International Journal of Civil Engineering最新文献

This study aimed to evaluate the mechanical properties and structural behaviors of reinforced concrete (RC) beams with various corrosion levels. For this purpose, six RC beams were subjected to accelerated corrosion tests, with three pairs corresponding to 1-month, 2-month, and 3-month corrosion degrees. After corrosion tests, the corroded reinforcing bars and concrete were tested to measure the mechanical properties of the materials, such as reinforcement strength, concrete strength, reinforcement diameter reduction, and rebar weight loss. Additionally, the three corroded RC beams with three levels of corrosion were subjected to bending tests to determine their remaining structural capacity and failure patterns. Furthermore, Atena software was used to perform a series of numerical finite element methods to verify the experiment results, which indicated that a good agreement of structural behaviors was observed between the experiment and FEM analysis. FEM analysis is successful when the error of maximum force between experiment and simulation is less than 3% and the error of displacement at maximum load between simulation and experiment is less than 1.8%. The results showed that the load–defection relationships and crack patterns of corroded RC beams were significantly influenced by corrosion level. In addition, predicting the dangerous cross-section of steel structures will support maintenance work to reduce risks for the project.

In this study, the dynamic properties of a mixture of granulated rubber and locally sourced Xiong’an clay are investigated, to promote the beneficial use of rubber–clay mixture (RCM) as a seismic isolation material in this area. A series of cyclic triaxial tests in the shear strain range of 10^–4 ~ 10^–2 is conducted, considering various scenarios of granulated rubber content, effective confining pressure, water content, dry density, cycle number, and consolidation time. The influences of these factors on the dynamic shear modulus and damping ratio of RCM are investigated and dominant factors are revealed. The results show that the shear modulus of RCM decreases with increasing rubber and water content whereas an opposite trend appears for the increased confining pressure, dry density, and consolidation time. Rubber content appears to be a dominant factor for the normalized shear modulus. The damping ratio of RCM is significantly related to the rubber content and effective confining pressure. A shear strain threshold of about 0.3% is observed concerning the influence of rubber content on the damping ratio. The G/G_max ~ γ and D ~ γ curves of RCM can be well described by the Hardin–Drnevich model. Based on the test results, correlations of the parameters of the Hardin–Drnevich model with rubber content and effective confining pressure are developed. The proposed empirical formulas can provide a useful guide in the estimation of dynamic properties of RCM for the preliminary design calculations before detailed laboratory measurements have been performed in the study area.

Particle breakage plays a pivotal role in shaping the deformation behavior of granular soils when subjected to compression. To comprehensively assess the influence of particle breakage on the evolution of particle size distribution and the compression characteristics of calcareous sand, this study conducted 63 sets of confined compression tests on calcareous sand, specifically under high-pressure conditions. The results indicated that the compression behavior of calcareous sand can be classified into three distinct stages within the logarithmic coordinate system of void ratio (e) and vertical pressure (σ_v): (1) σ_v < 2.18 MPa, (2) 2.18 MPa < σ_v < 4.35 MPa, and (3) σ_v > 4.35 MPa, with the first and third stages representing linear relationships. Furthermore, the concept of yield stress ascertained within the e–logσ_v coordinate system proves invaluable in assessing the effects of the initial void ratio (e₀) and particle size (d) on particle breakage. Notably, when σ_v exceeds 2.18 MPa, the relative breakage index experiences a substantial increase. The characteristic particle sizes (d₁₀, d₃₀, d₅₀, and d₆₀) of calcareous sands exhibit a consistent decrease with an increase in the relative breakage index (B_r); however, this relationship is independent of e₀ but is closely related to the particle size (d) of calcareous sands. The one-dimensional compression characteristics of calcareous sand are effectively represented using a power function relationship, and a formula for calculating the compression modulus (E_s) of calcareous sand is theoretically derived. The deformation (Δs) of calcareous sand can be calculated using the index parameters obtained through the E_s–σ_v curve method. In addition, a method for computing the preconsolidation pressure (p_c) of calcareous sand is introduced. This method uses the parameter (e_b) as an indicator of particle breakage and has been experimentally validated.

