Herein, a three-dimensional numerical model based on computational fluid dynamics (CFD) for fresh concrete is developed to predict the slump and slump flow. Fresh concrete is considered as a non-Newtonian fluid, and its rheological behaviour is characterised by the Bingham and Herschel-Bulkley (H-B) models, respectively. Experiments are also conducted to validate the reliability and accuracy of this model. Through parametric investigations, the influence mechanisms of relevant factors on the flow characteristics of fresh concrete are analysed and discussed. The results show that the model predictions agree well with the experimental results. The predicted results obtained using the H-B rheological model are more accurate compared to the Bingham model, with average relative errors of 1.73 %, 2.03 % and 3.95 % for slump, slump flow and T₅₀₀, respectively. The flowability of fresh concrete is negatively correlated with power index, yield stress and consistency, while it is positively correlated with density. Grey relational analysis indicates that density has the greatest effect on the results of slump and slump flow, followed by yield stress and consistency, and finally the power index. The CFD-based numerical model presented in this study provides an important approach for better understanding the flow behaviour of fresh concrete from a rheological perspective.

This paper aims to improve the activity of high-calcium fly ash (FA) by using a wet carbonation treatment process. The results indicated that carbonation products, i.e. calcite, were attached to the surface of FA, which accelerated cement hydration primarily at the early stage. Significant improvement of early age strength and a decrease in setting time were therefore found in blended cement. Additionally, carbonation significantly reduced the amount of free calcium oxide (f-CaO) in FA, increasing its volume stability. Krstulovic-Dabic model was used to simulate the hydration process of blended paste, and the distribution of pore sizes and hydration products were also measured. Together with the filler effect of nano-sized calcite, the formation of carboaluminate phases refined the pore structure of blended paste. Furthermore, the amounts and mechanical properties of outer hydration products in blended paste increased.

The microstructure of cement paste determines the overall performance of concrete and therefore obtaining the microstructure is an essential step in concrete studies. Traditional methods to obtain the microstructure, such as scanning electron microscopy (SEM) and X-ray computed tomography (XCT), are time-consuming and expensive. Herein we propose using Denoising Diffusion Probabilistic Models (DDPM) to synthesize realistic microstructures of cement paste. A DDPM with a U-Net architecture is employed to generate high-fidelity microstructure images that closely resemble those derived from SEM. The synthesized images are subjected to comprehensive image analysis, phase segmentation, and micromechanical analysis to validate their accuracy. Findings demonstrate that DDPM-generated microstructures not only visually match the original microstructures but also exhibit similar greyscale statistics, phase assemblage, phase connectivity, and micromechanical properties. This approach offers a cost-effective and efficient alternative for generating microstructure data, facilitating advanced multiscale computational studies of cement paste properties.

When serving in the marine environment, reinforced concrete structures are prone to be attacked by chloride ingress, which generally co-occurs with varying humidity and temperature changes. Therefore, considering the interaction between moisture transport and heat transfer, and their individual and coupling effects on chloride transport, this paper presents a novel numerical modelling framework for chloride penetration in concrete under different environmental conditions. In this framework, a novel thermal conductivity model and temperature-depended chloride binding isotherms are also developed, considering the heterogeneous characteristics of concrete. The proposed model is validated against a series of experimental data. By assuming the cyclic humidity and temperature boundary conditions as trigonometric type, this study further discusses the effect of average value, amplitude value and period length of cyclic environmental changes on the chloride transport in concrete. The results indicate that variation in humidity and temperature averages can alter the peak values of chloride content but have less effect on the chloride penetration depth. However, the increased humidity amplitude could significantly promote both the peaks and the penetration depths due to intensive chloride convection caused by moisture transport. This paper is supposed to provide a better understanding of chloride penetration in concrete under a realistic engineering environment.

Circulating fluidized bed fly ash (CFBFA) is a by-product from the combustion in circulating fluidized bed boiler in power plants. Herein, to resourcefully utilize CFBFA and reduce cement consumption, the CFBFA was ground (GCFBFA) and used to prepare low-carbon lightweight foamed concrete (LFC) for subgrade filling. The effect of GCFBFA substitution ratio on the blended cement binder and LFC was investigated. It was found that incorporation of 30 wt% GCFBFA stimulated cement hydration and produced more hydration products including C-S-H and AFt, thus enhancing the performance of binder. For LFC, GCFBFA improved the stability of fresh LFC slurry and the air-void structure by increasing the rheological properties of binder, thus improving the mechanical properties and durability including water stability and freeze-thaw resistance. The extension of setting time and reduction in hydration heat due to GCFBFA can be beneficial for transportation and massive construction. For subgrade filling, the GCFBFA content is limited to 50 wt% for LFC with wet density of 600 kg/m3 (D600) and up to 70 wt% for D700 and D800. Life cycle assessment (LCA) showed that a reduction of 52.3% in global warming potential and 43.2% in total cumulative energy consumption for the production of LFC was achieved when GCFBFA replaced 70% of cement.

