Search Results (85)

This present study proposes different machine learning-based predictors for the assessment of the residual compressive strength of Self-Compacting Concrete (SCC) subjected to high temperatures. The investigation is based on several literature algorithmic approaches based on Artificial Neural Networks with distinct training algorithms (Bayesian Regularization, Levenberg–Marquardt, Scaled Conjugate Gradient, and Resilient Backpropagation), Support Vector Regression, and Random Forest methods. A training database of 150 experimental data points is derived from a careful literature review, incorporating temperature (20–800 °C), geometric ratio (height/diameter), and corresponding compressive strength values. A statistical analysis revealed complex non-linear relationships between variables, with strong negative correlation between temperature and strength and heteroscedastic data distribution, justifying the selection of advanced machine learning techniques. Feature engineering improved model performance through the incorporation of quadratic terms, interaction variables, and cyclic transformations. The Resilient Backpropagation algorithm demonstrated superior performance with the lowest prediction errors, followed by Bayesian Regularization. Support Vector Regression achieved competitive accuracy despite its simpler architecture. Experimental validation using specimens tested up to 800 °C showed a good reliability of the developed systems, with prediction errors ranging from 0.33% to 23.35% across different temperature ranges. Full article

Alkali-activated binders (AAB) are a suitable and sustainable alternative to ordinary Portland cement (OPC), with reductions in natural resource usage and environmental emissions in regions where the necessary industrial residues are available. Despite its potential, the lack of mix design methods still limits its applications. This paper proposes a systematic parametric validation for AAB mix design applied to pastes and concretes, valorizing steel slag as precursors. The composed binders are based on coal fly ash (FA) and Basic Oxygen Furnace (BOF) steel slag. These precursors were activated with sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) alkaline solutions. A parametric investigation was performed on the mix design parameters, sweeping the (i) alkali content from 6% to 10%, (ii) silica modulus (SiO₂/Na₂O) from 0.75 to 1.75, and (iii) ash-to-slag ratios in the proportions of 75:25 and 50:50, using parametric intervals retrieved from the literature. These variations were analyzed using response surface methodology (RSM) to develop a mechanical model of the compressive strength of the hardened paste. Flowability, yield stress, and setting time were evaluated. Statistical analyses, ANOVA and the Duncan test, validated the model and identified interactions between variables. The concrete formulation design was based on aggregates packing analysis with different paste contents (from 32% up to 38.4%), aiming at self-compacting concrete (SCC) with slump flow class 1 (SF1). The influence of the curing condition was evaluated, varying with ambient and thermal conditions, at 25 °C and 65 °C, respectively, for the initial 24 h. The results showed that lower silica modulus (0.75) achieved the highest compressive strength at 80.1 MPa (28 d) for pastes compressive strength, densifying the composite matrix. The concrete application of the binder achieved SF1 fluidity, with 575 mm spread, 64.1 MPa of compressive strength, and 26.2 GPa of Young’s modulus in thermal cure conditions. These findings demonstrate the potential for developing sustainable high-performance materials based on parametric design of AAB formulations and mix design. Full article

Self-compacting concrete (SCC) is an innovative building material that is distinguished by its ability to flow and fill forms without the need for mechanical vibration. The aim of this research was to determine the effect of different types of fibres—steel, glass, and polypropylene—on the properties of both the fresh mix (consistency, density, air content, and viscosity) and the hardened concrete (compressive strength, tensile strength in bending, density, water absorption, and frost resistance). Attention was also paid to CO₂ emissions associated with cement production and the potential of their reduction by using alternative materials. The results of the conducted research demonstrate that, in terms of enhancing the mechanical properties of self-compacting concrete (SCC), the incorporation of glass fibres (GFs) leads to the most significant improvements in compressive and flexural strength—by 1.6% and 29.2%, respectively. Therefore, these fibres can be recommended for use in high-performance structural applications, such as precast elements, load-bearing components, and structures subjected to dynamic loading. Polypropylene fibres (PPFs), owing to their ability to reduce water absorption by 7.3%, may be suitable for elements exposed to high humidity and shrinkage risk, such as tunnels, fire-resistant barriers, or insulating layers. Steel fibres (SFs), in turn, have proven particularly effective in SCC used for industrial flooring and other elements exposed to cyclic dynamic loads. Full article

