °C. The carbon fibres with flexural strength of 4100MPa were applied in dosage 0.50 %, 0.75% and 1.00% of the total volume. The second investigated modification was mutual ratio between aluminous cement and fine ceramic powder. The influence of high temperatures was investigated by measuring the bulk density, compressive and flexural strength, dynamic modulus of elasticity and fracture energy; all measured on prismatic specimens 40 × 40 × 160 mm. The workability of fresh mixture was limited by the maximum dosage of carbon fibres in 1% of the total volume. Based on the workability and evaluation of residual mechanical properties after temperature loading, the best was found to be the combination of carbon fibres in dosage of 0.75% by volume.

This paper describes the effect of cyclic elevated temperature loading on refractory slabs made from high performance, fibre reinforced cement composite. Slabs were produced from aluminous cement-based composites, reinforced by different dosages of basalt fibres. The composite investigated in this study had self-compacting characteristics. The slabs used were exposed to different thermal loading – 600 °C, 1000 °C, six times applied 600 °C and 1000 °C. Then, flexural strength was investigated in all groups of slabs, including group reference slabs with no thermal loading. The results show that the appropriate combination of aluminous cement, natural basalt aggregate, fine filler and basalt fibres in dosage 1.00% of volume is able to successfully resist to cyclic temperature loading. Tensile strength in bending of these slabs (after cyclic temperature loading at 600 °C) achieved 6.0 MPa. It was demonstrated that it is possible to use this composite for high extensive conditions in real industrial conditions.

The aim of our study was to develop a composite material for industrial use that is resistant to the effect of high temperatures. The binder system based on aluminous cement was modified by adding finely-ground ceramic powder and metakaolin to reduce costs and also to reduce adverse effects on the environment due to high energy consumption for cement production. Additives were applied as a partial aluminous cement replacement in doses of 10, 20 and 30% by weight. The composites were evaluated on the basis of their mechanical properties and their bulk density after gradual temperature loading. The influence of basalt fibers and modifications to the binder system were studied at the same time. Basalt fibers were applied in doses of 0.5% and 2.0% by volume. The results confirmed the potential of the mineral additives studied here for practical applications, taking into account the residual mechanical parameters after thermal loading. The addition of ceramic powder reduced the bulk density by 5% for each 10% of cement substitution, but the residual values were very similar. The bulk density and the compressive strength were reduced when basalt fibers were applied, and the flexural strength was significantly increased in proportion to the fiber dosages. Metakaolin seems to be a more suitable additive than the ceramic powder that was applied here, because there was a significant increase in the mechanical parameters and also in the residual values of all properties that were studied.