Long-term Structural Performance Research Articles

Enhanced understanding on permanent deformation behaviour of subgrade compacted clay under long-term cyclic loading

The long-term performance of pavement structures is heavily reliant on the sustained load-carrying capacity of the subgrade soil. Under repetitive traffic loads, permanent deformation (PD) gradually accumulates in the subgrade due to plastic yielding and soil particle rearrangement, which can compromise the serviceability and durability of overlying pavement layers. This study aimed to enhance the understanding of compacted clay response under long-term cyclic loads through a systematic repeated load triaxial (RLT) testing approach. The proposed approach considered depth-dependent static and dynamic stresses exerted on compacted clay beneath pavement structures and traffic loads. A series of RLT tests were conducted to investigate the impact of key factors, including soil properties (moisture content and compaction degree), stress conditions (confining pressure and deviator stress), and load characteristics (load duration and rest period), on the PD behaviour of compacted clay subgrade. Stress-strain hysteresis loops and damping ratios were analyzed to enhance the fundamental understanding of subgrade PD evolution. The results showed that higher moisture content and lower compaction degree significantly increased PD, with the PD response transitioning from plastic shakedown to plastic creep. Greater deviator stress also exacerbated PD accumulation. Variations in loading duration and rest period influenced the PD behaviour, demonstrating the importance of accurately simulating the stress history experienced by subgrade soil elements under traffic loading. The findings provide valuable insights to optimize subgrade design and implement performance-based management of pavements.

Digital twin for smart metro service platform: Evaluating long-term tunnel structural performance

The metro system is crucial for urban transportation networks because it significantly improves traffic flow, with tunnels playing a key role in ensuring the safety and quality of metro services. Over time, the structural performance of metro tunnels deteriorates, posing risks to the system's operational dependability. This paper highlights the importance of accurately assessing the long-term structural performance of metro tunnels for operations and maintenance (O&M) decision-making. Digital twin (DT) technology is introduced as the core of the O&M management platform for metro tunnels. This paper presents the structure of a metro tunnel DT and designs a smart metro service platform (SMSP) based on the DT to enhance long-term structural performance through data collection, early warning, and maintenance management. The deployment of SMSP in a metro project and its effect on the long-term evolution of tunnel structural performance are examined.

Constitutive modeling and extended performance evaluation of concrete reinforced with non-hybrid waste tire steel fibers

This paper investigates the extended performance and constitutive modeling of waste tire steel fiber reinforced concrete (WFRC), making notable contributions to civil engineering materials. The study assesses constitutive modeling, reinforcement indices, and the long-term performance of concrete reinforced with varying percentages of waste tire steel fiber (WSF) ranging from 0.30 % to 1.75 %. A modified analytical model for predicting compressive stress-strain curves of WFRC is introduced and compared with previous analytical models for fiber-reinforced concrete. Additionally, a novel waste tire steel fiber reinforcing index, based on WSF properties, is proposed. Empirical relationships between strength properties and reinforcement indices are established. Experimental strength properties at the standard age, as well as water absorption, carbonation depth, and split-tensile strength of specimens aged beyond the standard age at 600 days and fiber-matrix interaction obtained by SEM analysis, are reported. Prediction models are proposed for estimating the mechanical properties of WFRC at the standard age, with results compared against existing codes. The proposed modified analytical model for the uniaxial compressive stress-strain curve demonstrates better coherence with experimental curves than existing models. Furthermore, empirical equations developed in terms of the waste tire steel fiber reinforcing index demonstrate satisfactory alignment between predicted and experimental strength properties. Significant improvements are observed in specimens aged 600 days, indicating the promising role of WSF in enhancing the long-term performance and serviceability of structures. Further studies are recommended to explore the performance of WFRC in aggressive environmental conditions.

