Pub Date : 2026-01-12DOI: 10.1016/j.cemconcomp.2026.106479
Chao Liu , Xianqin Chen , Zhiyu Luo , Huawei Liu , Chao Zhu , Yukun Zhang , Haohao Sun , Guoliang Bai
Reinforcement integration in 3D printed concrete (3DPC) creates complex interfacial microstructures that critically govern printed structural performance. This study systematically investigates the bond behavior between rebar and 3D printed natural coarse aggregate concrete (3DPNAC) under multiple loading conditions, with particular emphasis on process-induced interconnected pore defects. Comparative analysis demonstrates that coarse aggregates enhance interlayer tensile and shear strengths by 57.6 % and 70.3 %, respectively, through improved fracture tortuosity and mechanical interlocking. However, rebar placement generates interconnected pore networks that severely compromise interfacial load transfer, resulting in pronounced anisotropic bond-slip behavior (parallel > vertical >45° orientation). A novel rebar-3DPNAC interface structural zoning framework is proposed, which establishes explicit processing-structure-property relationships and reveals the fundamental conflict between pore-induced weakening and aggregate-induced strengthening at rebar-concrete interfaces. The findings provide critical mechanistic insights for optimizing reinforcement strategies in 3DPC structures, bridging the gap between material-level understanding and structural design requirements.
{"title":"Effects of pore defects on interfacial bonding between rebar and 3D printed coarse aggregate concrete under multiple loading conditions","authors":"Chao Liu , Xianqin Chen , Zhiyu Luo , Huawei Liu , Chao Zhu , Yukun Zhang , Haohao Sun , Guoliang Bai","doi":"10.1016/j.cemconcomp.2026.106479","DOIUrl":"10.1016/j.cemconcomp.2026.106479","url":null,"abstract":"<div><div>Reinforcement integration in 3D printed concrete (3DPC) creates complex interfacial microstructures that critically govern printed structural performance. This study systematically investigates the bond behavior between rebar and 3D printed natural coarse aggregate concrete (3DPNAC) under multiple loading conditions, with particular emphasis on process-induced interconnected pore defects. Comparative analysis demonstrates that coarse aggregates enhance interlayer tensile and shear strengths by 57.6 % and 70.3 %, respectively, through improved fracture tortuosity and mechanical interlocking. However, rebar placement generates interconnected pore networks that severely compromise interfacial load transfer, resulting in pronounced anisotropic bond-slip behavior (parallel > vertical >45° orientation). A novel rebar-3DPNAC interface structural zoning framework is proposed, which establishes explicit processing-structure-property relationships and reveals the fundamental conflict between pore-induced weakening and aggregate-induced strengthening at rebar-concrete interfaces. The findings provide critical mechanistic insights for optimizing reinforcement strategies in 3DPC structures, bridging the gap between material-level understanding and structural design requirements.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"168 ","pages":"Article 106479"},"PeriodicalIF":13.1,"publicationDate":"2026-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956776","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-12DOI: 10.1016/j.cemconcomp.2026.106466
Xingjie Huang , Xiang Hu , Hussaini Abdullahi Umar , Tianwen Bai , Caijun Shi
The performance of concrete in high-altitude environments presents distinct challenges due to harsh climatic conditions, including low atmospheric pressure, temperature fluctuations, and low relative humidity. The key factor influencing the performance of concrete in such environments is the air void system, which is critical to its resistance to frost damage. The introduction of air bubbles into concrete through air entrainment improves various properties, such as resistance to frost damage, rheology, and fire resistance. This review explores the mechanisms of bubble formation and stability in cementitious materials under low air pressure, focusing on the physicochemical interactions between air-entraining agents (AEAs) and cementitious materials, and the resulting influence on rheology and resistance to frost damage. The effects of low air pressure on air-entraining efficiency, as well as bubble formation and stability, are discussed. Furthermore, the relationship among air void parameters and rheological behaviour of concrete is discussed comprehensively, along with rheological models developed for air-entrained concrete. By summarizing current research, case studies, and empirical data, this review highlights the need to optimize air entrainment for enhanced concrete performance in low-pressure environments. The findings of the study also reveal the necessity for a deeper understanding of the complex relationship between bubble parameters and rheological properties, which is essential for optimizing the workability and durability of concrete. Moreover, the review reveals existing challenges and proposes research directions to expedite the application of air-entrained concrete in high-altitude construction projects.
