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Most studies of adding superabsorbent polymers (SAP) into concrete focus on high‐strength concrete, while this paper aims to understand the influence of SAP on "ordinary concrete" at a w/c ratio being 0.4 or 0.5. The proposed experiments include the effect of particle size, mixing methods, and dosages on the restrained shrinkage and mechanical properties of mortar and concrete. Mortar with varying dosages of SAP (0.1, 0.2, and 0.3 wt.%) and two types of SAP (type‐a of 30–60 mesh and type‐d of 300–400 mesh) was studied to evaluate the effect of SAP on mortar's cracking and strength. Two mixing processes of SAP (dry and pre‐wetted) were used to examine the effect of SAP on the mortar's shrinkage and mechanical properties. Furthermore, concrete specimens with a w/c ratio of 0.5 were prepared to investigate the cracking performance of concrete using the restrained squared concentric ring test method, a new approach which can predict the cracks location and pattern to evaluate the restrained shrinkage of concrete. The result revealed that the addition of SAP in a prewetted state decreased the mechanical properties at early curing age. The addition of 0.3 wt.% SAP was found to have mitigated the restrained shrinkage while prolonging the time to cracking of cementitious composites. The major finding is that adding SAP to ordinary concrete reduces shrinkage and improves mechanical strength, which should be further looked into and explored in its application in engineering work. [ABSTRACT FROM AUTHOR]

Alternative aggregates have undergone intensive research work that has led to confidence in its utilization in concrete. Likewise, various polymers have been investigated to enhance the strength parameters of concrete. This study was dedicated to studying the influence of PVA (poly‐vinyl alcohol) on fresh and hardened properties of rubberized concrete. In this study, nine different grades of concrete were cast containing two proportions of rubber, that is, 5% and 10% by mass of fine aggregate, while two dosages of PVA, that is, 1% and 2% by mass of cement. The results obtained for fresh properties of concrete indicate that rubber led to lower the workability and fresh density of concrete while PVA showed to enhance the workability but lowers the fresh density of concrete. Crumb rubber led to a reduction in mechanical strength parameters of concrete which were significantly recovered with the incorporation of PVA. It was witnessed that, both rubber and PVA substantially enhance the resistance of concrete to acid attack and the strain capacity of concrete. Moreover, PVA led to cause a tad increase in the modulus of elasticity (MOE) while rubber causes a dip in MOE. [ABSTRACT FROM AUTHOR]

The perforation of concrete‐like material targets against impact by nondeforming projectiles is always the research focus in engineering protective domain. In the present paper, a new punching plug model is proposed based on the similar features with punching shear in concrete slabs, utilizing the failure criterion of modified Mohr‐Coulomb. Semi‐empirical equations corresponding to ballistic limit, residual velocity, punching plug thickness are derived, where residual velocity is renewedly identified considering the effect of punching plug resistance. Eventually, the proposed punching plug model is validated and discussed by comparisons with perforation experiments. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and numerical study on the dynamic splitting tensile properties of ceramic aggregate concrete (CAC) that is composed of ceramic aggregates and mortar matrix. The maximum ceramic aggregate diameter includes 0.3, 0.6, and 0.9 cm. A series of split‐tension tests of CAC specimens were conducted first. Parametric studies such as the effects of aggregate size and strain rate, on the splitting tensile behaviors of CAC were presented in terms of tensile strength, stress–strain curve, failure patterns, and so on. Subsequently, we developed a three‐dimensional two‐phase mesoscale model for CAC, where the random distribution and size characteristics of ceramic aggregates in concrete were fully considered. Employing the developed mesoscopic model, systematic mesoscopic simulations were performed to investigate the mesoscopic responses of CAC under dynamic split‐tension loadings. Results indicated that the mechanic properties and cracking behaviors of CAC are associated with many factors, such as aggregate diameter, aggregate distribution and strain rate. Besides, there was a good agreement between the tested and numerical results, demonstrating that the developed mesoscale model has a significant reliability and potential in simulating the mechanical properties of CAC. [ABSTRACT FROM AUTHOR]

As a nanometer material, carbon nanotubes can inhibit the expansion of microcracks and is of great significance to improve the mechanical properties and durability of concrete. In order to explore the mechanism of dynamic mechanical properties enhancement of carbon nanotube reinforced concrete under impact load after freeze–thaw cycles, the dynamic compression test of carbon nanotube reinforced concrete samples was carried out by using the control variable method with freeze–thaw cycles and impact air pressure as variables. The results showed that under the same impact pressure, the peak stress of carbon nanotube reinforced concrete sample decreased gradually with the increase of freeze–thaw cycles. The corresponding strain increased slightly, and the stress–strain curve moved to the right and down as a whole. Under the same freeze–thaw cycle, the peak stress of carbon nanotube reinforced concrete sample increased with the increase of strain rate, and the dynamic strength growth factor DIF also increased, showing an obvious strain rate strengthening effect. In addition, under the same freeze–thaw cycles and external impact load, the dynamic strength of carbon nanotube concrete is 41.97 and 54.21 MPa, respectively, which is 22.27 and 25.81% higher than that of ordinary plain concrete. The results show that carbon nanotube reinforced concrete samples have higher dynamic mechanical properties and freeze–thaw cycle resistance than ordinary plain concrete samples. [ABSTRACT FROM AUTHOR]

The present study is focused on the compressive strength, water retention, and workability by varying the percentage of poly ethylene glycol 200 and liquid paraffin wax from 0% to 1% by weight of cement for self‐compacting concrete and compares it with conventional SCC. Percentages of 0.1%, 0.5%, and 1% (in proportion to the weight of cement) were adopted in the study. The comparison was done in a grade concrete and with cases such as indoor curing and water‐based curing. Slump‐flow test and V‐funnel tests were carried out on the fresh concrete to evaluate the workability of concrete. Concrete weight loss with time is evaluated to determine the water retention capacity. Compressive strength of cube specimens was conducted at the end of 7 and 28 days of curing. The durability of the concrete was assessed by immersing the concrete specimens in acids. The fresh properties were satisfied according to EFNARC specifications. Based on the weight loss percentage and satisfaction of compressive strength, the dosage of a self‐curing compound was determined. XRD analysis of the concrete was also performed on the concrete specimens. [ABSTRACT FROM AUTHOR]