Governing Lateral Load on Tall Buildings in Canadian Regions

Urbanization has led to a significant increase in the construction of tall buildings in Canada. The design of tall buildings must ensure structural integrity in withstanding lateral loads, such as wind and earthquakes. The tendency for a specific lateral load to govern building design varies based on the building characteristics, building height, and location of the building. There is a need to identify the governing lateral load (i.e., wind or earthquake) for use in the preliminary design and city-scale assessment. This study examines the governing lateral loads for tall buildings across different Canadian regions through a parametric analysis of a typical high-rise building based on the Commonwealth Advisory Aeronautical Council (CAARC) building. This research evaluates varying building heights, structural systems, and geographic locations under the guidelines of the National Building Code of Canada (NBCC). The analysis identifies the dominant lateral load, providing insights into assessing the existing infrastructure and optimal design strategies for enhancing building sustainability and resilience. Our findings highlight the critical role of geographic location in determining lateral load impacts and the necessity of context-specific design to promote long-term structural performance and environmental sustainability.

Durability of SFCB reinforced low-alkalinity seawater sea sand concrete beams in marine environment

Seawater sea-sand concrete (SWSSC) provides an alternative to normal concrete, while Steel-FRP Composite Bars (SFCB) offer corrosion resistance in offshore and marine structures. Despite their benefits, the long-term performance of SFCB-reinforced SWSSC structures remains under-explored. This study evaluated the durability of such beams, particularly focusing on the effects of using Portland cement versus low-alkalinity calcium sulphoaluminate (CSA) cement. The investigation involved tensile and pull-out tests conducted on SFCB, and flexural tests conducted on the beam components after accelerated marine environmental exposure over periods ranging from one to six months. Results highlighted that SFCB embedded in low-alkalinity CSA cement exhibited improved retention of tensile strength, elastic modulus, and bonding strength by 32.0 %, 39.1 %, and 56.7 % respectively, compared to that embedded in normal Portland cement concrete. Microstructural analyses showed much less hydrolysis of the resin matrix and shallower corrosion of the basalt FRP (BFRP) cover on the SFCB. Furthermore, flexural tests demonstrated superior cooperative performance between low-alkalinity CSA concrete with SFCB in beam components, showing only marginal degradation in crack density, crack strength, and yielding points. The ultimate failure load of beams made with CSA concrete was 1.89 times higher than those made with normal SWSSC after 6 months of exposure. These results underscore the potential of low-alkalinity concrete in improving the long-term durability and structural performance of SFCB-reinforced marine concrete infrastructures.

Durability of mass timber: managing moisture effectively

The durability of mass timber structures is greatly influenced by the extent to which the timber is exposed to moisture. Understanding the conditions in which moisture ingress, and associated biological agents, can become a problem and designing with durability in mind can ensure the long-term performance and resilience of mass timber structures. This article provides an introduction to moisture management in mass timber structures, including key design, site-handling and installation principles that will help to ensure longevity.

Foam concrete for lightweight construction applications: A comprehensive review of the research development and material characteristics

Abstract Foam concrete or foamcrete is a lightweight, porous material with a wide range of applications in the construction domain. This article focused on reviewing porosity, thermal conductivity, acoustic properties, compressive strength (f c′), elastic modulus (E), flexural strength (f y), stability, resistance to hostile environments, density, and fire resistance of foam concrete. A systematic literature analysis was conducted to identify relevant research trends on foam concrete. The challenges and limitations of foam concrete research were highlighted, including the lack of standardized testing methods and the need for more research on the long-term durability and structural performance of foam concrete. The analysis of the literature data revealed that there had been a growing interest in foamcrete research over the past decade. Foam concrete may be utilized in several construction applications due to its adaptability and wide range of uses. Its potential uses can be increased by developing new manufacturing methods and the inclusion of certain admixtures. The present research has the potential to be advantageous for scholars interested in collaborative advancement and the exchange of novel tactics and concepts, owing to the visual and statistical representation of the regions/countries and researchers that have contributed.

