The huge demand for natural sand in the global construction industry has caused resource shortages and severe environmental issues. Meanwhile, China produces massive annual iron tailings, and their stockpiling poses prominent potential safety hazards. At present, numerous investigations have been carried out on the fundamental properties of concrete prepared by replacing natural sand with iron tailings sand (ITS). However, most studies are limited to single replacement ratios and conventional strength mix proportions. Systematic research focusing on high-replacement-ratio systems, long-term durability performance, and supporting practical construction technologies for engineering applications remains insufficient. Obvious gaps still exist regarding the key mechanisms and practical operation standards for high-value and large-scale utilization. Against this background, this paper prepares concrete with three strength grades (C30, C40, C50) and six ITS replacement ratios (0%, 20%, 40%, 60%, 80%, 100%). Cube compressive tests and prism axial compressive tests are conducted, combined with SEM microscopic microstructure analysis. Axial compression tests and bearing capacity research are further carried out on reinforced concrete short columns (RCSC) with the optimal replacement ratio. The results show that concrete compressive strength increases first and then decreases with the rise in iron tailings sand concrete (ITSC), with 60% identified as the optimal replacement ratio. At this ratio, the compressive strength of C30, C40 and C50 concrete increases by 24.3%, 11.5% and 12.9%, respectively, while the bearing capacity of short columns rises correspondingly by 18%, 14.1% and 8.1%. Microscopic test results reveal that ITS exerts both physical filling and chemical active effects. Its fine particles fill internal pores inside the matrix and refine the pore structure. Meanwhile, the reactive mineral components contained in ITS can participate in the hydration reaction of the cementitious system, accelerate the hydration rate and generate more dense hydration products. Therefore, ITS facilitates the hydration process and improves the mechanical properties of concrete. A calculation method for the axial bearing capacity of RCSC incorporating ITS is proposed via theoretical analysis. This study provides a theoretical basis for preparing concrete by replacing natural sand with ITS. Using ITS as aggregate is expected to alleviate tailings stockpiling risks, reduce natural sand consumption, and realize solid waste resource recycling. It also offers valuable references for the green development of the construction industry and safety protection in mining areas.

The incorporation of coal gangue into construction materials offers a viable pathway to accelerate the recycling of industrial solid waste while alleviating the growing demand for natural aggregates. In this work, mechanical performance tests and SEM observations were carried out on coal gangue concrete with varying replacement ratios, aiming to clarify its performance degradation behavior. A comprehensive database was established based on published literature, in which nine parameters, namely coal gangue replacement ratio (CG), coal gangue density (ρCG), SiO₂ content, Al₂O₃ content, coarse aggregate content (CA), fine aggregate content (FA), water content, water-reducing agent content (WRA), and water–cement ratio (W/C), were adopted as input variables. The sole output variable was the 28-day compressive strength of coal gangue concrete (fcu). Six conventional machine learning algorithms were selected as base learners, and a Generative Adversarial Network–Artificial Neural Network (GAN-ANN) framework was implemented for data augmentation, resulting in a total of 12 predictive models for compressive strength. SHAP analysis was conducted to interpret the optimal model, and a graphical user interface (GUI) was developed to support visual design and prediction of coal gangue concrete properties. The results show that the compressive strength of coal gangue concrete exhibits a negative correlation with the coal gangue replacement level. When the replacement ratio increased from 0% to 100%, the compressive strength decreased by 37.34%. A multi-criteria evaluation using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), the GAN-ET model exhibits the optimal predictive performance, with R² = 0.949, RMSE = 1.910, MAE = 0.856, and MAPE = 2.444%. SHAP analysis reveals that CG, W/C, FA, ρCG, and Al₂O₃ are the primary factors governing the compressive strength of coal gangue concrete.