Crack propagation tests are conducted on expansive soil under various temperature (15 °C, 20 °C, 25 °C, and 30 °C) and relative humidity (31%, 43%, 52%, and 67%) conditions. An innovative method for determining the volumetric crack rate is proposed, and the following conclusions are drawn. (1) The rate of water evaporation in soil samples plays a decisive role in the expansion of apparent cracks in expansive soil. (2) The higher the environmental temperature is, the higher the cracking water content and the lower the stable water content. When the environmental humidity is high, the lower the cracking moisture content is, the higher the stable moisture content. (3) There is a unified law for the expansion of apparent cracks in expansive soil under different environmental factors. The variations in the plane crack rate over time under different conditions are found to conform to the logistic law. (4) The volumetric fracture rate is a key indicator that comprehensively reflects the degree of fracture development. With increasing environmental temperature, the fracture volume increases from 9 to 11%. With increasing environmental humidity, the fracture volume decreases from 10 to 7.5%. (5) When the evaporation of water and the exchange of air reach equilibrium, the moisture stress in the soil is balanced, and the cracks expand to a stable state.

Although the efficacy of stone columns as a ground improvement technique for soft soils is well-established, their effectiveness diminishes in very soft soils (q_u < 25 kPa) due to insufficient lateral support. In such situations, encasement with geosynthetics may be beneficial. This paper presents the results of model tests on various types of stone columns (floating and end-bearing) with different diameters (40 mm and 60 mm), both ordinary and geogrid-encased, in very soft clay with varying undrained shear strengths. The tests were conducted under monotonic and cyclic loading conditions in a plane-strain configuration. The study evaluates the impact of key parameters, including column length and diameter, base support conditions, undrained shear strength of clay, and geogrid encasement length, on the performance of improved ground through a total of 28 model tests. The results show that regardless of the soil's undrained shear strength, the encasement of stone columns with geogrids significantly enhances ground performance. Under monotonic loading, this improvement ranges from 22 to 140% depending on the length of geosynthetics encasement and base support conditions. Under incremental cyclic loads, the improvement varies from 25 to 50%. It is also observed that the geogrid encasement's effectiveness significantly increases when it encompasses the entire length of the stone columns, as it extends the lateral bulging zone below the encasement length.

Recent research on self-healing concrete has shown some drawbacks and conflicts between the different techniques such as difficulty in casting, healing agent release, preparation complexity, high safety requirements against bacteria protection, undesirable expansion, and uncertainty in healing product generation. Despite these limitations, the hybrid technique was suggested and showed promising results. This paper explores the hybridization of the two techniques; autonomous and autogenous by utilizing the B. subtilis bacteria, mineral admixtures like fly ash, and polyvinyl alcohol fibers (PVA) together. The experimental program involves assessing the self-healing efficiency when coupling the bacteria, fly ash, and PVA fiber by assigning six mixtures, including a control OPC. The six mixtures encountered the bacteria addition at certain concentrations and varying PVA fiber percentages; 1, 1.5, and 2% while partially replacing the cement replacement with 20% fly ash, while the last mixture combines both the bacteria, fly ash, and 1% PVA fiber. Mechanical properties such as compressive and flexural strength, in addition to, water absorption and sorptivity as transport properties were examined for concrete repair and restoration purposes. The results reveal that the B. subtilis bacteria significantly enhance the compressive and flexural strength recovery along with lowering sorptivity and absorption rate compared to those with PVA addition when exposed to wet and dry cycles of curing at 28 days of age. The coupling effect, on the other hand, provides a substantial gain in strength of 63% at a longer age (56 days), indicating the potential of this approach for long-term concrete repair. Despite the challenges of the B. subtilis survival bacteria, the coupling of both bacteria and PVA fiber demonstrates superior performance in maintaining the durability of repaired concrete in the long term.

The generation of CO₂ is an important element in assessing the environmental impact generated in a tunnel construction project, making this knowledge very useful for evaluating different alternatives. In this study, an analysis of the carbon footprint has been carried out, including the main elements during the construction phase of a tunnel employing a tunnel boring machine (TBM). The research proposes several options for an easy and quick calculation of CO₂ generation in a design phase. Its determination can be crucial for decision-making before and during the execution of any tunnel in the near future. The estimation models have been validated based on real case studies, defining the carbon footprint of each construction element. The proposed procedure can apply to any tunnel. However, it should be noted that it is an approximate analysis, and the limitations described in each section should be considered. The main CO₂ generator found in the construction process is the lining element; the percentage varies between 50% in tunnels with smaller diameters (4–5 m) and 75% for tunnels with larger diameters (9–10 m), followed by the auxiliary elements, 16%, and the operation of the tunnel boring machine itself, 11.2%, while the other parts remain in a range between 1.3 and 5.7%. This knowledge makes it possible to define the aspects on which efforts should be focussed to reduce the carbon footprint of the tunnel construction process.