{"title":"Formation and stability of bubbles in concrete and their influence on the performance of air-entrained concrete: A state-of-the-art review","authors":"Xingjie Huang , Xiang Hu , Hussaini Abdullahi Umar , Tianwen Bai , Caijun Shi","doi":"10.1016/j.cemconcomp.2026.106466","DOIUrl":"10.1016/j.cemconcomp.2026.106466","url":null,"abstract":"<div><div>The performance of concrete in high-altitude environments presents distinct challenges due to harsh climatic conditions, including low atmospheric pressure, temperature fluctuations, and low relative humidity. The key factor influencing the performance of concrete in such environments is the air void system, which is critical to its resistance to frost damage. The introduction of air bubbles into concrete through air entrainment improves various properties, such as resistance to frost damage, rheology, and fire resistance. This review explores the mechanisms of bubble formation and stability in cementitious materials under low air pressure, focusing on the physicochemical interactions between air-entraining agents (AEAs) and cementitious materials, and the resulting influence on rheology and resistance to frost damage. The effects of low air pressure on air-entraining efficiency, as well as bubble formation and stability, are discussed. Furthermore, the relationship among air void parameters and rheological behaviour of concrete is discussed comprehensively, along with rheological models developed for air-entrained concrete. By summarizing current research, case studies, and empirical data, this review highlights the need to optimize air entrainment for enhanced concrete performance in low-pressure environments. The findings of the study also reveal the necessity for a deeper understanding of the complex relationship between bubble parameters and rheological properties, which is essential for optimizing the workability and durability of concrete. Moreover, the review reveals existing challenges and proposes research directions to expedite the application of air-entrained concrete in high-altitude construction projects.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"168 ","pages":"Article 106466"},"PeriodicalIF":13.1,"publicationDate":"2026-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956775","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-09DOI: 10.1016/j.cemconcomp.2026.106463
Tiejun Ding , Jian Hou , Xuan Zhang , Abdulkareem Alsofi , Zihan Ma , Kai Cui , Long Jiang , Yi Jiang , Peiliang Shen , Christopher Cheeseman , Hong Wong , Chi Sun Poon
This study presents the preparation of calcium carbonate (CaCO3) ceramics using vaterite derived from recycled concrete powder (RCP) through a novel in-situ polymorph transformation-enhanced cold sintering process. The resulting chemically bonded CaCO3 ceramics consists of 100 % calcite and achieve high compressive strength and a relative density of up to 80.5 %. The initial transformation from vaterite to calcite occurs at particle surfaces, decreasing porosity between particles and gradually forming a core-shell structure with a dense outer shell and a porous interior. The fusion of these shells at the contact points of adjacent particles enhances the interparticle chemical bonding. Later polymorph transformations increase pore size and volume and promote particle fusion to form a more homogeneous microstructure. This increases strength by up to 40 % compared to CaCO3 ceramics produced by conventional cold sintering. The research highlights the potential of utilizing waste concrete for sustainable and high-value CaCO3 ceramic production.
