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Due to the demand for carbon neutrality, concrete carbonation has been reconsidered as an interesting topic because of its potential for capturing carbon dioxide (CO2) from the atmosphere. Concrete carbonation can significantly modify the chemical and microstructure properties of concrete and thus will have important effects on chloride diffusion. This paper presents a chloride diffusion model in which the concrete cover is divided into three different zones, each with their own defined porosity and chloride binding isotherm. The first is the fully carbonated concrete near the surface, where the porosity and chloride binding isotherm can be obtained from the experimental data of fully carbonated concrete. The second is the uncarbonated concrete near the reinforcement, where the porosity and chloride binding isotherm can be obtained from the experimental data of normal concrete. The third is the transition zone between the fully carbonated and uncarbonated concretes, where the porosity and chloride binding isotherm can be assumed to vary continuously from the carbonated concrete to uncarbonated concrete. To validate the present model, a comparison of the present model with published experimental results is provided, which demonstrates the importance of considering different zones in the chloride diffusion model when the concrete has a carbonated layer near the surface. [ABSTRACT FROM AUTHOR]

The construction industry is responsible for nearly half of the UK's carbon dioxide emissions and the use of an extremely large volume of concrete – the world's most widely used man-made material – accounts for more than 7% of global carbon dioxide emissions. The scale of this problem spawned research to explore the potential for structurally efficient non-prismatic geometries to reduce the amount of concrete used in building elements substantially, thus also reducing their embodied carbon dioxide footprint. In particular, the research focused on segmented thin concrete shells as floor slabs, leveraging computational design and digital fabrication methodologies to automate their production off site. An important part of this research was the development of a computational framework for the design of thin concrete shells in order to make such a construction methodology accessible to building designers in practice. The framework combines solutions for parametric modelling, finite-element analysis, isogeometric analysis, form-finding and optimisation, along with embedded fabrication constraints specific to the project's automated manufacturing system. The application of the developed computational framework in the design of a 4.5 m × 4.5 m prototype is documented in this paper, illustrating how automating concrete construction can transform the industry towards net-zero. [ABSTRACT FROM AUTHOR]

Cement and concrete are essential for global development. However, cement manufacture is responsible for around 7–8% of global greenhouse gas emissions, with significant growth anticipated. Beyond efficiencies in cement manufacturing, other strategies for using less cement in construction through applying the principles of efficient design, circular economy and reuse also have the potential to reduce emissions. A further option is to move towards cements with different compositions and inherently lower embodied carbon dioxide. This paper focuses on these materials and the challenges to their widespread adoption, drawing mainly on applied research, trials and standardisation activities conducted in the UK and the EU. In addition to modification of standards, basic technical and practical information such as strength development curves, durability, site considerations and a shared broad body of evidence are key for specifiers to consider when using any new cement. The paper describes the role of standards and specifications and the underpinning information (applied research, published case studies and experience) essential in getting any new cement adopted. It also shows how a range of evidence from research and application can feed into a simple conceptual model and evidence base. [ABSTRACT FROM AUTHOR]

The dielectric properties of cement concrete are not only related to the dielectric properties and volume ratio of each component, but also related to frequency and temperature. In order to analyse these influencing factors, a dielectric constant test was done in the laboratory. Experimental results show that the dielectric constants decrease linearly with increase of temperature and decreases exponentially with the increase of frequency. Based on the experimental rules, a new dielectric model including frequency and temperature is established and verified by experiments. The verification results show that the calculation accuracy of the comprehensive dielectric model after considering the influence of frequency and temperature is improved by 25.5%, which meets the requirements of engineering detection accuracy. The model is applied to engineering practice, and the calculation methods of pavement structural layer thickness and moisture content are developed. The results show that the comprehensive dielectric model established in this paper has smaller error and higher accuracy. Using this dielectric model, the data conversion between different frequency and temperature can be achieved. The research results of this paper can provide a reference and basis for the quality evaluation of concrete structures. [ABSTRACT FROM AUTHOR]

This technical note complements a published lining evaluation for a canal in Egypt. Concrete and geomembrane linings are compared regarding leakage control and cost. Published data on leakage with concrete and geomembrane linings are reviewed, and analyses show that the predicted leakage rate is significantly lower with a geomembrane lining than with a concrete lining. The findings presented herein on leakage control and cost are significantly different from the findings of the published lining evaluation. [ABSTRACT FROM AUTHOR]

The issue of early-age concrete cracking is challenging and relies on the state of concrete soon after it is placed in the formwork. The concrete state is a function of the strains associated with thermal and other dilatations and the level of in situ strength. Both strain and strength primarily require information on the temperature–time history of the concrete element. For larger elements, the thermal history varies significantly across the thickness and the concrete material itself acts as confinement for discrete elements. Due to complexity of this issue, designers currently rely on mock tests and/or finite-element (FE) modelling for structures that are deemed 'important'. Both approaches are costly and time consuming. It is therefore important to have a robust yet simple model to estimate the temperature variation experienced by concrete elements. The proposed spreadsheet-based model presented in this paper aims to provide a rapid estimate of the temperature profiles within a hydrating concrete element. The model uses the concept of effective thickness and the revised heat compensation technique. It was validated based on the measured temperature development of a concrete block of rectangular section. The proposed model was also successfully compared with output from FE software (TNO Diana). [ABSTRACT FROM AUTHOR]

