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13 pages, 3933 KiB

Open AccessArticle

Safety and Effect of Fly Ash Content on Mechanical Properties and Microstructure of Green Low-Carbon Concrete

by Zhijie Chen, Maohui Li and Lei Guan

Appl. Sci. 2024, 14(7), 2796; https://doi.org/10.3390/app14072796 - 27 Mar 2024

Viewed by 316

Based on the promotion and application of green and low-carbon technology, this study aims to develop a high-safety performance cement concrete incorporating a large dosage of fly ash (FA). The safety and effect of FA content on the mechanical properties of FA composited [...] Read more.

Based on the promotion and application of green and low-carbon technology, this study aims to develop a high-safety performance cement concrete incorporating a large dosage of fly ash (FA). The safety and effect of FA content on the mechanical properties of FA composited cement were studied through compressive strength, flexural strength, and microscopic tests. The results show that when the FA replaced 20% cement, the properties of concrete were the best in this study. The flexural strengths and compressive strengths of the standard cured concrete for 28 days with 20% FA content are 0.82 MPa and 4.32 MPa larger than that of the pure cement concrete. The XRD and SEM analysis suggested that the mechanical properties of the composite cement FA system are improved significantly since the replacement of cement by FA promotes secondary hydration of calcium hydroxide in the concrete, leading to a more compact and safe interface between cement and FA. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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23 pages, 4385 KiB

Open AccessArticle

Shaking Table Testing and Numerical Study on Aseismic Measures of Twin-Tube Tunnel Crossing Fault Zone with Extra-Large Section

by Fengbing Zhao, Bo Liang, Ningyu Zhao and Bolin Jiang

Appl. Sci. 2024, 14(6), 2391; https://doi.org/10.3390/app14062391 - 12 Mar 2024

Viewed by 428

Abstract

As transportation networks continue to expand into mountainous regions with high seismic activity, ensuring the seismic safety of tunnels crossing active faults has become increasingly crucial. This study aimed to enhance our understanding of the impact of fault zones on the seismic behavior [...] Read more.

As transportation networks continue to expand into mountainous regions with high seismic activity, ensuring the seismic safety of tunnels crossing active faults has become increasingly crucial. This study aimed to enhance our understanding of the impact of fault zones on the seismic behavior of tunnels and to provide optimized seismic design recommendations through a comprehensive experimental and numerical investigation. The focus of this research is the Xiangyangshan Highway Tunnel in China, which intersects a significant longitudinal fault. Large-scale shake table tests were performed on 1:100 scale physical models of the tunnel to analyze the seismic responses under various ground motion excitations. Detailed three-dimensional finite difference models were developed in FLAC3D and calibrated based on the shake table results. The tests indicated that strains, earth pressures, and accelerations experience localized amplification within 10–20 m of the fault interface compared to undisturbed ground sections. Common seismic mitigation measures, such as rock grouting, seismic joints, and shock absorption layers, were observed to effectively reduce the amplified seismic demands. Grouting, in particular, led to an average reduction of up to 56.3% in circumferential strain and 38.5% in earth pressure. It was concluded that 6 m thick grouted zones and 20 cm thick rubber interlayers between tunnel lining shells provide optimal structural reinforcement against the effects of fault zones. This study provides valuable insights for improving the seismic resilience of underground transportation corridors in seismically active regions. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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20 pages, 3768 KiB

Open AccessArticle

Laboratory Test and Constitutive Model for Quantifying the Anisotropic Swelling Behavior of Expansive Soils

by Zhengnan Liu, Rui Zhang, Tian Lan, Yu Zhou and Chao Huang

Appl. Sci. 2024, 14(6), 2255; https://doi.org/10.3390/app14062255 - 07 Mar 2024

Viewed by 449

Abstract

Expansive soils exhibit directionally dependent swelling that traditional isotropic models fail to capture. This study investigates the anisotropic swelling characteristics of expansive soil with a medium swelling potential through the use of modified oedometric testing. Vertical swelling strains can reach up to 1.71 [...] Read more.

