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Recycled gypsum powder from waste drywalls is a new alternative that has been recently introduced for partial cement replacement in concrete for construction applications. It has been shown that the recycled gypsum, alongside fly ash, can partially replace cement in concrete to some extent without hurting the required properties of concrete. In this paper, the impact of recycled gypsum content on the durability of concrete (hereafter called gypsum concrete) exposed to different environmental exposures is evaluated. A total of 153 concrete cylinders (100×200 mm) with different recycled gypsum contents (0%, 10%, and 20% of cement replacement) were considered. Each mix was exposed to air-dry, freshwater, seawater, freshwater–air dry cyclic, and seawater–air dry cyclic conditions. The specimens were tested in compression loading after 1,000, 3,000, and 6,000 h of exposure. Recycled gypsum used in this research was in two types of a powder with fine particles only (hereafter called fine gypsum) and in the form of mixed fine, coarse, and paper particles (hereafter called whole gypsum). Other mechanical and physical properties of concrete such as absorption, volume change, and ultrasonic pulse velocity were analyzed. It was observed that the compressive strength of the specimens with 10% and 20% fine gypsum content at Day 28 was about 36% and 40% lower than that of the control specimens, respectively. However, the strength gap was reduced to about 16% and 7% at the end of 6,000 h in the air-dry condition. The specimens submerged in freshwater and seawater showed a rate of strength gain higher than that of the control specimens, bringing the compressive strength of the gypsum concrete specimens slightly higher than that of the control specimens after 6,000 h exposure. Overall, recycled gypsum in combination with fly ash not only does not hurt the long-term strength of concrete but also can enhance the strength under certain conditions, mostly those exposures involving water exposure. [ABSTRACT FROM AUTHOR]

This paper comprehensively summarizes moisture transport, ion transport, and mechanical damage models applied to concrete under sulfate attack and drying–wetting cycles. It highlights the essential aspects and principles of each model, emphasizing their significance in understanding the movement of moisture and ions, as well as the resulting mechanical damage within the concrete during these degradation processes. The paper critically analyzes the assumptions made in each model, shedding light on their limitations and implications for prediction accuracy. Two primary challenges faced by current models under sulfate attack and drying–wetting cycles are identified: the limited consideration of the coupled effects of chemical and physical attacks from sulfate, and the unclear mechanism of the sulfate attacks. Future research directions are proposed, focusing on exploring the transport mechanism of sulfate ions under various driving forces and further clarifying the crystallization process and expansion damage mechanism in concrete pores. Addressing these research directions will advance our understanding of sulfate attack under drying–wetting cycles, leading to improved models and mitigation strategies for enhancing the durability and performance of concrete structures. [ABSTRACT FROM AUTHOR]

This review compiles the main scientific and technical findings on the viability of using paper sludge waste as a supplementary cementitious material in the manufacture of future eco-efficient cements. It contains a detailed analysis of the scientific (characterisation, activation conditions, pozzolanic activity, system reaction kinetics) and technical (rheology, physical and mechanical properties, and resistance to chlorides, sulphates, sea spray and CO 2 ) properties of this type of waste when used as a supplementary cementitious material. On the grounds of the literature reviewed, paper sludge waste can be confirmed to be an environmentally sound source of recycled metakaolinite, a conclusion with significant social and economic benefits. [ABSTRACT FROM AUTHOR]

Abstract: The use of paper-mill residuals in concrete formulations was investigated as an alternative to landfill disposal. The mechanical and durability properties of concrete containing paper-mill residuals collected from a wastewater treatment-plant were evaluated. Class F fly ash was used as a replacement for Portland cement (PC) when incorporated into concrete mixtures containing paper-mill residuals and the resulting products were compared to normal concrete. Compressive, splitting tensile, flexural strength and drying shrinkage tests were carried out to evaluate the mechanical properties for up to 90days. Rapid chloride-permeability tests and initial surface-absorption tests were carried out at 28days to determine the durability properties. Concrete containing paper-mill residuals showed improvement in the durability test results when PC was replaced with class F fly ash. [ABSTRACT FROM AUTHOR]

Concrete durability is greatly influenced by the transport rate of aggressive chemicals. Moisture diffusion plays a key role in the long-term performance of cementitious materials, as it facilitates the entry of aggressive chemicals into concrete. The pore size distribution plays a critical role in determining moisture diffusivity. However, the characteristics of the concrete pore structure have not been included comprehensively in the material models so far. In this paper, a theoretical model was developed to obtain the pore size volume fractions for each diffusion mechanism including Molecular, Knudsen and Surface diffusions. An effective moisture diffusivity in concrete was then obtained using the weighted average based on the diffusion mechanisms and pore size volume fractions. The model's validity was demonstrated by comparing model predictions with available experimental data. The findings of this study provide valuable insights into the behavior of the concrete pore structure and its impact on moisture diffusivity. [ABSTRACT FROM AUTHOR]

The mechanical properties of porous concrete, such as strength and durability, are significantly influenced by moisture transport, particularly in the case of recycled aggregate concretes. The pore distribution and pore size of the concrete, as well as the ambient temperature in the surrounding environment, exert a significant influence on the moisture transport. This paper establishes the fractal Fick’s law, the fractal Darcy law, and the fractal Richards equation. In conclusion, a fractal model for the diffusion and permeability in porous concrete is established. This study examines the mechanisms of moisture diffusion and water permeability in concrete. The comparison of the theoretical prediction with the experimental data indicates a high degree of congruence, thereby suggesting that the concrete’s relative humidity response can be predicted by the established model. This provides a foundation for the optimal design of concrete with required mechanical properties in special applications. [ABSTRACT FROM AUTHOR]

A large number of waste tires are discarded every year. These waste tires will have a great impact on the environment. If they can be recycled, environmental and economic benefits can be obtained. In this paper, rubber powder is added to concrete, and a variety of analytical methods are used to study the effect of rubber powder on the performance of concrete. Experiments show that the slump of concrete decreases with the increase of rubber powder substitution rate, and the rheological performance results show that the friction force increases with the increase of rubber powder substitution rate. The compressive strength of concrete decreases with the increase of substitution rate. The results of ICP show that rubber powder will adsorb cations to affect cement hydration. Nanoindentation shows that the addition of rubber powder leads to the decrease of high-density hydration products. The results of SEM-EDS show that rubber powder will affect the Si/Ca of hydration products. The results of UPV and MIP are similar. The hydrophobicity of rubber powder and the poor compatibility with hydration products are the key factors affecting the durability of concrete. Because the rubber powder only needs to be ground to avoid the related process of cement, it can obtain good economic and environmental benefits. In practical engineering, rubber powder can be added appropriately. [ABSTRACT FROM AUTHOR]

Due to rising living standards and population growth, saving fresh water will be a significant problem for the next generation. The Government is indirectly impacted by a significant financial burden due to the current usage of treated wastewater, in all of Egypt’s districts. As a case study, Egypt’s new administrative capital was chosen, given that it is today one of the most important cities and that its planning was predicated on making it a smart, sustainable city. The goal of the study was to develop methods for replacing potable water in the manufacture of concrete with tertiary-treated wastewater; however, used for concrete mixing or curing after concrete hardening. Property assessments of the fresh and hardened concrete were conducted, to ascertain the best water quality that can be used without compromising the quality or durability of the concrete. ; The results of this paper will serve as a guide for decision-makers looking to decrease costs and increase sustainability by using treated wastewater in making sustainable concrete for buildings, especially in recent decades, rising construction material usage has generated considerable environmental difficulties, particularly in the production of Ordinary Portland cement (OPC). [ABSTRACT FROM AUTHOR]

