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Due to the low water-cement ratio of ultra-high-performance concrete (UHPC), fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete. In this study, the effects of different types of cementitious materials, chemical shrinkage-reducing agents (SRA) and steel fiber (SF) were assessed. Compared with M2-UHPC and M3-UHPC, M1-UHPC was found to have better fluidity and shrinkage cracking performance. Moreover, different SRA incorporation methods, dosage and different SF types and aspect ratios were implemented. The incorporation of SRA and SF led to a decrease in the fluidity of UHPC. SRA internal content of 1% (NSRA-1%), SRA external content of 1% (WSRA-1%), STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%, 8.3%, 9.2% and 25%, respectively. However, SRA and SF improved the UHPC shrinkage cracking performance. NSRA-1% and STE-0.7 reduced the shrinkage value of UHPC by 40% and 60%, respectively, and increased the crack resistance by 338% and 175%, respectively. In addition, the addition of SF was observed to make the microstructure of UHPC more compact, and the compressive strength and flexural strength of 28 d were increased by 26.9% and 19.9%, respectively. [ABSTRACT FROM AUTHOR]

The use of recycled fine aggregate in the production of concrete mixes is one of the elements of a circular economy. However, it is important to ensure that such a modification does not significantly affect the durability of the produced concrete elements. One possible criterion to check whether this condition is met is the practical application of the concept of equivalent concrete properties. The presented studies analyzed the properties of concrete with multi-component cement CEM V/A (S-V) and with recycled fine aggregate. The conducted analyses of the research results showed that with a 15% replacement level of natural sand with recycled sand, it is possible to maintain durability characteristics compared to concrete using only natural sand. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents an innovative method to include creep deformations in the prediction of time to corrosion-induced cover cracking. Using experimental results, creep and cracking criteria used in this method are verified. It is argued in the paper that the cover cracking problem under corrosion is close to a relaxation problem and the conventional creep formulations based on the effective elastic modulus cannot be adopted. It is found in the paper that accurate consideration of creep deformation would lead to about 30–40% longer time to cover cracking when compared to no consideration of creep deformations whilst for the currently practiced methods, the time can be up to 200% longer, which is unconservative in predicting time to cover cracking. Results in this paper open the debate on modelling of creep in the analysis of corrosion-affected structures and serve as an important step towards the accurate prediction of corrosion-induced concrete cracking. [ABSTRACT FROM AUTHOR]

This paper mainly discusses the mechanical characteristics of steel-reinforced reactive powder concrete (SRRPC) columns with different geometrical dimensions after high-temperature treatment. The bearing capacity, axial stiffness, and ductility of 35 SRRPC column specimens after high-temperature treatment are investigated, considering two parameters: concrete cover thickness (30–100 mm) and slenderness ratio (3–50). The findings indicate that (1) the ultimate bearing capacity increases by 26.0–135.7% as the concrete cover thickness increases and decreases by 1.5–92.0% as the slenderness ratio increases. (2) The axial stiffness increases by 18.9–92.5% as the concrete cover thickness increases and sharply decreases by 31.9–92.6% as slenderness ratio increases, and change degree decreases. (3) As concrete cover thickness and slenderness ratio increase, the displacement ductility coefficient declines, and degree of decrease in displacement ductility coefficient becomes progressively smaller. (4) The bearing capacity, stiffness, and ductility are extremely sensitive to concrete cover thickness, followed by slenderness ratio. Considering confining effect of stirrups and section steel on concrete in the core area, methods for calculating bearing capacity after high-temperature treatment are proposed. From the perspectives of preventing buckling instability and cracking of components after high temperature, two methods for determining the critical concrete cover thickness are given. Finally, the calculation formula of the stability coefficient corresponding to various slenderness ratios after high-temperature exposure is provided, which provides a reference for postfire evaluation and reinforcement of SRRPC structure. [ABSTRACT FROM AUTHOR]

Despite their undeniable potential for promoting sustainability in construction materials, the characteristics of recycled aggregates (RCA), seawater, and sea sand may vary significantly, thereby affecting their use in structural concrete. This study exploits these materials to investigate their performance in producing sustainable concrete and establishing its mechanical and fracture behavior. The so produced material, referred to as seawater sea sand recycled aggregate concrete (SSRAC) could lend a hand in widening the usage of RCA and sea sand in a variety of applications where the use of ever-depleting natural materials as concrete constituents becomes an issue. Consequently, the variables of the study include the type of water (fresh versus seawater), type of coarse aggregate (RCA versus natural coarse aggregate, NCA), and the type of fine aggregate (dune sand versus sea sand). For each water type, three concrete mixtures are produced using NCA-dune sand, RCA-dune sand, and RCA-sea sand combinations. Analyses of the mechanical characteristics of the concrete, including compressive strength, flexural strength, modulus of elasticity, and fracture toughness, were conducted based on experimental tests. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses were also conducted on the designed specimens to investigate their microstructure. In terms of fracture characteristics, the use of seawater resulted in improvement in the fracture toughness. The use of recycled aggregate along with seawater resulted in improved compressive strength. However, natural aggregate concrete (NAC) showed higher flexural strengths than recycled aggregate concrete (RAC). The results also revealed that the addition of sea sand had a detrimental impact on all mechanical characteristics. Thus, optimizing the concrete composition in which the investigated materials partially replace the conventional concrete constituents is required in order to consider alternative constituents to generate sustainable concrete for practical applications. [ABSTRACT FROM AUTHOR]

Recycled aggregate concrete (RAC) is not widely used in construction because of the concerns related to its quality. This paper investigates the effect of the replacement levels of recycled concrete aggregate (RCA) on bulk and hardened densities of RAC. The analysis of variance (ANOVA) was used to investigate the sensitivity of bulk and hardened densities of concrete to the replacement level of RCA. Predictive equations were developed to estimate the 3-day, 7-day, and 28-day compressive strength of RAC from its fresh properties, which are helpful for early quality control inspection of RAC. Furthermore, a predictive equation has been proposed to determine the flexural strength of RAC based on its 28-day compressive strength. The comparison of the predictive capability of the proposed and widely used code equations showed the incapability of the latter to estimate the flexural strength of RAC. In contrast, the proposed equation demonstrated a high level of prediction accuracy. [ABSTRACT FROM AUTHOR]

