Printability of 3D printed cementitious materials depends on the pumpability, extrudability and buildability of fresh cementitious pastes, where static yield stress (SYS), dynamic yield stress (DYS) and thixotropy are the most commonly characterized parameters. However, researchers hold convergent opinions in DYS testing while no widely accepted protocols for SYS and thixotropy exist. In this study, a specific set of white Portland cement mixtures incorporating various silica fume (SF) contents were used to prepare cementitious pastes. Three different protocols were employed to measure SYS and thixotropy of 3D printed white cementitious materials (3DPWCMs), aiming to identify their relationships with the structural deformation rate of printed components. Specifically, Kolmogorov-Arnold Network (KAN) model was applied to explore the relevance between rheological parameters and structural deformation rate, achieving higher predictive accuracy than simple linear regression. Furthermore, published datasets from other cementitious composites were also collected to validate the outputs from the KAN model. Notably, within the tested systems, creep-based protocols appeared to be the most reliable indicators in predicting the structural deformation rate, outperforming both the small amplitude oscillatory shearing and shear-rate-controlled protocols for SYS, as well as the thixotropic loop area and viscosity recovery degree for thixotropy. Our work provides insights into the suitability of various rheological protocols for 3D printed cementitious materials and highlights the potential use of the KAN model in guiding the design and quality control of printable cementitious materials.

Accelerators that can significantly shorten the hardening time of sprayed cementitious composites are indispensable admixtures. However, traditional accelerators inevitably reduce the durability of sprayed cementitious composites and damage the environment because certain detrimental elements are used as primary components of accelerators, including alkali, fluorine, and chlorine. A novel polymeric aluminum-based liquid accelerator (PAA) with alkali-free, chlorine-free, and fluorine-free properties for cement-based materials was synthesized by an organic-inorganic hybrid method. The initial setting time of cement paste containing 5 wt % PAA was only 4 min, and the hardening interval between plasticity and solid phase can be shortened to 30 s. Meanwhile, the compressive strength and flexural strength of cementitious composites at 1, 7, and 28 days were 129.43, 112.03, 104.16, 108.43, 147.02, and 107.45% of the reference group, reaching 11.48, 32.44, 45.24, 3.22, 6.73, and 7.24 MPa, respectively. The transformation of aluminum sulfate with highly symmetric hexacoordinated aluminum into Keggin-type Al13 polymers characterized by tetracoordinated aluminum and aluminum-oxygen bonds is the classic feature of PAA. The PAA, characterized by high positive charge and abundant hydroxyl groups, can work as nucleation sites to enrich Ca2+ and SO42-. This significantly accelerates the nucleation of AFt crystals, thereby facilitating the rapid setting and enhancing the mechanical performance of the cementitious composites.

Carbon sequestration of cement-based composites is an essential pathway towards the strategic goal of achieving carbon neutrality. However, the efficiency of cement-based composites to sequester carbon dioxide (CO2) is limited. Inspired by legume structure, a sandwich-structured graphene oxide embedded with In(OH)3 (SGOI) was synthesized to simultaneously enhance the CO2 sequestration capacity, hydration kinetics, and mechanical performances of cement-based composites. The effect of SGOI content on the CO2 sequestration capacity, hydration kinetics, and mechanical performances of cement-based composites was evaluated. The results show that the CO2 sequestration, compressive strength, flexural strength, and eco-mechanical index of the hardened cement paste containing 0.03 wt% SGOI were achieved 52.55 g/kg, 105.1 MPa, 13.9 MPa, and 0.75 kgCO2/MPa, representing enhancements of 255.07 %, 32.70 %, 34.95 %, and 167.86 % compared to those of cement paste without SGOI, respectively. Meanwhile, the hydration reaction rate and hydration degree of cement at each stage were improved. The enhancement of these parameters is derived from the structural characteristics of SGOI, including the specific surface area (30.52 m2/g), interlayer distance (14.85 nm), and roughness (14.10 nm). One ton of hardened cement paste containing 0.03 wt% SGOI can sequestrate at least 31.09 kg of CO2 within 28 days, highlighting its significant potential for promoting CO2 neutrality.