3D printing is becoming increasingly popular in the construction sector. 3D printing offers the potential to reduce costs, construction time and construction waste. However, due to its high cement content, 3D printable concrete more expensive to produce. The article includes a brief literature survey on the possibility of using cement and aggregate substitutes in concrete mixtures and their impact on fresh composite properties and identifies a research gap. Herein, we propose the use of waste copper slag as a replacement for cement in 3D printable concrete. We examine the effect of replacing cement with copper slag at 5 and 10% on fresh properties of cementitious mortar. The results show that copper slag improves the workability of the mixture and lowers the design yield strength up to 44%, thereby facilitating printing. Even 30% higher fresh compressive strengths were also obtained, which suggest that the buildability of mortars containing copper slag will be improved.

Portland cement paste has a highly heterogenous evolving microstructure that complicates the development of stronger and greener cementitious materials. Microstructure is the fundamental input of multiscale studies on material behaviors. Herein, we propose a conditional generative AI framework for synthesizing high-fidelity 3D microstructures of hydrating cement paste (1–28 days) with varying water-to-cement ratios and Blaine fineness values. A latent diffusion transformer, operating within a compact two-stage latent space derived via a vector quantized variational autoencoder, efficiently captures and reproduces experimentally measured microstructural patterns. Statistical analyses confirm strong consistency in grey value distributions, micromechanical properties, hydration phase evolution, and particle size distributions, with only minor boundary-related discrepancies. Validation using a pretrained classifier further corroborates the fidelity of generated microstructures. This approach provides a robust tool for realistic cement paste microstructure generation, supporting multiscale modeling and advancing the design of sustainable cementitious materials.

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.

This paper aims at enhancing tensile properties of strain-hardening alkali-activated composite (SHAAC) by using a flow-induced casting approach. Ca(OH)₂-activated ground granulated blast-furnace slag (GGBS) was used as binder material and viscosity modifying admixture (VMA) was applied to adjust the rheology. Combined X-ray computed tomography (X-CT) scanning and image analysis were proposed to obtain the spatial distribution of polyvinyl alcohol (PVA) fibers in hardened SHAAC prepared with various VMA dosages using different (i.e. conventional and flow-induced) casting approaches. The results revealed optimal rheological properties (yield stress of 192 Pa, plastic viscosity of 17.6 Pa·s) of paste for fiber distribution and alignment. The SHAAC with fiber distribution and orientation factors of 0.91 and 0.83 was prepared using the flow-induced casting approach with a WMA dosage of 1.0 %. Its ultimate tensile stress and tensile strain capacity reached 6.1 MPa and 5.5 %, respectively, which was 37 % and 36 %, more than the conventionally cast SHAAC. In the end, an empirical equation for ultimate tensile strength and strain capacity prediction with high determination coefficient was proposed based on fiber distribution, orientation, and porosity.

Auxetic cementitious cellular composites (ACCCs) possess advantageous mechanical properties in static tests, such as high fracture resistance and efficient energy dissipation. However, little attention has been given to understanding the impact resistance of ACCCs. In this study, two typical elliptical-shaped ACCC specimens, P25 and P50, were designed with major axis lengths increased by 25 % and 50 %, respectively, compared to the reference P0 with circular holes. The specimens were architected through additive manufacturing (AM) assisted casting, and subjected to low-velocity impacts from Schmidt hammer with a consistent initial impact energy. Their impact resistance was assessed based on impact responses, including rebound value, absorption energy, localized damage in the impact zone, crack propagation, and peak reaction force during impact. Besides single impact tests, multiple impact tests were conducted until specimens failed. Their impact results were compared with those of the reference (P0). A high-speed camera was further used for Digital Image Correlation (DIC) to analyze strain distribution of the specimens during the brief impact period. Furthermore, a numerical model considering strain rate effects was developed to simulate the impact behavior of ACCCs, demonstrating good agreement with experimental data. On this basis, a parametric analysis was performed to evaluate the effects of impact energy, relative density, specimen size, and RVE size on impact resistance. Both experimental and numerical results indicate that ACCCs demonstrate superior impact resistance compared to the reference (P0). They exhibit mitigated localized damage in the impact zone and increased contact stiffness. Moreover, ACCCs show greater endurance under multiple impacts and higher accumulated energy absorption until failure. This enhanced performance is attributed to auxetic behavior, which draws more material into the impact zone for dispersing energy and reducing localized damage, thereby maintaining overall structural integrity. Specifically, P50 exhibits higher impact resistance than P25 due to the enhanced auxetic behavior resulting from its greater aspect ratio. This creates a greater bending moment to enable more ligaments to dissipate energy through rotation-induced plastic deformation, thereby reducing localized damage. Considering the widespread availability of cementitious materials, this study highlights the potential of ACCCs for lightweight, high-performance protective structural materials for impact mitigation in infrastructure.