Although research has shown a considerable influence of the pre-cracking phenomenon on steel-congested concrete members, only normal concrete (NC) has been considered in the literature. The intention in this paper is thus to study the effect of the pre-cracking phenomenon on the bond response of pre-cracked NC with different slump flow values and self-consolidating concrete (SCC). Initial crack widths ranging from 0.0 to 0.5 mm are studied. Results show that initial crack widths larger than 0.10 mm have a significant influence on bond properties, such that reduction factors greater than 30% and 50% are obtained for the maximum bond strength of concrete specimens exposed to initial crack widths of 0.2 mm and 0.4 mm, respectively. Results show that concrete mixtures with higher workability are less sensitive to the pre-cracking phenomenon as compared to NC mixtures. The average bond stress of steel rebar in the pre-cracked SCC is found to be similar to that of the NC with a slump flow of 200 mm, which is considerably better than for NC with a slump flow of 97 mm. Moreover, results show that 65.8, 80.6, 88.5 and 93.1% fracture energy reductions are obtained for crack widths of 0.20, 0.30, 0.40 and 0.50 mm, respectively, as compared to the small crack width of 0.15 mm. [ABSTRACT FROM AUTHOR]

Belitic calcium sulfoaluminate (BCSA) cement has well-established advantages such as a fast setting time, fast strength gain, long-term strength, shrinkage and sustainability. BCSA cement reaches an initial set in about 15 min at room temperature and can reach compressive strengths of over 27 MPa in about 2 h. While it can be mixed in a similar fashion to Portland cement (PC), a set retarder (such as citric acid) is usually required to achieve adequate working time and the design of mixtures differs slightly from PC designs. This paper provides guidance on establishing mix design criteria for BCSA cement. Slump and compressive strength studies measurements were taken for varying mixture proportions with strengths measured up to 1 year of hydration. For BCSA concrete mixtures, a relationship between water content and slump was established. Citric acid was found to increase the slump, especially at lower water contents. A relationship between setting time and citric acid dosage was proposed on the basis of mortar penetrometer and Vicat needle tests. X-ray diffraction analysis was also conducted on BCSA cement pastes with different water/cement (w/c) ratios. Crystalline structure growth was found to be directly related to the w/c ratio and inversely proportional to compressive strength. [ABSTRACT FROM AUTHOR]

The construction of high-rise buildings and tunnels necessitates pumping concrete over long distances. Concrete pumping is a complex physico-chemical process that results in the formation of different layers with distinct characteristics inside the pipe. A thin cement paste/mortar layer formed at the concrete–pipe interface, called the lubrication layer (LL), is vital for facilitating concrete pumping. Engineering the pumping process involves understanding the origin and controlling the onset, magnitude and velocity of the LL. However, the formation, evolution and characteristics of the LL are still largely unexplored. This paper presents a comprehensive review of the mechanistic origins of the LL, its influencing parameters and measured data on LL thickness using various techniques to date. An attempt is made to find an overall link between different theories (shear-induced particle migration, wall depletion theory etc.) in terms of concrete rheology. The paper also provides a fundamental understanding of the different mechanisms involved in LL formation, with the help of different theories put forth by researchers in the field of particle rheology. Based on the insights derived from the discussions, recommendations are made for future research directions in concrete pumping. [ABSTRACT FROM AUTHOR]

The ground response during diaphragm wall panel installation is strongly affected by the support slurry pressure, and by the subsequent lateral pressures during the tremie placement and set-up of wet concrete. The support slurry pressure can be reliably assumed as hydrostatic within the excavated trench, whereas the lateral concreting pressure is much more complex due to the stiffening effect of wet concrete. This paper reviews the measurements of wet concrete pressures from a series of instrumented diaphragm wall panels which show that lateral pressures in the concrete slurry increase as the tremie displaces bentonite slurry and reach a maximum condition about 1 h after placement, while conditions over the longer term closely approximate the hydrostatic pressure of the bentonite-filled trench. The maximum increase of pressure varies at different heights of the same trench, and also varies for two separate panels in the same project, reflecting the varying velocity of concreting. Model tests of concreting pressure on formwork also demonstrate that the lateral pressure reduces from hydrostatic wet concrete pressure a few hours after casting. A time-dependent lateral concreting pressure model is developed to represent these measurements more realistically. This proposed model is implemented into a finite-element program to investigate its effects on the ground response due to the concreting process. Computed results from a reference case can capture the progressive variations of ground movement, earth and pore water pressure in the soil adjacent to the trench during and shortly after the concreting process, which is consistent with the reported measurements. [ABSTRACT FROM AUTHOR]

For concrete materials, durability is closely related to the mass transport property. The tortuosity of concrete material is an important factor accounting for the transport property. In this paper, the tortuosity of concrete is studied by mercury intrusion porosimetry and permeation tests in order to consider the existence of aggregate induced in the interfacial transition zone (ITZ). Tortuosity gained through the corrugated pore structure model and the Katz–Thompson model are compared and analysed to quantify the tortuosity of fly ash concrete. The ITZ was observed by scanning electron microscopy. The results show that the effect of aggregate should be considered when studying the tortuosity of concrete materials. With an aggregate value fraction of 43.8%, when considering the ITZ around coarse aggregate, concrete tortuosity is 1.29–16.18 times higher than that of the mortar matrix. [ABSTRACT FROM AUTHOR]

Concrete remains a widely used material in construction. As structures become more optimised, a deeper understanding of the rheology of the concrete mixture is necessary. This paper aims to numerically simulate the flow of fresh concrete in the L-box apparatus, with the objective of gaining insights into its rheological behaviour and predicting its properties. The fresh concrete flowing through the L-box test is simulated from the moment that the gate is lifted until the stoppage and the material takes its final shape. The flow in this tool occurs on a free surface. In this work, a three-dimensional model has been developed using the computational fluid dynamics technique for simulation. The flow behaviour of fresh concrete was assumed to be non-Newtonian following the Bingham law, characterised by a non-linear shear stress–shear rate ratio, yield stress and plastic viscosity. A set of numerical simulations by varying workability were conducted. Furthermore, a parametric study was conducted to examine the impact of introduced parameters in the concrete flow, including the effect of yield stress, viscosity and density. [ABSTRACT FROM AUTHOR]