Anchor channels are frequently used in curtain wall applications and are expected to meet several requirements, such as installation in floor slabs with limited member thickness, small edge distances, pockets, etc. An extensive numerical parametric study and an experimental investigation were conducted to evaluate all the relevant parameters affecting the concrete edge breakout failure. The influence of member thickness and the influence of pockets on the concrete edge breakout capacity of anchor channels in uncracked and unreinforced concrete members is investigated. The results show that the current characteristic member thickness becomes too conservative with increasing edge distance, whereas the verification based on the current model may result in slightly overestimated capacities for thin members. Moreover, in some countries it is common to install the curtain wall fastening point in a recess of the concrete member often called a "pocket." The most important parameters affecting the capacity of anchor channels in pockets are the edge distance, pocket size and height, and reduced member thickness. Modifications of the current concrete design model are proposed, as well as an additional modification factor to account for the influence of pockets. [ABSTRACT FROM AUTHOR]

Concrete is one of the most important and versatile construction materials and variation in its properties is inevitable. Mix design of concrete is done in such a way that the design compressive strength is typically higher than the actual values specified by the structural engineer. The concept of reliability has not been explicitly used in regard of calculation of compressive strength using mix design and demands attention. A design procedure based on the reliability‐based index is presented. The design procedure is developed for the concrete mix with partial replacement of cement by marble dust. The mechanical property which is the compressive strength of the concrete mix design is considered as a random variable, assumed to be lognormally distributed. The present study makes an effort to design a concrete mix in accordance to theory of confidence level for various levels of reliability. Mix design guidelines and graphs for various levels of replacement of cement by marble dust have also been presented in the study. Also, the cost analysis of various design mix proportions used has been calculated and compared. Four different cases to illustrate the performance rating in accordance with replacement levels of Marble dust have been formulated. The concrete mixes with marble dust induced in concrete had lower partial safety factors than those without inclusion. The characteristics of Marble dust incorporated concrete have been assigned numerical performance index values. These values may constitute a reliable means for concrete producers in finding the rate of cement replacement by other cementitious materials. The compressive strength of most of mixes with marble dust had a coefficient of variation and within‐test coefficient of variation value ranging between 2% and 3% and less than 1.5%, respectively. This indicates toward improvement in quality of concrete with cement partially replaced by marble dust. [ABSTRACT FROM AUTHOR]

Self‐desiccation is one common phenomenon of concrete with low water‐to‐cement (w/c) ratios, which may lead to the decrease of internal relative humidity (IRH), and therefore causing autogenous shrinkage (AS). Superabsorbent polymers (SAPs) are used as a kind of internal curing material to mitigate AS of concrete. The IRH and AS are significantly affected by the w/c ratio, and several attempts have been made to investigate the IRH or AS of concrete with different w/c ratios. However, the prediction model of AS considering IRH and w/c ratio of internally cured (IC) concrete is limited. In the present study, the effect of w/c ratio on IRH and AS of IC concrete was investigated, and a two‐stage prediction model of AS based on the results of IRH for IC concrete considering the effect of w/c ratio was proposed. The experiment results and analysis indicated that IRH of IC concrete increased as increase of w/c ratio, and development of IRH experienced two stages: a water‐vapor saturated stage with 100% RH (stage I), and a gradually reducing stage in which IRH decreased gradually (stage II); critical time of IC concrete increased as increase of w/c ratio; expansion peak of IC concrete increased as increase of w/c ratio; AS and AS rate of IC concrete decreased as increase of w/c ratio; IRH, critical time, and expansion peak of IC concrete were higher than that of ordinary concrete; AS and AS rate of IC concrete were lower than that of ordinary concrete. [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 present scenario, sustainable materials which creates less impact on the environment are the need of the hour. Recycled fine aggregate self‐curing concrete (RFA‐SCRC) can play a significant role in reducing the utilization of natural river sand and also plays a vital role in conserving the water used for curing. This research work deals with the experimental investigations on the compressive strength, flexural strength and split tensile strength of RFA‐SCRC for various replacement proportions of RFAs using ordinary portland cement (OPC) and portland pozzolana cement (PPC) as different variants. The replacement proportions of RFAs considered for this study are 0%, 10%, 20%, 30%, 40%, and 50% to the weight of manufactured sand. Strength optimization was carried out by Taguchi optimization method using Minitab software tool. The parameters considered in this study are the replacement proportion of RFA, type of cement and type of curing. The optimization results indicate that, considering compressive and split tensile strength characteristics, RFA concrete produced using 40% RFA, OPC, and self‐curing process is found to be optimum whereas 30% RFA, OPC, and self‐curing process is found to be optimum with respect to flexural strength characteristics. [ABSTRACT FROM AUTHOR]

Elastic modulus (E) estimation forms an important element in the methods used to predict concrete creep deformation, which is an important structural design consideration. A variety of different E estimation models for concrete exist but there is uncertainty as to which of the models is the most accurate. This research study assesses the performance of models namely, the ACI 318, ACI 318 Simplified, Mendis et al., Rüsch et al., Carrasquillo et al., ACI 363, AS 3600, Omar et al., AS 3600, BS 8110, Alexander and Davis, SANS 10100, CEB‐FIP, and the EC 2. The included list of models is taken from national codes and includes their superseded and modified versions. The E values of 108 specimens, whose properties differed (in aggregate type, cement type, concrete strength, and curing age), were measured. The actual E value was compared to each model's estimations to determine which were most accurate statistically using the coefficient of variation (ωj). The ACI 363 model was the most accurate out of the 16 models assessed, yielding an overall ωj of 16%. The CEB‐FIP model was found to be the least accurate showing an overall ωj of 31.8%. From the 16 models considered, it was recommended that the ACI 363 model be utilized by creep prediction models. In addition, it was found that not all modified estimate models produced better estimates. [ABSTRACT FROM AUTHOR]

