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Ultra‐high performance concrete (UHPC) offers superior tensile properties in comparison to normal and high‐strength concrete. This is known to largely depend on the fibers included in the UHPC mixtures. Among the available types of fiber, steel fibers have been commonly used in the current practice. However, given the price and availability issues associated with steel fibers, there has been growing interest in benefiting from synthetic fibers in UHPC. This was the motivation for the current study to investigate the potential of five synthetic fibers by evaluating how the tensile properties of the UHPC mixtures made with a hybrid of steel and synthetic fibers are influenced under direct tension. The synthetic fibers of choice consisted of nylon, polypropylene, polyvinyl alcohol, alkali‐resistant glass, and carbon fibers. By using a dog bone test setup, the main tensile properties of the developed mixtures (i.e., direct tensile strength, elastic modulus, and stress–strain relationship) were systematically determined. The results extracted from direct tension tests were then further processed in conjunction with digital image correlation analyses to investigate the formation and propagation of cracks, as well as the post‐cracking response. The original findings reported from this study are expected to pave the way to broaden the fiber types that can be considered for the structural applications of UHPC, especially where high tensile stresses/strains are anticipated. [ABSTRACT FROM AUTHOR]

With the variety of supplementary cementitious materials (SCMs) available, there have been fundamental questions regarding how they influence the hydration development of ultrahigh-performance concrete (UHPC), especially at early age. To provide a holistic perspective and side-by-side comparisons, the current study explored the partial replacement of cement with silica fume, natural zeolite, and limestone, which represented artificial pozzolans, natural pozzolans, and non-pozzolanic SCMs, respectively. To evaluate the most critical micro- and macro-scale properties of UHPC, the experimental investigations included temperature and free water measurements, further to thermogravimetric analyses (TGA) performed to determine the amount of physically and chemically bound water in the developed mixtures. Moreover, the X-ray diffractometry (XRD) method was employed to obtain the XRD patterns, which were then paired with the TGA results to quantify the crystalline phases of the UHPC mixtures using the Rietveld refinement method. With a detailed assessment of the UHPC's degree of hydration over time, the outcome of this study shed light on how various SCMs are capable of reducing the heat of hydration, while enhancing the degree of hydration of cement particles. [ABSTRACT FROM AUTHOR]

Ultra‐high performance concrete (UHPC) is increasingly used for various engineering applications, owing to its superior strength properties. Such properties, however, can be accompanied by workability issues, especially if the dosage of steel fibers is significantly increased. As a potential solution, this study explored the use of a combination of steel microfibers and macrofibers through a holistic experimental testing program. This was to understand the effects of steel fiber combinations on the workability and flexural strength of various UHPC mixtures. The microfibers were investigated for five different dosages from 1.0% to 3.0% (with an increment of 0.5%). In parallel, two mixtures were prepared with a 2.0% dosage of macrofibers in the form of twisted wire and hooked fibers. At the next stage, six additional mixtures were prepared with a combination of microfibers and macrofibers of various dosages. Further to the measurements extracted from the workability and flexural strength tests, digital image correlation (DIC) analyses were employed to obtain firsthand information about the widths and depths of cracks observed in the flexural specimens tested under an increasing load. The outcome of this study showed how a combination of microfibers and macrofibers can contribute to improving the flexural response characteristics of UHPC, especially without having to increase the dosage of steel fibers to the ranges that can adversely affect the mixture's workability. [ABSTRACT FROM AUTHOR]

