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CONTENTS
Volume 22, Number 4, October 2026
 

Abstract
Rubberized geopolymer concrete (RuGC) is a novel material that combines the environmental and durability benefits of geopolymer concrete (GC) with the flexibility and energy absorption capabilities of rubber aggregates. This hybrid material holds strong potential for structural applications where enhanced tensile strength and impact resistance are desirable. However, its mechanical performance under various loading conditions remains insufficiently explored. In this study, the mechanical behavior of RuGC was evaluated through an experimental program in which aggregates were partially replaced with rubber aggregates at replacement levels of 5%, 10%, and 15%. Experiments were conducted to assess compressive strength, tensile strength, and load-bearing capacity, while the influence of rubber content and curing conditions on mechanical performance was systematically examined. The results indicate that incorporating 10% fine crumb rubber and 5% coarse crumb rubber caused only a marginal reduction in mechanical properties while maintaining satisfactory structural behaviour. These findings highlight RuGC as a promising construction material capable of reducing both rubber waste and the carbon footprint associated with traditional concrete production.

Key Words
coarse aggregate; fine aggregate; fly ash; GGBS; rubber crumbs; rubberized geopolymer concrete

Address
Suman Saha: Department of Civil Engineering, National Institute of Technology Durgapur, Durgapur, 713209, West Bengal, India
Najeeb Manhanpally, Praveen Nagarajan, P. Hridya: Department of Civil Engineering, National Institute of Technology Calicut, Kozhikode, 673601, Kerala, India

Abstract
To improve the performance and sustainability of cement mortar, this study investigates the effects of incorporating graphene oxide (GO) and metakaolin (MK) on the mechanical properties, durability performance, and microstructure of cement mortar. Among the investigated mixtures, the mortar containing 0.02 wt% GO and 3 wt% MK exhibited the best mechanical properties and durability performance. Compared with the reference mortar, the 28 d compressive and flexural strengths increased by 31.3% and 24.7%, respectively. Improvements were also observed in durability performance, including reduced water absorption, enhanced water penetration resistance, reduced drying shrinkage, and improved resistance to sulfate-induced strength deterioration. Microstructural characterization results suggested that GO may facilitate hydration product formation through nucleation effects, whereas MK consumed calcium hydroxide (Ca(OH)2) through pozzolanic reactions and contributed to the formation of additional hydration products. The incorporation of GO and MK refined the pore-size distribution and contributed to the densification of the interfacial transition zone (ITZ), thereby enhancing the mechanical properties and durability performance. These results indicate that low-dose GO combined with MK has potential for improving the mechanical properties and durability performance of cement mortar.

Key Words
durability performance; graphene oxide; mechanical properties; metakaolin; microstructural characterization

Address
Zhuoyu Chen: School of Civil and Transportation Engineering, Guangzhou University, Guangzhou 510006, China
Yunping Xu: China Resources Land Limited (Chongqing), Chongqing 400050, China
Changjiang Liu: School of Civil and Transportation Engineering, Guangzhou University, Guangzhou 510006, China; Guangdong Provincial Key Laboratory of Earthquake Engineering and Applied Technology, Guangzhou University, Guangzhou 510006, China
Weihua Ye, Xiaofeng Li, Shaokun Jiang, Junjie Wen, Jingxin Ren: School of Civil and Transportation Engineering, Guangzhou University, Guangzhou 510006, China

Abstract
Incorporating phase change materials (PCMs) into cementitious composites enhances latent heat storage but generally compromises mechanical performance. This study investigates the combined effects of microencapsulated tetradecane (m-PCM), incorporated at 5% and 10% by weight of cement, and 0.10 wt.% multiwalled carbon nanotubes (MWCNTs) on a high-strength cementitious composite (HSCC) for low-temperature thermal energy storage. Encapsulation increased the onset temperature of thermal degradation from 144.5oC to 226.9oC, while the m-PCM exhibited crystallization and melting enthalpies of 251.5 and 84.76 J/g, respectively. Relative to the 28-day reference strength of 119.83 MPa, m-PCM reduced compressive strength by 17.3% and 33.4%, whereas MWCNT incorporation mitigated these reductions to 12.6% and 18.3%. During five thermal cycles between −5oC and 15oC, the minimum internal temperature increased from −2.0oC for MPCM5% to −0.8oC for MPCM10% and −0.1oC for MPCM10%C. SEM-EDS and XRD indicated localized hydration retardation and a dilution effect associated with m-PCM incorporation. MPCM10%C exhibited the best thermal response while retaining a 28-day compressive strength of 97.92 MPa, demonstrating its potential for high-strength structuralfunctional cementitious composites with low-temperature thermal energy storage capability.

