The fatigue damage evolution and multi-factor coupling of multi-scale fiber reinforced engineered cementitious composites (ECC) under static and dynamic tensile loading remain insufficiently understood. To address this gap, this study uses response surface methodology (RSM) to investigate polyethylene (PE) fiber and carbon nanotubes (CNTs) synergistically reinforced ECC (MSF-ECC). Uniaxial tensile and tensile fatigue tests were conducted to quantify the effects of PE fiber content (1-2%), CNTs content (0.1-0.2%), and fatigue cycles (20,000-50,000) on tensile strength, peak tensile strain, and damage accumulation. The synergistic interaction between PE fibers and CNTs significantly enhances tensile performance. At the optimal ratio (PE 1.5%, CNTs 0.15%), tensile strength and peak tensile strain increased by 73.42% and 238.74%, respectively, compared to single-fiber systems. The RSM models reveal that fatigue cycles (C) and PE fiber content (A) dominate performance degradation (C approximate to A > B), with interaction intensity ranked as A-C > A-B > B-C. The study demonstrates that multi-scale fibers suppress crack propagation through nano-macro hierarchical bridging effects and validates RSM for optimizing fiber ratios. This work provides a comprehensive experimental dataset and a validated RSM-based optimization framework for MSF-ECC under static and fatigue tensile loading. The proposed multi-scale fiber design strategy enhances fatigue resistance of ECC, offering significant implications for durable civil infrastructure under cyclic loading. These findings serve as critical references for the precise design of ECC under dynamic loading conditions.

To investigate the influence of calcium carbonate whisker (CW) content on the mechanical properties of polyethylene fiber-reinforced engineered cementitious composites (PE-ECC), uniaxial compression tests, axial tensile tests, and axial tensile fatigue tests were conducted on five groups of PE-ECC specimens with varying CW volume fractions (0%, 0.5%, 1%, 2%, and 3%). The variations in compressive, tensile, and fatigue properties were systematically analyzed. The experimental results demonstrated that an appropriate amount of CW significantly enhanced the mechanical performance of PE-ECC by bridging and deflecting microcracks within the matrix. With increasing CW content, the compressive strength, tensile strength, and initial cracking strength of PE-ECC exhibited a trend of initial increase followed by a decline, with the optimal CW content identified as 1%. At this content, the compressive strength, tensile strength, and initial cracking strength of PE-ECC increased by 14.91%, 19.58%, and 31.31%, respectively, compared to the CW-free group. Furthermore, the tensile fatigue life of PE-ECC peaked at 1% CW content (93,665 cycles, representing a 32.29% improvement over the baseline group). However, excessive CW content (>1%) led to fiber agglomeration, increased matrix porosity, and microcrack proliferation, resulting in mechanical degradation. Microstructural analysis revealed that an optimal CW content enabled uniform dispersion within the matrix and formed a synergistic reinforcement network with polyethylene fibers, whereas excessive CW caused reduced dispersion and exacerbated interfacial defects. This study provides a theoretical foundation for the optimized design and engineering applications of PE-ECC.

[This retracts the article DOI: 10.1016/j.heliyon.2024.e32200.].

To conduct a comparative analysis of the impacts of nanosilica (NS) and carbon nanotubes (CNTs) on the mechanical properties of polyethylene fiber-reinforced cementitious composites, seven groups of ECC specimens with different nanomaterial contents were prepared. The uniaxial compression and tensile tests were conducted, the mineral composition of the specimens was analyzed via X-ray diffraction, and the microstructure of the specimens was examined using a scanning electron microscope. The results show that both types of nanomaterials can effectively enhance the mechanical properties of ECC. Meanwhile, the mechanical characteristics of ECC exhibit a pattern of initial increase followed by a decrease as the nanomaterial content rises. NS exhibited superior performance in augmenting the compressive strength and early tensile crack strength of ECC; however, CNTs were more effective in enhancing the peak compressive strain and peak tensile strain of ECC. The difference between NS and CNTs in the enhancement of tensile strength was not significant. NS can consume more CH crystals to generate C-S-H gels to make the matrix material more dense, and can improve the properties of the transition zone at the fibre-gel interface to enhance the strength of ECC. While CNTs can bridge and inhibit crack extension on the micron scale, and can form a fibre mesh structure with PE fibres for more effective stress transfer, and can improve the deformation capacity of ECC on a macroscopic scale.