Collision of overheight vehicles into bridge superstructures often leads to structural damage, posing an immediate risk to the safety of motorists and the functionality of bridges. Considering the proven vulnerability of current high-strength concrete (HSC) girders to impact-induced forces, the use of ultrahigh-performance concrete (UHPC) (to fully or partially replace HSC) is expected to improve the impact resistance of bridge superstructures. However, despite the growing attention that UHPC has received for various bridge applications, this important application has remained largely unexplored. This motivated the current study to perform a holistic investigation to (1) quantify how the performance of bridge girders subjected to overheight collision can be improved by a one-to-one replacement of HSC with UHPC; (2) assess how UHPC can be considered as a material of choice for repairing existing bridge girders impacted by overheight vehicles; and (3) examine how equivalent UHPC girders designed for a performance similar to HSC girders under service loads can introduce advantages when subjected to overheight collision. For this purpose, upon validating a set of finite-element models with experimental test results, numerical simulations are performed on two types of AASHTO girders. The simulations cover two impacting objects, i.e., a concrete conduit pipe and a cylindrical steel tank, in addition to a tractor–semitrailer. The structural performance measures of the bridge girders made of HSC (entirely), UHPC (entirely), HSC repaired with UHPC, and equivalent UHPC are then evaluated and compared based on the recorded damage patterns, impact forces, internal shears, and lateral displacements. The outcome of this study provides the necessary details to shed light on how a transition from HSC to UHPC can contribute to improving the overall safety and performance of new and retrofitted bridges, especially when subjected to overheight collision. [ABSTRACT FROM AUTHOR]

Given the widespread use of concrete as the construction material of choice, achieving sustainable development goals in the civil infrastructure sector directly relies on reducing the concrete's carbon footprint. For this purpose, a variety of innovative carbon sequestration and storage solutions have been introduced to date. This study focuses on the potential of such solutions individually and in comparison to each other. To offer a holistic perspective, the carbon sequestration strategies in concrete have been first reviewed, followed by investigating the effects of carbonation curing parameters. The carbon uptake potential of various binder compositions has then been explored, ranging from portland cement to pozzolanic binders, as well as non-cementitious binders. To further understand the carbon sequestration capability of concrete, carbon capture strategies that utilize concrete aggregates have been studied. Based on the collected results and findings, a synthesis of the available information has been performed and presented. The outcome of this comprehensive study provides original insights into the latest materials and methods developed for carbon sequestration and storage in concrete. Such insights are critical to guide future research and development required to achieve net-zero concrete structures, meeting sustainable development goals. • A variety of innovative carbon sequestration and storage solutions were investigated. • The identified solutions were explored individually and in comparison to each other. • The effects of various carbonation curing parameters were systematically studied. • The carbon uptake potentials of a range of binders and aggregates were evaluated. • Original insights into latest materials and methods for carbon sequestration were provided. [ABSTRACT FROM AUTHOR]

• Natural zeolite was studied for both internal curing and pozzolanic reactivity. • Synergistic effects of natural zeolite and silica fume were systematically identified. • Replacement of silica fume with natural zeolite improved cement hydration kinetics. • Optimal replacement dosages were determined to achieve maximum cement hydration. • Phase analyses explained in detail how the binder components change over time. Ultra-high performance concrete (UHPC) is often designed with a low water-to-binder ratio, which can potentially limit the hydration of cement particles. To address the hydration-related issues, the current study explored the use of natural zeolite, as it offers a superior porous structure for internal curing, further to pozzolanic advantages. For this purpose, the silica fume commonly used in UHPC was replaced with natural zeolite at various levels, while the cement content was maintained unchanged. The water desorption capability of zeolite in UHPC was investigated by measuring the free water content of the developed mixtures over time, supported by complementary autogenous shrinkage and SEM image analyses. Furthermore, the heat of hydration was evaluated through monitoring the temperature profile in the developed UHPC mixtures. This was paired with TGA and XRD analyses to obtain an in-depth understanding of how the hydration process of UHPC is influenced. The outcome of this holistic investigation indicated that the inclusion of natural zeolite is effective in enhancing the degree of hydration of cement particles. Additionally, the obtained results showed that if silica fume and zeolite are incorporated into the UHPC mixtures together (with optimum dosages), they further improve the entire hydration process, owing to the silica fume's high pozzolanic reactivity and zeolite's internal curing capability. [ABSTRACT FROM AUTHOR]