Owing to rapid industrialisation and urbanisation there has been a significant increase in the manufacture and application of cement, resulting in high carbon dioxide (CO2) emissions into the atmosphere. This paper investigates alternative binders that have reduced carbon dixoide emissions and better performance. The study elaborates the mix design of novel concrete, wherein the principle raw material used was locally available bio-based blended ash (BA) procured from the co-combustion process with sodium-based alkali activators. The physical, chemical, mineral and morphological characteristics of BA were studied. Beside this, the influence of parameters such as molarity of sodium hydroxide (NaOH), liquid sodium silicate (LSS) to NaOH ratio, fly ash (FA) to BA ratio and method of curing on the physico-mechanical properties of alkali-activated concrete as a sustainable construction material were studied. Higher characteristic strength was attained with an increase in these parameters. A maximum characteristic strength of 42.31 MPa at day 28 was obtained with 8 M NaOH, LSS/NaOH ratio of 1.5 and FA/BA ratio of 3. The average flexural and split tensile strength obtained were 3.70 and 2.72 MPa, respectively. The experimental investigation of the alkali-activated concrete using BA and FA proved to be an efficient solution for zero-cement concrete with improved performance. [ABSTRACT FROM AUTHOR]

Design for durability and performance-based standards and specifications for reinforced concrete infrastructure is limited by the lack of rapid, science-based test methods for characterising the deterioration resistance of concrete. In this paper, this issue is addressed though the application of two-point electrical impedance measurements taken within the frequency range 100 Hz–10 MHz. Data are presented for a range of industry-standard cement-based concrete mixes with and without supplementary cementitious materials. Nyquist plots (−iZ″(ω) against Z′(ω)) and Bode plots (Z*(ω) and θ against frequency) clearly highlight the frequency dependence of the electrical response. However, when presented in the form of permittivity and conductivity, a region of dispersion was evident over the entire frequency range for all concretes. The features of this response, which could be gainfully exploited as durability indices for assessing the long-term performance of concrete, are identified and discussed. A range of formalisms is presented and it is shown that, within this frequency range, conductivity was found to obey Jonscher's universal power law. Two novel durability parameters are presented based on features of Jonscher's model; from a practical viewpoint, the power-law model can be evaluated using conductivity measurements obtained at three, easily measured, spot frequencies (10 kHz, 1 MHz and 10 MHz). [ABSTRACT FROM AUTHOR]

The bond behaviour between fibre-reinforced polymer (FRP) composites and concrete is a complex problem that is influenced by material properties, joint geometric configuration and the surrounding environment. The three fundamental bond performance indicators of concern are interfacial fracture energy, bond strength and debonding strain. This paper introduces a new semi-empirical model for predicting interfacial fracture energy (Gf) between externally bonded FRP and intact concrete in terms of the most influential material and geometric parameters, namely concrete's compressive strength and maximum aggregate size, stiffness of FRP composites and bond width and length of FRP composites relative to the dimensions of the concrete member. The prediction of Gf helped generate accurate predictions for the other two bond performance indicators. The present model was developed using non-linear regression analysis before validation using almost one-third of the total database consisting of 425 points, collected from credible publications. The accuracy of the present model of Gf outperformed those of well-known literature. The excellent agreement in trend behaviour of the present model with those reported in related literature works postulated further the model's validity. The estimation of debonding strain and bond strength in terms of fracture energy demonstrated superior accuracy over those provided by different relevant literature models. [ABSTRACT FROM AUTHOR]

Prestressed hollowcore slabs are potentially critical segments in the construction sequence of a precast concrete structure, in which very early age strength is vital for ensuring factory productivity. Importantly, the construction industry is striving to reduce concrete's carbon footprint by using Portland cement substitutes, particularly using ground granulated blastfurnace slag (GGBS) in Ireland. This paper investigates the early age strength enhancement methods for slag-concrete mixes, in order to address the well-known retarding effects arising from slag's inclusion. The strength enhancement methods, including temperature curing and a novel accelerating admixture, are used to activate the slag in the concrete mixes, with replacement rates up to 50% GGBS. The efficacy of these methods is investigated in relation to establishing the development of compressive strength and modulus of elasticity over time (being relevant to stress transfer), particularly at very early and at later ages for strength compliance. The study demonstrates the potential for using up to 50% GGBS mixes for slab production while still maintaining the strengths sufficient to achieve existing productivity targets in precast concrete production. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the effects of lateral tension and loading rate on the local bond performance of ribbed bars in concrete. The results show that, up to a loading rate of 10 mm/s, the mode of bond failure is independent of the loading rate but is closely related to the cover depth, concrete grade and level of lateral tension. It is also shown that the bond strength of ribbed bars increases with the increase of loading rate but decreases with an increase in lateral tension. The increase or decrease ratio becomes larger when splitting failure occurs. Specifically, for pull-out and splitting failure, the bond strength decreases by 8% and 22% when the lateral tension increases from 0.0 to 0.6 times the tensile strength of concrete but increases by 22% and 28% when the loading rate increases from 0.01 to 10 mm/s, respectively. The slip at peak bond stress is rate-insensitive. It can be taken as 0.18 times the rib spacing for pull-out failure but decreases linearly with the increase of lateral tension for splitting failure. Finally, a bond stress–slip model with three parameters is suggested for different levels of lateral tension and loading rates. [ABSTRACT FROM AUTHOR]

