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Translation abstract Load absorption of deflection forces – Investigations into the break‐out resistance of concrete reinforcing barsIn curved reinforced concrete structures, the steel tensile forces result in radially directed deflection stresses in the concrete, which can cause the concrete cover to spall and the reinforcing bars to pull out. To investigate the absorption of these deflection forces by the concrete, the influence of various parameters on the break‐out forces of reinforcing bars was determined at Münster University of Applied Sciences. The influence of different bar diameters (16, 20, 25, 28 and 32 mm) and the influence of the interaction between several reinforcing bars with different concrete mix designs were investigated. The result of these tests is that larger rebar diameters and a higher concrete quality generally generated higher breaking loads. [ABSTRACT FROM AUTHOR]

In the process of pumping, the segregation of concrete mixture will lead to the difficulty of construction, and even the possibility of pipe blocking. There is a lack of a quickly evaluation for on‐site construction. In order to solve this problem, a rapid wet‐sieved test was proposed in this study and then its feasibility was evaluated based on concrete mixes with different water–cement ratios. Subsequently, the influence of sand ratio on the segregation degree of concrete was investigated. The test results show that a combination of 2.36 mm screen size and 20 s vibrating time did the best. The wet‐sieved mortar content and stratification degree were increased by 4.6%–25.2% and 0.3%–17.9% by pumping, respectively. With the sand ratio increasing from 0.40 to 0.60, the pumping pressure decreased by 51.9%. The linear fitting correlation between pumping pressure and wet‐sieved mortar content (0.96) is better than that between pumping pressure and stratification degree (0.85), which indicates that the proposed test method can reliably characterize the degree of segregation during the pumping of ready‐mixed concrete. [ABSTRACT FROM AUTHOR]

Ground Granulated Blast Furnace Slag (GGBS) is an effective supplementary cementitious material because of its pozzolanic properties and positive environmental impact. This research explores the flexural strength of concrete pavements by analyzing several high-volume formulations of GGBS concrete against conventional mixes. The study aims to assess the viability of incorporating high-volume GGBS mixes in pavement construction, with a particular emphasis on their flexural performance. The study employs various GGBS content levels (60%, 65%, 70%, and 75%) in concrete mixes, with the control mix containing ordinary Portland cement. Specimens are prepared according to standard procedures, and flexural testing is conducted to evaluate their performance. Statistical analysis is performed to compare the flexural strength and behavior of GGBS mixes with the control mix. The results obtained from the experiments revealed that the GGBS concrete mixes had better flexural performance than the control mix, with more strength and less cost. The results provide the performance of large-volume GGBS concrete mixes under flexural loading circumstances, which helps to understand whether these mixes are suitable for use in concrete pavements. Ultimately, this research sheds light on the possibilities of utilizing large- volume GGBS concrete mixes as long-term substitutes for traditional concrete pavements, which may help in the promotion of greener and more long-lasting infrastructure solutions. [ABSTRACT FROM AUTHOR]

Concrete pouring in winter is critical to both concrete manufacturers and end users owing to the possibility of concrete damage due to cold weather. In this context, various methods have been used to prevent frost damage to concrete in winter, including adjusting the concrete mix using a chemical admixture and heat-curing with tents. Of these methods, the insulated-gang-form approach does not require concrete-mix adjustment via a chemical-admixture addition. Furthermore, its positive effect on the initial quality of concrete during concrete construction in winter has previously been confirmed. In this study, the power consumption of the conventional gang form was compared with that of the insulated gang form to evaluate the efficiency of the two protection methods. A thermal vision camera was used to examine the surface heat loss of the gang forms after concrete pouring. The insulated gang form significantly outperformed the conventional one through its significantly reduced power consumption and reduced surface heat loss. These findings can contribute to the standardization of insulated gang form application to concrete protection in cold-weather conditions. [ABSTRACT FROM AUTHOR]

In order to be more efficient in the optimization of concrete mixture, a new intelligent optimization model of concrete mixture was established by using particle swarm optimization on the basis of the original optimization model, and the specific performance was fitted and predicted by using the support vector machine. Using the optimization model established in this work, the test results of 1,443 groups of mixed ratios show that the prediction accuracy of the new model is better than that of the traditional model. The average relative errors of the 7‐ and 28‐day compressive strengths and initial collapse were 10.42%, 7.43%, and 17.14%, respectively. This method is used in a practical project where a set of C25, C30, C35, and C40 concrete mix ratios are designed. The prediction and actual error of 7‐day intensity and 28‐day intensity are −14.4% to −6.1% and −17.6% to 0.6%, respectively, while the predicted value and actual slump error are 15%. The results show that the error between the measured value and the design value is basically within 15%, which meets the design requirements. The method can reduce the time and cost of concrete production, with the cost per cubic meter after optimization is 3.5–8 CHY lower than the concrete mix calculated by the conventional method. The relative decrease ranges from 1.53% to 3.22%. Finally, a practical quality and cost control system (compos) is established to make the strategy easier to apply. [ABSTRACT FROM AUTHOR]