This paper investigates the effects of silica fume, cenosphere, fly ash, and ground slag powder on the rheological properties and mechanical strengths of self-compacting ultra-high performance concrete (UHPC). The mass ratio of each mineral admixture varies from 0% to 15%, while the water-binder ratios are set at 0.18, 0.20, and 0.22. The slump flow and plastic viscosity of fresh UHPC are measured, and the corresponding flexural and compressive strengths of UHPC cured for 3 days and 28 days are determined. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are employed to elucidate the mechanisms underlying the observed performance changes. The results indicate that the addition of silica fume and mineral powder negatively impacts the fluidity of fresh UHPC but positively affects its plastic viscosity. Conversely, the inclusion of cenosphere and fly ash enhances the fluidity of fresh UHPC while having the opposite effect on its plastic viscosity. Increasing the water-binder ratio improves the fluidity of fresh UHPC but reduces its plastic viscosity. Mechanically, silica fume enhances the strengths of UHPC. In contrast, the cenosphere, fly ash, and mineral powder decrease the strengths of UHPC cured for 3 days but increase those cured for 28 days. UHPC containing silica fume exhibits the most compact hydration products and the lowest content of Ca(OH)₂. Full article

Concrete structures are prone to cracking and seepage issues due to material degradation during long-term service. Ionic chelating agents (ICAs) can significantly enhance the durability and extend the service life of concrete structures by chelating metal ions in the cement matrix and promoting the formation of crystalline products within pores. The study selected commonly used ICAs, including sodium gluconate, sodium maleate, and sodium citrate, as well as a self-made high-efficiency ICA, to compare their chelating abilities for metal ions (such as Al³⁺, Mg²⁺, Fe³⁺, and Ca²⁺). Their effects on the performance and microstructure of cement-based materials were evaluated through tests on hydration heat, mechanical strength, the chloride ion diffusion coefficient, pore size distribution, and microstructural analysis. The results showed that the stronger the chelating ability of the ICA, the more significant its improvement on the performance and microstructure of cement-based materials. Cement paste incorporating the high-efficiency ICA exhibited significantly accelerated hydration kinetics, with the hydration rate markedly increasing and the peak heat release rising from 0.0012 W/g to 0.0016 W/g, thereby effectively enhancing the early-age properties of the cement-based materials. After 28 days, compared to ordinary mortar, the flexural and compressive strengths of mortar containing the high-efficiency ICA increased by 17.1% and 11.6%, respectively, while the chloride ion diffusion coefficient decreased by 37.4%. Pore size distribution and microstructural analyses indicated that mortar incorporating the high-efficiency ICA exhibited the most compact internal structure, with abundant crystalline products such as CaSiO₃ and 3CaO·Al₂O₃·3CaSO₄·32H₂O (AFt) forming within the pores. These findings suggest that optimizing the ion-chelating capacity of ICA provides a feasible strategy to enhance the compactness, durability, and mechanical performance of cement-based materials in practical engineering applications. Full article

To address the issues of significant brittleness in self-compacting concrete (SCC), limited parameter ranges in existing steel fiber reinforcement studies, and incomplete performance evaluation systems, this study conducted mechanical performance tests on steel fiber-reinforced SCC (SFRSCC) with a wide range of volume fractions (1–3%) and multiple aspect ratios. A multi-indicator comprehensive evaluation model of compressive strength, flexural strength, and elastic modulus was established using an improved entropy-weighted TOPSIS method. Gray relational analysis was integrated to reveal nonlinear correlation patterns between fiber parameters (the volume fraction and aspect ratio) and mechanical responses. The experimental results demonstrated the following: (1) At a 3% fiber content, compressive and flexural strengths increased by 25.7% and 280%, respectively, compared to the control group; (2) the elastic modulus peaked at 2% fiber content, with excessive content (3%) causing an uneven fiber dispersion and diminishing performance gains; (3) short fibers (6 mm) achieved optimal compressive strength at 3% content and medium-length fibers (13 mm) significantly enhanced flexural strength, while long fibers (25 mm) maximized the elastic modulus at 2% content. The combined application of the improved entropy-weighted TOPSIS method and gray relational analysis identified that the high fiber content (3%) paired with medium-length fibers (13 mm) optimally balanced flexural strength and toughness, providing theoretical guidance for the application of SFRSCC in tensile- and crack-resistant engineering projects. Full article