Concrete-filled steel tube (CFST) columns incorporating iron tailings sand (ITS) provide dual environmental benefits by reducing natural sand consumption and promoting the utilization of iron tailings waste. However, the limited availability of experimental data hinders the accurate prediction of their compressive capacity. To address this challenge, a transfer learning-based prediction framework was developed using a source dataset of 333 conventional CFST specimens and a target dataset of 41 CFST specimens with ITS. Based on conventional machine learning models, transfer learning models were developed by incorporating a Sigmoid scheduling function and a boosting strategy to enhance knowledge transfer and prediction accuracy. Model hyperparameters were optimized using five-fold cross-validation, and the overall performance was evaluated through TOPSIS. The results indicate that the CFST columns achieved the optimal compressive performance at an ITS replacement ratio of approximately 60%. Among all models, the transfer learning-based model Tr-HGBT exhibits the best comprehensive performance, achieving an R-2 of 0.978, RMSE of 117.658 kN, MAE of 63.072 kN, and MAPE of 4.2%. Compared with the baseline model HGBT, Tr-HGBT improves R-2 by 4.9% and reduces RMSE by 31.4%. Feature importance analysis reveals the following overall ranking: D>e>L>t > f(y)>f(cu)>r > cross section type, where the SHAP values of D are 517.30 for r = 0 and 345.52 for r not equal 0. The novelty of this study lies in the development of a Dual-Learner Boosting-based Transfer Learning framework for CFST columns with ITS under small-sample conditions and the establishment of an interpretable GUI prediction tool, providing an efficient approach for the design and engineering application of sustainable CFST structures.

[Objective]To improve the mechanical properties of coal gangue concrete, [Method] this article designed a four-level and four-factor orthogonal test with coal gangue ceramide substitution rate, coal gangue ceramside sand substitution rate, steel fiber content, and polypropylene fiber content as independent variables. [Result]Through multi-dimensional data analysis of the test results, the primary and secondary factors and the optimal content of compressive strength of hybrid fiber coal gangue concrete were obtained. The grey prediction model GM (1,5) was obtained. The effect of fiber and coal gangue on the microstructure was studied by scanning electron microscopy, and the effect of the interfacial transition zone on the strength of concrete was investigated. [Conclusion]This research provided a theoretical basis for the application of coal gangue concrete in engineering.

The depletion of natural river sand resources in the construction industry and the pollution caused by iron tailings storage in the steel industry are the two major challenges currently faced. The use of iron tailings in construction materials is widely regarded as one of the most sustainable and cost-effective approaches. Based on C30 concrete, 12 steel tube iron tailings sand (IOT) concrete columns with different IOT substitution rates were designed and fabricated in this paper, and axial compression test research was conducted on them; finite element simulations were conducted for comparison with the experimental results, focusing on the influences of IOT substitution rate (0–100%), steel pipe wall thickness (1–4 mm), and steel strength (Q235, Q355, Q390, Q420, Q460) on the bearing capacity of concreted steel tube columns were parametrically analyzed. By comparing the calculation methods of the bearing capacity of concrete-filled steel tube columns in five relevant standards, the calculation formula for the bearing capacity of IOT columns was corrected and obtained. The results show that the failure mode of the IOT column is similar to that of the ordinary column, and the steel tube wall has all undergone circumferential band shear buckling. As the replacement ratio of IOT increases, the load-bearing capacity of columns initially improves and then declines. The finite element analysis results show that the bearing capacity of the IOT column is directly proportional to the wall thickness of the steel pipe, and increasing the wall thickness of the steel pipe can effectively improve the bearing capacity of IOT columns. The discrepancy between the predicted and experimental bearing capacities of IOT columns obtained based on the revision of the “Technical Code for Concrete-filled Steel Tube Structures” (GB 50936-2014) is within 10%, which can effectively predict the load-bearing capacity of IOT columns within a certain range.

To overcome the problem of bearing capacity degradation caused by cracks in traditional concrete structures, this paper explores the crack self-repairing technology of concrete beams based on Shape Memory Alloy (SMA). This paper designs specimens with different reinforcement rates of SMA wires (0-0.59%), pre-stretching degrees (4%, 6%, 8%, 10%, 12%), configuration forms and excitation modes as key parameters. Through the test process of loading-repair-reloading-rerepair, the influences of various parameters on the crack repairing effect and mechanical properties of SMA self-repairing concrete beams, as well as their degradation laws, were quantified. The results indicate that the crack repairing rate of SMA self-repairing concrete beams can reach 82.99-97.75%. After the secondary loading, the secondary cracks repair rate can still be maintained between 70.59% and 94.12%. Increasing the reinforcement ratio of SMA wires (multiple strands with fine diameters) and the pre-stretching degree (≤ 8%) can significantly enhance the ultimate bearing capacity and crack repairing rate under the loading-repair cycle, and resist the degradation of repair performance. Beams without longitudinal reinforcement achieve better crack repairing effects, but have lower load-bearing capacity and higher degradation rates. Additionally, employing a constant high current excitation mode can significantly shorten repair time without affecting the crack repairing effectiveness. The research provides referenceable parameters for the design of SMA self-repairing concrete specimens.