This paper describes a study of the chloride content in the concrete lagging of prestressed concrete elements of the roof structure of an aluminium foundry building. Sources of chloride pollution in industrial facilities are discussed. Methods for collecting dust deposited on the structure and sampling concrete for chloride concentration testing are presented in detail. The test methods used and the apparatus used to assess the chloride content at the thickness of concrete reinforcement lagging are presented. Investigations of the chloride content in the concrete of the reinforcement cover showed a very high concentration of chloride in the near-surface layer, depending on the location of the element in relation to the source of chloride emission into the environment. In contrast, the concrete of the deeper layers of the lagging contained very small amounts of Cl− chlorides. The results of the chloride content of the lagging concrete were plotted against the distance from the surface of the specimen and approximated by the function C(x,t) based on Fick's second law and its solution. A satisfactory fit of the course of this function to the experimental results was obtained. Based on the obtained C(x,t) function, the durability of the main structural components of an aluminium foundry industrial hall operating in a chloride environment was estimated. [ABSTRACT FROM AUTHOR]

Polypropylene fiber reinforcement is an effective method to enhance the durability of concrete structures. With the increasing public interest in the widespread use of polypropylene fiber reinforced concrete (PFRC), the necessity of evaluating the mechanism of polypropylene fiber (PF) on the permeability of concrete has become prominent. This paper describes the influence of PF on the concrete permeability exposed to freeze-thaw cycles under compressive and tensile stress. The permeability of PFRC under compressive and tensile loads is accurately measured by a specialized permeability setup. The permeability of PFRC under compressive and tensile loads, the volume change of PFRC under compressive load, and the relationship between compressive stress levels at minimum permeability and minimum volume points of PFRC are discussed. The results indicate that the addition of PF adversely affects the permeability of concrete without freeze-thaw damage and cracks. However, it decreases the permeability of concrete specimens exposed to freeze-thaw cycles and cracking. Under compressive load, the permeability of PFRC initially decreases slowly and follows by a significant increase as the compressive stress level increases. This phenomenon correlates with the volume change of the specimen. The compressive stress level of the minimum permeability point and compressive stress level of the minimum volume point of PFRC exhibit a linear correlation, with a fitted proportional function parameter γ ≈ 0.98872. Under tensile load, the permeability of PFRC increases gradually with radial deformation and follows by a significant increase. The strain-permeability curves of PFRC under loading are studied and consist of two stages. In stage I, the permeability of PFRC gradually decreases with the increase of strain under compressive load, while the permeability increases with the increase of strain under tensile load. In stage II, under compressive load, the permeability of PFRC increases with the increase of freeze-thaw cycles, whereas under tensile load, the permeability gradually decreases with the increase of freeze-thaw cycles. The reduction of PF on the permeability of PFRC under tensile load is greater than that under compressive load. In future research, the relationship between strain and permeability of PFRC can be integrated with its constitutive relationship between stress and strain to provide a reference for the application of PF in the waterproofing of concrete structures. [ABSTRACT FROM AUTHOR]

This work examined the performance of self-heating concrete under laboratory thermal conditions and outdoor real-time conditions during the fall and winter seasons. Snow-melting and freeze–thaw performance of low-temperature phase change materials (PCM) incorporated self-heating concrete slabs in various scales were evaluated. PCM exhibited high enthalpy of fusion (ΔHf≈170–180 J/g), long-term thermal stability, and desirable supercooling. The experimental program included (1) optimization of concrete mix designs for maximum PCM incorporation, (2) characterization of thermal properties of PCM-mortar specimens using longitudinal guarded comparative calorimetry (LGCC), and (3) large-scale PCM concrete slabs in outdoor conditions to evaluate the real-time thermal performance against freeze–thaw events and snow-melting efficiency. Two different approaches were used to incorporate PCM in concrete: (1) submersion of liquid PCM in porous lightweight aggregates (PCM-LWA); and (2) microencapsulated PCM (MPCM). Both PCM-LWA and MPCM concrete not only exhibited promising snow-melting capabilities but also lowered the number of freeze–thaw cycles during cold seasons. PCM-LWA concrete performed better in decreasing the number of freeze–thaw (F-T) cycles due to the undercooling phenomenon created by the LWA pore network confinement pressure, allowing gradual latent heat release; the undercooling phenomenon in PCM-LWA results in phase transformation in a wider low-temperature range (i.e., 3.94°C to −13.04°C). Therefore, the PCM-LWA concrete was effective in melting snow within a wider range of low temperatures. MPCM concrete was found to provide a rapid melting capability during a snowfall event due to its "one-shot" heat release phenomenon. Both LWA-PCM and MPCM concrete slabs demonstrated promising heat response and snow-melting capability. Snowfall and freeze–thaw cycles occur frequently during winter seasons in North American regions with cold climate, resulting in snow accumulation on concrete roads and flatworks as well as concrete freeze–thaw damage. In this paper, a "self-heating" concrete was developed via incorporation of low-temperature phase change material (PCM), and its promising snow removal and freeze–thaw improvements were validated. The self-heating concrete can be used to construct pavements, driveways, bridge decks, and any other types of flatworks. When the ambient temperature falls to ∼0°C , PCM will release desirable amounts of heat energy (ΔHf=170–180 J per g of PCM added) by changing its phase from liquid to solid. As a result, the accumulated snow and ice melts at a gradual pace. In addition, heat release from the incorporated PCM lowers the number of freeze–thaw cycles, improving freeze–thaw performance of concrete made elements in cold regions, which in turn improves concrete durability and service life by minimizing the susceptibility to freeze–thaw scaling and spalling. [ABSTRACT FROM AUTHOR]

Rubber concrete has been applied to a certain extent in fatigue-resistant structures due to its good durability. Based on a cohesive model of rubber composed of a five-phase material containing mortar, aggregate, rubber, aggregate-mortar interfacial transition zone (ITZ), and rubber-mortar ITZ, this paper studies the influence of the cohesive parameters in the rubber-mortar ITZ on the fatigue problem of rubber concrete on the mesoscopic scale. As the weak part of cement-based composite materials, the ITZ has a great influence on the mechanical properties and durability of concrete, but the performance of the ITZ is difficult to test in macro experiments, resulting in difficulties in determining its simulation parameters. Based on the cohesive model with a rubber content of 5%, this study uses Monofactor analysis and the Plackett-Burman test to quickly and effectively determine the primary and secondary influences of the cohesive model parameters in the rubber-mortar ITZ; further, the response surface method is used to optimize the cohesive parameters in the rubber-mortar ITZ, and the numerical simulation results after optimizing the cohesive parameters are compared and analyzed with the simulation results before optimization. The results show that, under the setting of the optimized parameters, the simulation results of each item of the optimal cohesive model parameters in the rubber-mortar ITZ are in line with the reality and closer to the experimental data, and they are also applicable to rubber concrete models with different rubber dosing. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present the methodology used to validate the threshold levels of durability indicators from data acquired from existing reinforced concrete structures that may present corrosion problems resulting from carbonation or chloride ingress. This study was conducted in the framework of the French National Project PERFDUB in close collaboration with the MODEVIE ANR project. Durability tests form the basis of a performance‐based approach for the durability of concrete structures, and in order to set the threshold level for each of these durability indicators, it is important to take into account the experience feedback that can be obtained from the actual behavior of existing structures. This paper presents the investigations carried out on eight reinforced concrete structures, all of them having an age well in excess of 50 years, and the main data gathered on some relevant durability and lifetime indicators. Based on all these data, predictive models of carbonation and chloride penetration are applied in order to validate the threshold levels to be adopted for the durability indicators, and several other conclusions are drawn. [ABSTRACT FROM AUTHOR]

