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Improved utilization of coal mine overburden material (CMOB)‐incorporated concrete in the construction sector can contribute to developing a more sustainable built environment if the results of proven research on the behavior of structures constructed of CMOB‐incorporated concrete are applied. Even though there have only been a few studies on CMOB‐incorporated concrete, no research has been done on how this type of concrete can be used in structures. In particular, researchers have not paid much attention to the fact that the strength properties of CMOB‐incorporated concrete tend to be very variable, even though this variability is needed for a wide range of structural applications (such as limit state design formulation, reliability‐based structural analysis, etc.). For the first time, this research provides quantitative estimates of the variability in compressive‐, flexural‐, and splitting tensile strengths of cured concrete using varying amounts of a CMOB sample as fine aggregate. Taking into account the suggested distribution model, the research also provides a reliability‐based seismic risk assessment of a standard CMOB‐incorporated framed building. The failure probability and dispersion in the drift demand were found to be the same for the frames modeled with CMOB and standard concrete (natural sand); the results demonstrate that CMOB samples can be safely used for earthquake‐resistant constructions. [ABSTRACT FROM AUTHOR]

Compared with the ground service environment, the evolution of concrete performance under a water pressure service environment is quite complex with variable conditions. Because of the coupling effect of load and pressure, water has a special impact on the strength and deformation of concrete. Meanwhile, harmful ions usually react with the cement matrix as pressure water seepages into concrete, resulting in the reduction of concrete durability. Based on this, this study provides a comprehensive review of the strength, deformation, and durability of concrete under water pressure environment. It is found that microcracks in concrete tend to propagate and connect after exposure to water pressure, leading to a decrease in strength and deformation performance. The average loss rate of strength and elastic modulus increased by 12.15% and 10.97%, respectively, when water pressure increased by 1 MPa. However, the loading process of water‐confining pressure makes concrete more compact, where the static and dynamic mechanical performance can be improved. Besides, due to the enhancement of excess pore water pressure, concrete strength under a high strain rate increases by 61.79% compared to static load. The effect of water pressure increases the ability of the liquid to penetrate concrete, and corrosive ions trapped within the liquid and freeze–thaw caused by external temperature changes would further reduce the concrete durability. This study points out that static and dynamic loading characteristics and durability of concrete under multi‐factor coupling in a water pressure environment will be the future research direction. The summarized contents can provide guidance for construction and research of concrete engineering under a water pressure environment. [ABSTRACT FROM AUTHOR]

The next edition of the fib Model Code for concrete structures, Model Code 2020 (MC2020), is under development with the aim of issuing a first partially harmonized draft for comment in early 2023. MC2020 is a single code dealing with both new and existing concrete structures, that is both the design of new structures and the various activities associated with the assessment, interventions upon and life‐cycle management (LCM) of existing concrete structures. The paper outlines the overarching sustainability framework and the performance‐based or outcomes‐based approaches (PBA) adopted by MC2020. There is a pressing need to reduce barriers to the evolution in concrete construction materials and the technical aspects of design and the LCM of existing structures, in order to meet pressing climate change drivers and the goal of achieving lower carbon construction. MC2020 also addresses significant advances made on a wide range of issues including those relating to structural design and analysis methods, seismic design and assessment procedures, durability, structural monitoring, service life design, structural assessment through‐life and making interventions to adapt existing structures or enhance their performance or extend their useful life. [ABSTRACT FROM AUTHOR]

High‐performance fiber‐reinforced concrete (HPFRC) can be considered a promising material for the construction of precast concrete girders for road bridges. This paper presents conceptual considerations and numerical analysis to support this statement. The HPFRC is a compromised alternative between FRC and UHPFRC mixes. Specifically, a tailor‐made mix design of HPFRC jointly developed by ACCIONA and the authors is presented, and then compared with the other types of fiber‐reinforced concretes collected from the technical literature. In addition, some trends observed in the database are described. This material characterization is followed by a conceptual analysis of the advantages of the application of HPFRC to road bridges. Specifically, a proposed bridge for the case of a 60 m‐span box girder is analyzed. A comparison between alternatives based on the use of HPFRC and conventional reinforced concrete is discussed. The results shed light on the viability of this material for bridge application. Specifically, the main finding show potential significant material savings in structural elements of the superstructure. Finally, ongoing and future research for a wide application to the construction sector are briefly discussed. [ABSTRACT FROM AUTHOR]