River sand (RS) has been the most popular fine aggregate in concrete production. Recently, because of the continuing decline in supply of RS, alternative source of fine aggregates is needed. Manufactured sand (MS), which is produced by mechanical crushing of virgin rock or construction waste, is becoming more popular for replacing RS. Concrete containing MS has higher compressive strength but is more brittle. To promote the application of MS in concrete, concrete‐filled‐steel‐tube (CFST) column is advocated to restore the ductility by composite action. It is believed that the improved strength and ductility of CFST column containing MS is due to the enhanced wet packing density (WPD) of concrete, which has been researched to affect significantly the mechanical performance of concrete. Nonetheless, there was very limited research carried out on the effect of WPD on the behavior of confined concrete and CFST column. Ergo, 15 CFST column specimens with MS replacing RS partially or totally were prepared and tested under uni‐axial compression. It is evident that CFST specimens with concrete containing blended fine aggregates showed different axial load‐strain behavior to those with RS concrete (especially the maximum strength and postelastic slope). More importantly, the normalized strength (maximum strength to squash load) of CFST specimens can be correlated positively to the WPD. This article thus provides a new insight into the interdependence between the uni‐axial strength of CFST columns and the WPD of the in‐filled concrete. [ABSTRACT FROM AUTHOR]

This study experimentally examines the effect of rubber aggregate size on the static and dynamic behavior of rubberized concrete. Rubberized concrete specimens were prepared with different maximum rubber aggregate sizes ranging from 1 to 3 mm to 3 to 5 mm while the rubber content was kept constant at 15% by volume. The dynamic compressive behavior of rubberized concrete was investigated by using split Hopkinson pressure bar (SHPB) tests. The experimental results have shown that rubberized concrete with smaller rubber aggregates showed higher static compressive strength as compared to that with larger rubber aggregates. Meanwhile, the rubber aggregate size did not considerably affect the density of rubberized concrete. The use of smaller rubber aggregate size mitigated the slump reduction of rubberized concrete. Rubberized concrete exhibited obvious sensitivity to strain rate and those with larger rubber aggregates showed higher strain rate sensitivity. The progressive damage of rubberized concrete showed more ductile behavior with bulging failure, which was different from the typical concrete under compression. In general, the use of smaller rubber aggregate size was beneficial to the static compressive strength but less effective to the dynamic compressive strength of rubberized concrete as compared to those with larger rubber aggregates. [ABSTRACT FROM AUTHOR]

To study the bond–slip behavior between reinforcing bars and reactive powder concrete (RPC), eccentric pull‐out tests of 20 groups of bonding specimens were conducted, and the variables in the test specimens included RPC strength, cover thickness, bond length, and reinforcing bar diameter. The effects of various parameters on the bond stress and peak slip were analyzed. A formula for calculating the average bond stress and between the reinforcing bar and RPC were established, and the bond–slip relationship between reinforcing bar and RPC was determined. The results indicated that the bond length had the most significant effect on the bond performance, followed by the strength of concrete, cover thickness, and reinforcing bar diameter. When the bond length increased from 3d to 4d, the average bond stress decreases by 13.2% to 23.7%. When reinforcing bar diameter increased from 16 to 20 and 25 mm, the average bond stress increased by 6.58% and 15.9%, respectively. The average bond stress increased with increase of the cover thickness. When the RPC strength increased from 105.2 to 124.8 MPa, the average bond stress increased by 7.0% to 13.2%. [ABSTRACT FROM AUTHOR]

The mechanical properties of concrete are one of the most important properties in a design code. Accurate prediction models for mechanical properties are always desirable. Given environmental benefits, fly ash (FA) is often used as a replacement for Portland cement. In this study, two mechanical properties of concrete with FA, that is, compressive strength f′c and splitting tensile strength fst were modeled by using gene expression programming (GEP). The GEP models were compared with response surface methodology, multiple linear and nonlinear regression. The sensitivity and parametric analysis were also performed. In addition, the influence of parameters of the GEP algorithm on the performance of the developed GEP models was evaluated by testing various linking functions, head sizes, number of genes, number of chromosomes, and fitness functions. It was revealed that the models developed by GEP have high predictive and generalization capability for both f′c and fst of concrete with FA as compared with the other modeling techniques. [ABSTRACT FROM AUTHOR]

Cores with diameters of 100, 75, and 50 mm and with varied length‐to‐diameter (l/d) ratios of 1.0, 0.9, 0.8, 0.7, and 0.6 were extracted from concrete panels of 11 different concrete mixtures and prepared in the lab. Compressive strength tests of concrete cores and cubic samples were performed at 7, 28, 60, and 120 days, respectively. Strengths of cores with l/d ratios ranging from 0.6 to 1.0 could be converted by the strength correction coefficient into that of the core with the l/d ratio of 1.0. The evidence for the reliability of compressive strength of cores with low l/d ratios is very seldom in literatures. The test results indicated that correction factors gradually decreased with the decrease in l/d ratio, the strength of the core increased and the effect was more pronounced for cores with smaller diameter and the maximum aggregate size. Correction factors of cores drilled from river gravel aggregate concrete are slightly higher than that from crushed stone aggregate concrete. The longer the age of concrete is, the lower the correction coefficient becomes. The proposed correction factor values for core test samples with the l/d ratios ranging from 0.6 to 1.0 differ from the prior researches. For compliance with the requirement of the test data variability, there is no reason to limit the ratio of aggregate sizes (da) to the diameter of the core (d) to a minimum of 3.0 (d/da). The results show that the concrete core with a diameter less than the standard size and l/d less than 1.0 can effectively reflect the variation of concrete strength with acceptable reliability. Drilling‐core with low l/d ratios will facilitate the reduction of the damage to the structures, so the members with thickness less than 150 mm (e.g., slab and shearwall) can be drilled and tested. [ABSTRACT FROM AUTHOR]

This article presented an efficient deep learning technique to predict the compressive strength of high‐performance concrete (HPC). This technique combined the convolutional neural network (CNN) and genetic algorithm (GA). Six CNN architectures were considered with different hyper‐parameters. GA was employed to determine the optimum number of filters in each convolutional layer of the CNN architectures. The resulted CNN architectures were then compared to each other to find the best architecture in terms of accuracy and capability of generalization. It was shown that all of the proposed CNN models are capable of predicting the HPC compressive strength with high accuracy. Finally, the best of the six considered models was validated through the 10‐fold cross‐validation method and compared to the previous studies on the same data set. Models were developed through a comprehensive data set consisting of 1030 HPC compressive strength test data. Comparing the proposed technique with previous studies showed that the proposed technique has a considerable advantage over previous methods and can be employed for reliable estimation of the mechanical properties of different engineering materials. [ABSTRACT FROM AUTHOR]

