This study presents a comparison of the protective properties of three concretes of similar composition on the effect of chloride ions. To determine these properties, the values of the diffusion and migration coefficients of chloride ions in concrete were determined using both standard methods and the thermodynamic ion migration model. We tested a comprehensive method for checking the protective properties of concrete against chlorides. This method can not only be used in various concretes, even those with only small differences in composition, but also in concretes with various types of admixtures and additives, such as PVA fibers. The research was carried out to address the needs of a manufacturer of prefabricated concrete foundations. The aim was to find a cheap and effective method of sealing the concrete produced by the manufacturer in order to carry out projects in coastal areas. Earlier diffusion studies showed good performance when replacing ordinary CEM I cement with metallurgical cement. The corrosion rates of the reinforcing steel in these concretes were also compared using the following electrochemical methods: linear polarization and impedance spectroscopy. The porosities of these concretes, determined using X-ray computed tomography for pore-related characterization, were also compared. Changes in the phase composition of corrosion products occurring in the steel–concrete contact zone were compared using scanning electron microscopy with a micro-area chemical analysis capability, in addition to X-ray microdiffraction, to study the microstructure changes. Concrete with CEM III cement was the most resistant to chloride ingress and therefore provided the longest period of protection against chloride-initiated corrosion. The least resistant was concrete with CEM I, for which, after two 7-day cycles of chloride migration in the electric field, steel corrosion started. The additional use of a sealing admixture can cause a local increase in the volume of pores in the concrete, and at the same time, a local weakening of the concrete structure. Concrete with CEM I was characterized as having the highest porosity at 140.537 pores, whereas concrete with CEM III (characterized by lower porosity) had 123.015 pores. Concrete with sealing admixture, with the same open porosity, had the highest number of pores, at 174.880. According to the findings of this study, and using a computed tomography method, concrete with CEM III showed the most uniform distribution of pores of different volumes, and had the lowest total number of pores. Depending on their location and function, building structures are exposed to many harmful factors. The most common causes of reinforcement corrosion and concrete damage are carbonation and chloride penetration . The fasA factor affecting the rate of chloride ion penetration into concrete is undoubtedly its porosity. However, the relationship between pore diameter and chloride diffusivity is reported to be linear by some researchers, such as Moon et al.  and SchuIn recent years, the X-ray computed microtomography method (XRD) has been used to determine the porosity of concrete. This method, although promising, is not without some disadvantages. The main problem is the relationship between sample size and spatial resolution. In order to obtain a sufficiently high spatial resolution, it is important to use a sufficiently small sample. However, such a small section of the tested material may not represent the properties of the whole object ,18. DespIn addition to evaluating the diffusion and porosity properties, it is necessary to assess the rate of development in corrosion processes against the reinforcement in concrete. To evaluate the rate of corrosion development, nondestructive polarization methods are used: the Linear Polarization Resistance (LPR) method , and ele3O4), and siderite (FeCO3) are common. However, under simulated coastal environments, ferrihydrite (Fe(OH)3) is also found [3 ⸱3H2O. In contrast, Fe(OH)2 and Fe(OH)3 hydroxides increase in volume by 2.17 and 1.76 times more than noncorroded steel, respectively. Determining the type of corrosion products is important in the process of modeling the cracking of concrete lagging [The type of corrosion products of reinforcement  depends on the environment in which the corroding elements are located. The initial stages of atmospheric corrosion of carbon steel in both rural and urban atmospheres leads to the formation of lepidocrocite (γ-FeOOH) and goethite (α-FeOOH), which are the main phases present in corrosion products, regardless of the environment. In chloride-containing coastal environments, akaganeite ), magnetite  were also compared. Using scanning electron microscopy (SEM) with microarea chemical analysis capabilities, as well as X-ray microdiffraction (XRD) to study microstructural changes, changes in the phase composition of corrosion products occurring in the steel–concrete contact zone were compared. It turns out that a slight modification of the composition of the concrete used can result in a huge improvement in its protective properties, ensuring the safety and durability of the reinforced concrete structures made from it.3); gravel, 2 ÷ 8 mm (512 kg/m3); and gravel, 8÷16 mm (681 kg/m3). The first tested concrete (B1) contained CEM I 42.5 R cement in its composition. The next concrete (B2) differed from the first only in the use of CEM III/A 42.5 N-LH/HSR/NA cement. The last concrete (B3) was further modified using a refining admixture in the amount recommended by the manufacturer (0.5% of the weight of the cement). The detailed compositions and properties of mixes are presented in The tests were performed on three types of concrete mix. All of the concretes tested were designed to be ordinary concretes (used for precast foundation elements). Three types of natural rounded aggregate  were utThe compressive strength of the concrete was determined using cubic samples possessing 150 mm sides, which were stored and made in accordance with PN-EN12350-3:2011 .Next, a series of tests was conducted to determine the protective properties of the tested concretes against the effects of corrosion on the concrete’s reinforcements by chloride ions. In order to perform these tests, 12 samples of each type of concrete were prepared.To determine the depth of penetration by the pressurized water, cubic samples with 150 mm sides were used. In order to perform these tests, 3 samples of each type of concrete were prepared.3) was used.To determine the open porosity of hardened concrete, 1 sample for every type of concrete  were carried out each time on 2 test pieces in the shape of cylinders that were 100 mm in diameter and 60 mm high, made of each of the three types of concrete. A reinforcing bar was placed in each cylinder. A reinforcement cover 20 mm in thickness was used .The research for phase identification and quantitative analysis (using the Rietveld method) of corrosion products was conducted on three rebar specimens in concrete lagging made of 3 types of concrete, following simulations of the deterioration process under the formation of corrosion hazards caused by the presence of chloride ions. The test was conducted after 1, 2, 7, and 28 days of concrete curing, which had been performed with the use of machine for testing the compressive strength of concrete. The results are shown in Testing the depth of water penetration under pressure was performed according to EN 12390-8, Testing of concrete: Part 8: Depth of water penetration under pressure . A waterOpen porosity was defined as the ratio of the differences between A Nikon Corporation Industrial Metrology Business Unit, Tokyo, Japan XT H 225 ST industrial microtomograph equipped with a reflection lamp was used for the tomographic study; at the maximum approximation of small specimens, it proposed a resolution of 3 µ. The optimal resolution used in this case was 10 µ, which made it possible to obtain reliable images of the scanned sample. The resulting images were then reconstructed using Nikon’s CTPro 3D 6th generation software. After reconstruction, data preparation and all analyses were carried out using the appropriate tools available in VGStudio MAX 3.1 software. Prior to defectoscopy, an area 13 mm in diameter and 15 mm in height, slightly smaller than the scanned area, was taken from each scanned core. Clipping was necessary due to artifacts and imperfections in the tomographic image created during scanning. The data prepared in this way was analyzed for porosity.The test was conducted in accordance with the standards NT BUILD 443  and ASTMD coefficient is determined by adjusting the chloride concentration graph. This graph is obtained by calculating the distribution of chloride ion concentration expressed to the cement mass according to the solution of the diffusion equation, with the concentrations of these ions determined in the test:The value of the c is the chloride ion concentration that was measured during the test at a distance x (mm) from the edge of the element (%), t is time (s), and n is the number of concrete layers in which the chloride concentration was determined. The determined values of the diffusion coefficient are presented in To determine the best fit calculation of the diffusion coefficient complying with the results of the experiment, the mean squared error was calculated based on the following formula:The study was conducted in accordance with the procedure described in standards AASHTO T 277  and ASTM2/s), 3), −1), L is sample thickness (m), V is electrical potential (V), A is the cross-sectional area of a sample (m2), and t is time (s).Based on the determined charge, the value of the diffusion coefficient was also calculated using the Nernst–Einstein equationThe tests were carried out in accordance with the procedure described in NT BUILD492 , being p3 solution, according to the formula:In accordance with the standard NT BUILD492 , the migThe depth of chloride penetration was determined in one of the three test samples made from each concrete.In turn, the other two samples were used to determine the distribution of chloride ion concentration in concrete using the method described in the papers ,9,37. In1 = 24 and t2 = 48 h. At the end of migration, the level of chloride ion concentration in the water extracts obtained from stratified stripped concrete was determined using a Profile Grinding Kid device with both a diamond drill and an attachment that allowed the extraction of 2 mm thick concrete layers, to a depth of 20 mm.Migration tests were conducted using the method described in the papers ,9, and . Six cylBased on measurements of the mass density distribution tionship ,9,37(6)− at the midpoints of consecutive intervals B = 0). Furthermore, z1 is the ion valence, R = 8.317 J/mol·K is the universal gas constant, F = 96 487 C/mol is the Faraday constant, U is the voltage between the electrodes, and h is the specimen height. The determined values of the diffusion coefficient are presented in In this expression, 3 = 30 and t4 = 60 days. After diffusion, the value of chloride ion concentration in the water extracts was