International Journal of Civil Engineering最新文献

With the advances in infrastructure construction in various countries around the world, extensive requirements have been promoted for the mechanical properties and durability of concrete. In this article, the effects of single and compound additions of nano-SiO₂ (NS) and nano-Fe₂O₃ (NF) on the mechanical properties and durability of concrete were evaluated through different experiments. Moreover, the optimal contents of these additions corresponding to their different properties were explored. The macroscopic test results indicated that the addition of nanomaterials had a perceptible effect on the mechanical properties and durability of concrete. The concrete mixed with 1.0% NS and 0.5% NF achieved optimal performance. With this composition, the compressive strength, flexural strength, water absorption rate, and chloride ion diffusion coefficient (corrosion resistance) of the 28 days concrete were 52.94 MPa, 7.27 MPa, 4.82%, and 4.52 × 10^–12 m²/s, respectively, which were 21.5%, 23.0%, 29.4%, and 37.2% higher than those of ordinary concrete at the same age. Microscopic observation and elemental analysis of the ITZ (interfacial transition zone) interface in concrete revealed that NS and NF contributed to nucleation. The two components reacted chemically with Ca (OH)₂ grains, resulting in the synergistic effect of the spatial morphology of the hydration products, thus increasing the density of the internal structure of the concrete. To facilitate the application of nanomaterials in engineering, functional relationships between the content of nanomaterials in concrete and the improvements in various properties of concrete were constructed with high accuracy. In addition, the time-dependent correlation coefficients of apparent chloride ion concentration and chloride ion diffusion were introduced based on Fick’s second law, and this model was applied to multiple long-term monitoring experiments to verify its accuracy under various exposure conditions, such as tidal zones, splash zones, and atmospheric zones. The improved Fick model was used to predict the service life of concrete. By taking the splash zone as an example, it was reported that under the same conditions, the expected lives of S2F0, S0F2, and S2F1 increased by 31.8%, 25.7%, and 50.2%, respectively, compared to that of OPC. The research results could provide a reference for the development of high-performance concrete.

Red clay exhibits characteristics such as softening owing to water absorption and cracking because of water loss, which can lead to slope instability, road cracking, and compromised structural integrity when used directly in roadbed filling. Although the addition of industrial materials such as cement is a common engineering treatment, it severely impairs soil renewability. Lignosulfonate (LS) extracted from paper plant waste fluids is a natural bio-based polymer with promising applications as a soil improver. In this study, the boundary moisture content and mechanical properties of LS-treated red clay were investigated using Atterberg, unconfined compressive strength, and direct shear strength tests. Additionally, the LS-treated red clay modification mechanism was explored at multiple scales using zeta potential analysis, X-ray diffraction, scanning electron microscopy coupled with energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The results indicated that the LS dosage significantly affected both the water content and mechanical strength of the red clay boundaries. The optimal dosage of LS for red clay was 3 wt. %, at which the liquid limit was reduced by 32.97%, the plastic limit by 19.33%, and the plasticity index by 48.37%. The 28-day compressive strength of LS-treated red clay was increased by 378.4%, and the direct shear strength was increased by 136%. Analysis of the microstructure and mineral composition revealed that the LS-treated red clay did not form new minerals, but primarily filled pores and connected soil particles. Through the combined effects of hydrogen bonds, electrostatic interactions, and cation exchange, the LS-treated red clay reduced the size of the mineral particles and the thickness of the mineral double electric layer, resulting in increased structural densification. These results are of great scientific significance for the ecological modification of soils.

