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
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
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.
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
Abstract
In order to investigate the influence of different factors on the performance of hybrid sand (desert sand &
manufactured sand) concrete (DMC), through the response surface methodology (RSM), quadratic polynomial
regression equations were established to systematically study the effects of water-binder (W/B) ratio, desert sand
(DS) replacement rate, and fly ash (FA) replacement rate on the slump, 28d compressive strength and 28d splitting
tensile strength of DMC. The results show that the coefficients of determination (R2) of the regression models
reached 0.9805, 0.9856 and 0.9781, respectively, indicating high accuracy and reliability. The compressive strength
and splitting tensile strength of DMC are mainly influenced by the W/B ratio, followed by the FA substitution rate,
and finally the DS substitution rate. Finally, through Non-dominated Sorting Genetic Algorithm (NSGA)-II analysis,
the optimal mix proportion was determined as W/B ratio of 0.35, DS replacement rate of 27.6%, and FA replacement
rate of 9.4%. Under these conditions, the comprehensive performance of DMC is optimal, and between the predicted
and experimental values is less than 5%.
Address
Deshun Hu, Mengru Wang, Mai Cao: Water Conservancy and Civil Engineering College, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia 010018, China
Hailong Zhou: Water Conservancy and Civil Engineering College, Inner Mongolia Agricultural University,
Hohhot, Inner Mongolia 010018, China; State Key Laboratory of Water Engineering Ecology and Environment in Arid Area, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia 010018, China
Abstract
Plain concrete features high resistivity that provides favorable anti-electrochemical corrosion performance, yet suppresses internal conductive networks and disables electrical self-sensing of structural stress and damage. Carbon fibers (CF) is incorporated into concrete to fabricate carbon fiber-reinforced mortar (CFRM) in order to improve the electrical conductivity of the material. The mechano-electrical response of CFRM under various loading conditions was experimentally investigated. The results indicate that with the increase in CF content, the sensitivity of CFRM's Fraction Change in Resistance (FCR) to stress response gradually improves and approaches saturation. FCR tends to first decrease and then increase with rising stress: in the initial loading stage, resistance decreases due to the optimization of the conductive network, exhibiting negative piezoresistivity; in the later stage, resistance increases significantly as cracks propagate and damage conductive paths, showing positive piezoresistivity. Specimens with a 7-day curing age exhibit better mechano-electrical sensitivity than those with a 28-day curing age, primarily attributed to their higher water content and weaker fiber-matrix interfacial bonding. Specimens with a high cement-sand ratio show uniform CF dispersion and significant crack propagation, resulting in more sensitive mechano-electrical responses during the elastic stage. A CF content of 0.8% was found to be high sensitivity to stress, making it suitable for early damage warning of civil engineering structures.
Key Words
carbon fiber; crack mouth opening displacement; fraction change in resistance; mechanoelectrical sensitivity
Address
Jinyan Wang, Chenyang Lou, Yazhi Du, Yingqi Zhang: School of Intelligent Construction and Architectural Engineering, Zhongyuan University of Technology, Zhengzhou 450007, China
Abstract
The accurate prediction of transfer length in pretensioned concrete members is crucial for structural safety and serviceability, yet traditional methods using structural experiments or international standard equations often show significant discrepancies. To address this gap, this study proposes a simplified finite element analysis method incorporating a cohesive damage model to predict transfer length in pretensioned concrete members. Through extensive parametric studies considering concrete cover, compressive strength, strand diameter, and initial prestress, the proposed model demonstrated excellent accuracy with error rates within 5% compared to experimental results. The research notably presents new equations for determining bond stress and initial slip in the transfer zone by using STSB (Standard Test for Strand Bond) test results, applying different multiplication factors by strand diameter (2.6 for 12.7 mm, 2.4 for 15.2 mm, and 1.25 for 17.8 mm) and achieving high R2 values of 0.84~0.87. This method offers a practical solution that can ensure safety while preventing overdesign, particularly in conditions where experimental data is limited.
Key Words
bond; cohesive damage; finite element analysis; pretensioned concrete; transfer length
Address
Jongwon Hong: Department of Architecture and Architectural Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
Deuckhang Lee: School of Civil, Architectural Engineering, and Landscape Architecture & Department of Global Smart City, Sungkyunkwan University, 2066 Seobo-ro, Suwon, 16419, Korea
Lapyote Prasittisopin: Faculty of Science, Chulalongkorn University, 254 Pathumwan, Bangkok 10330, Thailand
Thomas H.-K. Kang: Department of Architecture and Architectural Engineering, Seoul National University,
1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea; Faculty of Science, Chulalongkorn University, 254 Pathumwan, Bangkok 10330, Thailand
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