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• Setting time and engineering properties of BCSA concrete are studied. • Citric acid delays initial set from 15 min to as long as 3.5 h. • Retarding hydration does not affect the mechanical strength. • Design codes accurately predict the modulus of elasticity and tensile strength. This paper discusses the setting time and engineering properties (compressive strength, tensile strength, and modulus of elasticity) of belitic calcium sulfoaluminate (BCSA) cement and concrete. BCSA is an emerging alternative cement known for, among other things, its rapid setting behavior. This has long supported its use as a concrete repair material, but BCSA is also attractive for structural applications. Nevertheless, little information is available on the engineering properties of BCSA concrete. This paper quantifies the influence of mixture parameters on BCSA cement setting times, showing that they can be tightly controlled by altering the dosage of a citric acid retarder. It also quantifies the influence of mixture parameters and curing age on compressive strength, proposing predictive models and showing that retarding the hydration of BCSA does not affect its long-term strength. Finally, this paper measures the modulus of elasticity and tensile strength of BCSA concrete and attempts to predict these properties based on the compressive strength. Results suggest that predictive equations from ACI 318, CSA A23, and Eurocode-2 tend to predict the engineering properties of BCSA cement rather well. Together, these results support the feasibility of integrating BCSA cement into practical concrete construction. [ABSTRACT FROM AUTHOR]

Abstract: The dynamic strength enhancement of concrete under different initial static loadings is investigated in this paper. The mechanism of the influence of the inertia effect on the dynamic strength of concrete is discussed first by analyzing a single dimension of freedom system, which shows that the inertia effect only influences the dynamic loading part. The dynamic strength of concrete at initial static loading is calculated assuming a single crack model with consideration of free water viscosity using dynamic fracture mechanics. The dynamic stress intensity factor of the crack under linearly increasing loading on the basis of an initial static loading is achieved. The relationship between the dynamic strength increase factor and the static stress level is obtained. The comparison between the results by the model proposed in this paper and those by experiments in some available references indicates a good agreement. [Copyright &y& Elsevier]

This paper presents experimental and analytical studies on the flexural behavior of fully composite steel-concrete I-girders strengthened by externally bonded carbon fiber reinforced polymer (EB-CFRP) sheets. The experimental program consisted of four reduced-scale specimens composed of a hot-rolled steel I-girder section acting compositely with topping reinforced concrete slab using two rows of properly designed shear studs along the entire length of the girder flange. One girder was un-strengthened to act as a reference girder, while the remaining three girders were strengthened with 2, 3 and 4 layers of CFRP sheets mounted on the bottom side of the steel girder's tension flange considering complete anchorages of the CFRP sheets at both ends. The composite girders were tested under a four-point loading system in order to obtain a comprehensive overview of the flexural behavior of both un-strengthened and the CFRP-strengthened girders. Finally, an analytical design procedure was proposed in order to obtain the moment of resistance of the composite girders. Then, the proposed methodology was verified against the current experimental results as well as the experimental results obtained by other researchers. The comparison showed good agreement between the proposed analytical results and the experimental findings with a maximum variation less than 10%. Thus, the proposed equations for moment of resistance of CFRP-strengthened composite girders can be used by design engineers with confidence. [ABSTRACT FROM AUTHOR]