The present paper highlight upon research work is that curing is one of most important aspect of construction. The life of concrete and its serviceability depends heavily on curing. The method of curing applied on concrete will affect its final strength and durability. Owing to this fact this paper contains the research done on concrete under various curing methods. The standard method of curing concrete is done by water and results wastage of a lot of water. With the increase in the deficiency of availability of water, curing becomes a problem. Hence this research aims at providing better methods of curing which will not only improve the strength and durability of concrete but will also save water. The various methods that have been researched upon are plastic covered curing, addition of sodium silicate to curing water, and addition of curing compounds to curing water. The tests are carried on concrete with desirable strengths of M15 and M20. In this research the fine aggregate used in making of M15 and M20 concrete consists of a mixture of sand and crusher dust. Two mixes of ratio 50:50 and 60:40, sand to crusher dust have been taken and the effects of curing on these mixes are considered. Plastic curing is done by covering the concrete with plastic soon after demolding. Hence minimum water is required. The curing done by sodium silicate is done by adding 2% by weight of sodium silicate to curing water. Concrete is submerged in water containing sodium silicate. Once the concrete is cured, this water mix can be reused to cure freshly cast concrete, thereby saving more water. Curing by curing compounds is done in a similar way as that of curing with sodium silicate, only that instead of sodium silicate, curing compounds are used. The effect of these three methods on concrete is studied and discussions are made. [ABSTRACT FROM AUTHOR]

Cracks are inevitable in concrete structures, and the deterioration of concrete crack interfaces in intertidal zones is often accelerated due to seawater dry–wet cycles. This paper aims to analyze the morphology and deterioration of crack interfaces under seawater dry–wet cycles. First, concrete crack surface specimens were obtained through splitting tests. Then, the specimens were placed in seawater solutions of different concentrations to undergo seawater dry–wet cycles. Furthermore, three-dimensional (3D) laser surface profile scanning was performed on the specimens after 0, 10, 30, and 60 seawater dry–wet cycles. Finally, the changes in morphological parameters were analyzed and calculated to derive the effect patterns of seawater dry–wet cycles on the 3D morphology of concrete crack interfaces. The results showed that the crack surface deterioration of the specimens in clear water was only affected by the dry–wet cycles, while that in seawater was jointly affected by seawater erosion and dry–wet cycles. The crack surface deterioration of the specimens in seawater can be divided into two stages. In the first 10 seawater dry–wet cycles, the chemical products generated by seawater erosion played a dominant role. The 3D morphological parameters and 3D fractal dimension changes of the specimens in seawater showed opposite trends to those in clear water. From the 10th seawater dry–wet cycle, erosion and flaking by the dry–wet cycles were dominant. The changes in the 3D morphological parameters and 3D fractal dimension of the specimens in seawater were consistent with those in clear water. Moreover, higher seawater concentrations led to more significant trends in the crack surface 3D morphological parameter and 3D fractal dimension changes. Concrete structures are common in marine engineering, such as port wharves, sea crossing bridges, drilling platforms, and island reef revetments. Concrete structures exposed to tides/splashes for long periods are susceptible to seawater dry–wet cycles, which may lead to structural cracking during their service life. To ensure the safety and service life of concrete structures, cracks must be addressed with repairs or reinforcements. Numerous studies have shown that the concrete crack surface morphology determines the repair and reinforcement effects and affects the interfacial bonding performance, mechanical properties, and durability. Therefore, studying the surface morphology variation patterns of concrete cracks under seawater dry–wet cycles is important for concrete repair and reinforcement. In this paper, we produce concrete cracks through splitting and conduct seawater dry–wet cycle tests on concrete crack interfaces under different seawater concentrations to study the 3D morphological characteristics of cracks under seawater dry–wet cycles and provide experimental data to reveal the concrete crack surface changes for future repair. This study could serve as a guideline for repairing cracks in concrete structures in tidal/splash zones. [ABSTRACT FROM AUTHOR]

Phosphorus tailings are solid wastes generated from mineral processing. It limits the green development of phosphorus chemical industries. Phosphorus tailings mainly consist of dolomite, fluorapatite, and quartzite, so they are used as mineral admixtures to prepare concrete, which not only reduces carbon emissions but also eliminates phosphorus tailings and solves the issues caused by the large accumulation of phosphorus tailings. In this paper, C40 concrete was prepared with different content and fineness of phosphorus tailings, and the effects of phosphorus tailings on its workability, mechanical properties, and durability were investigated. The harm of heavy metals leaching of concrete mixing with phosphorus to the environment was evaluated. The mechanism of the effect of phosphorus tailings on concrete was also analyzed by using characterization methods such as heat of hydration, XRD, and SEM. The results showed that the workability of concrete increased with the phosphorus tailings amount increased, but the mechanical property of concrete decreased. The fineness of phosphorus tailings has little effect on the workability and mechanical properties of concrete. The durability properties of concrete were impaired with the increase in the admixture of phosphorus tailings, but the fineness of phosphorus tailings has no significant effect on the durability properties of concrete. With the increase of the curing time, the structure of the concrete mixed with phosphorus tailings became denser than the concrete without phosphorus tailings incorporated. The concrete mixing with phosphorus tailings had little detriment to the environment. Finally, using the particle size of 20 μm and the content of 20% of phosphorus tailing to replace the cement was suggested. [ABSTRACT FROM AUTHOR]

Freeze-thaw resistance ability of concrete is an important issue when evaluating its durability. In this research, the objective was to predict concrete resistance to such cycles by analyzing water absorption based on the critical water saturation theory. In order to achieve this goal, detailed experiments were conducted, including water absorption, pore structure scanning, and mercury intrusion porosimetry of concrete with air-entraining admixture and different fiber content to obtain critical indicators, such as water absorption, porosity, and air void spacing factor, which formed the basis for predicting the service life of concrete. To predict the service life of concrete under freeze-thaw cycles, the critical saturation theory was utilized, taking into account environmental parameters and experimental indexes. The service life of concrete against freeze-thaw using air-entraining admixture and fibers had been calculated quantitatively in this paper. The results show that the predicted service life of concrete with air-entraining admixture was increased by more than 50 times, and using both air-entraining admixture and fiber could increase the service life by more than 80 times, even reaching 249 years. [ABSTRACT FROM AUTHOR]

The durability of concrete structures, which are designed for long- -term use is predominantly determined by the resistance to chemical influences, i.e., the concrete's ability to protect the reinforcement steel. The carbonation and the chloride ingress into concrete are the most significant causes of steel corrosion and the potential failure of the structure. The primary goal is to ensure that any significant damage does not occur during the structure's service life, primarily achieved by selecting an adequate thickness of the concrete cover. The issue is approached through calculations based on performance analyses, and the use of appropriate models for these chemical phenomena. The paper provides a brief overview and the methodology for analysing the impact on the durability of concrete structures in accordance with the leading international normative documents. The emphasis is on the recent changes introduced in second generation of European Eurocode standards. The consequences of the analysed phenomena are presented through the results of field tests conducted at salt factories, coke industries, and thermal power plants, and through laboratory tests. The tests were performed in order to develop a rapid prediction method for the measure of chloride ingress into concrete without the stimulating chloride ion migration by electricity, as an alternative to standardized tests. [ABSTRACT FROM AUTHOR]