To make the gangue better applied to the engineering practice, a four-factor (coal gangue replacement ratio of ceramsite, coal gangue replacement ratio of ceramsite, Content of SF, Content of PPF) orthogonal test was adopted to conduct compression test and splitting tensile test on the mixed fiber gangue concrete, and the splitting tensile strength and compression strength ratio were analyzed. The results show that the factors that influence the ratio are substitution rate of coal gangue pottery sand > substitution rate of coal gangue ceramsite > steel fiber volume content > polypropylene fiber volume content. The optimum content is 30

Coal gangue is a solid waste produced in the process of coal mining, excessive accumulation will occupy land and pollute the environment. It is one of the most effective means to realize comprehensive utilization of coal gangue by replacing some aggregates in concrete and applying it to engineering structures. In this paper, based on C30 concrete, by changing the replacement rate of coal gangue, slenderness ratio, and steel pipe wall thickness, 17 Coal gangue concrete-filled steel tubular (CGC-FST) columns were designed and made, and the axial compression tests were carried out. The results show that the failure mode of the CGC-FST column is similar to that of CFST, and the annular band shear buckling occurs on the wall of the steel pipe, and the higher the slenderness ratio, the more the number of buckling in the middle. With the increase of coal gangue substitution rate, the ultimate bearing capacity of the CGC-FST column decreases gradually, and the ductility of the specimen decreases slightly. The increase in slenderness ratio reduces the ultimate bearing capacity of the member, the failure form changes from material failure to stable failure, and the material properties are not fully utilized. The most obvious way to improve the bearing capacity and ductility of gangue steel tube members is to increase the steel content. Through the finite element simulation analysis of more working conditions of the CGC-FST column, the calculation formula of the bearing capacity of the CGC-FST column is fitted, which can effectively predict the bearing capacity of the CGC-FST column in a certain range.

To study the application of steel fiber reinforced concrete in cold areas, a rapid freeze-thaw test was carried out for C30 grade steel fiber reinforced concrete with a steel fiber content of 0.4%, 0.8%, 1.2%, and 1.6%, respectively. The results show that in the case of increasing freezing and thawing times, the failure pattern of the specimen is aggravated obviously. However, with the addition of steel fiber, the mass loss rate of the specimen is gradually reduced, and the initial tangent modulus and flexural properties are improved. The freezing resistance of the specimens has been improved continuously. Steel fiber can effectively resist the durability damage of concrete after the freeze-thaw cycle.

The effect of three different shapes of PPF on the mechanical properties of concrete at different dosages was investigated. Cubic compressive ability test, split tensile ability test, and flexural ability test were conducted on polypropylene fiber concrete to analyze the effect of PPF on compressive ability, tensile compression ratio, and flexural compression ratio. The study shows that as the shape and admixture of polypropylene fibers have an impact on the compressive strength of concrete, monofilament-type polypropylene fibers will have the worst effect on the enhancement of the effect when the choice of a mixture of 0.90% of embossed polypropylene fibers on the role of the compressive ability of the concrete has the best effect. The concrete tensile compression ratio is mainly affected by the mixing amount of polypropylene fibers, and the main factors affect the concrete folding compression ratio of the polypropylene fibers of the shape of the main factors.

Concrete faces the difficulties of low tensile strength and poor crack resistance in building structures. In order to remedy this deficiency. In this paper, steel-polypropylene hybrid fiber reinforced concrete (SPFRC) was prepared by adding steel fiber (SF) and three kinds of polypropylene fiber (PF) to C50-grade concrete. The mechanical properties and microstructure of SPFRC were studied with different fiber combinations and content, obtaining the best hybrid combination. Based on this, the bending resistance and cracking of SPFRC beam members were investigated. The results demonstrate that the addition of fiber improves the compressive strength of ordinary concrete by 0.16% ∼ 17.69%, the splitting tensile strength by 15.18% ∼ 47.45%, and the bending strength by 3.54% ∼ 26.77%. Compared with single-fiber concrete, the hybrid fiber can achieve better internal microstructure, which further enhances the mechanical properties of the material. Hybrid fibers overlap within concrete beams, effectively redistributing stress and inhibiting the formation and propagation of cracks. For the three types of SPFRC beams, the cracking load is increased by 14.29% ∼ 28.57% compared with PC beam, the ultimate bearing capacity is increased by 9.68% ∼ 19.35%. The optimal dosage is determined as 1.0% SF, 0.6% Embossed polypropylene fiber (PBF). It provides reference for the application of SPFRC in flexural members.