Concrete, as a cornerstone of modern construction, heavily relies on the quality of its constituent materials, particularly aggregates. Among the critical factors contributing to high-quality concrete are proper gradation, absence of clay particles, and angular shape of aggregates. Adhering to these standards typically results in concrete with superior strength. However, aggregates sourced from riverbeds often possess a natural gradation, contain clay particles, and have rounded shapes. This study delves into a comparative analysis of aggregates sourced from two widely utilized riverbed regions, namely Hari-River and Kamar-Kalaq, situated within Herat province, Afghanistan. Given that over 90% of concrete in Herat province is sourced from these two riverbeds, the findings of this study carry immense significance. The research meticulously examines key parameters, including clay content, gradation, aggregate shape, and compressive strength, to determine the optimal choice for concrete production. Methodologically, samples were acquired following ASTM standards, and rigorous testing procedures were conducted, encompassing clay particle analysis, sieve analysis, and strength testing. The results reveal significant disparities between the two regions, with Hari-River demonstrating superior characteristics across various metrics. Particularly noteworthy is Hari-River's lower clay content of 2.7% compared to Kamar-Kalaq's 3.7%. The gradation of Hari-River for both coarse and fine aggregates is superior to that of Kamar-Kalaq when compared to size 67 aggregate range. Additionally, the average 28 days concrete compressive strength of Hari-River aggregates is 27.8 MPa, while that of Kamar-Kalaq is 23.4 MPa. [ABSTRACT FROM AUTHOR]

The development of new building elements, such as concrete and mortar with sustainable materials, which produce a lower carbon footprint, is an achievable milestone in the short term. The need to reduce the environmental impact of the production of cement-based materials is of vital importance. This work focuses on the evaluation of the life-cycle assessment, production costs, mechanical performance, and durability of three mortars and three concrete mixtures in which mixed recycled aggregates (MRAs) and biomass bottom ash from olive waste (oBBA) were included to replace cement and aggregates. Powdered MRA and oBBA were also applied as complementary cementitious materials with a reduced environmental footprint. Chemical and physical tests were performed on the materials, and mechanical performance properties, life-cycle assessment, and life-cycle cost analysis were applied to demonstrate the technical and environmental benefits of using these materials in mortar and concrete mixtures. This research showed that the application of MRA and oBBA produced a small reduction in mechanical strength but a significant benefit in terms of life-cycle population and environmental costs. The results demonstrated that finding long-term mechanical strength decreases between 2.7% and 14% for mortar mixes and between 1.7% and 10.4% for concrete mixes. Although there were small reductions in mechanical performance, the savings in environmental and monetary terms make the feasibility of manufacturing these cement-based materials feasible and interesting for both society and the business world. CO2 emissions are reduced by 25% for mortar mixes and 12% for concrete mixes with recycled materials, and it is possible to reduce the cost per cubic meter of mortar production by 20%, and the savings in the cost of production of a cubic meter of concrete is 13.8%. [ABSTRACT FROM AUTHOR]

Purpose: Evaluate the performance of progressive collapse of full-scale three-dimensional structure (3D) beam-slab substructures with and without the presence of reinforced concrete (RC) balconies using two concrete mixes [normal concrete (NC) and rubberized concrete (RuC)]. Design/methodology/approach: This study examines two concrete mixes to evaluate the progressive collapse performance of full-scale 3D beam-slab substructures with and without the presence of RC balconies using the finite element (FE) method. Findings: The results showed that the vertical loads that affect the structures of the specimens after including the balconies in the modeling increased by an average of 29.3% compared with those of the specimens without balconies. The specimens with balconies exhibited higher resistance to progressive collapse in comparison with the specimens without balconies. Moreover, the RuC specimens performed very efficiently during the catenary stage, which significantly enhanced robustness to substantial deformation to delay or mitigate the progressive collapse risk. Originality/value: All the experimental and numerical studies of the RC beam-slab substructures under progressive collapse scenarios are limited and do not consider the balcony's presence in the building. Although balconies represent a common feature of multistory residential buildings, their presence in the building has more likely caused the failure of this building compared with a building without balconies. However, balconies are an external extension of RC slabs, which can provide extra resistance through tensile membrane action (TMA) or compressive membrane action (CMA). All those gaps have not been investigated yet. [ABSTRACT FROM AUTHOR]

In this work, a particular type of carbon nano-material, like graphene oxide (GO), is synthesized in different batches by varying oxidation times, ranging from 1 to 4 days. The synthesis process initially starts with the oxidation of commercially available graphite powder and subsequently exfoliates the obtained graphite oxide in an aqueous solution using a high-frequency ultrasonication process. The synthesized GO batches were characterized using different characterization techniques to authenticate the formation of GO. The highly oxidized GO in an aqueous solution was selected and used as a strength-enhancing additive in concrete. The concrete mixes containing highly oxidized GO at the dosage of 0.01% 0.03%, 0.05%, 0.07%, and 0.09%bwoc were prepared to assess the strength and durability parameters. The GO (4 d) with 0.09%bwoc in concrete increases compressive strength by 58%, tensile strength by 41%, and flexural strength by 43% at 56 days. The results proved that the 0.09%bwoc GO dosage in cement concrete could effectively improve mechanical and durability performances compared to other mixes. Furthermore, the results are verified with the microstructural investigation using FE-SEM in secondary electron (SE) and backscattered electron (BSE) mode to monitor the microstructural changes and thickness of the interfacial transition zone (ITZ) during cement hydration. [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]