In this paper, based on pull-out test results, the influence of the number of chloride wetting–drying cycles, concrete strength, cover thickness, steel bar diameter and number of textile layers used in the textile-reinforced concrete (TRC) confinement on the bond property between concrete and a steel bar is analysed. Furthermore, a bond strength model is developed and the confinement effect of TRC and fibre-reinforced polymer is compared. The study results show that the ultimate bond strength decreased slightly as the number of chloride wetting–drying cycles increased, because only a slight corrosion of the steel bars was observed in this test. The influence of the concrete strength on the ultimate bond strength of the unconfined specimens was significantly higher than that of the TRC-confined specimens, and the improvement effect of TRC confinement was more pronounced for the low-strength concrete. Compared with the concrete strength, the cover thickness and steel bar diameter had less influence on the ultimate bond strength. With an increase in the number of textile layers, the ultimate bond strength improved significantly, and TRC confinement showed a better ability to limit the crack development in the confined specimens in which more than one layer of textile was used. [ABSTRACT FROM AUTHOR]

Carbon-conditioning or chemical permeation methods can provide excellent microstructural improvements to recycled concrete and brick aggregate; however, the applications have their limitations. Further, recycled brick aggregate cannot be effectively carbon-conditioned with conventional methods as it contains only trace amounts of reactive materials. It is therefore a necessity to use hybrid methods involving dual technologies combining carbon-conditioning and chemical permeation for its improvement. This paper is focused on developing a novel hybrid method for improving the microstructural properties of recycled concrete aggregate and recycled brick aggregate for concrete usage. This study conducts particle density, water absorption and crushing value tests to measure the physical improvements achieved with the novel hybrid method, and utilises a variety of chemicals and a reaction chamber for carbon-conditioning for aggregate treatment. The study evinces that both the recycled concrete aggregate and recycled brick aggregate experienced significant improvements, with 10 mm and 20 mm recycled concrete aggregate and 10 mm recycled brick aggregate exceeding the density of virgin aggregate. Magnesium hydroxide plus carbon dioxide (Mg(OH)2 (s) + CO2 (g)) treatment for recycled concrete aggregate and calcium hydroxide plus magnesium hydroxide plus carbon dioxide (Ca(OH)2 (s) + Mg(OH)2 (s) + 2CO2 (g)) treatment for recycled brick aggregate can be considered as potential candidates for optimal hybrid treatment methods. [ABSTRACT FROM AUTHOR]

Accurate modelling of transient creep strain (TRC) is crucial for reliable fire performance assessments of concrete structures, since it is the largest strain component for structural concrete subjected to thermal exposure. Nonetheless, the mechanism underlying TRC is still not fully understood and most of the available models were established based on ordinary Portland cement concrete. As the most widely used supplemental cementitious material, the effect of fly ash on the development of TRC still requires further study. For this paper, steady state tests and transient state tests were carried out on ordinary Portland cement concrete (CEM I 52.5 as per BS EN 197-1, water/cement = 0.5) and fly ash concrete (class F fly ash as per BS EN 450-1, 25% replacement percentage), respectively. It was found that replacing 25% ordinary Portland cement with class F fly ash in concrete can mitigate the development of TRC above 400°C. Based on the experimental results, one assumption of the influence mechanism of class F fly ash on TRC is made and a TRC model for fly ash concrete (class F, 25% replacement percentage) at elevated temperatures is proposed. [ABSTRACT FROM AUTHOR]

The expansion deterioration that occurs in concrete structures exposed to high temperature fluctuation in wet environments is often attributed to delayed ettringite formation (DEF). Due to the complex mechanism and various factors that influence DEF, it is difficult to establish effective methods for predicting the expansion and suppressing deterioration. With the aim of improving the durability and long-term maintenance of concrete structures at risk of DEF expansion, this review paper summarises the required conditions and factors influencing DEF and provides a detailed description of the DEF mechanism. Previously proposed methods for suppressing DEF expansion are summarised in detail and their practical applicability is discussed. Furthermore, a review of literature regarding methods for predicting expansion development is provided, considering prevention of DEF expansion. This work clearly highlights the current status of DEF research, and the data summarised in this paper are expected to be a valuable reference for investigating control or suppression of DEF expansion. [ABSTRACT FROM AUTHOR]

Fibre-reinforced polymer bars are rapidly becoming an approved alternative to conventional reinforcing steel bars, especially for severely exposed structures such as bridges. This paper reports on an experimental study on the bond characteristics of both sand-coated and ribbed-surface glass-fibre-reinforced polymer bars embedded in high-strength concrete (HSC). A total of 145 pull-out tests were conducted to examine the effect of varying parameters on the bond characteristics, namely embedment length, bar diameter, surface treatment and concrete cover. In addition, 45 pull-out tests were conducted to investigate the effect of providing headed-end anchorage for the sand-coated bars. The experimental results showed that the sand-coated bars exhibited better bond strength than the ribbed-surface bars, which entailed lower development lengths. Thus, based on the experimental results, expressions for the development length of both sand-coated and ribbed-surface bars embedded in HSC were developed and compared against the results of formulae in available design standards. The comparison revealed that ACI 440-1R-06 produced lower conservative results than CAN/CSA S806-12. [ABSTRACT FROM AUTHOR]

