A New Method to Determine the Steel Fibre Content of Existing Structures—Test Setup and Numerical Simulation

The diagnostics of constructions built with steel fibre reinforced concrete are extremely difficult to conduct because, typically, no information on the actual amount and orientation of the fibres is available. Therefore, it is of great interest to engineers to have the possibility to determine the steel fibre content and, at best, also the orientation of the fibres in existing structures. For this purpose, an easy-to-use test setup was developed and tested, in the course of laboratory investigations. This method can be used for cylinders, for example drilling cores, that can later be taken of existing structures, to determine both the fibre content and orientation. Based on these results, a model for cylindrical specimens was derived, which can be used for varying concrete compositions with steel fibre contents of up to 80 kg/m3. In the case of missing information concerning the concrete composition, it allows an initial estimation for the fibre content. In case additional information about the concrete composition is available, a much higher accuracy of the projected steel fibre content and therefore, an assessment of the building’s condition is possible.

Study of an Ecological Cement-Based Composite with a Sustainable Raw Material, Sunflower Stalk Ash

The use of plant ash as a sustainable cementitious material in concrete composition is a widely researched subject in the construction domain. A plant studied so far more for its thermal insulation properties, sunflower, was analyzed in this study with regard to its ash effects on the concrete composition. The present research aimed to analyze the effects of a 2.5%, 5%, 7.5%, 10%, 15%, 20%, or 30% volume replacement of cement by sunflower stalk ash (SA), a sustainable cementitious material, on the concrete compressive strength at 28 days and three months, the flexural and splitting tensile strengths, the resistance to repeated freeze–thaw cycles, and the resistance to chemical attack of hydrochloric acid. The elementary chemical composition of the SA and the composites was included also. According to the experimental results, SA decreased the values of the compressive and tensile strength of the concrete, but it improved the concrete behavior under repeated freeze–thaw cycles and under the action of hydrochloric acid. A percent of 10% of SA led to a much more pronounced development of compressive strength over time than conventional concrete (26.6% versus 12%).

Analysis of The Mechanical Properties of Concrete Based on Fly Ash and Palm Oil Clinkers

Concrete is the result of a mixture of cement, aggregate and water. Under certain conditions, the concrete mixture can be added with additives and admixture to get the concrete as needed. Cement is the most important material in the manufacture of conventional concrete. When cement is produced, the same amount of CO2 will also be generated as a side effect and pollute the atmosphere. Fly ash as an alternative to cement will be introduced as an alternative concrete material to reduce the use of cement in the concrete mix. In addition to the use of charcoal fly ash as a partial substitute for cement, this study also uses palm oil clinkers as a substitute for fine aggregate as much as 20%. This replacement material is an industrial waste which has the main content of silica and alumina which is similar to the main material for forming concrete. In addition, the use of these two materials also aims to reduce the exploration of the use of natural materials. This research introduces 3 kinds of concrete composition. The grouping is based on the ratio of fly ash and cement used, namely (60%:40%), (70%:30%) and (80%:20%). The test object used is a concrete cylinder with a diameter of 150 mm and a height of 300 mm. Tests were carried out at the age of 28 days of concrete. The compressive strength test showed that the best concrete was produced from the combination of the addition of 60% fly ash of coal aged 28 days, which was 4.21 MPa.

Study of High Strength Concretes with Variability of Composition Designs

High Strength Concretes (HSC) are concretes defined mainly by compressive strength. The strength of concrete can guarantee other excellent results of properties, namely durability. Essential for the production of HSC is a careful approach to the design of concrete composition, especially the quality of raw materials. It is primarily necessary to increase the content of the binder combined mainly with Portland cement and another admixture. Due to its excellent properties, Silica fume is largely used as an admixture, where it is necessary to consider its effective amount. It is also suitable to combine this admixture with other types of active admixtures. The question of the type of coarse aggregate fractions used is crucial. The quality and purity of aggregates is an essential part of the quality design of these concretes, influencing practically all the resulting parameters of concrete. The article presents a set of tests on designed High strength Concretes, differing in the composition of the concrete to demonstrate the variability of the design concept and its effect on the resulting values of strength and durability.

Optimization of the Concrete Composition Mix at the Design Stage

The problem of the composition optimization of concrete mixes seems to be quite urgent as errors at the composition design stage can lead to problems of concrete at the stage of exploitation such as delamination, cracking etc. Reasonable selection of concrete mix components guarantees the required strength of concrete and reinforced concrete structures in the future. This paper investigates the influence of the concrete mix composition on the strength of concrete. Firstly, typical risks that can occur on the composition design stage have been identified through the experts' interviews. Secondly, this risks were associated with indicators and characteristics that can be tested experimentally. Running of several mathematical models has allowed to outline concrete mix parameters of highest importance and formulate an empirical equation for the dependence of the strength of the concrete mixture on the values of the coarse aggregate quality factor, the fine aggregate fraction and the consumption of the Portland cement has been proposed. As a result, a methodology for controlling the quality of concrete at the stage of the composition design has been formulated. Doi: 10.28991/cej-2021-03091732 Full Text: PDF

Structural Changes in Concrete under the Influence of Reactor Spectrum Neutrons

The paper considers structural changes in the concrete composition that occur under the influence of neutrons of the reactor spectrum, using the example of the IR-100 research nuclear reactor, taking into account its real time and operating conditions. Thus, taking into account the energy output, power operation modes, and neutron flux density in the core, over time, nuclides that are not characteristic of the original composition of the concrete component are formed in the nodes of the crystal lattice. However, these changes do not lead to significant structural changes.

Electrical Resistivity of Steel Fibre-Reinforced Concrete—Influencing Parameters

This paper presents a systematic study of the electrical resistivity of different steel fibre-reinforced concretes with fibre contents from 0 kg/m3 to 80 kg/m3 in order to identify possible effects of interactions among concrete composition and fibre type and content regarding electrical resistivity. Based on a literature review, four parameters, w/c ratio, binder content, ground granulated blast-furnace slag (GGBS) and fineness of cement, which show a significant influence on the electrical resistivity of plain concrete, were identified, and their influence on the electrical resistivity as well as interaction effects were investigated. The results of the experiments highlight that the addition of fibres leads to a significant decrease in electrical resistivity, independent of all additional parameters of the concrete composition. Additionally, it was shown that a higher porosity of the concrete, e.g., due to a higher w/c ratio, also results in a lower electrical resistivity. These results are in agreement with the literature review on plain concrete, while the influence of the concrete composition on the electrical resistivity is weaker with the increase in fibre content. The influence of fibre reinforcement is thus not affected by changes in the concrete composition. In general, a higher fibre dosage leads to a decrease in electrical resistivity, but the impact on the electrical resistivity varies slightly with different types of steel fibres. Based on this study, the potential of determining the fibre content using electrical resistivity measurements could be clearly presented.