Digital fabrication of concrete structures has gained substantial research traction over the last decade, enabling efficient material use and adding more architectural freedom. Current research focuses on chemical and mineral admixtures, as well as manipulating the cement hydration reaction to control the yield stress evolution with time in the cement paste. Instead of providing yield stress through the concrete fluid properties, a high yield stress can be provided by interparticle friction from the use of high aggregate volumes and large nominal maximum aggregate size, with flow enhanced for material extrusion by vibration. Granular physics was applied to concrete mixture design to develop concrete mixtures with excellent edge retention abilities that flow easily under vibration. A linear regression analysis of concrete yield stress after vibration revealed that water content is most important, followed by fineness modulus of the aggregate combination and density after vibration. A decrease in water content, increase in fineness modulus and increase in density after vibration were found to increase the static yield stress after vibration. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) is a potential material for application as nano-reinforcements in cementitious composites owing to its high-water dispersibility, aspect ratio and outstanding mechanical characteristics. In this study, the combined effect of GO and fly ash on strength properties, stress–strain behaviour and static modulus of elasticity of high-strength concrete was investigated. In addition, microstructure has been characterized using SEM and EDS techniques. The addition of GO at 0.15% and the replacement of cement with fly ash at 10, 20 and 30% by weight was considered. The results exhibited that the addition of GO at 0.15% improved the compressive and flexural strength of concrete by 24.3 and 25.2%, respectively, at 7 days. The combined effect of GO and fly ash on the strength properties of concrete at 7 days was greater than control concrete demonstrating that GO can offset the effect of fly ash on delaying the strength growth at an early age. From the experimental results, it can be concluded that the addition of GO and fly ash into the concrete improved both the strength and elastic modulus, consequently exhibiting positive synergy in hybridizing GO and fly ash into the concrete. Also, the microstructure properties indicated that the GO and fly ash-based concrete mixes exhibited a denser microstructure. Furthermore, a nonlinear numerical model was also created for GO and fly ash-based concrete with finite element-based software ATENA-GiD to validate the experimental findings. The nonlinear numerical model successfully predicted the behaviour under monotonic axial compression and was quite beneficial in minimizing the tedious experimental testing. Finally, it is found that the findings of both the experimental and numerical investigations are in good agreement. [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]

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]

The microstructure of concrete can be affected by many factors, from non-destructive environmental factors through to destructive damage induced by transient stresses. Coda wave interferometry is a technique that is sensitive enough to detect weak changes within concrete by evaluating the ultrasonic signal perturbation compared to a reference state. As concrete microstructure is sensitive to many factors, it is important to separate their contributions to the observables. In this study, we characterize the relationships between the concrete elastic and inelastic properties, and temperature and relative humidity. We confirm previous theoretical studies that found a linear relationship between temperature changes and velocity variation of the ultrasonic waves for a given concrete mix, and provide scaling factors per Kelvin for multiple settings. We also confirm an anti-correlation with relative humidity using long-term conditioning. Furthermore, we explore beyond the existing studies to establish the relationship linking humidity and temperature changes to ultrasonic wave attenuation. [ABSTRACT FROM AUTHOR]

The feasibility of using the Semicircular Bending (SCB) test to control the quality of concrete for application in pavements was investigated. Two concrete mixtures incorporating high-strength cement with specified compressive strengths of 30 MPa and 40 MPa were manufactured. The results of the SCB test were correlated with those of the flexural strength of standardized beams and the compressive strength of cylinders. A statistical analysis of the goodness of fit of all the empirical models obtained was conducted to study the degree of association between the variables. Power models were the most appropriate to relate the mechanical properties studied, with Pearson's correlation coefficients higher than 0.93. These equations can feed the database of levels 1 and 2 of the Mechanistic-Empirical (ME) design method for concrete pavements. Models with unique values that allow quick calculations with good precision were also found. The results show that the SCB test is a promising option when estimating the flexural strength of concrete for use in pavement, as well as carrying out its control and quality assurance. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubes (CFSTs) have attracted increasing interest in research during the last decade as a construction system that increases its performance due to the use of self-stressing concrete. The efficiency and confining pressure of this construction solution mainly depends on the expansion of the concrete mixture introduced into the steel tube. This study shows the importance of the correct design of the expansive mixes and the correct selection of components. The effect of three types of chemical admixtures (air-entrained, setting retarder, and hardening accelerator) commonly used in the ready-mixed concrete industry when added to a self-stressing concrete made with a K-type calcium sulfoaluminate–based expansion agent has been analyzed. This study showed that certain chemical admixtures, added in a fixed proportion, conditioned both the compressive strength and the magnitude and kinetics of the expansion in a restricted regime of the reference self-stressing concrete mix. The efficiency of the CFST and self-stressing concrete construction solution represented by the bond failure strength and the sliding load of the concrete core against the steel tube was influenced not by the compressive strength of the expansive concrete but by the degree of restrained expansion (confinement effect) achieved. In this research, an alternative test method for measuring expansion was proposed, which allows continuous recording of positive strains (expansions), eliminating the dependence on setting time for demolding; this method even allows the exact identification of the expansion beginning. Finally, it was proposed that the ettringite detectable by the X-ray diffraction (XRD) technique was not representative of the magnitude of expansion generated from K-type calcium sulfoaluminate expansive agents because the proportion of ettringite was not related to the expansion determined by the different test methods proposed. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effects of using palm leaves ash, when it partially replaces the concrete cement content, to treat the effects of using seawater as a mixing water and curing water on concrete. The paper also explores the suitable replacement percentage of cement with palm ash to give the concrete more strength and suitable workability. A slump test was used to assess the fresh concrete's workability, as well as concrete strength testing after 7, 28, and 60 days. It was found that 5% of the cement replacement with palm leaves ash in conjunction with the full replacement of the mixing of pure water with seawater achieves an 84.188% increase in the ultimate compressive strength after 28 days of curing in tap water compared with that gained by normal concrete with mixing in seawater. Also, a reasonable workability was obtained. In the case of curing with seawater for 28 days, the partial replacement of 2.5% of cement with palm leaves ash achieves a 70.75% increase in the compressive strength when compared to normal concrete with mixing in seawater. [ABSTRACT FROM AUTHOR]