{"title":"Recycled concrete powder-derived calcium carbonate ceramics by in-situ polymorph transformation-enhanced cold sintering","authors":"Tiejun Ding , Jian Hou , Xuan Zhang , Abdulkareem Alsofi , Zihan Ma , Kai Cui , Long Jiang , Yi Jiang , Peiliang Shen , Christopher Cheeseman , Hong Wong , Chi Sun Poon","doi":"10.1016/j.cemconcomp.2026.106463","DOIUrl":"10.1016/j.cemconcomp.2026.106463","url":null,"abstract":"<div><div>This study presents the preparation of calcium carbonate (CaCO<sub>3</sub>) ceramics using vaterite derived from recycled concrete powder (RCP) through a novel <em>in-situ</em> polymorph transformation-enhanced cold sintering process. The resulting chemically bonded CaCO<sub>3</sub> ceramics consists of 100 % calcite and achieve high compressive strength and a relative density of up to 80.5 %. The initial transformation from vaterite to calcite occurs at particle surfaces, decreasing porosity between particles and gradually forming a core-shell structure with a dense outer shell and a porous interior. The fusion of these shells at the contact points of adjacent particles enhances the interparticle chemical bonding. Later polymorph transformations increase pore size and volume and promote particle fusion to form a more homogeneous microstructure. This increases strength by up to 40 % compared to CaCO<sub>3</sub> ceramics produced by conventional cold sintering. The research highlights the potential of utilizing waste concrete for sustainable and high-value CaCO<sub>3</sub> ceramic production.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"168 ","pages":"Article 106463"},"PeriodicalIF":13.1,"publicationDate":"2026-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145920294","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The hydration of alkali-activated slag (AAS) involves a dynamic interplay between water state transformation and pore structure evolution, both of which are strongly affected by the type of alkali activator and the curing environment. To clarify the coupled relationship between water evolution and pore development, AAS systems activated by sodium hydroxide (SH) and sodium silicate (SS) were studied under wet curing (WC) and dry curing (DC) conditions. The results reveal that the continuous conversion of free water into gel water serves as the main driving force for pore refinement and densification. Curing conditions govern water migration and hydration extent. WC maintains pore water, enhances gel water formation, and promotes the development of a compact microstructure, while DC accelerates water evaporation, hinders hydration, and results in a looser pore structure with more large pores. The SS-activated system exhibits a slower but more stable hydration process, characterized by continuous gel water formation and gradual pore refinement, leading to a relatively well-regulated pore structure evolution under different curing conditions. In contrast, the SH-activated system undergoes rapid early hydration, resulting in a more heterogeneous pore structure that is highly responsive to environmental humidity. The complementary findings from LF-NMR, BET, and MIP confirm the overall consistency of pore evolution trends while revealing distinct structural features across different scales. This study provides deeper insight into the coupled mechanisms of water evolution and pore structure development in AAS systems, offering a scientific basis for structural regulation and performance optimization under varying environmental conditions.
{"title":"Coupling mechanism of water state evolution and pore structure development in alkali-activated slag: synergistic effect of activators and curing conditions","authors":"Ruilin Cao , Haojie Zhao , Lingling Xu , Zijian Jia , Shunquan Zhang","doi":"10.1016/j.cemconcomp.2026.106471","DOIUrl":"10.1016/j.cemconcomp.2026.106471","url":null,"abstract":"<div><div>The hydration of alkali-activated slag (AAS) involves a dynamic interplay between water state transformation and pore structure evolution, both of which are strongly affected by the type of alkali activator and the curing environment. To clarify the coupled relationship between water evolution and pore development, AAS systems activated by sodium hydroxide (SH) and sodium silicate (SS) were studied under wet curing (WC) and dry curing (DC) conditions. The results reveal that the continuous conversion of free water into gel water serves as the main driving force for pore refinement and densification. Curing conditions govern water migration and hydration extent. WC maintains pore water, enhances gel water formation, and promotes the development of a compact microstructure, while DC accelerates water evaporation, hinders hydration, and results in a looser pore structure with more large pores. The SS-activated system exhibits a slower but more stable hydration process, characterized by continuous gel water formation and gradual pore refinement, leading to a relatively well-regulated pore structure evolution under different curing conditions. In contrast, the SH-activated system undergoes rapid early hydration, resulting in a more heterogeneous pore structure that is highly responsive to environmental humidity. The complementary findings from LF-NMR, BET, and MIP confirm the overall consistency of pore evolution trends while revealing distinct structural features across different scales. This study provides deeper insight into the coupled mechanisms of water evolution and pore structure development in AAS systems, offering a scientific basis for structural regulation and performance optimization under varying environmental conditions.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"168 ","pages":"Article 106471"},"PeriodicalIF":13.1,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145920296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-07DOI: 10.1016/j.cemconcomp.2026.106472
