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Alkali‐aggregate reaction (AAR) is a detrimental reaction between alkalis originating from cement and aggregates that contain reactive minerals. This reaction produces an expansive gel in hardened concrete that may cause internal stresses and cracking, after which it would be critical to evaluate the safety of the AAR‐affected structure. This paper presents a calculation framework primarily using the finite element method to simulate the structural behavior of reinforced concrete members affected by AAR. Numerical subroutines are used to calculate the anisotropic distribution of AAR‐induced expansions at each integration point, considering the stress field at each time step, whereas changes in the properties of concrete due to the progression of AAR are also considered. The modeling approach is successfully validated based on experimental data from several studies on AAR‐affected members that were reinforced in 1, 2, and 3 orthogonal directions in terms of load–deflection behavior and damage patterns. The mechanical properties of concrete were found to negligibly affect the distribution of AAR expansions. A better correlation was observed with experimental data if compressive and tensile strengths of concrete are assumed unchanged and only the modulus of elasticity of concrete is reduced as a function of AAR‐induced expansion. [ABSTRACT FROM AUTHOR]

There are several significant advantages to 3D concrete printing (3DCP) over conventional concreting techniques. Structures are built by printing them one layer at a time. This study aimed to improve the usability and accessibility of this technology to solve on‐site issues, such as those caused by chemical admixture. In order to construct concrete that can be printed in three dimensions, researchers added many chemical admixtures in controlled quantities. This experiment's main goals were to prepare 3D printable concrete (3DPC) without chemical admixture and to evaluate fresh and hardened properties. Slump, flow, extrudability, buildability, open time, and penetrometer tests were carried out for fresh properties. Compressive, flexural, splitting tensile strength, and modulus of elasticity were evaluated for hardened properties. The printed specimens in the longitudinal direction exhibited higher compressive strength than in the downward and lateral directions. Similarly, higher flexural and splitting tensile strength in the longitudinal direction of printed specimens than in the downward and lateral direction. The results of developing 3DPC without chemical admixtures demonstrated good performance in fresh and hardened properties. [ABSTRACT FROM AUTHOR]

Crystalline admixture (CA) has been extensively utilized as the commercial product for improving the performance associated with strengthening self‐sealing of cracks or decreasing the permeability of concrete. However, few researches characterizing the restrained shrinkage and cracking potential of concrete with CA at early age. This paper aimed to expand the limitation by means of the experiments including mechanical properties test and restrained ring test on high‐strength concrete (HSC) with CA from Xypex. The proportion of CA was 0%, 0.5%, 1.0%, and 1.5% by the mass of cement. The incorporation of CA enhanced the compressive and splitting tensile strength as well as modulus of elasticity tested in this paper. A significant increase was observed in free and restrained shrinkage of HSC with CA. Although incorporation of CA ameliorated the stress relaxation, residual stress in restrained concrete ring developed rapidly with the incorporation of CA due to the significant increase in restrained shrinkage at early age. Restrained concrete ring with CA demonstrated a higher stress rate, which implied a higher cracking potential. When CA proportion increased from 0% to 0.5%, 1.0%, and 1.5%, a higher cracking potential was revealed through calculation, and restrained concrete ring exhibited earlier cracking age. Caution should be exercised with the application of such CA in concrete mixtures under restrained conditions. [ABSTRACT FROM AUTHOR]

Despite offering several benefits in terms of environment and economics, few studies were conducted on the ground granulated blast furnace slag (GGBFS) based alkali‐activated concrete reinforced with recycled tire steel fibers (RTSFs). Therefore, this paper employed the Taguchi method to investigate and optimize the influence of GGBFS content, the alkaline solution to GGBFS content ratio, sodium hydroxide solution concentration, and RTSF volume fraction on splitting tensile strength (STS) of recycled tire steel fiber‐reinforced alkali‐activated slag concrete (RTSFR‐AASC). The microstructural evaluation was done through scanning electron microscopy, and Fourier transform infrared spectroscopy (FTIR) analyses. The results indicated that the fiber content, the most efficient parameter on STS, led to a considerable enhancement in the performance characteristic. Microstructural analysis proved the variations in formation of C–S–H gel. The results of the confirmation experiment on the proposed optimized RTSFR‐AASC mixture with the highest 28‐day STS (7.11 MPa) confirmed the effectiveness of the Taguchi method. [ABSTRACT FROM AUTHOR]