Expansive soils exhibit directionally dependent swelling that traditional isotropic models fail to capture. This study investigates the anisotropic swelling characteristics of expansive soil with a medium swelling potential through the use of modified oedometric testing. Vertical swelling strains can reach up to 1.71 times that of the horizontal movements, confirming intrinsic anisotropy. A nonlinear elastic constitutive model incorporates vertical and horizontal elastic moduli with respect to matric suction to characterize anisotropy. Three elastic parameters were determined through the experiments, and predictive equations were developed to estimate the unsaturated moduli. The constitutive model and predictive techniques provide practical tools to better assess expansive soil pressures considering anisotropy, offering guidelines for utilization and design. The outcomes advance understanding of these soils’ directionally dependent behavior and stress–strain–suction response. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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17 pages, 8080 KiB

Open AccessArticle

A Case Study of Pavement Foundation Support and Drainage Evaluations of Damaged Urban Cement Concrete Roads

by Weiwei Wang, Wen Xiang, Cheng Li, Songli Qiu, Yujin Wang, Xuhao Wang, Shanshan Bu and Qinghua Bian

Appl. Sci. 2024, 14(5), 1791; https://doi.org/10.3390/app14051791 - 22 Feb 2024

Viewed by 634

Abstract

Surface cracks and joint deteriorations are typical premature failures of urban cement concrete pavement. However, traffic loads on the urban pavement are much lower than those on highways. Limited research has been conducted to investigate the causes of accelerated damage in urban cement [...] Read more.

Surface cracks and joint deteriorations are typical premature failures of urban cement concrete pavement. However, traffic loads on the urban pavement are much lower than those on highways. Limited research has been conducted to investigate the causes of accelerated damage in urban cement concrete roads. To investigate the foundation issues that may cause the accelerated damage of urban cement concrete pavements, in this study, field evaluations were conducted to assess pavement foundation support and drainage conditions. Field visual inspections, Ground Penetrating Radar (GPR) survey, Dynamic Cone Penetrometer (DCP) test, and the Core-Hole Permeameter (CHP) test were performed. In urban residential areas with inadequate subgrade bearing capacity, cement concrete pavements are prone to early damage. Foundations with a higher content of coarse particles exhibit a higher CBR value, which can extend the service life of the pavement. The compaction of foundation materials near sewer pipelines and manholes is insufficient, leading to non-uniform support conditions. Moreover, the permeability of the foundation material can influence the service life of pavement surface structures. Foundation materials with fewer fine particles enhance drainage performance, contributing to a longer service life for PCC pavements. In areas with inadequate drainage, water accumulation reduces the bearing capacity of the foundation, thereby accelerating pavement deterioration. The poor bearing capacity and drainage conditions of the foundation lead to cavities between the surface layer and foundation material thus yielding stress concentrations on the pavement surface, which cause the formation of pavement surface cracks. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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18 pages, 7438 KiB

Open AccessArticle

Long-Term Maintenance Planning Method of Rural Roads under Limited Budget: A Case Study of Road Network

by Chao Han, Jiuda Huang, Xu Yang, Lili Chen and Tao Chen

Appl. Sci. 2023, 13(23), 12661; https://doi.org/10.3390/app132312661 - 25 Nov 2023

Viewed by 702

Abstract

At present, the task of maintaining and managing rural roads in China is becoming increasingly severe. To solve the problems of insufficient scheme benefits, complex feasible solutions, and low optimization efficiency in long-term maintenance planning of rural road networks under a limited budget, [...] Read more.

At present, the task of maintaining and managing rural roads in China is becoming increasingly severe. To solve the problems of insufficient scheme benefits, complex feasible solutions, and low optimization efficiency in long-term maintenance planning of rural road networks under a limited budget, it is urgent to develop maintenance decision-making models and optimization methods suitable for rural roads in China. This paper focuses on the critical aspects of performance evaluation, prediction, and decision-making. Firstly, this paper proposes evaluation indicators and maintenance countermeasures suitable for rural roads, combining them with the characteristics of rural road performance degradation. Based on different treatment measure levels, RPCI and RRQI performance prediction models are established. On this basis, an improved heuristic optimization method is proposed, which realizes rapid optimization of the most cost-effective solution. Finally, the model and method proposed in this paper are applied to the case analysis of 10 rural roads in Haimen City, generating 171 optimal maintenance sections, further verifying the feasibility and effectiveness of the model. The study provides a theoretical basis for the scientific management of rural road maintenance. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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16 pages, 5571 KiB

