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.@en

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.@en

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.

@en

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.

@en

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.@en

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.

@en

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.

@en

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.

@en

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.

@en

Temperature Stress Testing Machine (TSTM) is a universal testing tool for many properties relevant to early-age cracking of cementitious materials. However, the complexity of TSTMs require heavy lab work and thus hinders a more thorough parametric study on a range of cementitious materials. This study presents the development and validation of a Mini-TSTM for efficiently testing the autogenous deformation (AD), viscoelastic properties, and their combined results, the early-age stress (EAS). The setup was validated through systematic tests of EAS, AD, elastic modulus, and creep. Besides, the heating/cooling capability of the setup was examined by tests of coefficient of thermal expansion by temperature cycles. The results of EAS correspond well to that of AD, which qualitatively validates the developed setup. To quantitatively validate the setup, a classical viscoelastic model was built, based on the scenario of a 1-D uniaxial restraint test, to predict the EAS results with the tested AD, elastic modulus, and creep of the same cementitious material as the input. The predicted EAS matched the testing results of Mini-TSTM with good accuracy in 6 different cases. The viscoelastic model also provided quantitative explanations for why variations in early AD do not influence the EAS results. The testing and modelling results together validate the developed Mini-TSTM setup as an efficient tool for studying early-age cracking of cementitious materials. At the end, the potential limitations of the Mini-TSTM are discussed and its applicability for concrete with aggregate size up to 22 mm is demonstrated.

@en

Cenospheres are low-density and hollow microspheres derived from coal-fired power plant fly ash waste. This study aims to prepare ultra-light-weight (<1000 kg/m³ wet density) concrete using fly ash cenospheres (FAC). To begin with, FAC's shell thickness and the water absorption and desorption were characterized. A mixing procedure was designed to avoid the segregation between the FAC and cement slurry. FAC can affect the rheological properties of fresh mixture over time through absorption and desorption of free water. The presented ultra-light-weight concrete has several advantages compared to the ones prepared using foaming methods. First, shrinkage is significantly reduced due to FAC's internal restraint and curing effects. Secondly, it has good mechanical performance, especially in bending and is more environmentally friendly due to use of less cement. X-ray computed tomography illustrates that FAC ultra-light-weight concrete has smaller pores of more uniform size compared with those prepared using foaming methods. X-Ray diffraction, thermal gravimetry-derivative thermal gravimetry, fourier-transform infrared spectroscopy and scanning electron microscopy are employed for the hydration products and microstructure characterization. Outcomes prove that FAC can combine well with the cement matrix, and react with calcium hydroxide to produce C-A-S-H through pozzolanic reaction.

@en

Self-healing concrete using encapsulated healing agent has shown great potential in enhancing concrete durability. However, the capsules are expensive to make and can lower the mechanical properties of concrete. In this study, a new type of manufactured aggregate that employs waste-derived fly ash cenosphere as a carrier of healing agent (SH-CS) was designed and produced. The effect of SH-CS incorporation on hydration, engineering properties and self-healing efficiency of cement mortar was systematically evaluated, with a special focus on self-healing mechanism through the analysis of the mineral composition of the healing product. The results indicate that the prepared SH-CS has good stability in and compatibility with cement mortar. The addition of SH-CS has small influence on the fresh properties of cement mortar and less negative effect on compressive strength at the hardened stage compared to the existing study. By replacing 3 wt.% of fine aggregate with SH-CS, up to 71% of the crack opening area of mortar specimens with a crack width of about 0.3 mm was self-healed after 28 days of water exposure. The self-healing behaviour of SH-CS led to a maximal 41% drop in water adsorption and contributed to the recovery of flexural strength. The healing products precipitated on the fracture surface were mainly composed of amorphous C-S-H and Calcite. It can be estimated that incorporating SH-CS in concrete would result in only a moderate (∼29%) rise in cost for C40 concrete.

@en

One particularly interesting class of mechanical metamaterials are those having a negative Poisson's ratio, which are referred to as ‘auxetics’. Because of their geometrical complexity, auxetic designs cannot always be easily created. However, Additive Manufacturing (AM) methods like material extrusion in 3D printing present the opportunity to construct auxetic structures. Nevertheless, extruded 3D printed material can be highly anisotropic. Before 3D printed auxetics manufactured through material extrusion can be used in engineering applications, it is important to generate powerful simulation tools that can reliably reproduce and foretell their mechanical characteristics irrespective of their form and intricacy. In view of this, the current work proposes printing path-dependent models based on an experimentally validated multi-scale modelling scheme using the Lattice Beam Model (LBM). This is done by first representing idealized microstructures of extruded 3D printed polymers through geometric models and simulating these on the material scale. The aim is to explicitly model the inter-layer and intra-layer bonds that exist in material extruded 3D printed parts by assigning experimentally obtained interface properties that significantly differ from the bulk material. On the auxetic structure scale, two planar auxetic designs are modelled using the determined material scale relationships as input: Re-Entrant (RE) and Rotating Square (RS). In terms of mechanical response, the experimentally and numerically obtained force displacement curves agree reasonably well: the stiffness of the modelled auxetic designs fit well with the experimentally measured ones while the LBM simulations generally provide a good estimation in strength. Finally, it has been shown on both the material and auxetic structure scales that incorporation of the interfacial bond strengths in simulations of extruded 3D printed polymers is important, because neglecting these results in significant overestimation of the strength.