An advanced investigation of the core-drilling method (CDM) for direct application in bridge assessment is conducted. In the CDM, a small hole is drilled into concrete and the displacements that result are measured and related to the in situ stress. Knowledge of the stress profile within the concrete of a girder would allow determination of the magnitude and location of force in its prestressing steel. The programme described in this paper and its companion paper had two objectives - to demonstrate the effectiveness of the CDM in determining concrete stresses when using small-diameter holes and to demonstrate feasibility, accuracy and appropriateness of the CDM for the assessment of prestressed concrete bridge girders and for determining the existing prestress in their tendons. The method had never been applied to a prestressed beam. After verifying the method in concrete slabs in part I of this work, the technique was used with 75 mm holes to investigate the stresses in a prestressed beam and to determine the force in its prestressing steel. The tendon forces determined by drilling any single hole using the CDM are accurate, with an average error of 58·5 kN and a relative error of 15·94%. They are also consistent, with a standard deviation in error of 75·2 kN. The tendon force in a prestressed concrete beam can be determined to within ±8% if three holes are drilled. [ABSTRACT FROM AUTHOR]

A companion paper described the partial-interaction localised properties that require the development of pseudo properties. If the quantification through experimental testing of these pseudo properties could be removed by the use of mechanics-based models, which is the subject of this paper, then this would: () substantially reduce the cost of developing new reinforced concrete products by reducing the amount of testing; () increase the accuracy of designing existing and novel reinforced concrete members and structures, bearing in mind that experimentally derived pseudo properties are only applicable within the range of the testing from which they were derived; and () reduce the cost and increase the accuracy of developing reinforced concrete design rules. This paper deals with the development of pseudo properties and behaviours directly through mechanics, as opposed to experimental testing, and their incorporation into member global simulations. It also addresses the need for a fundamental shift to displacement-based analyses as opposed to strain-based analyses. [ABSTRACT FROM AUTHOR]

The elevated temperature behaviours of concrete specimens made of three different concrete grades are presented in this paper. Cylindrical specimens of concrete mixes with 17 MPa (designated as M17), 21 MPa (designated as M21) and 27 MPa (designated as M27) target strengths were employed. Different temperature progression in the core of the concrete cylinders was observed for specimens of different concrete grades. Concrete discoloration started at 300°C, while hairline cracks appeared at 400°C on the surface of the cylinders. Pore pressure generated by steam and carbon dioxide during heating of the cylinders caused explosive spalling at a furnace temperature of 400-600°C. Similar loss of compressive strength of concrete was found for all the employed mixes, which reached to nearly 70% at 800°C. The ultimate strain of concrete increased at higher temperatures. The loss of concrete elastic modulus reached 80%, whereas nearly 50% tensile strength was lost at 600°C. A comparison of observed data with the theoretical predictions based on the analytical models suggested by some of the international codes was made and differences between the predicted and observed data were found. Coefficients of strength reduction and corresponding strains were proposed, which correlated well with the observed stress-strain curves. [ABSTRACT FROM AUTHOR]

An improved analytical model to predict the ultimate shear capacity of a self-consolidating concrete (SCC) flexural member is presented. SCC behaves differently to normal concrete because of its unique composition and mix proportions, which alter the shear resisting mechanisms in the member. SCC has found a wide range of applications due to its excellent deformability and high resistance to segregation and bleeding, but the lack of an adequate model that could help analysts predict the shear capacity of SCC beams is one of the main barriers to its acceptance in routine design practice. The model presented in this paper was developed considering all the factors that influence the shear capacity of SCC beams. The test results of an experimental study conducted to validate the accuracy of the proposed model are also provided in this paper; the model's efficacy was also checked using test results reported by other researchers. The results predicted by the model showed good agreement with the experimental test data. [ABSTRACT FROM AUTHOR]

This paper investigates the mechanisms of corrosion of seven-wire strands and the reasons for failures in detecting corrosion at early stages. As per ASTM G109 and ACI 222 R-01, a 1-year study on chloride-induced corrosion of seven-wire prestressing strands embedded in various concretes was conducted. The type of corrosion current circuits in the prismatic specimens with one top and two bottom strands was investigated. Unlike solid rebars, the concrete resistivity had a limited role on the type of corrosion circuits in strand systems, with a high probability of corrosion occurring between different wires in the top strand itself. This may be due to the flower-like geometry and the complex corrosion mechanisms within the top strand. It is recommended to perform other electrochemical measurements on the top strand – prior to making conclusions. Also, until about 6% corrosion loss is reached, the rust will fill the interstitial space between the seven wires and will not exert expansive stresses on the surrounding concrete. Hence, no staining/cracking will be visible on the concrete surface – a serious structural safety issue – necessitating frequent chloride/corrosion condition assessment of prestressed-concrete structures. [ABSTRACT FROM AUTHOR]

Tests have shown that providing passive confinement to concrete, either through the use of internal stirrups, external fibre-reinforced polymer (FRP) wraps, FRP tubes or steel tubes, can increase the concrete strength and, in particular, the concrete ductility, thereby allowing greater absorption of energy and consequently ductile failure. The problem of including the benefits of passive confinement in design is in generalising the effect of passive confinement because it varies with the member size, the configuration of the confining reinforcement and material properties. In this paper, all aspects of the complex fundamental mechanics of passive concrete confinement are explained both qualitatively and quantitatively through the use of shear–friction and bond–slip mechanics. The mechanics model was found to have a good correlation with test results. An analysis-oriented procedure is described for quantifying the passive stress–strain of concrete for rectangular sections and it is envisaged that this can be used to develop simplified rules for design, in particular for new types of members and those with new materials. [ABSTRACT FROM AUTHOR]