determined in the same way as after migration tests.Diffusion tests were carried out using the method described in the papers ,9,37. SiPolarization studies of the corrosion rate in the reinforcements using a polarization resistance measurement method (LPR) were carried out using a potentiostat , coupled with a computer set. The measurement was recorded in a three-electrode system in which the working electrode was the sample reinforcement, the reference electrode was a silver chloride electrode, and the counterelectrode was a stainless-steel circle with a diameter close to that of the concrete samples. In order to accelerate the very long timescale for adequate chloride diffusion in the concrete, accelerated electromigration of chloride ions was used, similar to the works ,25, whil2))k is electrochemical equivalent, and t is time. The above relationship shows the correlation of the corrosion current density, with the linear corrosion rate , concrete resistance (Rc), and constant phase element describing concrete cover (CPEc). The impedance spectra at medium and high frequencies characterizes steel, and corresponds to the right-hand part of the electrical equivalent circuit, which contains the ohmic resistance in pits or defects of the passive layer (Rpit), the constant phase element for passive surface (CPEpas), the charge transfer resistance (Rct), constant phase element describing double layer on the steel (CPEdl), and the Warburg  impedance (W).The impedance spectra obtained were analyzed using the electrical equivalent circuit shown in Phase Identification”, in addition to the International Centre for Diffraction Data’s PDF-4+ database. Quantitative analysis was performed using the Rietveld method, in accordance with the accredited procedure M2-RTG, entitled “Quantitative Phase Analysis.” Observations were carried out using a JSM 7200F scanning electron microscope from JOEL, with a BSE backscattered electron detector and an EDS detector, to perform microarea chemical analysis.Measurements were performed with an Empyrean X-ray diffractometer acquired from PANalytical, using filtered iron radiation in a pixel detector configuration. Identification of phase composition was carried out in accordance with the M1-RTG accredited procedure, entitled “Changing the cement from Portland cement (for B1 concrete) to metallurgical cement (for B2 and B3 concretes) caused a reduction in compressive strength in the first 7 days of maturation. This reduction in compressive strength could also have been caused by the sealer admixture (B3 concrete). After the 28th day of maturation, the strength of concrete with metallurgical cement was the highest, and a clear upward trend was also visible. The properties of blast furnace slag, which is a component of metallurgical cement, allow us to hypothesize that the strength of B2 and B3 concretes will be higher than that of B1 concrete after a longer maturation time.The use of metallurgical cement significantly reduced the depth of pressurized water penetration. However, the addition of a sealing admixture did not significantly improve the achieved effect in B3 concrete. It should be noted that the penetration of water deep into each sample was of a local nature. The magnitude of penetration forming about 20 mm was small and appropriate for concretes with a good quality of cement matrix.As can be seen from the results, the tested concretes did not differ substantially in terms of open porosity as determined using the gravimetric method. Concrete B3  had slightly better properties than the other concretes.These were based on tomographic studies of a smaller cylindrical sample, measuring 18 mm in diameter and 21 mm in height.1 = 14%, p2 = 6%, and p3 = 6% for concretes B1, B2, and B3, respectively. According to these tomograph tests, it can be said that the replacement of the ordinary cement (CEM I) with metallurgical cement (CEM III) resulted in a reduction in the porosity of the concrete by almost half. On the other hand, the use of a sealing agent had practically no effect on the porosity.On the basis of the analysis performed, the porosity of the concretes was calculated, expressed as the percentage of the sum of all air voids (imaged using the tomograph) against the volume of the fragment of the cylindrical sample with a diameter of 18 mm and a height of 21 mm, amounting to pAll three concretes were tested using both standard methods and the thermodynamic method. A detailed discussion of the methods, including a comparison with the results obtained in different concrete mixtures, are presented in the paper . Table 41202-997  after apUILD 492 , based oUILD 492 . On the UILD 443 ; this waAccording to an analysis of various methods of determining the diffusion coefficient in different types of concrete, each of which having been carried out in the paper , the valt of chloride concentration at the reinforcement–concrete interface of the lagging  are shown in It was assumed that the threat of corrosion of the reinforcing bars causes, according to the standard PN-EN 1992-1-1 Eurokod 2 , chloridThe corrosion hazard of the reinforcement in B1 concrete will occur after just 2 years of using the structure with the applied lagging thickness of 15 mm, while with the application of a lagging thickness of 25 mm the corrosion hazard will occur after 5 years. Application of the minimum thickness of lagging around the reinforcement required by the standard EN-PN 1992-1-1  in constThe specimens, for which a number of measurements were taken during the whole research process, were analyzed. They were the B1_P1, B1_P2 and B2_P1, B2_P2 and B3_P1, and B3_P2 specimens. The first measurement was a reference, prior to the chloride migration in the concrete. The second measurement was taken after 7 days of chloride migration onto concrete. After waiting a further 7 days, the third measurement was taken after 14 days of chloride migration into concrete. After waiting 7 days again, the fourth measurement was taken, 21 days after chloride migration into the concrete. Likewise, the fifth measurement, taken after 28 days of chloride migration into the concrete and after waiting 7 days. Three seven-day cycles of chloride ion recharge with an electric field were performed for B1 concrete. For B2 concrete, five seven-day cycles of chloride ion recharge were carried out using an electric field. For B3 concrete, four seven-day cycles of recharging chloride ions with an electric field were carried out. Each time the seven-day migration process was completed, post measurements of the corrosion current density were made after waiting seven days from the electric system being turned off. Charging cycles were applied until the corrosion current density value that would indicate advanced corrosion was obtained. Exemplary shapes for the six selected measuring elements are illustrated in corrE = 236 mV corrE = 90 mV corrE = 15 mV. After the second charge, the values of the corrosion potential in both samples reached a value above the 200 mV A similar change in the distribution of polarization curves over time was observed for the specimens B1_P1 and B1_P2 a,b afterIn B3 concrete, a decrease in corrosion potential was also observed during all test cycles, but the initial values in one of the samples currence .corri) of the steel reinforcement in concrete from two chosen test elements made of tested concretes. corrE) of the steel reinforcement in concrete from two chosen test elements made of tested concretes.The analysis was made on the basis of assumptions made in the work . The firBefore the injection of chloride ions into the concrete, fragments of large arcs were visible on the Nyquist spectra for steel . This ise + Rc) associated with an increase in the conductivity of the concrete due to an increase in the ion concentration in the concrete pore liquid. The sum of Re + Rc determined from the analysis of the spectra for concretes B2 and B3 was greater than it was for concrete B1  decreased with the duration of the tests  started to corrode after the shortest time following chloride introduction into the concrete. The Rp values determined from the analysis of the impedance spectra of steel in concrete confirmed the results obtained from the analysis of the steel polarization curves.The determined polarization resistance Rhe tests . The valdl) were also observed , equipped with microarea chemical analysis capabilities and X-ray microdiffraction (μXRD), were used to study microstructural changes, in addition to changes in the phase composition of corrosion products occurring in the steel–concrete contact zone. These changes were observed during the development of corrosion processes caused by an increase in the concentration of chloride ions in the concrete. Examples of tests performed using X-ray microdiffraction (XRD) and surface micrography are shown in The use of phase identification showed that there are differences in the iron compounds formed depending on the type of sample. Lepidocrocite and akaganeite are present in all areas tested, while the presence of δ-type iron oxide was only confirmed in the sample from B2 concrete; likewise, goethite was identified only in the sample from B3 concrete. The only iron compound containing chlorine is akaganeite, though chlorine–calcium compounds also appeared in the sample from concrete B3. In addition, the presence of hydrated iron–potassium oxide was possible. No reflections of chlorine, potassium, or sodium compounds were registered in any of the samples.2O) to gypsum (CaSO4 2H2O) controls the setting process of gypsum plaster [Only a small amount of bassanite was identified in the B1 concrete sample. Aqueous conversion of bassanite , while akaganeite was 24% of the mass. In the B3 concrete sample, goethite was the most abundant at 48.7% of the mass; lepidocrocite was at the same level as it was in the B1 concrete sample, i.e., 35.9% of the mass. In this sample, the share of akaganeite was the lowest, at about 10% of the mass. This was also the lowest share of this mineral in all the samples tested.It can be concluded that a common feature of the tested samples was the presence of lepidocrocite and akaganeite, although their proportions varied from sample to sample. In each of the samples, a different phase was dominant; in the B1 concrete sample, all three iron compounds were found in similar amounts, while in the B2 concrete sample, half of the tested material was formed of iron oxide type δ, and in sample No. 3, the main phase was goethite. Since lepidocrocite was the result of hydration of goethite (and there was the least amount of it in the B2 concrete sample), it can be assumed that corrosion processes in the B2 concrete sample occurred more slowly than in the other samples.The type of cement influences the rate of chloride diffusion in the concrete, and thus the duration of corrosion initiation of the reinforcement by chlorides penetrating into the concrete from the environment.Of the concretes tested, concrete B2 with CEM III cement was the most resistant to chloride ingress, and therefore provided the longest period of protection for the reinforcement against chloride-initiated corrosion. The fastest, occurring after only two 7-day cycles of chloride migration in the electric field, was the steel corrosion that started in concrete with CEM I cement (concrete B1).The results of the concrete diffusion and porosity tests correlated with the time of the onset of steel corrosion in the tested concretes due to chloride penetration into the concrete.Similarly, studies of both the microstructure and changes in the phase composition of corrosion products occurring in the steel –concrete contact zone confirmed these observations as having the smallest amount of lepidocrocite, which was the result of goethite hydration in the smallest amount, occurring in the sample made of B2 concrete.The additional use of a sealing admixture did not seem to be the most effective strategy, as it can cause a local increase in the volume of pores in the concrete, and, at the same time, a local weakening of the concrete structure, as can be seen from the distribution of the number of pores in a given volume found using computed tomography. According to the study conducted with this method, B2 concrete shows the most uniform distribution of pores of different volumes, with the lowest total number of pores.The test results obtained were consistent with the results obtained in the work , where t