Crack initiators in reinforced concrete structures can facilitate fulfilling the serviceability requirements. They can be used as a design parameter to diminish the minimum reinforcement for members subject to imposed deformation and exposed to the environment as they reduce the crack spacing and width when arranged close enough. While crack initiators in conventional concrete construction are cumbersome to provide (e.g., by construction joints or taperings), they are inherent to layered extrusion processes with digital fabrication technologies: the tensile strength is typically reduced locally in interfaces between layers. Rather than trying to avoid these weak interfaces, this paper discusses the potential of taking advantage of them to act as crack initiators reducing the minimum reinforcement content. A tension chord‐based model is developed to (i) account for the local strength reduction and (ii) predict the effect of weak interfaces on the expected crack spacing and width. As a key finding, the model predicts a reduction of the required minimum reinforcement ratio proportional to the locally decreased concrete tensile strength for a specified maximum crack width requirement under imposed deformations. An experimental campaign on five layered and three reference tension ties confirmed the clearly positive impact of weak interfaces on crack spacings and widths. [ABSTRACT FROM AUTHOR]

Compressive strength is considered to be one of the most important mechanical properties of high‐strength concrete (HSC). In this study, three machine learning models, ELM, PSO‐ANN, and GS‐SVR were employed to predict the compressive strength of HSC using 681 data records. The five ingredients and the compressive strength of HSC were regarded as input variable features and output target, respectively. Results indicated that the GS‐SVR model showed the best performance in forecasting with the R of 0.992, MAPE of 0.016, RMSE of 1.241, MAE of 0.842, and RRMSE of 0.024, which could be an alternative candidate for strength prediction. Additionally, a sensitivity analysis was performed within the GS‐SVR model to achieve an in‐depth examination of the effect of each single input variable on the compressive strength. The sensitivity of input variables demonstrated that the water is the most sensitive parameter to the compressive strength of HSC, while the superplasticizer is less sensitive. The research of this paper can provide reference and guidance for concrete design and construction. [ABSTRACT FROM AUTHOR]

The construction of concrete structures for radiological protection in sanitary facilities requires a series of constructive conditions that guarantee safety. The influence of the correct bunkers design, wall thicknesses and the type of materials used is essential to ensure effective protection. The use of barite aggregate concrete is a common resource to improve the radiation attenuation capacity of concrete walls. The present study analyses the structure of a bunker during a renovation work, studying the construction characteristics of the chamber, the state of its elements, the characterization of materials, the identification of the emissions of the possible isotopes present, beta radioactive contamination and the measurement of equivalent dose rates at different points in the concrete. The results made it possible to determine the use of conventional concrete and barite concrete, the latter presenting a BaO content of around 40% and particularly low resistance values, not observing alteration processes in the materials. [ABSTRACT FROM AUTHOR]

In the worst-case scenario, a projectile would penetrate the whole thickness of the "absorbing" energy shield layer, bounce off the ordinary concrete, and lose the rest of its energy while ricocheting inside the shield layer. The proposed concrete, intended as a shield layer covering structural concrete, is based on light aggregates and is modified by fiber.[[4], [6]] The created porous and weakened (in terms of compressive strength)[[7]] matrix is easily penetrated by a projectile. Anti-terrorist concrete shields absorbing projectiles with no ricochets. [Extracted from the article]

Mass concrete (MC) is widely used in dam concretes due to their large aggregate grain diameters, low cement dosage, and low hydration temperatures. Monitoring of the hydration temperature and compressive strength is an important consideration during the casting of MC in the field. The purpose of this study is to determine the relationship between the compressive strengths of cylindrical specimens with different maximum aggregate grain diameters (Dmax) and different dimensions in MCs used in dam construction and to investigate the usability of the weighted maturity method in determining the compressive strength of dam MC. In this study, the compressive strength transition coefficient (fck ø15 × 30/fck ø25 × 50) of the cylindrical samples with different dimensions in MC was found to be 1.135. It was found that the weight maturity method can be used to estimate concrete strength in dam MC with low hydration temperature. [ABSTRACT FROM AUTHOR]