The massive accumulation of coal gangue (Waste from coal mining) harmed the environment and occupied the land. Replacing aggregate with coal gangue (CG) is an effective way to solve the accumulation problem. The purpose of this paper is to expand the utilization of CG in construction in cold area. Steel fiber (SF) is used as enhancement method to improve the performance of coal gangue aggregate concrete (CGC). In addition, there are few researches on the relationship between frost resistance and the age of SFCGC materials, and they mainly focus on the material level. Therefore, the optimal mixture of SFCGC is studied by orthogonal test. On this basis, the frost resistance and bearing capacity damage of SFCGC and SFCGC columns at different ages during freeze-thaw cycle (FTC) were investigated. Indicate that the optimal mixture is determined as 35 % coal gangue ceramsite (CGc), 35 % coal gangue ceramic sand (CGs), and 0.9 % SF. The ranking of factors affecting mechanical properties is analyzed as SF content > CGc substitution rate > CGs substitution rate. And the GM (1,4) strength prediction grey model of SFCGC is established. SFCGC can reach 125 FTCs, and the material freeze-resistance diminishes as the curing age shortens, and the loss rate of compressive strength boosts with the increase of FTCs (reached 61.9 % in 125 FTC). Under identical conditions, the SFCGC column with steel reinforcement exhibited more severe deterioration, culminating in failure after 100 FTCs. The damage laws and failure patterns of SFCGC reinforced columns under FTCs are obtained. The established model can provide effective support for the application of SFCGC in engineering.

With the continuous upgrading of infrastructure construction and the gradual development of theoretical research about engineering construction, higher performance requirements have been put forward for concrete materials. Therefore, to meet the engineering quality requirements of various concrete structures, the research direction of engineering materials has shifted towards developing new concrete with high strength, high ductility, high toughness, and other multifunctional properties. Mixing two or more types of fibers with conductive properties with the cement matrix material allows various fibers to leverage their strengths and weaknesses, thereby utilizing their respective characteristics. This results in the formation of a complex-phase conductive fiber cementitious material (CFCM), which enhances the safety, durability, and toughness of the structure. It enables the engineering structure to exhibit intelligence and resourcefulness, thereby improving its service life and reducing the full life cycle cost of the cementitious material structure. Additionally, this approach relatively eases the demand for concrete materials and reduces material consumption. This method represents one of the research directions for new concrete. Complex-phase CFCMs are essentially smart materials capable of sensing not only compressive or tensile stresses but also temperature. The emergence of CFCM represents a significant step forward in enhancing the mechanics, functionality, and sustainability of modern infrastructure. In this experiment, an orthogonal test involving 16 working conditions with three factors and four levels was designed, with steel fiber (SF) type, SF content, and carbon fiber (CF) content as the factors. The study focused on the physical and mechanical properties of composite conductive fiber cement-based materials containing both SF and CF. Performance indicators such as flexural strength, volume resistivity, and energized temperature rise of the composite conductive fiber cement-based materials were tested. The analysis of orthogonal tests produced the following results regarding the degree of influence of each factor on the mechanical and physical properties: the order of influence on flexural strength was SF doping > SF type > CF doping. Further analysis revealed that the best combination was A4B4C4. The relationship between the effect of each factor on resistivity is as follows: carbon fiber doping > SF doping > SF type. Comparing the weights between the levels, it can be observed that the optimal combination of conductivity schemes is also A3B4C4. SF and CFs, respectively, enhanced the mechanical and physical properties of complex-phase conductive fiber cementitious materials. The results of the temperature rise test on cementitious materials concluded that there is a certain relationship between the temperature rise and electrical conductivity. Specifically, the higher the electrical conductivity, the greater the temperature rise observed. Through orthogonal analysis of electrical conductivity, disregarding the effect of the non-significant influence factor SF type on the conductive heating test, the impact of two factors, CF doping and SF doping, on the heating test was investigated under 16 sets of conditions, and the data were analyzed visually. The optimal mix ratio for the test is A3B4C4, determined through comprehensive optimization of orthogonal and intuitive analyses. This means that the optimal physico-mechanical properties are achieved when using copper-plated SFs, with a SF dosage of 1.25% and a CF dosage of 0.48%. As a preceding study in the field of intelligent concrete, this experiment explores the research path of intelligent concrete, which holds positive significance for subsequent, more intricate research endeavors.