Organic corrosion inhibitors (OCI) have been widely accepted as a reliable method for enhancing the durability of marine reinforced concrete structures. However, the effect of OCI on steel corrosion is not clear in the case of cracks appearing in the concrete cover. In this paper, steel corrosion behaviors in cracked concrete with different crack widths, intact concrete containing OCI, and cracked concrete containing the OCI exposed to the marine tidal zone were investigated through open-circuit potential tests and EIS measurements. The obtained results illustrate that the corrosion rate of steel in cracked concrete is reduced with the decrease of crack width having an initial width of less than less than or equal to 200 μm in the marine tidal zone. Based on the Rf and Rct values, it is found that the alcohol amine-based OCIs can improve the corrosion resistance of steel in intact concrete and concrete with microcracks (with a width of less than 100 μm) exposed to the marine tidal zone. The carboxylic acid-based OCIs aggravate the steel corrosion due to the hydrophobicity provided by carboxylic acids for seawater transport through cracks. The ester-based OCIs also increase the steel corrosion rate as it accelerates concrete carbonation. [ABSTRACT FROM AUTHOR]

The porosity of concrete affects the durability of reinforced concrete structures, wherein high levels of porosity are linked to a shorter service life. Recent works have noted that high porosity levels naturally exist in the aftermath of a fire exposure - especially when concrete is classified as high strength concrete (HSC). To shed more light into this phenomenon, this paper showcases a method for measuring the porosity of HSC under elevated temperatures through scanning electron microscopy (SEM). In this method, SEMbased images were examined to quantify the surface porosity of fire-affected HSC. Detailed image analysis was performed for HSC exposed to various heating durations. The study concludes that the surface porosity obtained via the SEM processing method is in good agreement with that from the SEM-based method (with a minor average difference of 3.8%). As such, the proposed method is expected to be reliable for the porosity analysis of fire-damaged concrete. [ABSTRACT FROM AUTHOR]

As a pozzolan, waste glass powder (WGP) can improve the mechanical properties and durability of concrete, especially at a later age. However, the modification mechanisms should be fully understood and discussed. One of the effective approaches is to investigate the improvement in interfacial transition zones (ITZs) between aggregate and mortar matrix. In this paper, soda-lime WGP was used as a supplementary cementitious material and replaced 20% by weight cement in the sample with modeled aggregate. The phases and chemical composition within the ITZs and the adjacent mortar matrix were investigated by backscattered electron (BSE) imaging combined with image analysis. Advanced nanomechanical techniques were simultaneously applied, and the results obtained from nanoindentation and nanoscratch were compared. The results show that WGP can significantly reduce the width of ITZs and increase the content of calcium-silicate-hydrate (C-S-H) and Si/Ca ratio in both ITZs and matrix. The high heterogeneity of ITZ with WGP made it susceptible to errors caused by unreacted WGP during the measurement of C-S-H nano- and micromechanical properties. For the control group without WGP, the test results of nanoindentation and nanoscratch showed a high degree of consistency. However, for the samples with 20% by weight WGP, there are some differences in the test results between nanoindentation and nanoscratch. Nanoscratch was able to acquire abundant data in a short testing time and proved more suitable for the tests of homogeneous materials. On the other hand, for the sample with 20% by weight WGP, nanoindentation was found to more likely to reflect the real micromechanical properties of ITZs based on abundant indentation tests. [ABSTRACT FROM AUTHOR]

The moisture content within the concrete pore network significantly influences the mechanical, thermal, and durability characteristics of concrete structures. This paper introduces a novel fully embedded wireless temperature and relative humidity sensor connected to an automatic acquisition system designed for continuous concrete monitoring. Relative humidity measurements from this new sensor are compared with those obtained by a commercial system based on the borehole method at different depths (2.5 and 4.0 cm) and exposure conditions (oven drying and humid chamber). The results allow for proving that both systems provide consistent internal relative humidity measurements aligned with the exposure conditions and highlight the capability of fully embedded wireless sensors as a practical and reliable alternative to the conventional borehole method. Additionally, the continuous monitoring of the wireless cast-in sensor exhibits reliability during unintended temperature fluctuations, emphasizing the effectiveness of permanently installed sensors in promptly detecting unintended curing variations in real time. The continuous real-time information provided combined with the practicality of these sensors might assist construction managers to improve the quality control of the concrete curing process and shrinkage behavior, and ensure the integrity of concrete surface finishing. [ABSTRACT FROM AUTHOR]

Chloride ion corrosion has been considered to be one of the main reasons for durability deterioration of reinforced concrete structures in marine or chlorine-containing deicing salt environments. This paper studies the relationship between the amount of fly ash and the durability of concrete, especially the resistance to chloride ion erosion. The heat trend map of total chloride ion factor correlation displayed that the ranking of factor correlations was as follows: sampling depth > cement dosage > fly ash dosage. In order to verify the effect of fly ash dosage on chloride ion resistance, three different machine learning algorithms (RF, GBR, DT) are employed to predict the total chloride content of fly ash proportioned concrete with varying admixture ratios, which are evaluated based on R2, MSE, RMSE, and MAE. The results predicted by the RF model show that the threshold of fly ash admixture in chlorinated salt environments is 30–40%. Replacing part of cement with fly ash in the mixture of concrete below this threshold of fly ash, it could change the phase structure and pore structure, which could improve the permeability of fly ash concrete and reduce the content of free chloride ions in the system. Machine learning modeling using sample data can accurately predict concrete properties, which effectively reduce engineering tests. The development of machine learning models is essential for the decarbonization and intelligence of engineering. [ABSTRACT FROM AUTHOR]

The durability of concrete is critical for the service life of concrete structures, and it is influenced by various factors. This paper investigates the impact of the relative humidity (RH) of the curing environment on the durability of five different concrete types. The aim is to determine a suitable approach for designing concrete that is well-suited for use in the salt lake region of Inner Mongolia. The concrete types comprise ordinary Portland cement (OPC), high-strength expansive concrete (HSEC), high-strength expansive concrete incorporating silica fume, fly ash, and blast furnace slag (HSEC-SFB), steel fiber-reinforced high-strength expansive concrete (SFRHSEC), and high elastic modulus polyethylene fiber-reinforced high-strength expansive concrete (HFRHSEC). All these concrete types underwent a 180-day curing process at three distinct relative humidities (RH = 30%, 50%, and 95%) before being subjected to freeze–thaw cycles in the Inner Mongolia salt lake brine. The curing environment with a 95% RH is referred to as the standard condition. The experimental results reveal that the durability of OPC and HSEC decreases significantly with increasing relative humidity. In comparison with the control sample cured in 95% RH, the maximum freeze–thaw cycles for concrete cured in lower RHs are only 31% to 76% for OPC and 66% to 77% for HSEC. However, the sensitivity of the durability of HSEC-SFB, SFRHSEC, and HFRHSEC to variations in RH in the curing environment diminishes. In comparison with the corresponding reference value, the maximum freeze–thaw cycles for samples cured in dry conditions increase by 14% to 17% for HSEC-SFB and 21% for SFRHSEC. Specifically, the service life of HFRHSEC cured in a low RH is 25% to 46% higher than the reference value. The durability of HSEC-SFB, SFRHSEC, and HFRHSEC has been proven to be appropriate for structures located in the salt lake region of Inner Mongolia. [ABSTRACT FROM AUTHOR]

