Controlling the structural build-up in fresh cementitious composites is crucial for 3D printing. This study revealed that continuous shearing can be an effective tool for controlling the structural build-up in fresh cementitious pastes. The tool's sensitivity to the water‑to‑binder ratio and Class C fly ash (FAC) was also examined. Using a rheometer, the structural build-up evolution was obtained by measuring the static yield stress (τsy) at 10-min intervals until the paste reached a rigid τsy threshold. Two binder systems were tested at w/b of 0.40 and 0.48: (i) 100
Multi-blending of supplementary cementitious materials (SCMs) can offer enhanced performance compared to single SCM systems, but this requires a clear understanding of SCM-SCM interactions. This study investigates the kinetic interactions between various SCMs in blended lime-based systems. Binary blends of metakaolin (M) with ground granulated blast furnace slag (S) (M-S) and natural pozzolans, i.e., trass (P) (M-P) and clinoptilolite zeolite (Z) (M-Z), were evaluated. To induce competitive interactions, formulations at three calcium hydroxide (CH) to SCM mass ratios: 3:1, 1:1, and 1:2 were studied. This work introduces a new approach combining isothermal calorimetry and selective dissolution to determine the degree of reaction (DoR) of each SCM within the blend. Complementary analyses included CH consumption, hydrates identification and quantification via XRD-Rietveld refinement and compressive strength testing. Results show that CH availability is the primary driver of SCM reactivity and competition in binary blends. At low CH:SCM ratios, highly reactive SCMs capture CH preferentially, surpassing their reactivity in single systems and partially suppressing the less reactive SCM counterpart. This behavior is formalized through the introduction of a “reactive filler effect”. A competition model proportional to the reactivity difference between the SCMs was proposed to estimate competition behavior, offering quantitative insight into blend behavior across CH:SCM ratios and SCM blends. Overall, this work advances the understanding of the fundamental SCM-SCM interactions in multi-component systems and provides a novel quantitative framework to assess how SCM interactions shape reaction kinetics in binary blended systems.
To address the complex processing and poor storage stability of raw materials in the prepolymer method for synthesising polyurethane modified asphalt (PUMA), this study employed a one-step in-situ synthesis method. The effects of polyol parameters on the microstructure, performance and aging resistance of PUMA were analyzed, and the production cost and cradle-to-gate carbon footprint of the one-step method were evaluated. Results showed that increasing polypropylene glycol (PPG) molecular weight induced polymer agglomeration and phase separation, impairing storage stability, whereas polycaprolactone diol (PCL) inhibited phase separation and enhanced storage stability. PPG favoured urea bond formation, while PCL favoured urethane bond formation, which partly accounted for the superior rutting resistance of PPG-based PUMA relative to its PCL-based counterpart. Sulfoxide index (SI) index analysis revealed that the aging resistance of PCL-based PUMA was 33.3
During the rehabilitation and expansion of existing expressways and high-speed railways, the performance development of newly cast concrete is significantly affected by disturbances from vehicle-bridge coupling vibration loads through adjacent operational structures. Existing research suggests that the severity of such disturbance depends largely on the stage of concrete performance development at the time of disturbance. The most pronounced deterioration occurs between the initial and final setting stages, a critical window known as the disturbance-sensitive period. Accurate identification of this period is therefore essential for effectively mitigating disturbance-induced damage. To this end, a laboratory concrete re-vibrating table was used to simulate disturbances from vehicle-bridge coupling vibration loads. Based on real-time in situ monitoring of early-age concrete pore water pressure (PWP), this study employs the development of PWP to define disturbance stages. It then systematically investigates the effects of such re-vibration disturbance-induced damage on the early-age macroscopic mechanical properties, durability and microstructure of concrete at different stages of PWP development. The experimental results showed a significant correlation between the evolution of early-age PWP and penetration resistance. Both the initial and final setting of concrete occurs concurrently with the period when PWP begins to rise, ranging from 2 to 60 kPa. Re-vibration disturbances during this period caused the most severe damage, reducing concrete strength by approximately 15
Foamed concrete (FC) is widely used in engineering owing to its low self-weight and ease of construction. Accurate characterization of its mechanical properties is essential. The mechanical behavior and failure characteristics of FC with different densities were investigated through uniaxial compression tests. X-ray computed tomography (X-CT) was used to quantitatively characterize the pore structure. Based on the extracted pore parameters, digital cores were constructed using an improved quartet structure generation set (QSGS) method and converted into discrete element models to investigate the size effect of FC under uniaxial compression. The pore structure was characterized using the lineal-path function and pore size distribution. Results show that the compressive strength of FC increases with density but decreases with increasing specimen size. A representative area element (RAE) assessment identified 30 mm as the representative size. Within the size range of 30–100 mm, the mean compressive strength decreases with increasing size, and the failure mode gradually evolves from brittle to more ductile behavior, accompanied by an increase in microcrack number and the formation of complex crack networks. Macroscopic cracks can be classified into I-, X-, Y-, and H-shaped, and the failure mechanism transitions from tensile-dominated to tensile–shear coupled behavior. Grey relational analysis (GRA) indicates that porosity has a stronger correlation with compressive strength (0.747) than the Lp area (0.620), highlighting its dominant role in the mechanical performance of FC. The adopted size-effect models effectively capture the variation of FC strength with size, providing a theoretical basis for evaluating size effects in engineering applications.