Glass and ceramics have a fundamental and crucial role in our lives due to their properties and aesthetic decoration. However, they create serious environmental problems, mainly due to their high occupation of landfills and harmful emissions. Both wastes could be utilized to reduce the natural resources’ adverse environmental effects and exhaustion. With increasing environmental concerns to reduce solid waste as much as possible, the concrete industry has adopted several methods to achieve this goal. Hence, this study examines the performance of self-compacted concrete (SCC) utilizing various percentages of recycled waste materials such as those deposited from glass and ceramic industries. The idea of utilizing recycled waste materials in concrete manufacturing has gained massive attention due to their impressive results in rheological and mechanical states. Recycled glass (RG) and ceramic waste powder (CWP) were utilized to replace fine aggregate and cement, respectively. Five mixes were designed, including the control mix, and the other four mixes had different dosages of RG and CWP as fine aggregate and cement replacement ranging between 5 and 25%. Mixes were tested for both rheological and mechanical properties to evaluate their compliance with SCC requirements as per codes and guidelines. The results revealed that 20% CWP or less as cement replacement and 10% or less of RG as a fine aggregate replacement would provide suitable rheological properties along with mechanical ones. Utilizing recycled glass and ceramic waste powder provides strength similar to the mix designed with natural resources, which helps us keep structures economically and environmentally friendly. Full article

The CRTS III (China Railway Track System Type III)-girder is susceptible to fatigue damage under high-frequency train loads. However, existing research lacks sufficient focus on the CRTS III-girder and the transverse wheel–rail forces encountered during train operation. To better replicate the stress conditions experienced by high-speed railway track systems, a 1:4 scale CRTS III-girder was fabricated following the principle of mid-span concrete stress equivalence. Subsequently, 9 million transverse and vertical fatigue load cycles were applied to the specimen, leading to the following conclusions: First, no visible cracks appeared on the CRTS III-girder surface during the experiment, indicating strong fatigue resistance under train loads. Second, the box girder primarily exhibited a linear elastic response with minimal stiffness variation. Meanwhile, the upper ballastless track structure experienced a highly complex stress state, with significant variations observed across different layers under cyclic fatigue loading. Third, under fatigue loading, the longitudinal strain of the mid-span track slab and the self-compacting concrete (SCC) layer exhibited an overall decreasing trend, with reduction rates of −66% and −57.9%, respectively. Conversely, the longitudinal strain of the base plate and the top and bottom of the box girder gradually increased, with respective increases of 38.6%, 10.4%, and 12.2%. Finally, the connection between the base plate and the box girder remained robust, showing no relative slippage in the transverse, longitudinal, or vertical directions. The sliding layer exhibited stable performance in the longitudinal direction, with no significant degradation observed under cyclic fatigue loading. However, with increasing load cycles, the transverse relative displacement of the sliding layer gradually increased, reaching a maximum of 0.1 mm. This displacement, in turn, contributed to transverse rail movement, potentially affecting driving safety. Full article

The mechanical properties of High-Performance Self-Compacting Concrete (HPSCC) are strongly influenced by its pore structure, but the impact of varying water–binder ratios (W/C) on this relationship remains unclear. To address this, the present study investigates HPSCC with W/C ratios ranging from 0.19 to 0.23, aiming to elucidate the connection between pore structure, fractal characteristics, and mechanical performance. Through a combination of compressive strength testing, low-temperature nitrogen adsorption, and Scanning Electron Microscopy (SEM) observations, this study reveals key insights. First, compressive strength initially increases with a decreasing W/C ratio but plateaus beyond W/C = 0.21, identifying an optimal range for balancing strength and workability. Second, the pore structure of HPSCC is characterized by cylindrical, ink-bottle, and planar interstitial pores, with significant fractal characteristics. Notably, the fractal dimension decreases as the W/C ratio increases, indicating reduced pore complexity and improved homogeneity. Finally, a strong linear correlation (R² > 0.9) between the W/C ratio, fractal dimension, and compressive strength provides a predictive tool for assessing HPSCC performance. This study concludes that the internal pore structure is a critical determinant of HPSCC strength, and the identified optimal W/C ratio range offers guidance for mixture designs. Additionally, fractal dimension analysis emerges as a novel method to evaluate HPSCC’s microstructural quality, enabling predictions of long-term performance and durability. These findings contribute to the scientific basis for designing high-performance concrete materials with improved mechanical properties and durability. Full article