High-strength large-volume marine concrete is a critical material required for the construction of large-span sea-crossing bridges. However, the widespread issue of cracking in this concrete type significantly impacts the durability and load-bearing capacity of concrete structures. Dealing with these cracks not only delays construction schedules but also increases project costs. Addressing these pressing technical issues, this project proposes the use of newly developed high-modulus heat-shrinkable fibers  from the textile industry. These fibers utilize the heat generated during the hydration of large-volume concrete to trigger its contraction, applying three-dimensional micro-prestressing stress to enhance its crack resistance, while simultaneously incorporating prewetted aggregates with high-performance micro-porous structures and utilizing their internal curing effect to reduce concrete shrinkage. This helps to minimize the loss of micro-prestressing stress caused by concrete shrinkage and creep. This synergistic approach aims to improve the crack resistance of high-strength large-volume marine concrete. By employing modern testing and simulation analysis techniques, this study aims to uncover the mechanism by which the heat-shrinkable fibers exert micro-prestressing stress on concrete and the water release mechanism of internal curing aggregates during the temperature rise and fall stages of large-volume concrete. It seeks to elucidate the cooperative regulation of the microstructure and performance enhancement mechanisms of high-strength large-volume marine concrete by the heat-shrinkable fibers and internal curing aggregates. This research will lead to the development of novel methods for the design and crack control of high-strength large-volume marine concrete, which will be validated through engineering demonstrations. The outcomes of this study will provide theoretical foundations and technical support for the preparation of the crack-resistant large-volume marine concrete used in large-span bridges. With the advancement of the “Belt and Road Initiative,” the strategic development of becoming a maritime power, and the progress in the development plan for the Greater Bay Area of Guangdong, Hong Kong, and Macau, numerous large-span sea-crossing bridge projects are either under construction or about to commence . In addiThese extensive sea-crossing bridge projects not only provide support for the development of transportation infrastructure but also play a pivotal role in driving regional economic growth and cooperation. The application of high-strength large-volume marine concrete ensures the load-bearing capacity and durability of these bridges, enabling them to address the challenges posed by the maritime environment, such as salt spray, seawater erosion, and climate change. The design and construction of these projects necessitate a comprehensive consideration of material performance, structural stability, and environmental impacts. Amidst this developmental trend, domestic research institutions and construction companies continually strive to innovate materials, technologies, and methodologies to meet the demands of these large-volume marine engineering projects. These efforts not only contribute to the successful completion of engineering endeavors but also hold the potential to significantly enhance the technological prowess of domestic engineering construction. The construction of these expansive sea-crossing bridges will further facilitate interconnectivity between regions, bolster international collaboration, and pave new pathways for economic development.The practical results of engineering endeavors indicate that compared with the commonly used large-volume C30 to C40 concrete in bridge projects, the design requirements for high-strength marine mass concrete exceeding C50 entail higher strength and enhanced resistance to chloride ion penetration. This necessitates a lower water–cement ratio and a higher amount of cement and binder materials. The greater heat generated during hydration accumulates, even when employing measures such as low-heat cement, substantial mineral admixtures, the circulation of cooling water, and controlling the temperature during casting. Consequently, the internal maximum temperature can still reach 70 to 90 °C ,3,4, witAfter the cracking of large-volume marine concrete, chloride ions in seawater readily penetrate through the cracks and reach the reinforcing steel, resulting in steel corrosion and concrete structural damage and thereby compromising the load-bearing capacity and durability of the concrete structure ,6,7. TheLarge-volume marine concrete is a critical material for the construction of marine bridge projects. The key to enhancing its performance lies in addressing the issues of cracking and chloride salt erosion. For commonly used C30 to C40 large-volume marine concrete, measures to improve crack resistance and chloride salt resistance include optimizing the mix design through the use of low-heat cement or reducing the cement content, incorporating high-volume mineral admixtures, and adding retarding agents to prepare low-heat hydration temperature rise large-volume concrete ,9,10,11.During the construction of large-volume marine concrete ,22,23,24Engineering practice has demonstrated that the addition of hydration heat suppressants in large-volume concrete can reduce the temperature rise caused by hydration heat and delay the occurrence of temperature peaks, resulting in a decrease of up to 5–8 °C in the maximum concrete temperature. For C30~C40 large-volume marine concrete, the inclusion of hydration heat suppressants can effectively control cracking when cooling water pipes are not installed . HoweverFurthermore, for high-strength large-volume marine concrete above C50, the low water-to-cement ratio and the inclusion of fine reactive powder materials such as silica fume result in significant shrinkage. On the other hand, the addition of expansive agents competes for limited water  with cemWith the increasing span of bridges, researchers have proposed the use of steel–concrete composite structures to address the crack resistance issues of large-volume concrete. In non-marine environments, the use of steel shells or steel tubes filled with expansive large-volume concrete can effectively address the challenges of crack control. However, in marine environments, particularly in splash or tidal zones, the steel shells or steel tubes are at significant risk of corrosion. Therefore, for the application of steel–concrete composite structures in high-strength large-volume marine concrete under marine conditions, it is imperative to address the long-term corrosion protection of the steel shells or steel tubes.The process of marine erosion is a complex interplay of multiple factors. It triggers a cascade of profound physicochemical responses within the matrix of cementitious and slag-based slurries, as depicted in Furthermore, sulfate ions in seawater can react with compounds such as calcium aluminosilicates within the cementitious matrix, forming sulfate precipitates. The generation of sulfates triggers the degradation of calcium aluminosilicates, causing volumetric expansion and diminished strength in the slurry and thus severely compromising its mechanical properties and stability. Moreover, oceanic elements such as waves, tides, and currents instigate physical impacts and abrasion upon the cementitious and slag-based slurries. The force of waves and the abrasive action of particles induce the detachment and erosion of particles from the surface of the slurry, consequently affecting its appearance and mechanical attributes.Lastly, the salts and alkaline substances present in seawater may incite alkali–aggregate reactions within the cementitious and slag-based slurries. These reactions lead to internal expansion and contraction phenomena, engendering micro-volume damage that diminishes the mechanical integrity and stability of the slurry. On the whole, the impact of marine erosion on cementitious and slag-based slurries encompasses a spectrum ranging from chemical reactions to physical degradation. To mitigate these effects, measures such as using materials with resistance to chloride intrusion, incorporating corrosion-resistant additives, enhancing density, and implementing protective coatings should be adopted. These measures can ensure the performance and reliability of cementitious and slag-based slurries in marine environments. In practical engineering applications, it is imperative to comprehensively consider these factors when formulating tailored strategies for material selection and structural design. This approach ensures the long-term stability and sustainable operation of structures.Foreign researchers were the first to introduce polypropylene fibers and steel fibers into large-volume concrete to enhance its crack resistance. Polypropylene fibers effectively improve the toughness of concrete and significantly reduce the cracks caused by plastic shrinkage. However, they have lower modulus, poor dispersion, and can affect the pumpability of concrete. Steel fibers have higher elasticity and tensile strength. When added to large-volume concrete, they can increase the tensile strength by approximately 15% to 20%, thereby enhancing its crack resistance. However, conventional steel fibers carry the risk of corrosion in marine engineering and also increase construction costs. Furthermore, both the fibers currently used and the concrete itself are materials that undergo thermal expansion and contraction. When the concrete undergoes temperature rise and expansion, the fibers expand accordingly. Similarly, when the concrete cools down and contracts, the fibers also contract. Taking steel fibers as an example, they have