Shilang Xu, Zizhuo Su, Qinghua Li, Xing Yin, Zixiang Shen, Qingmin Wang
A novel lightweight ultra-high-toughness cementitious composite (LW-UHTCC) was developed by incorporating silica aerogel and polyethylene (PE) fibers into a tailored cementitious matrix. The matrix was designed based on micromechanical and fracture mechanics principles to achieve moderate fracture toughness, enabling an optimal balance of fiber-matrix bridging strength, which facilitates strain-hardening and multiple microcracking. Toughening mechanisms were investigated by quantifying matrix fracture toughness and fiber bridging performance using three-point bending and single-crack tensile tests, respectively. The addition of highly porous silica aerogel significantly reduced the composite density (from 2235 to 1624 kg/m3), while PE fibers contributed to strong crack-bridging, synergistically enhancing both tensile ductility and energy dissipation. Mercury intrusion porosimetry (MIP) revealed that the aerogel-modified matrix exhibited a refined, multiscale pore structure. Direct tensile tests exhibited robust strain-hardening behavior, marked by the formation of multiple cracking and over-saturation phenomenon, accompanied by stress fluctuation signifying stable crack growth. The inclusion of aerogel not only reduces the density of UHTCC but also shifts the cracking pattern from saturated to over-saturated cracking, significantly enhancing its toughness under both tensile and compressive stresses. The developed LW-UHTCC achieved an excellent combination of low density, high energy absorption, and superior tensile performance, with tensile strain capacities of 5.1–6.8 %, tensile strengths up to 8.5 MPa, and compressive strengths ranging from 66.5 to 124.1 MPa. These attributes make LW-UHTCC a potential candidate for lightweight, high-ductility structural components and resilient infrastructure systems.
{"title":"Utilizing aerogel to tailor flaws for lightweighting, toughness improvement, and cracking pattern transition of ultra-high toughness cementitious composite","authors":"Shilang Xu, Zizhuo Su, Qinghua Li, Xing Yin, Zixiang Shen, Qingmin Wang","doi":"10.1016/j.cemconcomp.2026.106472","DOIUrl":"10.1016/j.cemconcomp.2026.106472","url":null,"abstract":"<div><div>A novel lightweight ultra-high-toughness cementitious composite (LW-UHTCC) was developed by incorporating silica aerogel and polyethylene (PE) fibers into a tailored cementitious matrix. The matrix was designed based on micromechanical and fracture mechanics principles to achieve moderate fracture toughness, enabling an optimal balance of fiber-matrix bridging strength, which facilitates strain-hardening and multiple microcracking. Toughening mechanisms were investigated by quantifying matrix fracture toughness and fiber bridging performance using three-point bending and single-crack tensile tests, respectively. The addition of highly porous silica aerogel significantly reduced the composite density (from 2235 to 1624 kg/m<sup>3</sup>), while PE fibers contributed to strong crack-bridging, synergistically enhancing both tensile ductility and energy dissipation. Mercury intrusion porosimetry (MIP) revealed that the aerogel-modified matrix exhibited a refined, multiscale pore structure. Direct tensile tests exhibited robust strain-hardening behavior, marked by the formation of multiple cracking and over-saturation phenomenon, accompanied by stress fluctuation signifying stable crack growth. The inclusion of aerogel not only reduces the density of UHTCC but also shifts the cracking pattern from saturated to over-saturated cracking, significantly enhancing its toughness under both tensile and compressive stresses. The developed LW-UHTCC achieved an excellent combination of low density, high energy absorption, and superior tensile performance, with tensile strain capacities of 5.1–6.8 %, tensile strengths up to 8.5 MPa, and compressive strengths ranging from 66.5 to 124.1 MPa. These attributes make LW-UHTCC a potential candidate for lightweight, high-ductility structural components and resilient infrastructure systems.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"168 ","pages":"Article 106472"},"PeriodicalIF":13.1,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145949857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nano-C-S-H is well known to serve as crystal nuclei in ordinary Portland cement, and its dispersion and mechanical properties can be enhanced by modification. In this study, we used graphene oxide (GO) as a modifier to prepare nano-C-S-H-GO (CG) seeds through a nucleation and growth separation method. Hydration kinetics, XRD, FT-IR, TG-DSC, MIP, SEM, and EIS were used to analyze the properties of CG seeds and their effects on cement performance, including the heat of hydration, phase of hydration products, pore structure and mechanical properties. The research shows that GO intercalation within the C-S-H matrix enhanced crystallinity and promoted the formation of highly polymerized, flocculent C-S-H structures. Incorporation of CG significantly accelerates hydration kinetics and shifted the reaction mechanism from NG-I-D to NG-D, leading to higher compressive and flexural strength at 1 day. Moreover, CG accelerated the transformation of petal-shaped hydration products into rod-like crystals and acted as a “bridge,” connecting AFt and C-S-H gels, contributing to a 0.8 %–2.1 % increase in gel pore population. Besides, EIS analysis confirms a progressive increase in the semicircle diameter of the Nyquist curve and a corresponding reduction in pore connectivity with increasing CG content and curing age. These findings highlight the potential of CG for utilize as an effective hardening accelerator for enhancing early-age performance in cementitious systems.