• Healing efficiency theory developed based on geometric probability. • New self-healing capsules, called engineered aggregates, are introduced. • Self-healing efficiency calculated for different cracking conditions. • Effect of size, shape and dosage of capsules on healing efficiency is evaluated. This paper presents optimal self-healing configurations in concrete using a new concept referred to herein as engineered aggregates (EA). EA are hollow particles designed to carry healing agents into the cracks in concrete. The concept of EA has been developed by the authors as a cost-effective method for self-healing in conventional concrete without having to modify the existing materials or mixing procedures. EA have an internal brittle capsule carrying the healing agents and they are covered with a cementitious coating. They are similar in size to a concrete coarse aggregate and they are added during the mixing process replacing a portion of the coarse aggregates. Similar to other self-healing materials with cast in capsules, one of the basic requirements of EA is that when concrete cracks, the cementitious coating and the embedded brittle capsule break to release the healing agents into the cavity of the crack. The goal of this study is to identify the optimal shapes and sizes of EA that can be effectively used in self-healing concrete while minimizing the volume fraction of the added healing agent (and thereby EA). The tools of geometric probability are used to determine the probability of intersection of cracks with EA and the probability of healing of cracks with different geometries: a single crack, parallel cracks, mapping cracks and multiple discrete penny-shape cracks. As such, the optimal size and shape of EA are selected based on the density and type of cracking that might occur in concrete. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of an experimental program developed to study the feasibility of producing prestressed concrete girders using lightweight concrete. During the experimental campaign, bond tests were performed in push-in (TL bond test) and pull-out (FB bond test) types of specimens. To-scale prestressed concrete elements were produced, implemented, and tested. The variables studied were the type of concrete, the test age, and the delayed effects of bond. The TL bond test allowed the behavior of the transfer length to be characterized, governed by the Hoyer effect. Equations have been calibrated to identify the upper and lower transfer lengths using the experimental results of this trial. The proposed equations delimit the safety boundaries of the experimental transfer length values obtained in the experiments performed on the beams. The results obtained in the experimental phase discourage the use of the studied lightweight concrete for producing pre-tensioned concrete elements. [Copyright &y& Elsevier]

Abstract: Knowledge of the compressive strength evolution of concrete is critical for activities such as stripping formwork, construction scheduling and pre-stressing operations. Although there are several procedures for predicting concrete compressive strength, reliable methodologies involve either extensive testing or voluminous databases. This paper presents a simple and efficient procedure to predict concrete strength evolution. The procedure uses an experimentally-determined parameter called the Equivalency Point as an indicator of equivalent degree of reaction. Equivalency Points are based on early age concrete deformation and temperature variations. Test results from specimens made from seven concrete types validate the approach. [Copyright &y& Elsevier]

Abstract: This paper intends to express the physical model ClinConc in a more engineer-friendly way. Through the numerical evaluation it has been found that there exist good correlations between the time-dependent factors for chloride binding and for diffusion coefficient, and between the laboratory measured diffusion coefficient and the apparent one, the latter is a result of the combined effects of material properties and environmental actions. Therefore, the ClinConc model can be expressed by the similar error function as used in many empiric models, but with the proper physical procedures, that is, modeling free chloride transport taking free chloride as diffusion potential and then calculating the total chloride content taking into account the non-linear chloride binding. The modeled chloride profiles are in good agreement with the measured ones, even though further study is needed to clarify the expansion coefficient for the concrete containing silica fume and other pozzolanic additions. [Copyright &y& Elsevier]

Abstract: This paper describes the development of a hybrid model for a concrete batching and mixing plant. The model is sufficiently detailed so as to ensure that it can be used to establish the control system within an industrial monitoring and control framework. Since the concrete batching and mixing plants are hybrid systems, Global Automata were used to build the model of the physical system, since they provide greater “modeling power” being suitable for modeling of a wider variety of systems than other types of automata. Various modeling methods based on the classical hybrid systems theory are rather applied in research works with academic orientation and usually are far from the engineers of industry. A fundamental objective of this work was to adopt a development environment which will be familiar to the industrial people. The developed model entails a hierarchical structure with an automaton as supervisor and several other interactive automata describing the subsystems of the plant. The model was then used to understand the influence of various design and operating parameters on plant performance. The model was also used to establish the control strategy. Both were implemented in a SCADA (Supervisory Control and Data Acquisition) environment which monitors and controls the overall operation of the plant. This framework has been applied on a real plant of West Greece with success in all realistic tests concerning either the control operation or the model validation. [Copyright &y& Elsevier]

Abstract: Standard methods for the dynamic identification of civil engineering structures and mechanical systems generally rely on the determination of eigenfrequencies/eigenvectors and damping. A basic assumption for the use of these methods is the linear elastic behaviour of the tested structures. Nevertheless many structures exhibit a non-linear behaviour even at low levels of external excitation. For instance, reinforced concrete structures cracked by shrinkage or by the overcoming of the concrete tensile strength, exhibit different values of the flexural stiffness depending on the opening of the cracks. In the present paper a new methodology is presented to identify the characteristics of a non-linear mechanical system using the Fokker–Plank Equation (FPE) that allows evaluating the probability density function of the response of structural systems loaded with Gaussian white noise. [Copyright &y& Elsevier]

