open access
Contrasting effects of nanobubble water on the tensile behavior of PE-AAS and PBO-OPC composite systems Jaewon Lee, Se-Eon Park, Hyeongki Kim, Young-sang Kim, Bang Yeon Lee
Abstract; Full Text (1457K) .	pages 293-308.	DOI: 10.12989/acc.2026.22.3.01

Abstract
This study experimentally investigates the effects of nanobubble water (NBW) on the mechanical and microstructural properties of two fiber-reinforced composites: an alkali-activated slag (AAS) matrix reinforced with polyethylene (PE) fibers, and an ordinary Portland cement (OPC) matrix reinforced with polybenzo-bis-oxazole (PBO) fibers. Macroscale tests and mercury intrusion porosimetry (MIP) were conducted. Results showed NBW improved compressive strength across both binders, particularly in the AAS system. Under tension, the NBWincorporated PBO-OPC system exhibited simultaneous increases in tensile strength (19%) and strain capacity (46%). Conversely, the PE-AAS system experienced a slight decrease in tensile ductility due to weakened interfacial bonding. Microstructural analysis of the OPC matrix confirmed substantial matrix densification, with NBW reducing the total pore area by approximately 61%. Finally, theoretical micromechanical fiber-bridging analysis validated the macroscopic experimental observations, demonstrating that NBW-induced modifications in pore structure and interfacial properties directly dictate the pseudo-strain-hardening and multiple cracking behaviors of the composites.

Key Words
cement; composite; fiber; nanobubble water; slag

Address
Jaewon Lee: Department of Architecture and Civil Engineering, Chonnam National University, Gwangju, 61186, Republic of Korea
Se-Eon Park: School of Architecture, Chonnam National University, Gwangju, 61186, Republic of Korea
Hyeongki Kim: School of Civil and Environmental Engineering, College of Engineering, Kookmin University, 77 Jeongneung-ro, Seongbuk-gu, Seoul, 02707, Republic of Korea
Young-sang Kim: Department of Architecture and Civil Engineering, Chonnam National University, Gwangju, 61186, Republic of Korea; Department of Civil Engineering, Chonnam National University, Gwangju, 61186, Republic of Korea
Bang Yeon Lee: Department of Architecture and Civil Engineering, Chonnam National University, Gwangju, 61186, Republic of Korea; School of Architecture, Chonnam National University, Gwangju, 61186, Republic of Korea

open access
Mechanical performance of barite-based reactive powder concrete produced by CaO pre-setting pressure and thermal curing for precast applications Dursun Bakir, Sedat Savaş, Ufuk Arazsu, Hakan Çoban
Abstract; Full Text (2716K) .	pages 309-329.	DOI: 10.12989/acc.2026.22.3.02

Abstract
This experimental study investigates the mechanical performance of steel-fibre-reinforced, barite-based ultra-high-strength reactive powder concrete (UHS-RPC) produced under CaO-based chemical pre-setting pressure and thermal curing. The aim is to develop a vibration-free, precast production route for high-density components with high compressive and flexural strength. Twenty-nine mixtures were designed by varying silica fume content (10-80% of cement mass), water-to-binder ratio (0.15-0.35) and steel-fibre content (0-6.3% by volume). A CaOexpansion chemical generating a measured pre-setting pressure of 53 MPa was combined with thermal curing regimes between 90 and 400oC. In paired comparisons of otherwise identical mixtures, pre-setting pressure increased compressive strength on average by 69% (up to 170%) and flexural strength by 27%, confirming matrix densification. A short, 3.5-day protocol combining pre-setting pressure with 400oC thermal curing reached an average compressive strength of 262 MPa (peak 322 MPa) and a flexural strength of 20 MPa. A gradient-boosting model (R2=0.91) with SHAP analysis identified steel-fibre content and pre-setting pressure as the dominant factors governing compressive strength, with curing temperature acting mainly in combination with these variables. Theoretical y-ray attenuation coefficients estimated from mixture composition indicate a 10-24% reduction in halfvalue layer relative to normal concrete, suggesting material-level shielding potential that warrants dedicated experimental verification. Overall, the combined chemical pre-setting pressure and short-duration thermal curing offer a scalable, energy-efficient route for precast components requiring high strength and dimensional stability.

Key Words
barite; CaO pre-setting pressure; gamma-ray attenuation; precast components; reactive powder concrete; steel fibre; thermal curing

Address
Dursun Bakir: Department of Civil Engineering, Faculty of Engineering and Architecture, Bitlis Eren University, Bitlis, Türkiye
Sedat Savaş: Department of Civil Engineering, Faculty of Engineering, Firat University, Elaziğ, Türkiye
Ufuk Arazsu: Institute of Natural Sciences, Firat University, Elaziğ, Türkiye
Hakan Çoban: Department of Civil Engineering, Faculty of Engineering and Architecture, Bitlis Eren University, Bitlis, Türkiye

open access
Synergistic protection of coconut fibre-reinforced coral mortar against UV ageing via heat-silane composite coating Qian Mo, Xiaoping Yu, Dalian Bai, Jialiang Wang, Cunpeng Liu
Abstract; Full Text (2574K) .	pages 331-353.	DOI: 10.12989/acc.2026.22.3.03

Abstract
The long-term durability of natural fibre-reinforced cementitious composites in harsh marine environments is a critical challenge. In this study, the ultraviolet (UV) ageing resistance of coconut fibre-reinforced coral mortar (CFRCM) modified with a heat-silane composite coating (HSCC) was investigated and compared with that of CFRCM subjected to conventional alkali treatment. An accelerated ageing protocol coupling UVB-313 irradiation and seawater spray was conducted on mortar specimens for up to 100 days. A fibre concentration of 0.2% was selected on the basis of prior experimental optimisation. The results showed that HSCC-treated CFRCM retained 90.2% of its flexural strength after 100 days of accelerated ageing, which was significantly higher than that of the alkali-treated samples (approximately 85%). Multiscale characterisation, including scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), revealed three synergistic protection mechanisms: (i) a dense nano-SiO2 physical barrier that shields fibres from UV radiation and moisture ingress, as confirmed by SEM; (ii) hydrothermal pretreatment that removes hemicellulose and enhances fibre crystallinity, as evidenced by FTIR (reduced C=O intensity) and XRD (increased crystallinity index), contributing to improved interfacial stability; and (iii) enhanced intrinsic fibre thermal stability, with the onset decomposition temperature increasing from 188oC (alkali-treated group) to 284oC (HSCC-treated group with metakaolin), as demonstrated by TGA. The HSCC-treated group with metakaolin (M6) achieved the highest absolute flexural strength and the best overall performance on the basis of multicriteria assessment. This work elucidates the mechanistic origins of UV resistance and validates HSCC as an effective fibre modification strategy for durable natural fibre-reinforced materials in coastal infrastructure.

Key Words
coastal infrastructure; coconut fibre; coral mortar; fibre-reinforced composites; heat-silane coating; thermal stability; UV ageing

Address
Qian Mo: School of Intelligent Construction and Low Altitude Technology, Guangxi Transport Vocational and Technical College, 530023, Nanning, China
Xiaoping Yu: School of Civil Engineering and Geomatics, Guilin University of Technology at Nanning, 530001, Nanning, China
Dalian Bai, Jialiang Wang, Cunpeng Liu: School of Civil Engineering and Geomatics, Guilin University of Technology at Nanning, 530001, Nanning, China; Guangxi Key Laboratory of Green Building Materials and Construction Industrialization, 541004, Guilin, Guangxi, China