纳米c - s - h作为晶核存在于普通硅酸盐水泥中，通过改性可以提高其分散性和力学性能。在本研究中，我们以氧化石墨烯（GO）为改性剂，通过成核和生长分离的方法制备了纳米c - s - h -GO （CG）种子。采用水化动力学、XRD、FT-IR、TG-DSC、MIP、SEM、EIS等分析了CG种子的水化热、水化产物相、孔隙结构、力学性能等对水泥性能的影响。研究表明，在C-S-H基体中嵌入氧化石墨烯增强了结晶度，促进了高聚合絮状C-S-H结构的形成。CG的加入显著加速了水化动力学，将反应机制从NG-I-D转变为NG-D，导致第1天的抗压和抗弯强度更高。此外，CG加速了花瓣状水化产物向杆状晶体的转变，并充当了连接AFt和C-S-H凝胶的“桥梁”，使凝胶孔数量增加了0.8% - 2.1%。此外，EIS分析证实，随着CG含量和龄期的增加，Nyquist曲线的半圆直径逐渐增大，孔隙连通性相应降低。这些发现强调了CG作为一种有效的硬化促进剂的潜力，可以提高胶凝体系的早期性能。
{"title":"Impact of synthetic C-S-H-GO seeds on hydration kinetics and pore structure evolution of cement pastes","authors":"Jixi Chen , Jinqing Jia , Zhiyong Qi , Shun Dong , You Mou , Mengyu Zhu","doi":"10.1016/j.cemconcomp.2026.106470","DOIUrl":"10.1016/j.cemconcomp.2026.106470","url":null,"abstract":"<div><div>Nano-C-S-H is well known to serve as crystal nuclei in ordinary Portland cement, and its dispersion and mechanical properties can be enhanced by modification. In this study, we used graphene oxide (GO) as a modifier to prepare nano-C-S-H-GO (CG) seeds through a nucleation and growth separation method. Hydration kinetics, XRD, FT-IR, TG-DSC, MIP, SEM, and EIS were used to analyze the properties of CG seeds and their effects on cement performance, including the heat of hydration, phase of hydration products, pore structure and mechanical properties. The research shows that GO intercalation within the C-S-H matrix enhanced crystallinity and promoted the formation of highly polymerized, flocculent C-S-H structures. Incorporation of CG significantly accelerates hydration kinetics and shifted the reaction mechanism from NG-I-D to NG-D, leading to higher compressive and flexural strength at 1 day. Moreover, CG accelerated the transformation of petal-shaped hydration products into rod-like crystals and acted as a “bridge,” connecting AFt and C-S-H gels, contributing to a 0.8 %–2.1 % increase in gel pore population. Besides, EIS analysis confirms a progressive increase in the semicircle diameter of the Nyquist curve and a corresponding reduction in pore connectivity with increasing CG content and curing age. These findings highlight the potential of CG for utilize as an effective hardening accelerator for enhancing early-age performance in cementitious systems.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"168 ","pages":"Article 106470"},"PeriodicalIF":13.1,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956759","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-04DOI: 10.1016/j.cemconcomp.2026.106467
Yan Sun, Guoqiang Du, Xiaowei Deng, Ye Qian
This study investigates nozzle channel designs to enhance fiber alignment and tensile properties in 3D-printed Ultra-High Performance Strain-Hardening Cementitious Composites (3DP-UHP-SHCC). Conventional rectangular nozzles ([5 × 30]) achieved moderate fiber alignment (with an average angle of 14.1°) but exhibited significant disparity between middle- (21.2°) and side-section fibers (10.6°), limiting tensile performance. Baffled nozzles ([5 × 30-I/II]) reduced the middle-section fiber angle by 59 % (to 8.7°), but resulted in an increased nozzle pressure of 67.9 kPa, a 100 % clogging risk, a 227 % increase in porosity, and a 14.2 % reduction in tensile strength. Novel V-shaped nozzles ([5 × 30-V180°/135°/90°]) addressed these issues by leveraging flow confinement and pressure gradients, aligning fibers without physical contact. The [5 × 30-V90°] nozzle achieved 11.3° middle-section fiber angle, 9.43 MPa strength, and 11.47 % strain. The optimized N-shaped nozzle ([5 × 30-N90°]) delivered near-isotropic alignment (10.1° middle section, ≤0.5° deviation) and superior tensile performance: 9.93 MPa (+17.8 %) strength and 11.76 % (+15.7 %) strain. Results demonstrate that geometric nozzle optimization enhances fiber alignment and tensile properties while maintaining extrusion reliability.