Open AccessArticle

An Investigation of Particle Motion and Energy Dissipation Mechanisms in Soil–Rock Mixtures with Varying Mixing Degrees under Vibratory Compaction

by Wei Wang, Wei Hu and Shunkai Liu

Appl. Sci. 2023, 13(20), 11359; https://doi.org/10.3390/app132011359 - 16 Oct 2023

Viewed by 613

Abstract

Soil–rock mixture (S–RM) is a heterogeneous granular material commonly used in engineering applications, but achieving uniform particle mixing is challenging. This study investigated the effect of mixing homogeneity on the compaction of S–RM using the discrete element method (DEM). Specimens with varying degrees [...] Read more.

Soil–rock mixture (S–RM) is a heterogeneous granular material commonly used in engineering applications, but achieving uniform particle mixing is challenging. This study investigated the effect of mixing homogeneity on the compaction of S–RM using the discrete element method (DEM). Specimens with varying degrees of mixing were modeled under realistic vibration loading. The results showed that a higher degree of mixing resulted in a smaller void ratio after compaction. The analysis of particle motion and energy dissipation revealed that not all particle motion during vibration compaction was aligned with the direction of the particle system. However, rotation was more prevalent and contributed to densification. Dashpot energy dissipation did not solely promote changes in the void ratio, while slip energy dissipation did lead to changes in the void ratio, but not entirely towards compaction. Rolling slip energy dissipation primarily occurred during the stage of void ratio changes and significantly promoted compaction. The change in strain energy aligned with the trend of the void ratio but did not directly contribute to its promotion. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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20 pages, 14407 KiB

Open AccessArticle

Study on the Properties and Mechanism of Recycled Aggregate/Asphalt Interface Modified by Silane Coupling Agent

by Jiawang Zhou, Kui Hu, Junfeng Gao, Yujing Chen, Qilin Yang and Xiaotong Du

Appl. Sci. 2023, 13(18), 10343; https://doi.org/10.3390/app131810343 - 15 Sep 2023

Cited by 1 | Viewed by 709

Abstract

The use of recycled concrete aggregates (RCA) instead of natural aggregates in hot-mix asphalt mixtures is one of the ways to achieve energy savings and reduce carbon emissions in road engineering. However, the cement mortar on the surface of RCA adversely affects the [...] Read more.

The use of recycled concrete aggregates (RCA) instead of natural aggregates in hot-mix asphalt mixtures is one of the ways to achieve energy savings and reduce carbon emissions in road engineering. However, the cement mortar on the surface of RCA adversely affects the adhesion properties between asphalt and aggregates, leading to a reduction in the performance characteristics of asphalt mixtures. In this study, a silane coupling agent (SCA) was employed to improve the adhesion properties of the RCA/asphalt interface. The enhancement mechanism of SCA on the RCA/asphalt interface was investigated from multiple perspectives, including macroscopic properties, interfacial microstructure, and nanoscale interfacial interactions. Firstly, the adhesion behavior and tensile strength of the interface between RCA and asphalt were determined through a boiling water test and direct tensile test, both before and after SCA modification. Secondly, scanning electron microscopy (SEM) was employed to observe the surface microstructure of RCA and the microstructure of the RCA/asphalt interface. Finally, the main component of mortar, calcium silicate hydrate (C-S-H), was taken as the research subject of investigation to examine the hydrogen bonding, interaction energy, and interface transition zone of the C-S-H/asphalt interface system using the molecular dynamics methodology. The results demonstrate a two-level enhancement in the adhesion performance of the interface at the macroscopic scale following SCA modification. The interface tensile strength increased by 72.2% and 119.7% under dry and wet conditions, respectively. At the microscopic scale, it was observed that the surface pores of RCA were repaired after SCA modification, resulting in a more tightly bonded interface between the RCA and asphalt. At the nanoscale, SCA modification reduces the hydrophilicity of the C-S-H surface, increases the interaction energy and water resistance of the C-S-H/asphalt interface, and enhances the weak interface transition zone between C-S-H and asphalt. This study provides a theoretical basis for using SCA to enhance the bond strength of the RCA/asphalt interface and lays the foundation for the application of RCA asphalt mixtures on highways. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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14 pages, 1252 KiB