a higher thermal expansion coefficient than concrete. During the temperature rise phase of large-volume concrete, the disparate thermal expansion coefficients between steel fibers and the cementitious paste in the concrete induce tension at the paste–fiber interface, resulting in the formation of microscopic cracks. The contraction of fibers during the cooling phase further promotes crack development . TherefoIn recent years, the textile industry has developed a novel type of fiber that is distinct from the aforementioned heat-expansion fibers. Known as thermal shrinkage fibers, these fibers exhibit a contraction effect with an increase in temperature. They possess remarkable features, such as high modulus, adjustable shrinkage rate, a wide range of thermal contraction temperatures, high strength, chemical corrosion resistance, and cost effectiveness. Among these fibers is PET fiber, which is derived from the polymerization of polyethylene terephthalate. The specific parameters are detailed in The utilization of heat-shrinkable fibers within voluminous high-strength marine concrete finds its purpose in meeting the demands of extreme engineering requisites intrinsic to maritime environments in an endeavor to heighten the durability, crack resistance, and overall performance of concrete structures. The intricate nature of marine surroundings renders high-strength concrete susceptible to minute crack propagation arising from challenges such as chloride ion erosion and thermal cycling, which in turn imperil structural stability and long-term reliability. The incorporation of heat-shrinkable fibers, owing to their exceptional mechanical attributes and thermal contraction properties, heralds a novel and promising avenue for tackling such issues. These fibers, typically crafted from materials such as polypropylene and polyester, in this conceptualization, employ PET fibers. When incorporated into concrete, they create a three-dimensional cohesive network. Throughout the process of concrete hydration and setting, these fibers, courtesy of their intrinsic thermal contraction tendencies, seamlessly integrate with the concrete matrix, thereby notably enhancing the overall performance of the concrete. Their salient application effects encompass, yet are not confined to, the following aspects: Firstly, in the realm of crack resistance, heat-shrinkable fibers exert a notable impediment to the formation and extension of cracks. The susceptibility of high-strength marine engineering concrete to fissures under the influence of factors such as seawater corrosion and temperature fluctuations is mitigated by the introduction of these fibers, effectively elevating the concrete’s ductility and facilitating control over crack propagation. Secondly, these fibers exert a vital role in enhancing durability. The presence of chloride ions in seawater substantially impacts the corrosion of concrete rebars, and the introduction of fibers can decelerate the ingress of chloride ions, thereby retarding the internal corrosion process of concrete and enhancing structural durability. Furthermore, the addition of fibers significantly augments concrete’s toughness and load-bearing capacity, thereby bolstering overall performance. In the realm of high-strength marine concrete structures, this reinforcement effect proves crucial in withstanding the challenges posed by waves, surges, and external loads, ensuring the long-term stability of structures. However, it is pertinent to underscore that the application of heat-shrinkable fibers necessitates a comprehensive consideration of engineering design and practical construction requirements. Although fibers can markedly enhance the concrete’s properties, they do not supplant the role of conventional steel reinforcement. Consequently, in engineering practice, a judicious amalgamation of diverse reinforcement materials and methodologies is requisite to attain optimal structural performance. In summation, the application of heat-shrinkable fibers in high-strength large-volume marine concrete not only effectively augments crack resistance, durability, and overall performance but also offers valuable technological support to address the rigorous demands of marine environments, thus enhancing the sustainability and reliability of marine engineering endeavors.Based on the characteristics of heat-shrinkable fibers developed and applied in the textile industry, the introduction of these high-modulus fibers into high-strength large- volume marine concrete has proven to be beneficial. The fibers are evenly dispersed throughout the concrete matrix, ensuring a uniform distribution by implementing surface roughening and hydrophilic modification techniques ,32,33. DHigh-strength large-volume concrete undergoes both heating and cooling stages. During the heating stage, the concrete undergoes thermal expansion, where the heat-shrinkable fibers are thermally stimulated to shrink, exerting micro-prestress on the concrete . In the The investigation into the impact of internal curing materials on concrete shrinkage is a pivotal subject within the realm of concrete technology. This topic revolves around comprehensively understanding the influence of various types of internal curing materials on concrete shrinkage performance and seeks to optimize their practical application to control concrete shrinkage. In recent years, both the academic and engineering communities have exhibited an increasing interest in this subject and aimed to gain a deeper grasp of the essence of concrete shrinkage issues and potential solutions. Internal curing materials exert their influence on concrete shrinkage performance through various mechanisms. Firstly, these materials effectively retain moisture within the concrete, thereby slowing down the rate of moisture loss and consequently mitigating drying shrinkage. Secondly, the introduction of internal curing materials can decrease the evaporation rate from the concrete surface, thereby alleviating the impact of drying shrinkage. Moreover, some internal curing materials might interact with the cementitious gel in the concrete, influencing the progress of hydration reactions and thus, to some extent, controlling concrete shrinkage. Internal curing materials come in a diverse array of guises, including, but not limited to, liquid membranes, dampened paper, wet cloths, polymer films, etc. Research indicates that the selection and application methodology of these materials can yield varying degrees of influence on different types of concrete shrinkage, such as drying shrinkage and thermal shrinkage. For example, materials such as liquid membranes and wet cloths can create a sealed physical barrier, effectively slowing moisture evaporation and thereby reducing drying shrinkage. On the other hand, the introduction of polymer films and similar materials might influence hydration reactions and thus control thermal shrinkage.In concrete shrinkage studies, measurement techniques are indispensable tools. Strain gauges, drying shrinkage tests, thermoluminescence measurements, and other techniques are extensively utilized to evaluate the influence of internal curing materials on concrete shrinkage. These techniques provide quantifiable data that aid researchers in more accurately revealing the relationship between internal curing materials and concrete shrinkage. In studies of internal curing materials, performance comparisons are often crucial. Researchers frequently compare the performance of concrete using internal curing materials with concrete cured through traditional methods. Such comparative studies not only evaluate the practical effectiveness of internal curing materials but also explore their effects on shrinkage control, strength development, and durability. In terms of practical engineering application, an increasing number of studies are examining the effects of internal curing materials in real-world projects. These studies consider not only the material’s cost, feasibility, and construction conditions but also involve long-term monitoring and assessment of the material’s performance. This contributes to guiding the selection and utilization of internal curing materials in engineering practice and provides a scientific basis for the durability and reliability of projects.In conclusion, research on the influence of internal curing materials on concrete shrinkage is continuously advancing, offering fresh insights into more effective methods of controlling concrete shrinkage. However, certain aspects still require further exploration, such as the mechanisms behind the influence of various types of internal curing materials and the feasibility and longevity of their application in real-world projects. With increasing research in these domains, a deeper comprehension of the interaction between internal curing materials and concrete shrinkage can be attained, providing a more robust scientific basis for enhancing the design and execution of concrete engineering projects.Research indicates that the incorporation of internal curing materials can mitigate concrete shrinkage. The commonly used internal curing materials for concrete are lightweight aggregates and superabsorbent polymers (SAP) that are primarily used due to their affordable price and abundant availability. SAP, compared with lightweight aggregates, exhibits superior desorption capacity . HoweverIn order to address potential issues arising from internal curing materials in high-strength large-volume concrete, researchers have been exploring innovative solutions. One promising alternative approach involves the use of nanomaterials, such as nano oxides or carbon nanotubes, as internal curing agents. These nanomaterials possess extremely small dimensions, allowing them to more effectively fill the micro-voids within the concrete, and their adsorption and release of moisture can be fine-tuned by controlling particle size and surface modifications. As a result, nanomaterials can provide more stable moisture release under high-temperature conditions, contributing to the preservation of concrete’s mechanical properties and durability. Furthermore, some advanced high-performance concrete technologies have embraced the concept of self-healing materials. These materials can autonomously repair microcracks within the concrete, alleviating shrinkage concerns. These self-healing materials may include microcapsules containing healing agents that can be released when needed or micro/nanofibers that can bridge microcracks and enhance the continuity of the concrete.In recent years, researchers have developed a spherical high-microscopic interconnected-pore internal curing aggregate with a diameter ranging from Φ1.00 to 4.75 mm. This aggregate ,46 exhibMethods for the preparation of high-microscopic interconnected-pore internal curing aggregates with water absorption, medium-high strength, and a predominant presence of microfine interconnected pores have been proposed and industrially produced in Yichang. A water release model for prewetted internal curing aggregates  in cemenThis novel type of highly interconnected micro-porous internal