In this study, the pore structure and gas permeability of river sand concrete and manufactured sand concrete (mixed with various stone powders) are examined under dry and wet conditions. First, the pore structure of concrete was tested using the mercury-in-pressure (MIP), hydrostatic balance (HB), and nuclear magnetic resonance (NMR) methods. Second, the gas permeability of concrete was measured using the quasi-stationary flow method. Finally, a numerical model was developed based on the relationship between the pore structure and gas permeability. The results indicated that the gas permeability of dry concrete has a quadratic linear relationship with the porosity and volumetric characteristic pore size. The pore structure of partially water-saturated concrete can be corrected using a correction factor and the relaxation rate of the dry material. Finally, a random hierarchical bundle model using the HB–NMR method is proposed. The maximum relative deviation between the predicted and experimental values is 48.28%. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Even though carbon fibres (CFs) have been increasingly used, their end-of-life (EOL) handling presents a challenge. To address this issue, we evaluated the use of recycled CFs (rCFs), produced through pyrolysis, as rovings to be used in textile reinforced concrete structures. Mechanical processing (hammer mill) with varying machine settings was then used to assess EOL handling, considering the separation potential of rCFs and the length of separated rCFs. The results showed that rCF rovings can be separated from concrete with an average of 87 wt.-%, whereas the highest rCF length and separation yield were observed in different machine settings. In addition, a techno-environmental assessment on the mechanical process was performed to compare different machine settings. The machine settings with the highest yield of rCF rovings also had the highest fine fraction that cannot be further separated. Furthermore, life cycle assessment (LCA) was conducted covering three life cycles of CFs and an additional LCA for comparing rCF with virgin CF. LCA results revealed that CF reinforced plastic and concrete productions are the two main contributors to environmental impacts. The comparative LCA between virgin CF and rCF also showed that using rCF is environmentally advantageous, as virgin CF production causes 230% more global warming potential compared to rCF. Future studies assessing different allocation approaches, quantifying the quality of rCF, and its inclusion in LCA are relevant. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The inherent brittle behavior of cementitious composite is considered one of its weaknesses in structural applications. This study evaluated the impact strength and failure modes of composite U-shaped normal concrete (NC) specimens strengthened with polyurethane grout material (NC-PUG) subjected to repeated drop-weight impact loads (USDWIT). The experimental dataset was used to train and test three machine learning (ML) algorithms, namely decision tree (DT), Naïve Ba yes (NB), and K-nearest neighbors (KNN), to predict the three failure modes exhibited by U-shaped specimens during testing. The uncertainty of the failure modes under different uncertainty degrees was analyzed using Monte Carlo simulation (MCS). The results indicate that the retrofitting effect of polyurethane grout significantly improved the impact strength of concrete. During testing, U-shaped specimens demonstrated three major failure patterns, which included mid-section crack (MC), crushing foot (CF), and bend section crack (BC). The prediction models predicted the three types of failure modes with an accuracy greater than 95%. Moreover, the KNN model predicted the failure modes with 3.1% higher accuracy than the DT and NB models, and the accuracy, precision, and recall of the KNN model have converged within 300 runs of Monte Carlo simulation under different uncertainties. [ABSTRACT FROM AUTHOR]

Copyright of Industrial Minerals & Processing / Huagong Kuangwu yu Jiagong is the property of Industrial Minerals & Processing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The magnetite ore was taken as the partial aggregate to prepare two types of concrete specimens mixed with magnetite and without magnetite. Both were cured in water and 5 wt % Na2SO4 solution at 20 and 80°C, respectively, to study the influence on the strength of concrete. In addition, the magnetite ore was ground into powder, and cured in simulated concrete pore solution and 5 wt % Na2SO4 solution respectively, and the mineral and morphological change at different ages was tested by X-ray diffraction (XRD) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS). The experimental results show that the strength of concrete with magnetite ore is a little higher than that of concrete without magnetite ore whether cured in water or in Na2SO4 solution, and the magnetite transforms into Fe2O3, ferrihydrite and other minerals in simulated concrete pore solution and in 5 wt % Na2SO4 solution. The experimental results also demonstrate that using some magnetite ore as aggregate for concrete is beneficial for improving the sulfate resistance of concrete. [ABSTRACT FROM AUTHOR]

Concrete is the most commonly used construction material. However, its production leads to high carbon dioxide (CO2) emissions and energy consumption. Therefore, developing waste-substitutable concrete components is necessary. Improving the sustainability and greenness of concrete is the focus of this research. In this regard, 899 data points were collected from existing studies where cement, slag, fly ash, superplasticizer, coarse aggregate, and fine aggregate were considered potential influential factors. The complex relationship between influential factors and concrete compressive strength makes the prediction and estimation of compressive strength difficult. Instead of the traditional compressive strength test, this study combines five novel metaheuristic algorithms with extreme gradient boosting (XGB) to predict the compressive strength of green concrete based on fly ash and blast furnace slag. The intelligent prediction models were assessed using the root mean square error (RMSE), coefficient of determination (R2), mean absolute error (MAE), and variance accounted for (VAF). The results indicated that the squirrel search algorithm-extreme gradient boosting (SSA-XGB) yielded the best overall prediction performance with R2 values of 0.9930 and 0.9576, VAF values of 99.30 and 95.79, MAE values of 0.52 and 2.50, RMSE of 1.34 and 3.31 for the training and testing sets, respectively. The remaining five prediction methods yield promising results. Therefore, the developed hybrid XGB model can be introduced as an accurate and fast technique for the performance prediction of green concrete. Finally, the developed SSA-XGB considered the effects of all the input factors on the compressive strength. The ability of the model to predict the performance of concrete with unknown proportions can play a significant role in accelerating the development and application of sustainable concrete and furthering a sustainable economy. [ABSTRACT FROM AUTHOR]

Freeze–thaw damage gradients lead to non-uniform degradation of concrete mechanical properties at different depths. A study was conducted on the stress–strain relationship of stressed concrete with focus on the freeze–thaw damage gradient. The effects of relative freeze–thaw depths, number of freeze–thaw cycles (FTCs) and stress ratios on the stress–strain curves of concrete were analyzed. The test results demonstrated that freeze–thaw damage was more severe in the surface layers of concrete than in the deeper layers. The relative peak stress and strain of concrete degraded bilinearly with increasing depth. The stress–strain relationship of stressed concrete under FTC was established, and it was found to agree with the experimental results. [ABSTRACT FROM AUTHOR]