Open AccessFeature PaperArticle

Reliability Investigation of Pavement Performance Evaluation Based on Blind-Number Theory: A Confidence Model

by Hui Wei, Yunyao Liu, Jue Li, Lihao Liu and Honglin Liu

Appl. Sci. 2023, 13(15), 8794; https://doi.org/10.3390/app13158794 - 30 Jul 2023

Viewed by 775

Abstract

The evaluation of in-service pavements’ performance is a complex system that encompasses a variety of uncertain factors. These uncertainties include random, fuzzy, gray, and unascertained information, and their interrelationships are intricate, making comprehensive quantification unachievable. Nonetheless, current highway management organizations rely on a [...] Read more.

The evaluation of in-service pavements’ performance is a complex system that encompasses a variety of uncertain factors. These uncertainties include random, fuzzy, gray, and unascertained information, and their interrelationships are intricate, making comprehensive quantification unachievable. Nonetheless, current highway management organizations rely on a comprehensive indicator, namely, the Pavement Quality Index (PQI), to assess the level of pavement performance. This paper introduces a novel approach that employs blind number theory to evaluate the reliability of pavement performance test data. The proposed method aims to enhance the representativeness of PQI and is demonstrated using detection data from highway asphalt pavements in Hunan Province. The method takes into account the probability distribution characteristics of evaluation metrics and incorporates the blind number representation format of PQI. A confidence model for pavement performance evaluation is established to assess the reliability of pavement detection results. The method also integrates expert empowerment and entropy weight to consider both the subjectivity of evaluation and the objectivity of measured data. The method presented in this study has demonstrated superior performance compared to traditional evaluation index systems. This is attributed to the effective utilization of blind information to accurately characterize the discreteness of pavement performance indexes. Consequently, pavement performance can be quantitatively graded based on anticipated issues and data. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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26 pages, 5497 KiB

Open AccessArticle

Experimental Study on the Cracking Resistance of Asphalt Mixture with Different Degrees of Aging

by Shuyao Yang, Zhigang Zhou and Kai Li

Appl. Sci. 2023, 13(15), 8578; https://doi.org/10.3390/app13158578 - 25 Jul 2023

Viewed by 783

Abstract

The cracking resistance of asphalt mixture is a non-negligible issue. However, the cracking resistance evolution law, motivated by two factors (thermos-oxidative aging degree and test temperature), is not yet well understood. The aim of this investigation is to gain more insight into the [...] Read more.

The cracking resistance of asphalt mixture is a non-negligible issue. However, the cracking resistance evolution law, motivated by two factors (thermos-oxidative aging degree and test temperature), is not yet well understood. The aim of this investigation is to gain more insight into the effect of thermos-oxidative aging and test temperature on the cracking resistance of asphalt mixture. Asphalt mixture (AC-13) and stone mastic asphalt mixture (SMA-13) were selected and exposed to different thermo-oxidative aging degrees (unaging (UA); short-term thermo-oxidative aging (STOA); long-term thermo-oxidative aging for 2/5/8 days (LTOA2d/LTOA5d/LTOA8d)). A direct tension test at different test temperatures (10 °C, 20 °C, 30 °C, 40 °C) was adopted to obtain their stress–strain curves and evaluation indexes (tensile strength, ultimate strain, pre-peak strain energy density, and post-peak strain energy density). The comprehensive index-cracking resistance index (CRI) was established by the entropy weight method combined with the technique to order preference by similarity to ideal solution (TOPSIS) method and the corresponding aging coefficient was determined. The results showed that STOA can increase the aging coefficient of asphalt mixture, thereby boosting the cracking resistance. Additionally, the effect can be weakened by elevations in the test temperature. Meanwhile, LTOA can decrease the aging coefficient and thereby weaken the cracking resistance. This effect becomes more prominent with elevations in the test temperature. SMA-13 possesses a superior cracking resistance to AC-13, with a gap in CRI value of 3–69%, regardless of the aging degree and test temperature. A good relationship exists between the aging coefficient and the two factors (aging degree and test temperature). Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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13 pages, 3539 KiB