curing aggregate brings a significant innovation to concrete technology in the field of marine engineering. Its unique attributes, including high strength, adjustable water absorption capacity, and exceptional micro-interconnected pore structure, render it an ideal choice for large-span sea-crossing bridge projects. These attributes not only significantly enhance the durability and crack resistance of concrete but also help mitigate the impact of temperature variations on the concrete surface, thereby reducing the potential for cracks and damage. The application of internal curing aggregates has been validated in engineering practice, especially in the maintenance and reinforcement project of the Fuhexi Bridge in Wuhan. By partially substituting traditional fine aggregates with these highly interconnected micro-porous internal curing aggregates, a highly abrasion-resistant ultrahigh-performance concrete was successfully developed, showcasing its feasibility and effectiveness in real-world projects. This successful case serves as a robust reference for future similar projects while also paving the way for new directions in the innovation and advancement of concrete technology in China. The introduction of this new type of internal curing aggregate enriches the array of choices for marine engineering concrete materials and promotes the sustainable development of marine engineering construction. Against the backdrop of strategies such as the “Belt and Road Initiative,” this innovation not only strengthens China’s technological prowess in the field of marine engineering but also provides robust support for regional cooperation and international exchange. Through continuous research and practical applications, we can foresee that this novel internal curing aggregate will play an increasingly significant role in future marine engineering projects, offering a reliable foundation for more durable and dependable engineering structures.However, the mechanisms of water release during the temperature changes and their effects on the microstructure of the concrete in the ascending and descending phases are yet to be fully understood. Moreover, there is currently a lack of research on the synergistic control of microstructure and performance enhancement in high-strength large-volume concrete in marine engineering using both shrinkage-reducing fibers and internal curing aggregates ,46,48. TBased on the aforementioned analysis, considering the developed application of heat-shrinkable fibers and highly micro-connected-pore curing aggregates ,50,51,52(1) Concept for synergistically enhancing concrete crack resistance: leveraging the high modulus of the heat-shrinkable fibers and their coupled effect of thermal shrinkage-induced contraction at the interface with the cementitious slurry, exerting three-dimensional micro-prestress on the concrete to improve its tensile strength and ductility, while simultaneously enhancing the mechanical properties of the arch-shell structure at the interface between the internal curing aggregate and the cementitious slurry; employing the internal curing aggregate to suppress concrete shrinkage and reduce the loss of micro-prestress caused by concrete shrinkage and creep; dispersing internal stresses by forming an arch-shell structure at the interface between the internal curing aggregate and the cementitious slurry ,54,55,56(2) Concept for synergistically enhancing concrete resistance to chloride salt erosion: utilizing the three-dimensional micro-prestress induced by the heat-shrinkable fibers to improve the inherent defects of the cementitious slurry; forming an arch-shell structure at the interface between the internal curing aggregate and the cementitious slurry to enhance its interface microstructure; synergistically improving the fiber, concrete aggregate, and internal curing aggregate interface microstructure by means of the three-dimensional micro-prestress and internal curing.In The microstructure of high-strength large-volume marine concrete directly influences its macroscopic performance. Understanding the mechanisms through which heat-shrinkable fibers and high-performance micro-porous internal curing aggregates jointly regulate the microstructure of the concrete is crucial for enhancing its crack resistance. Additionally, understanding the inherent relationship between microstructure formation and crack resistance improvement in concrete is key to guiding the enhancement of concrete crack resistance. Therefore, elucidating the mechanisms by which heat-shrinkable fibers and internal curing aggregates co-regulate the microstructure and crack resistance of high-strength large-volume marine concrete represents the core and pivotal scientific challenge to be addressed in this project.In response to the technical challenges posed by high-strength marine concrete, the proposed concept combines the characteristics of thermal shrinkage fibers and highly interconnected micro-porous internal curing aggregates to achieve a synergistic enhancement of concrete performance. In terms of crack resistance, the high modulus and thermal shrinkage effects of thermal shrinkage fibers, combined with the collaborative action of internal curing aggregates, establish a three-dimensional micro-prestressing effect. This leads to an improvement in the concrete’s tensile strength and ductility while effectively reducing the occurrence of cracks. This innovative concept paves a new path for the application and technological advancement of high-strength marine concrete. By implementing this concept in practical engineering projects, critical issues such as crack control and resistance to chloride salt intrusion can be effectively addressed, thereby enhancing the reliability and durability of marine engineering structures. This not only drives innovation and development in the field of marine engineering but also offers valuable insights and guidance to similar projects both domestically and internationally. Through continuous research and practical application, we can further refine and apply this concept, providing more dependable solutions for future marine engineering construction.This paper presents a comprehensive review and analysis of the research achievements in the field of the crack resistance of high-strength marine concrete. It explores future research directions concerning the synergistic regulation of crack resistance in large-volume concrete through the utilization of thermally shrinkable fibers and internal curing aggregates. The findings are summarized as follows(1)The current status of high-strength marine concrete has been analyzed, elucidating the developmental trends and crack control methods in this domain.(2)The mechanism of applying micro-prestress to concrete using thermally shrinkable fibers has been identified. Due to their high modulus, adjustable shrinkage rate, excellent dispersibility, and strong interface bonding with the concrete matrix, thermally shrinkable fibers can effectively regulate cracking in large-volume high-strength marine concrete.(3)The water release mechanism during the temperature rise and fall stages of large-volume concrete and the effective control of crack formation and propagation in the early curing stage through the utilization of fine interconnected internal curing aggregates have been investigated.(4)The synergistic regulation of microstructure and performance in high-strength marine concrete through the combined use of thermally shrinkable fibers and internal curing aggregates, as well as a coordinated design approach for crack resistance and resistance to chloride ion erosion based on these materials, have been proposed.This study introduces innovative technologies and materials to tackle cracking and chloride ion erosion in high-strength marine concrete. It also has theoretical significance by bridging textile and building materials and offers insights for designing more durable large-span sea-crossing bridges.


Fiber-reinforced polymer (FRP) composites have gained increasing recognition and application in the field of civil engineering in recent decades due to their notable mechanical properties and chemical resistance. However, FRP composites may also be affected by harsh environmental conditions  and exhibit mechanical phenomena  that could affect the performance of the FRP reinforced/strengthened concrete (FRP-RSC) elements. This paper presents the current state-of-the-art on the key environmental and mechanical conditions affecting the durability and mechanical properties of the main FRP composites used in reinforced concrete (RC) structures . The most likely sources and their effects on the physical/mechanical properties of FRP composites are highlighted herein. In general, no more than 20% tensile strength was reported in the literature for the different exposures without combined effects. Additionally, some provisions for the serviceability design of FRP-RSC elements  are examined and commented upon to understand the implications of the durability and mechanical properties. Furthermore, the differences in serviceability criteria for FRP and steel RC elements are highlighted. Through familiarity with their behavior and effects on enhancing the long-term performance of RSC elements, it is expected that the results of this study will help in the proper use of FRP materials for concrete structures. Corrosion is a major problem for steel-reinforced concrete (RC) structures, being responsible for the deterioration of the physical-mechanical properties of the rebar , the rebar to concrete interface , and the concrete cover (cracking from expansive corrosion) ,2. ThereFRP composites consist of reinforcing fibers embedded in a polymer matrix. Continuous glass, carbon, basalt, and aramid fibers are the types of fibers in composites that are used for structural engineering applications , and theDespite their favorable properties, FRPs may be subject to fatigue and creep rupture which, together with their low modulus of elasticity (compared to steel) make the serviceability limit states typically control the flexural design of concrete members reinforced with GFRP (Glass/vinyl-ester FRP) bars that exhibit lower stiffness . AdditioThe present paper reviews the current state-of-the-art on the main environmental and mechanical conditions affecting the mechanical properties of FRP composites and their impact in the design requirements for RSC elements. First, a brief background on FRP composites and their use as reinforcement and strengthening materials is presented, followed by a classification and presentation of the factors leading to the deterioration of FRP composites. Chapter 3 examines the main environmental effects on FRP composites, including exposure to water, saline, alkaline, UV, freeze-thaw, and elevated temperatures exposure. Chapter 4 focuses on the main mechanical effects affecting the mechanical properties of FRP composites and FRP-RSC elements, including fatigue, creep rupture, and shrinkage. In Chapter 5, the impact on design requirements of GFRP-RSC structures is discussed. Finally, the paper concludes with a summary