In the context of a joint research project, a system for monitoring, protection and strengthening of bridges by using a textile reinforced concrete interlayer has been developed; the system consists of two carbon layers with a spacing of 15 mm and a special mortar. This setup led to the idea of building up an electrical field between the carbon meshes, to suppress the ingress of chlorides into the concrete. This paper focuses on the question of which voltages and electrical field strengths are necessary to prevent critical chloride contents at the reinforcing steel. For this purpose, extensive laboratory tests have been performed, followed by a numerical simulation study. By applying an electrical field, the negatively charged chloride ions are forced to move to the upper carbon mesh, which is polarised as an anode. It has been investigated whether the voltages to implement an electrochemical chloride barrier are smaller than they have to be for the common preventive cathodic protection. One advantage of this chloride barrier is that, because of the lower current densities, the anodic polarisation of the carbon meshes can be reduced. Therefore, different voltages, electrical field strengths, anode materials and anode arrangements were investigated. [ABSTRACT FROM AUTHOR]

The last few years have seen the publication of many papers in the field of vibration-based structural health monitoring (SHM). Methods to detect structural anomalies including damage have received much attention, but there is still some scepticism about their use in practice. Part of this can be explained by the lack of robustness and practicality of the proposed algorithms, which are challenged to detect small structural changes quickly and accurately with low rates of false alarms. Several approaches for SHM rely on modal parameters for structural damage identification, so the correct evaluation of these parameters is of paramount importance. This paper presents an enhanced methodology capable of performing automated identification of modal data. To validate such an approach, two applications are studied - one based on numerically generated signals with different noise levels and one based on experimental data acquired during tests on a high-speed train viaduct in France. The results obtained show that the proposed approach is automated, accurate and insensitive to noise. [ABSTRACT FROM AUTHOR]

It is well known that the mechanical properties of a material are related to lateral confinement. In this paper, 60 cylindrical high-performance concrete (HPC) specimens with different concrete strength grades were cast and subjected to a conventional triaxial experiment to study the mechanical properties of the material. The experimental results indicated that the specimens exhibited longitudinal splitting failure patterns under uniaxial compression and inclined plane shear failure patterns under triaxial compression. The stress–strain curves were divided into three stages: an elastic rising stage, a plastic rising stage and a softening descending stage. The application of lateral confining pressure effectively increased the triaxial compressive strength. As the concrete strength increased, the descending stage of the stress–strain curves became steeper, indicating an increase in brittleness. Based on the experimental results, the failure criterion of the HPC was analysed using the Drucker–Prager yield criterion and Kotsovos failure theory. The parameters of the Drucker–Prager yield criterion were determined, and the applicable range of the Kotsovos failure theory was also obtained. [ABSTRACT FROM AUTHOR]

Concern has been expressed in the recent decades about the corrosion prediction of concrete structures in a chloride environment. This paper summarises the corrosion prediction models developed for chloride-contaminated concrete, including both the empirical and electrochemical corrosion models. The definition methods of the steel de-passivation process for electrochemical models, such as anode–cathode ratio (Aa/Ac), critical chloride concentration (CCl,crit), modification of anodic Tafel slope (βa) or passive film resistance (Rf), are considered essential and discussed in detail. Furthermore, electrochemical parameters regarding the definition and selection in electrochemical models and experimental measurements are discussed. This study confirms that Aa/Ac and CCl,crit have been generally used in recent years, and that the modifications of βa and Rf related to free chloride concentration are technically feasible. In addition, the discreteness of electrochemical parameters in electrochemical models and experimental measurements are observed, and time-dependent characteristics of electrochemical parameters are scarcely presented in the existing literature. [ABSTRACT FROM AUTHOR]

Concrete, the most widely used construction material in the world, consumes a large amount of resources and emits significant greenhouse gases during production. Previous studies have adopted a deterministic method to confirm that substituting fly ash for cement in concrete can reduce carbon dioxide emissions. However, the life-cycle assessment involves a lot of assumptions and associated uncertainties. This paper reports on an investigation to consider those uncertainties. Two types of uncertainty – parameter uncertainty and uncertainty due to the choice of functional units – were investigated using the Monte Carlo simulation method and scenario analysis method, respectively. The results indicated that results varied significantly with the preset functional units. When considering volume and strength, although the addition of fly ash in concrete can reduce emissions, compressive strength is also decreased resulting in a zero net change in emissions performance. When adopting other functional units, the addition of fly ash has emission-reduction potential. By considering parameter uncertainty, although average emissions decrease with addition of fly ash, the standard deviation increases with addition, indicating an increasing discreteness. It is concluded that considering the uncertainty in the life-cycle emission analysis of fly ash concrete leads to more rational decision-making for concrete selection. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) design is in a state of perpetual revision of ever-increasing complexity. However, preventing the recurrence of unexpected types of brittle failure is yet to be achieved. It is argued that the causes of such types of failure reflect conflicts between assumed and actual behaviour of concrete at both material and structural levels. This paper presents available information on the fundamental properties of concrete, which current design assumptions are incompatible with, and points towards the work required for really improving RC design. [ABSTRACT FROM AUTHOR]

Biomineralisation is a process of formation of calcite from supersaturated solution due to the presence of bacterial cells and biochemical activities. In this article, a biological approach towards the development of sustainable construction materials is studied. Evidence of bacterial precipitation of calcite has led several research groups to explore the possibility of adopting this process in the area of construction materials. The goal of this review paper is to highlight the application of biomineralisation in concrete. The effect of a bio-based agent and bacterial solution on various properties of concrete is discussed. Additionally, the factors in the choice of bacteria for the biomineralisation process are also elaborated. This green biotechnology concept is a promising, environmentally safe substitute for conventional and current remediation methods to mitigate environmental problems in multidisciplinary fields. [ABSTRACT FROM AUTHOR]