Open AccessArticle

Effects of Lime Content on Road Performance of Low Liquid Limit Clay

by Jinli Zhang, Hai Li, Junhui Peng and Zhe Zhang

Appl. Sci. 2023, 13(14), 8377; https://doi.org/10.3390/app13148377 - 20 Jul 2023

Viewed by 931

Abstract

Low liquid limit clay has a low plastic index, displays poor strength, and is sensitive to water, and its mechanical qualities decline as the water content changes, making it difficult to employ directly in the construction process. Adding lime is a fantastic way [...] Read more.

Low liquid limit clay has a low plastic index, displays poor strength, and is sensitive to water, and its mechanical qualities decline as the water content changes, making it difficult to employ directly in the construction process. Adding lime is a fantastic way to improve it. The influence of lime concentration on the road performance of low liquid limit clay is investigated in this research using a limit water content test, compaction test, and California bearing ratio test. The results show that the original plain soil does not meet the requirements of highway subgrade filling, and the basic properties of subgrade soil are improved to varying degrees after adding lime, resolving the problem regarding the original well-cultivated soil’s inability to meet the requirements of construction. The plastic limit of the improved soil increased by roughly 3% as the lime content increased, but the maximum dry density decreased dramatically by 9.03%, 5.71%, and 5.98%, respectively. With an increase of 57.3% in lime content and compaction times, the California bearing ratio increases dramatically. The ideal moisture content rises as the lime content rises. The optimal dosage is 6%, according to a rigorous study of several performance metrics. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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15 pages, 2794 KiB

Open AccessArticle

Fibre-Microbial Curing Tests and Slope Stability Analysis

by Weijian Jiang, Wen Yi and Lei Zhou

Appl. Sci. 2023, 13(12), 7051; https://doi.org/10.3390/app13127051 - 12 Jun 2023

Viewed by 661

Abstract

In response to the deformation resistance deficiency and poor toughness characteristics of soil after microbial curing, a combination of fibre reinforcement technology and microbial curing technology was used to conduct microbial curing tests using basalt fibres and denitrifying bacteria. In this paper, the [...] Read more.

In response to the deformation resistance deficiency and poor toughness characteristics of soil after microbial curing, a combination of fibre reinforcement technology and microbial curing technology was used to conduct microbial curing tests using basalt fibres and denitrifying bacteria. In this paper, the effects of fibre on the strength and toughness of soil consolidation were analysed by unconfined compressive strength test and direct shear test, and the stability of reinforced slope was analysed by numerical simulation. The results show the following. (1) Basalt fibre can effectively improve the characteristics of brittle damage of microbially consolidated soil while increasing the compressive and shear strength. (2) Fibre dosing and fibre length have important effects on the mechanical properties of microbially consolidated soil. (3) The appropriate amount of basalt fibre can promote the generation of calcium carbonate. (4) The plastic strain area of the slope decreases after microbial reinforcement and the maximum equivalent plastic stress decreases by 65 kPa. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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18 pages, 5159 KiB

Open AccessArticle

Performance and Modification Mechanism of Recycled Glass Fiber of Wind Turbine Blades and SBS Composite-Modified Asphalt

by Yihua Nie, Qing Liu, Zhiheng Xiang, Shixiong Zhong and Xinyao Huang

Appl. Sci. 2023, 13(10), 6335; https://doi.org/10.3390/app13106335 - 22 May 2023

Cited by 3 | Viewed by 1356

Abstract

Efficient disposal of composite materials recycled from wind turbine blades (WTB) at end-of-life needs to be solved urgently. To investigate the modification effects and mechanism on SBS-modified asphalt of the recycled glass fiber (GF) from WTB, GF-WTB/SBS composite-modified asphalt was prepared. Dynamic shear [...] Read more.

