Michal Ženíšek

Thin Lightweight Panels Made of Textile Reinforced Concrete

Use of high performance concrete with reinforcement made of technical textile is increasing and new applications are being found. This paper presents new technology for the lightening of the panels made of textile reinforced concrete, which is being developed. The main focus of this research is to produce concrete elements suitable for use as facade panels with the least possible weight and environmental impact. Mechanical characteristics were measured on testing specimens with thickness of 18 mm with lightening representing 47% of their volume. Minimum thickness of concrete was 4 mm and therefore the reinforcement was covered by approximately 1.5 mm of concrete matrix. The strength of experimental test panels was measured in four-point bending stress test. Due to one-sided lightening and asymmetrical cross-section therefore, the tests were performed in both directions. For better interpretation of the results were the specimens of lightened panels tested alongside non-lightened specimens with the same thickness. Based on measured values, maximal dimensions of lightened facade panels were designed.

Dosage of Silica Fume in High Performance Concrete

Durability and high strength of concrete are closely associated with low porosity and generally denser material structure. This is achieved using the addition, which include also silica fume. This article deal with an effective dosage of silica fume in high performance concrete, in a proportion of 0-25 % by the weight of cement. Compressive strength, rheological behaviour and economic benefits were the main questions in this work. The expected increase in compressive strength showed itself in lower doses of silica fume, while higher doses did not produce a further increase in strength. In the case of rheological behaviour, we can confirm lower bleeding and segregation, but also faster drying of the surface layer. From the economic point of view, a small doses of silica fume are better, because then we have observed the highest increase in strength.

Dosage of Metakaolin in High Performance Concrete

This article deals with optimal dosage of metakaolin as addition in high performance concrete. The main criteria for assessing the optimal dosage of metakaolin was compressive strength, rheological behaviour and economic benefits. Metakaolin was added to the mixture of high performance concrete in the range from 0 to 25% weight of cement. The comparison of metakaolin and microsilica, which is often used by concrete producers due to its excellent properties, is also performed in this article. The experiments showed that using metakaolin as addition in high performance concrete affects the compressive strength and rheological behaviour positively. While the compressive strength increases especially at lower doses of metakaolin and at higher doses remained unchanged, changes in rheological behaviour were most obvious at the higher doses. From this point of view, it is possible to recommend a higher dose of metakaolin.

The Effect of Surface Treatments of Textile Reinforcement on Mechanical Parameters of HPC Facade Elements

Development of extremely thin concrete structures and demand for extremely thin elements are the reason of using composite non-traditional materials as reinforcement. Steel reinforcement is not very chemically resistant and it limits the thickness because of the required concrete cover as protection. This is the reason why textile reinforced concrete (TRC) going to be very famous and modern material. TRC in combination with fine grain high performance concrete (HPC) allows a significant saving of concrete. Due to its non-corrosive properties of composite technical textiles it is possible to design very subtle structures and elements. TRC and HPC in general are developed at the Faculty of Civil Engineering and the Klokner Institute, CTU in Prague. This present paper investigates the cohesion influence of textile reinforcement on four point bending test. All small experimental panels were reinforced with the same 3D technical textile from AR-glass roving with different type of cover layer. Different conditions of interaction between technical textiles and HPC were ensured by modified surface using silica sand and silica flour.

Comparison of Different Types of Glass Reinforcement for HPC Facade Elements from Mechanical and Economical Aspects

Concrete as the one of the most used material in civil engineering has also a very high negative environmental impact. In recent years’ environmental parameters of all building materials become the most important aspect. Especially reduction of concrete is becoming a very hot topic around the word because it can lead to the reduction of environmental impacts especially the consumption of primary energy, primary non-renewable materials and CO2 production. Textile reinforced concrete (TRC) is one of the possibilities to reduce amount of concrete in the structures. It is possible to design very thin structures because of non-corrosive properties of textile reinforcement and thus distinctly reduce the thickness. Combination with high performance concrete (HPC) allows to creating construction with mechanical properties on a required high level. This paper presents mechanical and economical comparison of different types of AR-glass reinforcement for HPC facade elements with the same amount of concrete.

Efficiency Evaluation of Concrete Surface Treatment

This paper presents the simplified method of efficiency evaluation of surface protection products for concrete elements. This evaluation method was designed to consist of as few testing procedures as possible and to use as few specimens as well. Several testing processes most of which were based on the European technical standards were used to compare five commercially available products. Those comparisons served to assess whether the chosen method has sufficient informative value and does not require a disproportionate amount of time and money. The main examined properties were impact on color and reflectivity of the original surface, durability of the coating in extreme weather conditions, wettability of the surface and amount of labor needed for its maintenance. All of these experiments were optimized so that they could be performed on one type of specimen.

Segregation of Steel Fibres of UHPFRC

The mixture of ultra-high performance concrete is often supplemented by steel fibres which can significantly improve the fracture energy of the concrete. The incorporation of steel fibres results in especially a significant increase of tensile strength and minimize the risk of brittle failure. However, these positive properties can be fully realised only if the fibres are uniformly distributed. Otherwise, that leads to different quality of the concrete and to deterioration of strength characteristics. The subject of this article is the segregation of steel fibres which is one of the frequent problems of poor distribution of fibres. The degree of segregation has been investigated depending on amount of fibre dosage, size of maximum aggregate size and degree of consistency of fresh concrete. Two types of steel fibres with circular cross-section of a diameter of 0.4 mm but with different lengths (12.5 and 25 mm) were used for experiments. The segregation was evaluated by the drop of the fibres on the cutting surface of specimens. The results showed that segregation was the most affected by the consistency of fresh concrete. The amount of fibre dosage as well as the size of maximum aggregate size did not significantly affect segregation.

Soft Insert for Support Modeling of Slightly Textile Reinforced Concrete

This paper presents a model of small experimental facade panel using four-point bending test. The facade panel with dimensions 100 x 360 mm and thickness approximately 18 mm was slightly reinforced using two layers of impregnated technical fabric from AR-glass roving. The amount of reinforcement in cross-sectional area of the concrete element is small and it is a reason of plastic joints initiation under the loading supports. The purpose of this experiment was validation of all used material parameters from the previous research in the program for nonlinear analysis of concrete and reinforced concrete Atena Engineering. For slightly reinforced concrete elements are monitored parameters better visible especially interaction between reinforcement and used concrete. The load transfer to the concrete element from the testing machine is typically modeled using some small steel plate. This paper shows the difference in results if we insert another flexible plate between the steel plate and the concrete element with a small defined stiffness.

Aggregate Segregation of Ultra-High Performance Concrete

This article deals with the aggregate segregation of ultra-high performance concrete. The main objective of this research was to determine which aspects of the design most affect segregation. It was studied the change of grading curve, water/powder ratio and consistency. Quartz sand with approximately rounded grains and maximum aggregate size up to 4 mm was used for the production of specimens. Segregation was evaluated after cutting the hardened concrete specimens according to the drop of grains of aggregate. The results show that segregation is by the far most affected by the consistency of concrete. Change of the grading curve or change the water/powder ratio has had no or little influence on segregation.

Lightweight TRC Facade Panels with the LEDs

High performance concrete reinforced by technical textiles has found a wide range of applications in recent years. One of the most widespread is the use of this composite for the very thin facade panels of various shapes and technical solutions. This paper presents an unique way how to lighten the facade panels made of high performance concrete (HPC) reinforced by technical textiles, which are additionally equipped with LEDs, so that a sufficient distance can be watch programmed based image displays.