This study utilizes the machine learning technique to solve the complex fatigue problem of concrete materials. To this end, several learning algorithms were addressed including the random forest (RF), support vector machine (SVM), and artificial neural networks (ANNs) models. Extensive experimental data were collected from literature to train the machine learning models for estimating the maximum number of cycles at failure (i.e., the so‐called fatigue life). A machine learning model providing the best correlation was chosen through verifications. On this basis, a strength degradation model of concrete under fatigue loading was finally proposed to evaluate the residual strength of concrete after fatigue damage, which is a key factor in determining the remaining service life of concrete structures. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of aggregate packing optimization based on a particle packing method (PPM) and cement paste volume (CPV) on the workability and mechanical properties of both natural aggregate concrete (NAC) and recycled aggregate concrete (RAC). The slump, compressive strength, flexural strength and Young's modulus of concrete were first examined, followed with the characterization of macro‐pore structure inside RAC by using X‐ray computed tomography (CT). The results indicate that the PPM can help to densify the granular skeleton of aggregates in concrete by reducing the void around the aggregates and the cement paste film thickness, and subsequently enhances the mechanical properties of the concrete with a constant CPV. This enhancement is higher for RAC than NAC, particularly for the Young's modulus. The particle packing optimization can also decrease the number of macro pores in RAC, contributing to the enhancement in the mechanical properties of RAC. Moreover, increasing CPV in concrete with a maximum aggregate packing status considerably decreases the mechanical properties of concrete, whereas increases its workability. This is mainly caused by the increased number of macro pores in the cement paste and at the interfaces between RCAs and hardened cement paste. [ABSTRACT FROM AUTHOR]

Concrete exhibits a different deformation behavior in tension and compression when subjected to uniaxial and biaxial loads. It also reveals crack‐opening and crack‐closing effects under cyclic loads. This paper discusses a gradient‐enhanced continuum damage model to investigate the deformation and damage behavior of concrete subjected to cyclic and multiaxial loading conditions. An activating variable introduced in the model distinguishes the multiaxial stress states. A single damage criterion that relates the history variable to the equivalent strain limits the elastic domain. The evolution of internal variables confirms their thermodynamic consistency. The gradient enrichment of equivalent strains leads to proper localization of deformation. Comparison of numerical predictions with relevant experimental data and some previous models validates the capability of the model to describe softening/crack‐closure behavior under various loading. Application of the model to fracture problems demonstrates the ability of the model to describe damage initiation and propagation, and its localization. [ABSTRACT FROM AUTHOR]

The stacking of worn out tyres on the environment is the major concern in the world due its non‐biodegradable nature. Environmental issues related with disposal of rubber and also the mining of river sand could be minimized by using crumb rubber as fine aggregate. The objective of the article is to strengthen the interfacial bonding of crumb rubber with cement paste using modified clay for counteracting the strength reduction of rubberized concrete. The microstructure of rubber was examined to study the effectiveness of modified clay treatment of rubber using scanning electron microscopy (SEM). The cement was partially replaced with silica fume (0%, 5%, 10%, 15%, and 20%) and GGBS (30%). The properties of concrete such as workability, unit weight, compressive strength, split tensile strength, flexural strength, and impact strength were studied. The results showed that the inclusion of modified clay treated rubber with silica fume exhibited a low strength reduction of 0.45% compared with control mix which makes the rubberized concrete suitable for the structural elements. [ABSTRACT FROM AUTHOR]

The importance of using sintered fly ash aggregates (SFAs) as coarse aggregate and metakaolin (MK) as partial replacement of cement for generating sustainable concrete has been accessed in this research. For this, concrete mixes are designed by replacing 0%, 15%, 30%, and 45% natural coarse aggregates (NCAs) by SFA and incorporating 0%, 10%, 15%, and 20% MK in place ordinary Portland cement (OPC) along with a constant water‐binder ratio (0.42). Workability, compressive, split tensile and flexural strength, and nondestructive parameters and other characteristics (water absorption, volume of voids, and density) of designated mixes are evaluated by performing various experiments in the laboratory. The study demonstrates that significant degradation in concrete behavior has been observed with the use of 45% SFA and 20% MK. However, usage of 30% SFA in place of NCA and 10–15% MK as cement replacement is beneficial in achieving the desired target strength and fulfills other concrete requirements for practical use. [ABSTRACT FROM AUTHOR]

The effect of the boundary conditions, defined as the thermal expansion restraint imposed by the external uniaxial compressive load in plain concrete subjected to high temperatures, is discussed. A numerical mesoscopic investigation uncoupled the load induced thermal strain (LITS) into three main components (aggregates and matrix strain contributions and the effect of the thermal expansion restraint). The analyses demonstrate that LITS depends on the materials properties (viscous‐plastic behavior) and also on the boundary conditions, which is function of the test setup and seems to be not related to the material properties. In this paper, the role of the boundary conditions on 1‐phase (homogeneous) and 2‐phase (matrix + aggregates) numerical analyses are investigated. A LITS semi‐empirical model is incorporated in the numerical modeling to account for the stiffness degradation. It is demonstrated that in 1‐phase models, the effect of the boundary conditions is absent, which is not true for mesoscale analyses. In this case, the effect of the boundary conditions should be taken into account and subtracted from the results to avoid an overestimation of the material response. It is important mentioning that the analyses of concrete behavior at elevated temperatures and transient creep experimental procedures completely neglect the role of the boundary conditions. [ABSTRACT FROM AUTHOR]