Efficient disposal of composite materials recycled from wind turbine blades (WTB) at end-of-life needs to be solved urgently. To investigate the modification effects and mechanism on SBS-modified asphalt of the recycled glass fiber (GF) from WTB, GF-WTB/SBS composite-modified asphalt was prepared. Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) were adopted to evaluate its performance. FTIR, SEM, EDS, and AFM methods were used to assess coupling agent pretreatment effects on GF-WTB and observe the modification mechanism. The macroscopic tests show that reasonable addition of GF-WTB effectively raises the high-temperature performance and low-temperature crack resistance evaluation index k-value of SBS-modified asphalt, and the optimal content is 2 wt% GF-WTB with 4 wt% SBS. FTIR, SEM, and EDS tests show GF-WTB can be successfully grafted by UP152 coupling agent and show that adhesion of the GF-WTB to the SBS-modified asphalt can be improved. AFM observation shows SBS and GF-WTB have good compatibility, improving the asphalt elasticity and toughness. This study provides a feasible solution for environmentally friendly regeneration of the composite materials from WTB and contributes to the development of the secondary modifier of SBS-modified asphalt. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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14 pages, 4043 KiB

Open AccessArticle

Discussing the Negative Pressure Distribution Mode in Vacuum-Preloaded Soft Foundation Drainage Structures: A Numerical Study

by Ming Lei, Jin Chang, Jianqing Jiang and Rui Zhang

Appl. Sci. 2023, 13(10), 6297; https://doi.org/10.3390/app13106297 - 21 May 2023

Viewed by 1003

Abstract

The aim of this paper is to clarify the negative pressure distribution in drainage structures of soft foundations reinforced by vacuum preloading. The focus of this study was an actual engineering project, the Beijing–Shanghai high-speed railway; four different soil consolidation models were established [...] Read more.

The aim of this paper is to clarify the negative pressure distribution in drainage structures of soft foundations reinforced by vacuum preloading. The focus of this study was an actual engineering project, the Beijing–Shanghai high-speed railway; four different soil consolidation models were established using FLAC^3D to consider various loading conditions. The consolidation process of the soft foundation was calculated and analyzed in detail. The results show that (1) the settlement developed rapidly within the first 30 days, slowed during the period between 20 and 30 days, and finally stabilized. (2) The settlement curves obtained from the four different models were highly consistent with the site monitoring curve for the first 5 days, after which point significant differences appeared. (3) During the first 20 days, the pore water pressure decreased noticeably within the depth range of 0–18 m. Between days 20 and 30, the rate of pore water pressure decrease slowed down, and after the 30th day, the pore water pressure remained constant at all depths. (4) Vacuum preloading affected the soil to a depth of approximately 16 m. A concave or linear distribution of negative pressure in the drainage structure was found to be a reasonable assumption, providing a reference for the numerical analysis of vacuum preloading. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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20 pages, 12239 KiB

Open AccessArticle

Laboratory Investigation of the Composite Influence of Rock Asphalt and Montmorillonite on the Performance of Bio-Asphalt

by Minghao Mu, Chaochao Liu and Zhengnan Liu

Appl. Sci. 2023, 13(8), 5174; https://doi.org/10.3390/app13085174 - 21 Apr 2023

Viewed by 1034

Abstract

To improve the rutting resistance and anti-aging performance of bio-asphalt, the composite modifier of rock asphalt and montmorillonite is used to modify the bio-asphalt. The optimum content of each component was determined by orthogonal tests based on the results from penetration, softening point, [...] Read more.