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.

Cement-based materials (CBMs) are multiscale composites whose macroscopic properties largely depend on their micro/nanoscale features. Micro and nanomechanical properties of CBMs are typically characterized using local techniques such as nanoindentation. Compared with nanoindentation, the nanoscratch allows for continuous measurement of CBMs to acquire more comprehensive and reliable nanomechanical information, which has provided a powerful tool for the characterization of CBMs at nanoscale. However, previous reviews on the application of nanoscratch in CBMs are relatively scarce and lack detailed guidance regarding specimen preparation methods and the testing procedure. This review presents a detailed discussion of specimen preparation procedures and requirements, measurements, and data analysis methods for nanoscratch testing applied to CBMs. Then, the nanomechanical properties derived from nanoscratch tests, including hardness, friction coefficient, elastic recovery ratio and fracture properties, have been summarized and discussed. Furthermore, the current uses of nanoscratch technique in CBMs, including characterization of nanoscale micorstructure, interface, tribological features, and fracture properties, are elaborated. On the nanoscale, the nanomechanical properties are employed for phase identification and to obtain the corresponding volume fractions. In addition, nanoscratch is widely utilized to identify the width, hardness, and fracture toughness of the interfacial transition zones, and to distinguish the interface between unreacted phases and hydration products. The combination of nanoscratch and other advanced techniques, such as atomic force microscopy, backscattered electron imaging, and acoustic emission to characterize the nanoscale micorstructures of CBMs is further discussed, which contributes to improving the accuracy of nanoscratch test results and broadens their applicability. In addition, some perspectives on testing methods, data analysis, and multifunctional applications of nanoindentation technology are proposed. This review aims to assist researchers in developing robust and reliable protocols for nanoscratch testing, thereby advancing the deeper understanding of the nanoscale features of CBMs.

The use of 3D printed polymers in the form of lattice reinforcement can enhance the mechanical properties of cementitious composites. Methods like Fused Deposition Modelling (FDM) 3D printing enable their creation, but this process has a large (negative) effect on their mechanical properties, with a large dependency on the printing direction. Continuing on our previous study concerned with modelling the anisotropic behaviour of 3D printed polymeric reinforcement, this work focuses on the reinforcement-matrix bond. Because of the layer-by-layer filament extrusion process of the 3D printing technique, the edges of FDM 3D printed polymers are typically composed of ellipses. Based on this, it is hypothesized that morphological effects as a result of the 3D printing technique enhance the bond between 3D printed reinforcement and cementitious matrix: The elliptic geometry potentially facilitates interlocking with the cementitious mortar, thereby possibly enhancing the bond behaviour in certain directions. To investigate the geometrical directional-dependent features at the edges of 3D printed polymers in more detail, micro-scale models are developed. Geometrical effects induced by different printing configurations are studied. The simulation results are verified through meso-scale pull-out experiments. The interlocking effects as a result of the 3D printing technique show to be significant seeing a bond strength increase of up to 56 % in one of the print configurations compared to the direction without any geometrical effects.

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.

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.

This study presents comprehensive numerical modeling methods for simulating early-age stress (EAS) relaxation in cementitious materials, based on the autogenous deformation (AD), elastic modulus, creep, and stress continuously tested by a mini temperature stress testing machine (Mini-TSTM) and a mini AD testing machine from a very early age (i.e., from a few hours to a week). Four methods for converting creep compliance to relaxation modulus were discussed in detail and used for the one-dimensional (1D) and three-dimensional (3D) simulation of stress evolution in the Mini-TSTM test. Furthermore, virtual creep and relaxation tests were conducted using an exponential algorithm with either the Kelvin or Maxwell chains to show their applicability in simulating the viscoelastic behavior of early-age cementitious materials. The results showed that the exponential algorithm with the Maxwell chain using an exponential conversion function from creep to relaxation obtains good prediction accuracy of EAS in 3D analysis. The numerical solutions of the Volterra integral of creep compliance can lead to a negative relaxation modulus, thus introducing stress calculation errors in both 1D and 3D analysis.