The correct workability of concrete is an essential parameter for its placement and compaction. However, an absence of automatic and transparent measurement methods to estimate the workability of concrete hinders the adaptation from laborious traditional methods such as the slump test. In this paper, we developed a machine-learning framework for estimating the slump class of concrete in the mixer using a stereovision camera. Depth data from five different slump classes was transformed into Haralick texture features to train several machine-learning classifiers. The best-performing classifier achieved a multiclass classification accuracy of 0.8179 with the XGBoost algorithm. Furthermore, we found through statistical analysis that while the denoising of depth data has little effect on the accuracy, the feature extraction of mixer blades and the choice of region of interest significantly increase the accuracy and the efficiency of the classifiers. The proposed framework shows robust results, indicating that stereovision is a competitive solution to estimate the workability of concrete during concrete production. [ABSTRACT FROM AUTHOR]

The development of geopolymer concrete offers promising prospects for sustainable construction practices due to its reduced environmental impact compared to conventional Portland cement concrete. However, the complexity involved in geopolymer concrete mix design often poses challenges for engineers and practitioners. In response, this study proposes a simplified approach for designing geopolymer concrete mixtures, drawing upon principles from Portland cement concrete mix design standards and recommended molar ratios of oxides involved in geopolymer synthesis. The proposed methodology aims to streamline the mix design process while optimizing key factors such as chemical composition, alkali activation solution, water content, and curing conditions to achieve desired compressive strength and workability. By leveraging commonalities between Portland cement concrete and geopolymer concrete, this approach seeks to facilitate the adoption of geopolymer concrete in practical construction applications. The proposed mix design guidelines have been validated through examples for concrete cured under different conditions, including outdoor and oven curing. Future research should focus on validating the proposed methodology through experimental studies and exploring cost-effective alternatives for alkali activation solutions to enhance the feasibility and scalability of geopolymer concrete production. Overall, the proposed simplified approach holds promise for advancing the utilization of geopolymer concrete as a sustainable alternative in the construction industry. [ABSTRACT FROM AUTHOR]

Across the world, the acceptance criterion for concrete made with non-potable water (SA) is stipulated for mean strength with reference to similar concrete made with potable water (SP). The basis for the strength design of concrete is the characteristic strength. The effect of the acceptance criteria on the characteristic strength of SA and SP was examined using statistical simulations, for the first time. It was found that, compared with a two-sample set, using a three-sample set would improve the characteristic strength of SA. A higher allowable ratio between the means of SA and SP and a lower deviation of individual samples from the mean would improve the characteristic strength of SA. The effect of the coefficient of variation (CoV) of the original population on the characteristic strength of SA varied. On the one hand, a higher CoV reduced the characteristic strength of SP, thereby increasing the probability of SA strength being higher than SP strength. On the other, a higher CoV of SP meant a wider spread of the samples and that could increase the CoV of SA, thereby reducing the characteristic strength of SA. Probabilistic charts were developed for the characteristic strengths of SA and SP for different combinations of the aforementioned variables, with guidance for practical application. [ABSTRACT FROM AUTHOR]

Concrete 3D printing, an innovative construction technology, offers reduced material waste, increased construction speed, and the ability to create complex and customized shapes that are challenging to achieve with traditional methods. This study delves into the unique fresh-state performance required for 3D printing concrete, discussing buildability, extrudability, and shape retention in terms of concrete rheology, which can be modified using admixtures. Currently most 3D printing concretes feature high cement contents, with little use of secondary cementitious materials. This leads to high embodied carbon, and addressing this is a fundamental objective of this work. The research identifies attapulgite, bentonite, and sepiolite clay as potential concrete admixtures to tailor concrete rheology. Eight low-carbon concrete mixes are designed to incorporate GGBS at a 50% replacement level and are used to measure the influence of each clay on the concrete rheology at varying dosages. A comprehensive rheological test protocol is designed and carried out on all mixes, together with other tests including slump-flow and compression strength. The objective is to determine the applicability of each clay in improving the printability of low-carbon concrete. The findings reveal that at a dosage of 0.5%, sepiolite was seen to improve static yield stress, dynamic yield stress, and rate of re-flocculation, resulting in improved printability. The addition of attapulgite and sepiolite at a dosage of 0.5% by mass of binder increased compressive strength significantly; bentonite had very little influence. These gains are not repeated at 1% clay content, indicating that there may be an optimum clay content. The results are considered encouraging and show the potential of these clays to enhance the performance of low-carbon concrete in 3D printing applications. [ABSTRACT FROM AUTHOR]

This study investigates the individual and combined effects of micro and nano lead monoxide (PbO) and granodiorite (GD) on concrete's mechanical and radiation shielding properties. Both materials were partially substituted for cement at varying ratios. Additionally, mixtures with optimal radiation shielding performance were prepared to explore the synergy of combining them. The mentioned materials are used for the first time in an extensive study at the nano scale to investigate their impact on concrete's mechanical properties, microstructure, and gamma radiation attenuation. Two gamma ray sources of uranium (U238) and cesium (Cs137) were used measure the radiation attenuation coefficients for all designed concrete mixes. A simple methodology was followed to assess the concrete shields efficiency via utilizing portable handheld gamma‐ray spectrometer that offers two reading modes. Results indicated that increasing the ratio of PbO is directly proportional to the concrete ability to attenuate radiation, where the optimal individual replacement ratios were recorded at 5% for micro and nano particle sizes. At this ratio, the linear attenuation coefficient (μ) values were improved by 39.57% and 24.78% for the nano and micro PbO, respectively. Additionally, the optimal ratio for improving mechanical properties was at 3% and 2% for nano and micro PbO, while the higher ratios showed a decline in mechanical properties especially at 5% micro PbO with 7.02% reduction in the compressive strength value. Regarding GD powder, the optimal replacement ratios for improving concrete radiation shielding were consistent with those enhancing its mechanical properties at 4% and 7% in both nano and micro scales, respectively. The combined mixes further enhanced the overall concrete performance, especially its radiation shielding ability. Compared to the control mix, the compressive strength, tensile strength, and μ were increased by 25.7%, 16.2%, and 44.7% at the optimal mixture of 5% nano PbO + 4% nano GD. [ABSTRACT FROM AUTHOR]

