CivilEng

Conventional strengthening measures for existing structures are usually not effective for the self-weight, which accounts for around 70% of the total load in reinforced concrete structures. Therefore, their effect on the overall load-bearing capacity is low. A self-weight-effective alternative for flexural strengthening is the thermal prestressing of additional reinforcement installed on the structure. In this method, reinforcing bars are slotted into the tensile zone, embedded in filler material, and tempered from the outside. They are thermally stretched, and once cooling starts, the bond with the hardened filler prevents re-deformation. The induced prestressing force counteracts dead loads and relieves the tensile zone, making the additional bars effective for the self-weight. In this paper, the effectiveness of the strengthening method is experimentally investigated in the serviceability and the ultimate limit states. Experiments involve strengthening a reinforced concrete beam under load by a thermally prestressed additional bar. Moreover, two reference tests are made to evaluate the method. An unstrengthened beam characterizes the lower capacity limit. Another beam with the same reinforcement amount as the strengthened one, but completely installed at casting, serves as the upper benchmark. All beams are loaded until bending failure. The strengthening method is assessed by means of the load-bearing behavior, deflection, crack development, and the strains in the initial as well as the added reinforcement. The results demonstrate the effectiveness of the strengthening method. The thermally prestressed bar achieves an effective pre-strain of approximately. 0.4‰ by heating at about 70 °C. The induced prestressing force and associated compression reduce tensile cracks by approx. 45% and increase stiffness. The strengthened beam reaches the maximum load of the upper benchmark, but with about 33% less deflection. The filler, which also expands thermally, generates an additional prestressing force that is effective up to about 20% of the load capacity. Beyond this, the filler begins to crack and its effect decreases, but the pre-strain in the reinforcing bar remains until maximum load. Full article

This study presents the outcomes of a comprehensive experimental investigation focused on the bond behavior between reinforcing steel bars and tremie concrete, assessed through standardized pull-out tests. The objective was to evaluate the influence of some key parameters: reinforcement bar diameter, concrete age (and associated compressive strength), steel fiber content, and a bentonite coating on rebar surfaces. Experiments were conducted under laboratory conditions according to relevant standards. Slip between the reinforcement and tremie concrete was measured using a sophisticated high-precision optical laser device, enabling accurate assessment of bond characteristics. A large, i.e., a statistically sufficient, number of specimens was tested, allowing the results to be analyzed using the ANOVA technique to determine the statistical significance of each parameter. The results show that, under most test conditions, the influence of the bentonite suspension coating on the bond strength was not statistically significant. Similarly, variations in the bar diameter and fiber content showed no statistically significant impact within the tested ranges. In contrast, concrete age (compressive strength) exhibited a statistically significant influence, confirming that concrete maturity is a dominant factor in bond development. The results contribute to a better understanding of the bond mechanisms in reinforced concrete and can assist in optimizing design strategies where bond performance is critical. Full article

The growing application of 3D concrete printing (3DCP) in construction has raised important questions regarding its long-term durability under freeze–thaw (F–T) exposure, particularly in cold climates. This review paper presents a comprehensive examination of recent research focused on the F–T performance of 3D-printed concrete (3DPC). Key material and process parameters influencing durability, such as print orientation, admixtures, and layer bonding, are critically evaluated. Experimental findings from mechanical, microstructural, and imaging studies are discussed, highlighting anisotropic vulnerabilities and the potential of advanced additives like nanofillers and air-entraining agents. Notably, air-entraining agents (AEA) reduced the compressive strength loss by 1.4–5.3% after exposure to F–T cycles compared to control samples. Additionally, horizontally cored specimens with AEA incorporated into their mixture design showed a 15% higher dynamic modulus after up to 300 F–T cycles. Furthermore, optimized printing parameters, such as reduced nozzle standoff distance and minimized printing time gap, reduced surface scaling by over 50%. The addition of a nanofiller such as nano zinc oxide in 3DPC can result in compressive strength retention rates exceeding 95% even after aggressive F–T cycling. The lack of standard testing protocols and the geometry dependence of degradation are emphasized as key research gaps. This review provides insights into optimizing mix designs and printing strategies to improve the F–T resistance of 3DPC, aiming to support its reliable implementation in cold-region infrastructure. Full article