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Considering the increasing need for optimal use of water resources, using types of waste water instead of part of the water for making concrete and also reducing the use of potable water in concrete is particularly important, especially in developing countries. Accordingly, this study aimed to investigate and reinforce using greywater as a potential alternative to mixing water in concrete. The specimens’ fresh, hardened, and durable properties from 14 concrete mix designs containing six mixing water types, three natural zeolite levels (0, 10, and 20%), and two silica fume levels (0 and 8%) were tested to achieve that. Mixing waters in this study consisted of distilled water, raw greywater, diluted greywater (50% greywater, 50% distilled water), simulations of greywater’s salt and organic pollutants, and synthetic greywater. The results showed that raw greywater reduced average compressive strength by 8%, while diluted greywater caused a 1.5% increase instead. Mixing water standards requirements were satisfied on both raw and diluted greywater cases. The results also showed that the impact of greywater on the durability properties of concrete was non-critical in most cases, while diluted greywater, even slightly (4%), improved bulk electrical resistance (RCPT). The test results of synthetic waters showed that reducing chemically active salts and/or organic pollution in greywater can effectively increase the performance of the produced concrete. Using 8% silica fume as cement replacement improved the compressive strength of greywater-made concrete by up to 16% and reduced the cracks and porosity of the specimens based on SEM images. On the other hand, using 20% natural zeolite as cement replacement increased surface (using Wenner probes) and bulk chloride ion penetration by 36 and 78%, respectively. Based on these results, silica fume and natural zeolite replacement are impressive tools to reinforce greywater-made green concrete so that it can properly rival and even replace regular concrete even when using more polluted greywater. Furthermore, these replacements can be great potential alternatives to wastewater dilution or treatments.

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

Shear strength of sandy gravel with cobbles is difficult to determine for usually an in situ test needs to be performed. Six group of in situ tests were conducted to investigate the shear strength of sandy gravel with cobbles. However, the inner friction angle was highly underestimated compared with those from the other methods. This failure result could be explained comprehensively. The strength parameters were also investigated using a DCP test, an experimental method and a theoretical method. Moreover, a numerical simulation method was also used to determine the failure mode of the in situ test. Through comprehensive comparison of these results, the soil failure mechanism in the tests did not follow the direct shear failure but did follow the bearing-capacity failure model. The bottom boundary could not provide enough capacity during the test; hence, the shear strength was underestimated. Moreover, the in situ test results could be explained through the Meyerhof bearing-capacity theory on shallow foundations subjected to inclined loads. With increasing normal load, the horizontal force decreased, resulting in a small inner-friction angle. The theoretical result of the inner-friction angle of sandy gravel with cobbles was 42 ~ 47.5° in these test, which coincided with the numerical simulation and empirical methods.

The energy-dissipation mechanism of an external replaceable mild steel energy dissipater suitable for self-centering hybrid connections under repeated tensile and compressive loads was investigated. The effects of the slenderness ratio and energy consumption section diameter on the bearing ability, energy-dissipation capacity, displacement ductility and stiffness degradation of the dissipater were also evaluated. The research results showed that when the hysteretic curve of the energy-dissipation device is full, the slenderness ratio has a great influence on the overall performance of the energy-dissipation device. The ratio of the end diameter of the dissipater to the weakening section should not be less than 4/3. The energy-consuming devices have good-displacement ductility, up to 4.97. Simplified models of the dissipater-force mechanism were established. Two stress stages of the replaceable mild steel energy dissipater under cyclic tension–compression loading were defined. A parametric model of the hysteresis curve under cyclic tension–compression loading was established via theoretical calculations and experiments.

Most natural sandy deposits contain low amounts of fine content (< 10%), which is usually anisotropic and characterized by complex microstructures. The present study investigates the influence of low silt content on the anisotropic behaviour of sand. For this purpose, 30 undrained tests were performed using a hollow cylindrical apparatus with constant α° and b values on Firoozkuh sand. The specimens had silt contents of 0, 3, 5, 7 and 10%, and the inclination angle (α°) was varied from 15° to 60°. The specimens were prepared with the dry deposition method and subjected to confining pressures of 100 and 200 kPa. The equivalent intergranular relative density parameter was then introduced in order to create a comparative basis for the specimens. The experimental results show that increasing α leads to more contractive behaviour in the pure sand. By adding silt particles to the host sand up to 5%, the peak strength of the specimen is increased (18.5%, 12% and 7.7% for α = 15°, 30° and 60°, respectively), and the strength of the specimen is decreased. It should be noted that with a silt content of 10%, the strength of the specimen was lower than that of the host sand (about 12%). On the other hand, it can be seen that with the increase of α, the influence of fine grains as an important parameter in sand-fine mixtures is decreased.