To improve the rutting resistance and anti-aging performance of bio-asphalt, the composite modifier of rock asphalt and montmorillonite is used to modify the bio-asphalt. The optimum content of each component was determined by orthogonal tests based on the results from penetration, softening point, ductility and viscosity tests. The rheological properties and anti-aging performance of rock asphalt and montmorillonite composite-modified bio-asphalt (RAMB) with the optimum content were evaluated as compared to those of matrix asphalt (MA), untreated/treated bio-asphalt (UBA/TBA) and rock asphalt-/montmorillonite-modified bio-asphalt (RMB/MMB). The test results illustrated that the optimum content of each component in the rock asphalt/montmorillonite composite-modified bio-asphalt—as determined by orthogonal experimental design and penetration, softening point, ductility and viscosity tests—was 7% bio-oil treated by thermostatic water bath, 5% rock asphalt and 30% montmorillonite. The high-temperature performance, low-temperature performance and anti-aging performance of RAMB were studied by comparison to those of matrix asphalt, UBA, TBA, RMB and MMB. Additionally, the composite modification mechanism was studied by Fourier transform infrared spectroscopy (FTIR). The results suggested that the high-temperature of TBA was obviously improved compared with UBA. The reason, as seen from infrared spectrum tests, was that the amount of ester compounds decreased after water bath treatment. The light components and soluble substances in bio-oil decreased. Compared to UBA, the unrecoverable creep compliance (J_nr) of RAMB decreased by 66.6% and the recovery rate (R) increased by 75.9% at 0.1 KPa. The stiffness modulus (S) of RAMB was 0.87 times that of matrix asphalt and the creep rate (m) was 1.03 times that of base asphalt. Compared to single-modified asphalt, the high- and low-temperature performance of RAMB was good. Meanwhile, the complex modulus aging index (CMAI) and stiffness modulus aging index (SAI) of RAMB were lower than all other asphalt studied, while the phase angle aging index (PAAI) and creep rate aging index (mAI) of RAMB were the largest. The results of infrared spectroscopy also suggest that the mixing of rock asphalt, montmorillonite, bio-oil and matrix asphalt is a physical blending process. During the process, no functional groups are formed. Pretreatment and addition of rock asphalt and montmorillonite can improve high-temperature performance, low-temperature performance and anti-aging performance of the bio-asphalt. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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16 pages, 5067 KiB

Open AccessArticle

Permanent Deformation and Its Unified Model of Coal Gangue Subgrade Filler under Traffic Cyclic Loading

by Zong-Tang Zhang, Yan-Hao Wang, Wen-Hua Gao, Wei Hu and Shun-Kai Liu

Appl. Sci. 2023, 13(7), 4128; https://doi.org/10.3390/app13074128 - 24 Mar 2023

Cited by 3 | Viewed by 994

Abstract

Using coal gangue as subgrade filler can not only solve the environmental problems of coal mine waste accumulation but also decrease the subgrade cost, which has important theoretical and practical significance. A series of cyclic triaxial tests was carried out using the large-scale [...] Read more.

Using coal gangue as subgrade filler can not only solve the environmental problems of coal mine waste accumulation but also decrease the subgrade cost, which has important theoretical and practical significance. A series of cyclic triaxial tests was carried out using the large-scale dynamic and static triaxial apparatus (LSDSTA) to investigate the permanent deformation (

ε

) of coal gangue subgrade filler (CGSF) under cyclic loading. Experimental grading was designed by using the fractal model grading equation (FMGE), and then well-grading limits of CGSF were captured. The relationship curve between

ε

and the numbers of cyclic loading (N) can be divided into three stages, i.e., the rapid growth phase, the deceleration growth phase, and the approaching stability phase. N = 1000 can be used as the criterion for reaching the stable stage of CGSF. The effect of confining pressure (

σ_{3}^{'}

) on

ε

is related to the level of

σ_{3}^{'}

. The effect of

σ_{3}^{'}

on

ε

is significant when

σ_{3}^{'}

is smaller, whereas the influence of

σ_{3}^{'}

on

ε

is smaller when

σ_{3}^{'}

is larger. Furthermore, the influence of grading (

D_{f}

) on

ε

of coal gangue samples is significant. With the increase of

D_{f}

,

ε

first increases and then decreases, reflecting that there is an obvious optimal grading for coal gangue samples under cyclic loading. Moreover, the effect of compaction degree (

D_{c}

) on

ε

of CGSF depends on the level of

D_{c}

.