Cracking induced by shrinkage, especially drying shrinkage, has become the critical barrier to improving the durability of cement-based materials. Aluminum sulfate reacts with calcium hydroxide, a product of cement hydration, to form expansive needle-like ettringite. This reaction increases the tensile strength of the cement-based materials, compensates for drying shrinkage, reduces the cracking index and thereby significantly enhances the durability of cement-based materials. In this study, aluminum sulfate was used as a shrinkage-reducing admixture in cement mortar to investigate its effects on the crack resistance and durability of mortar. Experimental results show that the optimal aluminum sulfate dosage of 0.2 wt.% significantly reduces 28-day drying shrinkage by 57%, increases splitting tensile strength by 26%, and decreases cracking rate by 68%. The dual mechanisms of chemical shrinkage mitigation and controlled ettringite expansion synergistically enhance impermeability and freeze-thaw resistance. The maximum impermeability pressure can be elevated to 1.2 MPa. After 50 freeze-thaw cycles, the mortar exhibits significantly lower strength and mass losses of 30% and 1%, respectively, compared to control values. In conclusion, the present work identifies aluminum sulfate as a multifunctional additive for creating high-performance cementitious composites with enhanced crack resistance.

Polymer cement-based coatings (PCC) have great potential in protecting underground structures, while their flame -retardancy is limited by the flammability of the polymer components. Developing multifunctional inorganic fillers that can enhance both mechanical properties and flame retardancy is crucial for improving the safety and durability of the coatings. In this study, an ettringite (AFt) modified by amphiphilic group and aluminum hydroxide (AH) was subjected to surface functionalization treatment and then incorporated into the PCC to enhance the overall performance of the material. The tensile strength and bond strength of the coatings modified by amphiphilic group with AFt were increased by 27.7% and 22.4%, respectively. Meanwhile, the flame burn time, flameless burn time, and carbonization length were reduced by 89.1%, 80.6%, and 90.2%, respectively, and the limiting oxygen index (LOI) increased by 28.9%. The amphiphilic groups act as molecular bridges that couple the inorganic modified AFt with the organic VAE phase, thereby strengthening the organic-inorganic interface and promoting a more integrated polymer-cement network. Meanwhile, the well-dispersed inorganic phases provide endothermic dehydration and a protective residue during heating, jointly improving the mechanical reliability and fire safety of the PCC.

Although recycled fine aggregate (RFA) derived from construction waste offer an eco-friendly alternative to natural aggregate resources in concrete, their high chloride ions (Cl-) permeability harms the durability of concrete structures, particularly in marine field. In this study, a layered double hydroxides@colloidal nanosilica (LDHs@CNS) composite was synthesized to enhance Cl-adsorption in simulated marine concrete solutions (SMCSs), aiming to improve mechanical strength and durability of RFA marine concrete. The results showed that well-dispersed CNS effectively inhibited LDHs layer stacking via electrostatic repulsion and spatial steric hindrance, greatly improving Cl-adsorption in SMCSs. Thus, the LDHs@CNS showed excellent Cl-adsorption performance (up to 53.3 mg/g), demonstrating pH-dependent behavior with an inverse correlation. Optimal adsorption conditions of LDHs@CNS in SMCSs were identified at artificial seawater dilution ratios of 0, W/C ratios of 2.0, and hydration time of 1.5-h. Besides, compared to the control, adding 0.8 wt% LDHs@CNS enhanced RFA concrete performance, increasing flexural strength by 23.1 % (12.15 MPa), compressive strength by 15.2 % (94.5 MPa), and Cl-penetration resistance by 28.8 % (2.74 x10-12 m2/s). This study demonstrates an effective strategy to enhance Cl-adsorption, strength, and penetration resistance in RFA marine concrete through LDHs@CNS incorporation, which operates via three mechanisms: CNS-induced LDHs morphological control, secondary hydration, and micro-nano filling. This multifunctional approach resolves the dual challenges of low strength and poor durability, enabling high corrosion resistance for marine use.