High-strength engineered cementitious composites (ECC) typically require higher cement content, which is negative from the sustainability point of view. To alleviate this problem, herein a low-cost and eco-friendly high-strength ECC (with a compressive strength of over 100 MPa) was developed, and diatomite was used to replace a small amount of cement. An appropriate amount of diatomite was found to improve the compressive strength, tensile strength and first cracking strength of ECC, but at the expense of part of the strain capacity (still all higher than 2.9%). Furthermore, the high pozzolanic activity and specific surface area of diatomite also increased the autogenous shrinkage, but reduced the drying shrinkage of ECC due to its internal curing effect. The incorporation of diatomite improved the pore structure of ECC, consumed more Ca(OH)_2, and enhanced the hydration degree of the mixture. In the end, the economic and environmental benefits of diatomite-modified ECC were also evaluated, and the cost, non-renewable energy demand, and global warming potential of ECC with 3% diatomite were reduced compared to plain ECC by 12.9, 15.1, and 13.3%, respectively. The developed high-strength ECC is therefore a low-cost and eco-friendly alternative to the traditional one.

Engineered cementitious composite (ECC) is widely employed in engineering due to its high toughness and ductility. The Interfacial Transition Zone (ITZ) between the fibers and the matrix plays a vital role in influencing the strength and durability of ECC. This study introduces a numerical method to simulate fiber pull-out behaviors, specifically the fiber debonding and slipping. A birth-death method is proposed to account for the mechanical transition from fiber debonding stage to slipping stage. The contributions of various phases in the ITZ are explicitly considered. Furthermore, nanoindentation tests and Backscattered Electron (BSE) imaging were conducted to determine the microstructures of ITZ and local mechanical properties of each phase within the ITZ. A series of fiber pullout experiments with polyvinyl alcohol (PVA) fibers were conducted to calibrate and validate the model. Subsequently, the validated model was employed to explore the influence of w/c ratios, fiber orientations and bonding properties on the interfacial behavior. The microstructure-informed model proposed herein effectively predicts fiber pull-out behavior, facilitating a thorough exploration of fracture mechanisms throughout the pull-out process, and serves as the basis for multiscale modeling of ECC.

The production of low-emission additive manufactured cementitious composites using functionalized rock powders offers promising mechanical properties and significantly reduces cement consumption. The effect of powder functionalization on the rheological properties of the mixture remains unclear, so this study investigated how mechanical and chemical functionalization of granite powder waste affects the viscoelastic properties of a cementitious mixture for additive manufacturing. Compression tests were used to track stress-strain changes over time, while Vane and slug tests measured yield stress in mixes with 20 % and 40 % cement replaced by natural (NGP), sieved (SGP), and carbonated granite powder (CGP). The results showed that all three powders (NGP, SGP, and CGP) increased yield stress compared to the reference mix, with CGP having the smallest effect. The functionalization of granite powder may enable the creation of desirable viscoelastic mixtures using sustainable materials. We observed that functionalizing granite powder (SGP and CGP) accelerated changes in the mixture rheological properties, with yield stress increasing by up to 33 %, while NGP showed minimal impact, similar to the reference mix. Differences between the Vane and Slug test results were also identified and their limitations described.

This paper presents a state-of-the-art review on the application of additive manufacturing (AM) in self-healing cementitious materials. AM has been utilized in self-healing cementitious materials in three ways: (1) concrete with 3D-printed capsules/vasculatures; (2) 3D concrete printing (3DCP) with fibers or supplementary cementitious materials (SCMs); and (3) a combination of (1) and (2). 3D-printed capsules/vascular systems are the most extensively investigated, which are capable of housing larger volumes of healing agents. However, due to the dimension restraints of printers, most of the printed vasculatures/capsules are in small scale, making them difficult for upscaling. Meanwhile, 3DCP shows great potential to lower the environmental footprint of concrete construction. Incorporation of fibers and SCMs helps improve the autogenous healing performance of 3DCP. Besides, 3D-printed concrete with hollow channels as the vasculature could further improve the autonomous healing and scalability of self-healing cementitious materials. Finally, possible directions for future research are discussed.