In this paper, the effect of different kind of glass fiber on hydric properties of ultra-high performance concrete and normal strength concrete is determined. It was the use several types of micro fine high-dispersible alkali resistant fibers that prevent the formation of shrinkage cracks caused by tensions. Comparative measurements with both concrete without glass fibers are done as well. The main aim of this experimental work is to obtain sufficiently accurate input data for the estimate of durability surface layers of concrete which are connected with water transport and its accompanying effects such as biological degradation, water soluble salt transport or degradation by rainwater absorbing oxides of sulfur and carbon from air.
Properties of water transport and depth of chloride penetration into the Ultra High Performance Concrete (hereafter as UHPC) with mild steel fibres are presented in this paper. The main aim of this experimental part of work is to obtain sufficiently accurate input data for the evaluation of long-term durability of architectural concrete which are connected with water transport and its accompanying effects such as biological degradation or chloride transport. The article also presents the one dimensional chloride diffusion into UHPC which can be potentially dangerous particularly for durability of reinforced concrete structures. For the simulation of aggressive environments the concrete samples were exposed to chloride solution for one year. Measured data were examined in relation to the depth of penetration of chloride ions into the UHPC structure. Comparative measurements with normal strength concrete (hereafter as NSC) are done as well. An about five-time lower value of moisture absorption of UHPC compared to the NSC was observed and further the curve of chloride penetration into the structure is significantly steeper for UHPC samples.
Outstanding features of UHPC - Ultra High Performance Concrete are generally known. It has become increasingly used worldwide. For a better understanding of the material some features like the bond of reinforcement and UHPC has to be quantified. Research is focused on determination the bond stress between two types of the reinforcement (prestressing strands and bars) and different types of UHPC. Main goal of the research is to show significant increase in the shear stress in bond of UHPC compared to ordinary concrete. For evaluation of the bond stress the pull-out test were carried out. Specimens were prepared according to standard and tested in the laboratory. The influence of different material properties and different anchorage length of reinforcement to bond behaviour was examined.
Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) is fine-grained cement-based material characterized by high compressive strength (exceeding 150 MPa) and high modulus of rupture (over 15 MPa). The results of strengths depend on the size of the tested element, the loading rate and the boundary conditions during a testing. This type of material is used in a lot of countries (e.g. Germany, France, the USA, Japan, Austria, and the Netherlands) but it is not commonly used in the Czech Republic. The bridge over R10 road from Prague to Mlada Boleslav near Benatky nad Jizerou was the first structure where UHPFRC materials were used for lost shuttering slabs. Due to inhomogeneity of the steel fiber distribution the maximum attained force ranged between 9.6 kN and 25.7 kN for different lost shuttering slabs. The amount of steel fibers was very low at a tension zone at slabs with the lower load-bearing capacity. Steel fibers in these slabs were at the bottom of the formwork. The inhomogeneity of the steel fiber distribution was the foundation for producing of functionally layered beams with controlled inhomogeneity due to the mixtures with different fibers volumes. The results and behaviors of the layered beams and the homogeneous beams are presented in this paper.
This article deals with the development of concretes intended to be used as construction materials in the Czech deep repository for radioactive waste. The basic requirements for this concrete are a reduced pH value, which must maintain a constant reduced pH with a value of around 11 in the long term, and mechanical properties comparable to conventional concrete. The raw materials for the production of the proposed low pH concrete come exclusively from the Czech Republic. Material characteristics were measured on fresh mixtures and concrete after 28, 56, and 90 days of curing. In addition to the basic raw materials (aggregate, cement, water), plasticizers, microsilica or slag, and defoaming agents were added to the mixture. The aggregate:binder ratio was approximately 5:1 and the w/c water coefficient was approximately 0.6. The mechanical properties of the final concrete were similar to the reference recipe of conventional concrete (the decrease was less than 10%) and the pH value was even below 11 after 90 days. The issue of a sprayed variant of the LPC mixture was solved within the project.
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