Chloride ion permeation into concrete in marine environments initiates reinforcement corrosion, compromising structural integrity. Nano-metakaolin (NMK) effectively reduces concrete permeability. To investigate microstructural changes in NMK concrete under electric fields and the evolution of acoustic emission (AE) signals throughout corrosion stages, experiments monitored AE signals during accelerated corrosion-induced cracking of reinforced concrete under full immersion conditions. Characteristic AE signals at different stages were summarized, alongside an analysis of changes in hydration products. The findings indicate that NMK, rich in Si, Al, and other elements with pozzolanic activity, promotes the formation of hydration products. This improves the concrete microstructure, effectively impeding chloride ion migration within the matrix and thereby slowing reinforcement corrosion rates. After 48 h of electrification, the corrosion rate in the N5 group decreased by 59.80
Optimizing the heating efficiency of induction-heated asphalt mixtures requires a systematic understanding of multistage energy-conversion mechanisms at the micro- and mesoscales. In this study, three induction media with distinct morphologies, namely steel fibers (SF), steel wool (SW), and steel chips (SC), were investigated. A numerical response chain linking magnetic flux (Φ), induced electromotive force (U), Joule heat (Q), and temperature (T) was established, together with multiphysics experiments involving electromagnetic response, apparent electrical resistance, and induction-heating response, to compare the electromagnetic–thermal characteristics of the different media. The results showed that medium morphology dominated the electromagnetic response. Under ideal non-contact dispersion conditions, SF exhibited the strongest magnetic-flux response, 148.2
To mitigate bleeding and segregation caused by excessive superplasticizer, this study proposes a modified mixing strategy for limestone–calcined clay cement (LC3), in which calcined clay is added with delay (DCAS). The effects of DCAS on flowability, rheology, superplasticizer (PCE) adsorption, hydration kinetics, and mechanical properties were investigated. At a PCE dosage of 0.20
To overcome the low-temperature brittleness caused by the crystallization of natural Eucommia ulmoides gum (EUG) and achieve precise tuning of asphalt properties, three performance-adjustable modified asphalts—vulcanized (VEMA), epoxidized (EEMA), and hydroxylated (HEMA) EUG modified asphalts—were prepared via chemical modification. A multi-scale experimental framework combining rheological testing and physicochemical characterization was utilized to systematically investigate the tuning laws and intrinsic mechanisms of these modifiers on asphalt behavior. The results indicate that all three chemically modified asphalts exhibit significantly superior rutting and permanent deformation resistance compared to base asphalt and raw EUG modified asphalt, while simultaneously maintaining excellent low-temperature cracking resistance. Microscopic analysis reveals that chemical modification disrupts the regularity of EUG molecular chains, effectively suppressing crystallization and remarkably lowering the glass transition temperature. The modification process is predominantly governed by chemical mechanisms: in-situ vulcanization crosslinking, epoxy ring-opening covalent bonding, and intensive hydroxyl hydrogen bonding networks promote the transformation of small molecules into large molecular size components. This reconfigures the microscopic "bee-like" structures and facilitates their uniform dispersion, thereby substantially enhancing micro-adhesion and phase compatibility. This study demonstrates that the macro–micro performance of EUG-modified asphalt can be directionally optimized by controlling chemical modification degrees and ratios, providing a solid theoretical foundation for the engineering application of high-performance bio-based green pavement materials.