• Six high-performance cementitious materials were studied for repair applications. • A holistic set of compressive, splitting tensile, and slant shear tests were performed. • The bond characteristics were assessed individually and in comparison to each other. • The adequacy of bond was evaluated with respect to code-specified requirements. • Adhesion and friction coefficients were determined for future design applications. Repair of damaged concrete structures with patching materials is required for a wide variety of bridge and building applications. Despite the capabilities of conventional patching materials in replacing the spalled concrete, they are often unable to restore the original structural capacity. This has motivated research investigations to develop high-performance patching materials that can help damaged concrete structures regain their strength and durability characteristics. Such characteristics, however, are not properly achieved without a satisfactory bond between the concrete substrate and the patching material applied. To investigate this critical aspect, six high-performance patching materials, i.e., proprietary and nonproprietary ultra-high performance concrete, polypropylene and alkali-resistant glass fiber-reinforced concrete, high-early strength concrete, and shrinkage-compensating cement concrete, were systematically investigated and compared in the current study. The conducted experiments included a holistic set of splitting tensile and slant shear tests performed on the samples prepared with various surface roughnesses. The experimental test results provided firsthand information about the bond characteristics between normal-strength concrete and six high-performance patching materials. With the determination of corresponding adhesion and friction coefficient factors, the outcome of this study facilitates the selection and use of high-performance patching materials, depending on the availability of materials and repair needs. [ABSTRACT FROM AUTHOR]

• Full-scale box beams connected with shrinkage-compensating cement concrete were investigated. • The expansion of shrinkage-compensating cement concrete addressed early-age cracking concerns. • The test setup was found to maintain its full integrity under various temperature gradient scenarios. • Based on the transverse strain/stress data, the joint effectively contributed to the structural response. • Numerical simulations showed the promise of the developed joint for various climate conditions. Longitudinal joints that connect adjacent box beams in bridges are known to experience early-age cracks due to temperature and shrinkage effects. Such cracks can open a direct path for water and deleterious agents to penetrate into the bridge, causing corrosion of embedded steel rebars and degradation of superstructure and substructure elements. To mitigate this problem, a solution explored in this study is to use Type K shrinkage-compensating cement, which has the promise to enhance the volume stability of concrete, minimize early-age cracks, and thus, increase the service life of the entire structure. For achieving a holistic assessment of this solution, a test setup consisting of two full-scale box beams connected with concrete made with Type K shrinkage-compensating cement was investigated in the laboratory setting under various temperature profiles. Response data, including temperature, longitudinal and transverse strain/stress, and deflection, were collected at the joint and each box beam during the thermal tests. To extend the scope of investigations beyond the temperature profiles tested in the laboratory, a set of three-dimensional finite-element simulations were performed as well. The results obtained from both experimental tests and numerical analyses showed that the stresses in the joint made with shrinkage-compensating cement concrete remain below the cracking threshold under temperature and shrinkage effects. With maintaining a proper bond with the box beams, the developed joint was found to provide superior performance, especially at early age, addressing the issues associated with the use of conventional concrete in longitudinal bridge joints. [ABSTRACT FROM AUTHOR]

• This study evaluates four concrete constitutive models for low velocity impact simulations. • The constitutive models are first examined under various stress paths at the material level. • Post-peak softening, shear dilation, and confinement effects are investigated. • Both reinforced concrete and concrete-filled steel tube beams are evaluated at the structure level. • A detailed insight for the selection of material models and their parameters is provided. Concrete structures are commonly exposed to low velocity impact loads originating from windborne/waterborne debris, vehicle/vessel collision, and rock fall. For the performance assessment of concrete structures under such loads, several constitutive models have been developed to date. To compare the accuracy of the available models for practical applications, the current study evaluates four constitutive models, i.e., continuous surface cap model (CSCM), elasto-plastic damage cap (EPDC) model, Karagozian and Case concrete (KCC) model, and Winfrith concrete model. For this purpose, the constitutive models are first examined at the material level through single element simulations under basic stress paths, such as uniaxial compression and tension, as well as triaxial compression. A range of measures, such as post-peak softening, shear dilation, and confinement effect, are extracted and compared. The investigation is then extended to understand how the concrete constitutive models perform at the structure level. This is achieved by replicating drop hammer tests on reinforced concrete (RC) and concrete filled steel tube (CFST) beams. Investigation of these two structural categories provides a unique opportunity to further evaluate the accuracy of the concrete constitutive models in interaction with the most common reinforcement details. To achieve this goal, the impact responses of RC and CFST beams are compared with full-scale experimental test data. Upon understanding the capabilities of each constitutive model in predicting the structural behavior and damage, the most important modeling parameters are examined. The outcome of this study facilitates the selection and use of concrete constitutive models for the design and assessment of concrete structures subjected to various low velocity impact loads. [ABSTRACT FROM AUTHOR]