The aim of the study involves determining the added value of shells of sunflower seeds ash (SSA) as a mineral admixture in concrete and the effects/mechanisms through which it affects the concrete microstructure. The chemical effect of this type of ash was estimated by examining its chemical composition, pozzolanic activity index, and SEM investigation while its physical effect was observed at the level of concrete with ash incorporated. Four concrete mixtures with different shares of cement replacement by ash were prepared (0, 5, 7.5, and 10%). The water to binder ratio was 0.5, and binder content 400 kg/m3 in all mixtures. The properties of fresh and hardened concrete with ash incorporated were compared with the corresponding properties of the reference concrete. The results indicate that SSA achieved all the known possible effects of mineral admixtures; filler effect, heterogonous nucleation effect, dilution effect, and a certain degree of chemical effect. However, replacing more than 5% of cement mass with SSA will adversely affect mechanical properties of concrete. [ABSTRACT FROM AUTHOR]

In 2015, there was one of the awful incidents in civil engineering. That was the collapse of the formwork strength of the building inside the Qassim University, resulting in the death and injury a number of engineers and workers. This is just an example of the long‐recorded history which tells us about a large number of different collapses of formwork, which resulted in the loss of many lives and equipment. Therefore, it is necessary to provide a new vision for the design of formwork using many different sectors to ensure access to the lowest possible cost, taking into account the safety aspect. This goal can be achieved by certifying the stability of the sectors when taking into account the effects of bending stresses, shear stresses, and deflection. Calibration was achieved using the beforehand published method in 2000. This method is used to ensure the results obtained for the slab thickness less than 15 cm then the results were extrapolated to include slabs with a larger thickness. The results of the present search come out into a set of indicating curves point to the required quantity of lumber for each sector. This strategy is much easier and straightforward to help in the design process rather than using conventional equations. [ABSTRACT FROM AUTHOR]

Disposal of fresh concrete waste is a worldwide problem. In recent years, many studies have claimed that fresh concrete waste from a reclaiming system can be efficiently recycled into concrete. This paper gives a comprehensive review of the characteristics and applicability of fresh concrete waste in phase of slurry wastewater, fresh paste, and recycled solids. The effects of fresh concrete waste in the three phases on workability, strength, and durability such as permeability, water absorption, shrinkage, and acid resistance of concrete have also been reviewed in this paper. [ABSTRACT FROM AUTHOR]

Using a multiscale approach, the critical compressive load of a cylindrical shell made by concrete/graphene nanocomposite is computed. At the first step, using a multiscale method, the elastic modulus of concrete/graphene nanocomposites with different graphene volume percentages and sizes are evaluated. Then, the finite element method is used to obtain the critical compressive load of a cylindrical shell made by the concrete/graphene nanocomposites. It is observed that the elastic modulus and buckling load of the concrete/graphene nanocomposites are reduced by increasing the temperature. It is also shown that when the graphene sheets are directed along the external force, the mechanical properties of the concrete are improved more than the case in which the graphene sheets are randomly directed in the concrete matrix. [ABSTRACT FROM AUTHOR]

During the concrete production, we attempt to adjust its viscosity to allow optimal implementation. In this article, we have proposed a correlation between the plastic viscosity of concrete, the time, and the characteristics of the flow final profile from the V-Funnel coupled to a horizontal channel Plexiglas. The proposed approach, verified by experimental results, represents a simple, economical, and usable tool on building site, and it allows to characterize rheologically the concrete from its flow. The comparison between our approach and the experimental values of the plastic viscosity shows that, in a laboratory or on site, instead of using a rheometer, we can use our approach to characterize the rheological behavior of a self-compacting concrete. [ABSTRACT FROM AUTHOR]