The influence of microstructural changes on concrete properties at elevated temperatures is presented and discussed in this paper, as the exposure to elevated temperatures brings in marked changes in concrete thermal, mechanical and kinematic properties owing to the heat‐induced evolution of material's microstructure. The major microstructural changes consist in increasing pore size, occurrence of microcracking and activation of chemo‐physical processes in the hardened cement‐paste. These processes (like portlandite dissociation and crystalline change in quartzitic aggregate) occur above 400°C and are more pronounced in high‐strength than in normal‐strength concrete. Increasing pore size and microcracking, however, yield the largest contribution to concrete strength‐loss, that occurs mainly between 400 and 800°C, depending on aggregate type and initial moisture content in the mix. On the whole, calcareous (or carbonate) aggregate behaves better than siliceous aggregate face to increasing temperatures. Initial moisture content favors concrete thermal spalling, mostly between 200 and 400°C, but such a complex phenomenon is still open to investigation, as demonstrated by the various theories found in the literature, each with its chemo‐physical mechanisms and limitations. Three theories are discussed in this paper, and these theories together with other critical issues allow to focus on future work. [ABSTRACT FROM AUTHOR]

Although steel fiber reinforced concrete is becoming increasingly popular in the construction industry, its application is currently limited to certain areas. One reason is the lack of an economical non‐destructive testing method to determine the content, distribution, and orientation of steel fibers in fresh and hardened concrete. However, these parameters are decisive for the assessment of the static performance of a building component. In this article a new test method is proposed, which is based on the electrical conductivity of concrete. Using a two‐electrode experimental set‐up, measurements of the electrical conductivity were done on hardened concrete cubes with defined fiber content and a correlation between electrical conductivity and fiber content could be identified. Within the scope of extensive test series, the fiber content and the age of specimens were varied, and several identical series were produced and observed to ensure statistically verified results. At this stage of research the test method based on electrical conductivity measurement provides reliable results on the fiber content of preconditioned concrete cubes. Based on the results a new model was developed to quantify the fiber content of the examined cubes. This model is based on the estimation of the relative conductivity, the so‐called increase of conductivity. Undesired influences caused by aging, respectively hydration in the young concrete age were eliminated, by relating the conductivity of fiber reinforced concrete to an unreinforced concrete. Further investigations with focus on the influence of concrete composition and other specimen sizes are going to be conducted as next steps for the development of an in situ test setup for the diagnosis of concrete structures. [ABSTRACT FROM AUTHOR]

Calculation of service life costs allows for a holistic assessment of the cost‐effectiveness of options in design regarding materials and intervention strategies for an infrastructure object. A method is presented in which probabilistic service life modeling and cost calculations are combined. This method is exemplified by two cases of reinforced concrete structures exposed to a chloride‐bearing environment. Two different types of reinforcing steel and several intervention strategies are analyzed. The results show that the method is suitable for decision‐making on the most economical solution. The solution with the lowest initial construction costs does not necessarily result into the lowest service life costs, depending on chloride exposure conditions and the anticipated interventions. [ABSTRACT FROM AUTHOR]

Strengthening is often required for reinforced concrete, steel, and masonry structures or structural elements when they possess insufficient performance against external loads such as earthquakes. Recently, the use of carbon fiber‐reinforced polymers (CFRP) has been considered a viable strengthening technique alternative to traditional methods. The major concern is premature debonding failure hindering the efficient use of CFRP systems. FRP anchor systems have been used to avoid this phenomenon. This paper employs a machine learning (ML)‐based algorithm (support vector regression) to propose predictive models to simulate the bond‐slip behavior of anchored CFRP strips externally bonded to the concrete surface. A comprehensive database was constructed using the previous reports on the bond‐slip behavior of FRP‐to‐concrete joints anchored with CFRP strips. Afterwards, the collected database was used to train and validate the proposed models. The input parameters cover all possible factors, that is, compressive strength of concrete, width of concrete block, anchor hole diameter, anchor hole depth, number of anchors at one row, number of anchors at one column; elastic modulus, width, bonding length, and thickness of CFRP strip. The output parameters are maximum shear capacity, residual shear capacity, displacement values at peak shear, and residual shear. Results imply that the proposed models have high prediction accuracies with low error rates. Proposed models are also presented in code format to be easily incorporated into analysis software for practical use. [ABSTRACT FROM AUTHOR]

This article presents results of an investigation that focuses on assessing bondline strength of carbon/epoxy fiber reinforced polymeric (CFRP) precured strips embedded in concrete for near‐surface‐mounting (NSM) strengthening applications. In this study, experimental evaluation and nonlinear numerical analysis of CFRP/concrete interfacial bond behavior are investigated. In this study, 15 pull‐out tests were performed on different reinforced concrete (RC) U‐shaped column specimens with different NSM groove configurations to evaluate the effect of groove size, groove depth, and adhesive bondline thickness on overall performance of the CFRP‐NSM system and to identify the optimum groove dimensions. Experimental results indicated that changing groove geometries of the NSM‐FRP reinforcements significantly affect bondline strength and associated mode of failures of NSM‐CFRP system. It was also shown that increasing bondline length lead to an increase in ultimate failure load and CFRP rupture strain. Based on results of this study, NSM materials with lower longitudinal moduli and higher rupture strains (e.g., E‐glass/epoxy or basalt/epoxy), may increase toughness and enhance performance of the NSM strengthening system. [ABSTRACT FROM AUTHOR]

The precious collection of the Museum Boijmans van Beuningen in Rotterdam has regularly suffered from floods in the past. When the depot in the museum's basement flooded for the umpteenth time in 2004, it was time for action and the idea for the "Depot Boijmans van Beuningen" was born. Initially conceived as a traditional depot, the decision was later made to make the building fully accessible to the public, thus providing insight into the preservation and management of the important art collection. This concept, unique in the world, does, however, involve considerable challenges, such as maintaining the indoor climate and guaranteeing the security of the public building. For the client and the architect, it was a major task to define the design for the Boijmans van Beuningen Depot and the indoor usage as well. For the structural engineer, it was a challenge to design a rational and functional construction. Concrete plays an important role in addressing this challenge. Obviously, all options had to be examined and alternatives had to be proposed to achieve the most optimal integral result. [ABSTRACT FROM AUTHOR]