This study investigates the partial and total replacement of CaSO4 by BaCO3 in calcium sulfoaluminate (CSA) cement systems through a systematic compositional series to examine the coupled effects of decreasing initial sulfate content, carbonate incorporation, and BaSO4 formation on hydration. Six pastes with different BaCO3/CaSO4 ratios were evaluated by isothermal calorimetry, X-ray diffraction, FTIR, thermogravimetry, SEM–EDS, and nitrogen adsorption. The progressive replacement of CaSO4 by BaCO3 altered hydration kinetics and phase assemblage as a function of replacement level. At 25
Porous Asphalt Mixtures (PAMs) are widely used in permeable pavement systems for Blue–Green Infrastructure (BGI) applications to manage and treat surface runoff in urban and transport infrastructures. However, their hydrological and structural performance can be compromised by compaction-induced anisotropy and cracking. In this context, the valorisation of industrial by-products and the implementation of heating-based self-healing technologies can improve the performance of the PAMs. This study investigates the combined effects of Blast Furnace Dust (BFD) and microwave heating on crack-healing and vertical permeability in Superpave-compacted PAM for BGI applications. Asphalt mixtures containing 0
The increasing accumulation of plastic waste and the depletion of natural mineral aggregates have driven interest in the use of recycled plastic particles as alternative aggregates in concrete. However, weak interfacial bonding between hydrophobic plastic particles and the cement matrix remains a critical limitation. This study investigates the effect of oxygen plasma surface modification on the mechanical performance of concrete incorporating recycled polypropylene flakes (PPF) and polyethylene agglomerates (PEA). Compressive and flexural strength tests, together with triaxial tests under confined conditions, were performed. Surface wettability was evaluated using contact angle measurements, and interfacial morphology was analysed by scanning electron microscopy (SEM). Although plastic particles reduced compressive strength compared to reference concrete, plasma treatment improved mechanical performance, particularly for PEA mixtures, with compressive strength increasing by up to 33
This study evaluates the structural behavior of hybrid bolted beam-to-beam connections for precast reinforced-concrete members through coupled testing and nonlinear simulation. Six full-scale assembled beams were tested in monotonic four-point bending, with three anchor-bolt diameters (16, 20, 24 mm) and two assembly conditions: perfectly aligned joints and intentionally imperfect joints with 1.2° face rotation. Global load-deflection response, and local moment-rotation response, crack evolution, and failure mechanisms were documented. All specimens displayed an initial quasi-linear regime followed by stiffness degradation and a ductile post-yield phase governed by anchor-bolt plasticity. The imposed imperfections mainly penalized pre-yield stiffness, resulting in reductions of 31
In addition to the technological properties of concrete, ecological requirements will become increasingly important in the production of concrete in the future. In recent years, numerous international assessment and classification systems have been developed to transparently communicate and classify the environmental impact of concrete using quantitative parameters. These systems define corresponding classes or levels based on the specific CO2-emissions of concrete. Such systems for measuring and classifying CO2-emissions of concrete are becoming increasingly important in the planning, tendering, and execution of future construction projects. It is therefore crucial to provide generally applicable methods and classification systems for the assessment of CO2-emissions of concrete. This study compares nine recently developed classification systems for evaluating CO2-reduced concrete, describing their specific features, limitations and potential. On this basis, a novel approach was developed that combines the international systems into a single concept for compressive strength classes from C20/25 to C50/60. The proposed approach provides a simple and transparent framework that combines existing European classification systems and can therefore support the future implementation of uniform standardized international CO2-classes for concrete. In addition, the current practical availability of such CO2-reduced concretes is described in relation to the reduction classes of the individual systems.
Europe’s abundant hardwood resources are primarily used for energy rather than for timber construction. The lack of precise mechanical characterisation limits their use as structural elements. With regard to shear strength, the current normative European test (EN 408) has drawbacks and is difficult to perform with hardwood. This study aims to develop an asymmetric four-point bending test setup to characterise the shear strength of hardwoods. A numerical model was used to analyse the shear stress distribution under the proposed test setup. Experimentally, three European hardwoods (ash, beech and oak) were tested and the shear strength was retrieved using the stress distribution from the numerical model. Twin tests were also performed with softwood for comparison with the normative test setup. The numerical model confirmed a homogeneous shear stress distribution in the central beam zone, as well as low undesirable other stresses. Experimentally, 80
This study integrates newly developed nail-laminated engineered bamboo (NLB) structural components into conventional light-frame systems and presents a two-story residential demonstration project. The mechanical properties and fabrication details of multidirectional laminated engineered bamboo are provided and compared with those of sawn timber. The connection system linking key structural elements is introduced, with its performance determined by (i) the lateral resistance of bamboo–bamboo, bamboo–timber, and bamboo–steel connections, and (ii) the withdrawal behavior of steel connectors embedded in bamboo. Relevant studies on the above two aspects are reviewed and discussed. Methods for calculating the brittle shear resistance of bamboo connections are also analyzed to determine suitable overstrength factors for capacity-based design. The manufacturing details of main structural elements—bending members, hybrid shear walls, and roof trusses—are described. Experimental evaluations of connector performance in bending members, as well as load-bearing capacities of shear walls and roof trusses, are reported. Finally, the construction and assembly of the full-scale residential building are presented, demonstrating the practical application and promising potential of this nail-laminated bamboo construction method.