Key Words
high strength; microencapsulated-PCM; MWCNT; PCM; thermal energy storage

Address
Xinghan Jin, Muhammad Zeeshan Haider, Syed Nayyar Raza Naqvi, Jong Wan Hu: Department of Civil and Environmental Engineering, Incheon National University, Incheon, 22012, Republic of Korea; Incheon Disaster Prevention Research Center, Incheon National University, Incheon, 22012, Republic of Korea

Abstract
Under freeze-thaw conditions, steel corrosion becomes more pronounced, leading to structural damage such as cracking, spalling, and strength reduction, which adversely affects the flexural strength, flexural-tensile strength, and freeze-thaw resistance of concrete. To address this, a study was conducted on the degradation performance of polypropylene fiber-reinforced concrete considering steel corrosion during freeze-thaw cycles. Polypropylene fiber-reinforced concrete was prepared by mixing pretreated polypropylene fibers with cement and other admixtures. The flexural strength, flexural-tensile strength, and elastic modulus of polypropylene fiberreinforced concrete with fiber contents of 0.2%, 0.4%, and 0.6% were tested before and after corrosion and under different numbers of freeze-thaw cycles. The experimental results indicate that, compared with plain concrete, the polypropylene fiber-reinforced concrete exhibited less degradation under freeze-thaw cycles and corrosion, exhibiting reduced surface damage and mass loss. The flexural strength and flexural-tensile strength of concrete with 0.2% polypropylene fiber were lower than those with 0.6% polypropylene fiber, and the elastic modulus test results were also inferior. The performance of concrete with 0.4% polypropylene fiber was moderate. Comprehensive analysis demonstrates that polypropylene fiber-reinforced concrete with a 0.6% fiber content exhibited the least deterioration in freeze-thaw damage after corrosion in salt solution.

Key Words
bending and tensile strength; concrete; freeze-thaw damage deterioration; polypropylene fiber; reinforcement corrosion; saline solution

Address
Ping Song: Cost Consulting Department, Jiaxing Zhongcheng Construction Investment Consulting Co., Ltd., Jiaxing 314001, China
Jinquan Qian: School of Architecture and Environmental Engineering, Shaoxing Institute of Technology, Shaoxing 312000, China

Abstract
This paper experimentally investigates the freeze-thaw resistance of polyvinyl alcohol (PVA) fiberreinforced concrete in which a portion of the cement was replaced with wood-based biochar. Concrete specimens were fabricated with three biochar replacement levels (0%, 5%, and 10%) and subjected to 300 rapid freeze-thaw cycles in accordance with ASTM C666. The surface change, compressive strength, tensile strength, relative dynamic modulus of elasticity, and durability index were systematically measured at designated intervals (0, 150, and 300 cycles). The results indicated that the 5% replacement mixture exhibited the highest compressive strength and demonstrated superior durability performance up to 150 cycles. In contrast, the 10% replacement mixture showed lower strength from the initial stage and after 300 cycles. All mixtures underwent significant deterioration, as indicated by reductions in the relative dynamic modulus and durability index.

Key Words
biochar; durability; fiber-reinforced concrete; freeze-thaw cycles; PVA fiber

Address
Sangwoo Kim: Engineering Research Institute, Gyeongsang National University, Jinju 52828, Republic of Korea
Yeji Hong, Jinsup Kim: Department of Civil Engineering, Gyeongsang National University, Jinju 52828, Republic of Korea

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