Pore fluid salinity effects on post-stabilization performance of cement-treated Marl

Soil improvement using chemical admixtures has been extensively investigated in the recent past and these admixtures are abundantly being used on various construction projects. However, there is a need to elucidate the long-term performance of stabilized geomaterials under aggressive pore fluid environments such as high salinity of groundwater in coastal areas. This study presents the effects of the concentration of pore fluid salinity on the post-stabilization behavior of cement-treated Marl specimens to brine solution from Sabkha deposits and rejected water from a water treatment plant. Unconfined compressive strength (UCS), mineralogy, chemical, and microstructural evaluations have been carried out in this regard. minerals like albite and muscovite completely leached out of the samples after 28 days of soaking in a saline environment. A new mineral Attapulgite was formed at various concentration levels of the pore fluid. Significant changes in the chemical composition were also observed in various phases of the experiments. Moreover, at all salinity levels, the UCS initially increased to a maximum of 75 % which later reduced to a value less than the original strength whereas the elastic modulus (E50) increased as the soaking period progressed. Lastly, it is emphasized that the engineering properties of treated soils exposed to aggressive pore fluids should be carefully assessed for a reliable prediction of the long-term performance of geotechnical structures.

Physicochemical-mechanical simulation of the short- and long-term performance of FRP reinforced concrete beams under marine environments

To broaden the applications of fiber reinforced polymer (FRP) reinforced concrete structures under marine environments, it is crucial to gain a fundamental understanding of their short- and long-term performance. In this study, the effectiveness of the proposed multi-scale simulation platform, which incorporates the proposed degradation model of FRP bars, is quantitatively assessed via the comparison between the predicted results and experimental load-displacement curves under different marine conditions (continuous immersion, wet-dry cycling and subtropical marine atmosphere). The spatially physical, chemical and mechanical information, such as pH value, moisture, hydration degree, strength, porosity during the exposure was also revealed. Finally, the long-term structural performance of FRP-reinforced concrete beams exposed to the predefined environmental conditions over durations of 20, 50 and 100 years are assessed using the multi-scale simulation platform. After 50 years of exposure, the load-bearing capacity of GFRP-reinforced concrete beams was found to decrease by 35.8 % in immersion conditions and by 17.9 % in subtropical marine atmosphere. The degradation of the load-bearing capacity in the case of 100 years exposure to subtropical marine atmosphere was found to be less severe than that (23.1 %) in the case of 50-year immersion. These findings not only deepen our understanding of the material and structural properties of FRP-reinforced concrete beams under various environmental conditions, but also validate the effectiveness of the proposed multi-scale platform.

Review of the Modelling of Corrosion Processes and Lifetime Prediction for HLW/SF Containers—Part 1: Process Models

The disposal of high-level radioactive waste (HLW) and spent nuclear fuel (SF) presents a unique challenge for the prediction of the long-term performance of corrodible structures since HLW/SF containers are expected, in some cases, to have lifetimes of one million years or longer. Various empirical and deterministic models have been developed over the past 45 years for making predictions of long-term corrosion behaviour, including models for uniform and localised corrosion, environmentally assisted cracking, microbiologically influenced corrosion, and radiation-induced corrosion. More recently, fracture-mechanics-based approaches have been developed to account for joint mechanical–corrosion degradation modes. Regardless of whether empirical or deterministic models are used, it is essential to be able to demonstrate a thorough mechanistic understanding of the corrosion processes involved. In addition to process models focused on specific corrosion mechanisms, there is also a need for performance-assessment models as part of the overall demonstration of the safety of a deep geological repository. Performance-assessment models are discussed in Part 2 of this review.