The widespread use of carpets in residential and commercial buildings and their relatively short life span result in large volumes of carpet being landfilled. A potential solution to this problem is the use of post-consumer carpet fibers in concrete. To this end, this paper systematically identifies the common fiber types in a typical post-consumer carpet fiber bale and evaluates their durability under exposure to varying levels of alkalinity. The tensile strengths and toughness of the fibers belonging to the nylon and polyethylene terephthalate (PET) families (the dominant fibers in most post-consumer carpets) are reduced by up to 50% following exposure to extreme alkalinity, the reasons for which are determined using spectroscopic and microscopic evaluations. The chloride ion transport resistance of concretes (~40 MPa strength) containing 2.5% carpet fibers by volume (~25 kg of fibers per cubic meter of concrete) is comparable to that of the control mixture, while mortar mixtures containing the same volume fraction of carpet fibers demonstrate negligible enhancement in expansion and loss of strength when exposed to 1 N NaOH. This study shows that moderate-strength concretes (~40 MPa) for conventional building and infrastructure applications can be proportioned using the chosen volume of carpet fibers without an appreciable loss of performance. Consideration of low volume fractions of carpet fibers in low-to-moderate-strength concretes thus provides a sustainable avenue for the use of these otherwise landfilled materials in construction applications. [ABSTRACT FROM AUTHOR]

Cold weather conditions pose significant challenges to the performance and durability of concrete materials, construction processes, and structures. This paper aims to provide a comprehensive overview of the material-related challenges in cold weather concrete construction, including slow setting, reduced curing rate, and slower strength development, as well as frost damage, early freezing, and freeze–thaw actions. Various innovative materials and technologies may be implemented to address these challenges, such as optimizing the concrete mix proportions, chemical admixtures, supplementary cementitious materials, and advanced construction techniques. The paper also examines the impact of weather-related challenges for personnel, equipment, and machinery in cold environments and highlights the importance of effective planning, communication, and management strategies. Results indicate that the successful implementation of appropriate strategies can mitigate the challenges, reduce construction time, and enhance the performance, durability, and sustainability of concrete structures in cold and freezing temperatures. The paper emphasizes the importance of staying updated about the latest advancements and best practices in the field. Future trends include the development of smart and functional concrete materials, advanced manufacturing and construction techniques, integrated design, and optimization of tools, all with a strong focus on sustainability and resilience. [ABSTRACT FROM AUTHOR]

The paper concerns destructive and non-destructive (NDT) evaluation of the effect of the addition of superabsorbent polymer (SAP) used as a carrier of mixing water and a means of internal curing on the durability of concrete. The research concerns testing of five concretes—an ordinary reference concrete and four concretes differing in the content of mixing water introduced into the concrete mix in the form of pre-saturated SAP particles (25%, two variants of 50% and 75% of the total mixing water in the form of SAP hydrogel). The research consisted of 4 stages of tests. The subsequent stages involved the analysis of the effect of using SAP as a carrier of mixing water on the particular characteristics of concrete mix and hardened concrete, i.e., consistency and density of concrete mix (1st stage), carbonation tested using two indicators—phenolphthalein and thymol phenolphthalein (2nd stage), and finally: the homogeneity of the concretes' structure by means of ultrasonic method (determination of ultrasonic pulse velocity) 28 days after production (3rd stage) and 3 years after production (4th stage). The ultrasonic pulse (or wave) velocity was then correlated with the content of water applied in the form of SAP hydrogel. The statistical analysis of results showed that the method of introducing the mixing water into the concrete mix in the form of pre-absorbed superabsorbent polymer, although it changed the concrete mix consistency, did not significantly affect the concrete ability to resist carbonation. Meanwhile, after 3 years, the densification of the microstructure of concrete with SAP has been observed. [ABSTRACT FROM AUTHOR]

Durability plays a crucial role in maintaining the service life of a structure. This paper focuses on examining the durability of a building with a reinforced concrete structure that has been exposed to an offshore environment for 35 years. The study involved on-site inspections to assess external damage, including testing parameters such as the compressive strength of the concrete material and the overall tilt of the building. Additionally, microscopic inspection techniques, such as X-ray fluorescence (XRF), thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM), were employed to analyze the corrosion products and microstructure associated with the damage mechanism. Based on the data obtained from the on-site inspections, structural calculation software was used to calculate and verify the overall load-bearing capacity of the building, aiming to determine its safety level. The evaluation results revealed severe safety issues within the building, despite it not having reached its designed service life, particularly in relation to reinforcement corrosion. [ABSTRACT FROM AUTHOR]

The causes of cracks in concrete are varied, and regardless of their origin, these cracks invariably have a detrimental impact on the durability of concrete structures and escalate their maintenance costs. This paper presents a comprehensive review of current knowledge regarding the methods of self-healing in concrete, ranging from autogenic and improved autogenic self-healing to the autonomous self-healing of concrete. Particular emphasis is placed on the methods of autonomous concrete self-healing: the bacterial healing method, the crystalline hydrophilic additives healing method, and the capsule-based self-healing method. The hypothesis is that applying these self-healing methods could potentially prevent damages or cracks in concrete caused by freeze–thaw cycles, thereby extending the lifespan of concrete structures. The mechanism of action and current achievements in the field are provided for each method. [ABSTRACT FROM AUTHOR]

Freeze–thaw (F-T) is one of the principal perils afflicting concrete pavements. A remedial strategy used during construction encompasses the integration of hybrid fibers into the concrete matrix. An extant research gap persists in elucidating the damage mechanism inherent in hybrid steel fiber (SF)- and basalt fiber (BF)-reinforced concrete subjected to F-T conditions. This paper empirically investigated the durability performance of hybrid fiber-reinforced concrete (HFRC) subjected to F-T cycles. The impact of SF/BF hybridization on mass loss, abrasion resistance, compressive strength, flexural strength, damaged layer thickness, and the relative dynamic modulus of elasticity (RDME) was examined. The damage mechanism was explored using micro-hardness and SEM analysis. The results indicate that incorporating hybrid SF/BF effectively enhances the F-T resistance of concrete and prolongs the service life of concrete pavement. The mechanisms underlying these trends can be traced back to robust bonding at the fiber/matrix interface. Randomly dispersed SFs and BFs contribute to forming a three-dimensional spatial structure within the concrete matrix, suppressing the expansion of internal cracks caused by accumulated hydrostatic pressure during the F-T cycle. This research outcome establishes a theoretical foundation for the application of HFRC to concrete pavements in cold regions. [ABSTRACT FROM AUTHOR]

This paper studied the effects of basalt fibers (BF), polypropylene fibers (PF), end-hooked steel fibers (HSF), and wavy steel fibers (WSF) on the durability (impermeability and frost resistance) and mechanical properties (compressive, flexural, uniaxial tensile, and splitting tensile strength) of concrete based on the original mix proportion (water-binder ratio of 0.41). The results demonstrate that 0.5% of HSF has the best impact on enhancing concrete's compressive, flexural, and splitting tensile strength, with improvements of 10.88%, 21.02%, and 16.76%, compared to the control group. Meanwhile, 0.2% of BF has the best impact on improving the uniaxial tensile strength of concrete, with an improvement value of 18.91%. For concrete impermeability and frost resistance, 0.1% and 0.2% BF were the optimal fiber and content. However, PF was not very effective in improving the durability and mechanical property of concrete. Considering the scope of the investigated fiber content, the mechanical properties of concrete declined as fiber content rose. Still, the uniaxial and splitting tensile strengths improved as BF content rose. As the content of fiber in concrete increased, its impermeability weakened, and its ability to frost resistance improved. The above conclusions are highly significant for selecting fiber concrete types in future studies. [ABSTRACT FROM AUTHOR]