ε

is hardly affected when

D_{c}

is smaller, whereas increasing

D_{c}

has a significant effect on restraining

ε

when

D_{c}

is bigger. In addition, according to the analysis of the permanent deformation curve for CGSF, the unified calculation model of permanent deformation for CGSF under cyclic loading is established. Compared with the existing permanent deformation models, the proposed model in this paper can better describe the permanent deformation of CGSF under cyclic loading. Finally, the model parameters are analyzed, and the model is verified. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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14 pages, 5533 KiB

Open AccessArticle

Experiments on the State Boundary Surface of Aeolian Sand for Road Building in the Tengger Desert

by Zhigang Ma and Xuefeng Li

Appl. Sci. 2023, 13(2), 879; https://doi.org/10.3390/app13020879 - 09 Jan 2023

Viewed by 1114

Abstract

As a special road-building material widely distributed in desert areas, critical state soil mechanics is used to study the mechanical properties of sand and make up for the lack of research on its engineering characteristics. A series of drained and undrained triaxial compression [...] Read more.

As a special road-building material widely distributed in desert areas, critical state soil mechanics is used to study the mechanical properties of sand and make up for the lack of research on its engineering characteristics. A series of drained and undrained triaxial compression tests with a loading rate of 0.12 mm/min medium-density aeolian sands taken from Tengger Desert in the northwest of China was carried out to obtain the three-dimensional state boundary surface. The test results reveal that the strength gained from drained and undrained tests increased, respectively, linearly and non-linearly with the increase of the effective confining pressure. Affected by the variation of pore pressure and shear rate, the undrained strength was higher than the drained strength at low effective confining pressures, and the two types of strengths tend to be consistent when the effective confining pressure becomes greater than 800 kPa. The volumetric changes of the aeolian specimens transition from dilatation to contraction when the effective confining pressures increase. The investigation of the strength, deformation and failure characteristics gives rise to the shape parameters of its state boundary surface, which provides not only a basis for the constitutive modelling of the aeolian sand, but also a reference for roadbed construction and other foundation engineering in desert areas. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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Review

Jump to: Research

19 pages, 4142 KiB

Open AccessReview

State-of-the-Art Review of Utilization of Microbial-Induced Calcite Precipitation for Improving Moisture-Dependent Properties of Unsaturated Soils

by Jue Li, Wenwei Bi, Yongsheng Yao and Zhengnan Liu

Appl. Sci. 2023, 13(4), 2502; https://doi.org/10.3390/app13042502 - 15 Feb 2023

Cited by 4 | Viewed by 2253

Abstract

Unsaturated soil is a form of natural soil whose pores are filled by air and water. Different from saturated soil, the microstructure of unsaturated soil consists of three phases, namely, the solid phase (soil particle), vapor phase, and liquid phase. Due to the [...] Read more.

Unsaturated soil is a form of natural soil whose pores are filled by air and water. Different from saturated soil, the microstructure of unsaturated soil consists of three phases, namely, the solid phase (soil particle), vapor phase, and liquid phase. Due to the matric suction of soil pores, the hydraulic and mechanical behaviors of unsaturated soils present a significant dependence on the moisture condition, which usually results in a series of unpredictable risks, including foundation settlement, landslide, and dam collapse. Microbial-induced calcite precipitation (MICP) is a novel and environmentally friendly technology that can improve the water stability of unsaturated soft or expansive soils. This paper reviews the microscopic mechanisms of MICP and its effect on the mechanical properties of unsaturated soils. The MICP process is mainly affected by the concentration of calcium ions and urea, apart from the concentration of bacteria. The moisture-dependent properties were comparatively analyzed through mechanical models and influence factors on the experimental data among various unsaturated soils. It suggests that the variations in resilient modulus and permanent deformation are strongly related to the extent of MICP applied on unsaturated soils. Finally, the problems in the MICP application, environmental challenges, and further research directions are suggested. Full article

(This article belongs to the Special Issue New Trends in Long-Life Road Infrastructures: Materials and Structures)

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