To make the coal gangue better applied and engineered, through four factors (Coal gangue ceramicist [CGc] Substitution, coal gangue ceramic sand [CGs] Substitution, end-hooked steel fiber [SF], polypropylene fiber [PF]) four-level orthogonal test was conducted to explore the variation of Split-tensile strength of mixed-fiber coal gangue concrete and the strengthening mechanism of hybrid fiber on split-tensile strength of Coal-gangue concrete is analyzed from the microscopic point of view. The results show that the sequence of factors affecting the split-tensile strength is substitution rate of CGs > substitution rate of CGc > incorporation amount of SF > incorporation amount of PF. The optimal admixture combination is: CGc substitution rate of 30%, CGs substitution rate of 25%, SF incorporation rate of 1.00%, and PF incorporation rate of 0.2%. The spatial framework formed by hybrid fibers can enhance the stability of the ITZ to bond inner material tightly, thus enhancing the split-tensile strength of concrete.

智能混凝土作为一种新型的材料,通过在混凝土中掺入导电相材料后拥有机敏性能,本文为了探究导电相材料的掺入对混凝土力学性能的影响,对单掺、复掺下的纳米炭黑和铣削型刚纤维的混凝土试件进行了立方体抗压强度试验以及弯曲韧性试验,研究表明:随着铣削型钢纤维掺量的增加立方体抗压强度逐渐提高,纳米炭黑的掺量对混凝土抗压强度影响较小;随着钢纤维掺量的提高,混凝土的弯曲韧性越好,纳米炭黑掺量在 0.25%～0.75%时随着纳米炭黑掺量增加,混凝土弯曲韧性逐渐提升,掺量超过 1%弯曲韧性下降.

Due to adverse factors such as load and environment exposure, concrete structures often work with cracks during their service period. The occurrence and growth of cracks significantly reduces safety and durability of the structures. It is thus significant to track and monitor cracks in concrete structures in real-time. This paper studies strength, toughness, and crack self-monitoring performance of a large number of smart concrete mixes through addition of two conductive materials, i.e., steel fiber and nano carbon black, into the concrete. Firstly, effect of adding the individual and hybrid conductive materials to concrete mixes on compressive strength, bending toughness and electrical conductivity was investigated. This was followed by studying crack self-monitoring performance and mechanism of the smart concrete beam members under load. The research provides insight and new results of material properties and crack self-monitoring performance in research and development of low-cost smart concrete.

产教融合是新时代应用型本科院校协调促进社会经济发展的重要选择,是支撑高素质应用型人才培养的力量所在.产教融合以"校企合作"为切入点,深化教育教学改革,促进高校与企业耦合发展.通过分析目前产教融合的现状、影响因素及现实意义,并以应用型本科院校土木工程专业为例,从以行业接轨为纽带创新育人模式、以校企合作为桥梁加强专业建设、以新形态教研室(专业)为平台深化课程建设、以职业素养为核心构建"双师型"教师队伍、以工程教育认证为标准培养高素质应用型人才等五个方面,阐述了对土木工程专业产教融合的理论思考和实践经验,为应用型本科院校土木工程专业产教融合的实践研究提供借鉴与参考.

为了对钢纤维混凝土的研究热点与前沿趋势进行更细致的分析,基于中国知网数据总库(CNKI),以国内 2008～2022 年发表的 524 篇关于钢纤维混凝土的核心文献作为研究对象,利用CiteSpace软件从发文量、发文作者、关键词和发文机构等方面进行了可视化分析.结果表明:钢纤维混凝土的发文量随年份波动,近两年呈降低趋势;研究者和机构整体关系均较为分散;当前研究热点主要集中于力学性能、耐久性等基础性能,以及模拟和工作机理研究;前沿趋势主要聚焦于钢纤维混凝土与其他材料的复合研究.据此提出以下建议:创新与拓展对钢纤维混凝土科研领域的深入研究,建立高校之间的联系,加强校企合作;根据钢纤维类型分类建立更为贴切的本构模型,更细化地分析构件性能;拓宽钢纤维混凝土复合其他材料的研究,增强钢纤维混凝土的耐久性能.

In order to study the seismic performance of the U-shaped reinforced concrete (RC) cross-section shear wall, the U-shaped cross-section shear wall with a 1/5 scale was tested under low cyclic loading based on the subway operation library in Changchun. The skeleton curve, bearing capacity, ductility, and stiffness degradation were analyzed. Based on the experimental study, the finite element simulation of the specimen was carried out by ABAQUS software, and the calculation results were compared with the experimental results. The results show that the U-shaped shear wall has good seismic performance and should be applied to more projects through practical design.