This study investigates the influence of the deformability and fracture energy of the constituent material on the compressive response of auxetic cellular composites, using the finite element method (FEM) in ABAQUS/Explicit (version 2019). Four constitutive models were implemented: elastic-brittle, ideal elastic-plastic, strain-hardening, and strain-softening. The unit cell model was validated numerically against a larger 4 × 4 cellular structure and experimentally using strain-hardening cementitious composites with various deformability. Results show that auxetic behavior is unattainable with elastic-brittle constituent materials. For ideal elastic-plastic and strain-hardening materials, increasing the deformability and/or fracture energy leads to a larger critical strain, defined as the strain at which Poisson's ratio recovers from negative to zero under compression. Conversely, strain-softening materials exhibit the opposite trend. For structures comprising three ductile constituents, both load-bearing capacity and energy absorption performance improve with enhanced material properties, most notably for the strain-hardening material. However, a key finding is that increasing the deformability or fracture energy of the constituent material causes a significant reduction in the ratio of energy absorption of the structure to that of its constituent material. This indicates that merely enhancing the deformability and fracture energy of the constituent material does not guarantee improved energy absorption of cellular composites, demonstrating that optimal design of cellular composites requires a synergistic balance between the material and structure, rather than solely maximizing material properties. These insights provide critical guidance for designing high-performance auxetic cellular composites.

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.

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.

The extensive use of Ordinary Portland cement (OPC) in foamed lightweight concrete (FLC) contributes significantly to its carbon footprint. Concurrently, the disposal of industrial by-products carbide residue slag (CRS) and ground granulated blast furnace slag (GGBS) poses challenges. This study developed a sustainable foamed lightweight concrete system employing CRS-activated GGBS as a complete OPC substitute to address both engineering performance and environmental concerns. An optimal CRS/GGBS ratio (10/90) was determined for achieving the maximum compressive strength in the binder system. Compared to OPC, the CRS/GGBS binder exhibits remarkably low heat of hydration, enabling safer large-volume placements and effectively mitigating the risk of early-age thermal cracking. The prepared CRS/GGBS foamed concrete has much higher compressive strength than those made with cement due to refined air void structure with increased sphericity and improved flexural strength of the solid matrix. The life cycle assessment demonstrated that CRS/GGBS foamed concrete has the ability to decrease carbon emissions by as much as 80 % when compared to cement foamed concrete. This work establishes CRS/GGBS as a technically viable and environmentally superior binder for foamed lightweight concrete, offering enhanced compressive strength, lower thermal cracking risk, and a reduced carbon footprint compared to conventional cement systems in civil engineering.

A compounded system of fly ash (FA) and carbide slag (CS) was proposed for CO₂ mineralization using the aqueous approach to prepare supplementary cementitious material. Influence of CS dosage on the morphology, particle size distribution, and chemical phases of the carbonation products were characterized. It is found that the mineralization products (calcite) cover on the surface of FA leading to a remarkable synergistic effect in which the CO₂ uptake is improved by about 50%. Furthermore, FA with calcite attached effectively mitigates the set retardation in OPC/FA blends by about 30% and improved the 3- and 28-day compressive strengths by 37.2% and 24.3% respectively due to combined physical and chemical effects. The results indicate that a high-volume cement replacement can be achieved using the carbonated FA produced by the proposed synergy CO₂ mineralization.

This study investigates the size effect on the compressive strength of foamed concrete at the mesoscale level combining X-ray computed tomography (X-CT) and a discrete lattice model. Image segmentation techniques and X-CT were employed to obtain virtual specimens comprising hydrated cement paste and air voids. The lineal-path function and pore size distribution was used to characterise the air void structure. A two-dimensional lattice fracture model of foamed concrete considering different wet densities was established. The model was verified experimentally at a wet density of 700 kg/m³ and then used to predict the strengths of specimens with wet densities of 600 and 800 kg/m³. Square and rectangular specimens (slenderness ratio = 2) with widths of 10, 20, 40, 70.7, and 100 mm were investigated. Results show that the air void structure significantly influences the observed size effect on the compressive strength in the investigated size range. A random forest regressor was used to predict the compressive strength of the foamed concrete; the regressor yielded satisfactory results. Finally, existing analytical size effect models were used to fit the simulated strength. Although good fitting was achieved, special attention should be given to the applicable range and physical meaning of fitted empirical parameters.

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.

This paper presents a research on the chloride penetration behavior of engineered cementitious composites (ECC) under sustained flexural loads. Three load levels, i.e. 30 %, 60 % and 75 % of the ultimate flexural load were used. Chloride diffusion depth and concentration profile were measured 30, 60 and 150 days after the specimen was exposed to NaCl solution and compared with pre-loaded specimens. Influence of the sustained local bending stress and microcracks were investigated. It shows that under sustained loads, the relationship between the surface chloride content and maximum normal tensile stress can be described using an exponential equation. A binary model was developed to explain the correlation among the chloride ion diffusion coefficient, maximum normal tensile stress and exposure time. Changes of capillary pore structure and phase compositions were measured using mercury intrusion porosimeter and X-ray diffraction, respectively. Unlike mortar, the fiber bridging of ECC helps with limiting crack width and thus the diffusion process, and the measured results were used to explain the observed penetration behavior of ECC. It is believed that the current study provides theoretical foundation for the durable design of the ECC/concrete composite structure.

White mud is a solid waste from the papermaking industry, composed mainly of CaCO₃ and residual alkali metal ions (such as Na+, Mg²⁺). In the current study, the feasibility of using white mud as partial replacement of slag in alkali activated materials is explored. The fluidity, setting time, autogenous shrinkage, mechanical properties, hydration products and microstructure of alkali activated slag containing different amount of white mud are studied. The results show that adding white mud reduces the fluidity of freshly mixed paste, setting time and autogenous shrinkage. The ions released from the white mud participate in the polymerization reaction, accelerate the hydration reaction in the early stage, and promotes the precipitation of Mg-Al and the formation of hydrotalcite. However, excessive quantities of white mud (above 15% of the binder) leads to the reduction of compressive strength. As the content of white mud is enhanced, the Ca/(Si + Al) ratio of the gel increases and the degree of polymerization is reduced. It has been shown that white mud has potential reactivity and can partially replace slag to prepare new alkali activated materials.

The classically lattice model assumes the local elements behave elastic brittle, neglecting the ductility of the mortar matrix. This leads to the simulated load⁃displacement response more brittle than the realistic. To solve the aforementioned issue, a piece⁃wise approach was introduced to describe the elastic⁃plastic constitutive relation of lattice element. The fracture process and the load⁃displacement response were obtained through the sequentially⁃linear solution approach. The model was calibrated using the uniaxial tension and compression tests. It is found that the model can precisely simulate the fracture process and load⁃displacement response. Moreover, the model was used to model the size effect in uniaxial tension and the influence of the specimen’s slenderness and boundary confinement on the fracture behavior under compression. It offers a new theoretical method and approach for studying the fracture of concrete.

Carbide residue activated blast furnace slag is a relatively new kind of eco-friendly construction materials. This work addresses the design of foamed lightweight concrete as road embankment material using such material. A statistical mixture design approach was adopted to assess the influence of each ingredient as well as the interaction between these on the spreadability and compressive strength and thus allowing mixture design. The fitted models were validated using analysis of variance, residual analysis and confirmed by the experiments. Afterwards, the proposed models were used to optimize the mixture. The mixture with the highest compressive strength and the maximum content of carbide residue that allows the mixture to meet the required properties were obtained, respectively.