@en

3D printed polymeric reinforcement has been found able to improve the ductility of cementitious materials. However, due to the hydrophobic nature of commonly used 3D printing polymers, the bonding strength between the 3D printed polymers and cementitious matrix is extremely weak, which potentially hinders the mechanical performance of the reinforced composites. This work aims to improve the bonding properties by applying surface modifications on the 3D printed reinforcement, and eventually enhance the mechanical performance of the reinforced cementitious composites. Three types of surface coatings ingredients: epoxy resin (EP), sand sprinkled epoxy (SA) and short steel fibers sprinkled epoxy (SF) were used. Pull-out experiments are performed to study the bonding properties of the 3D printed reinforcement with different coatings. Then, uniaxial tensile and four-point-bending experiments are used to investigate the mechanical performance of the reinforced cementitious composites. A lattice type numerical model is applied to simulate the pull-out and tensile tests. The pull-out experiments indicate that the SA and SF reinforcement achieved approximately two times higher bonding strength than the uncoated and EP reinforcement. The tensile and flexural results suggest that the cementitious composites with SA and SF reinforcement achieved significantly better ductility (manifested by strain-hardening and deflection-hardening behavior) than the composites with uncoated and EP reinforcement. The numerical simulation results highly agree with the experimental findings, and further confirmed that the improved reinforcement-mortar bonding strength is the determinative factor that enhanced the composites mechanical performance. The findings of this work suggest that the sand and steel fiber surface coatings can effectively enhance the ductility of cementitious composites reinforced by 3D printed polymers.@en

Vascular self-healing concrete (SHC) has great potential to mitigate the environmental impact of the construction industry by increasing the durability of structures. Designing concrete with high initial mechanical properties by searching a specific arrangement of vascular structure is of great importance. Herein, an automatic optimization method is proposed to arrange vascular configuration for minimizing the adverse influence of vascular system through a reinforcement learning (RL) approach. A case study is carried out to optimize a concrete beam with 3 pores (representing a vascular network) positioned in the beam midspan within a design space of 40 possibilities. The optimization is performed by the interaction between RL agent and Abaqus simulation environment with the change of target properties as a reward signal. The results illustrates that the RL approach is able to automatically enhance the vascular arrangement of SHC given the fact that the 3-pore structures that have the maximum target mechanical property (i.e., peak load or fracture energy) are accessed for all of the independent runs. The RL optimization method is capable of identifying the structure with high fracture energy in the new optimization task for 4-pore concrete structure.

@en

In the race to achieve global climate neutrality, carbon intensive industries like the clinker and cement industry are required to decarbonize rapidly. The environmental impacts related to potential transition pathways to low-carbon systems can be evaluated using prospective life cycle assessment (pLCA). This study conducts a pLCA for future global clinker production, integrating long-term transition pathways from the IMAGE integrated assessment model (IAM) to maintain global consistency. It systematically modifies the ecoinvent v3.9.1 database using the Python library premise to create future database versions representing future clinker production embedded in a future economy according to a 3.5°C-baseline, a 2°C-compliant and a 1.5°C-compliant scenario. Our study indicates that climate change impacts of clinker production may decrease from about 1.03 kg CO₂-eq/kg clinker in 2020 to 0.94 (3.5°C-baseline), 0.20 (2°C-compliant), and 0.16 (1.5°C-compliant) kg CO₂-eq/kg clinker in 2060 for the global average. This corresponds to a 10% (3.5°C-baseline), 81% (2°C-compliant) and 84% (1.5°C-compliant) decrease by 2060 compared to 2020. Under these scenarios, global clinker production alone would require 5%–11% of the remaining end-of-century carbon budget for the 2 °C and 1.5 °C-target, respectively. While the climate change impacts are substantially reduced, our study also indicates that the transition pathways shift the burden towards other impact categories, such as ionizing radiation, ozone depletion, material resources and land use. Developing IAM-compatible scenarios for more product groups helps to increase the coherence of pLCA studies. As this study is based on an IAM heavily reliant on carbon capture and storage and bioenergy, future research should explore the effects of different technology pathways and alternative mitigation strategies.

@en

Early-age cracking risk induced by autogenous deformation is high for cementitious materials of low water-binder ratios. The autogenous deformation, viscoelastic properties, and stress evolution are three important factors for understanding and quantifying the early-age cracking risk. This paper systematically reviewed the experimental and modelling techniques of the three factors. It is found that the Temperature Stress Testing Machine is a unified experimental method for all these three factors, with a strain-controlled mode for stress evolution, hourly-repeated loading scheme for viscoelastic properties, and free condition for autogenous deformation. Such unified method provides basis for developing various models. By coupling a hydration model for volume fractions of hydrates, a homogenization model for upscaling of viscoelastic properties, and capillary pressure theory for self-desiccation shrinkage, a unified model directly mapping the mix design to the early-age stress can be constructed, which can help optimize the mix design to reduce the early-age cracking risk.

@en

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.@en

3D printed concrete (3DPC) creates opportunities, including a reduction in construction waste and time and increased design freedom. However, because of the differences in the construction technique compared to traditional concrete casting, the structures also perform differently; namely, the micro- and meso-structure and durability are shown to be different. For the 3DP technology to find its way to the market, one needs to be aware of these differences and needs to know how to quantify the above-mentioned properties, as differences in the testing methodologies impose themselves when characterizing printed instead of cast concrete. In this paper, we elaborate on the test methods to investigate the micro- and meso-structure and the durability of 3DPC. We start with a discussion on the micro- and meso-structure of the 3D printed concrete and how it is different from conventional mold-cast concrete. An in-depth discussion of the test methods to assess the durability of 3D printed concrete is outlined. Reported findings related to the two aforementioned properties are discussed. In addition, we report on the technologies proposed to improve the durability performance of 3DPC, and we highlight the remaining challenges and opportunities related to 3DPC.@en

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.

@en