The inevitable volume shrinkage of concrete during the hardening process can lead to the formation of cracks. The existence of cracks can significantly reduce the mechanical properties and durability of concrete. A novel polycarboxylate superplasticizer (NPM) with crack resistance was designed to improve the crack resistance of cement-based materials by regulating the molecular structure of polycarboxylate superplasticizers. The structure, molecular weight and reaction degree of NPM were precisely determined. The effect of NPM on the mechanical performance of cement-based materials has been comprehensively analyzed. The results revealed that the NPM can reduce the peak heat release of cement hydration and increase the cumulative heat of cement hydration. The autogenous shrinkage, drying shrinkage, cracking index and harmful pores of the sample were decreased by 87.0 %, 48.83 %, 51.80 %, and 27.21 %, respectively. The improved crack resistance can be attributed to the introduction of amphiphilic groups, which effectively reduce surface tension and capillary stress within the pore solution, thereby mitigating the shrinkage and cracking behaviour of the cement-based materials.

Early particle evolution including particle size distribution, specific surface area and zeta potential, critically regulates the rheological properties of cement by governing interparticle interaction forces. Existing researches focuse on the influence of FA incorporation on rheological and mechanical properties. This study investigated FA-induced particle evolution and its relationship with rheological properties. FA triggered rapid particle agglomeration within 30 min (increasing median diameter by 366.5 % at 15 % FA compared to the control group), concurrently reducing specific surface area and redistributing surface charge through accelerated hydration product nucleation. This particle restructuring enhanced interparticle attraction, substantially elevating static yield stress from 559.19 Pa to 2998.36 Pa, and increasing thixotropic area to 3.13 x 104 Pa/s at 15 % FA content. The transition of Lissajous-Bowditch curve from elliptical to linear profile confirmed the enhancement of viscoelasticity. Furthermore, FA promoted K-struvite crystallization and M-S-H gel formation, while FA-released Al3+ generated AlPO4 as a distinct crystalline phase through independent hydration reaction. These findings expand the understanding of driving forces for the early rheological properties of 3D-printed MSPPC and provide an effective reference for regulating the rheological properties through the basic parameters of admixtures.

Retarders are indispensable admixtures for ensuring sufficient printability time of 3D printing gypsum-based materials. However, a well-established fact related to high retarder content that excessive retarder content can reduce the mechanical properties of gypsum pastes. Therefore, the crucial strategy for expanding the application of 3D printing gypsum-based materials is to achieve efficient retarder at ultralow content. This study systematically analyzed the mechanisms of sodium citrate, sodium tripolyphosphate, and the plant protein retarder on gypsum-based 3D printing materials at ultralow content by workability, mechanical properties, and microstructure test. The results demonstrated that the plant protein retarder exhibited optimal performance in enhancing the workability and mechanical properties of the paste. When the content of this retarder was 0.4 parts per thousand, the initial setting time of the gypsum paste was extended from 7 min to 56 min, while increasing the 7-day compressive and flexural strengths of the gypsum specimens by 81.63 % and 47.19 %, respectively. Mechanistically, the three retarders differed in gypsum particle adsorption due to distinct anionic structures, regulating setting time differently. These retarders complexed with Ca2 + to form insoluble compounds, reducing hemihydrate gypsum dissolution and transforming dihydrate gypsum crystals from elongated prisms to plate-like structures. Enhanced crystal interlocking reduced hardened paste porosity, ultimately improving mechanical strength.