and conclusions.To narrow the wide range of composite materials that are available, this review only focuses on Glass/vinyl-ester FRP bars for internal application and Carbon/epoxy FRP fabrics for external application, which are the most commonly studied in the literature and present in the US market. In addition, for internal application, the new ACI 440.11 code  referencThe development of FRP composites began in the 1930s when the first patented fiberglass was produced by Owens Glass company, who joined with the Corning company . Later, The internal application of FRP composites is strongly related to locations where the corrosion of traditional steel reinforcement is an economic and safety concern . The gooDespite some challenges, new construction projects using FRP as the primary or auxiliary reinforcement in concrete structures have been developed all over the world ,37,38,39The external application of FRP composites has primarily been implemented for the rehabilitation of structures when design defects are noticed, an in-service element’s load-bearing capacity is modified, the materials have begun to deteriorate, or extreme events have occurred  . In addiExternal FRP systems are generally applied to RC elements to enhance the flexural, axial, shear, and torsional strength, and, in seismic zones, FRP wraps can be used for columns to increase ductility due to the induced confinement of the concrete ,44,45,46Experimental studies have shown different failure modes in elements strengthened with FRP fabrics. The most prevalent failure modes, as per ACI 440.2R-17 , includeThe mechanical and environmental effects on FRP composites have been extensively discussed in the available literature . HowePhysical-mechanical properties of the FRP composites, as well as the concrete surrounding or supporting them, could be affected when they are subjected to harsh environmental conditions. Nevertheless, due to the variety in fibers ; polymer resins ; fiber volume fractions; solution concentrations; temperature; among others, it is not proper to stipulate a single range of deterioration, even for a specific composite  subjected to a specific harsh environment . CurrentThe fibers, matrix, and fiber-matrix interface of an FRP composite can degrade when exposed to water, high moisture, or high humidity. The degradation mechanisms of Glass FRP composites under water exposure include the entry of moisture through the fiber-matrix interface , leadingGFRP barsKim et al.  stated tFurthermore, as GFRP bars are embedded in concrete for internal application during their service life, Nepomuceno et al.  reviewedCFRP fabricsIn FRP fabric systems (sheets), the polymer resin  is utilized as a primer, putty coat, and saturant in externally bonded applications. To serve as an adhesive between the FRP system and the concrete surface, the resin is primed onto the surface of the element. Therefore, the presence of humidity or water during installation or the service life of the element could be detrimental to epoxy resin due to its water absorption capacity ,62,63. TCivil structures exposed to marine environments or deicing salts during the winter are generally subjected to saline environments. Studies have found that the intermolecular bonds in the matrix as well as in the fiber-matrix interface could strain or rupture in the presence of salts . SimilarGFRP barsGFRP bars immersed in a saline solution do not necessarily have a significant difference in strength and stiffness when compared to those in a solution without salt ,71. LaboCFRP fabricsFRP strengthening systems may go through a significant reduction in bond strength between the FRP and the bonded surface when exposed to saline environments . The durGiven the alkalinity environment of concrete, FRP composites could be affected when embedded in it or when exposed to an alkaline environment. Among the available fiber types, carbon fibers are resistant to alkalis and do not degrade as much as glass and basalt fibers . Silica,GFRP barsAlkaline solutions with pH values ranging between 11.5 and 13.0 degrade the tensile strength and stiffness of GFRP bars . BenmokrRobert et al.  comparedFurthermore, due to the diffusion of carbon dioxide from the atmosphere and the ingress of chloride ions, the natural alkalinity within the concrete is lost. In RC-elements reinforced with steel, this can result in a reduction of the pH, which breaks the passive layer of iron oxide around the steel rebar, and consequently the steel can start corroding ,88. HoweCFRP fabricsAs it relates to external FRP applications, some laboratory tests have indicated that the tensile properties of CFRP fabrics are barely affected by alkaline solutions, although a reduction in flexural strength was observed . The fleThe ultraviolet (UV) exposure may result in surface oxidation due to different chemical mechanisms related to the resin type ,95. UV rGFRP barsTests on GFRP bars showed a tensile strength loss after 3 years of exposure of about 10% . AdditioCFRP fabricsOn the other hand, the effect of ultraviolet (UV) radiation is more relevant in external applications, as the CFRP fabric will be directly exposed to UV lights ,104. In Freeze-thaw cycles along with the coupled effect of high moisture may lead to the deterioration of FRP composites ,107. FRPGFRP barsExperimental studies on FRP bars have shown different performances when exposed to freeze-thaw cycles. Pull-out test results of GFRP bars (freeze-thaw cycles ranging from 50 to 600) showed that the bond strength between the FRP bar and concrete surface was not considerably influenced by the environmental conditions . Other tThe results on sand coated GFRP reinforced concrete (6% entrained air content) beams exposed up to 360 freeze/thaw cycles (−20 to 20 °C), either in an unstressed state or loaded in bending, showed no significant effect on the behavior in terms of deflections, strains, or ultimate capacity for the two actions when compared to control specimens . Some spCFRP fabricsProgressive degradation of the FRP composite and the weakening of the interfacial bond at the FRP to concrete interface can occur as a result of freeze-thaw cycles . Chajes Homam and Sheikh  immersedDue to the anisotropic behavior of FRP composites, the coefficient of thermal expansion (CTE) is different in longitudinal and transversal directions; the first one controlled by the fibers and the second one controlled by the resin ,121. In GFRP barsTests on GFRP bars have evidenced a reduction in their tensile strength and bond properties at temperatures between 100 °C and 350 °C ,123. TenRelated to fire exposure, a study carried out by Kodur and Bisby  showed tNigro et al.  tested fCFRP fabricsModerate ranges of temperature variation of around ±28 °C (±50 °F) has been shown not to affect the bond between the surfaces of FRP strengthening elements . A studyMechanical effects such as cyclic fatigue, creep (static fatigue), or relaxation could affect the properties of the FRP composite and impact the serviceability performance of the FRP-RSC element. This mainly occurs in internal applications due to FRP characteristics that may control the design and cause structural elements to perform differently under time-dependent phenomena.Cyclic fatigue, commonly called fatigue, is a degradation of the capacity of a material caused by repeated applications of a large number of load cycles . Most ofGFRP barsInitial studies in GFRP bars observed a cyclic tensile fatigue effect of an approximately 10% loss in the initial static capacity per decade of logarithmic lifetime . HoweverCFRP fabricsThe various modes of fatigue failure in CFRP laminates have been recognized as comprising matrix cracking, transverse cracking, interfacial debonding, delamination, and fiber breaking. The occurrence of failure is influenced by factors such as the types of fibers and resins used, the structure of the textile, the surface treatments applied, the fatigue stress ratios, and stress levels ,146. IniZheng et al.  examinedStatic fatigue or creep rupture is a phenomenon produced by constant tension over time that can lead to sudden failure after a period called the “endurance time” . In FRP GFRP barsInitial studies on GFRP bars observed a creep strain under a sustained load at 80% of the ultimate tensile strength (UTS) of the GFRP bar after 50 days, ranging from 0.3 to 1.0%. Other studies observed a creep strength rupture equal to 55% of the UTS for an extrapolated endurance time of 50 years . It was CFRP fabricsThe shear stress to shear strength ratio is a primary factor affecting the long-term behavior of the concrete-CFRP interfaces. Results focused on the epoxy resin have indicated an ultimate creep coefficient (the ratio between the time dependent creep strain and the instantaneous elastic strain) of 3.0, and a creep retardation time (the time when 63% of the creep has occurred) between 1 and 2 days compared to the typical retardation time of concrete that ranges between 300 and 900 days . ResultsExternally bonded systems are generally used for strengthening applications when an element is expected to carry increased service loads. Al Chami et al.  tested CWhen manufacturing FRP composites, the resin shrinks during the curing cycle. This occurs due to a chemical loss of volume followed by thermal contraction during cool-down after cure . ShrinkaShao and Mirmiran  tested fDeflections in FRP-RC elements tend to be greater in magnitude with comparable steel reinforcement because of the lower stiffness associated with commercially available FRP reinforcement. FRP reinforced flexural concrete elements typically go through extensive cracking and large deflections prior to failure, which could be considered a warning for failure similar to the concept of ductility for steel-RC elements . HoweverFRP-RC members are more sensitive to the parameters affecting deflection. Generally, the FRP design for flexural strength may not satisfy serviceability criteria for deflection and crack control ,166,167,At present, most of the available design guides and recommendations for FRP reinforced concrete elements are focused on GFRP rebars ,17,18,20The strength and stiffness of the FRP composite may change under harsh environmental conditions and could limit the service life of the structure. Even though FRP rebars do not exhibit corrosion the same way as steel rebars, as referenced earlier, long-term exposure to harsh environments such as moisture and alkaline solutions may deteriorate them and lead to a loss of tensile and bond strength. Furthermore, unlike the visible warning signs of steel-RC elements , the deterioration of FRP rebar does not result in a noticeable increase in volume and hence does not lead to the cracking and/or spalling of the concrete cover ,171. It fuf] as the guaranteed tensile strength [fuf*]  times an environmental reduction factor [EC] to account for the long-term environmental degradation of GFRP bars in service, as shown in Equation (1) and The absence of warning for failure of the FRP-RC element when exposed to harsh environmental conditions can be seen as a deficiency for the FRP-RC members. This