External sulfate attack is a remarkable and complex phenomenon of degradation of cement matrixes. This paper proposes a method to calculate sulfate diffusion coefficients based on ion migration testing, in order to establish parameters for concrete service life prediction models based on a fast test. The influence of the type (sodium and magnesium) and concentration (5% and 10% SO42−) of the sulfate solution for a concrete matrix was evaluated in the tests. Sulfate concentrations were monitored by measuring the electrical conductivity of the anode compartment. The results were validated by comparing them with those obtained in natural diffusion tests. Similar sulfate profiles were obtained for concrete samples after 1 month of migration and after 3 and 6 months of diffusion, mainly for magnesium sulfate. The greatest correlations between the calculated diffusion coefficients were achieved at higher concentrations of SO42− in the cathode compartment. The results indicated that the proposed migration method enables the calculation of the sulfate diffusion coefficients in concrete. [ABSTRACT FROM AUTHOR]

Carbon dioxide, or CO2, is responsible for most global greenhouse gas emissions. Sequestering CO2 in concrete can potentially reduce carbon emissions while simultaneously improving concrete's characteristics. This study's main objective is to use carbon dioxide in the Ready-Mix Concrete (RMC) during the mixing phase. This study also investigates the effects of carbon dioxide incorporation on the properties of concrete at different dosages (0% to 0.20% by weight of the binder) and binder types such as Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC). Through a detailed experimental study, the paper seeks to understand the changes in the various mixes' fresh, hardened, and microstructural properties. The results indicate that carbon dioxide had no adverse effect on fresh concrete properties, with minor changes leading to improved performance in concrete samples at precise dosages. The microstructural results reveal that the concrete tends to densify by utilizing the optimum dosage of carbon dioxide and thus achieve the best performance. Concrete mixtures treated with CO2 showed increased compressive strength; 0.10% CO2 in OPC-based mixes gave up to 30% benefit, and 0.05% in PPC-based mixes gave up to 25%. PPC-based had the highest compressive strengths at later ages, OPC-based at early ages. The time of set was reduced by 18% in OPC mixes and 28% in PPC mixes. Furthermore, the addition of CO2 during mixing had a positive impact on the concrete's durability. Therefore, it can be concluded that utilizing CO2 in concrete can help produce sustainable RMC with enhanced properties and reduced emissions. [ABSTRACT FROM AUTHOR]

The laboratory test and numerical calculation were carried to explore the durability and service life of the grout-reinforced geological foundation. In this paper, the simulation test for determining penetration properties of grouting was carried out with the self-designed experimental device, and the mechanical properties and permeability coefficient were obtained. The results show that the seawater ions corroded the grout-reinforced body, and the properties had deteriorated. Meanwhile, the service life cycle prediction model was obtained according to the weakening of the deformation modulus. The calculated results demonstrate that the grout-reinforced body will fail in 29–63 years, which was far less than the concrete service life (100–120 years). In addition, the compressive strength obtained after the end of the service life was obtained as 9–27 MPa, less than the concrete strength at the same curing age. In conclusion, the failure of marine engineering is not only caused by concrete but more by the failure of the weak geological foundation strengthened by the grouting reinforcement. [ABSTRACT FROM AUTHOR]

In practice, assessing the mechanical behavior of seawater sea sand concrete under severe environmental conditions is urgently needed to evaluate the service life of the prepared concrete. In this paper, the influence of carbonation on the mechanical properties, especially the stress–strain relationship of seawater and sea sand concrete (SSC), sea sand concrete (SC), and ordinary concrete (OC), were investigated by experimental and theoretical means. The microstructural analysis revealed that SSC and SC have higher CO2 sequestration than OC. Although the compressive strength of all concrete specimens increased during the carbonation time, the net increase of compressive strength (excluding cement hydration) contributed by the carbonation of SSC and SC was less than that of OC. The stress–strain curves' ascending branches of the three types were roughly similar; for the descending branch, the slope of SSC and SC became steeper compared with OC after carbonation. The results also revealed that the brittleness of SSC and SC increased orderly with the extension of carbonation time. Finally, an empirical expression for the stress–strain relationship of SSC and SC considering the effect of carbonation was proposed, which provides an analytical base for concrete structure design and practical application for marine infrastructures. [ABSTRACT FROM AUTHOR]

During the service life of reinforced concrete beams (RC beams), they may experience impact loadings induced by various falling objects, such as falling rocks and fragments of upper floors. Therefore, the RC beam's impact resistance is important to its application in structures. This paper investigated the impact mitigation performance of polyurea coatings on RC beams by drop weight impact tests with different impact velocities and hammer shapes. According to the test results, the polyurea coatings can significantly reduce the RC beams' local damage and midspan displacement. Moreover, it was found that the RC beams' plateau impact forces were notably increased by the polyurea coatings. Besides, comparisons between impact tests with different impact loads indicated that the polyurea coatings' protection effect was not noticeably influenced by the hammer shape or impact velocity. Based on the test results, a numerical model was established and validated, and the model was used to study the mechanism and the parameter influence of polyurea coatings. By simulating the response of upper- and lower-side coated beams, it was revealed that the polyurea coating reduced the RC beam's overall damage by reducing its local damage and increasing its bending moment. Parametric studies showed that the mitigation effect increased with coating thickness and the increase rate decreased with the thickness. In addition, the effect of longitudinal coating length was also studied via numerical simulation, and it was found that the mitigation effect increased with coating length, and it became nearly identical to that of the fully coated beam when the coating length exceeded 60 cm. [ABSTRACT FROM AUTHOR]

When aluminium-rich phase minerals are added to Portland cement, Al atoms will enter the C-S-H and Al, then a substitution reaction will occur, forming a hydrated silica-calcium aluminate (C-A-S-H), which changes the molecular structure of the cement material. Due to limitations in experimental methods, the research on the bonding effect between corroded ions and Al-substituted structures is still unclear. Here, the mechanism of an Al substitution reaction affecting the adsorption of chloride and sulphate ions was studied using simulation. The C-A-S-H model of aluminium random substitution was built, evaluating the binding effects among the C-A-S-H, and sulphate and chloride ions. The results demonstrated that the C-A-S-H structure generated by the Al substitution reaction increased the physical adsorption capacity of the chloride and sulphate ions. The adsorption capacity of the sulphate ions was 13.26% higher than that before the Al substitution, and the adsorption capacity of chloride ions was 21.32% higher than that before the Al substitution. The addition of high aluminium phase minerals caused the interfacial flocculants C-A-S-H and C-S-H to connect and intertwine in the the interface transition zone (ITZ) structure. The addition of high-alumina phase minerals improves the microstructure of concrete hydration products, improving the physical and mechanical properties and durability of concrete. After the addition of 20% lithium slag, the sulphate ion erosion content and the chloride ion erosion content of the concrete decreased by 13.65% and 15.72%, respectively. This paper provides a deeper understanding of the effect of high-alumina phase admixtures on concrete at the micro-scale. [ABSTRACT FROM AUTHOR]