The uncontrollable setting time of white Ordinary Portland Cement restricts its application in 3D printed architectural decoration field. This study systematically investigated the effect of aluminum sulfate (AS) on the early-age rheological properties, hydration kinetics and structural build-up of 3D printed white cementitious materials (3DPWCMs). AS enhanced the dynamic, static yield stress (SYS) and thixotropy as well as structural stability of 3DPWCMs, among which 2 % was considered as the optimized content due to moderate yield stress and reduced structure deformation. This improvement is attributed to accelerated formation of C-S-H gel and ettringite, driven by faster hydration of C3A and C3S with AS. In addition, a strong correlation was observed between bound water content and rheological properties evolution of 3DPWCMs with 2 % AS over 50 min. Elastic modulus was found to be more reliable for predicting the printability of 3DPWCMs with AS. These findings offer mechanistic insights into the interaction between hydration and rheology during the critical early stage of 3D printing.

The application of graphene oxide (GO) in cementitious composites is always limited by the aggregation of GO caused by the 'calcium bridge' structure composed of Ca2 + and GO. Inspired by the structure of beanpod, an insitu structural regulation strategy was proposed for the construction of In(OH)3 nanoparticles within GO (IG) to suppress the aggregation of GO. The Density Functional Theory (DFT) calculations verified the mechanism of in situ spontaneous construction between In3+ and GO. The interlayer vertical distance and dispersion of the IG samples were improved by 1041.2 % and 172.32 % compared to those of GO without in-situ structural regulation, respectively. Meanwhile, the flexural and compressive strength of cement pastes containing IG (IGC) were enhanced by 25.26 % and 17.20 %, respectively. The beanpod-inspired in-situ structural regulation strategy provides innovative design concepts to address the aggregation of GO and potentially facilitate the engineering applications of cementitious composites containing GO.

Despite proven improvements in chloride-ion (Cl ) adsorption capacity and corrosion inhibition in cementitious materials through layered double hydroxides (LDHs)-based composites, the long-term performance remains unclear. This study investigated the time-dependent Cl adsorption behavior of multiple LDHs-based composites in sulphate-resistant Portland cement (SRPC) mortar with different protective layer thickness (T-50 and T-35), aiming to evaluate the influencing factors of the adsorption kinetics. The results showed that Cl adsorption in all specimens increased with soaking time but remained below the theoretical maximum even after 120-day soaking. Among the tested adsorbents, mortars with LDHs-strongly basic anion exchange resin (LDHs-SBAER, 1.424 mg/g after 120-day, T-35) and layered double oxide (LDO, 1.449 mg/g after 120-day, T-35) showed superior Cl adsorption and potential for long-term performance. Besides,the Cl adsorption kinetics conformed to the ExpAssoc kinetic model (R2 >= 0.99), demonstrating a distinct biphasic behavior: an initial rapid adsorption phase followed by a slower equilibrium stage. Interestingly, the time-dependent Cl adsorption revealed strong dependence on the two key parameters of adsorbent types and protective layer thickness.

Developing hydrophobic agents that minimize the strength loss of bulk hydrophobic cementitious materials (BHCM) remains a formidable challenge. Substances such as siloxanes can hinder cement mineral hydration and prevent the formation of an initial network structure during the early hydration stages. In this study, a novel hydrophobic emulsion in which polydimethylsiloxane (PDMS) wrapped with modified nano silica (MNS) is designed to enhance the hydrophobic property of cementitious materials while minimizing strength loss. The results show that BHCM exhibits good hydrophobicity (water contact angle 121.8 degrees) while significantly reducing strength loss (decreased by 10.3 %). The presence of MNS effectively shields PDMS from direct contact with cement minerals during the initial stages. Moreover, MNS can react with portlandite (CH) to generate C-S-H phase and optimize the pore structure of hardened cement pastes. This study contributes to promoting the structure-function integration of cement composites and achieving an extended service life for concrete.

