The effect of supplementary cementitious materials on transport properties of cementitious materials - state-of-the-art

The supplementary cementitious materials (SCMs) have recognized many of the beneficial influences on concrete ability to resist the penetration of chloride ions, such as fly ash, slag, silica fume, metakaolin, and other natural pozzolans; this benefit has primarily been ascribed to the refined pore structure that results from the appropriate use of SCMs, which, in turn, results in reduced permeability and ionic diffusivity. The paper illustrates the state-of-the-art research findings on; (1) the classification of the SCMs and physicochemical properties; (2) the influences of SCMs on cement binder and the pore structure under chloride ion permeability; (3) the influences of the SCMs on the carbonation process of the cement binder that aims to determine the optimum relationship between SCMs and concrete transport properties. The interesting experimental investigations of the combined influence of chloride and carbonate permeation in cement binder that implement the latest methods in different curing conditions, types, and level contents of the SCMs will yield new scientific results and proposals for the industrial applications auxiliary materials.

The tensile strength: The most fundamental mechanical characteristics of concrete

Concrete is an inhomogeneous building material. It has a considerable and reliable compressive strength and a relative low tensile strength which can be even exhausted locally under unfortunate conditions. It is quite obvious that the concrete tensile strength was always reprehended as the most unreliable concrete property. A simple relationship between tensile- and compressive strength is introduced. The mechanical background of the relation tensile- to compressive strength in case of ‘normal’ and high strength concretes is elucidated. Mechanical bond, too, relies completely on the tensile strength. In the design of structural concrete members the tension fields are more characteristic than the compression fields. Effective concrete strengths are not successful. Tensile strength can be applied as ‘yield condition’ for the lower bound solution in the theory of plasticity. The paper intends to contribute to the acceptance of the tensile strength as the more fundamental concrete characteristics.

Comparison of the result of notched three point bending test with Model Code 2010 formulas

The primary application of the notched three point bending test (3PBT) is to determine the fracture energy of concrete. However, the measurement setup is also suitable for determining additional mechanical parameters: flexural tensile strength, modulus of elasticity, and indirectly the compressive strength also. The aim of this paper is to present the calculation methods of the mechanical properties that can be determined from the results of a test series in which mixtures with different types of aggregates were used (quartz, dolomite, limestone, andesite, expanded clay). To validate the obtained results, the parameters determined from the measurements are compared to the formulas of the fib Model Code 2010. A recommendation is also presented for the calculation of the fracture energy by using compressive strength values measured on a half prism.

Modern numerical modeling of reinforced concrete structures

Nowadays, many computer software products are available for the numerical modeling of reinforced concrete structures; however, the accuracy of the numerical models created by the programs can only be accepted with a properly developed and verified modeling procedure. Within the framework of the present article, we present the numerical modeling possibilities of reinforced concrete structural elements and their connections through numerical models made by a modeling procedure we have built. In our studies, we also dealt with quasi-static unidirectional (horizontal and vertical) and cyclically variable direction and magnitude loads. The numerical models were created using the ATENA 3D three-dimensional nonlinear finite element software developed specifically for the study of concrete and reinforced concrete structures. In many cases, the results obtained by numerical experiments were compared with the results obtained by laboratory experiments, and some of our numerical experiments were compared with the results obtained using two-dimensional finite element software. Within the framework of this article, we would like to give a comprehensive picture of the numerical studies we have performed. We have also briefly summarized the results and experiences obtained from 3D nonlinear finite element studies.

Proposed simplified method of geopolymer concrete mix design

The research aims to determine the best combination of the controlling factors that govern geopolymer concrete’s mechanical and physical properties by utilizing industrial waste. Therefore, a review on the controlling factors was conducted. Firstly, it is to identify the controlling factors, namely chemical composition, alkali activation solution, water content, and curing condition. Secondly, understanding the relationship between these controlling factors and the properties of geopolymer concrete. These factors are analysed to the mix proportion components. Finally, a new proportion method is proposed based on combining ACI 211 standard and recommended molar ratios of oxides involved in geopolymer synthesis. The effect of aggregate has been taken into account by applying the absolute volume method in mix design. Based on the results of the study, it is expected to determine the optimal mix proportions based on multi-responses.