In this study, the effect of nano-CaCO3 on the durability of concrete was investigated by simulating the attack of semi-buried concrete structures in saline soil. Different nano-CaCO3 contents were used to enhance the durability of concrete. The durability of different areas of nano-CaCO3 modified concrete, partially exposed to sulfate solution, was evaluated, and a reliability analysis was conducted. The results indicated that appropriate nano-CaCO3 content can improve the durability of concrete. In this study, concrete with a nano-CaCO3 content of 1% exhibited the highest durability. The corrosion degrees of different areas of the nano-CaCO3 modified concrete partially exposed to the sulfate solution decreased in the following order: dry–wet transition areas (M area) > fully immersed areas (D area) > exposed air areas (T area). A sulfate chemical attack occurred inside the concrete in the dry–wet transition areas, while a sulfate physical attack occurred on the surface concrete. The predicted values of the model agreed well with the test results. The bivariate Wiener process can effectively describe the whole process of performance deterioration of nano-CaCO3 modified concrete. [ABSTRACT FROM AUTHOR]

This study focuses on the essential task of monitoring the strength of structural concrete in construction and rehabilitation projects. The conventional non-destructive testing (NDT) approach offers an indirect estimation of concrete compressive strength. However, the existing models lack the ability to address the estimation of compressive strength in concrete mixtures containing bottom ash (BA) and recycled coarse aggregate (RCA). This study aims to bridge this gap by accurately estimating the compressive strength of such concrete using the ultrasonic pulse velocity (UPV) technique. To achieve this objective, various concrete specimens with different cement content, water–cement ratios (w/c), recycled coarse aggregate, and bottom ash contents through weight batching, were prepared. UPV and compressive strength measurements were taken on cylindrical concrete specimens after 28 and 90 days of curing. The analysis revealed an exponential relationship between the compressive strength and UPV, with a high correlation coefficient across the evaluated concrete mixes, independent of the curing time. Ultimately, two robust models were developed to predict the compressive strength of concrete mixes containing different percentages of RCA and BA, respectively, at 28 and 90 days of curing. These models offer valuable insights and practical tools for ensuring the structural integrity of concrete in construction and rehabilitation projects involving bottom ash and recycled coarse aggregate. [ABSTRACT FROM AUTHOR]

Concrete is a material used in modern construction and is a very important component in the manufacture of structures. Concrete has advantages, but also disadvantages, namely low tensile strength. To increase the tensile strength of concrete, fibers are added to the mix. One of the efforts made to increase the tensile strength of concrete is the addition of fibers to the fiber-concrete mixture. The purpose of this study is to examine the compressive strength and tensile strength values in fiber concrete if added with variations in fiber addition. An innovation in increasing the value of mechanical quantities in concrete is the use of bent wire fibers as a mixture in fiber concrete. This material is taken from former pieces in construction projects to connect steel reinforcement with Sengkang reinforcement and is also widely found in building shops. The fibers were also analyzed for microstructure using SEM (Scanning Electron Microstructure) tools. The length of this bent wire fiber is 13 mm with a diameter of 0.82 mm and has a minimum tensile strength value of 334.5 MPa. The variations in the addition of these bent wire fibers are 0%, 3%, 6%, and 9% of the total weight of the steel fiber. The soaking life of concrete is 7 days, 14 days, and 28 days. The results of this study show that the more variations in the addition of bent wire fibers, the compressive strength value of concrete and the tensile strength value of concrete will also increase. It can be seen that fiber concrete with an immersion life of 28 days with a variation of 9% added bent wire fiber has a maximum compressive strength value of concrete which is 63,645 MPa and a maximum value of tensile strength of 3,294 MP. [ABSTRACT FROM AUTHOR]

The environmental impact of traditional construction materials necessitates the development of sustainable alternatives. This study evaluates eco-cobbles as novel building materials designed to reduce environmental footprint while maintaining performance standards. The objectives were to develop an eco-friendly cobble alternative and assess its effectiveness through laboratory tests. Eco-cobbles were synthesized using recycled and bio-based materials and tested for compressive strength, flexural strength, and water absorption at 14 and 28 days. The compressive strength ranged from 11.5 MPa to 26.8 MPa, with a maximum value observed at 28 days in a mixture containing 95% concrete and 5% polyethylene terephthalate (PET). Flexural strength varied from 9.1 MPa to 28.7 MPa, with the highest value achieved in a mixture of 95% concrete and 0% fibers. Water absorption rates ranged from 2.1% to 6.6%, demonstrating an effective balance between performance and durability. Environmental assessments indicated a 30% reduction in resource consumption and a 40% decrease in carbon footprint compared to traditional cobble production methods. The findings demonstrate that eco-cobbles not only meet performance standards but also offer significant environmental benefits with a 99% compliance from the results obtained by response surface methodology plots, confirming that eco-cobbles offer a viable, sustainable alternative to conventional materials, with the potential for broader application in eco-friendly construction practices. [ABSTRACT FROM AUTHOR]

Researching the mechanical characteristics of concrete subjected to the freeze–thaw cycle is crucial for building engineering in cold climates. As a result, uniaxial compression tests were performed on concrete samples exposed to various freeze–thaw (F–T) cycles, and the measurements of the pore size distribution, porosity, and P-wave velocity of the saturated concrete samples were obtained, both before and after being exposed to the F–T cycles. Concrete's F–T damage mechanism and damage evolution model were thoroughly examined. Using rock structure and moisture analysis test equipment to observe the T2 spectrum, the results showed that the F–T cycles can cause the internal structure of the samples to deteriorate. Porosity and F–T cycles have a positive correlation, although P-wave velocity has a negative correlation with the F–T cycles. As the F–T cycles increased, the specimens' peak strength and elastic modulus steadily declined, while the peak strain clearly exhibited an increasing trend. A microscopic F–T damage model that takes into account the pore size distribution was developed, based on the relative changes in the pore structure distribution (PSD), before and after the F–T cycles. The concrete sample damage evolution law under various F–T cycles was examined using the following metrics: total energy, pore size distribution, static and dynamic elastic moduli, porosity, and P-wave velocity. Uniaxial compressive strength (UCS) and peak strain tests were used to evaluate the accuracy of the pore size distribution damage model, as well as that of five other widely used damage models. [ABSTRACT FROM AUTHOR]