There is a growing demand for sustainable solutions in civil engineering concerning the carbon footprint of cementitious composites. Alkali-Activated Binders (AAB) are materials with great potential to replace ordinary Portland cement (OPC), with similar strength levels and lower environmental impact. Despite their improved environmental performance, their durability remains a gap in the literature, influenced by aspects of mechanical behavior, physical properties, and microstructure. This paper aims to assess the impact of steel slag aggregates and curing temperature of a proposed AAB based concrete formulation by characterizing fresh state, mechanical behavior, and microstructure. The proposed AAB is composed of fly ash (FA) and basic oxygen furnace (BOF) steel slag (SS) as precursors, sodium silicate and sodium hydroxide solution as activators, in total replacement of OPC, using baosteel slag short flow (BSSF) SS as aggregate in comparison with natural aggregate. The concrete formulation was designed to achieve a high-performance concrete (HPC) and a self-compacting concrete (SCC) behavior. Mechanical characterization encompassed hardened (compressive strength and Young’s modulus), fresh state (J-ring, slump flow, and T50), and durability tests (scanning electronic microscopy, water penetration under pressure, and chloride ion penetration). The compressive strength (64.1 ± 3.6 MPa) achieves the requirements of HPC, while the fresh state results fulfill the SCC requirements as well, with a spread diameter from 550 mm to 650 mm (SF-1 class). However, the flow time ranges from 3.5 s to 13.8 s. There was evidence of high chloride penetrability, affected by the lower electrical resistance inherent to the material. Otherwise, there was a low water penetration under pressure (3.5 cm), which indicates a well-consolidated microstructure with low connected porosity. Therefore, the durability assessment demonstrated a divergence in the results. These results indicate that the current durability tests of cementitious materials are not feasible for AAB, requiring adapted procedures for AAB composite characterization. Full article

Self-compacting concrete (SCC) is a relevant technology and an alternative to conventional concrete in complex structures due to its exceptional workability. The rheological parameters demonstrated by SCC provide high fluidity and cohesion, resulting in high mould-filling capability and segregation resistance, as well as optimising concreting processes and reducing costs. In view of this, self-compacting lightweight concrete (SCLC) has emerged as a possible alternative as it combines the benefits of SCC and lightweight aggregate concrete (LWAC). In the production of LWC, the most widely used lightweight aggregate in the world, and also in Brazil, is still expanded clay; however, Brazilian production is restricted to the southeast region. In this context, previous studies have verified the feasibility of producing lightweight aggregates from the sintering of industrial waste and regional raw materials (Rio Grande do Norte/Brazil), such as sugarcane bagasse ash (SBA), scheelite mining residue (SMR), and local clay. Therefore, this study evaluates the influence of three lightweight aggregates, analysing their performance in comparison with SCLC produced with commercial lightweight aggregate (expanded clay). The concretes studied were subjected to characterisation tests in a fresh state; fluidity, apparent viscosity, visual stability, and passing ability were assessed through slump flow tests, flow time (T500), visual stability index, and J-ring, respectively, as well as measurement of the fresh specific mass. In the hardened state, tests were carried out to determine the compressive strength at 7 and 28 days, the dry specific mass, the chloride ion diffusion coefficient, and the thermal conductivity. The new concretes had density values ranging from 1.94 to 2.03 g/cm³ and compressive strength values at 28 days between 26.11 and 36.72 MPa. The results obtained show that it is feasible to produce SCLC with unconventional lightweight aggregates based on sugarcane bagasse waste and scheelite mining waste. Full article

The application of self-compacting concrete in massive structures is still low due to the perceived high cracking tendency associated with high shrinkage and heat of cement hydration. This conclusion is from short-term research work of up to 3 months after casting. The purpose of this study is to evaluate the influence of drying shrinkage on the cracking resistance of massive self-compacting concrete with blast furnace slag using a three-dimensional finite element method of analysis (3D FEM). The restraint stress experiment results of the self-compacting concrete beam under drying conditions are compared with those of similar concrete beam models obtained from 3D FEM analysis. The value of the reduction coefficient for Young’s modulus of elasticity was proposed to consider the effect of stress relaxation due to creep in concrete. By using the proposed value of the reduction coefficient, thermal stress analysis was performed on a 1 m thick massive concrete wall member, and the cracking resistance of self-compacting concrete with different replacement ratios of blast furnace slag is discussed. By using the proposed reduction coefficient to evaluate concrete stress due to drying, the accuracy of thermal stress analysis results can be improved to a marginal error of ±15% from the experiment results. Also, the low-temperature rise caused by the high replacement ratio of blast furnace slag at 50% and 70%, respectively, contributed to improved cracking resistance. Furthermore, the optimum blast furnace slag replacement for better cracking resistance depends on the expected exposure condition of the structure. Full article

