Chloride-induced rebar corrosion and concrete cracking are complex processes driven by interacting multi-physics mechanisms and multiple contributing factors. This study proposes an innovative multi-physics modeling framework to comprehensively analyze the entire degradation process, from ionic transport to corrosion initiation and cracking induced by corrosion expansion. A multi-ionic transport model is developed to quantify the impact of electrochemical processes and crack propagation on ionic transport. Based on phase-field theory and corrosion kinetics, a corrosion model is then proposed to describe corrosion product loss, filling, and accumulation. A multiphase phase-field cracking model is hence developed to characterize fracture behavior and degradation induced by corrosion product pressure. Third-party data are used to validate the proposed models and framework. Results indicate ignoring multi-ion interactions overestimates pore-solution chloride, while neglecting electromigration distorts local ion distributions. Explicit crack representation generates preferential transport pathways, accelerates ingress, and increases peak current density and electrochemical potential by over 10%. Coupling the displacement field enhances crack-growth predictions and avoids premature or excessive cracking. This work offers a new perspective on cracking and durability deterioration in reinforced concrete by establishing a mechanistic framework that enables more reliable predictions in the cracked state, thereby reducing reliance on empirical formulations.

The use of Additive Manufacturing (AM) to create reinforcements for cementitious composites has become a popular research topic in recent years. One illustrative example is the integration of 3D-printed auxetic reinforcements into cementitious matrices, which exhibit superior energy absorption due to their negative Poisson's ratio. This presents the opportunity to tailor the Poisson's ratio of reinforcements to align with local stress distributions and enhance structural efficiency. In this study, Tailored Poisson's Ratio-reinforcements (TPR) were proposed, characterized by a linear gradient of Poisson's ratios along the height of the reinforcement to accommodate varying stress profiles within beams. Specifically, the top chords of TPR exhibit negative Poisson's ratios (auxetic), undergoing lateral contraction under compression and providing confinement to the surrounded matrix. Conversely, the bottom chords possess positive Poisson's ratios, contributing to lateral contraction under tension. These lateral deformations cause a shift in the principal stress state of the confined matrix, extending the loading path in stress space and actively delaying failure. Three novel Tailored Poisson's Ratio-reinforced Cementitious Composite (TPRCC) designs are developed and tested under four-point bending in this study. Experimental recordings indicate increases in load capacity and toughness of up to 191% and 6900% with respect to plain mortar, respectively.

This study systematically investigates the role of lattice–matrix stiffness contrast in governing confinement and mechanical performance of cementitious composites reinforced by 3D-printed auxetic (negative Poisson's ratio) lattices. Through combined compression testing, numerical simulations, and representative volume element (RVE) analysis, the mechanistic link between stiffness ratio and macroscopic response is established. The results demonstrate that sufficient stiffness contrast is a prerequisite for activating auxetic-induced confinement, enabling the translation of lattice lateral contraction into effective confinement on the cementitious matrix. Auxetic cementitious composites with 3D-printed steel lattice achieved a compressive strength exceeding 80 MPa (nearly 300% higher than plain mortar and polymer lattice reinforced composites). The specific energy absorption was 90% greater than the theoretical sum of the steel lattice and matrix, owing to the strong confinement and synergy enabled by the stiffness contrast. In contrast, polymer lattice reinforced composites, despite possessing the same geometry and similar negative Poisson's ratios, exhibited limited confinement efficiency as the low stiffness suppressed the transfer of auxetic deformation to matrix. RVE analyses revealed that the stiffness contrast between the lattice and matrix governs the mesoscale confinement behavior, which in turn influences the macroscopic strength, ductility, and energy dissipation capacity of auxetic cementitious composites. These findings establish stiffness contrast as the governing design parameter for auxetic cementitious composites and provide a basis for tailoring architected cementitious composites.

Low-calcium fly ash is widely used in cementitious materials to improve their resistance to external sulfate attack (ESA). This study presents a meso-scale numerical framework to evaluate the durability of systems incorporating different levels of fly ash under ESA conditions. The initial phase assemblage is determined using a hydration model that accounts for various fly ash chemical compositions and replacement ratios. The degradation process is simulated by coupling chemical reactions, ion transport, calcium leaching, porosity development, and mechanical damage. A random porosity field, characterized by both statistical distribution and spatial correlation, is introduced to represent material heterogeneity. Following model validation, the framework is applied to investigate the effects of sulfate concentration, specimen size, and fly ash content on sulfate resistance. The study further investigates the interaction between sulfate attack and calcium leaching, the influence of fly ash chemical composition on expansion strain, and the relationship between mineralogical indicators and ESA performance. Results indicate that neglecting the coupling between sulfate attack and calcium leaching leads to a significant underestimation of material degradation. In addition, smaller specimen sizes, neglecting porosity evolution, and a higher coefficient of variance (CV) of the porosity field result in increased expansion. Among the hydration products, the equivalent calcium aluminate (CA) content shows a positive linear correlation with expansion. Fly ash-related chemical indicators exhibit considerable variability and limited predictive accuracy; nevertheless, lower indicator values are generally associated with improved resistance to external sulfate attack.