The paper presents the results of an experimental program carried out on 96 concrete pullout specimens prepared with natural and recycled aggregates using 10 and 12 mm diameter deformed steel bars. Steel rebars were concentrically embedded in pullout specimens with two embedded length of 5 and 10 times the rebar diameter. The present work includes six recycled concrete aggregate mixtures and two conventional concrete mixtures with C25/30 and C35/45 target class of compressive strength and S4 class of workability. For both series, specimens were fabricated with different incorporation ratios of fine and coarse recycled aggregates and only coarse recycled aggregates. Tensile load was applied gradually until the pullout failure occurred and the slip between the rebar and concrete was measured at the free and loaded ends for each loading level. Furthermore, systematic observations of failure surface have been made at both macroscopic and microscopic scales. Test results showed that for the same class of compressive strength the bond strength and related failure mechanisms remain very close and the obtained values are, at least, four times higher than the predicted values by Eurocode 2. The experimental results of this study, together with an extensive number of results reported in the literature, were used to describe the variation of bond strength with concrete compressive strength, embedded length, and concrete cover. In addition, an analytical bond-slip relationship is proposed and the parameters of bond-slip law were calibrated by an optimization algorithm. [ABSTRACT FROM AUTHOR]

Contents Issue 3 (2016) | Technical Council meets in Madrid · 2017 AAYE · Redefining fib Commission · fib Bulletin 78 · ICCS16 · Short notes · Congresses and symposia [ABSTRACT FROM AUTHOR]

The transport mechanism of chloride ions in concrete during wetting and drying cycles of varying duration is evaluated in this paper. The experimental test results were used to validate a numerical simulation model in order to assess the influence of diffusion coefficient, surface chloride ion concentration and ratio of dry-wet cycle durations on the transport mechanism of chloride ions in concrete. Experimental and numerical analysis results indicate that the maximum transmission depth of chloride ions in concrete depends on the diffusion coefficient and the dry-wet cycle regime but has little relationship with the surface concentration of chloride. The chloride ion transmission in the surface zone accelerates only if the dry-wet ratio is > 1. As the dry-wet ratio increases, so the chloride ion transmission accelerates. It tends to become stable when the dry-wet ratio reaches 5:1. The dry-wet cycles accelerate the transport process of chloride ions within a certain distance from the surface; beyond this distance, chloride ions in the complete immersion specimen migrate more rapidly than those under dry-wet cycles. The peak concentration of chloride ions within the convection zone has a relationship with the diffusion coefficient, the surface chloride ion concentration and the dry-wet regime. The smaller the diffusion coefficient, the higher the surface chloride concentration; the greater the dry-wet ratio, the higher the peak of convection can be. [ABSTRACT FROM AUTHOR]

Conceptual design is the approach that creates an idea in order to find a solution to a new proposal for a structure or solve a detail in a specific structure. It is a personal approach that is learned over time and with experience. It is not normally dealt with at university, but is vitally important for producing sound structures. The fib Model Code for Concrete Structures 2010 introduced this concept in the first section of chapter 7 'Design'. The content of that section explains the general approach to developing conceptual design. This paper will show different examples of conceptual design following the general guidelines stated in the Model Code. [ABSTRACT FROM AUTHOR]

Nowadays, it is more and more often necessary to design two-dimensional reinforced concrete elements to satisfy both architectural demands and to comply with traffic safety requirements in the design of road and railway infrastructures. In fact, the demand for non-regular structural geometry is increasing in both cases. As a consequence, the use of finite element analyses to model structures and calculate internal actions is constantly growing because closed-form solutions are generally unavailable for irregular shapes. Therefore, the problem of reinforcement design needs our attention because steel bars, in general, should be placed in non-orthogonal directions and can vary over the structure. Consequently, there are two different kinds of design problem: choice of reinforcement direction and evaluation of the reinforcement ratio between the chosen directions, with the aim of minimizing the total amount. Such problems can be easily overcome by generalizing a mechanical model consolidated in the literature for orthogonal reinforcement for skew directions. The model is set up according to the ultimate plastic behaviour of the elements. An optimization technique based on genetic algorithms is then applied to the new model to reduce the amount of reinforcement. This paper describes both the ultimate resisting mechanism with generic reinforcement directions and the way genetic algorithms are employed to optimize the amount of reinforcement. [ABSTRACT FROM AUTHOR]