The energy consumption of buildings presents a significant concern, which has led to a demand for materials with better thermal performance. Thermal conductivity (TC), among the most relevant thermal properties, is essential to address this demand. This study introduces a methodology integrating a Multilayer Perceptron (MLP) and a Generative Adversarial Network (GAN) to predict the TC of concrete based on its mass composition and density. Three scenarios using experimental data from published papers and synthetic data are compared and reveal the model's outstanding performance across training, validation, and test datasets. Notably, the MLP trained on the GAN-augmented dataset outperforms the one with the real dataset, demonstrating remarkable consistency between the model's predictions and the actual values. Achieving an RMSE of 0.0244 and an R2 of 0.9975, these outcomes can offer precise quantitative information and advance energy-efficient materials. [ABSTRACT FROM AUTHOR]

It is essential to understand how failure mechanisms work in arch dams and, in particular, their most common manifestation: cracking. In this paper, the different types of cracking are explained in terms of their causes and consequences. Then, an exhaustive literature review is carried out that results in a detailed compilation of the characteristics of 38 cracked arch dams from all over the world, including crack characteristics (zone, position, dimensions and probable cause). This review is restricted to only those dams for which information on the position of the cracks or dam displacements is publicly available. As part of the review, a brief summary of key data for each dam is included, as well as a compilation of published crack diagrams. The positions of the cracks of all the dams are classified using diagrams in relation to the type of dam and the origin of the crack. Finally, the distribution of some dam parameters and crack features is analyzed by studying the relationships between them. [ABSTRACT FROM AUTHOR]

The quality of the air void system is essential for the frost resistance of concrete. Therefore, it is crucial to assess the quality of the air void system in hardened concrete in an appropriate way. In this study, the shape from focus (SFF) method is applied to identify the focused image of each point on the polished surface of hardened concrete and thereby acquire the depth information of the entire surface. The performance of various focus measure operators and window sizes is evaluated. Thereafter, the selected focus measure operator and window size are applied for the SFF analysis of all samples. Based on the obtained depth map, the voids are identified, and the void parameters of the hardened concrete are determined by an automated procedure. The main advantage of the SFF method is that it is possible to carry out an automated air void analysis without contrast enhancement. [ABSTRACT FROM AUTHOR]

This study presents a methodology to optimize concrete mixtures by integrating machine learning (ML) and genetic algorithms. ML models are used to predict compressive strength, while genetic algorithms optimize the mixture cost under quality constraints. Using a dataset of over 19,000 samples from a local ready-mix concrete producer, various predictive ML models were trained and evaluated regarding cost-effective solutions. The results show that the optimized mixtures meet the desired compressive strength range and are cost-efficient, thus having 50 % of the solutions yielding a cost below 98 % of the test cases. CatBoost emerged as the best ML technique, thereby achieving a mean absolute error (MAE) below 5 MPa. This combined approach enhances quality, reduces costs, and improves production efficiency in concrete manufacturing. [ABSTRACT FROM AUTHOR]

As an environmentally friendly and renewable energy solution, wind power is rapidly gaining favour worldwide due to its gentle impact on the environment. Nevertheless, the potential environmental risks posed by discarded wind turbine blades still need to be brought to our attention. Therefore, exploring ways to recycle and reuse discarded wind turbine blades has become an urgent task in the field of environmental protection. This study focuses on the incorporation of recycled glass fibres from crushed wind turbine blades into concrete to assess their benefits in engineering practice. In this study, we used four different particle sizes of recycled glass fibres, 0-5mm, 5-10mm, 10-15mm and 15-20mm, and incorporated them into the concrete at four different admixture levels of 0.2%, 0.4%, 0.6% and 0.8%. By comprehensively examining its workability, mechanical properties and microstructure, we found that although the incorporation of glass fibres reduced the apparent density, slump and compressive strength of the concrete to a certain extent, it significantly improved the split tensile and flexural strengths of the concrete, as well as effectively improved the brittleness of the material and enhanced its toughness. These findings reveal the feasibility of recycling glass fibres from decommissioned wind turbine blades and applying them to concrete. This study not only opens up a new path for environmentally friendly recycling and reuse of wind turbine blades, but also provides a valuable reference for practical engineering applications, with significant social and economic benefits. [ABSTRACT FROM AUTHOR]

The research paper investigates the impact of fire on concrete structures, focusing on evaluating the temperatures reached during the fire using the colorimetry test method. It examines color changes as indicators of temperature, assesses the extent of damage to building components, and determines the depth of carbon penetration within the structure. The study employs various assessment techniques, including rebound hammer test, colorimetry test to evaluate structural integrity post-fire. Key findings include the correlation between color changes and temperature, the effectiveness of rebound hammer tests in assessing structural integrity, and the importance of considering aggregate type in color analysis. The study was conducted using prescribed nondestructive testing (NDT) techniques. For the investigation of the fire-damaged building, the Rebound number (RN) values were used to correlate the in-situ compressive strength of concrete using the standard curves developed in the laboratory for this purpose. Moreover, the approximate temperature to which any structural element had reached was determined approximately by colorimetry test. Further the residual compressive strength of concrete of these elements was also derived applying the reduction factors in Eurocode 2 for concrete exposed to varied temperatures. The maximum percentage difference between these two sets of values was 15.46% except for one case. The residual strength values of concrete of the structural elements paved a way for satisfactory evaluation of the need of retrofitting of these elements, Overall, the research offers practical insights for assessing the residual compressive strength of concrete of structural elements of fire-damaged concrete structures by two different techniques thus aiding in decision-making for rehabilitation or reconstruction efforts of such structures. [ABSTRACT FROM AUTHOR]

To optimally preserve and manage our civil structures, we need to have accurate information about their (1) geometry and dimensions, (2) boundary conditions, (3) material properties, and (4) structural conditions. The objective of this article is to show how imaging and image fusion using non-destructive testing (NDT) measurements can support structural engineers in performing accurate structural evaluations. The proposed methodology involves imaging using synthetic aperture focusing technique (SAFT)-based image reconstruction from ground penetrating radar (GPR) as well as ultrasonic echo array (UEA) measurements taken on multiple surfaces of a structural member. The created images can be combined using image fusion to produce a digital cross-section of the member. The feasibility of this approach is demonstrated using a case study of a prestressed concrete bridge that required a bridge load rating (BLR) but where no as-built plans were available. Imaging and image fusion enabled the creation of a detailed cross-section, allowing for confirmation of the number and location of prestressing strands and the location and size of internal voids. This information allowed the structural engineer of record (SER) to perform a traditional bridge load rating (BLR), ultimately avoiding load restrictions being imposed on the bridge. The proposed methodology not only provides useful information for structural evaluations, but also represents a basis upon which the digitalization of our infrastructure can be achieved. [ABSTRACT FROM AUTHOR]