• Material models for ultra-high performance fiber-reinforced concrete were studied. • The models were first examined under various stress paths at the material level. • Post-peak softening, shear dilation, and confinement effects were investigated. • Calibrated models were evaluated for simulating full-scale structures under impact. • A metamodel-based sensitivity analysis was conducted on material model parameters. Among various alternatives developed for conventional reinforced concrete, ultra-high performance fiber-reinforced concrete (UHPFRC) is proven to provide superior mechanical properties, making it appropriate for impact-resistant structures. While several experimental tests have been conducted to determine the static and dynamic response of UHPFRC, the simulation of this important category of concrete materials, especially under impact loads, is still in need of extensive effort. To address this issue, the current study investigates how two widely-used concrete constitutive models, i.e., Continuous Surface Cap Model (CSCM) and Karagozian and Case Concrete (KCC), can be reliably employed for modeling UHPFRC subjected to low-velocity impact. Utilizing the available experimental test data, a rigorous calibration process has been developed in the current study for the two constitutive models, capturing the main strength parameters, damage evolution parameters, and strain rate effects. This process begins with single-element simulations performed under various stress paths to generate the information necessary for post-peak softening and confinement factors. The investigations with single-element simulations consist of four element sizes to study the mesh size sensitivity of both constitutive models. The study is then extended to examine the capabilities of the calibrated models in simulating the response of full-scale structural elements made with UHPFRC. For this purpose, the drop hammer tests are replicated on both plain and reinforced UHPFRC, and the performance of the two constitutive models is evaluated in comparison to the experimental tests. Specifically, this evaluation examines peak impact forces and displacements, considering various hourglass coefficients and drop hammer heights. Furthermore, a metamodel-based sensitivity analysis is conducted to quantify the effects of uncertainty inherent in the input parameters on the predicted impact response measures, in terms of force, displacement, and duration. [ABSTRACT FROM AUTHOR]

Shrinkage-compensating cement (a.k.a., Type K expansive agent) is a calcium sulfoaluminate cement with the ability of providing volume expansion during early age, primarily due to the formation of ettringite. Despite the past studies on the strength, shrinkage, and hydration of shrinkage-compensating cement concretes, there was no systematic investigation to understand the performance of this type of concrete under exposure to aggressive agents, particularly chloride ions. To address this gap, a holistic testing program was established in this study to evaluate the strength, dimensional stability, and transport properties of concretes made with various dosages of Type K expansive agent. This included compressive strength, drying shrinkage, rapid chloride penetration, electrical resistivity, rapid chloride migration, and absorption tests. Both helium and mercury intrusion porosimetry analyses were also performed to further explain the experimental test results with the findings related to the distribution of pores. The results of this study confirmed the benefits of using Type K expansive agent (up to a certain dosage) in terms of increased compressive strength and reduced drying shrinkage. However, it was revealed that the permeability of concretes made with this type of cement is adversely affected. This issue was addressed by the identification of optimal dosages of supplementary cementitious materials, including fly ash and silica fume. Upon completing the necessary experiments on the improved mixtures, this study reported how low-shrinkage concretes with low susceptibility to chloride penetration can be developed with the promise of application in a wide variety of civil infrastructures exposed to harsh environmental conditions. [ABSTRACT FROM AUTHOR]