Dynamic deformation and meso-structure of coarse-grained saline soil under cyclic loading with freeze-thaw cycles

The cumulative deformation properties of subgrade soil under cyclic traffic loads are critical for optimizing pavement structure design and ensuring long-term highway structural performance. This study aims to investigate the coupling effect of freeze-thaw cycles and cyclic loads on the cumulative deformation behaviors and meso-structure of coarse-grained saline soil (CGSS) subgrade filling in high-cold areas. Dynamic triaxial tests and computed tomography (CT) scanning were conducted to analyze the CGSS under different working conditions. The research focused on the dynamic deformation development and damage evolution under varying freeze-thaw cycles and load amplitudes. The research results show that the cumulative deformation behavior of CGSS under cyclic loading is relatively sensitive to the freeze-thaw process. The cumulative dynamic strain increases as the freeze-thaw cycles, with a critical freeze-thaw cycle number of five. The stable cumulative dynamic strain curve exhibits clear three-stage characteristics when plotted in semi-log coordination, with critical loading cycles at 20 and 1,000. After 10–100 loading cycles, the cumulative strain curve quickly shows failure. The CGSS’s low density and pore regions greatly increase after a freeze-thaw cycle. The rise in dynamic stress amplitude notably affects the bonding between soil particles and crystalline salts. The coupling effect of the freeze-thaw cycle and dynamic activity exacerbates the deterioration of soil structure, resulting in variations in CT values within the scanning layer in the final state.

Research on time-varying degradation of RC buildings coupled environmental effects and corrosion-induced damage from multi-scale

Corrosion of steel reinforcement in reinforced concrete (RC) buildings is influenced by several factors, including oxygen content, chloride ion diffusion, concrete damage, and humidity. A numerical method is presented to evaluate the long-term structural performance of RC buildings under environmental conditions, which takes into account the impact of steel corrosion-induced damage from multi-scale. The macro-index used for calculation is the level of reinforcement corrosion-induced damage, which considers the inter-connected effects of oxygen content, chloride ion, moisture transport, mechanical stresses, and corrosion uncertainties. In the case of RC beams, corrosion tends to occur more severely on the outer edge near concrete surface. When the corrosion factor is taken as 1.0, the calculated compression side corrosion rate of RC beam agrees well with experimental results. Due to the influence of multiple factors, the corrosion of tension-side reinforcement exhibits some degree of variability. Furthermore, the corrosion of tension-side longitudinal reinforcement in RC beams gradually intensifies from beam ends towards mid-span, with corrosion at mid-span being particularly significant. The relationship between corrosion rate and corrosion time obtained from tests falls within the range of calculation results, and the calculated results from micro-scale align favorably with tests conducted to measure crack width.

Sensing Systems in Construction and the Built Environment: Review, Prospective, and Challenges.

This article is a comprehensive review of state-of-the-art sensors of the built environment, applicable in construction, structural engineering, management, and planning industries. This review is framed within the technical definition of sensing systems and their components. Existing sensors are listed and described in two broad categories of structural health monitoring (SHM) and building environment monitoring (BEM). The SHM systems are used for monitoring the long-term performance of structures, such as bridges and buildings. BEM systems are employed to ensure the safety and comfort of the built environment's occupants, as well as the general monitoring of the environment for any required maintenance. The applications and implementation challenges of both systems are discussed, with emphasis on common sensing system limitations such as energy supply, packaging, network layout, and performance validation. Finally, the prospect of sensing systems as part of a digital twin that incorporates multifunctional sophisticated monitoring systems and intelligent analysis methods is discussed.

Evaluation of the Fracture Toughness of Short Carbon Fiber Reinforced Thermoplastic Composites