Concrete is the second most common material demanded over the world. Recently, a trending issue is the vast tracking in constructing infrastructure to ensure traffic movement and life quality. Concrete types such as self and rolled compacted concrete offer magical solutions ensuring vast infrastructure and life quality. However, these structures must be assessed using non-destructive testing methods to observe the difference between the concrete types. Several studies have used recycled waste, specifically the crumb rubber extracted from old tires, as a potential replacement for natural aggregate in concrete manufacturing. However, limited research has been devoted to nondestructive testing of produced concrete to further evaluate existing concrete elements containing crumb rubber. This study investigates the self and rolled compacted concrete in comparison with normal ones, in addition to using chopped rubber as recycled materials. This study examines the concrete manufactured destructively by evaluating its compressive, tensile, and flexural strength, in addition to impact resistance, and correlates those results with the non-destructive such as Schmit hammer and Ultrasonic Pulse (UPV) for extended utilization of the concrete produced and data publication. The results showed unique performance and a high potential for data contribution to the extensive utilization of self-compacted rubberized concrete and rolled compacted concrete. [ABSTRACT FROM AUTHOR]

Due to its significant non-linear softening characteristics and its wide variety of use cases, concrete has received considerable attention for the modeling of its mechanical behavior. The non-linear simulation of linear concrete structures is often associated with mesh dependency, the resolution of which requires some form of regularization. While most of the past research has focused on tension energy regularization for better mesh-objectivity, the compression behavior has been partly left out, even though it may have a significant impact for particular applications. By starting from the failed attempt to simulate a pushout test from the literature, this paper focuses on the enhancements brought by the energetic regularization in compression to an isotropic damage model based on Mazars' equivalent strain. The resulting model is applied in three representative case studies where the enhanced mesh-objectivity is shown relative to the load–displacement behaviors and the damage patterns that are produced, and compared to those obtained by the classical model. [ABSTRACT FROM AUTHOR]

Anchor bolts are often used in nuclear power plants to connect equipment and equipment foundations. Under a severe earthquake, tensile breakout failure is prone to occur in the anchor bolts. As the total amount of installed machines rises, the inertial forces transferred to the anchor bolts under seismic loads also increase significantly. Therefore, the capacity is no longer satisfied by concrete alone, and specialized supplementary reinforcement needs to be installed around the bolts. The study analyzed the tensile behavior of anchor bolts in foundations with supplementary reinforcement experimentally. A total of 16 single-headed anchors in RC foundations with various diameters, yield strengths, and forms of supplementary reinforcement were tested under monotonic tensile loading. The results show that supplemental tie bars and supplemental U-shaped bars, respectively, rely on the bond with the concrete and their own tensile strength to increase the tensile breakout capacity. Furthermore, based on the failure mechanism, a new model considering the terms of concrete resistance and reinforcement resistance for the tensile breakout capacity of headed anchors around with supplementary reinforcement was proposed. Compared with the strut–tie model by EN 1992-4:2018, the predicted results of the model proposed by this study are relatively consistent with the experimental results, while the results by EN 1992-4:2018 are overly conservative. [ABSTRACT FROM AUTHOR]

The durability and strength of concrete in construction can be significantly compromised by permeability issues, which pose considerable challenges to its long-term effectiveness and reliability. By analyzing six selected articles from the Scopus database, this study meticulously synthesizes findings on the effectiveness of CAs in improving these essential properties of concrete. The research meticulously documents and analyzes key variables such as the CA dosage, water–cement ratio, evaluation duration, and treatment conditions, providing a thorough understanding of the factors that influence the performance of CAs in concrete. The results robustly indicate that CAs significantly reduce concrete permeability, thereby enhancing its resistance to water and other detrimental substances, and simultaneously boosts the compressive strength, leading to stronger and more durable concrete structures. However, the study also reveals that the impact of CAs can vary considerably depending on the specific conditions and methodologies employed in the individual studies. This underscores the importance of standardized testing procedures to ensure consistent and comparable results across different studies. This research provides valuable insights for optimizing the use of CAs in concrete formulations, ultimately aiming to improve the durability, performance, and sustainability of concrete in construction applications. [ABSTRACT FROM AUTHOR]

In this study, experiments were conducted on the freeze–thaw performance of manufactured sand cement concrete with different sand ratios and fly ash contents. The research found that during 200 freeze–thaw cycles, as the fly ash content increased, the concrete exhibited a higher mass loss rate and a decline in the relative dynamic modulus of elasticity. This was due to the lower activity of SiO2 and Al2O3 in the fly ash, which reduced the hydration products. Incorporating an optimal amount of manufactured sand can increase the density of concrete, thereby improving its resistance to freeze–thaw cycles. However, when the content of manufactured sand was high, its large surface area could interfere with the hydration process and reduce strength, thereby diminishing the freeze–thaw resistance of the concrete. Given that studying the freeze–thaw resistance of manufactured sand concrete is time-consuming and influenced by many factors, a prediction model based on a BP (back propagation) neural network was developed to estimate the mass loss rate and the relative dynamic modulus of elasticity following freeze–thaw cycles. After validation, the model was found to be highly reliable and could serve as a foundation for mix design decisions and freeze–thaw performance prediction of manufactured sand cement concrete. [ABSTRACT FROM AUTHOR]

The concrete used in the main structures of subway stations has a high degree of constraint. Consequently, temperature changes and shrinkage during construction frequently lead to significant constraint stress, which can result in structural cracking. Therefore, cement with low hydration heat is commonly used in engineering to reduce the temperature of concrete during its age. Aiming at the problem of hydration and heat release caused by concrete construction, based on the principles of concrete hydration heat release and a numerical analysis method, an optimized semi-adiabatic temperature rise test method has been introduced to investigate concrete temperature rise characteristics with different mineral admixtures. The following conclusions were obtained: The effect of reducing the heat of hydration is related to the content and material properties of different mineral admixtures, but not the type of mineral admixture to be incorporated. The temperature rise performance of four common mineral admixtures is as follows: ① total cooling capacity: limestone powder > slag, fly ash > metakaolin; ② early heat generation rate: metakaolin > slag > fly ash > limestone powder; ③ heat reduction rate in the middle and late periods: metakaolin > limestone powder > fly ash > slag. [ABSTRACT FROM AUTHOR]