is mainly because of the brittle failure characteristic of FRP . To addrAASHTO  states tThe critical glass transition temperature of FRP is generally much lower than that which causes a loss of stiffness in steel. The impact of elevated temperatures of FRP composites is swift and leads to a severe decline in both cross-sectional and bond properties. The critical temperature for tensile reinforcement is traditionally defined as “the temperature at which it experiences a significant loss of strength (50% loss of room temperature yield strength) and becomes unable to sustain applied load”. For reference, this temperature is 593 °C for reinforcing steel . HoweverTo prevent the failure of GFRP reinforcing bars due to creep, the sustained stress must be restricted to the creep rupture stress. This will ensure that the stress levels remain within the elastic range of the member  . DetermiConcrete elements subjected to any load condition resulting in tensile stresses are prone to cracking and, in order to provide a good quality appearance, crack control provisions are aimed at controlling the crack width through the rebar distribution. Moreover, the crack width limits for FRP reinforced concrete elements under service are recommended to limit fluid ingress that could degrade the FRP bars while also ensuring their acceptable aesthetic appearance . The maxShrinkage in concrete can also influence the crack width and, therefore, minimum shrinkage and temperature reinforcement provisions are specified in the design guidelines based on the 0.0018 reinforcement ratio required by ACI 318  for GradFRP laminates along the tension face of RC elements is an effective method to increase the flexural strength where different schemes may be used to install the laminate/sheets . FlexuraThe serviceability limits of the externally strengthened concrete elements are usually limited by the original design  and the condition of the RC element substrate . The avaIn order to avoid inelastic deformations in the existing steel-RC element, the stress in the steel rebars under service load is limited to 80% of the yield strength ,19. In aAs previously discussed, harsh environmental conditions may affect the mechanical properties of the FRP composite  . Table 9GFRP barsOverall, moisture and alkaline environmental conditions have a more degrading influence on GFRP bars than the other environmental factors . When GFIn addition, the mechanical effects also have a significant impact, since the serviceability limit state typically controls the flexural design. Although a similar approach to that of steel-RC structures is used, there are different requirements, such as the creep and fatigue limits, and its limitation for use as a compressive reinforcement. The ACI code establishes a sustained load of a maximum 30% of the design tensile strength . This value includes a 1.67 safety factor and was derived based on creep-rupture tests that projected a 50.7% of the average UTS for a 114-year endurance time . The creCFRP fabricsOn the other hand, for elements strengthened with FRP systems, since they are usually exposed to the weather, the impact can be more severe if adequate protection measures are not taken. The debonding of the interface between the CFRP layer and the concrete is one of the most crucial aspects due to the vulnerability of the resin to harsh environments. In terms of serviceability, the original steel-RC design plays an important role in limiting the stresses and strains in the overall element. When subjected to cyclic loading, it has been observed in most cases  that failure is initiated by the successive yielding of the steel rebars in tension, leading to the debonding of the CFRP laminate, the latter of which is considered to be a secondary failure mode . The ancRecent developments in the FRP industry have resulted in improvements in material properties, overcoming some of the past disadvantages. Cost-related limitations are a market- and project size-varying parameter, and it might be priced the same as steel bars. Furthermore, in terms of bendability, the problem could be addressed with the use of thermoplastic resins so that bars can be bent at the fabricator’s shop instead of during pultrusion. Further research is needed.Harsh environmental exposure can affect the mechanical properties of the FRP composites where tensile and bond properties are most commonly affected. The available data focus mainly on GFRP and BFRP bars for internal application and CFRP laminate/sheets for external application. Notwithstanding the information collected by various authors, it remains inadequate for conducting diverse analyses that would incorporate the impact of various parameters. In certain studies, the results of bars have been combined with those of laminates, and the findings of carbon have been mixed with those of glass, which can lead to mixed test outcomes. Furthermore, some disregard the influence of parameters such as fiber content, type of matrix, bar diameter, etc. This is the main reason why a clear degradation pattern cannot be specified, even for a specific composite . Improvements in material properties also affect the prediction models by enhancing the performance under different environmental/mechanical conditions, therefore making the data from early generations of FRP composites unrepresentative of those of today.Alkaline exposure is the most detrimental exposure to the FRP composites. CFRP remains the composite with the best performance in aggressive environments. GFRP shows good performance in different environments. The environmental reduction factors available in the U.S. design guidelines account for the high pH level of both pore-water solutions and the presence of alkali ions, the mean temperature and the humidity, for an assumed service life of 75–100 years. The studies agreed on the need to conduct field research to evaluate and compare the results of short-term laboratory tests.Code Requirements for Structural Concrete Reinforced with Glass FRP Bars (1st ed.) [LRFD Bridge Design Guide Specifications for GFRP-Reinforced Concrete (2nd ed.) [Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures [Guide Specifications for Design of Bonded FRP Systems for Repair and Strengthening of Concrete Bridge Elements (1st ed.) [Due to its low modulus of elasticity and its special characteristics, FRP reinforced concrete structures perform differently from steel-RC under time-dependent phenomena. This frequently leads to designs that are controlled by serviceability criteria which can differ from that of steel-RC by having stronger reduction factors applied to the strength and strain of the FRP composite. Some of requirements are based on those of the steel approach. Further studies should be conducted to assess the applicability of these limit requirements. While the design approach between the ACI 440.11-22 (1st ed.) ) and AAS2nd ed.) ) for FRPructures ) and AAS1st ed.) ). The [11st ed.)  is becomThis state of the art review is a starting point for future work aimed at understanding the implications of environmental/mechanical effects on FRP-RSC element properties, as well as the approach used to evaluate serviceability limit states and reinforcement requirements. Furthermore, since the number of FRP structures has been increasing, it is likely that guidelines for the inspection of FRP concrete elements will be required.This paper reviewed the state-of-the-art on the durability and mechanical properties of FRP composites when used for FRP-RSC structures. Glass/Vinyl-ester FRP rebars and Carbon/epoxy FRP fabrics were found to be the most commonly used for internal and external applications, respectively. Additionally, the impact on design requirements was discussed further. It is clear from the data review that as improvements in the material properties are developed and more laboratory results are available, less scattering and more confidence exists to select the appropriate factors to account for long-term exposure. The findings can be summarized as follows:


The RAPIDS GN trial, a prospective randomized controlled trial, showed that rapid blood culture antibiotic susceptibility testing (AST) led to faster antibiotic therapy changes compared to standard of care (SOC) testing for Gram negative bacteremia  73:e39-e46). A secondary analysis of the data was conducted to assess impact of rapid testing on appropriateness of antibiotic spectrum by pathogen and resistance profile.Empiric treatment (0 to 2 h post randomization) among subjects with antibiotic-susceptible isolates of monomicrobial, on-panel Gram negative species (N = 320). For this analysis subjects from both SOC and rapid testing groups were included. Black: Excluded from treatment definition if subjects received no antibiotics, antibiotics without susceptibility results reported, or only an aminoglycoside, azithromycin, penicillin, rifaximin, or atovaquone.Antibiotic treatment appropriateness for antibiotic-susceptible Escherichia coli, and Klebsiella and Proteus isolates (N= 240) by time after randomization and treatment arm. Black: Excluded from treatment definition if subjects received no antibiotics, antibiotics without susceptibility results reported, or only an aminoglycoside, azithromycin, penicillin, rifaximin, or atovaquone. AXDX, rapid susceptibility testing group.rd generation cephalosporin non-susceptible or carbapenem-resistant isolates.Subjects enrolled in the RAPIDS GN trial who had blood cultures with monomicrobial Gram negative bacilli that were “on-panel” for the rapid test were included. Antibiotics administered from randomization (0 h) through 52 h were evaluated. Antibiotic therapy was classified based on SOC AST as: undertreatment (antibiotic to which the blood isolate was resistant), appropriate treatment (narrowest spectrum antibiotic to which the blood isolate was susceptible), and overtreatment [overly broad-spectrum antibiotic(s) based on blood isolate AST]. Antibiotic-resistant isolates were defined as 3Antibiotic treatment appropriateness for antibiotic-resistant  Escherichia coli, and Klebsiella and Proteus isolates (N= 50) by time after randomization and treatment arm. Black: Excluded from treatment definition if subjects received no antibiotics, antibiotics without susceptibility results reported, or only an aminoglycoside, azithromycin, penicillin, rifaximin, or atovaquone. AXDX, rapid susceptibility testing group.Escherichia coli, and Klebsiella and Proteus species than for other species . Among 290 E. coli, Klebsiella and Proteus isolates, treatment appropriateness improved with time after randomization in both SOC and rapid testing groups. The proportion with appropriate treatment was higher in the rapid testing group than the SOC group at all time points after 24 h post-randomization and differed by resistance. Overtreatment was common for susceptible isolates while undertreatment was common for resistant isolates . Among resistant isolates, by 52 h post-randomization undertreatment decreased to 15% in the rapid testing group but only 35% in the SOC group .388/448 (87%) subjects were included . Among susceptible isolates, between 0 through 2 h post-randomization (before AST results), overtreatment was more common for E. coli, Klebsiella, and Proteus bacteremia. These findings can inform antibiotic stewardship and design of future blood culture diagnostic trials.In the RAPIDS GN trial, rapid AST had the greatest benefit on management of antibiotic-resistant Ritu Banerjee, MD, Ph.D, bioMerieux: Grant/Research Support|bioMerieux: company is providing partial support for an ongoing trial unrelated to submitted abstract Sarah B. Doernberg, MD, MAS, Basilea: Clinical events committee/adjudication committee participation|F2G: Grant/Research Support|Genentech: Advisor/Consultant|Gilead: Grant/Research Support|Janssen/J+J: Advisor/Consultant|Pfizer: Grant/Research Support|Regeneron: Grant/Research Support|Shinogi: Clinical events committee/adjudication committee participation Robin Patel, MD, Abbott Laboratories: Advisor/Consultant|Adaptive Phage Therapeutics: Grant/Research Support|Adaptive Phage Therapeutics: Mayo Clinic has a royalty-bearing know-how agreement and equity in Adaptive Phage Therapeutics.