This work investigates the effect of olive waste ash (OWA) on the durability of concrete exposed to alkali-silica reaction (ASR). Three OWA contents were considered in the work: 7, 15 and 22 %, with crushed Pyrex glass used as reactive fine aggregate. The other experimental parameters investigated in the study were: w/c ratio (0.4 and 0.5) and air content (non-air-entrained and air-entrained). The OWA concrete specimens were submerged in 1-N NaOH solution at 40 °C to accelerate the ASR. The ASR damage was monitored by measuring the expansion of concrete prisms and the decrease in compressive strength. The study demonstrates that OWA concrete is more resistant to ASR deterioration than plain concrete. The durability of OWA concrete with respect to ASR damage improved with the increase in OWA content. The OWA concrete with a w/c ratio of 0.4 exhibited a better performance with respect to ASR deterioration than the OWA concrete with a w/c ratio of 0.5. The air-entrained OWA concrete exhibited better durability with respect to ASR damage than the non-air-entrained OWA concrete. [ABSTRACT FROM AUTHOR]

Spatial and temporal temperature variations in a concrete structure due to variations in the surrounding climate will produce movements which, if restrained, may induce stresses in the structure. To get a better understanding of transverse thermal stresses due to climatic effects in concrete box cross-sections, the FE simulations in this study have been performed using extensive climatic input data directly or by using simplified methods to simulate the temperature and resulting stress fields in a section of the hollow concrete arch of the New Svinesund Bridge. Studies of other cross-sections with varying depth, width and wall thicknesses have also been performed to investigate the geometrical influence. The results reveal an overestimation of the maximum thermal tensile stress when using a linear temperature differential approach compared with the direct use of climate data that includes the non-linear part of the temperature distribution. The effect of depth, width and orientation is negligible compared with variations in thickness between slabs and walls. For box sections with slabs/walls having different thicknesses, the transverse thermal stresses will be significantly larger in the thinner members, irrespective of the actual orientation and position of the member. [ABSTRACT FROM AUTHOR]

The disparity between theoretical and experimental results reveals that the creep of concrete is often underestimated by most, if not all, codes of design; this is particularly true in the case of Eurocode 2. Thus it is necessary to calibrate the present code models. Bayesian-type inferences turn out to be an especially suitable tool for the work needed in revising and updating design codes. This is by virtue of their capability to incorporate additional information resulting from current practice and research so as to improve existing models. In this paper, corrective coefficients are proposed for the Eurocode model, allowing better estimation of the long-term creep of concrete. To achieve this aim, the authors rely on a large database of experimental results compiled by collecting data from several research institutions in Europe. Two descriptive statistical methods are applied in order to compare the experimental results from the above-mentioned database with results calculated using the Eurocode 2 model for the same input parameters. A Bayesian-type statistical inference is then performed to evaluate the corrective coefficient for different categories of concrete strengths using various prior distributions. The approach presented here has proven to be an effective and systematic framework for the consideration of all possible types of uncertainties in model calibration. The results obtained are very interesting for engineers involved in design and supervision of structures. The adoption of such a design approach would improve long-term serviceability of structures subjected to creep. [ABSTRACT FROM AUTHOR]

Ductility, particularly the plastic rotation capacity of critical regions, conditions the available degree of moment redistribution and the ability to exploit the additional resistance of hyperstatic structures. A theoretical model for calculating plastic rotation capacity, considering the influence of the main factors, is presented. Special attention has been paid to the influence of the tensile reinforcement ratio, the shear force and the confinement of compressed concrete on plastic rotation capacity. Theoretical results are compared with those obtained using an experimental programme designed to study the influence of these factors. Some extrapolations are made on the basis of the model, and conclusions are drawn. [ABSTRACT FROM AUTHOR]