This article studied the mechanical properties and constitutive model of fiber‐reinforced coral aggregate concrete (FRCAC). The test results show that basalt fibers, carbon fibers, and polypropylene fibers (BFs, CFs, and PFs) can enhance the cube compressive strength and splitting tensile strength of coral aggregate concrete (CAC), but there are optimum contents. The optimal content of BFs, CFs, and PFs are 0.8%, 1.5%, and 0.3%, respectively. Fibers increase slightly the elastic modulus of FRCAC. The peak stress, peak strain, and ultimate strain of CAC can be improved by fibers, and the improvement effect is CFs, BFs, and PFs in descending order. According to the experimental results, a damage constitutive model suitable for FRCAC was proposed, which can efficiently indicate the stress–strain relationship of FRCAC. The damage parameter in the model can predict the damage evolution process of FRCAC. [ABSTRACT FROM AUTHOR]

In order to comprehensively examine the influence of basalt fiber on the basic mechanical properties of concrete, the axial compression, axial tension and direct shear tests were carried out on basalt fiber reinforced concrete (BFRC) with different fiber contents and fiber lengths. The failure modes and stress–strain curves under different loading modes were obtained from the test data, and the basic mechanical parameters of BFRC were extracted from the curves. Based on the results, the following conclusions were drawn. With the increase of fiber content, both the compressive strength and tensile strength showed an upward trend first followed by a downward trend. In general, the shear strength of BFRC was lower than that of ordinary reinforced concrete with no fiber (RC). All BFRC specimens had an increased peak strain and significantly improved deformability compared to RC. Based on a comprehensive analysis, the specimen with a fiber content of 0.2% and a fiber length of 6 mm (BFRC‐0.2%‐6) exhibited the best mechanical properties. In addition, mathematical regression analysis was performed on the normalized stress–strain curves of BFRC, and the influencing parameters model of basalt fiber was proposed based on the fiber content and fiber length. Moreover, scanning electron microscopy (SEM) and computed tomography were utilized to analyze the influencing mechanism of basalt fiber content and fiber length on the mechanical properties of concrete from the microcosmic and mesoscopic perspectives. [ABSTRACT FROM AUTHOR]

This study explores the effects of mixture design parameters on the residual mechanical properties of lightweight expanded clay aggregate (LECA) concrete exposed to elevated temperatures. A total of 30 lightweight concrete mixtures were cast and exposed to three elevated temperatures, namely 250°C, 500°C, and 700°C. The test variables comprised the LECA percentage used as partial volume substitution for natural sand (0%, 25%, 50%, 75%, and 100%), silica fume partial replacement for cement by weight (5%, 7.5%, 10%, 12.5%, and 15%), cement content (300, 400, 500, 600, and 700 kg/m3), and different water‐to‐cement (W/C) ratios (0.25, 0.313, 0.375, 0.438, and 0.5). The compressive and indirect tensile strengths were measured before and after exposure to elevated temperatures. The results indicate that the lightweight concretes incorporating higher contents of cement and silica fume and made with lower W/C ratio exhibited higher initial mechanical properties yet incurred more significant drop in mechanical properties after exposure to 500°C and 750°C. [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]

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]

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]

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]

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]

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]

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]

There is an increasing trend towards using recycled aggregate (RA) in concrete due to the shortage of high quality natural aggregates. The use of RA in concrete results in the conservation of natural resources, protects the environment and encourages sustainable construction. Though some studies have been conducted on the use of recycled aggregate concrete (RAC), the effect of mixture composition on its properties has not been well addressed. In the reported study, the effect of mixture composition, namely cement content and water/cement ratio and the proportion of RA on the mechanical properties of RAC was evaluated, with the intention of developing varying grades of RAC. As reported in earlier studies, the properties of RAC were generally inferior to that of normal aggregate concrete (NAC). Notwithstanding this, RAC with acceptable mechanical properties can be produced utilizing RA, for example RAC with low strength can be used in non‐structural applications. The construction industry should be encouraged to use RAC in building construction; as its use will lead to technical, economic and environmental benefits. Further, the use of RAC will lead to a sustainable development of the construction industry, particularly in regions that lack good quality natural aggregates. Based on the data developed in the reported study, the following quantities of RA are recommended to produce RAC: (i) 20% to produce low strength (20–30 MPa) concrete, (ii) 40% to produce medium (30–50 MPa) concrete and high strength (more than 50 MPa) concrete. Mathematical correlations between the mechanical properties of RAC with varying mix design parameters, such as cement content and water cement ratio and the quantity of RA, are also reported. These correlations can be used to predict the properties of RAC prepared with other proportions of RA and mix design parameters. [ABSTRACT FROM AUTHOR]