Auxetic cementitious cellular composites (ACCCs) offer high deformability that is attractive for mechanical energy harvesting when integrated with flexible piezoelectric materials. However, the intrinsic brittleness of cement-based materials and the complex coupling between auxetic geometry and damage evolution hinder the efficient design of ACCC energy harvesters. This study proposes a novel learning-driven design framework that, for the first time, integrates a physics-based energy harvesting model with Bayesian Optimization (BO) to directly optimize the recoverable hinge-like strain capacity of ACCCs for enhanced electrical output. The optimization maximizes the voltage generated by piezoelectric materials bonded at hinge regions, while using constraints to prevent splitting failure and non-auxetic behavior under compression. The energy harvesting model combines the concrete damage plasticity (CDP) model for pre-compression damage with a secondary elastic model for cyclic loading, enabling prediction of recoverable strain in generalized ACCC geometries. The learning-driven approach proved far more efficient than random generation in identifying optimal ACCC configurations. Experimental validation of the optimized design achieved a peak-to-peak voltage of nearly 15.0 V per cycle, about 2.7 times higher than a reference design. This study provides a learning-driven approach to designing enhanced compliant auxetic cementitious energy harvesters for smart infrastructure applications.

Concrete durability has become a central concern in civil engineering as structures are increasingly exposed to complicated and aggressive environments. In practical service conditions such as marine tidal zones, cold regions, sulfate-rich soils, or industrial atmospheres, deterioration rarely occurs in isolation. Instead, chloride ingress, carbonation, sulfate attack, calcium leaching, freeze–thaw damage, and load-induced cracking often coexist and interact on multiple physicochemical and geometric levels. These complex processes alter transport behavior, pore structures, chemical equilibria, and mechanical integrity, resulting in highly nonlinear deterioration that accelerates beyond the sum of individual mechanisms. As conventional models cannot fully capture such synergistic effects, advanced numerical modelling has emerged as a vital tool for durability prediction under multi-deterioration scenarios . This paper reviews recent progress in modelling durability degradation under multiple deterioration mechanisms, with emphasis on both chemically driven and physically driven coupling effects. In chemically dominated degradation, chloride ingress is recognized as the most rapid and detrimental process, and it is strongly modified by concurrent chemical reactions. The interaction between carbonation and chloride transport is particularly complex: carbonation can decompose chloride-binding phases, releasing previously bound chlorides, while simultaneously refining the pore structure through calcium carbonate precipitation. Numerical models incorporating carbonation rate, degree, and pore structure evolution have enabled more accurate quantification of chloride distribution in fully carbonated and partially carbonated regions. Similarly, for combined sulfate–chloride attack, competitive adsorption and expansion-induced microcracking play decisive roles. Thermodynamic equilibrium models and reaction-kinetic models have been used to capture the competition among ions, the formation of expansive products, and the resulting effects on transport properties. These approaches highlight the necessity of considering multi-ion coupling and electrochemical interactions when assessing deterioration severity. Calcium leaching represents another critical chemical mechanism that strongly influences chloride behavior. The dissolution of calcium-bearing hydrates coarsens the microstructure, increases pore connectivity, and reduces binding capacity, thereby accelerating chloride ingress. Multi-ionic transport frameworks have been adopted to simulate these processes, showing that electrochemical coupling initially promotes leaching but later tempers its progression as chemical gradients evolve. Such findings emphasize the importance of capturing time-dependent feedback within reactive transport models. On the physically driven side, processes such as freeze–thaw damage and load-induced cracking profoundly alter the geometric pathways of ionic transport. Freeze–thaw cycles induce pore dilation, microcracking, and structural weakening, forming preferential channels for chloride ingress. Models coupling thermal transfer, moisture and ionic transport have shown that although higher salt concentrations reduce freezing rates, the overall deterioration remains accelerated due to increased permeability. The synergistic effects of freeze–thaw damage and chloride transport thus demand integrated modelling strategies capable of representing dynamic pore evolution. Load-induced cracking also creates high-permeability pathways that significantly influence harmful ions transport. Mesoscale lattice models, multi-ionic models, and other models have demonstrated that crack width, shape, and orientation govern diffusion and migration behavior. However, establishing fully bidirectional coupling, where chloride ingress promotes crack propagation and crack propagation further accelerates chloride ingress, remains an unresolved challenge. Existing methods rely on staged or quasi-coupled approaches, often assisted by statistical learning, yet true geometric updating during crack evolution is still computationally difficult. This limitation highlights a critical frontier for future numerical modelling. Summary and Prospects Research on durability degradation under multiple deterioration mechanisms has made remarkable progress, yet several breakthroughs are needed to achieve reliable long-term predictions. First, advancing the coupling of multi-mechanism models is essential. The mutual interactions between crack propagation and ionic transport, as well as pore-structure evolution under multiple deterioration modes, requires future numerical models that can dynamically update geometry and transport properties over time. More comprehensive physical representations of environmental effects such as temperature, humidity, salt concentration, freeze–thaw intensity will further enhance predictive accuracy. Second, there is an urgent need to improve the geometric dimensionality and computational efficiency of multi-scale, multi-physics frameworks. High-resolution three-dimensional modelling is still limited for multi-ion systems due to nonlinear chemical reactions and the complexity of heterogeneous microstructures. Future work should focus on algorithm optimization, parallel computing, and innovative discretization schemes to enable large-scale simulations with realistic material characteristics. Third, the scope of durability research must expand across both spatial and temporal scales. Linking micro-level deterioration mechanisms with macro-scale structural performance remains a key challenge, particularly for reinforced concrete exposed to multiple aggressive agents. Early-age behavior, interfacial transition zone development, and long-term interaction between mechanical and chemical processes should also be considered into lifecycle-oriented predictive frameworks. Finally, as sustainable and alternative binders such as alkali-activated materials and high-performance composite cements become more prevalent, existing models must be adapted or reconceptualized to accommodate their unique microstructure, chemical composition, and transport properties. Understanding multi-deterioration behavior in these emerging materials will be essential for their safe and widespread engineering application. Overall, progress in numerical modelling, strengthened by data-driven techniques, multi-scale experiments, and advanced characterization methods, is expected to transform our ability to predict durability degradation under complex service conditions. These advances will ultimately support the development of more resilient, sustainable, and long-lasting concrete structures.