The use of hot mix asphalt (HMA) has several drawbacks, such as the emission of harmful gases into the atmosphere, difficulties in maintaining temperature over long distances, and the requirement for high energy consumption during preparation and installation. In order to solve these issues, this research aimed to produce High-Performance Cold Mix Asphalt (HP-CMA), in which Ordinary Portland Cement (OPC) is used as a filler to replace limestone filler at 0%, 1.5%, 3%, 4.5%, and 6% of the aggregate weight. Indirect Tensile Stiffness Modulus (ITSM), moisture susceptibility, temperature susceptibility, and microstructural analysis tests were carried out. The results showed that the ITSM was considerably enhanced when OPC was utilized. When comparing HP-CMA with 3% OPC to the control HMA (100–150 pen), the ITSM increased by approximately 80% after three days. In contrast, HP-CMA with 4.5% OPC achieved the same ITSM as the control HMA (40–60 pen) after seven days. Moreover, the ITSM of the HMA 40–60 pen decreased by 91.93% when the temperature rose from 20 °C to 45 °C, whereas the ITSM of the HP-CMA with 6% OPC decreased by 42.47% over the same temperature range. This suggests that HP-CMA is more stable than the HMA 40–60 pen at elevated temperatures. The superior performance of the HP-CMA can be attributed to two essential factors: the improved binding effect due to the demulsification of the asphalt emulsion used as a binder, and the formation of hydration products from the added cement. Full article

Ground penetrating radar (GPR) is a non-destructive testing (NDT) method increasingly used for evaluating concrete structures by identifying internal flaws and embedded objects. This study presents a structured image-based methodology for interpreting GPR B-scan data using a practical flowchart designed to aid in distinguishing common subsurface anomalies. The methodology was validated through a laboratory experiment involving four concrete slabs embedded with simulated defects, including corroded rebar, hollow pipes, polystyrene sheets (to represent delamination), and hollow containers (to represent voids). Scans were performed using a commercially available device, and the resulting radargrams were analyzed based on signal reflection patterns. The proposed approach successfully identified rebar positions, spacing, and depths, as well as low-dielectric anomalies such as voids and polystyrene inclusions. Some limitations were noted in detecting non-metallic materials with weak dielectric contrast, such as hollow pipes. Overall, the findings demonstrate the reliability and adaptability of the proposed method in improving the interpretation of GPR data for structural diagnostics. The proposed methodology achieved a detection accuracy of approximately 90% across all embedded features, which demonstrates improved interpretability compared to traditional manual GPR assessments, typically ranging between 70 and 80% in similar laboratory conditions. Full article

Recycled asphalt pavement (RAP) can support traffic loads comparable to those of roads constructed with conventional materials. The structural evaluation of RAP is performed through the deflection generated by vehicles via recoverable deflection in the pavement layers. The deflection record is translated into a curve that geometrically interprets the behavior of the layers that make up the pavement. In this study, a falling weight deflectometer (FWD) was used to emulate transit loads and measure deflection in two models. Both contained 30% RAP, and one of them had fiberglass geogrid in the center of the asphalt layer. Through normalized maximum deflection (limit value based on constant stress), the structural index (SI), and the dynamic stiffness modulus (DSM), the structural behavior of the models under different load levels was evaluated. The pavement structure exhibited similarities in strength for both models subjected to impact. The presence of the geogrid reinforcement (Z1) showed structural index values ranging between 0.17 and 0.54, while the layer without geogrid (Z2) presented structural index values in a range of 0.23 to 0.78. In addition, the dynamic stiffness modulus presented a difference of 10 kN/mm between the maximums of the models in favor of reinforcement with glass fiber geogrid. Therefore, low structural index values are associated with the interaction between RAP and geogrid, highlighting this combination as an innovative and functional system for road surfaces, while the dynamic stiffness modulus indicates the stability and structural integrity of sustainable pavement, which has the potential to extend its lifespan. Full article