Pub Date : 2026-01-02DOI: 10.1016/j.cemconcomp.2026.106468
Weihsiu Hu , He Zhu , Yonghui An , Aamer Bhutta , Georgios Zapsas , Waleed Nasser , Brian R. Ellis , Victor C. Li
The unavailability of fly ash (FA), high embodied carbon, and drying shrinkage present challenges in developing engineered cementitious composites (ECC) for pavement applications. This study aims to develop FA-free high-performance ECC to address these concerns. Firstly, locally available volcanic ash (VA) was utilized to fully replace the FA in ECC. Then, calcium sulphoaluminate cement (CSA) was incorporated to compensate for the high shrinkage of VA ECC. By deliberately designing the curing regime with wet-curing (at least 24 h), VA-ECC can achieve intrinsic self-stressing capacity with a relatively low content of CSA (100 kg/m3 herein), which shows advantages for thinner pavements with a sufficient construction time window during the summer season. The shrinkage, working time window, mechanical performance, and sustainability evaluations of this VA-ECC were investigated. Results suggested that the self-stressing VA-ECC possesses a maximum expansion of 5275 με, an average compressive strength of 40.9 MPa, and a tensile strength of 9.03 MPa. Working time window was defined by the time duration between the casting and time that spread diameter drops to 130 mm per ASTM C1437. The working time window of the designed ECC was extended to 120 min due to the low CSA content combining with wet curing method. Benefiting from the high flexural strength, VA-ECC reduced the pavement thickness by up to 66 %, resulting in a 48 % reduction of CO2 footprint compared to traditional concrete pavement. This developed VA-ECC demonstrates potential as a candidate material for ultra-thin low-carbon pavements, for which the design method warrants future studies.
{"title":"Development of volcanic ash based self-stressing engineered cementitious composites (ECC)","authors":"Weihsiu Hu , He Zhu , Yonghui An , Aamer Bhutta , Georgios Zapsas , Waleed Nasser , Brian R. Ellis , Victor C. Li","doi":"10.1016/j.cemconcomp.2026.106468","DOIUrl":"10.1016/j.cemconcomp.2026.106468","url":null,"abstract":"<div><div>The unavailability of fly ash (FA), high embodied carbon, and drying shrinkage present challenges in developing engineered cementitious composites (ECC) for pavement applications. This study aims to develop FA-free high-performance ECC to address these concerns. Firstly, locally available volcanic ash (VA) was utilized to fully replace the FA in ECC. Then, calcium sulphoaluminate cement (CSA) was incorporated to compensate for the high shrinkage of VA ECC. By deliberately designing the curing regime with wet-curing (at least 24 h), VA-ECC can achieve intrinsic self-stressing capacity with a relatively low content of CSA (100 kg/m<sup>3</sup> herein), which shows advantages for thinner pavements with a sufficient construction time window during the summer season. The shrinkage, working time window, mechanical performance, and sustainability evaluations of this VA-ECC were investigated. Results suggested that the self-stressing VA-ECC possesses a maximum expansion of 5275 με, an average compressive strength of 40.9 MPa, and a tensile strength of 9.03 MPa. Working time window was defined by the time duration between the casting and time that spread diameter drops to 130 mm per ASTM <span><span>C1437</span><svg><path></path></svg></span>. The working time window of the designed ECC was extended to 120 min due to the low CSA content combining with wet curing method. Benefiting from the high flexural strength, VA-ECC reduced the pavement thickness by up to 66 %, resulting in a 48 % reduction of CO<sub>2</sub> footprint compared to traditional concrete pavement. This developed VA-ECC demonstrates potential as a candidate material for ultra-thin low-carbon pavements, for which the design method warrants future studies.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"168 ","pages":"Article 106468"},"PeriodicalIF":13.1,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894549","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-02DOI: 10.1016/j.cemconcomp.2026.106465