This study investigates the structural characteristics of SFRC with different amounts of steel fibers following exposure to freeze–thaw cycles, while taking into account various levels of confinement pressure and rates of deformation. The focus of the research is to examine the dynamic mechanical properties of SFRC exposed to freeze–thaw cycles. The inclusion of steel fibers improves the strength of concrete during freeze–thaw cycles, with 1% steel fiber content being the most effective. Strain rate and confining pressure significantly impact the strength and failure mode of SFRC. The strength of concrete increases linearly with the strain rate. With no confining pressure, the cracks in the concrete specimen align with the direction of the applied stress. And with confining pressure, concrete exhibits diagonal shear failure. Microstructural analysis results from scanning electron microscopy are consistent with the macroscopic properties. [ABSTRACT FROM AUTHOR]

Precast rectangular reinforced concrete (PRRC) beams are joined on construction sites using concrete in situ to achieve the desired length. Limited research exists on the effect of intermediate connection shapes and the types of infilled concrete on the flexural performance of PRRC beams. This paper presents a comprehensive experimental and numerical investigation into the performance of PRRC beams with various intermediate connection geometries and infilled materials under flexural loading. The study examines rectangular, triangular, and semi-circular intermediate connections, along with the performance of beams infilled with normal concrete (NC), engineered cementitious composites (ECC), ultra-high-performance ECC (UHPECC), and rubberized ECC (RECC). The experimental results indicate that the rectangular intermediate connection exhibits superior performance in terms of strength and energy absorption compared to the triangular and semi-circular shapes. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC for any shape of intermediate connection. Moreover, beams with rectangular connections and UHPECC infill exhibited the most significant increase in energy absorption and ultimate load compared to the beams with ECC and RECC. The ultimate load of the beams with UHPECC and tensile reinforcement bar diameters of 10 mm and 12 mm increased by 13% and 29%, respectively, compared to the control beam. The energy absorption of the beams with tensile reinforcement bar diameters of 10 and 12 mm was found to be 75% and 184% higher, respectively, than the control beam. In addition, an increase in tensile bar diameter was found to enhance both the energy absorption and the ultimate load capacity of the beams, regardless of the type of infill concrete. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC. In particular, beams with rectangular connections and UHPECC infill exhibited an increase in energy absorption and ultimate load of up to 184% and 29%, respectively. UHPC was calculated to be as high as 184%, and 29%, respectively, compared to the control beams. In addition, an increase in tensile bar diameter was found to enhance both energy absorption and ultimate load capacity. Finite element modeling (FEM) was developed and validated against the experimental results to ensure accuracy. A parametric study was conducted to study the effects of various concrete types in triangular and semi-circular connections, as well as the influence of intermediate connection length on semi-circular connections under flexural loads. The findings reveal that increasing the length of intermediate connections increases the ultimate load of the beams. [ABSTRACT FROM AUTHOR]

Phase change materials can be converted between solid, liquid, and gaseous states, absorbing or releasing a large amount of heat. PCM is incorporated into concrete to adjust the temperature difference between inside and outside of concrete, which can reduce cracking. In this paper, the finite element analysis method is used to establish the model of an ordinary concrete structure, doped with phase change materials, on the basis of mechanical properties and a temperature regulation test performed by calculating the adiabatic temperature rise of concrete with different contents of composite phase change material, comparing the experimental and simulation results of the ordinary concrete structures with phase change materials, and analyzing the change in temperature field of the concrete structure with the content of self-prepared composite phase change materials. It is found that the addition of self-prepared composite phase change materials reduces the temperature peak of the concrete structure in the stage of hydration heat and delays the time taken to reach the temperature peak. Then, the temperature field of the phase change mass concrete structure is established, and the influence law of composite phase change material admixture on the temperature field of mass concrete is summarized through the time–temperature curves of different admixture amounts and positions so as to predict the possibility of cracks in mass concrete. [ABSTRACT FROM AUTHOR]

Recently, the world population surpassed 8000 million people. Providing housing for such a large population poses a great challenge for the building industry and its impact on the planet. The rise in the urban population leads to greater impacts not only on the environment but also on economies and societies. Consequently, reducing these externalities is mandatory to preserve the welfare of the world. One way of optimising the economic cost of housing is through industrialising the production of housing. However, a balance between housing optimisation and the management of the social/environmental impacts has not yet been achieved. In order to bridge this gap, in this study, a holistic evaluation of several housing systems was performed using the MIVES ("Modelo Integrado de Valor para una Evaluación Sostenible")-based multicriteria decision-making method (MCDM method). Moreover, the obtained results were compared, showing which industrialised building technique might enhance the sustainability of housing production. [ABSTRACT FROM AUTHOR]

Many production activities contribute to environmental degradation by emitting greenhouse gases. The construction sector, one of the main sectors contributing to a country's economic growth, also contributes to greenhouse gas emissions (especially CO2). Concrete, one of the most commonly used materials in this sector, is a source of CO2 emissions due to its cement content. The purpose of this article is to examine the decoupling status between environmental degradation caused by CO2 emissions from ready-mixed concrete production and the economic growth of 20 OECD (Organisation for Economic Co-operation and Development) countries. This study consists of four stages and three periods. In the first stage, the variables are selected; in the second stage, the data are created; and in the third stage, data analysis is performed. In the final stage, the type of decoupling between economic growth and environmental degradation is separately determined for 20 OECD countries. These stages were completed for the pre-commitment period (2000–2007) of the Kyoto Protocol, the first commitment period (2008–2012), and the second commitment period (2013–2019). According to our findings, during the second commitment period of the Kyoto Protocol, only Switzerland and Belgium achieved absolute decoupling between the environmental degradation caused by CO2 emissions from concrete production and economic growth. [ABSTRACT FROM AUTHOR]