Although interest in incorporating recycled concrete powder (RCP) into 3D-printed concrete has increased, challenges in regulating the rheological properties continue to hinder printing accuracy and overall printability, limiting its practical and sustainable application. This study investigates the mix design of 3D-printed cementitious materials (CM) containing RCP and applies response surface methodology (RSM) to achieve precise rheological control, targeting controllable rheology and stable structural application. The results demonstrate that RCP significantly enhances the static yield stress and elastic modulus of the 3D-printed CM. Furthermore, a synergistic optimization, reducing the water-to-cement (W/C) ratio while adjusting the dosage of water-reducing agent (WRA), effectively regulates hydration kinetics, ultimately improves resistance to deformation during multi-layer deposition, and enhances stable structure formation. RSM analysis reveals critical interactions among variables, establishes a predictive model for printability optimization, and identifies optimal ranges: RCP content (15-25 %), W/C ratio (0.4-0.45 %), and WRA dosage (0-0.30 %). Importantly, the incorporation of RCP achieves dual benefits by reducing carbon emissions and cutting raw resource consumption. This approach enables a cleaner production pathway that converts solid waste into high-value construction materials and advances lowcarbon 3D printing technology.

Colloidal nano silica (CNS) demonstrated positive effects in enhancing the water stability of magnesium phosphate cement (MPC), and the underlying mechanism was investigated systematically in this paper. The experimental results showed that the nucleation effect of CNS accelerated the intermediate phase transition process and significantly enhanced the struvite early formation rate of MPC. Moreover, the addition of CNS led to a shift from macropore to gel pores observed from pore size distribution. Notably, the filling effect of CNS and the formation of novel hydration products were identified as critical factors in enhancing water stability and optimizing pore structure. Simulation experiments provided further validation that CNS could directly react with dead-burnt magnesium oxide to generate a novel gel phase-magnesium silicate hydrate (M-S-H) which confirmed a possible hydration reaction of silica in MPC.

Magnesium potassium phosphate cement-based material (MKPCs) of MgO-SiO2-K2HPO4 with varying wollastonite powder (WS) contents (0-20 %) were developed. Rheological performance (thixotropy, yielding behaviours and viscoelasticity) and mechanical strength were studied. Test results show that the addition of 15 % WS improved the thixotropy significantly. A thixotropy index was introduced to model the variation of static yield stress, which increased with increasing content of WS but decreased with the resting time. The fast fluctuation of thixotropy changes in early age was in favor of decreasing the structure deformation of bottom layer. The critical stress and the LVR were enlarged with the increasing WS contents. The Lissaju-Bowditch curves show that the inclusion of WS changed the rotation variation of curves from elliptic to straight-line, representing the slurry behave as elastic-solid state. The strength of mixture with 15 % WS reached to the maximum value, but excessive 20 % WS showed adverse effect on strength. It was verified mixture modified by suitable amount of 15 % WS would generally favor the excellent strength and printability. Detailed SEM images and rheological plots effectively illustrated the microstructural changes and flow behavior, enlarging the understanding of MgO-SiO2K2HPO4 for 3D printing applications.

Reinforcement corrosion caused by chloride-ion (Cl-) in marine concrete severely affects its durability. To address this, two types of synthetic layered double hydroxides (LDHs) 2D nano-flakes based on CaFe-NO3 and CaFeAl-NO3, colloidal nanosilica (CNS), and nano-montmorillonite (NM) were developed for improving the compressive strength, Cl-adsorption behavior, and corrosion resistance of concrete. In this study, the LDHs, CNS, and NM were introduced in the sulphate-resistant Portland cement (SRPC) pastes, aiming to investigate the effect of admixture on the compressive strength and free chloride content concerning admixture content using response surface methodology (RSM). Experimental results showed that the incorporation of LDHs, CNS, and NM significantly decreased the free chloride content of the SRPC pastes. RSM optimization determined optimized dosages: 1.2-1.4 wt% LDHs, 0.1-0.3 wt% CNS, and 0.4-0.6 wt% NM. Electrochemical analysis (OCP/EIS/PDP) revealed that the LDHs-CNS-NM cement composite demonstrated superior corrosion resistance with lower corrosion rate, higher impedance modulus, and larger arc radii. The enhanced properties benefit from the LDHs-induced chloride adsorption, CNS-activated secondary hydration, and LDHs-, CNS-, NM-enabled seed and internal curing, and micro-filling effects through nanoparticle. Notably, PVP demonstrated supplementary corrosion protection via metal surface passivation film formation. In conclusion, this systematic establishes theoretical and practical guidance for developing LDHs-based composites in marine concrete with excellent durability.