In the construction sector, cement and concrete are among the most widely utilized manufactured materials, yet their environmental impact remains a significant concern. The concrete industry is a major contributor to carbon dioxide emissions, accounting for over 8% of global greenhouse gas emissions annually. Several reports have estimated that between 1930 and 2013, a total of 4.5 gigatons of carbon was sequestered through the carbonation of cement-based materials. This process offset approximately 43% of the carbon dioxide (CO₂) emissions resulting from cement production during the same period, excluding emissions related to fossil fuel consumption in the manufacturing process. It is well established that producing one ton of cement results in approximately 0.60–0.98 tons of CO₂ emissions, coupled with substantial energy consumption. To mitigate these environmental effects, developing low-carbon or cement-free binders has become crucial. Alkali-activated binders (AABs), derived from industrial by-products or agricultural waste materials and activated with a low-molarity or one-part activator, are increasingly recommended as sustainable alternatives to reduce greenhouse gas emissions in the cement industry and minimize the consumption of natural resources. The production of alkali-activated concrete (AAC) involves several critical factors that significantly influence its mix design, fresh properties, and compressive strength (CS) performance. This study aims to provide a comprehensive review of the key factors affecting AAC’s mix design, workability, and CS characteristics. Firstly, the study discusses various methods employed for AAC mix design and the factors influencing these designs. Secondly, it examines the impact of binder type, source, chemical, mineralogical, and physical properties, as well as alkaline activator solutions, water content, and fillers on AAC’s workability, setting times, and strength development. Additionally, the study explores the correlation matrix and predictive performance models for fresh and strength properties. Lastly, the relationship between workability and CS is extensively analyzed. The review concludes by highlighting the existing challenges and prospects of AACs as sustainable construction materials to replace traditional cement and reduce carbon emissions. Full article

This study presents a comprehensive analysis of hydration heat-induced temperature and stress fields in a U-shaped aqueduct during the casting phase, integrating field measurements and numerical simulations. The key findings are as follows: (1) Thermal Evolution Characteristics: Both experimental and numerical results demonstrated consistent thermal behavior, characterized by a rapid temperature rise, subsequent rapid cooling, and eventual stabilization near ambient conditions. The peak temperature is observed at the centroid of the bearing section’s base slab, reaching 83.8 °C in field tests and 87.0 °C in simulations. (2) Stress Field Analysis: Numerical modeling reveals critical stress conditions in the outer concrete layers within high-temperature zones. The maximum tensile stress reaches 6.37 MPa, exceeding the allowable value of the tensile strength of the current concrete (1.85 MPa) by 244%, indicating a significant risk of thermal cracking. (3) Temperature Gradient and Cooling Rate Anomalies: Both methodologies identify non-compliance with critical control criteria. Internal-to-surface temperature differentials exceed the 25 °C threshold. Daily cooling rates at monitored locations surpass 2.0 °C/d during the initial 5–6 days of the cooling phase, elevating cracking risks associated with excessive thermal gradients. (4) Mitigation Strategy Proposal: Implementation of a hydration heat control system is recommended; compared to single-layer systems, the proposed mid-depth double-layer steel pipe cooling system (1.2 m/s flow) reduced peak temperature by 23.8 °C and improved cooling efficiency by 28.7%. The optimized water circulation maintained thermal balance between concrete and cooling water, achieving water savings and cost reduction while ensuring structural quality. (5) The cooling system proposed in this paper has certain limitations in terms of applicable environment and construction difficulty. Future research can combine with a BIM system to dynamically control the tube cooling system in real time. Full article