In recent years, nanomaterial have garnered significant interest for enhancing engineered cementitious composites (ECC). This study employs response surface methodology (RSM) to conduct multi-objective optimization of the mechanical properties of nanomaterial-reinforced ECC (NR-ECC), aiming to determine the optimal dosages of silica nanoparticles (NS) and carbon nanotubes (CNTs). A central composite design (CCD) was utilized to formulate 13 mixtures with varying NS (1–3

The aim is to research the fatigue life of basalt fiber-reinforced concrete (BFRC) under axial constant-amplitude cyclic tension. The two factors, stress level and basalt fiber volume fraction, were considered. Twelve sets of concrete specimens were designed and fabricated to carry out axial tensile fatigue test studies by means of a self-developed concrete axial tensile test device. The whole process of BFRC axial tensile fatigue was analyzed and the effects of fiber content and stress level on the tensile fatigue life of concrete specimens were investigated. The research results show that the tensile fatigue deformation of BFRC can be divided into three stages: rapid growth stage, stable development stage, and fatigue damage stage. Compared with normal concrete, basalt fibers enhance toughness and resistance to cracking, the ultimate fatigue strain of BFRC is relatively large, and the tensile fatigue damage shows certain plastic damage characteristics. The addition of basalt fibers improves the tensile fatigue strength of concrete by about 5%-8%. With the increase of the volume fraction of basalt fiber, the fatigue life of BFRC showed the change rule of increasing first and then decreasing. When the volume fraction of basalt fibers was 0.3%, the fatigue life increased the most. The probability distribution of the BFRC fatigue life conforms to the two-parameter Weibull distribution, and its correlation coefficient is greater than 0.92. Based on the fatigue test data, the tensile fatigue equation containing fiber characteristic parameters under different failure probabilities was established, which can effectively predict the fatigue life of BFRC. The research results can provide a reference for the fatigue-resistant design of BFRC structures.

This study explores the mechanical properties and synergistic mechanisms of silty sand modified with guar gum (GG) and polypropylene fiber (PP fiber) through a series of unconfined compressive strength (UCS) tests, direct shear tests, and direct tensile tests. The test results reveal that the unconfined compressive strength (UCS) of silty sand can be dramatically improved by incorporating GG, boosting its strength by up to 23 times compared to the natural soil. Adding PP fiber further enhances the UCS and effectively mitigates brittle failure. GG dominates the increase in shear strength by enhancing cohesion, while the PP fiber optimises the shear stability by increasing the internal friction angle. The shear strength of the GG-PP fiber-enhanced soil can be boosted by 235

Conducting research on the fatigue performance of concrete materials is of great significance for the anti fatigue design of concrete structures. Currently, indirect tensile or compressive strength tests are commonly used to study the fatigue performance of basalt fiber reinforced concrete, but there is little research on its fatigue performance under direct tensile conditions. Using a fatigue testing machine and a self-developed concrete axial tensile device, direct tensile fatigue tests of basalt fiber reinforced concrete were conducted under different fiber content and stress levels. Based on fatigue test data, the entire fatigue tensile process of basalt fiber reinforced concrete was analyzed, and the effects of fiber content and stress level on the fatigue life of concrete specimens were explored. Strain fatigue life curves of concrete with different fiber content were plotted. The experimental results indicate that the failure mode of basalt fiber reinforced concrete under cyclic loading is brittle failure; with the increase of basalt fiber content, the fatigue life of concrete first increases and then decreases. When the fiber content is 0.3%, the fatigue life of basalt fiber concrete is the highest compared to the benchmark concrete. When the fiber content is the same, the fatigue life of concrete decreases with the increase of stress level. The fatigue deformation process of basalt fiber reinforced concrete can be divided into three stages: the stage of fast strain growth, the stage of uniform strain growth, and the stage of rapid strain growth.

Aiming at the difficult problems of the large deformation in weakly cemented soft rock roadways, the reasons of large deformation are analyzed for roadways in Hongqingliang coal mine. On this basis, the principle of step by step combined support technology based on allowable deformation + limiting shape for weakly cemented soft rock roadway is proposed, and the optimal support parameters of step by step combined technology are determined by FLAC3D. Step by step combined support technology includes the primary support of anchor bolt + anchor cable + initial shotcrete and the secondary support of U-shaped steel shed + filling flexible material behind shed + control of key parts. The comparative analysis on the site shows that the deformation rate and final deformation amount of the surrounding rock after the step by step combined support are less than those of the primary support, and the deformation of the surrounding rock can be controlled effectively after the secondary support is added. Step by step combined support is superior to the traditional bolt + anchor cable combined repair in terms of economy and efficiency. The optimal construction period of each working procedure of the step by step combined technology is 28 days after the completion of the first support, and the step by step combined support based on allowable deformation + limiting shape is an effective way to control the surrounding rock of soft rock roadway.