This paper discusses the influence that two types of drilling fluid, bentonite and a polymer, have on the bond capacity of reinforcement bars that are cast in concrete placed under them. Test results from both laboratory specimens and site tests are discussed and the results compared to capacities predicted by various codes. It is shown that Eurocode 2 predicts the bond capacity of bars in concrete cast under bentonite well, providing the assumption of poor bond conditions is made. The results for bars in concrete cast under polymers are less clear and there appear to be significant differences between the performance on site and that in the laboratory. [ABSTRACT FROM AUTHOR]

Innovations in concrete construction can be held back by the inability of codes of practice to accommodate new materials. The current design and safety philosophy (DSP) of reinforced concrete relies heavily on the properties of steel reinforcement. The need to embrace new materials, such as fibre-reinforced polymer (FRP) reinforcement, led to an in-depth examination of the DSP of European concrete codes of practice and resulted in a new philosophy, presented in this paper. The basis of the new philosophy remains the limit-state design and achievement of target notional structural reliability levels, but aims at the attainment of a desired failure mode hierarchy. The implementation of the philosophy, through a proposed framework, utilises the concept of average measure of closeness for the determination of appropriate material partial safety factors. An example of the application of the proposed framework is presented for FRP reinforcement. [ABSTRACT FROM AUTHOR]

The beam-column joint is one of the important structural elements of reinforced concrete structures. It has been the subject of intensive research for the past four decades. To date, most of the design procedures of joints have been devoted to ordinary-strength concrete as implemented in the current international design codes. The use of high-strength concrete has become useful because of the advantages of member size limitation and higher structural capacity. However, its applicability is still limited because its behaviour, especially under combined stresses and shear, differs from ordinary-strength concrete in the presence of axial loading on the column. Consequently, the existing design guidelines are not completely applicable. In order to establish the salient features of the behaviour, namely modes of failure, deformational characteristics, strength parameters and strain development, an experimental programme was performed on beam-column joints under quasi-static monotonic loading. The influence of axial compression, along with other actions imposed on the joint including shear and bending moment, was taken into consideration. The practical aspects of using a composite structure—that is, ordinary-strength concrete of different grades at floor level and high-strength concrete along the rest of the column—were considered. The effects of different permutations of longitudinal as well as transverse reinforcement and various configurations of stirrups were also investigated. [ABSTRACT FROM AUTHOR]

This paper provides a brief overview of Session 8 `Durability of Concrete Structures' of the fib 2002 congress on Concrete Structures in the 21st Century, which was held in Osaka on 13-19 October 2002. The keynote speaker of the session, Dr Odd E. Gj&3x00F8;rv, Professor and Head of the Department of Building Materials at the Norwegian University of Science and Technology at Trondheim, has conducted concrete research for more than 40 years. His research has focused on a broad range of topics related to the durability of reinforced and prestressed concrete structures in severe environments. His paper addressed durability and service-life issues of concrete structures. In addition to the keynote address, more than 50 papers were considered for this session, covering topics in the following areas: general issues related to concrete serviceability and durability, corrosion of reinforcement, and grouting of post-tensioned systems, as well as several case studies. The highlights of some of the papers are described here. [ABSTRACT FROM AUTHOR]

This article reports that a series of bulletins for the subscription year 2003 continued with "Monitoring and Safety Evaluation of Existing Concrete Structures," and "Environmental Effects of Concrete." "Monitoring and safety evaluation of existing concrete structures" states that the condition assessment of aged structures is becoming an increasingly important issue for civil infrastructure management systems. "Environmental Effects of Concrete" intends to serve as a source of information on the generally accepted and proven state of knowledge about environment related aspects of concrete as a structural material.

This article focuses on various awards related to concrete structures. Rolf Eligehausen, long standing FIB member, convener and member of several Special Activity and Task Groups, and his former co-worker Utz Mayer received the Jose-Calavera-Award given by Anifer, the Spanish national association of producers of reinforcing bars. The jury had to choose among submissions for highly interesting research on the influence of rib-geometry of reinforcing bars on the performance of concrete structures. The Scientia Building of the University of New South Wales, Australia, was one of the two winners in the 2002 FIB Awards for Outstanding Concrete Structures, receiving a bronze commemorative plaque.