Yuan Feng , Huaicheng Zhong , Junda Fang , Weisen Liu , Zhan Jiang , Jian Yang , Jianhe Xie
Using construction waste recycled powder (RP) in alkali-activated concrete (AAC) is highly sustainable, but its inherent low reactivity hinders high-volume utilisation. This study employed an innovative NaHCO3 solution carbonation technique to treat RP, producing NCRP with enhanced performance as a ground granulated blast-furnace slag (GGBFS)-based AAC precursor. Compared with a conventional wet carbonation product (WCRP), the compressive strength of AAC with 40 % NCRP doping reached 56.3 MPa. This was 38.4 % and 15.1 % higher than the compressive strength of untreated RP and WCRP, respectively, and significantly exceeded that of the conventional fly ash (FA)/GGBFS system (48.9 MPa). NaHCO3 accelerates the carbonation process by promoting CO2 dissolution through the pH buffering effect of HCO3−, while Na + promotes Ca2+ dissolution through ion exchange. During the alkali activation stage, the residual Na+ further synergistically builds a denser microstructure by promoting the dissolution-condensation reaction of silica-aluminate. These dense microstructures render NCRP/GGBFS-based AAC highly durable, with a 36 % reduction in water penetration depth and chloride ion erosion resistance, and a 25 % reduction in carbonation depth compared to untreated RP. Notably, while the conventional FA/GGBFS system exhibited a 37 % loss of strength upon carbonation, the NCRP/GGBFS system demonstrated a 9.4 % increase in strength due to the stabilising carbonate matrix. Environmental analyses further revealed that NCRP enhanced CO2 sequestration capacity by 20 % compared to WCRP and reduced its global warming potential (GWP) by 30 % compared to the FA/GGBFS system. This work validates the use of NaHCO3 carbonation for optimising AAC performance, enabling high-volume CDW recycling.
{"title":"NaHCO3 solution carbonation recycled powder for novel alkali-activated concrete: Synergistic enhancement in mechanical properties, durability, and environmental impact","authors":"Yuan Feng , Huaicheng Zhong , Junda Fang , Weisen Liu , Zhan Jiang , Jian Yang , Jianhe Xie","doi":"10.1016/j.cemconcomp.2026.106465","DOIUrl":"10.1016/j.cemconcomp.2026.106465","url":null,"abstract":"<div><div>Using construction waste recycled powder (RP) in alkali-activated concrete (AAC) is highly sustainable, but its inherent low reactivity hinders high-volume utilisation. This study employed an innovative NaHCO<sub>3</sub> solution carbonation technique to treat RP, producing NCRP with enhanced performance as a ground granulated blast-furnace slag (GGBFS)-based AAC precursor. Compared with a conventional wet carbonation product (WCRP), the compressive strength of AAC with 40 % NCRP doping reached 56.3 MPa. This was 38.4 % and 15.1 % higher than the compressive strength of untreated RP and WCRP, respectively, and significantly exceeded that of the conventional fly ash (FA)/GGBFS system (48.9 MPa). NaHCO<sub>3</sub> accelerates the carbonation process by promoting CO<sub>2</sub> dissolution through the pH buffering effect of HCO<sub>3</sub><sup>−</sup>, while Na <sup>+</sup> promotes Ca<sup>2+</sup> dissolution through ion exchange. During the alkali activation stage, the residual Na<sup>+</sup> further synergistically builds a denser microstructure by promoting the dissolution-condensation reaction of silica-aluminate. These dense microstructures render NCRP/GGBFS-based AAC highly durable, with a 36 % reduction in water penetration depth and chloride ion erosion resistance, and a 25 % reduction in carbonation depth compared to untreated RP. Notably, while the conventional FA/GGBFS system exhibited a 37 % loss of strength upon carbonation, the NCRP/GGBFS system demonstrated a 9.4 % increase in strength due to the stabilising carbonate matrix. Environmental analyses further revealed that NCRP enhanced CO<sub>2</sub> sequestration capacity by 20 % compared to WCRP and reduced its global warming potential (GWP) by 30 % compared to the FA/GGBFS system. This work validates the use of NaHCO<sub>3</sub> carbonation for optimising AAC performance, enabling high-volume CDW recycling.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"167 ","pages":"Article 106465"},"PeriodicalIF":13.1,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894548","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-02DOI: 10.1016/j.cemconcomp.2026.106469