In order to investigate the tensile properties of basalt fibre reinforced recycled aggregate concrete (BFRAC), the axial tensile tests were carried out on BFRAC specimens using the concrete axial tensile testing device. The effects of basalt fibre (BF) content and recycled aggregate replacement rate on the tensile properties of BFRAC were quantitatively investigated, and the tensile damage mechanism of BFRAC was analysed. The following conclusions were drawn: The volume fraction of BF had the most prominent effect on the axial tensile properties of BFRAC. The axial tensile strength and peak tensile strain of BFRAC both showed the change rule of first increasing and then decreasing with the increase of BF volume fraction. The replacement rate of recycled aggregate is negatively correlated with the tensile properties of BFRAC. The larger the replacement rate, the worse the tensile properties of BFRAC. When the replacement rate of recycled aggregate is 30 % and the volume fraction of BF is 0.3 %, the tensile properties of BFRAC are better, as well as its economic and environmental performance. The axial tensile strength and peak tensile strain were 2.08 MPa and 114 × 10−6, respectively. BFRAC exhibits the toughening and crack arresting effect of BF, and the crack development is relatively slow, showing more obvious plastic damage characteristics.

The mechanical properties of polyethylene fibre reinforced cementitious composites (PE-ECC) and polyethylene fibre-calcium carbonate whisker reinforced cementitious composites (PECW-ECC) were tested after exposure to different temperatures. And the microstructure changes of ECCs were observed by scanning electron microscope. The results showed the compressive and tensile strengths of PE-ECC and PECW-ECC tended to increase and then decrease with the increase of exposure temperature. The incorporation of CW improved the mechanical properties of PE-ECC to a certain extent. At the same exposure temperature, the compressive and tensile strengths of PECW-ECC are better than that of PE-ECC, and the plastic deformation capacity is also better than that of PE-ECC. The reason is that CW can be tightly bonded with the matrix material, and it has a filling effect on matrix defects, a bridging effect on the microscopic cracks, and a deflecting effect on the microscopic cracks.

During the process of rock failure, the characteristics of crack propagation affect the fracture characteristics and macroscopic mechanical behavior of rocks, indirectly affecting the safety and stability of rock engineering. In order to study the evolution characteristics of cracks during rock failure under different lateral pressure, based on an improved digital image correlation (DIC) and acoustic emission (AE) signal recognition method, a visual biaxial servo loading device was developed to conduct biaxial compression tests on mudstone with prefabricated cracks of the same inclination angle. The research results indicate that the stages of crack propagation include microcracks propagation, crack tip formation, stable macroscopic cracks propagation, and unstable macroscopic cracks propagation. As the lateral pressure increased, the initiation frequency of cracks decreased, the quantity of propagation decreased, and the propagation path shortened, indirectly increasing the bearing strength of rocks. The initiation stress, peak stress, and elastic modulus of pre-cracked rocks with lateral pressure ≤ 2 MPa were lower than those of pre-cracked rocks with lateral pressure > 3 MPa, with the minimum reduction amplitude of 14.1

The surrounding rock pressure of vertical shafts is one of the basic parameters of shaft lining design. Investigating its calculation methods and applicable scopes has great engineering significance. The paper classifies and compares the calculation methods, discusses the application scopes of various calculation methods, and proposes that the axisymmetric layered method is highly consistent with the field monitoring data for the calculation of surrounding rock pressure of vertical shafts in bedrock sections on the basis of practical engineering examples. On the basis of Terzaghi theory, the calculation formula of surrounding rock pressure of vertical shaft in inclined rock strata with single group joints is derived. The formula can reflect the influence of rock strata dip angle and joints.

AbstractThe low liquid limit silty soil in the North China plain area is generally unsuitable for direct use as roadbed and slope soil. In order to improve the performance of low liquid limit silty soil, xanthan gum was used as an improver. Through a series of tests, the improvement effect of xanthan gum on low liquid limit silty soil was studied. The test results showed that Xanthan gum as an improver could significantly improve the unconfined compressive strength of silty soil. With the increase in dosage and curing age, the unconfined compressive strength of improved silty soil continued to improve and eventually tended to stabilize. The optimal dosage and curing period were 2% and 7 days, respectively. In addition, Xanthan gum could greatly improve the permeability and disintegration of low liquid limit silty soil. The permeability coefficient of improved silty soil with a content of 0.75% Xanthan gum and a 7-day curing period was 4.73 × 10−4 m·s−1, which was only 1.10% of that of plain silty soil at the same curing period. After immersion in water for 12 h, the soil only experienced slight disintegration. The scanning electron microscope image showed that the gel generated by the hydration reaction of Xanthan gum could improve the compactness and integrity of the soil by filling the voids, thus significantly improving the mechanical and hydraulic properties of the low liquid limit silty soil.