With rising global temperatures and increasing sustainability demands, the need for advanced pavement solutions has never been greater. This study breaks new ground by integrating phase change materials (PCMs), including paraffin-based wax (Rubitherm RT55), hydrated salt (Climator Salt S10), and fatty acid (lauric acid), as binder modifiers within warm mix asphalt (WMA) mixtures. Moving beyond the traditional focus on binder-only modifications, this research utilizes recycled cigarette filters (CFs) as a dual-purpose fiber additive, directly reinforcing the asphalt mixture while simultaneously transforming a major urban waste stream into valuable infrastructure. The performance of the developed WMA mixture has been evaluated in terms of stiffness behavior using an Indirect Tensile Strength Modulus (ITSM) test, permanent deformation using a static creep strain test, and rutting resistance using the Hamburg wheel-track test. Laboratory tests demonstrated that the incorporation of PCMs and recycled CFs into WMA mixtures led to remarkable improvements in stiffness, deformation resistance, and rutting performance. Modified mixes consistently outperformed the control, achieving up to 15% higher stiffness after 7 days of curing, 36% lower creep strain after 4000 s, and 64% reduction in rut depth at 20,000 passes. Cost–benefit analysis and service life prediction show that, despite costing USD 0.71 more per square meter with 5 cm thickness, the modified WMA mixture delivers much greater durability and rutting resistance, extending service life to 19–29 years compared to 10–15 years for the control. This highlights the value of these modifications for durable, sustainable pavements. Full article

In this study, to solidify the silt in an expressway, a stabilizing agent composed of industrial wastes, such as ordinary Portland cement (OPC), calcium based alkaline activator (CAA), silicate solid waste material (SISWM) and sulfate solid waste material (SUSWM) was developed. Orthogonal experiments and comparative experiments were carried out to analyze the strength and water stability of the stabilized silt, and get the optimal proportion of each component in the stabilizing agent. A series of laboratory tests, including unconfined compressive strength (UCS), water stability (WS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analyses, were conducted on solidified silt samples treated with the stabilizing agent at optimal mixing ratios of OPC, CAA, SISWM, and SUSWM to elucidate the evolution of mineral composition and microstructure. Full article

Earthen flood protection structures are planned and constructed with an expected service life of several decades while being exposed to environmental impacts that may lead to structural or hydraulic failure. Current maintenance procedures involve only repairing external damage, leaving internal processes contributing to structural damage often undetected. Through structural health monitoring (SHM), structural deficits can be detected before visible damage occurs. To improve maintenance workflows and support predictive maintenance of dikes, this paper reports on the integration of digital twin concepts with SHM strategies, referred to as “digital-twin-based SHM”. A digital twin concept, including a standard-compliant building information model, is proposed and implemented in terms of a digital twin environment. For integrating monitoring and sensor data into the digital twin environment, a customized webform is designed. A communication protocol links preprocessed sensor data stored on a server with the digital twin environment, enabling model-based visualization and contextualization of the sensor data. As will be shown in this paper, a digital twin environment is set up and managed in the context of SHM in compliance with technical standards and using well-established software tools. In conclusion, digital-twin-based SHM, as proposed in this paper, has proven to advance predictive maintenance of dikes, contributing to the resilience of critical infrastructure against environmental impacts. Full article

Concrete resistivity is a critical parameter for assessing durability and monitoring the structural health of reinforced concrete. This study systematically evaluates the effects of the water-to-cement (w/c) ratio, saturation ratio (SR), and temperature on concrete resistivity using three different predictive models: linear regression, cubic Support Vector Machine (SVM), and Gaussian Process Regression (GPR). Each model was independently trained and tested to assess its ability to capture the nonlinear relationships between these key parameters. Experimental results show that resistivity decreases significantly under increasing load due to geometrical effects. For a w/c ratio of 0.4, resistivity decreases by −12.48% at 100% SR and by −6.68% at 60% SR under 20% loading. Higher w/c ratios (0.5 and 0.6) exhibit more pronounced resistivity reductions due to increased porosity and ion mobility, with a maximum decrease of −13.68% for w/c = 0.6. Among the developed predictive models, the Matern 5/2 Gaussian process regression (GPR) model demonstrated the highest accuracy, achieving an RMSE of 5.21, R² of 0.99, MSE of 27.19, and MAE of 3.40, significantly outperforming the other approaches. Additionally, a permutation importance analysis revealed that the saturation ratio (SR) is the most critical variable influencing resistivity, followed by the water–cement ratio, while temperature has the least impact. These findings provide valuable insights into the durability assessment and corrosion prevention of reinforced concrete, offering practical implications for the optimization of material design and structural health monitoring in civil engineering. Full article