Bugholes are usually considered an aesthetic problem rather than a durability problem. Surface bugholes often appear on the sidewalls of a tunnel's lining concrete, which can be mitigated but never eliminated. However, the impact of surface bugholes on concrete durability is still unidentified. In cold regions, the lining concrete of a road tunnel is exposed to de-icer solutions splashed by traffic, and it is additionally exposed to freeze–thaw (F–T) cycles. This study focuses on the durability to F–T cycles of tunnel lining concrete with surface bugholes. For the objectives, the study was carried out on a laboratory-scale F–T test using large concrete blocks. An image analysis based on the RGB values of each pixel in the coloured photographic image was performed to detect and quantify deterioration of the concrete surface throughout the F–T cycles. Although severe scaling never occurred during the 300 F–T cycles, the concrete with bugholes indicated a significant local scaling at the edges of the bugholes. Some bugholes enlarged and some merged with existing bugholes, in accordance with such local scaling. The paper presents synergetic and negative effects of bugholes on the local scaling of tunnel lining concrete exposed to F–T cycles. [ABSTRACT FROM AUTHOR]

In this paper, a washing-machine-shaped experimental device is presented to investigate the effect of marine environments on the penetration of chlorides in concrete. The proposed experiment is used to simulate different flow speeds and wave patterns surrounding the concrete and examine their effects on the penetration of chlorides in the concrete. The obtained experimental results show that there is a significant difference in chloride profiles between the specimens exposed to a marine environment with flow and wave actions and those immersed in a stationary solution. The difference is found to increase with exposure time, suggesting the importance of considering the marine environment when predicting the long-term durability of concrete exposed in a marine environment. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) in aggressive environments has higher concrete clear cover provided to protect the reinforcement against corrosion. However, providing such higher cover in severe environments could result in increased crack widths for the structural member. Hence, using a combination of fibre-reinforced polymer (FRP) bars and steel reinforcement bars (hybrid reinforcement) has been considered as a suitable solution to develop the full flexural capacity of the section without significantly affecting the serviceability and ductility requirements. This includes utilising the non-corrodible nature of FRP by adding a layer of longitudinal reinforcement made of FRP bars at the corner areas of the cross-section and keeping the main steel reinforcement at sufficient cover depth. This paper studies the flexural behaviour of hybrid glass-fibre-reinforced polymer (GFRP) beams consisting of continuous GFRP bars along with conventional steel reinforcement and comparing them with conventional RC beams through experimental and analytical studies. The test results indicated that the hybrid GFRP beams possess better flexural strength and ductility compared to conventional RC beams and could be considered as a suitable alternative to replace RC beams in aggressive environments. [ABSTRACT FROM AUTHOR]

The repair and management of Britain's concrete highway structures has significantly improved since the publication of specific guidance in 1990 in the UK Design Manual for Roads and Bridges (DMRB) This guidance was updated in 2020 to include an improved approach to managing deteriorated structures. This paper focuses on the additional requirements or significant modifications in the updated guidance and explains their rationale. Key changes include the overall management strategy of deteriorated structures, repair strategies and deterioration mitigation measures, including control of the incipient anode effect and concrete injection to improve the safety and durability of a repaired structure. Internal deterioration of concrete and thaumasite sulfate attack are also covered. The related UK Manual of Contract Documents for Highway Works also provides an updated specification for concrete repairs. Predominantly performance-based, it covers proprietary concrete repair products complying with British standards and other materials and construction methods for maintenance, repair or strengthening. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation into the mechanisms altering the pull-out behaviour of partially pulled hooked-end steel fibres inside an artificial crack exposed to wet–dry cycles of chlorides and carbon dioxide for 6 months. Mechanical and corrosion damage at the surface of the steel fibre was investigated using three-dimensional optical interferometric profiling, and petrographic analyses were used to describe damage and healing processes at the matrix surrounding the fibre. Mechanical damage observed in the cementitious matrix and at the fibre's surface confirmed that the pull-out process was governed by yielding of the fibre, fracture of the adjacent matrix, and friction between the hook and the matrix. Increases in the pull-out force of partially pulled-out fibres after exposure were connected to accumulation of corrosion products from the steel fibre and to alteration of the cement matrix surrounding the fibre. This study concluded that autogenous healing and carbonation of the damaged cement matrix around the fibre are the main mechanisms responsible for the increase in the fibre–matrix bond strength of hooked-end steel fibres bridging cracks in concrete exposed to wet–dry cycles. [ABSTRACT FROM AUTHOR]

This paper examines the mechanical behaviour of concrete following exposure to elevated temperature up to 800°C through experimental investigation, with emphasis on the effect of microstructure evolution on the deterioration of concrete compressive strength. First, a specially built electrical furnace is employed for the application of high temperature to 21 concrete cylinders before static compression tests. The static stress–strain relationships of the concrete cylinders are presented and compared. Furthermore, a series of experimental techniques are employed to examine the development of concrete microstructure, including thermogravimetric analysis, scanning electron microscope test and mercury intrusion porosimetry investigation. The inherent reason for concrete strength deterioration following elevated temperatures is revealed to be the combined action of decomposition of concrete hydration products, deterioration of the cement paste–aggregate bond, crack development and an increase in porosity. Meanwhile, based on comparison with existing data, the effect of water/cement (w/c) ratio on the mass loss and porosity increase of hydrated cement paste following high temperatures is preliminarily examined. It is found that higher w/c ratio resulted in larger total porosity, and the increase of total porosity as well as the large proportion of harmful pores generally led to the degradation of the concrete's compressive strength. [ABSTRACT FROM AUTHOR]