The repair efficiency of fiber‐reinforced polymer (FRP) is crucially linked to bond strength between FRP and concrete. Artificial neural networks (ANNs) technique is employed for the prediction of FRP–concrete bond strength based on more than 440 data points collected from literature work for training and testing of the proposed ANNs model. Such a model facilitates investigating the effect of various key parameters in controlling the bond. These are concrete compressive strength, maximum aggregate size, FRP thickness and modulus of elasticity, FRP‐to‐concrete length and width ratios, and adhesive tensile strength. The proposed ANNs model shows high fitting and prediction capability of training and testing data, respectively, with low mean square errors. Its accuracy of prediction far exceeds that of literature empirical models. Furthermore, the present comparative and sensitivity study of the predicted bond strength promotes the understanding of the impact of the above key parameters. [ABSTRACT FROM AUTHOR]

The brick, stone, and construction industries produces huge quantities of non‐biodegradable waste materials and incorporation of such waste materials in concrete eventually leads to the green and sustainable construction. The present paper study the effect of partial substitution of brick dust (BD), stone dust (SD), and recycled fine aggregate (RFA) as fine aggregate on the properties of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC). In the present investigation, two groups of mixes were considered: Group A consists of 100% natural coarse aggregate (NCA) and group B consists of 50% NCA and 50% recycled coarse aggregate. In each group, the natural fine aggregate was partially replaced with 30% BD, 30% SD, and 30% RFA separately. All mixes were designed for M25 grade concrete with a constant w/c ratio of 0.45. The properties viz. compressive strength, density, indirect tensile strength, water absorption, ultrasonic pulse velocity of all mixes was performed. Also, durability performance of all the mixes under acid conditions viz.: HCl and H2SO4 solutions were studied. From the results it was found that the compressive strength and split tensile strengths (27.95–23.23%) of both natural and recycled aggregate concrete were significantly increased with the partial substitution of SD. Also, the results reveal that the water absorption decreased by 57.14–69.64% and 4.67–34.67%, respectively, when the replacement of NFA with BD and SD in both NAC and RAC. Both natural and recycled aggregate concrete were more susceptible for H2SO4 than HCl acid in terms of loss of weight and compressive strength. [ABSTRACT FROM AUTHOR]

Investigation of mechanical properties and thermal behavior of expanded polystyrene concrete (EPS) and exfoliated vermiculite (EV) concrete has been accomplished in this research. It includes how EPS concrete is prepared by substituting the coarse aggregate with 0, 10, 15, and 20% with EPS aggregates. Similarly, EV concrete is prepared by replacing the fine aggregates with 0, 15, 45, and 60% with EV aggregates. The influence of EPS and EV proportion on mechanical and thermal properties was detected. Thermal properties were studied with an adiabatic box technique. Clear improvement in thermal behavior was observed in comparison with normal concrete and reduction in compressive strength was observed for an appreciable increase in the amount of EPS and EV. Also, the properties like split tensile strength, load–deflection curves, and durability properties of the EPS and EV concretes were experimented. [ABSTRACT FROM AUTHOR]

Shape is an important physical property of aggregates. However, the large amount of work required to measure with precision the size of coarse aggregate and the lack of relevant tests obscure how the shape of the coarse aggregate affects the strength of concrete. In this work, granite coarse aggregate was first divided into flaky stone and massive stone by manual screening. Next, the coarse aggregate was selected at random for size and volume measurements to obtain and analyze the aggregate shape parameters such as sphericity and flatness. Based on the selected aggregate, three aggregate combinations were designed according to the content of flaky stone. Finally, we measured the compressive strength and splitting tensile strength of hydraulic concrete (7, 28, and 60 days) with water‐binder ratios of 0.33, 0.41, and 0.5. The results show that the three aggregates clearly differ in shape, and the measured compressive strengths and splitting tensile strengths of the concrete with water‐binder ratios of 0.41 and 0.5 are similar. However, the compressive strength of the concrete with water‐binder ratio of 0.33 is significantly correlated with the three selected aggregate combinations. [ABSTRACT FROM AUTHOR]