Geopolymeric recycled concrete (GRC) is a new low-carbon building material that uses both construction and industrial solid waste to replace natural aggregate and cement. GRC is similar to geopolymeric concrete (GPC) in that it has good mechanical properties but needs to be improved in terms of frost resistance. Previous studies have shown that polyoxymethylene fiber (POM fiber) can improve the shrinkage and durability of concrete and is superior to other commonly used fibers. Therefore, this paper explores adding POM fiber to GRC to improve its frost resistance. In this paper, the influence of different volumes and lengths of POM fiber on the frost resistance of geopolymeric recycled concrete (PRGRC) is studied. By measuring the changes in mass loss rate, relative dynamic elastic modulus, and compressive strength of PRGRC under different cycles, the improvement effect of POM fiber on the freeze-thaw damage of GRC is analyzed, and the strength attenuation model of PRGRC is established. The results show that the increase in POM fiber content can effectively slow down the mass loss of PRGRC in the freeze-thaw cycles, the reduction rate of relative dynamic elastic modulus, and the reduction rate of compressive strength. This shows that POM fiber can effectively improve the frost resistance of PRGRC, and the effect of 6 mm POM fiber on the freeze-thaw damage of PRGRC is better than 12 mm POM fiber. According to the test results, the existing strength attenuation model is further modified, the attenuation model of PRGRC compressive strength under the freeze-thaw cycle is obtained, and the model fitting effect is good. The strengthening mechanism of POM fiber is explained by the structural relationship between POM fiber and concrete matrix in the SEM micrograph of PRGRC. The research results provide a scientific basis for the applicability of POM fiber in geopolymeric cementitious materials and improving the frost resistance of PRGRC. [ABSTRACT FROM AUTHOR]

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) technique is known as a promising alternative to the externally bonded (EB) FRP technique for strengthening reinforced concrete (RC) members, on account of its many advantages such as high bond efficiency with concrete and good durability. Shear strengthening of RC beams by near-surface mounting the FRP bars/strips into the concrete cover on beam sides is one of the most prevalent applications of NSM FRP. Abundant experimental studies have been conducted to investigate the behaviour of NSM FRP shear strengthened beams, and many strength models for predicting the contribution of NSM FRPs to the shear capacity of the beam have been proposed. The present paper presents a comprehensive review of these strength models, in which all the models collected from the existing literature are first classified into three categories based on their used approach and then summarized and discussed. This paper not only aims to bring a deep understanding of the existing strength models for NSM FRP shear strengthened RC beams, but also provides a background and basis for the assessment of these models by using the newly-generated experimental database in the companion paper. [ABSTRACT FROM AUTHOR]

Under corrosive environments, concrete material properties can deteriorate significantly, which can seriously affect structural safety. Therefore, it has important engineering applications to improve the durability performance at a lower economic cost. This paper proposes a new, highly durable concrete using inexpensive construction materials such as basalt fiber, sodium methyl silicate, and inorganic aluminum salt waterproofing agent. With the massive application of sewage treatment projects, the problem of concrete durability degradation is becoming more and more serious. In this paper, five types of concrete are developed for the sewage environment, and the apparent morphology and fine structure of the specimens after corrosion in sewage were analyzed. The density, water absorption, and compressive strength were measured to investigate the deterioration pattern of concrete properties. It was found that ordinary concrete was subject to significant corrosion, generating large deposits of algae on the surface and accompanied by sanding. The new concrete showed superior corrosion resistance compared to conventional concrete. Among other factors, the inorganic aluminum salt waterproofing agent effect was the most prominent. The study found that the strength of ordinary concrete decreased by about 15% in the test environment, while the new concrete had a slight increase. Comprehensive evaluation showed that the combination of basalt fiber and inorganic aluminum salt waterproofing agent had the best effect. Its use is recommended. [ABSTRACT FROM AUTHOR]

“Polyurea coatings as a possible structural reinforcement system” is a research project aimed at exploring possible applications of polyurea coatings for improving structural performance (including steel, concrete, wooden and other structures used in the construction industry). As part of the project, this paper focuses on evaluating the performance of bent reinforced concrete (RC) beams covered with a polyurea coating system. Easy polyurea application and its numerous advantages can prove very useful when existing RC structural elements are repaired or retrofitted. Laboratory tests of three types of RC beams with three different longitudinal reinforcement ratios were performed for the purposes of this paper. The tests were designed to determine the bending strength, performance and cracking patterns of the coated RC beams. In addition, a theoretical model was developed to predict the impact of the polyurea coating on the bending strength of the RC beams. On this basis, the effect of the coating on the bending strength and the performance of the coated beams at the ultimate limit state (ULS) was examined and analyzed. The results showed that the use of the polyurea coating has a positive impact on the cracking state of the RC beams subject to bending and little effect on their bending strength. [ABSTRACT FROM AUTHOR]

The near‐surface mounted (NSM) technique over the years has become the most popular retrofitting technique for obtaining enhanced strength and durability in reinforced concrete structural elements. It is mostly preferred for its easy application of composites in grooves cut on specimen concrete cover. The specimen surface is prepared with slits where polymer composite laminates are placed along with adhesives as filler to attain good bonding between laminates and the surface. The paper reviews the NSM carbon fiber reinforced polymer technique and its ascendancies over externally bonded composites retrofitting approach. Members strengthened with the NSM technique show enhanced shear strength, flexural capacity, and fatigue resistance. Motivated by the urge of gaining knowledge on various advantages of this emerging method, the paper reviews the load‐carrying capacity, failure modes, durability, and bonding behavior along with the enhancement ascertained in shear, flexure, and fatigue resistance by the NSM technique. In addition to offering guidance on the experimental and computational investigations on the overall behavior of the technique, the present review also intends to encourage further development in the near‐surface mounted carbon fiber polymer strengthening system of retrofit. [ABSTRACT FROM AUTHOR]

Fire has been a scourge of society for a very long time due to its impact on the human and economic aspects. Fire resistance is a characteristic of concrete buildings, and residential buildings made of concrete are often subject to fire. Fire causes serious damage to the concrete members, which may require substantial demolition. High temperatures decrease the stability and durability of concrete structures; therefore, understanding the effect of fire on concrete walls can help in reduce the environmental fire impact and lower rehabilitation costs. Several studies investigated the impact of fire on the response of concrete walls. This paper reviews previous studies until 2020. The paper aims to discuss the effect of fire load on the behaviour of concrete walls and panels. To this end, 102 previous studies were selected for the review. This paper commences by illustrating fire scenarios, heat and moisture transfer in concrete walls, and the influence of elevated temperature on concrete performance. This is followed by a discussion of structural analysis and failure limit states of concrete walls during fire. Next, the impact of applying different parameters on the structural and thermal behaviour of concrete walls exposed to fire is addressed, and significant parameters including axial load, lateral load, compressive strength, reinforcement ratio, concrete cover, moisture content, aggregate type, fire period, slenderness ratio, and load eccentricity are provided. Spalling, thermal response, and deformation of concrete walls during fire are also discussed. The paper concludes with recommendations for further studies. [ABSTRACT FROM AUTHOR]

• An original multielectrode embedded capacitive sensor is developed. • Multielectrode embedded capacitive sensor allows to assess permittivity in concrete. • Optimum dimensions chosen for capacitive electrodes are rectangular 30 × 10 mm2. • Measurements in liquids and concrete show a very repeatable and reproducible system. • Permittivities obtained with the developed embedded sensor are validated. This paper discusses the development of a capacitive sensor embedded within concrete blocks in order to continuously monitor water content, which is a crucial parameter in the assessment of concrete degradation. The embedded capacitive sensor undergoes continuous interrogation by an automatic monitoring system, in order to track permittivity changes over time through a frequency measurement system. The methodology involves a two-step calibration process: first, obtaining permittivity from frequency, then converting permittivity profiles into water content profiles. This paper focuses on the sensor design and first calibration in the aim of assessing permittivity profiles. Numerical methods enable optimizing both electrode geometry and design of the embedded capacitive sensor. Experimental validation of the sensor in liquid and concrete environments, along with a metrological validation, reveals the sensor's ability to monitor permittivity profiles as well as its uncertainty at 8 different depths inside the concrete structure. Permittivity measurements were also conducted using reference methods. The results demonstrate very good agreement with less than 10% difference between the embedded sensor and the reference results. This step provides insights into its applicability and potential perspectives for future research. [ABSTRACT FROM AUTHOR]