Research argues in favor of using recycled aggregates in structural concrete. However, lack of specific clauses in standards for recycled aggregate concrete design hinders the use of recycled aggregate concrete by the industry. Recycled aggregate concrete‐specific design clauses are hindered because conventional research must be complemented with experiments directed towards stochastic modeling, so that reliability concepts may evaluate whether the probabilities of failure of design comply with the expectations of Society or whether specific design rules are needed. This article compares the within‐batch variability of carbonation under accelerated conditions of four natural aggregate concrete and four analogue recycled aggregate concrete mixes and analyses the reliability of Eurocode 2 cover design for carbonation exposure. In general, the incorporation of coarse recycled concrete aggregates worsened the mean durability behavior of concrete, including resistance to carbonation. However, the variability of carbonation depth was not meaningfully affected by the recycled aggregates used (coarse recycled aggregates produced from concrete waste) and the reliability of concrete cover design only decreased due to the effect of the recycled aggregates on the mean resistance to carbonation. A 5 mm increase of concrete cover was found to more than offset the detrimental influence of full incorporation of recycled aggregates on the reliability of concrete cover design. [ABSTRACT FROM AUTHOR]

When designing steel fiber‐reinforced concrete, for example, according to Model Code 2010, the residual flexural strength values must be specified as fundamental properties. It is often difficult to establish the relationship between residual flexural strength values and the required dosage of steel fibers depending on the type of steel fibers and the concrete quality. For an estimation of the presumably necessary dosage of steel fibers, various empirical approaches exist for the approximate determination of the residual flexural strength values, which, however, are based on different tests and have been almost exclusively been derived on the basis of few or "own" test results of the respective institute. For this reason, the validity of the respective approximation approach is often limited. Using the bending beam database "Steel Fibre Reinforced Concrete", selected approaches were systematically analyzed and an improved approach for determining the residual flexural strength values of steel fiber‐reinforced concrete was developed. [ABSTRACT FROM AUTHOR]

Steel corrosion is a significant problem of concrete‐based infrastructure, and it increases the repair costs of the damage to structures. Glass‐fiber‐reinforced polymer (GFRP) composite bars are corrosion‐proof and exhibit relatively higher strength than ordinary steel reinforcement. However, GFRP bars degrade when exposed to the highly alkaline environment of concrete over extended periods. This study focuses on the effect of the high alkalinity of concrete on the tensile strengths of several types of GFRP bars. Different accelerated aging techniques were employed to evaluate the effects of GFRP characteristics (fiber volume fraction, matrix composition, bar diameter, and presence of protective coating) on the alkali resistance. The test results indicated that the alkali attack significantly decreased the tensile strength of GFRP, increasing with age. The alkali resistance of the GFRP bars increased up to a fiber volume fraction of 50% but decreased when the fiber volume fraction increased to 60% and above. The effects of protective coating on alkali resistance were generally positive but not consistent, and the effects of the matrix type and bar diameter on the alkali resistance of GFRP bars were insignificant. Accelerated aging did not change the bond strength but altered the failure mechanism associated with the bond failure of the specimens. [ABSTRACT FROM AUTHOR]

Strengthening of existing reinforced concrete (RC) structures by means of externally applied fiber‐reinforced polymer (FRP) reinforcement was and still is an important research topic. CFRP reinforcement is particularly suitable for infrastructure projects where the actual loads have exceeded the predictions made in the past decades and high chloride input due to de‐icing salts is also present. This article presents experimental and theoretical investigations on the structural behavior of RC members strengthened with an externally applied CFRP textile‐reinforced concrete layer under monotonic and cyclic long‐term loading. A precise analysis of the cross‐sectional behavior and the calculation parameters to determine deflections and load‐bearing capacities of the strengthened RC members is conducted. It is shown that the load‐bearing capacity is not influenced by the preceding monotonic or cyclic long‐term loading and despite the many influencing factors, a good agreement between the calculations and experimental data can be achieved. [ABSTRACT FROM AUTHOR]

Conformity control is applied in order to safeguard the quality of produced lots. Conformity criteria are characterized by an operating characteristic curve, quantifying the probability of acceptance in relation to a concrete lot with a specific quality. By applying conformity control, certain lots of concrete are accepted or rejected. This induces a filtering effect, which in case of conformity control of durability parameters leads to an effect on the design service life. For durability, limiting values for durability‐related properties can be proposed. Specifying conformity criteria for the durability parameters of concrete can enable to safeguard the quality of concrete products in relation to durability. This conformity control has a filtering effect on the distribution of these durability parameters. When, for example, considering the diffusion coefficient of concrete, this filtering effect results in a lower mean value and standard deviation, consequently (positively) influencing the service life. In this paper, conformity criteria for durability parameters are developed, and their effect on the design service life of reinforced concrete elements is quantified. [ABSTRACT FROM AUTHOR]

With the aim of reducing life cycle costs and dead weight, there are various concepts for replacing bridge pavements and sealants with high‐performance concrete. The corrosion resistance of textile reinforcements allows the realization of thin reinforcement layers that fulfill this objective. However, the textile‐reinforced concrete used as a road surface must meet the particular requirements relating to frost resistance and, specifically, scaling. An investigation on an existing structure indicated the influence of textile reinforcements on frost resistance. Therefore, the present investigations focus on the frost scaling of different combinations of a carbon reinforcement and fine‐grained concrete. For this purpose, a multistage research design is used. First, the influence of the reinforcement and the concrete mix on the capillary porosity is investigated. The capillary porosity of concrete is directly related to its resistance to freeze–thaw scaling. This resistance is examined using the slab‐test method. Finally, the influence of the frost exposure on the pull‐off strength, which is crucial for the strengthening of structures, is determined. [ABSTRACT FROM AUTHOR]

The durability of concrete material after exposure to elevated temperatures is important for the serviceability prediction of concrete structures in a fire disaster scenario. Existing researches show that an appropriate amount of basalt fiber can significantly improve the splitting tensile strength and chloride penetration resistance of concrete. However, the mechanical properties of basalt fiber concrete after elevated temperatures and its durability properties are still not clear. In this paper, the mechanical properties, carbonization law, and chloride ion penetration law of ordinary concrete and basalt fiber concrete under high temperatures are studied. The concept of a burnt layer for concrete exposed to elevated temperatures is proposed, and the thickness of this burnt layer for concrete under different temperatures was measured. The results show that the addition of basalt fiber can inhibit the carbonization of concrete at elevated temperatures, diminish the thickness of the burnt layer, and significantly improve the chloride penetration resistance of concrete. [ABSTRACT FROM AUTHOR]