Abstract Short carbon fiber (SCF) reinforced thermoplastic composites (SCFRTCs) are attracting broad attention in various fields for their excellent mechanical properties. The fracture toughness, an essential characteristic of the resistance of materials to crack propagation, is considered a critical aspect of the long-term performance of SCFRTCs structures. The fracture toughness of SCFRTCs depends on two competing mechanisms: the interface between SCFs and polymer matrix may promote crack initiation, while the SCFs hinder the crack propagation. In this study, the fracture toughness of SCFRTCs with varying SCFs volume fractions is first determined by a three-point bending test. The results show that adding SCFs effectively improves the fracture toughness of SCFRTCs, and an increase of up to 73.7% at the SCFs volume fraction of 5.45 vol%. In addition, it is found that heat treatment and its temperature have no effect on the fracture toughness of SCFRTCs. Subsequently, the full-field strain around the crack tip is analyzed by digital image correlation (DIC), and the strain level significantly decreases after adding SCFs. The fracture surface of the SCFRTCs specimen is much rougher compared with HDPE, and obvious bridging SCFs are observed, which make it to absorb more energy for fracture, thus explaining the toughening mechanism of SCFs on SCFRTCs.

Chloride penetration resistance and chloride binding capacity under different application environments of ferroaluminate cement

Free chloride is a crucial factor that threatens the long-term performance of marine concrete structures. The resistance of cement to chloride penetration and its capacity to bind chloride are important parameters for assessing the ability of cement-based materials to resist chloride invasion. Ferroaluminate cement (FAC) has considerable application potential in concrete used for marine structures; however, its resistance to chloride invasion and mechanism of chloride binding have not yet been revealed. In this study, the chloride diffusion coefficient and chloride binding capacity of FAC, for both internal and external chloride ions, are experimentally investigated and compared with that of ordinary Portland cement (OPC). The results show that the chloride diffusion coefficient of FAC mortar is approximately 2.5 times lower than that of OPC mortar. FAC exhibits finer overall pore distribution and the number of pores with sizes within 10–100 nm is reduced, which is responsible for its notably lower chloride diffusion coefficient. The chloride binding capacity of FAC to internal chloride ions is slightly lower than that of OPC, and a portion of the chloride ions are chemically bound by reacting with ye'elimite during hydration. The chlorides bound by physical adsorption constitute a dominant portion of the entire bound chloride content. In the case of external chloride ions, the bound chloride content of FAC is lower than that of OPC. The chemical chloride binding capacity of FAC is comparable to that of OPC and the lower physical adsorption capacity for chloride in FAC leads to a weaker chloride binding capacity compared to that of OPC.

A hierarchical creep model for cement paste: From decoding nano-microscopic C-S-H creep to considering microstructure evolution

The creep of cement paste significantly affects the long-term performance of concrete structures. However, the accurate prediction of cement paste creep remains to meet enormous challenges. This work proposes a hierarchical creep model of cement paste considering the hydration microstructure evolution. First, the microstructural evolutions are quantitatively captured by a cement hydration model. The creep property of cement paste is upscaled from high-density (HD) and low-density (LD) calcium silicate hydrate (C-S-H) at the nanoscale, via C-S-H gels at the sub-micrometer scale to the microscopic scale by coupling the mean-field theory with the transfer function method. The creep behavior of HD and LD C-S-H is described using a fractional Maxwell model in the time domain and its corresponding transfer function in the Laplace-Carson domain. The creep parameters of HD and LD C-S-H are identified through a back-analysis approach. The determined creep parameters and the hierarchical creep model are validated by comparing them with extensive experimental data. Furthermore, the proposed model quantitatively evaluates the influences of various factors on the creeps of cement paste and C-S-H gels. The results indicate that C-S-H gels should not be treated as a phase with stable viscoelastic creep properties, and cement paste creep can be tailored via proper design for these factors.