Xi Chen, Weiyi Ji, Chunpeng Zhang, Jian-Xin Lu, Chi-Sun Poon
The low strength and elastic modulus of lightweight aggregate (LWA) are the main factors restricting the development of lightweight concrete (LWC). To address this issue, a core-shell lightweight structure comprising a lightweight core and a strong shell toughened by carbon nanotubes (CNTs) was designed to fabricate high-strength LWA. Incorporating 0.3 % CNTs resulted in a remarkable reduction in LWA porosity by over 97 %, while the elastic modulus of LWC was enhanced by 31.7 %. Experiments and simulations were employed to elucidate the role of CNTs in toughening the hydrated cementitious shell from hydration to cracking. Through TEM, SEM, X-CT, and nanoindentation, it was demonstrated that CNTs played a limited role in nucleation and marginally accelerated the hydration process. The shell and the adjacent interfacial transition zone were enhanced mainly because CNTs significantly rendered a tighter packing of hydration products and optimized the interconnected pores in sphericity and volume. Simulation results revealed that achieving a high modulus hinged on establishing a multi-layer synergy between the shell and the matrix, which was accomplished by forming an evenly distributed dense CNT-cement composite to mitigate stress concentration. This work harnesses the potential of CNTs to refine the unique pore distribution of LWA and optimize the stress distribution pattern of the core-shell structure within the matrix, which would facilitate the realization of LWC applications with high strength and modulus.
{"title":"Development of core-shell lightweight aggregate with carbon nanotube towards high elastic modulus: experiment and modeling","authors":"Xi Chen, Weiyi Ji, Chunpeng Zhang, Jian-Xin Lu, Chi-Sun Poon","doi":"10.1016/j.cemconcomp.2026.106469","DOIUrl":"10.1016/j.cemconcomp.2026.106469","url":null,"abstract":"<div><div>The low strength and elastic modulus of lightweight aggregate (LWA) are the main factors restricting the development of lightweight concrete (LWC). To address this issue, a core-shell lightweight structure comprising a lightweight core and a strong shell toughened by carbon nanotubes (CNTs) was designed to fabricate high-strength LWA. Incorporating 0.3 % CNTs resulted in a remarkable reduction in LWA porosity by over 97 %, while the elastic modulus of LWC was enhanced by 31.7 %. Experiments and simulations were employed to elucidate the role of CNTs in toughening the hydrated cementitious shell from hydration to cracking. Through TEM, SEM, X-CT, and nanoindentation, it was demonstrated that CNTs played a limited role in nucleation and marginally accelerated the hydration process. The shell and the adjacent interfacial transition zone were enhanced mainly because CNTs significantly rendered a tighter packing of hydration products and optimized the interconnected pores in sphericity and volume. Simulation results revealed that achieving a high modulus hinged on establishing a multi-layer synergy between the shell and the matrix, which was accomplished by forming an evenly distributed dense CNT-cement composite to mitigate stress concentration. This work harnesses the potential of CNTs to refine the unique pore distribution of LWA and optimize the stress distribution pattern of the core-shell structure within the matrix, which would facilitate the realization of LWC applications with high strength and modulus.</div></div>","PeriodicalId":9865,"journal":{"name":"Cement & concrete composites","volume":"167 ","pages":"Article 106469"},"PeriodicalIF":13.1,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145894550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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