Three kinds of slump-retention polycarboxylate superplasticizers(52HPC4, 52IPC4, and 52EPC4) were synthesized by using HPEG, IPEG, or EPEG as macromonomers. The effects of polycarboxylate superplasticizers on the slump-retention of cement and concrete were investigated. The mechanism of action was explained by the composition of PCE polymers and monomer sequences (EHE, HHE, or HHH), which were investigated by using conductivity, GPC, 1H-NMR, and 13C-NMR. The results indicated that the slump flow of cement paste mixed with 52EPC4 was increased quickly within 120 min, while 52IPC4 doesn't change within 240 min. Concrete mixed with 52IPC4 had the best slump-retention performance reaching 440 mm after 150 min, but concrete mixed with 52HPC4 was almost no fluidity after 120 min which had the largest slump flow loss through time than that containing other PCEs, and the conductivity of 52IPC4 aqueous solution decreased more slowly than other PCEs. Because of the highest content of effective PCE polymers, and the largest steric hindrance to ester bond resulting in the concrete had the best slump-retention performance when mixed with 52IPC4, because of the smallest steric hindrance to ester bond resulting in the fastest increase spread flow of cement paste which mixed 52EPC4, because of the highest content of low molecular polymers and the lowest content of effective PCE polymers in 52HPC4 resulting in the smallest initial slump flow of concrete, and the largest slump flow loss through time of concrete, even though the steric hindrance effect was larger than 52EPC4. [ABSTRACT FROM AUTHOR]

This study investigates the enhancement of Euphorbia Tortilis Cactus (ETC) infused concrete, focusing on its microstructural characteristics and mechanical properties. ETC concrete, known for superior tensile ductility and durability, was characterized using advanced 3D X-ray tomography and energy dispersive X-ray spectroscopy (EDX) analysis. Specimens with a 9% ETC extract mix underwent high-resolution Micro Computed Tomography scanning, revealing an average porosity of 3.3% and providing detailed insights into internal features like pores, fibers, and aggregates. EDX mapping identified key elements, including Si, O, Mg, and Ca, highlighting calcium carbonate and brucite formations. This research addresses gaps in understanding ETC concrete's microstructure and mechanical behavior, using non-destructive imaging and chemical analysis to offer comprehensive insights. The findings suggest that ETC concrete can be optimized for enhanced performance in sustainable construction, highlighting its potential for applications requiring high durability and ductility. The study's novelty lies in its application of advanced imaging and analysis techniques to optimize ETC concrete mix designs, assess durability, and develop strategies for mitigating structural issues, thus providing valuable insights into the material's properties and behavior. [ABSTRACT FROM AUTHOR]

Creep is a complex behavior of concrete since it induces different stages of response under loading and unloading with time. It represents the time-dependent strain as a result of a constant sustained load applied with time. In cementitious materials such as engineered cementitious composite concrete, ECC, the loaded cement paste is the principal source of creep strain. Therefore, investigating the overall creep behavior, under the loading and unloading stages, will be beneficial in providing data for the performance of ECC concrete. The test for compressional creep strain is done according to the ASTM C- 512 under controlled temperature (21 oC) and relative humidity (40%). In this research, the loading stage lasted for 9 months, and the unloading stage lasted 3 months. The total creep strain, creep coefficient, and specific creep were recorded for six ECC concrete mixes. The mixes have two strength levels, 30 and 60 MPa at 28 days, and contain polypropylene and polyvinyl alcohol fibers. Results revealed significant enhancement, and lower creep behavior, in mixes including fibers compared to plain mixes. The best promising results for the creep coefficient and specific creep were recorded when using mixes of 60 MPa containing polyvinyl alcohol fibers compared to plain mixes. [ABSTRACT FROM AUTHOR]

This comprehensive literature review delves into the application of Scheffe's Simplex Lattice Model for optimizing cement concrete mixtures, with a particular emphasis on its impact on material properties and sustainability. The review meticulously outlines the principles, historical context, and advantages of Scheffe's model, providing a nuanced understanding of its significance. Comparative analyses with traditional and alternative optimization techniques in concrete mix design illuminate the distinct advantages of statistical methods, especially Scheffe's model. The review critically examines the challenges and limitations associated with applying Scheffe's model, addressing issues related to the complexity of concrete mixtures and computational demands. Potential avenues for improvement are explored, suggesting refinements to handle non-linearity, incorporate advanced optimization algorithms, and streamline computational requirements. Additionally, the review highlights emerging trends in statistical modeling for concrete mixture optimization, such as the integration of machine learning and data-driven approaches, signaling the evolving landscape of concrete technology. In conclusion, the literature underscores Scheffe's Simplex Lattice Model as a valuable and versatile tool with far-reaching implications for the advancement of concrete mixture design methodologies. The call to action encourages ongoing research and development to refine the model, explore emerging trends, and address practical challenges, positioning Scheffe's model as a cornerstone in the pursuit of sustainable, resilient, and high-performance concrete materials. [ABSTRACT FROM AUTHOR]