This paper presents experimental and numerical studies investigating the impact of three curing conditions on temperature evolution in concrete cubes. The tests were performed on samples of the same volume (3.375 dm³) under different curing conditions: room temperature, insulation boxes, and adiabatic calorimeter. Various cements (Portland cement, Portland composite cement, and blast furnace slag cement) and aggregates (gravel and basalt) were examined. The temperature evolution for all mixtures was analyzed, revealing a correlation between temperature increase and concrete type. Under insulation and adiabatic curing, Portland cement with gravel aggregate exhibited the highest temperature rise, while blast furnace slag cement with basalt aggregate showed the lowest increase. The incorporation of slag, ash, or other mineral additives reduced temperature rise. Additionally, basalt aggregate’s higher heat capacity and thermal energy accumulation led to a decreased temperature increase compared to gravel. Using recorded thermal data, a numerical procedure predicting temperature development in nonadiabatic conditions through direct adiabatic tests is proposed. Comparisons between experimental and numerical temperature evolutions confirmed the model’s accuracy.

A large-scale foundation pit with an area of 39,677 m² (B2) was excavated to the south of an existing 25,720 m² Chengdu Universal Trade Plaza (CDUTP) foundation pit (B1) in Chengdu, China. The purpose of this manuscript was to investigate the deformation characteristics of B2 and compare the difference of deformation characteristics between foundation pits B1 and B2. Direct monitoring results of foundation pit B2 were comprehensively investigated and compared with that observed in B1, which include lateral movement, column movement, stress in the columns, and axis force in the anchor cable. Additionally, a strategic approach to mitigate potential extensive lateral deformation was introduced. The monitored results for B2 revealed that the deflection and vertical movement of the columns were comparatively smaller than the reported lower boundaries. The maximum excavation-induced lateral column deflection exhibited a notable 35% reduction in comparison to the lateral deflection observed in the new excavation. However, vertical column movements were approximately twice as pronounced as those in B1. Furthermore, the installation of temporary columns with anchor cables in front of permanent columns proved effective in limiting the vertical deformation during excavation in close proximity to the permanent columns. This research provides valuable insights into the documentation of large-size excavations in soft soil, along with corresponding mitigation approaches.

In this study, asymmetrical and symmetrical pile length model tests were performed to investigate the interaction between retaining piles with asymmetrical excavation. The deformation, earth pressure, and bending moment of the retaining pile on both sides were measured during asymmetrical excavation. The numerical analysis using PLAXIS 2D was validated by comparing the results with experimental data. Through numerical studies, the horizontal displacement, bending moment, and earth pressure of the piles were studied with asymmetrical excavation in terms of three design factors: asymmetrical pile length, pile stiffness, and bracing stiffness. Results show that asymmetrical excavation induces a “push-back effect”, and the pile-top displacement on the shallower side decreases from 0.54 mm to 0.49 mm and from 0.47 mm to 0.42 mm for asymmetrical and symmetrical pile lengths, respectively. The deformation, earth pressure, and bending moment of the retaining pile develop asymmetrically during asymmetrical excavation. The lateral earth pressure distribution was closely related to pile deformation, while the pile bending moment was related to the lateral earth pressure and the axial force of the bracing. With a decrease in the retaining pile stiffness and an increase in the bracing stiffness, the deformation mode of the retaining pile transitioned from a cantilever type to a bulging type, which further influences the distribution of earth pressure on the retaining pile and the distribution of the pile bending moment. For asymmetrical excavation, a deformation-based asymmetrical design for the retaining pile length is recommended to make good use of the push-back effect.