Steel fibers are a promising reinforcement for 3D concrete printing (3DcP), which enhance post-cracking mechanical strength and fracture resistance. However, during the printing process, fibers tend to align with the printing direction, which exacerbates the inherent anisotropy of 3DcP structural components. Accurate prediction of fiber orientation is therefore essential for mitigating this effect. Traditional numerical approaches, however, are often limited by prohibitive computational costs due to the large number of fibers and the complex fluid–fiber interactions involved. This study proposes a computationally efficient three-dimensional coupled computational fluid dynamics–discrete element method (CFD–DEM) model for the rapid simulation of fiber orientation during the extrusion process. To improve computational efficiency, fluid–fiber interactions are treated using a one-way coupling framework, in which fiber rotation is analytically resolved based on Jeffery’s rotation equations. Validation against experimental measurements demonstrates the reliability of the proposed model. Parametric studies reveal that smaller nozzle openings, longer fiber lengths, and higher printing speeds promote stronger alignment of fibers along the printing direction, whereas the influence of rheological properties is relatively limited. In addition, shear-induced rotation is identified as one of the dominant mechanisms governing fiber orientation during extrusion. Increasing the size of the shear-dominated region near the nozzle exit can therefore improve fiber alignment in the printing direction. Beyond its engineering implications, the proposed modeling framework provides a design-oriented tool for fiber-reinforced 3DcP systems. By enabling the prediction and control of fiber orientation fields, the approach opens opportunities for directionally informed structural design in robotic concrete construction and can be extended to other short-fiber-reinforced material systems.
This study explores the feasibility of using alkali-activated regolith for construction in lunar environment. The composition of the reactive glassy fraction present in lunar regolith simulant is assessed in detail, with the aim of tailoring suitable alkaline activators that can maximise the reactivity of the system without leading to the release of excess alkali in solution or formation of unwanted products such as amorphous silica. The obtained results suggest that the low amount of reactive aluminium present in the regolith can be compensated by either the addition of moderate amounts (< 10 wt
At the mesoscale, concrete is recognized as a three-phase composite comprising aggregates, mortar, and the interfacial transition zone. Despite mortar’s critical role in concrete’s mechanical behavior, its properties are frequently approximated by simply scaling down those of concrete without rigorous calibration. This approximation hinders a precise understanding of mortar’s contribution to the overall mechanical response and failure mechanisms of concrete. To address this, both quasi-static and dynamic compression tests were conducted to characterize the stress–strain responses and failure patterns of mortar specimens and to establish a quantitative characterization of strain-rate sensitivity. Complementary numerical simulations were performed with a modified Karagozian Case model calibrated by experimental findings. Comparative analyses were conducted to elucidate distinct differences in failure behaviors between mortar and concrete under dynamic compressive loading. The results revealed that while concrete exhibits greater compressive strength, mortar demonstrates a more pronounced strain-rate effect. This study provides new insights into the dynamic failure behavior of cementitious materials and advances the modeling and safety assessment of concrete structures under impact or blast loading.
The paper presents structural analysis of reinforced wide concrete corbel. The article may be considered part of expert bearing capacity assessment of reinforced wide concrete corbel. The term wide corbel here is related to a corbel whose width is more than one and a half times its height. Wide corbels, due to width effects that affect the 3D stress distribution, require appropriate central part reinforcement. Wide corbel indicates incorrect reinforcement placement due to design deficiency. The paper starts with a literature survey on chosen investigations into reinforced concrete corbels. Next, analytical and numerical modelling of reinforced concrete corbel through 3D models are presented. The description of the reinforced concrete corbel, including basic details and the results of structural analysis, is addressed too. Comparison of analytical results (Franz [1], Hagberg [2], Nagrodzka-Godycka [3]) and selected standards (PN-B-03264 [4], EN-1992-1-1 [5], ACI318-19 [6]) is also regarded. Finally, the conclusions are presented. Reinforcement bars of wide corbels should be designed properly across the corbel width, to distribute the primary and secondary reinforcement in a repetitive, overlapping and interchangeable way to ensure that the main bars and stirrups are located within an entire corbel core. It is recommended to introduce guidelines into standards for reinforcement bar layout to ensure a uniform primary reinforcement layout in the cross-section of wide corbels. This paper provides scientists, engineers and designers with a background for structural analysis of reinforced concrete corbels.