The process of concrete production involves mixing cement, water, and other materials. The quantity of each of these materials results in a performance that is particularly estimated in terms of compressive or flexural strength. It has been observed that the final performance of concrete has a high variance and that traditional formulation methods do not guarantee consistent results. Consequently, designs tend to be over-designed, generating higher costs than required, to ensure the performance committed to the client. This study proposes the construction of predictive machine learning models to estimate compressive or flexural strength and concrete slump. The study was carried out following the Team Data Science Process (TDSP) methodology, using a dataset generated by the Colombian Ready Mix (RMX) company Cementos Argos S.A. over five years, containing the quantity of materials used for different concrete mixes, as well as performance metrics measured in the laboratory. Predictive models such as XGBoost and neural networks were trained, and hyperparameter tuning was performed using advanced techniques such as genetic algorithms to obtain three models with high performance for estimating compressive strength, flexural strength, and slump. This study concludes that it is possible to use machine learning techniques to design reliable concrete mixes that, when combined with traditional analytical methods, could reduce costs and minimize over-designed concrete mixes. [ABSTRACT FROM AUTHOR]

Ensuring precise estimation of creep characteristics is critical for the efficient design of structures prone to creep deformation. Creep is an indicator of permanent and gradual deformation that transpires within a material when it is continuously subjected to a burden for an extended duration. In addition to the temperature and duration of load application, the degree of creep in concrete is also affected by the material's inherent properties and the length of time it has been exposed to the load. The enduring consequences of creep might result in significant distortions that give rise to structural deficiencies inside the edifice. Multiple factors, including the concrete's mixing ratios and compressive strength, affect the initial hardening of the material. The data pertaining to the early creep behaviour of high-strength concrete were gathered from relevant literature sources for the purposes of this study. The research utilised artificial neural network methodology and relative importance analysis to ascertain the most influential parameters on the early creep behaviour of high-strength concrete. Understanding the components that contribute to creep is crucial in mitigating the detrimental effects of creep on concrete and concrete structures. [ABSTRACT FROM AUTHOR]

This work aims at comparing the splitting tensile strength of basalt concrete mix with granite concrete mix. A total of 24 cylindrical concrete specimens of diameter 100mm and length 200mm were made in the laboratory. The British standard mix design method was used to obtain four different mix designs for batching the ingredients comprising ordinary Portland cement, river sand, water, granite and basalt with two mix designs each corresponding to basalt and granite samples. The specimens were cured for 28 days and tested for splitting tensile strength. The results show equivalent values of splitting tensile strength for basalt and granite samples with values for granite samples slightly higher than those of basalt samples. The average splitting tensile strength of the basalt samples B1, B2, B3, B4, B5 and B6 are 11.10 N/mm², 10.37 N/mm², 11.37 N/mm², 10.13 N/mm², 11.60 N/mm², 10.25N/mm² respectively while that of the granite samples G1 and G2 are 11.52 N/mm² and 10.58N/mm² respectively. The corresponding mix ratios are 1:1.96:2.81 for B1, B3, and B5 samples, 1:2.25:2.75 for B2, B4, and B6 samples, 1:1.80:2.75 for G1 sample and 1:2.07:2.76 for G2 sample. [ABSTRACT FROM AUTHOR]

The effects of grades of coarse aggregates on the cost of concrete was studied. Several times in real life practice, the engineer at construction site is faced with the problem of not having the required grade of coarse aggregate for a given project. . This could be caused by several reasons such as; non-availability of desired grade, the different grades of coarse aggregate being obtained as a left over from a sister project, etc. In Nigeria, coarse aggregate for concrete is very expensive and thus, the engineer will think of how to use the available grade of coarse aggregate in his concrete mix design to achieve the desired results instead of discarding it. In this study, seven different grades of coarse aggregate were investigated. The fineness modulus of the fine aggregate and bulk densities of the various grades of coarse aggregate were determined. The results were used together with tables from American Concrete Institute (ACI) code to carry out concrete mix design on all the various grades of coarse aggregate to calculate the quantities of the different elements of concrete. From the mix design, the cost of the materials for producing one cubic meter of concrete was determined. The result showed that the Well graded aggregate had the highest bulk density of 1717Kg/m³ while uniformly graded retained on 10mm sieve had the least bulk density of 1580Kg/m³. Uniformly graded aggregate retained on 10mm sieve required the highest cost of N58,278.81 to produce a cubic meter of grade 25 concrete while the cost was least at N56,242.52 when uniformly graded retained on 20mm sieve and Gap-graded without 5mm size were used. This suggests that the larger the size of coarse aggregate (within the size limits studied) the less the cement paste required and hence the less the cost. [ABSTRACT FROM AUTHOR]

Modern concrete mix design is a complex process involving superplasticisers, fine powders, and fibres, requiring time and energy due to the high number of trial tests needed to achieve rheological properties in the fresh state. Concrete batching involves the extensive use of materials, time, and the testing of chemical admixtures, with various methodologies proposed. Therefore, in some instances, the required design properties (physical and mechanical) are not achieved, leading to the loss of resources. The concrete equivalent mortar (CEM) method was introduced to anticipate concrete behaviour at fresh and hardened states. Moreover, the CEM method saves time and costs by replacing coarse aggregates with an equivalent sand mass, resulting in an equivalent specific surface area at the mortar scale. This study aims to evaluate the performance of fibre in CEM and concrete and determine the relationships between the CEM and the concrete in fresh and hardened states. Steel and polypropylene fibres were used to design three series of mixtures (CEM and concrete): normal-strength concrete (NSC), high-strength concrete (HSC), high-strength concrete with fly ash (HSCFA), and equivalent normal-strength mortar (NSM), high-strength mortar (HSM), and high-strength mortar with fly ash (HSMFA). This study used three-point bending tests and digital image correlation to evaluate load and crack mouth opening displacement (CMOD) curves. An analytical mode I crack propagation model was developed using a tri-linear stress–crack opening relationship. Post-cracking parameters were optimised using inverse analysis and compared to actual MC2010 characteristic values. The concrete slump is approximately half of the CEM flow; its compressive strength ranges between 78% and 82% of CEM strength, while its flexural strength is 60% of CEM strength. The post-cracking behaviour showed a significant difference attributed to the presence of aggregates in concrete. The fracture energy of concrete is 28.6% of the CEM fracture energy, while the critical crack opening of the concrete is 60% of that of the CEM. [ABSTRACT FROM AUTHOR]