The transport properties obtained from the accelerated tests on the concrete mixtures that contain shrinkage-compensating cement have indicated that addressing the issue of shrinkage may come with the expense of increased permeability. This raised a fundamental question concerning the long-term durability of reinforced concrete structures made with this type of cement. In the absence of similar studies, a comprehensive experimental testing program was devised in the current study to understand the vulnerability of steel bars embedded in shrinkage-compensating cement concretes exposed to corrosive environments. This included a long-term corrosion monitoring of reinforced concrete specimens made with different dosages of shrinkage-compensating cement. In addition to finding the corrosion rate of embedded steel bars, air permeability, capillary absorption, and chloride diffusion tests were conducted to determine the transport properties of the concretes made with this type of cement. The experimental test results were then further supported and explained using mercury intrusion porosimetry analyses. [ABSTRACT FROM AUTHOR]

• Non-proprietary UHPC mixtures were investigated under exposure to chloride ions, moisture loss, and freeze-thaw cycles. • Various performance measures were obtained and compared for non-proprietary and proprietary UHPC mixtures. • Effects of water-to-cement ratio, sand-to-cement ratio, and silica fume content were explored for an optimized mixture. • Feasibility of development of cost-effective, non-proprietary UHPC mixtures with desired properties was outlined. This study focuses on the assessment of non-proprietary ultra-high performance concrete (UHPC) mixtures exposed to the penetration of chloride ions, shrinkage due to moisture loss, and freeze and thaw cycles. For achieving a proper assessment, several non-proprietary UHPC mixtures were designed, cast, and tested for flow, compressive strength, tensile strength, surface resistivity, rapid chloride penetration, rapid chloride migration, autogenous shrinkage, drying shrinkage, and loss of mass and dynamic modulus due to freeze and thaw cycles. The performance measures of the developed mixtures were then compared with those of two proprietary UHPC mixtures. The results obtained from this rigorous set of experimental tests showed how non-proprietary UHPC mixtures can be designed to experience chloride penetration as low as their proprietary counterparts, maintain high volume stability under both autogenous and drying shrinkage, and benefit from negligible degradation under freeze and thaw cycles. This study also quantified how the water-to-cement ratio, sand-to-cement ratio, and inclusion of silica fume can have substantial effects on the properties of non-proprietary UHPC mixtures. Considering the significant cost advantages of non-proprietary UHPC mixtures, the outcome of this study shed light on the feasibility of developing non-proprietary UHPC mixtures with desired properties, taking into account short- and long-term performance considerations. [ABSTRACT FROM AUTHOR]

• A comprehensive bibliometric analysis of the applications of zeolite in concrete. • Leveraging natural zeolite as a replacement for cement to improve concrete sustainability. • Exploring future prospects on the innovative use of natural zeolite in cementitious composites. Pozzolanic materials or industrial wastes can be used to partially replace cement, minimizing the carbon footprint of concrete structures. Zeolite, silica fume, fly ash, and metakaolin are some of the most frequently used supplementary materials that reduce the concrete's permeability and, therefore, play a significant role in improving its durability and strength. Among the available alternatives, the application of natural zeolite as a pozzolanic material, in concrete has increased in recent years. In particular, a range of studies have focused on including natural zeolite to produce mortar and concrete with a reduced cement content, and thus, environmental impact. Through a consistent and comprehensive blended evaluation method, this research aims to evaluate past studies that utilized natural zeolite for various concrete applications. A total of close to 2,000 papers were screened, and more than 60 of them were selected for relevance. Bibliometric mapping was used for keyword occurrences and zeolite-related details. This study provides a state-of-the-art review of research on natural zeolite through a critical analysis of various research studies carried out in the past. The ultimate goal is to provide an in-depth understanding of the effects of zeolite on the performance of concrete mixtures, in terms of workability, strength, and durability. Furthermore, the current challenges and future prospects of using natural zeolite have been outlined, paving the way to expand the use of this category of supplementary materials. [ABSTRACT FROM AUTHOR]