In this research, the mechanical behavior of structural concrete made with materials in Iran has been experimentally investigated after experiencing high temperatures. For this purpose, six different mix designs were selected in accordance with Iranian Concrete Standard (ABA). Six different target temperatures (25, 100, 250, 500, 700, and 900°C) were also selected for the purpose of fire experience. Compressive and tensile strength tests were carried out on all of the samples and their behavior was evaluated after experiencing different target temperatures. The results show a strong drop in compressive and tensile strength at temperatures above 700°C. It can be noted that at 900°C all specimens lost their strength. Finally, thanks to the large number of experiments, different relationships are presented based on the results to determine the mechanical properties of different mix designs at different temperature levels. [ABSTRACT FROM AUTHOR]

This article presents a refined version of the rotating‐angle softened truss model (RA‐STM) with efficient solution procedure to predict the full behavior of prestressed concrete (PC) membrane elements under in‐plane stresses. The refined model incorporates the concrete tensile strength in the perpendicular direction to the concrete struts and an additional smeared constitutive law for the tensile concrete. In order to avoid the classical trial and error solution procedure used in previous versions of the RA‐STM, a new algorithm is presented which lead to a more efficient solution procedure with higher numerical stability. The reliability of the proposed model is verified with experimental data related with PC plates under in‐plane stresses, where good agreement is observed. [ABSTRACT FROM AUTHOR]

Geopolymer concrete as a green concrete has attracted great attention among scientists to reduce cement consumption and emissions. This study examines the use of recycled aggregates in geopolymer concrete as a substitute for coarse aggregates. To assess the mechanical performance, compressive strength, tensile strength, and flexural strength were measured for 20 mixing designs and their relationships with suitable convergence were obtained. The scanning electron microscope (SEM) images taken from the samples made with the highest and lowest resistance showed that the formation of hardened geopolymer gel depends on the concentration of chemical solutions. The results of the freezing and thawing cycle and mass loss of samples showed that the compressive strength of the geopolymer concrete had not decreased significantly and had a good durability in these conditions. [ABSTRACT FROM AUTHOR]

In this paper the relationships between the mechanical and fracture properties of recycled aggregate concretes (RAC) are investigated based on the own research programs results and an extensive number of experimental data from the literature. The primary aim is the extension of design standards empirical models to the case of RAC with particular emphasis on the effect of replacement ratio on mechanical properties, uniaxial stress–strain curve, fracture energy, and stress–strain softening curve's parameters. It was pointed out that relationships dedicated to assess the mechanical properties of natural aggregate concretes (NAC) are not fully adequate to predict the behavior of RAC. It was established that the elastic modulus Ecm, the tensile splitting strength fctm,sp are related to the mean compressive strength fcm as well as to a parameter taking into account the effect of the recycled aggregates replacement ratio. The validity of many analytical expressions of the stress–strain relationship has been also studied and the effect of replacement ratio was taken into account. The comparison between experimental and analytical stress–strain curves shows that, with the proposed modifications, some models satisfactorily describe the behavior up to failure while others either overestimate or underestimate the postpeak branch. Due to the limited number of available data, no well‐defined relation was found between fracture energy, compressive strength, and formulation parameters. [ABSTRACT FROM AUTHOR]

The principal air pollution within the concrete enterprise is cement in charge of roughly 5–7% of manufactured CO2 emissions. For reducing CO2 emissions and improving concrete properties, new types of natural cementitious materials have been served in concrete throughout the last two decades. In this study, a mineral powder (MP) as a type of supplementary cementitious material has been introduced and the chemical and physical properties of this MP and mechanical properties of the produced concrete were investigated. In this regard, the total number of 24 concrete mixes with 0 to 40% replacement of Portland cement (PC) with MP was designed. Concrete samples were tested for compressive, flexural, splitting tensile strengths, and elastic modulus at the age of 7, 28, 42, and 90 days. The experimental results indicate that the maximum compressive, flexural, and splitting tensile strengths are obtained by replacing about 5% PC with MP. Finally, the amount of CO2 emission reduction for concrete specimens containing MP was evaluated. [ABSTRACT FROM AUTHOR]