The use of silico-manganese slag as a substitute for cement in the preparation of concrete will not only reduce pollution in the atmosphere and on land due to solid waste but also reduce the cost of concrete. To explore this possibility, silico-manganese slag concrete was prepared by using silico-manganese slag as an auxiliary cementitious material instead of ordinary silicate cement. The mechanical properties of the silico-manganese slag concrete were investigated by means of slump and cubic compressive strength tests. The rates of mass loss and strength loss of silico-manganese slag concrete were tested after 25, 50, and 75 cycles. The effect of the silica–manganese slag admixture on the microfine structure and properties of concrete was also investigated using scanning electron microscopy (SEM). Finally, the damage to the silica–manganese slag concrete after numerous salt freezing cycles was predicted using the Weibull model. The maximum enhancement of slump and compressive strength by silica–manganese slag was 17.64% and 11.85%, respectively. The minimum loss of compressive strength after 75 cycles was 9.954%, which was 34.96% lower than that of the basic group. An analysis of the data showed that the optimal substitution rate of silica–manganese slag is 10%. It was observed by means of electron microscope scanning that the matrix structure was denser and had less connected pores and that the most complete hydration reaction occurred with a 10% replacement of silica–manganese slag, where an increase in the number of bladed tobermorite and flocculated C-S-H gels was observed to form a three-dimensional reticulated skeleton structure. We decided to use strength damage as a variable, and the two-parameter Weibull theory was chosen to model the damage. The final comparison of the fitted data with the measured data revealed that the model has a good fitting effect, with a fitting parameter above 0.916. This model can be applied in real-world projects and provides a favorable basis for the study of damage to silica–manganese slag concrete under the action of salt freezing. [ABSTRACT FROM AUTHOR]

To accurately quantify the time-varying pattern of concrete's compressive strength, selecting an appropriate curve model is of paramount importance. Currently, widely adopted models such as polynomial, hyperbolic, and exponential models all possess limitations, particularly in terms of low fitting accuracy during the ultra-early-age stage. This paper innovatively introduces a mathematical model that utilizes a combined curve approach. This model boasts a simplified structure with only two fitting parameters. Compared to traditional models, when utilizing three or more sets of experimental data on compressive strength across different ages, the new model is capable of yielding more precise strength predictions. Due to its minimal reliance on experimental data, the new model exhibits high practicality and convenience in real-world applications. To validate its superiority, a detailed comparison between the new model and existing models was conducted based on several sets of experimental data. The results demonstrate that the new model has significant advantages in terms of mean fitting error and standard deviation, making its predictions the most reliable. For most cases, the standard deviation of the new model is reduced by approximately 30% to 80% compared to the second-best model, underscoring its exceptional stability and consistency. Additionally, the predicted long-term compressive strength values of the new model are closer to the design strength grade of the concrete. This model can also be successfully applied to predict the tensile strength of concrete during its ultra-early age. It has been demonstrated that the combined model proposed in this paper shows promising application prospects in evaluating the time-varying behavior of concrete strength. [ABSTRACT FROM AUTHOR]

The main objective of this research is to investigate experimentally the effect of crushed and uncrushed coarse aggregate on the properties of hardened concrete (compressive strength) by adopting the American Concrete Institute (ACI) and the British Department of Environment (DoE) methods. Concrete mixes were designed, concrete cubes and cylinders were prepared and casted by using DoE and ACI respectively. DoE concrete design method considers both types of aggregates; crushed and uncrushed, while the ACI method does not take into account the effect of uncrushed coarse aggregate in design provisions. Then compressive strength tests of concrete samples were determined at ages of 7 and 28 days full curing period. The results obtained show that ACI gave higher values of compressive strength than that obtained by DoE for M30 and M40 except M25, which resulted in lower values than that obtained by DoE for crushed coarse aggregates. The 7-day compressive strength represents 75% of the 28-day compressive strength for ACI method, whereas in DoE reaching up to 73% and 77% for crushed and uncrushed coarse aggregate, respectively. [ABSTRACT FROM AUTHOR]

This research delves into the utilization of microwave hybrid heating as a curing technique for producing fine aggregates from fly ash. Various concentrations of alkali activator solutions were employed as binders to pelletize the fly ash (ranging from 0% to 10%). The resultant green fly ash-based geopolymer (FAG) aggregates were subjected to a 15-minute microwave kiln treatment. The microwave-sintered FAG fine aggregates, varying in sizes from 0.60 to 2.36 mm, were then utilized to fabricate 50 mm cubic cement mortar samples. Findings indicated that the density of FAG aggregates was approximately 36% lower than that of natural sand, while the water absorption capacity of FAG aggregates exhibited a fivefold increase compared to natural sand. Notably, cement mortar samples made with FAG aggregate of 4% alkali activator exhibited maximum compressive strengths of 31, 37, and 42 MPa at 7, 14, and 28 days of curing, respectively. These compressive strengths were only 12% lower than those of cement mortars made with natural sand across all curing periods. The use of microwave hybrid heating to transform fly ash into aggregates with sufficient strength appears viable, suggesting that these manufactured FAG aggregates could serve as substitutes for natural aggregates in concrete production. [ABSTRACT FROM AUTHOR]

This study explores the use of secondary gold tailings (SGTs) in concrete production to solve sand sustainability issues. This approach addresses waste issues and presents a sustainable material alternative to conventional sand, investigating different SGT proportions (ranging from 0% to 100%) to replace fine aggregate in structural concrete. This study examined the fresh, mechanical, and durability properties of concrete containing SGTs. Incorporating SGTs reduced the concrete's workability, but up to a 75% replacement level resulted in a high fresh concrete density compared with the reference concrete. The results indicated that up to 25% replacement level increased the compressive strength and up to 50% replacement level improved the splitting tensile strength compared with reference concrete. However, all concretes containing SGTs exhibited satisfactory strengths. The statistical analysis confirmed the significant influence of SGTs on concrete strength. In addition, the durability results of the concrete demonstrated good resistance to oxygen, water, and chloride penetration, indicating good concrete quality. SGTs are recommended as a substitute for crusher sand to reduce production costs, conserve natural resources, and promote a sustainable and greener environment. [ABSTRACT FROM AUTHOR]

Purpose: To effectively address the disposal issues of gold tailings and alleviate the shortage of sandstone resources,this study investigated the potential of utilizing gold tailings as a partial replacement for natural sand in the production of gold tailings concrete. Method: Through a series of cube compressive strength tests and orthogonal experimental methods,this research conducted a comprehensive analysis of the impacts of four factors: water-binder ratio, go Id tailings substitution rate, sand ratio, and fly ash content, on the 28-day compressive strength of gold tailings concrete. The systematic analysis was performed using range and variance analysis methods, which determined the relative importance of each factor in influencing the 28-day compressive strength of the concrete. Furthermore,a multiple regression equation was established for predicting the compressive strength of gold tailings concrete based on the orthogonal experimental data. Conclusion: The results indicated that the water-binder ratio had the most significant effect on the compressive strength, followed by the gold tailings substitution rate, fly ash content,and sand ratio. The regression equation,with an R2 value of 0. 872,can predict the compressive strength to a considerable degree. Significance: The research results can provide some reference value for the comprehensive utilization of gold tailings resources. [ABSTRACT FROM AUTHOR]