Elastic and electromagnetic monitoring of TRC sandwich panels in fracture under four-point bending

Textile-reinforced cementitious (TRC) sandwich panels with insulation core are mechanical- and material-efficient composites, however, under service loads might develop complex fracture that is still inadequately detected. Among damage mechanisms, the weak core-facing interfacial bond can substantially reduce its load-bearing capacity and lead to premature failure; therefore, early detection of damage is crucial to guarantee optimal long-term structural performance. Periodic inspection is necessary during the service life, however, there is neither a standardized methodology nor monitoring protocol that detects and characterizes premature interfacial debonding. In this study, a novel multi-modal monitoring is developed for the first time, based on acoustic emission (AE), digital image correlation (DIC), and millimeter wave (MMW) spectrometry, to characterize the response to bending of TRC sandwich beams. The core-facing interlaminar bond is artificially weakened during casting to simulate manufacturing defects. The proposed methodology showed high sensitivity to damage and complementarity of the techniques, where, AE allowed to characterize and locate damage, MMW showed high sensitivity to progressive failure, and DIC provided the strain data to validate and interpret AE, and MMW results.

Petrographic Evaluation of Aggregate from Igneous Rocks: Alkali–Silica Reaction Potential

A thorough petrographic evaluation of aggregates from igneous rocks in terms of their alkali–silica reaction (ASR) potential is crucial in ensuring the durability and long-term performance of concrete structures, especially those where access to additional alkalis is possible, such as from de-icing agents. The aim of the research was to assess the potential reactivity of aggregates from igneous rocks, as only such aggregates are used for concrete airport pavements in Poland. Petrographic analysis was conducted to identify the reactive minerals in the aggregate, and it was extended by quantitative image analysis. The strained, microcrystalline and cryptocrystalline quartz were found to be reactive components but significantly differed in content. It was found that aggregates from igneous rocks were characterized by different susceptibility to ASR and that methods to mitigate the occurrence of ASR should be considered to be used in airfield concrete. A relationship between the content of analyzed reactive minerals and the expansion of mortar bars in AMBT, as well as of the concrete prism in the CPT method, was revealed.

Long-term performance of basalt fibre-reinforced marine geopolymer concrete in harsh environment

The current study reports on the long-term structural performance of novel reinforced marine geopolymer concrete beams under accelerated weathering conditions. The study covers the flexural performance of 40 geopolymer concrete beams reinforced with basalt fibre-reinforced polymer (BFRP) bars, including 12 beams under sustained loading when exposed to 3, 6 and 12 months of accelerated marine environment consisting of tidal cycles of seawater at a temperature of 50°C. The experimental results revealed that the novel marine geopolymer concrete reinforced with BFRP bars reported minimal micro- and macro-mechanical degradation compared to geopolymer concrete or ordinary concrete beams under the same exposure environment, with and without sustained loading. The BFRP-reinforced self-compacting geopolymer concrete (SCGC) beams reported 87% residual ultimate load after 12 months of exposure to marine environments, while the sustained loaded BFRP-SCGC beams reported a residual strength of 79%. In addition, microstructural assessment using scanning electron microscopy and energy dispersive X-ray spectroscopy analysis revealed that after 12 months of exposure there was a trace of chloride salts, indicating the chemical ingress over time; however, the impact on structural properties is not distinct.

Thermal response of the bridge supported longitudinal CRTS II slab track subject to diurnal temperature variation

As a kind of multi-layer concrete structure, thermal responses China Railway Track System type II (CRTS II) slab track subject to diurnal temperature variation could significantly affect its long-term structural performance of slab track, and ultimately the safety of the high-speed train. However, the thermal responses of the bridge supported longitudinal CRTS II slab track have not been fully understood due to the complex of the structural system. The purpose of this study is to systematically investigate the thermal responses of the bridge supported CRTS II slab track system by conducting experimental testing on the scaled models with different boundary conditions in conjunction with theoretical modelling. The results show that the boundary conditions of the CRTS II slab track haveasignificantinfluenceon thermal responses of the slab track. For example, the heat transfer from the track slab to the cement asphalt mortar (CAM) layer could be accelerated under fixed boundary condition. In addition, the longitudinal thermal stress within the CRTS II slab track under the fixed boundary condition is higher that under free boundary condition. Importantly, it indicates that the vertical thermal gradient in the CRTS II slab track induced by the diurnal temperature variation could lead to the damage of the interface between the track slab and CAM.