In the design of new structures, EN 1992‐1‐1 normatively regulates the correlation between the compressive strength and tensile strength of concrete, in accordance with EN 206‐1. However, as there are many time‐ and load‐dependent impacts on existing structures, the relationship described by EN 1992‐1‐1 cannot be assumed without any further observations for existing structures. At the moment, there is no comprehensive investigation on the influences of, for example, subsequent hardening and carbonation on the concrete compressive or tensile strength. The tensile strength of concrete defined in EN 1992‐1‐1 is based on a water storage and a testing age of 28 days. Furthermore, the in‐situ tensile strength is affected by micro‐crack formation cause of internal stresses due to outflow of hydration heat, for example. Generally, there is a different influence of micro‐crack formation on the tensile strength of concrete than on the compressive strength of concrete. The actual value of the in‐situ tensile strength of concrete affects the shear force resistance and the load‐bearing capacity of anchors with concrete cone failure as decisive failure mode. Within the framework of a research project (SWD‐10.08.18.7‐13.01), financed by "Forschungsinitiative Zukunft Bau", an initiative of the Federal Institute for Research on Building, Urban Affairs and Spatial Development (BBR) structural investigations on the correlation between the compressive and tensile strength of old concretes have been performed. Below, the results of the research project are presented. [ABSTRACT FROM AUTHOR]

Concrete screws have become increasingly significant in recent years as a result of their availability on the market and their easy application. Still, the influence of reinforcement on deterioration and load‐bearing behavior of concrete screws is an open question. Different tests series with concrete screws in concrete C20/25 were performed to evaluate the influence of the reinforcement on damage grade and bearing capacity. These tests were carried out in full contact with reinforcement, nearby reinforcement, non‐influenced by reinforcement and as setting tests with following pull‐out tests. These tests in uncracked concrete show that a damage is only influenced by the pull‐out load on the screw threads and not by the reinforcement itself. Due to the fact that the load transfer zone of concrete screws is similar to the embedment depth, it was investigated, if the position of the reinforcement bar influences the load‐bearing capacity of concrete screws. Tests were performed to show if the testing procedure in the test with reinforcement contact according to the corresponding European Assessment Document is the most unfavorable situation. Testing has shown that the vertical position of the reinforcement does not have an impact on the maximal load capacity in concrete, but the horizontal distance does. [ABSTRACT FROM AUTHOR]

In this study, 120 pullout specimens with anchorage length of 5d and 3d (where d denotes the diameter of the rebar) have been tested to investigate the bond performance under dynamic loading. The specimens were divided into 8 groups, with 5 loading rates applied to each group. Besides the loading rate, concrete strength, rebar diameter, and bond length were taken into account. In general, the experimental results indicated that most of the specimens demonstrated a splitting failure pattern, for which abrupt drops in measured load were usually observed following the peak of load–displacement curves. In addition, the bond‐slips during the load drop were almost equal to the distance of the ribs of the reinforcing bars. Following the drop, the bond stress increase or decrease periodically with slip induced by the ribs on steel reinforcing bars. Both the bond strength and the bond stiffness showed noticeable increases following the increase of loading rate. An empirical model was developed to describe the bond strength with respect to concrete strength and loading rate. Eventually, the predicted results agree well with the experimental data. [ABSTRACT FROM AUTHOR]

This paper statistically investigates the influence of parameter, namely curing temperature, molarity, NaOH/Na2SiO3, and activator‐to‐fly ash ratio on the compressive strength of low calcium fly ash‐based geopolymer concrete. This paper also investigates the effect of delay time prior to curing on the compressive strength of geopolymer concrete. The results of the experimental investigation show that these parameters notably influence the development of the mechanical strength of the final product. The statistical investigation shows that the early compressive strength is significantly affected by the synergistic effect of a linear term of curing temperature, molarity, and activator‐to‐fly ash ratio while NaOH/Na2SiO3 ratio was found to be not so statistically significant. The numerical algorithm formulated using regression analyses were simultaneously optimized by utilizing response optimizer method. A constitutive model which represents a relationship between the compressive strength and splitting tensile strength is also proposed. [ABSTRACT FROM AUTHOR]

This paper presents a simple yet accurate technique for determining the strength of steel fiber reinforced concrete beams loaded in pure torsion. The results of the model are compared with 21 beams found in the literature as well as two new beams tested by the authors and reported herein. The model considers the beneficial effect of the fibers in resisting tension after the concrete matrix has cracked, and it is implemented into the widely accepted space truss analogy for reinforced concrete members subjected to pure torsion. The proposed model provides good correlations to the collected test data with a test to predicted ratio of 1.10 and COV of 0.19. A simplified method of the aforementioned model, suitable for design, is also presented and is shown to provide good predictions to the test data. [ABSTRACT FROM AUTHOR]