In order to study the axial tensile properties of polypropylene fiber reinforced concrete, an axial tensile test device for concrete is developed in this paper. The device is composed of three parts: rigid frame, spherical hinge and puller, and specimen fabrication part. The test device can accurately measure the tensile strength and peak tensile strain of concrete, and perfectly solves the eccentricity problem of concrete specimens under tension. It can measure the post peak segment tensile strain, such that the whole process tensile stress–strain curve can be obtained. The axial tensile test of polypropylene fiber concrete was carried out using the above test device, and the results show that the tensile strength of concrete can be clearly improved by adding polypropylene fiber, which makes the tensile failure of concrete show certain plastic characteristics. The test results show that with the increase in fiber content, the tensile strength of concrete increases first and then decreases. The effects of polypropylene fiber content and curing age on the tensile properties of concrete were studied and the optimum polypropylene fiber content was determined. When the fiber content is 0.9 kg/m 3 , the tensile strength of concrete reaches the maximum value. The splitting tensile test of concrete under the same condition was carried out simultaneously. The damage phenomenon and test results of the axial tensile test and splitting tensile test of concrete were compared and analyzed, and the applicability of the new developed device in the concrete axial tensile test was verified.

To solve the problem that the traditional empirical method is not universal, the regional multivariable settlement prediction model is constructed and applied to the settlement prediction of high-rise residential buildings in Liaocheng. The regional multivariable settlement prediction model is constructed as follows: Based on the measured data of the settlement of high-rise residential buildings in the region, the regional foundation settlement law is fitted with the BNGM (1,1) model. Then, the final settlement value of the building is fitted by multiple nonlinear regression model. Finally, the regional multivariable settlement prediction model is obtained by combining the regional foundation settlement law and the final settlement of buildings. The case study results show that, compared with the Logistic models, the regional multivariable settlement prediction model has higher accuracy and reliability; the comparative analysis of the measured settlement of high-rise residential buildings shows that the actual foundation settlement of high-rise residential buildings under similar conditions in the region can be accurately demonstrated by the regional foundation settlement law. The regional multivariable settlement prediction model has high accuracy and good universality.

The surrounding rock of swelling soft rock roadway has high clay mineral content, strong expansibility after encountering water, low strength and poor cementation. The roadway is prone to large deformation under the influence of complex geostress. Combined with the support change of the development roadway of 2# coal in Hongqingliang mine, through geological survey, field observation and indoor test, the failure mechanism of the traditional support method of “anchor bolt + anchor cable + anchor mesh + shotcrete” was revealed by the adjustment of the surrounding rock stress after the excavation and support of the adjacent chambers. The research results show that the surrounding rock stress will cross the adjacent chambers and form a concentrated area near the weakly cemented roadway, and the maximum stress increase ratio of surrounding rock within the stress concentration range will reach 50%. The farther the chambers are from the weakly cemented roadway, the smaller the range of the surrounding rock stress concentration area. When the distance exceeds about 12 times the average height of the chambers, the surrounding rock stress concentration tends to disappear. Based on the fully enclosed combined support method of the "U-shaped steel sheds closure roof and sides + filling flexible material behind the sheds + laying reinforcement mesh and concrete in floor + strengthening key parts", the construction process flow applicable to the working condition of swelling soft rock roadway is formulated.

聊城大学的工程硕士实践教学以工程实践和创新能力培养为导向确立实践教学目标，构建与理论教学有机融合、分层次、多模块、相互衔接的实践教学内容，以师资队伍和实践基地为主要支撑建设实践教学保障体系，构建四位一体的实践教学评价体系，逐步使工程硕士做到学思结合、知行统一，不断提高工程硕士的创新能力和解决实际工程问题的能力。该校的系列做法对工程硕士培养质量的提升和全日制工程硕士实践教学改革具有重要的理论和实践意义。

针对传统灰色模型要求原始实测数据是等时距的特点,基于某项目实测数据,利用三次样条插值良好收敛性、优越稳定性以及二阶光滑度的独特性质,将实测数据转化为等时距序列,建立非等时距灰色模型,并采用控制变量法,对时间间隔和观测次数这两种因素进行精度分析,为构建高精度非等时距灰色模型提供借鉴.研究结果表明,三次样条插值具备强大插值能力与高度契合的插值效果,所构建的非等时距灰色模型精度较高,所得到的预测值与实测值误差在3％左右,是高层建筑沉降预测的一种有效方法.

针对混凝土结构课程实践教学中存在的问题,基于成果导向的教育理念从社会及学生的职业需求出发,以工程实践和创新能力培养为导向确立实践教学目标,构建了与理论教学有机融合,分层次、多模块、相互衔接的混凝土结构课程实践教学体系.从课程实践教学内容的确定、实践教学的保障条件及评价指标三个层面阐述实践教学体系的构建与实施过程.