|BIOFIRE: Grant/Research Support|CARB-X: Advisor/Consultant|ContraFect: Grant/Research Support|Day Zero Diagnostics: Advisor/Consultant|HealthTrackRx: Advisor/Consultant|Mammoth Biosciences: Advisor/Consultant|Netflix: Advisor/Consultant|Oxford Nanopore Technologies: Advisor/Consultant|PhAST: Advisor/Consultant|See details: Patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication with royalties paid by Samsung to Mayo Clinic|See details: continued, patent on an anti-biofilm substance issued|TenNor Therapeutics Limited: Grant/Research Support|Torus Biosystems: Advisor/Consultant|Trellis Bioscience, Inc.: Advisor/Consultant


Mobile health platforms like smartphone apps that provide clinical guidelines are ubiquitous, yet their long-term impact on guideline adherence remains unclear. In 2016, an antibiotic guidelines app, called SCRIPT, was introduced in Auckland City Hospital, New Zealand, to provide local antibiotic guidelines to clinicians on their smartphones.We aimed to assess whether the provision of antibiotic guidelines in a smartphone app resulted in sustained changes in antibiotic guideline adherence by prescribers.We analyzed antibiotic guideline adherence rates during the first 24 hours of hospital admission in adults diagnosed with community-acquired pneumonia using an interrupted time-series study with 3 distinct periods post app implementation .P=.07 vs baseline). However, increased adherence was sustained in patients with pulmonary consolidation on x-ray .Adherence increased from 23% (46/200) at baseline to 31% (73/237) at 3 months and 34% (69/200) at 12 months, reducing to 31% (62/200) at 24 months post app implementation (An antibiotic guidelines app increased overall adherence, but this was not sustained. In patients with pulmonary consolidation, the increased adherence was sustained. Antibiotic stewardship programs in hospitals and community clinics strive to improve rates of appropriate antibiotic prescribing through a wide variety of methods  both to optimize the treatment of patients with bacterial infections and to reduce inappropriate antibiotic prescribing . GreaterA small number of studies have suggested that apps displaying antibiotic guidelines improve antibiotic prescribing behavior in the short term , while tWe performed an interrupted time-series study to test the hypothesis that the provision of the SCRIPT app would increase prescriber adherence to antibiotic guidelines for hospitalized adult patients with CAP. We further hypothesized that adherence to antibiotic guidelines would be higher in cases with chest x-ray evidence of CAP than in cases without chest x-ray evidence of CAP . TheACH has a multifaceted approach to antimicrobial stewardship , which continued unaltered throughout the study period. The hospital antibiotic guidelines remained on the hospital intranet. No other interventions impacting CAP management were introduced during the study period.We retrospectively collected data during 4 periods, as follows: “baseline” pre-app implementation ; “immediate” post-app implementation ; 12-month post-app implementation ; and 24-month post-app implementation .Adult patients (aged ≥18 years) admitted to ACH for ≥4 hours with a discharge diagnosis of CAP  were included. Patients were excluded if they were not diagnosed with CAP during the first 24 hours of admission; had incorrectly coded diagnoses ; or were transferred from another secondary or tertiary care facility where antibiotics had been administered.All CAP cases during each period were identified. We used Microsoft Excel’s random number generator to randomly select ≥200 cases per period . We calculated that inclusion of these case numbers would achieve 90% power to detect an absolute 15% increase in guideline adherence (=.05) .All patients had a chest x-ray at admission to detect radiological features of consolidation, defined as 1 or more opacities in the lung fields consistent with the diagnosis of pneumonia.Electronic health record data were collected using REDCap  to record demographic  and clinical data  as well as antibiotics prescribed  during the first 24 hours post admission.Adherence was defined as prescription of antibiotic(s), including dose(s) and route(s) of administration, according to local guidelines, during the first 24 hours post admission. The ACH antibiotic guidelines for CAP vary by the CURB-65 pneumonia severity score, where a point is given for each of the prognostic features . Cases with a total CURB-65 score of 0-1 were considered to be at low risk (<10%) of mortality; those with a score of 2 were at intermediate risk (10%-20%) of mortality; and a score of 3-5 indicated high risk (20%-60%) of mortality . In caseOther antibiotic(s), prescribed in addition to guideline-adherent antibiotic(s), were considered unnecessary additional antibiotics. Undertreatment was defined as prescription of an inappropriately narrow-spectrum regimen .These definitions were applied by 2 physicians (CHY and SRR) and an infectious diseases specialist pharmacist (EJD) based on the assumption that the patient had CAP, regardless of the presence of pulmonary consolidation on chest x-ray  .Statistical analyses were performed using R . Rates of adherence, use of unnecessary additional antibiotics, and undertreatment were compared between study periods and between cases with or without pulmonary consolidation on the admission chest x-ray (based on the reporting radiologist’s assessment), using Pearson chi-square test or Fisher exact test (significance level: α=.05). One case, in the immediate follow-up group, did not have a chest x-ray and was excluded from analyses that compared patients with or without pulmonary consolidation.All analyses were performed in accordance with the study protocol for which ethics approval was granted .P<.001).The sex, median ages, and ethnicities of the patients in the 4 cohorts were broadly similar . The proP=.01), which was not sustained in the 24-month cohort , there was a nonsignificant increase in prescriber adherence to the antibiotic guideline in the immediate cohort  but a significant increase in adherence in the 12-month cohort  in the baseline cohort to 30% (23/77) in the immediate cohort—a change that was sustained in the 12-month cohort  and in the 24-month cohort ,” guideline adherence was not sustained. The sustained improvement in adherence to the guidelines for treatment of CAP in patients with consolidation on chest x-ray indicates that clinicians were adapting their use of the guideline to increase their use of it in those patients for whom they thought the guideline was most appropriate. This evolution of prescriber use of the guideline over time is an encouraging feature, particularly given the absence of other initiatives to improve prescribing for CAP, suggesting that prescribers were intellectually engaging with the guideline. An appropriate response by those responsible for maintaining and updating the guideline might be to include the presence or absence of consolidation on the chest x-ray as a decision point in the treatment algorithm.The only other published study of the long-term impact of an antibiotic guidelines app on prescriber adherence was performed in 3 hospitals in west London, where baseline rates of adherence were high 75%-90%) [0% [9]. TAlthough very high uptake and use of the app at ACH  enabled this real-world evidence study, there were no data directly matching the use of the SCRIPT app by the clinicians whose antibiotic prescriptions were analyzed in this study, that is, we were not able to measure the direct influence of using the app on individual cases of antibiotic prescription but rather the average net effect of making such an app available. Other limitations included the unmeasured impact of team-based decisions  for antibiotic prescriptions and of junior doctors changing clinical jobs every few months at ACH, moving to or from other hospitals, which would periodically and variably diminish the proportions of doctors using the app at ACH. We were not able to assess the app’s impact relative to other antibiotic stewardship methods nor to other variables that may influence guideline adherence, such as the prescriber’s level of seniority, where they had previously worked, their specialty, and patient-related factors like comorbidity and illness acuity.A range of technological advances, including antibiotic guidelines apps and computerized decision support systems appear to offer opportunities to dramatically improve adherence to prescriber guidelines. However, as with our study, it is rare that such advances provide a silver bullet for the widespread, recalcitrant problem of low adherence to antimicrobial prescribing guidelines. Instead, it is common for such advances to provide modest improvements, commonly of a 10%-20% absolute improvement in guideline adherence, when a 30%-50% absolute increase would have been required to achieve adherence rates above 90% -19. AlthCauses of failure to achieve large changes in antibiotic guideline adherence include within-team dynamics that may contribute to lack of support for changes in prescriber behavior. Junior clinicians, who write almost all prescriptions, may be more influenced by the entrenched opinions of their senior colleagues than by the advice contained in a guideline ,21. OtheOverall, our results suggest that a highly used antibiotic guidelines app can help to increase overall rates of prescriber adherence, especially in those patients with the strongest evidence that they fall into the diagnostic group the treatment advice is intended for and in those patients with more severe diseases. Sustaining increased rates of adherence likely requires refinement of the app algorithms in response to evidence that prescribers are selective in their adherence to guidelines and may respond to clinical features that are not included in the app algorithms. As with all innovations, a continuous process of development, testing, analysis, and modification is necessary to achieve the best results.