In recent years, research on self-compacting concrete (SCC) has gradually shifted towards high-strength development, while high-strength self-compacting concrete has been widely used in applications such as precast bridge components and high-rise building projects. Using manufactured sand as an aggregate can effectively address the challenges posed by the depletion of natural sand resources. This study optimized the mix design for high-strength self-compacting concrete with manufactured sand (MSH-SCC) and explored the effects of the fine aggregate replacement rate, sand ratio, and maximum particle size of coarse aggregate on the performance of MSH-SCC. The results indicated that the optimized mix designs for various strength levels met the performance requirements. The fine aggregate replacement rate and the maximum nominal aggregate size significantly affected the workability of the concrete, while variations in the sand ratio had a smaller impact. The yield stress of the MSH-SCC showed a positive correlation with the fine aggregate replacement rate and the maximum nominal aggregate size, whereas the plastic viscosity reached its maximum value under specific conditions. Additionally, the mix design parameters had a limited effect on the mechanical strength of the MSH-SCC. This study provides a scientific basis for the design of high-strength self-compacting concrete with manufactured sand, contributing to the promotion of manufactured sand use and advancing low-carbon development in the construction industry. Full article

To investigate the distribution characteristics of the micropore structure in high-performance self-compacting concrete (C80), high-resolution X-ray computed tomography, AVIZO software (version 2024.1), and scanning electron microscopy were employed to observe and analyze the internal pore structure of C80 self-compacting concrete specimens. The main conclusions are as follows: There is a large number of pore structures within the carbonate rock-based high-performance self-compacting concrete. At a testing precision range of 10 μm, the micropores exhibit a circular feature with good overall circularity. Observations through SEM, scanning electron microscopy, reveal that there are micro-cracks or interconnected crack structures within the high-performance concrete, with widths ranging from 0.5 to 2 μm, and the sample contains tiny voids of 3 to 10 μm. A statistical analysis of the micropores within the carbonate rock-based self-compacting concrete indicates that the pore diameter follows a three-parameter normal distribution. Due to the limitations of experimental observation and precision, the experimental statistical results show a positively skewed (high peak and left-skewed) phenomenon. This paper proposes a “correction of skewed peak” method for the analysis and discussion of the calculation of the “third parameter C” in the statistical results. The results show that the method proposed in this paper can quickly, objectively, and optimally determine the third parameter, compensating for the missing data not accounted for below 10 μm and the limitations of the finite number of experimental samples, providing a reference for examining the distribution of pores within concrete. Full article

This paper investigates the strength and behaviour of high-strength self-compacting concrete-filled steel tubular (HSSC-CFST) stub columns under axial compression. HSSC-CFST columns are high-performance structural members with wide applications in engineering structures. Nevertheless, relevant studies have commonly focused on the mechanical performance of HSSC-CFST in indoor environments. A finite element (FE) model was developed to predict the axial load capacity of HSSC-CFST stub columns subjected to chloride corrosion. According to this, several crucial geometric and material parameters were designed to investigate the influences on strength, initial stiffness, and ductile performance. Moreover, the analysis on failure mechanisms was investigated by N-ε curves and stress development in the whole loading process. The impacts of key parameters on the reduction factor of axial load capacity were also identified. The numerical analysis results indicate that the axial strength of HSSC-CFST stub columns under chloride corrosion was significantly heightened by increasing the strength of core self-compacting concrete, while contrary results were found with the increase in the steel ratio and yield strength of the steel tube. Lastly, design recommendations for the axially loaded HSSC-CFST were presented by modifying the design codes in CECS104-99. The proposed model is shown to be able to estimate the axial load-bearing capacity of HSSC-CFST stub columns more accurately. Full article