Electrochemical chloride extraction (ECE) is an effective method to remove chloride ions in reinforced concrete. In addition, cracks in concrete have self‐healing properties. The self‐healing properties of concrete may affect the ECE process. Based on moving mesh technology, this paper simulates the ion migration process of ECE in crack‐self‐healing concrete. According to the simulation results, the distribution of ions in the reinforced concrete and the electric potential change law inside the concrete are analyzed during the ECE process. The effects of cracks or no cracks in the anode area of ECE, self‐healing or no self‐healing, and different self‐healing rates on the efficiency of ECE were discussed. This research will have a positive impact on ECE's research. [ABSTRACT FROM AUTHOR]

Cores were drilled from the panels made of different concrete mixtures. The compressive strength and splitting strength of core and cube specimens were tested at the ages of 7, 28, 60, 90, and 180 days. The effect of the diameter on concrete core splitting strength was examined. The strength correction factors were determined to convert the splitting strength of the core with diameter of 75 mm to that of the core with diameter of 100 mm. The regression analysis was carried out using experimental data to evaluate the core splitting strength as a function of the compressive strength of the concrete core. Then, the reliability of the proposed equation based on experimental data for compressive strength ranging from 20 to 80 MPa was assessed with the integral absolute error (IAE). Other existing relations between splitting strength and compressive strength of the cylinder were also evaluated with IAE, and most of the existing relations are not suitable for splitting strength of cores. The accurate power function relation formula is obtained with the test data. Only compressive test can be carried out by using drilling core samples in existing buildings, and the compressive strength and tensile strength of concrete can be obtained simultaneously, thus the numbers of splitting tests can be reduced and the mechanical property of existing buildings can be evaluated. [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]

The above article, published online on 29 December 2022 in Wiley Online Library (wileyonlinelibrary.com) has been retracted by agreement between the journal's Editor‐in‐Chief, Professor Luc Taerwe, the fib, and John Wiley & Sons Ltd. The retraction has been agreed given the journal has received evidence confirming that the peer review process of this paper was manipulated. As a result, the conclusions reported in the article are not considered reliable. [ABSTRACT FROM AUTHOR]

Alkali‐activated materials are increasingly being used in practical applications as potential alternatives to Portland cement. If alkali‐activated slag (AAS) is to be applied to prestressed engineering and large‐size structures, it is necessary to study the creep performance of AAS. Existing studies have found that the creep of AAS concrete is larger than that of ordinary Portland cement (OPC) concrete, and adding fiber is an effective way to overcome this defect. In this study, we investigated the creep of basalt fiber–reinforced AAS (FRAAS) concrete for fiber contents ranging from 0% to 0.9% (by volume) at a stress–strength ratio of 0–0.6. After analyzing the experimental results, it was found that the basalt FRAAS concrete had no obvious linear creep range. It was observed that with an increase in the fiber content, the inhibition effect of fiber on creep became stronger initially and then weaker. The inhibitory effect of fiber on creep was strengthened by the increase in the stress–strength ratio. The creep coefficient showed no obvious change when the fiber content was in the range of 0%–0.9%. Based on the existing OPC concrete creep models, a method for predicting the creep of basalt FRAAS concrete was proposed. [ABSTRACT FROM AUTHOR]

This study investigates the early mechanical strength, and shrinkage crack resistance of ultra‐high molecular weight polyethylene (UHMWPE) fiber concrete with different lengths and contents. The microstructure of UHMWPE fiber concrete is investigated by scanning electronic microscope (SEM) to analyze the distribution and mechanism of action of UHMWPE fiber in concrete. The mechanical strength results indicate that the compressive strength and splitting tensile strength of concrete increase first and then decrease by adding fibers. The maximum compressive strength and splitting tensile strength at age of 28d are 42.9 and 3.32 MPa, which is 41.1% and 55.9% higher than that of the benchmark group. The SEM results show that when the UHMWPE fiber content is small, the fibers are evenly distributed in concrete and tightly bonded to the matrix. While the fibers will agglomerate and entangle with the increase of the fiber content, the results of shrinkage resistance test demonstrate that the 12 mm fiber with 0.24% fiber volume content can obtain the best shrinkage crack resistance. [ABSTRACT FROM AUTHOR]

The application of ultra‐high performance concrete (UHPC) in the bridge deck effectively increases the strength, ductility, and durability of the deck system, while the problem of fiber discontinuity at the joint‐deck interface remains unsolved. This study proposes an innovative UHPC joint to create steel fiber continuity at the interface and experimentally investigates its tensile behavior. Test parameters include fiber content, fiber length and diameter, fiber shape, and fiber strength. Test results indicate that the joint tensile strength increases with fiber content, fiber length, and fiber strength. The specimen with hooked end fibers also develops higher joint tensile strength compared with the specimen with straight fibers. It is recommended to use fibers with a smaller diameter to increase the interfacial bonding area between the fibers and the matrix. High‐strength fibers are also recommended to achieve the best efficiency in a high‐strength matrix, like UHPC. The tensile performance of the joint with a fiber content of no less than 0.5%, and an embedment length of 15 mm (with a fiber length/diameter ratio of 50), and a diameter of 0.3 mm is similar to the performance of the specimen cast as one piece. Therefore, a properly designed UHPC fiber continuous joint is recommended in engineering practice to improve the integrity of the joint‐deck system. [ABSTRACT FROM AUTHOR]