Experiments and field observations have shown that supplementary cementitious materials (SCMs) mitigate the risk of alkali-silica reaction (ASR) in Portland cement blends, but this is difficult to describe thermodynamically due to the lack of appropriate thermodynamic database information, and challenges in defining the kinetic factors. This paper examines how four well-known SCMs (namely ground granulated blast furnace slag, silica fume, metakaolin, and fly ash) mitigate ASR, by using a multi-stage simulation and a newly extended thermodynamic database. Calcium hydroxide consumption by SCM hydration, dilution of available alkalis, and alkali binding in calcium-alkali-aluminosilicate hydrate solid solutions, play pivotal roles in understanding the influence of SCMs in ASRs. Blending aluminium-rich SCMs in ASR-prone systems appears to act by preventing the dissolution of reactive silica in aggregates rather than by suppressing the formation of ASR products. This paper provides new thermodynamic insights into the mechanisms by which SCMs enhance concrete durability against ASR. [ABSTRACT FROM AUTHOR]

Glass Fiber-Reinforced Polymer (GFRP) bars can enhance the flexural bearing capacity and durability of concrete beam members under sustained loading and alkaline environment over an extended period. However, addressing the challenges related to durability and deformation resistance remains crucial for long-term service. In this paper, the flexural performance of GFRP-reinforced concrete beams with different glass fiber contents under the coupling action of the alkaline environment and continuous load is studied, and the mechanism of improving the flexural performance of GFRP-reinforced concrete beams by dispersed fibers is analyzed from a microscopic point of view by scanning electron microscope (SEM) test. In addition, the finite element analysis software was used to simulate and verify the improvement effect of singly dispersed fiber on the bending of GFRP-reinforced concrete beams. The results demonstrate that GFRP-RC beams containing 0.5%, 1.0%, or 1.5% glass fiber exhibit a reduction in deflection ranging from 11% to 23% compared GFRP-RC beams without glass fiber, thereby improving their deformation resistance. The optimal glass fiber content is 1.5%. Simulation analysis demonstrates that the model exhibits enhanced resistance to deformation when the glass fibers are randomly dispersed. Specifically, increasing the random scattering of fibers at the bottom of the beam by two to three times results in a reduction of 7%-12% in mid-span displacement of the model. Additionally, within the cracked area, the fibers bear greater tensile stress compared to those in other uncracked regions, effectively preventing further cracking of GFRP-RC beams. This study offers valuable design guidance for enhancing performance of GFRP-RC members during long-term service. • This paper studied glass fiber GFRP-RC beams. • The working condition is the coupling of sustained loading and alkaline environment. • The influence of fiber on the flexural property of beam was investigated by finite element method. • The corrosion age of alkaline environment is 450 d. [ABSTRACT FROM AUTHOR]

This paper develops the mechanical and durable samples of C50 high-performance concrete, studies the mechanical properties, crack resistance, sulfate attack resistance, frost resistance, and impermeability of concrete with different mineral admixtures of mineral powder and fly ash, and obtains the best mineral admixture of mineral powder and fly ash to improve the performance of high-performance concrete. The results show that the doping effect is the best when the ratio of prepared mineral powder to fly ash is 3:2. With the increase in the mineral powder–fly ash admixture, the slump and expansion of high-performance concrete decrease rapidly at first and then slowly. In total, 60% doping is the turning point; the compressive and flexural strengths of concrete decreased slowly at first and then rapidly. Taking 30% of the admixture as the turning point, 35% of the mineral powder fly ash is generally selected. By mixing and adding a certain proportion of fly ash and mineral powder admixtures, the crack resistance of concrete is enhanced, and the shrinkage and cracking are reduced. The corrosion resistance coefficient will exceed 88%, the relative dynamic elastic modulus will exceed 95%, and the impermeability grade will reach P17. The durability of concrete can be improved by adding mineral admixtures. [ABSTRACT FROM AUTHOR]

This research paper systematically investigates the combined influence of fly ash, cementitious capillary crystalline waterproofing (CCCW) materials, and polypropylene fibers on the mechanical properties and impermeability of concrete through comprehensive orthogonal tests. Microscopic morphological changes in the concrete induced by different composite materials are examined via scanning electron microscopy (SEM) and X-ray diffraction (XRD) testing. The objective is to facilitate a beneficial synergetic interaction among these materials to develop highly permeable, crack-resistant concrete. Key findings of this study are: (1) The study unveils the impact of the concentration of three additive materials on the concrete's compressive strength, tensile strength, and penetration height, thereby outlining their significant influence on the mechanical properties and impermeability of the concrete; (2) An integrated scoring method determined the optimal composite dosage of three materials: 15% fly ash, 2% CCCW, and polypropylene fibers at 1.5 kg/m3. This combination increased the concrete's compressive strength by 12.5%, tensile strength by 48.4%, and decreased the average permeability height by 63.6%; (3) The collective introduction of these three materials notably augments the hydration reaction of the cement, resulting in denser concrete microstructure, enhanced bonding between fibers and matrix, and improved concrete strength and durability. [ABSTRACT FROM AUTHOR]

The structural performance and durability of reinforced concrete (RC) dapped‐end beams may be significantly threated by the effects of deterioration and environmental actions, compromising the structural robustness of important infrastructures such as bridges. The study of the critical role of dapped‐ends has grown in recent years, focusing in particular on the implementation of innovative retrofit solutions capable of extending the service life of these structural elements. In this paper, an experimental investigation on the contribution of Fabric‐Reinforced Cementitious Matrix (FRCM) retrofitting system to the load bearing capacity of RC dapped‐end beams is presented. A set of eight full‐scale dapped‐ends was subjected to monotonic loading tests. The presence of cracks prior to the application of the retrofitting composite, which may represent the actual state of conservation of existing RC half‐joints subjected to heavy traffic loads, is reproduced by testing the specimens up to the reaching of the ultimate design load. Different orientations of the alkali‐resistant glass fabric composing the FRCM system were tested, and the results allow to discuss the effectiveness of the retrofitting solution. [ABSTRACT FROM AUTHOR]

Sulfate attack is one of the main factors affecting the durability of concrete structures. In recent years, multi-walled carbon nanotubes (MWCNTs) have attracted the attention of scholars for their excellent mechanical properties and durability performance. In this paper, the influence of sulfate attack and dry–wet cycles on the performance of multi-walled carbon nanotube–lithium slag concrete (MWCNT-LSC) with varied MWCNT content (0 wt.%, 0.05 wt.%, 0.10 wt.%, and 0.15 wt.%) and varied water–cement ratios (0.35, 0.40, and 0.45) were investigated. In addition, scanning electron microscopy (SEM) and X-ray computed tomography (CT) tests were conducted to analyze the microstructure and pore structure of the concrete. The results showed that concrete incorporated with MWCNTs could effectively mitigate sulfate attack. The resistance to sulfate attack of concrete was negatively related to the water–cement ratio when the dry–wet cycle was fixed. The MWCNT-LSC showed the best compressive strength at the water–cement ratio of 0.35 and 0.10 wt.% MWCNTs. The SEM test results showed that the MWCNTs filled the pores and cracks within the specimen and formed bridges between the cracks, enhancing the resistance to sulfate attack. The CT test results also showed that the addition of MWCNTs could reduce the porosity of concrete, refine the pore size and inhibit the generation and development of cracks, thus optimizing the internal structure of concrete and improving its resistance to sulfate attack. [ABSTRACT FROM AUTHOR]