In this study, we aim to analyze the dispersion of ultrasonic waves due to second-gradient contributions and attenuation within the framework of continuum mechanics. To investigate dispersive behavior and attenuation effects, we consider the influence of both higher-order gradient terms (second gradients) and Rayleigh-type viscoelastic contributions. To this end, we employ the extended Rayleigh–Hamilton principle to derive the governing equations of the problem. Using a wave-form solution, we establish the relationship between the phase velocity and the material’s constitutive parameters, including those related to the stiffness of both standard (first-gradient) and second-gradient types, as well as viscosity. To validate the model, we use data available in the literature to identify all the material parameters. Based on this identification, we observe that our model provides a good approximation of the experimentally measured trends of both phase velocity and attenuation versus frequency. In conclusion, this result not only confirms that our model can accurately describe both wave dispersion and attenuation in a material, as observed experimentally, but also highlights the necessity of simultaneously considering both second-gradient and viscosity parameters for a proper mechanical characterization of materials. Full article

Although prefabricated buildings offer environmental advantages, their construction process inevitably generates environmental impacts. However, current research on prefabricated buildings focuses on the environmental impact level, and there is a lack of intelligent tools for analyzing their spatial and temporal dimensions. Therefore, this study develops a framework using 5D building information modeling (BIM) to monetize environmental impacts into environmental costs for prefabricated building construction. This framework includes defining boundaries and indicators, obtaining a resource inventory using the 5D BIM coding system, calculating environmental impact results, and converting environmental impacts into environmental costs. Taking a prefabricated substation as a case study, its environmental costs are 172.81 CNY/m², with these costs caused by climate change accounting for the largest proportion (91.2%). This study unifies different environmental impacts into a single monetary form, providing stakeholders with intuitive indicators. It also expands 5D BIM applications from conventional costs to environmental costs, which can display their spatiotemporal changes. Full article

The Deep Cement Mixing Integrated Drilling, Mixing, and Jetting (DMJ) technique was innovatively developed by incorporating high-pressure jetting apertures into the mixing blades to enhance the bearing capacity of deep cement-mixed piles. In this study, the bearing characteristics of DMJ pile composite foundations under embankment loading are investigated using numerical simulation. Through comparative simulations involving various pile configurations, the results demonstrate that DMJ pile composite foundations exhibit significantly enhanced settlement control compared to conventional deep mixing piles. Notably, under identical area replacement ratios, the use of DMJ piles reduces total foundation settlement by approximately 30%. Furthermore, the findings indicate that larger pile diameters and smaller spacing are particularly effective in minimizing settlement. In terms of load transfer efficiency, DMJ piles are capable of transmitting embankment loads to depths of up to 15 m, surpassing the 10 m transfer depth observed in conventional pile systems. An analysis of excess pore water pressure further reveals that DMJ piles promote more effective dissipation, highlighting their superior performance in maintaining foundation stability under embankment loading. Full article

The present research aims to the evaluation of the deformation capacity of existing reinforced concrete shear walls designed with past non-conforming seismic regulations. A refined analytical model (referred to as the Proposed Model) is presented for generating Load–displacement (P-d) curves for RC shear walls. The model is applicable to medium-rise walls designed with or without modern seismic provisions and incorporates shear effects in both deformation and strength capacity. The application of the Proposed Model is assessed through comparison with numerical models implemented in the widely accepted OpenSees platform. Specifically, two types of elements are examined: the widely used flexural element Force-Based Beam-Column Element (FBE) and the Flexure-Shear Interaction Displacement-Based Beam-Column Element (FSI), which accounts for the interaction between flexure and shear. The results of both analytical and numerical approaches are compared with experimental data from four RC shear wall specimens reported in previous studies. Full article