Macro‐synthetic fiber‐reinforced iron ore tailings (IOT) concrete is an environment‐friendly building material featured by recycling IOT and improving performance of IOT concrete due to fiber incorporation. In this study, the mechanical properties of macro‐synthetic fiber‐reinforced concrete incorporating IOT were investigated. Two different replacement ratios of IOT (i.e., 0% and 50%) and six types of macro‐synthetic fibers at 1.0 vol% were adopted to investigate the effects of IOT, aspect ratio, elastic modulus, and tensile strength of macro‐synthetic fibers on mechanical properties of concrete. The results indicate that the concrete with IOT for natural sand (NS) replacement in 50 wt% demonstrates no loss in compressive strength and a minor loss of 7.67% in fracture energy, but the incorporation of IOT lowers splitting tensile strength and limit of proportionality, especially the splitting tensile strength with a decrease of 18.50%. The splitting tensile strength, equivalent flexural tensile strength, residual flexural tensile strength, and fracture energy were notably improved by adding macro‐synthetic fibers. Experimental results using Tukey test and Student's t test demonstrated that the fiber aspect ratio was more effective in improving equivalent flexural tensile strength, residual flexural tensile strength, and fracture energy than the elastic modulus and tensile strength of fibers, and the residual flexural tensile strength fR,4 was enhanced by 146.34% when increasing the fiber aspect ratio from 36 to 60. [ABSTRACT FROM AUTHOR]

The elastic modulus of concrete is required for the design of reinforced concrete structures, including in predicting creep deformation. Current models that estimate the elastic modulus (E), primarily on the basis of concrete compressive strength, vary in their accuracy and have hence proved to be inadequate to apply to the wide range of concretes. In this investigation, the E values of 108 concrete specimens which differed in aggregate type, cementitious material (binder) type, strength and curing age were measured. Seven factors were assessed for their degree of influence on concrete's elasticity, namely, aggregate type, aggregate percentage content, cementitious binder type, curing age, strength, water/cement ratio and density. The aggregate type, in particular, correlated significantly with the E value. In addition, the influence of density on E was highly significant (P = 2.39 × 10−5%). Concrete compressive strength, by contrast, was less influential than the aggregate type and density, and did not generally significantly correlate with the E value. This study provided additional confirmation that concrete strength is an unreliable primary factor on which to base concrete E estimations, as is the current common practice. It is therefore recommended that models to estimate E values of concrete should be based primarily on the type of aggregate used and the density of concrete. [ABSTRACT FROM AUTHOR]

Cut off walls are used under dams for the control of sub surfaces seepage and permeability of cut off wall was important. In the construction of cut off walls, plastic concrete is used and the amount of plastic concrete permeability is important. In this study, the permeability of plastic concrete was investigated and the effect of replacing nano silica instead of cement to reduce permeability was studied. So in this research, compressive strength, elastic modulus, and permeability parameters of plastic concrete specimens at different ages (7, 14, 28, and 56 days) and with different percentages of nano silica (0, 1.5, 3, 4.5, and 6%) were investigated. Also, scanning electron microscopy was used to investigate the effect of nano silica on plastic concrete specimens. The results show that as the age of the specimens increases, the compressive strength and elastic modulus increase, and the permeability of the plastic concrete decreases. Also, by adding nano silica to plastic concrete, the compressive strength of the plastic concrete increases and the plastic concrete permeability decreases significantly while its elastic modulus is almost constant. [ABSTRACT FROM AUTHOR]

The concrete undergoes brittle failure, which is a disadvantage for stability and safety analysis. This drawback was compensated by addition of different types and size of fibers for improving the compressive and fracture characteristics. The incorporation of multi‐scale hybrid fibers in concrete showed enhanced performance at multi‐level than that of single type or size of fiber. This study examined the influence of basalt fiber length (12, 25, 37, and 50 mm) and content (0.15% and 0.3%) on compressive and fracture parameters of hybrid fiber reinforced concrete (HyFRC). Systematic experimentations were performed on mechanical properties which include compressive strength (f'c), toughness index (ɳ) and capability coefficient index (ξ), initial fracture toughness (KiniIC), unstable fracture toughness (KunsIC), and fracture energy (GF). The crack resistance process and fiber‐matrix interaction obtained by scanning electron microscopy analysis were also discussed. The proposed analytical models of HyFRC stress–strain equations indicated great suitability for fitting of experimental behavior with R2 ≥ 0.92. The basalt fiber with different length and contents showed a great potential in HyFRC and indicated a substantial degree of enhancement for the compressive and fracture properties, as compared to that of PC and HyFRC without basalt fiber. [ABSTRACT FROM AUTHOR]

This paper deals with numerical analysis on the mechanical behavior of ultrahigh performance concrete (UHPC) under uniaxial compression. For the modeling of the mechanical behavior of UHPC, the mesh‐free discrete element method was applied. To calibrate the model parameters and validate the numerical simulation results, a set of experimental investigations including mechanical tests, microscopy and tomography analysis, were performed. The scanning electron microscopy and polarized light microscopy were used to examine cross sections of UHPC as well as to characterize interfacial transition zone and aggregate in detail. X‐ray microtomography analysis was used to obtain information about the nonspherical shape of aggregate and to generate a realistic structural model. Simulation results have shown that the developed model predict stiffness reliably, strength, and breakage pattern of UHPC and shows good agreement with experimental results. Finally, the model has been applied to analyze the main crack initiation in static failure and to investigate the influence of different parameters such as aggregate content as well as aggregate and binder stiffness on the mechanical behavior of UHPC. [ABSTRACT FROM AUTHOR]

An investigation is carried out into the applicability of self‐compacting high‐performance fiber concrete (HPFC) in foundations. A concrete mixture has been designed with a concrete cube strength of about 110 MPa. The concrete contains 60 kg/m3 steel fibers. The properties of the HPFC developed are very suitable for structural applications, especially because the post‐cracking tensile strength, provided by the fibers, is higher than the axial tensile strength of the concrete so that hardening in tension occurs after crack formation, often characterized by multiple cracking. This not only results in a high bearing capacity but as well in substantial durability. As a potential application foundation elements are considered. Experiments have been carried out to determine the pre‐ and post‐cracking strength properties, the shear resistance of short beams with loads near to the supports, the anchorage length of reinforcing bars, and the shear capacity of pile caps. The results of the tests are used for verification of the applicability of the general design rules for fiber concrete, as found in the fib Model Code 2010, to the HPFC developed. The HPFC developed is characterized by high strength and ductility, is durable and self‐compacting. The research program showed that the design of structures with the HPFC considered can be based on existing design rules with some extensions. [ABSTRACT FROM AUTHOR]