Abstract: This paper presents a spatial time-dependent reliability analysis to predict the likelihood and extent of cracking for reinforced concrete structures exposed to chloride ion attack. A reinforced concrete surface is discretised into a large number of smaller elements and random field methods used to simulate the variability of the concrete damage over the entire area. Models predicting corrosion initiation and propagation, crack initiation and crack growth are used to track the evolution of the corrosion process for each element and thus allow the extent of damage as a function of time to be determined. A range of durability design specifications are investigated and maintenance thresholds are defined as being reached when a specified proportion of the bridge deck is damaged, say 1%. This will enable the minimum time to first repair to be estimated. The results provide a comparative tool to assist designers in selecting design specifications and possible maintenance regimes to achieve an optimal outcome in terms of service-life and life-cycle cost of the structure. [Copyright &y& Elsevier]

Abstract: The paper gives the results of an analytical method proposed to predict the load deflection behaviour of partially restrained slab strips. The effect of deflection prior to yield line load on the development of compressive membrane forces was incorporated in the theoretical analysis. An experimental programme was designed to cast and test ten partially restrained slab strips with different edge rigidity. A comparison has been made between the results of the proposed and one of the other methods available in the literature. The results indicate that the proposed method can predict the load deflection behaviour satisfactorily. A parametric study has been made on the load enhancement beyond yield line load and the results are presented. [Copyright &y& Elsevier]

Abstract: In the present paper the results of a finite element study of single headed stud anchors loaded in tension (concrete cone failure) are discussed. Anchors with extremely large embedment depths (up to 1500mm) for which few experimental data is available are investigated. Many such anchors are used in engineering practice, therefore, the aim of the study was to investigate their safety. The numerical analysis is performed using a three-dimensional finite element code based on the microplane model. Calculated concrete cone capacity for large anchors with small heads shows good agreement with the current LEFM based design formula for anchors. The numerical study and the available test data show that the ultimate strength of anchors with larger heads is higher than predicted by the design code formula. Furthermore, the size effect on the ultimate load of these anchors is less pronounced. It is shown that the current design formula is conservative for anchors with large heads. A correction factor is proposed to account for the effect of the size of the headed stud and to improve design formula. Further theoretical, experimental and numerical work is needed to investigate the performance of large single anchors and anchor groups and to verify and improve current design recommendations. [Copyright &y& Elsevier]

Abstract: Softening and time-dependence of fracture are two complex and coupled phenomena that have to be taken into account in order to simulate realistic concrete or rock behaviour. Understanding the interaction between these two phenomena is important to design reliable civil engineering structures subjected to high level loading during a long time. The aim of this paper is to develop a simple time-dependent softening model applied to quasi-brittle materials such as rock or concrete. A three-dimensional constitutive visco-damage model describes phenomena like relaxation, creep and rate-dependent loading using a unified framework. The model could be viewed as a generalisation of a time-independent damage model and is based on strong thermodynamical arguments. A general material stability analysis is proposed in case of uniaxial monotonic loading. Phenomena as creep failure under high-sustained load are explained quite simply within stability theory. Creep failure appears as the manifestation of a bifurcation phenomenon. Consequently, this model is able to predict creep failure for various stress level. Conversely, for low-sustained load, the motion asymptotically converges towards an equilibrium configuration, also called equilibrium curve. As for endochronic models, no initial threshold is assumed. Nevertheless, an apparent elastic domain is identified for constant strain rate tests, which reveals the competition between the internal kinetics of damage and the strain rate imposed on the material. [Copyright &y& Elsevier]

Non-destructive evaluation appears more and more important in the civil engineering economic stakes. In this context electrical resistivity measurements get sensitivity to parameters allowing to assess concrete structures conditions. This article analyses the ability of the resistivity measurement to study cracks in concrete. Its ability to detect and to locate cracks and spalling is shown with on site measurements on a damaged slab. Then specific studies on such disorders allow to distinguish the influence of their characteristics.The sensitivity of the method to cracks depth, according their moisture conditions, is assessed by computation. Experimental works on a reinforced concrete beam, ideally cracked, confirmed these results.Some assumptions based on measurements realised on a size-one structural component allow to assess the general influence of crack opening and bridging degree between crack lips.Qualitative results show the similar effects on measurement of various cracking parameters. Prospective works presented in the paper lead us to say that electrical resistivity method applied to civil engineering structures is a relevant tool for the assessment of structural damage. [Copyright &y& Elsevier]