Chlorides are the agents responsible for starting the process of corrosion of steel reinforcement, thus reducing the service life of concrete structures, especially in marine environments. The penetration of chloride ions depends on several factors linked to the nature of the concrete cover and the exposure environment. The diffusion coefficient may establish the depth of chloride penetration in concrete in a given time and therefore this coefficient is related directly to the service life of reinforced concrete structures. This paper presents a methodology for determining the chloride diffusion coefficient using a mathematical model based on fuzzy logic. The following parameters were considered in the modelling: water/cement ratio, concrete compressive strength and the temperature during mixing of the concrete. The results show the feasibility of using fuzzy logic for the development of models to estimate the chloride diffusion coefficient in concrete. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study into the fundamental response of reinforced concrete members, which incorporate rubber particles obtained from recycled tyres, subjected to combined axial–bending loading conditions. Tests on confined circular members with and without internal hoops or external fibre-reinforced polymer (FRP) sheets are described. The results show that the rubber particles enhance the confinement level activated, with confined/unconfined strength and deformation capacity ratios at least twice those of conventional concrete members. The hoop-confined members provided with 30% rubber developed a typical reinforced concrete behaviour, with relatively limited deformation capacity in comparison with FRP-confined members. The external confinement substantially enhanced the ultimate rotation of members incorporating 30% rubber, with ductility factors reaching up to ten for relatively small eccentricity levels. An increase in rubber content to 60% had a detrimental effect on the axial capacity, but increased the ultimate rotation up to twice in comparison with members with 30% rubber. Based on the test results, a design-oriented constitutive model for FRP-confined concrete and a variable confinement procedure for assessing the strength interaction of circular sections are proposed. The suggested procedures capture, in a realistic manner, the influence of rubber content on the strength and deformation characteristics of confined members. [ABSTRACT FROM AUTHOR]

Long-span bridges are constructed to cross oceans or rivers. With the rapid growth of waterway transportation, vessel–bridge collision incidents now occur in large numbers. In order to provide better understanding of the actual responses of bridge structures under impact load, vessel–bridge collisions were simulated using the non-linear finite-element method. Four commonly used dynamic constitutive models of concrete are described in this paper. Two impact tests (a rigid ball striking a target concrete wall and a hammer striking a reinforced concrete (RC) beam) were simulated using LS-Dyna. It was found that the RC damage model was more suitable for simulating the inelastic responses of cracks than the other three models. Based on the RC damage model, a typical bridge substructure subjected to a 1000 dead-weight-tonnage vessel collision was numerically simulated. An empirical formula for estimating the maximum impact force was then developed. This formula, which considers the reinforcement ratio and the vessel collision velocity, is suggested for practical vessel–bridge design. The proposed empirical formula and the equations recommended in codes from different countries were compared and it was found that the assessment of vessel collision force using the new formula is significantly improved. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) walls subject to in-plane lateral loads are essentially subject to axial compression and tension forces in the respective end regions of the wall. The tension forces initially result in elastic tensile stresses in both the concrete and longitudinal reinforcement. Cracking occurs after the maximum tensile stress of the concrete has been exceeded and results in the reinforcement providing the sole tensile resistance at each crack location. The mechanical interlock between the reinforcement and concrete means that a portion of the tensile stress in the reinforcement at each crack is transferred back into the concrete between adjacent cracks. This mechanism stiffens the concrete in tension and is referred to as tension stiffening. This paper presents a generalised tension stiffening model developed for limited ductile (i.e. lightly confined) RC walls. However, it is also applicable for lightly confined RC elements generally. The model was validated against 14 boundary element prism specimens subject to cyclic loading, with very good correlation observed between the theoretical model and the experimental results. This model can easily be adopted into a sectional analysis procedure to account for tension stiffening in both the elastic and inelastic regions of response in an RC wall. [ABSTRACT FROM AUTHOR]

A novel phosphorus slag-based concrete is illustrated and provided in the paper with the aim of investigating experimentally the water temperature and age effects on its mechanical behaviour. The compressive and splitting tensile experiments of this concrete with different water temperatures (5, 10, 20, 30 and 40°C) and ages (7, 24, 72, 168, 336 and 672 h) are carried out to reveal the corresponding strength change laws and the relationship between strength and curing parameters. The failure modes and internal cracks evolution of the phosphorus slag-based concrete are depicted through strength tests and acoustic emission (AE) tests. The results show that water temperature and age effects on the development of compressive strength of the phosphorus slag-based concrete are very significant. The relationships between compressive strength and curing age of concrete under different water temperatures can be described by a logarithmic model based on the experimental data. Finally, the effectiveness of the test results has been confirmed by comparing the results from AE location with the macroscopic failure mode of concrete. The present results can provide a reference for engineering application in underwater buildings repair, such as discharge holes and spillways. [ABSTRACT FROM AUTHOR]

Concrete is extensively used in the construction industry, but the formation and development of cracks undermines the integrity of concrete structures. Improving the mechanical properties of concrete and developing efficient health monitoring of structures are thus essential tasks to be tackled. The research described in this paper was concerned with the effect of nanofibres on the mechanical properties of concrete as the use of nanofibres such as carbon nanofibres (CNFs) within cementitious materials has been found to be effective in enhancing the mechanical properties of concrete as well as its sensing ability. Most previous works have focused on evaluating the microstructure and mechanical behaviour of nano-reinforced mortar. Only a few studies have attempted to evaluate the mechanical and sensing properties of nano-reinforced concrete made with coarse aggregates. The objective of this work was to fill this gap in the literature by evaluating the mechanical and self-sensing properties of CNF-reinforced concrete (CNFRC). Material tests were conducted on CNFRC cylinders and beams in order to determine the full compressive, tensile and flexural constitutive behaviour, including the post-peak response, as well evaluating the self-sensing capability. The results obtained are valuable for analysis and design of large critical infrastructures employing CNFRC. [ABSTRACT FROM AUTHOR]