Lattice reinforcement (LR) demonstrates great potential in enhancing cementitious matrices due to its ability to be strategically designed and additively manufactured to optimize composite properties. To fully exploit the synergy between LR and cementitious matrix, a deep understanding of the reinforcing mechanisms is essential. In this study, five lattice designs with various configurations and sizes were examined through uniaxial tensile tests on dog-bone specimens. It was observed that geometric characteristics, including auxetic behavior, significantly influenced the mechanical properties of lattice structures. At the composite level, the flexural performance of lattice-reinforced cementitious composites (LRCC) was investigated through four-point bending tests. It was found that up to 23-fold enhancements in energy absorption capacity can be achieved with a low reinforcing ratio of 3.5 %. Acoustic emission tests and CT scanning provided valuable insights into the distinct reinforcing mechanisms between auxetic and non-auxetic lattice designs. Furthermore, Finite Element Method (FEM) simulations confirmed that auxetic LR effectively mitigated interfacial debonding.

Anisotropy in 3D-printed concrete structures has persistently raised concerns regarding structural integrity and safety. In this study, an architected 3D printing strategy, “stitching”, was proposed to mitigate anisotropy in 3D-printed Engineered Cementitious Composites (ECC). This approach integrates the direction-dependent tensile resistance of extruded ECC, the mechanical interlocking between three-dimensional layers, and a deliberately engineered interwoven interface system. As a result, the out-of-plane direction of the printed structure can be self-reinforced without external reinforcements. Four-point bending tests demonstrated that the “stitching” pattern induced multi-cracking and flexural-hardening behavior in the out-of-plane direction, boosting its energy dissipation to 343 % of the reference “parallel” printing and achieving 48.6 % of cast ECC. Additionally, micro-CT scanning and acoustic emission tests further validated the controlled crack propagation enabled by the engineered interface architecture. The proposed strategy has been proven to substantially alleviate anisotropy and enhance structural integrity.