Ceiling and floor slabs made of horizontal layers of regular and lightweight concrete could lead to an efficient use of materials. In this context, the bond between the different types of concrete is of particular importance. This paper shows the shear strength and failure mode of unreinforced concrete interfaces with high‐quality, lightweight concretes in dependence of different interface roughness. To achieve this, a regular and a structural lightweight concrete were bonded to an infra‐lightweight and a foam concrete. Small‐scale shear specimens consisting of five layers were manufactured and loaded to investigate their shear behavior as a whole. Both concrete and interface failures were detected in dependence of interface roughness and the type of core layer concrete. Additionally, it is shown that the observed behavior can be satisfactorily reproduced by a finite‐element model using the material parameters of concrete standard tests. The experimental and numerical investigations provide clearly defined interface parameters to design efficient load‐bearing slabs made of different concrete layers. [ABSTRACT FROM AUTHOR]

In this paper, a three‐dimensional finite element method (FEM) model of push‐off tests for specimens made with recycled aggregate concrete (RAC) was presented. The FEM model used ABAQUS/Standard module software. The model considered the plasticity of concrete and the concrete‐to‐concrete contact properties, and was found to agree with experimental data from shear transfer tests. The verified model was then used for a parametric study that investigated lateral reinforcement, concrete strength, and recycled coarse aggregate (RCA) replacement ratio. The parametric study shows that the ultimate shear strength increases by 23.1% when the lateral reinforcement ratio increases from 0.56% to 1.12%; the ultimate shear stress increases almost linearly when the concrete strength increases from 30 MPa to 60 MPa; the ultimate shear stress is reduced by 13.8% when the RCA replacement ratio increases from 0% to 100%. [ABSTRACT FROM AUTHOR]

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

The primary aim of this paper is to analyze the impact of mechanical pre-damage and alkali-silica reaction (ASR) on the fracture mechanical properties of pavement concrete. For this purpose, a four point bending test was applied to large format beams to produce a defined level of cyclic pre-damage. The fatigue-induced concrete degradation process was simultaneously recorded using a testing procedure specifically developed for the purpose. In addition, fatigue-induced cracks on extracted drilling cores were spatially visualized and quantified using micro X-ray 3D-computed tomography (3D-CT). The storage of the small-format test specimens, with and without cyclic pre-damage, in an ASR-conducive environment showed that pre-damage leads to an increase in ASR damage processes. Subsequent structural mechanical investigations on small format specimens with and without pre-damage show that fatigue loading and ASR significantly influence fracture mechanical parameters of the concrete. [ABSTRACT FROM AUTHOR]

This paper presents the preliminary results of the effect of ultrafine fly ash (UFFA) on the properties of concretes containing recycled coarse aggregates (RCA) originating from construction and demolition (C&D) wastes. The effect of 10 % UFFA on the compressive strength, tensile strength, sorptivity and chloride ion permeability of concretes containing 25 and 50 % RCA is evaluated at 7, 28 and 56 days. The addition of UFFA increased the compressive strength of recycled aggregate concretes at all ages up to 56 days. However, a slight reduction in the tensile strength of recycled aggregate concretes was observed. Concrete containing 25 % RCA and 10 % UFFA achieved 94 % of the control concrete's compressive strength at 56 days. In both recycled aggregate concretes tested, the sorptivity and chloride ion permeability are much lower at all ages due to the addition of 10 % UFFA. This is because it serves to promote hydration and block the large capillary pores within the concrete. [ABSTRACT FROM AUTHOR]

This paper concerns the relationship between compressive, tensile and flexural creep behaviours related to the same concrete. Experimental tests and a numerical simulation are performed in the scope of this work. The main conclusion of this study is that due to the strong scale effect related to the tensile and bending creep behaviours of a 'standard' concrete mix design, it is not possible to simulate numerically (with classical Kelvin-Voigt chains) the bending creep behaviour of that type of concrete knowing the compressive and tensile creep behaviours obtained using the specimen geometries normally used in laboratories. [ABSTRACT FROM AUTHOR]