Coatings play a crucial role in coal mine tunnels, aimed at preventing gas leakage. This risk means that the coating must have a qualified flame retardancy and excellent deformation capabilities. Polymer-modified cement-based coatings present a viable option to satisfy these demands. This study focuses on the impact of ethylene-vinyl acetate (EVA) powders on the properties of polymer-modified cement-based coatings for preventing gas leakage in coal mines. The results show that the coatings' elongation at break increases as the EVA content rises. The 28-day-cured coating had an elongation at a break of 8.2 % when the EVA content was 20 wt. %. The tensile strength and bond strength of the 20 wt. % EVA-containing coating were 12.9 and 127.3 % higher than the control group, reaching 3.9 and 2.5 MPa, respectively. However, a higher amount of EVA led to reduced flame retardancy. The coating with 20 wt. % EVA content not only met the flame retardancy requirements, but also had excellent mechanical properties and workability. During the hydration process, EVA affected the heat release and promoted cement hydration.

Incorporating aluminum dihydrogen phosphate into magnesium phosphate cement (MPC), including magnesium ammonium phosphate cement (AMAPC) and magnesium potassium phosphate cement (AMKPC), significantly enhances both compressive strength and water resistance. The results show that AMAPC-3 exhibited a remarkable increase in compressive strength, maintaining a compressive strength retention ratio of 0.83 after 60 days. The addition of aluminum dihydrogen phosphate introduced extra phosphate ions that facilitated the hydration of unreacted MgO, resulting in an increased formation of hydration products such as struvite and kstruvite. Furthermore, it participated in independent hydration reactions, generating new phase Al(OH)3 gel and Al(PO4)& sdot;2H2O gel, which contributed to a denser microstructure. Microstructural analysis confirmed a refined pore structure and reduced porosity in the modified cements. These findings position aluminum dihydrogen phosphate as an effective modifier for enhancing the water resistance and mechanical properties of MPCs.

Graphene oxide (GO) significantly enhances cement hydration at the nanoscale; however, its tendency to complex and agglomerate with Ca2⁺ in cement paste remains an unresolved issue. To improve the dispersibility and enhance the reinforcing effect of GO in cement paste, polycarboxylate (PC) superplasticizer was used to disperse GO (PC@GO). This study uniquely divided PC into two parts, with one modifying GO and the other acting as a water-reducing agent, to explore the effects on GO dispersion and analyze the rheological, carbon emission, mechanical, and hydration properties of cement paste. The experimental results show that the dispersion of GO modified by PC was improved, resulting in a significant enhancement in the performance of the cement paste containing PC@GO. The flexural and compressive strength of cement paste containing PC@GO4 cured for 7 days increased by 23.7% and 12.6%, respectively, meanwhile, the carbon-to-strength ratio (CI) decreased by 14.8%. In addition, the hydration acceleration period shortened by 7.50%, and the water absorption and porosity of the cement paste containing PC@GO4 decreased by 35.2% and 45.3%, respectively. Incorporating PC@GO into cement paste significantly enhances the dispersion of GO, substantially improves its mechanical properties, and positions it as a promising solution for the development of high-performance cementitious materials.