The imperative to enhance the quality of precast concrete is evident, with a particular focus on augmenting its physical and mechanical attributes by incorporating concrete admixtures. This research centers on the utilization of phosphate minerals and finely ground glass within concrete mixes, with substitution ratios ranging from 15% to 60% of fine sand within the mix. The investigation encompasses multiple facets, including examining material blending, assessing fresh concrete properties (slump), and evaluating both physical and mechanical characteristics of hardened concrete at 7-day and 28-day intervals, juxtaposed against the properties of a control concrete mix. The findings reveal several significant outcomes. Firstly, the incorporation of phosphate minerals leads to a remarkable increase in the slump of concrete, reaching 75mm, in stark contrast to the 20mm slump observed in the control mix. Conversely, introducing fine glass elevates the slump to 60mm while maintaining a constant water-to-cement ratio of 0.48 across all concrete mixtures. Furthermore, the density of the hardened concrete demonstrates notable variations. The control mix boasts a density of 2375kg/m3, whereas the phosphate minerals and fine ground glass result in reduced densities of 2258kg/m3 and 2100kg/m3, respectively, at the 7-day and 28-day intervals. In terms of compressive strength, the 7-day results indicate a decrease to 8MPa with the use of phosphate and fine ground glass minerals, compared to the 13MPa strength observed in the control mix. At the same time, the compressive strength increases to 21MPa for phosphate "Shedyah," compared to 20MPa for the control mix. Phosphate "Abiad" and fine ground glass yield compressive strengths of 15MPa and 16MPa, respectively, at the 28-day mark. Regarding tensile strength, the 7-day figures reveal 1.25MPa for the control mix, and the introduction of phosphate materials results in both increases and decreases, with values remaining similar to the control mix. Conversely, the 28-day tensile strength diminishes to 2.75MPa and 2.5MPa for "Shedyah" and "Abiad," respectively, in contrast to the 3.5MPa exhibited by the control mix. The use of fine ground glass materials results in a tensile strength of 1.8MPa. Lastly, the flexural strength of the control mix stands at 2.5MPa, a value that can be maintained with "Shedyah" phosphate but reduces to 2MPa when "Abiad" phosphate is introduced. Fine ground glass fines maintain a flexural strength of 1.5MPa at 7-day, compared to the 3.25MPa of the control mix, with subsequent fluctuations resulting in strengths of 2.75MPa for "Shedyah" phosphate, 2.5MPa for "Abiad" phosphate, and 2.25MPa for ground glass fines. [ABSTRACT FROM AUTHOR]

The blast resistance of a typical two-lane steel girder highway bridge structural system was modeled using a nonlinear finite-element approach that considered material damage, fracture, and separation. Critical blast scenarios were based on field observations of terrorist attacks on bridges in Iraq, while system failure was defined in terms of practical emergency serviceability criteria used on actual blast-damaged bridges. The blast resistance of various design parameters was assessed, including the number of girders, deck concrete strength, reinforcement ratio, slab thickness, girder and reinforcement yield strength, girder sectional dimensions, and pier column width. The presented approach uniquely quantifies structural system blast resistance in terms of the charge weight that can be applied at different locations until failure. A sensitivity analysis was conducted to determine the most influential design parameters. It was found that system blast capacity was primarily influenced by the number of girders and girder yield strength, while additional significant parameters were deck compressive strength, deck thickness, web stiffener width, and girder depth. Secondary parameters were deck reinforcement ratio, girder flange, and web thickness, while deck reinforcement yield stress was found to be insignificant. Based on the results, recommendations for improving blast resistance are provided. [ABSTRACT FROM AUTHOR]

Abstract This research aimed to examine the effects of an acidic environment on the mechanical properties and durability of bio-mortar (BM) encapsulated with Bacillus subtilis bacteria, in comparison to normal mortar (NM). The results at 28 days indicated that both 3% and 6% HCl significantly increased the compressive strength of the BM by 25% and 50%, respectively, compared with that of the NM. However, when 11% HCl was introduced, the compressive strength of the BM decreased to 50% lower than that of the NM. Furthermore, the water absorption rate of the BM was 33% lower than that of the NM. The mass loss for both 3% and 6% HCl was comparable, whereas at 11% HCl, BM experienced a mass loss that was 68% greater than that of NM. These findings suggest that with 3% and 6% HCl, the microbially induced calcium carbonate precipitation (MICP) process effectively generated CaCO3, which filled the pores and enhanced the structural integrity of the BM, leading to improved compressive strength and durability. Conversely, at 11% HCl, the MICP benefits in BM were diminished due to adverse environmental conditions that negatively affected the bacterial cells, highlighting the limitations of the HCl concentration for optimizing MICP efficiency in mortar.

This is an article in the field of ceramics and composites. Taking ilmenite ore as the research object, the possible phase transformation of FeTiO3 in concrete liquid phase environment was analyzed in order to provide a basis for the utilization of ilmenite tailings. The thermodynamic stability of ilmenite (FeTiO3) was analyzed by thermodynamic calculation. Ilmenite ore powder was soaked in simulated concrete pore solution at 20 ℃ and 80 ℃ for 28 d and 270 d, XRD and SEM/EDS were used to detect mineral transformation. Using ilmenite ore to replace part of the gravel to prepare concrete, the influence on concrete strength at 20 ℃ and 80 ℃ was studied respectively. The results of thermodynamic calculations show that FeTiO3 is unstable in the environment of O2 and converts into Fe3O4 or Fe2O3 and TiO2. The immersion experiment of ilmenite in the simulated concrete pore solution shows that ilmenite has no obvious changes. The concrete strength test shows that at 20 ℃ and 80 ℃, when ilmenite ore replaces 5% crushed stone, the compressive strength of concrete increases, and when the replacement is 15%, the compressive strength decreases, the reason is that the quartz in the ilmenite ore has undergone an alkali aggregate reaction.