This study is a preliminary investigation of the independent utilization of two types of fly ash (FA)–FA Type C and FA Type F-as partial replacement of fine aggregate (sand) and cement in Portland cement concrete (PCC) mixes. The main objective was to determine an optimum substitution range for each type of FA that would offer well-performing concrete in terms of workability, compressive strength, and durability. To this end, multiple concrete batches were prepared, incorporating each type of FA at four different levels: 5%, 10%, 15%, and 20% by weight of fine aggregate replacement and 10%, 20%, 30%, and 40% by weight for cement replacement. Then, concrete samples (100 mm diameter × 200 mm tall cylinders) were cast from each batch and were moisture-cured for 7, 14, and 28 days prior to testing. The addition of FA contributed positively to the strength development at specific replacement levels: all percentages for both FA Type C and Type F for fine aggregate replacement and up to 30% FA content for both Type C and F for cement replacement, 10% for both FA Type C and Type F provided the higher strength for aggregate replacement, and 10–20% for both types of FA provided the higher strength for cement replacement. Furthermore, these additions of FA exhibited comparable workability and durability except for FA Type F, which did not exhibit comparable workability for aggregate replacement. FA Type C can be recommended for both early and long-term strength for fine aggregate replacement, whereas FA Type C is suggested to be used for early strength and Type F provides for long-term strength for cement replacement. Type C provides better durability and Type F provides better workability for cement replacement. Full article

As transportation infrastructure systems continue to expand, the demand for unmanned aerial vehicle (UAV) technologies in the assessment of urban infrastructure is expected to grow substantially, due to their strong potential for efficient data collection and post-processing. UAVs offer numerous advantages in infrastructure assessment, including enhanced time and cost efficiency, improved safety, and the ability to capture high-quality data. Furthermore, integrating various data-collecting sensors enhances the versatility of UAVs, enabling the acquisition of diverse data types to support comprehensive infrastructure evaluations. Numerous post-processing software applications utilizing various structure-from-motion (SfM) techniques have been developed, significantly facilitating the assessment process. However, researchers’ efforts to find the potentialities of this technology will be in vain if its applications are not utilized effectively in the practical field. Therefore, this study aims to determine the adaptation condition of UAV technologies in different Department of Transportation (DOT) and Federal Highway Administration (FHWA) agencies to assess transportation infrastructure systems. This study also explores the quantitative analysis of benefits and challenges/barriers, expectations for every UAV and post-processing software, and the cutting-edge features that should be integrated with UAVs to effectively evaluate transportation infrastructure systems. A comprehensive survey form was distributed to all 50 DOTs and the FHWA, and 35 complete responses were recorded from 27 DOTs and the FHWA. The survey results show that 25 agencies currently use UAVs for roads or highways, and 23 DOTs for bridges, confirming these as the most commonly assessed infrastructure systems. The top benefits found in this study include safety, cost effectiveness, and time efficiency (mean ratings: 3.95–4.28), while weather, FAA regulations, and airspace restrictions are the main challenges. Respondents emphasize the need for longer flight times, better automation, and advanced data tools, underscoring growing adoption and highlighting the need to overcome technical, regulatory, and data privacy challenges for optimal UAV integration within transportation infrastructure systems management. Full article

Over the past several decades, extensive research has advanced the understanding of liquefaction in clean sands and sand–silt mixtures under seismic loading. However, the influence of plastic (i.e., clayey) fines on the liquefaction behavior of sandy soils remains less well understood. This study investigates how the quantity and plasticity of fines affect both the susceptibility to liquefaction and the resulting failure mode. A series of stress-controlled cyclic triaxial tests were conducted on sand specimens containing varying proportions of non-plastic silt, kaolinite, and bentonite. Specimens were prepared at a constant relative density with fines content ranging from 0% to 37%. Two liquefaction modes were examined: flow liquefaction, characterized by sudden and large strains under undrained conditions, and cyclic mobility, which involves gradual strain accumulation without complete strength loss. The results revealed a clear relationship between soil plasticity and liquefaction mode. Specimens containing non-plastic fines or fines with a liquid limit (LL) below 20% and a plasticity index (PI) of 0 exhibited flow liquefaction. In contrast, specimens with LL > 20% and PI ≥ 7% consistently displayed cyclic mobility behavior. These findings help reconcile the apparent contradiction between laboratory studies, which often show increased liquefaction susceptibility with plastic fines, and field observations, where clayey soils frequently appear non-liquefiable. The study emphasizes the critical role of plasticity in determining liquefaction type, providing essential insight for seismic risk assessments and design practices involving fine-containing sandy soils. Full article