To study the freezing characteristics and the effects of the horizontal freezing method of shield tunneling on the surrounding environment at a complex site, a systematic study with field measurements of the temperature and frost heave displacement fields of horizontal cup-type freezing was conducted on the south end shield tunneling of the Shuanghehu station of Zhengzhou metro line 17. The conclusions of the current research are: (1) the soil has a greater effect on freezing than the average moisture content of the soil layer. On the premise of a similar average moisture content, silt continues to cool at a faster rate after reaching the freezing point; (2) within the outer circle of the freezing tube, the rate of expansion of the freezing curtain decreases with distance from the freezing tube. The rates of development measured by the outer holes of the left and right line tests are 2.40 and 6.03 times those of the inner holes, respectively; (3) frost heave displacements are larger near the frozen area. The maximum frost heave in the frozen area is about 1.60–1.83 times that in the unfrozen area; (4) the temperature measurement holes in the left line fell below 0 °C 6 days later than the right line. The flow of groundwater has an adverse effect on the effect of freezing consolidation.

Using existing resources more efficiently and effectively becomes important currently. The question of how to make the best use of resources arises in the choice between constructing new roads and improving deteriorated existing roads. It is also important to reduce the amount of consumption and cost of materials. This has emerged the need to use waste materials by recycling and reusing. In this study, a new hot-mix asphalt (HMA) mixture was developed using recycled asphalt pavement (RAP), which was obtained by excavating the surface of a road at the end of its service life, together with a waste material namely natural pozzolan (NP). The final obtained mixture was used as a wear layer on an active highway. Core specimens were extracted from the paved layer for one year and subjected to dynamic and mechanical laboratory tests. Adding NP improved the resistance of the HMA mixture under heavy seasonal effects and traffic loads. In addition, NP increased the tensile strength, making the HMA mixture more resistant to deformation than control and RAP HMA mixtures. Dynamic creep test results showed that the control asphalt mixture had the most deformation and that the RAP mixture with NP had the least. According to the laboratory results, NP addition increased the stability value of the control mixture by 40%. Especially in cold seasons, the role of NP was more evident. In the performance tests that were applied on core samples taken from the field, ITS values for September increased by 98%, and the deformation values obtained as a result of the dynamic creep test decreased by 12%. In summary, adding NP to RAP HMA improves the performance of the pavement and the cost-effectiveness of the environmentally friendly use of RAP in HMA.

Abstract

In this study, the effect of median guardrails in no-passing zone sections of a two-lane two-way highway was investigated. In this regard, the Firuzkuh-Qaemshahr highway in Mazandaran province of Iran which has 5.5 km median guardrails was selected. All types of crashes studied in two periods, before-and after-the implementation of median guardrails, were considered, and using crash predictive models for the two-way two-lane highway, the effect of implementation was explored. To evaluate the economic effects of this treatment, various crash cost factors were converted to monetary equivalents to compare the cost of crashes before-and after-applying the treatment. This study revealed that using median guardrails caused the monthly average of fatal and injury crashes to decrease by 84% and 29%, respectively. Moreover, the proportion of fatal and injury crashes to total crashes had a 55% drop, indicating that the severity of crashes was reduced, leading to fewer deaths or injuries. Also, this treatment had an impressive reduction in the average monthly cost of crashes, so that the largest reduction among all cost factors belonged to the cost of fatalities in traffic crashes with an 85% reduction, followed by the cost of lost time due to the traffic jams caused by fatal crashes with an 84% decrease. Furthermore, the economic analysis of the implementation of median guardrails revealed that this treatment reduced the average monthly traffic crash cost by 65%. Therefore, the median guardrails in no-passing zone sections of the two-way two-lane Firuzkuh-Qaemshahr highway had a remarkable economic benefit.