Auxetic cementitious cellular composites (ACCCs) exhibit hinge-type recoverable deformation during auxetic behavior phase, a rare pseudo-elastic property in cementitious materials. However, their low load-bearing capacity during this phase restricts their use in high-load applications. This study developed ACCCs using strain-hardening cementitious composites (SHCCs) with short (SHCC-SS) and long (SHCC-LS) softening tails, fabricated by additive manufacturing-assisted casting. Uniaxial compression tests employing Digital Image Correlation (DIC) evaluated their compressive behavior, peak strength, Poisson's ratio variation, and energy dissipation. Cyclic tests after pre-compression assessed their recoverable deformation resilience, with fiber bridging at joint cracks examined using digital optical microscope. Results were compared to a reference using fiber-reinforced cementitious materials with strain softening (SS). Compared to the reference (SS), ACCCs using SHCC mixtures exhibit superior load-bearing capacity and stable auxetic behavior under compression. After self-contact, they maintain a negative Poisson's ratio up to a considerably high compressive strain, preventing splitting failure and preserving structural integrity. This is because incorporating SHCC enables greater joint rotation by promoting multiple cracks with strain hardening, which delays primary crack formation and reduces its opening. During cyclic tests, P1-shaped ACCCs with SHCC-LS and SHCC-SS enhance the elasticity modulus of recoverable deformation by 4.8 and 3.0 times, respectively, compared to SS. SHCC-LS outperforms SHCC-SS in compressive resilience due to its prolonged softening tail, which improves fiber bridging in primary cracks and increases rotational stiffness in hinge joints. SHCC mixtures with initial strain hardening and extended softening enable scalable design of advanced auxetic cementitious materials across various load levels.

This study develops a novel class of 3D-printed auxetic lattice reinforced foamed cementitious composites, aimed at overcoming the brittleness and low strength of conventional foamed cement while maintaining lightweight characteristic. Polymeric auxetic lattices (mechanical metamaterials with negative Poisson's ratio) were 3D printed and embedded in foamed cement matrix. Static and cyclic compression tests were conducted to evaluate load-bearing capacity, energy absorption, and failure mechanisms. X-ray computed tomography (CT) analysis was performed to examine interfacial behavior between the lattice and cement matrix. Results indicate that 3D auxetic lattices significantly enhance strength and ductility through multidirectional lateral confinement, where the energy absorption increased by up to 2.8 times compared to unreinforced foamed cement at a density of 550 kg/m³. Specifically, the 3D auxetic lattices reinforced composites showed pronounced resilience under cyclic loading, exhibiting gradual and ductile damage evolution while sustaining performance beyond 700 cycles. In comparison, 2D auxetic lattices which provide negative Poisson's ratio only in-plane are less effective in reinforcing foamed cement matrix. Additionally, although non-auxetic lattice increased load-carrying capacity to some degree, the corresponding composites structure showed localized shear failure and premature structural degradation under cyclic loading. Overall, the active reinforcement effect of auxetic lattices enables the development of advanced foamed cementitious composites for impact mitigation, blast protection, and buoyant components requiring energy absorption and repeated-load resilience.

A novel highly compressible auxetic cementitious composite (ACC) is developed in this work. Contrary to conventional cementitious materials, such as plain concrete and fiber reinforced concrete, the ACC shows strain-hardening behavior under uniaxial compression: the stress continuously increases with strain up to approximately 40 % strain. On one hand, in the early compression stage, the ACC exhibit highly recoverable deformability of 10 % strain under cyclic loading (20 times higher than the constituent cementitious material). In addition, the ACC shows fatigue damage until the stiffness/strength and energy dissipation plateau values are reached after 500 cycles. At 2.5 % strain amplitude, the plateau stiffness/strength is approximately 120 MPa/3 MPa, while these values are only 25 MPa/1.2 MPa at 5 % strain amplitude. In contrast, the energy dissipation plateau of the ACC is independent from the amplitude and remains at 0.05 J/cm3. On the other hand, due to the strain-hardening behavior, the ACC exhibits significantly improved energy dissipation capacity compared to both the conventional cementitious materials and the auxetic frame. This behavior is achieved by a tailored composite action: integrating cementitious mortar with 3D printed thermoplastic polyurethane (TPU) auxetic frame. A rotating-square auxetic mechanism was designed for the TPU frame for the ACC to achieve the tailored cracking behavior. The horizontal ACC cells enable large deformability by enlarging the crack width under the confinement of the auxetic frame, while the vertical cells work as stiffening phase to ensure load resistance. Owing to the outstanding mechanical properties, the ACC shows great potential to be applied in engineering practice where high compressive deformability is required, for instance yielding elements for squeezing tunnel linings.