Each component of the material that makes up concrete has a significant influence on its mechanical properties, so a mix design is needed to obtain the optimum concrete quality. This research uses three mix design methods, namely based on SNI 03-2834-2000, SNI 7656:2012, and Dreux Gorisse. SNI 03-2834-2000 refers to the DOE method from the UK, while SNI 7656:2012 adopts the ACI method from America. SNI 03-2834-2000 and SNI 7656:2012 are the applicable methods in Indonesia. While Dreux Gorisse is a concrete mix design method originating from France. This study aims to analyze the effect of concrete mix design and maximum aggregate size variation on the compressive strength of normal concrete. The maximum size of coarse aggregate used was 10, 20, and 40 mm. The planned concrete quality (f'c) was 25 MPa with cylindrical specimens measuring 15x30 cm. The highest compressive strength test results at the age of 28 days are with the SNI 7656:2012 method for a maximum aggregate size of 10 mm at 31.33 MPa. While the lowest compressive strength value with Dreux Gorisse for a maximum aggregate size of 40 mm was 25.38 MPa. In all mix design methods, the smaller the maximum size of coarse aggregate, the higher the compressive strength value. The maximum aggregate size of 10 mm in the SNI 7656:2012 method resulted in an increase in the maximum compressive strength by 25.31% from the planned compressive strength because it has a lower w/c ratio and slump values of 0.49 and 65 mm. [ABSTRACT FROM AUTHOR]

Raw-crushed wind-turbine blade (RCWTB), a waste from the recycling of wind-turbine blades, is used as a raw material in concrete in this research. It contains not only fiberglass-composite fibers that bridge the cementitious matrix but also polyurethane and balsa-wood particles. Therefore, concrete containing RCWTB can be notably affected by moisture and temperature fluctuations and by exposure to high temperatures. In this research, the performance of five concrete mixes with 0.0%, 1.5%, 3.0%, 4.5%, and 6.0% RCWTB, respectively, is studied under moist/dry, alternating-sign-temperature-shock, and high-temperature-shock tests. Two damage mechanisms of RCWTB within concrete were found through these tests: on the one hand, micro-cracking of the cementitious matrix, which was verified by microscopic analyses and was dependent on concrete porosity; on the other, damage and degradation of the RCWTB components, as the polyurethane melted, and the balsa-wood particles burned. Both phenomena led to larger remaining-strain levels and reduced concrete compressive strength by up to 25% under temperature and humidity variations, although the bridging effect of the fiberglass-composite fibers was effective when adding RCWTB amounts higher than 3.0%. The compressive-strength loss after the high-temperature-shock test increased with the RCWTB content, reaching maximum values of 8% after an exposure time of 7 days. Statistical analyses revealed that effect of the RCA amount in the concrete was conditioned by the exposure times in all the tests. The accurate definition of those times is therefore key to set an RCWTB content in concrete that ensures its suitable behavior under the environmental conditions analyzed. [ABSTRACT FROM AUTHOR]

The mechanical characteristics of concrete are crucial factors in structural design standards especially in concrete technology. Employing reliable prediction models for concrete's mechanical properties can reduce the number of necessary laboratory trials, checks and experiments to obtain valuable representative design data, thus saving both time and resources. Metakaolin (MK) is commonly utilized as a supplementary replacement for Portland cement in sustainable concrete production due to its technical and environmental benefits towards net-zero goals of the United Nations Sustainable Development Goals (UNSDGs). In this research work, 204 data entries from concrete mixes produced with the addition of metakaolin (MK) were collected and analyzed using eight (8) ensemble machine learning tools and one (1) symbolic regression technique. The application of multiple machine learning protocols such as the ensemble group and the symbolic regression techniques have not been presented in any previous research work on the modeling of splitting tensile strength of MK mixed concrete. The data was partitioned and applied according to standard conditions. Lastly, some selected performance evaluation indices were used to test the models' accuracy in predicting the splitting strength (Fsp) of the studied MK-mixed concrete. At the end, results show that the k-nearest neighbor (KNN) outperformed the other techniques in the ensemble group with the following indices; SSE of 4% and 1%, MAE of 0.1 and 0.2 MPa, MSE of 0, RMSE of 0.1 and 0.2 MPa, Error of 0.04% and 0.04%, Accuracy of 0.96 and 0.96 and R² of 0.98 and 0.98 for the training and validation models, respectively. This is followed closely by the support vector machine (SVM) with the following indices; SSE of 7% and 3%, MAE of 0.2 and 0.2 MPa, MSE of 0.0 and 0.1 MPa, RMSE of 0.2 and 0.3 MPa, Error of 0.05% and 0.06%, Accuracy of 0.95 and 0.94, and R² of 0.96 and 0.95, for the training and validation models, respectively. The third model in the superiority rank is the CN2 with the following performance indices; SSE of 15% and 4%, MAE of 0.2 and 0.2 MPa, MSE of 0.1 and 0.1 MPa, RMSE of 0.3 and 0.3 MPa, Error of 0.08% and 0.07%, Accuracy of 0.92 and 0.93 and R² of 0.92 and 0.93, for the training and validation models, respectively. These models outperformed the models utilized on the MK-mixed concrete found in the literature, therefore are the better decisive modes for the prediction of the splitting strength (Fsp) of the studied MK-mixed concrete with 204 mix data entries. Conversely, the NB and SGD produced unacceptable model performances, however, this is true for the modeled database collected for the MK-mixed Fsp. The RSM model also produced superior performance with an accuracy of over 95% and adequate precision of more than 27. Overall, the KNN, SVM, CN2 and RSM have shown to possess the potential to predict the MK-mixed Fsp for structural concrete designs and production. [ABSTRACT FROM AUTHOR]

