Advanced Materials Research Vol. 1054

Abstract: This article deals with cement matrix for textile reinforced concrete. The main topic of this article is study of the development of the mechanical properties of the cement matrix. It was studied cube compressive strength and tensile strength in bending. The cement matrix has a similar composition as high performance concrete. Commonly used concrete was made to compare with the cement matrix. The cubes and prisms were made for the experimental program. The mechanical properties were studied at the age 12, 15, 18 and 21 hours and 1, 2, 3, 7, 14, 21 and 28 days.

Abstract: Currently, high performance concrete (HPC) is becoming more and more popular mainly because of its great mechanical parameters. As in the case of ordinary power concrete (OPC) it is necessary to improve the load bearing capacity with using of reinforcement. The present age calls for using of very thin structures for reasons of both environmental parameters and visual quality. Based on this fact, reinforcement start to use durable composite materials, such as technical textiles made of them. Element of HPC with this type of reinforcement is called textile reinforced high performance concrete (TRHPC). It is impossible to use the traditional approach for usually used steel reinforcement if we want to design these extra-thin structures. Modeled structures are very sensitive for input parameters and the development of standards for TRC material lags. The present study is focused on the different method of approach for the determination of tensile modulus of composite reinforcement. Three used methods are compared with each other using numerical analysis of four point bending test of façade element for one type of used reinforcement. Curves from numerical analysis are finally compared with the curve from real experiment and based on this the final evaluation is generated.

Abstract: In civil engineering, steel reinforced concrete is currently still the most widely used composite material. For broad spectrum of utilization is the most important combination of a high compressive and tensile strength [1]. The increasing demand for subtle concrete elements gave impetus to the development of the new materials for the reinforcement of concrete which are non-corrodible and thus do not need such a thick coating layer-technical textiles. These composite materials are known under the title Textile Reinforced Concrete – TRC. The current research reported the use of AR glass fibers reinforced material for HPC and comparison with other reinforced materials.

Abstract: The paper is a follow-up to previous presentations regarding the experience with ultra-high-performance (UHPC) concrete in the Czech Republic. It will present specific production and testing of pre-stressed beams in the company Skanska a.s. In 2013, the manufacturing facility of the company Skanska a.s. in Štětí, the Prefa plant, produced several series of pre-stressed beams made of ultra-high-performance concrete. The last series of pre-stressed beams was kept in a storage facility in Štětí over winter. In February 2014, destructive tests were carried out on two of the beams in the Štětí facility directly. Another two beams are used for monitoring the long-term changes under continuous load. A description of the tests and their results will be published in the paper. At the same time, a number of accompanying tests were carried out in the Klokner Institute of ČVUT in Prague. The results of these tests will also be mentioned in this paper. The experience and results have been achieved thanks to the grant project no. TA01010269 “Applied research of ultra-high-performance concrete (UHPC) for precast units of structures” subsidized by the Technology Agency of the Czech Republic.

Abstract: When designing the technological process for producing prestressed concrete sleepers on a large scale, it is especially important to achieve substantial reduction of production time due to the economic aspect. In this study, an estimation of the earliest possible time to release prestressing force from the wire with respect to bond development is presented, thus, allowing earlier removal and reuse of a prestressed concrete sleeper formwork. Time-dependent development of concrete compressive and tensile strength is defined according to fib Model Code 2010. A Strut-and-Tie Model has been adapted as a design method for establishing the transmission length required for anchoring prestressed wires in a prestressed concrete sleeper in accordance with the bond stress. Additional calculations have established that the method is consistent with the Eurocode approach.

Abstract: The paper presents obtained results of self-compacting concretes with various compositions with focus on basic characteristics development. Firstly the fresh concrete properties are summed and self-compactness classes are categorised and subsequently the values of compressive strength, static and dynamic modulus of elasticity of hardened concretes are compared. All the stated parameters were monitored during different ages of the concrete and therefore they provide a view of its development in time. With still enlarging scale of concrete types and development of their application it is necessary to monitor common parameters which due to the application of new concepts in raw material compositions and use of higher amounts of additives may notably differ compared to applied orthodox concrete parameters.

Abstract: The paper focuses on the problems of concrete for watertight tunnel lining. The theme is currently quite topical in the Czech Republic and abroad. The accent is put particularly on determination of level of dependence of different parameters of aeration of fresh and hardened concrete (determined in accordance with standardized procedures in common use) and durability of the concrete based on observation of properties of aerated concrete. Fluctuation of values of air content in hardened and fresh concrete are observed as well as influence of this fluctuation on durability of concrete.

Abstract: The company is still trying to the sustainable development. This trend also applies to the construction industry. One way to contribute is to use waste materials. Such a material with untapped potential is also fly ash. Fly ash is already partly used, mainly just in construction, but this use has still reserves. Fly ash is problematic material, when used correctly, also has positive benefits. One of the important of questions for the use of fly ash is the price. This paper provides an economic analysis of the binder in concrete with high content of fly ash and also comparing with other types of binder in concrete.

Abstract: The paper describes problems of using fly ash in concrete. Using fly ash produced during high temperature combustion in power plants as addition for concrete has been known since the 60s of the past century. The Standard EN 206 Concrete - Specification, performance, production and conformity characterizes high temperature combustion fly ash as an addition of the type II, i.e. active addition with pozzolanic properties. Use of fly ash as an active addition also enables partial replacement of cement. The paper solves the extent of cement which can be replaced with fly ash in this manner. Influence of addition of fly ash on consistency of concrete, development of compressive strength and elasticity modulus at the age of 7, 28, 60 and 90 days of concrete are observed.

Abstract: Fly ash is a waste product produced during combustion of coal. There are two basic types of fly ash. According to the type of combustion, there is produces pulverised coal combustion (PCC) fly ash or fluidized bed combustion (FBC) fly ash. Use of fly ash additives influences moisture properties of binder gels (cement paste). The particular object of interest of this post is capillary action of water in the binder gels with different concentration of fly ash in the mixture. There are substantial differences among moisture properties of binder gels with FBC fly ash additives compared with the binder gels with PCC fly ash additives.