This study investigates the mechanical properties of cementitious composites with 3D-printed auxetic lattices, featuring negative Poisson's ratios (auxetic behavior) in multiple directions. These lattices were fabricated using vat photopolymerization 3D printing, and three base materials with varying stiffness and deformation capacities were analyzed to determine their impact on the composites’ mechanical behavior. To unravel the reinforcing mechanisms of multidirectional auxetic lattices, which exhibit auxetic behavior in both planar and out-of-plane directions, X-ray computed tomography (X-ray CT) was utilized to analyze composite damage evolutions under different strain levels. The micro-CT characterization reveals that auxetic lattices more effectively constrain crack growth and dissipate energy by distributing stress evenly within the cement matrix. In contrast, due to lack of lateral confinement, the non-auxetic lattice reinforced composites primarily dissipate energy through extensive crack propagation and interfacial damage, leading to lower peak strength. When strain exceeding 5%, although the confinement from the auxetic behavior diminished with crack propagation, the lattice can still maintain the composite's structural integrity, resulting in 1.7 times higher densification energy than conventional cement-based materials. These findings provide valuable insights for designing auxetic lattice-reinforced cementitious composites with enhanced load-bearing capacity and improved dissipation capabilities.

Auxetic cementitious cellular composites (ACCCs) exhibit desirable mechanical properties (e.g., high fracture resistance and energy dissipation), due to their unique deformation characteristics. In this study, a new type of cementitious auxetic material, referred to as peanut shaped ACCC, has been designed and subsequently architected using additive manufacturing techniques. Two peanut shaped ACCCs specimens with different pseudo-minor axes have been tested under uniaxial compression with Digital Image Correlation (DIC) to assess their compressive behavior, peak strength, Poisson's ratio, and energy dissipation capacity. Additionally, cyclic tests were conducted to investigate their compressive resilience properties, further elucidated through microstructural analysis using a digital optical microscope. The mechanical test results were also compared with those of previously developed elliptical-shaped ACCCs. Furthermore, a numerical model was used to simulate the mechanical behavior of peanut shaped ACCCs under uniaxial compression, and showed a good agreement with the experimental data. The auxetic behavior observed in peanut shaped ACCCs arises from the rotation of sections facilitated by fiber bridging at the ligament of adjacent holes within the cementitious unit cell. In comparison to elliptical-shaped ACCCs, peanut shaped ACCCs can exhibit a slightly more negative Poisson's ratio and mitigate stress concentration. The reduction of stress concentration enables peanut shaped ACCCs to dissipate substantial energy, showcasing enhanced ductility and toughness. In cyclic tests, peanut shaped ACCCs exhibit superior recoverable deformation elasticity, attributed to robust fiber bridging capacity. The exceptional mechanical properties exhibited by peanut shaped ACCCs offer a scalable solution for developing energy-absorbent and multifunctional cementitious materials for smart infrastructure.

Cementitious materials exposed to marine and saline environments are commonly threatened by a combined attack of sulfate and chloride ions. This study developed a numerical framework to investigate two combined coupling mechanisms of 1) coupled solid-liquid chemical reactions for competitive chloride-sulfate attack and 2) electrostatic multi-ion coupling effect on reactive-transport mechanisms. Various chemical reactions including sulfate attack with anhydrous calcium aluminates, secondary precipitation of expansive minerals, competitive binding, and calcium leaching have been quantified. The electrostatic potential caused by multi-ions coupling was solved according to constitutive electrochemical laws. After model validation, the chemical coupling mechanisms for solid-liquid reactions during competitive chloride-sulfate binding were investigated. On this foundation, the influence of electrostatic multi-ionic coupling effects on ionic transport and its interaction with chemical coupling were disclosed. It was found that neglecting multi-ions coupling effect would result in an underestimated chemical coupling strength in competitive chloride-sulfate binding.

Understanding the transport mechanisms within unsaturated porous media is essential to the durability problems associated with cement-based materials. However, the involvement of multi-ions electrochemical coupling effect, especially under unsaturated condition makes the transport mechanisms even more complex. In this study, the moisture and multi-ionic transport in unsaturated concrete have been modeled in three-dimensional cases. The contribution from both water vapor and liquid has been considered in moisture transport. By adopting the constitutive electrochemical law, the electrostatic potential induced by inherent charge imbalance was calculated. With parameter calibration, the numerical results agreed well with the experimental data, proving the validity of the presented model. Results from a parametric analysis showed that neglecting multi-ions coupling effect will lead to an underestimated chloride concentration, and saturated degree has an obvious impact on the coupling strength among different ions. In addition, the existence of coarse aggregates will not only block mass transport but also make the discrepancies between two-dimensional model and three-dimensional model results more obvious. Other findings which have not been reported in existing studies are also highlighted.