Radiation shielding structures : Concepts, behaviour and the role of the heavy weight concrete as a shielding material - Rewiev

The construction of radiation shielding buildings still developed. Application of ionizing radiations became necessary for different reasons, like electricity generation, industry, medical (therapy treatment), agriculture, and scientific research. Different countries all over the world moving toward energy saving, besides growing the demand for using radiation in several aspects. Nuclear power plants, healthcare buildings, industrial buildings, and aerospace are the main neutrons and gamma shielding buildings. Special design and building materials are required to enhance safety and reduce the risk of radiation emission. Radiation shielding, strength, fire resistance, and durability are the most important properties, cost-effective and environmentally friendly are coming next. Heavy-weight concrete (HWC) is used widely in neutron shielding materials due to its cost-effectiveness and worthy physical and mechanical properties. This paper aims to give an overview of nuclear buildings, their application, and behaviour under different radiations. Also to review the heavy-weight concrete and heavy aggregate and their important role in developing the neutrons shielding materials. Conclusions showed there are still some gaps in improving the heavy-weight concrete (HWC) properties.

Effects of pouring technique on orientation of steel and synthetic macrofibres in fibre-reinforced concrete

Fibre-reinforced concrete is a short-fibre composite material, whose properties are significantly dependent on the orientation of the mixed fibres. As a starting point, the fibres are assumed to be uniformly distributed and have a uniform orientation. However, in reality, they have a non-uniform distribution owing to various factors. Such deviations in the orientation may have a significant effect on the material parameters, both favourable and unfavourable. In this study, the orientation factors determined based on the mixing models reported in the literature are compared with the results of experimental tests performed in the laboratory, and the effects of the formwork and the pouring methods used on the orientation of both steel and synthetic macrofibres are investigated. Based on the results of the study, the orientation of the fibres (both, steel and macro synthetic) significantly depends on the pouring method, which considerably influences the material parameters of fibre-reinforced concrete.

Steel stress patterns between two primary cracks in concrete

The national and international codes and standards and the literature consider the stress patterns either in case of a single crack or of equidistant primary cracks which developed at the same load level. Moreover, most FE models consider smeared cracks which do not allow for any insight in the real inner behavior of structural concrete. This paper considers the stochastic character of the concrete tensile strength’s distribution along the reinforced concrete element and a realistic local bond stress vs. slip relationship with its hysteretic character when the sign of local slip changes due to the occurrence of a new primary crack.

Effects of polypropylene fibers on ultra high performance concrete at elevated temperature

This paper presents an experimental study to evaluate the influence of polypropylene on fire resistance of ultra-high performance concrete (UHPC). Concrete mixtures are prepared by using different percentages of polypropylene fibres 0%, 0.75% and 1.5%, by volume. Samples are heated to 250 or 500 °C, for exposures 2.5 or 5 hours, and tested after cooling for compressive strength and flexural tensile strength. The research includes the use of mineral admixture of a recognized, polypropylene fibre, quartz sand, superplasticizers and without using any type of aggregates other than the quartz sand. The effect on subjected samples to elevated temperature up to 250 ºC and 500 ºC for durations 2.5 hours and 5 hours was studied for each mix and comparing the results of compressive strength and tensile strength among the mixes. Results obtained, showed that adding 0.75% of polypropylenes fibres only to a concrete mixture, improved the fire resistance of the concrete by 27% and 72% when the samples exposed to 250 ºC and 500 ºC for 2.5 hours respectively, compared with concrete mixes without fibres. In addition, the residual strength was improved by 39% and 14% when the samples exposed to 250 ºC and 500 ºC for 5 hours, respectively.