One way of recycling waste materials such as tyres and glass is to use them in concrete. The effects of the simultaneous use of waste rubber particles (RPs) as a partial substitute for fine aggregate and glass powder (GP) as a partial substitute for cement on the workability and mechanical properties of concrete at ambient temperature and after exposure to high temperature (600°C) were investigated in this work. In total, 13 mixes were prepared. Except for the reference mix, all the other mixes contained a combination of RPs replacing fine aggregate at percentages of 5% or 10% by volume and GP replacing cement at percentages of 10%, 15% or 20%. Two different sizes of RPs were investigated (0.15–1 mm and 3–5 mm). Slump tests were carried out on the fresh concretes. Tests for compressive strength and tensile strength before and after thermal exposure, and tests for mass loss after exposure to elevated temperature were also carried out. To obtain an understanding of the behaviour of the waste materials in concrete, scanning electron microscopy and energy-dispersive X-ray spectroscopy were conducted. In terms of compressive and tensile strengths, of all the mixes containing RPs and GP, the best results were for the mix with 5% RPs of 3–5 mm and 10% GP. [ABSTRACT FROM AUTHOR]

Research on the combined substitution of supplementary cementitious materials (SCMs) has already demonstrated that it might be one of the few viable options to produce low-carbon concrete at scale. This paper presents an experimental investigation on the performance and durability of rice husk ash (RHA) and calcined clay (CC) in ternary blended concrete exposed to chloride attacks under wet/dry cycles. Portland cement (PC) was replaced by RHA and CC up to 50% by weight to produce low-carbon concrete. Samples were subjected to wet/dry cycles in 3.5% NaCl water, with mineralogical composition and microstructure development before and after exposure analysed by TGA-DSC, MIP, XRD, and SEM. The durability of the concrete against wet/dry cycles was investigated in terms of compressive strength, water absorption, open porosity, density, thermal conductivity, and electrical resistivity. The results showed that concrete mixes with CC and RHA up to 60% exhibited an increase of 33% in compressive strength, followed by minimal changes in water absorption. While a decrease in electrical resistivity was measured in all samples with RHA and CC, increasing the CC content to 50% resulted in improved resistance to chloride penetration. Increasing the CC content resulted in a more refined microstructure, with an overall decrease in porosity of up to 32% compared to the control series. While RHA alone did not contribute to significant improvements after wet/dry cycles, the combined substitution of RHA and CC at SCM replacement levels of 60% showed an overall improvement in hardened properties and durability. This investigation provides valuable insights into the long-term performance and strength of innovative low-carbon concrete. [ABSTRACT FROM AUTHOR]

Geopolymer concrete emerges as a promising avenue for sustainable development and offers an effective solution to environmental problems. Its attributes as a non-toxic, low-carbon, and economical substitute for conventional cement concrete, coupled with its elevated compressive strength and reduced shrinkage properties, position it as a pivotal material for diverse applications spanning from architectural structures to transportation infrastructure. In this context, this study sets out the task of using machine learning (ML) algorithms to increase the accuracy and interpretability of predicting the compressive strength of geopolymer concrete in the civil engineering field. To achieve this goal, a new approach using convolutional neural networks (CNNs) has been adopted. This study focuses on creating a comprehensive dataset consisting of compositional and strength parameters of 162 geopolymer concrete mixes, all containing Class F fly ash. The selection of optimal input parameters is guided by two distinct criteria. The first criterion leverages insights garnered from previous research on the influence of individual features on compressive strength. The second criterion scrutinizes the impact of these features within the model's predictive framework. Key to enhancing the CNN model's performance is the meticulous determination of the optimal hyperparameters. Through a systematic trial-and-error process, the study ascertains the ideal number of epochs for data division and the optimal value of k for k-fold cross-validation--a technique vital to the model's robustness. The model's predictive prowess is rigorously assessed via a suite of performance metrics and comprehensive score analyses. Furthermore, the model's adaptability is gauged by integrating a secondary dataset into its predictive framework, facilitating a comparative evaluation against conventional prediction methods. To unravel the intricacies of the CNN model's learning trajectory, a loss plot is deployed to elucidate its learning rate. The study culminates in compelling findings that underscore the CNN model's accurate prediction of geopolymer concrete compressive strength. To maximize the dataset's potential, the application of bivariate plots unveils nuanced trends and interactions among variables, fortifying the consistency with earlier research. Evidenced by promising prediction accuracy, the study's outcomes hold significant promise in guiding the development of innovative geopolymer concrete formulations, thereby reinforcing its role as an eco-conscious and robust construction material. The findings prove that the CNN model accurately estimated geopolymer concrete's compressive strength. The results show that the prediction accuracy is promising and can be used for the development of new geopolymer concrete mixes. The outcomes not only underscore the significance of leveraging technology for sustainable construction practices but also pave the way for innovation and efficiency in the field of civil engineering. [ABSTRACT FROM AUTHOR]