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25 pages, 8960 KB  
Article
Analysis on Durability of Bentonite Slurry–Steel Slag Foam Concrete Under Wet–Dry Cycles
by Guosheng Xiang, Feiyang Shao, Hongri Zhang, Yunze Bai, Yuan Fang, Youjun Li, Ling Li and Yang Ming
Buildings 2025, 15(19), 3550; https://doi.org/10.3390/buildings15193550 - 2 Oct 2025
Abstract
Wet–dry cycles are a key factor aggravating the durability degradation of foam concrete. To address this issue, this study prepared bentonite slurry–steel slag foam concrete (with steel slag and cement as main raw materials, and bentonite slurry as admixture) using the physical foaming [...] Read more.
Wet–dry cycles are a key factor aggravating the durability degradation of foam concrete. To address this issue, this study prepared bentonite slurry–steel slag foam concrete (with steel slag and cement as main raw materials, and bentonite slurry as admixture) using the physical foaming method. Based on 7-day unconfined compressive strength tests with different mix proportions, the optimal mix proportion was determined as follows: mass ratio of bentonite to water 1:15, steel slag content 10%, and mass fraction of bentonite slurry 5%. Based on this optimal mix proportion, dry–wet cycle tests were carried out in both water and salt solution environments to systematically analyze the improvement effect of steel slag and bentonite slurry on the durability of foam concrete. The results show the following: steel slag can act as fine aggregate to play a skeleton role; after fully mixing with cement paste, it wraps the outer wall of foam, which not only reduces foam breakage but also inhibits the formation of large pores inside the specimen; bentonite slurry can densify the interface transition zone, improve the toughness of foam concrete, and inhibit the initiation and propagation of matrix cracks during the dry–wet cycle process; the composite addition of the two can significantly enhance the water erosion resistance and salt solution erosion resistance of foam concrete. The dry–wet cycle in the salt solution environment causes more severe erosion damage to foam concrete. The main reason is that, after chloride ions invade the cement matrix, they erode hydration products and generate expansive substances, thereby aggravating the matrix damage. Scanning Electron Microscopy (SEM) analysis shows that, whether in water environment or salt solution environment, the fractal dimension of foam concrete decreased slightly with an increasing number of wet–dry cycle times. Based on fractal theory, this study established a compressive strength–porosity prediction model and a dense concrete compressive strength–dry–wet cycle times prediction model, and both models were validated against experimental data from other researchers. The research results can provide technical support for the development of durable foam concrete in harsh environments and the high-value utilization of steel slag solid waste, and are applicable to civil engineering lightweight porous material application scenarios requiring resistance to dry–wet cycle erosion, such as wall bodies and subgrade filling. Full article
(This article belongs to the Section Building Structures)
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25 pages, 4181 KB  
Article
Mechanical Properties Quantification of Steel Fiber-Reinforced Geopolymer Concrete with Slag and Fly Ash
by Reem Adam, Haya Zuaiter, Doha ElMaoued, Adil Tamimi and Mohammad AlHamaydeh
Buildings 2025, 15(19), 3533; https://doi.org/10.3390/buildings15193533 - 1 Oct 2025
Abstract
This study examines the influence of steel fiber reinforcement on the mechanical properties of geopolymer concrete incorporating different slag to fly ash binder ratios (75:25, 50:50, and 25:75). Three fiber contents (0%, 1%, and 2%) by volume were used to assess their impact [...] Read more.
This study examines the influence of steel fiber reinforcement on the mechanical properties of geopolymer concrete incorporating different slag to fly ash binder ratios (75:25, 50:50, and 25:75). Three fiber contents (0%, 1%, and 2%) by volume were used to assess their impact on compressive strength, flexural strength, initial stiffness, and toughness. Compressive tests were conducted at 1, 7, and 28 days, while flexural behavior was evaluated through a four-point bending test at 28 days. The results showed that geopolymer concrete with 75% slag and 25% fly ash experienced the highest compressive strength and modulus of elasticity, regardless of the steel fiber content. The addition of 1% and 2% steel fiber content enhanced the compressive strength by 17.49% and 28.8%, respectively, compared to the control sample. The binder composition of geopolymer concrete plays a crucial role in determining its compressive strength. Reducing the slag content from 75% to 50% and then to 25% resulted in a 15.1% and 33% decrease in compressive strength, respectively. The load–displacement curves of the 2% fiber-reinforced beams display strain-hardening behavior. On the other hand, after the initial crack, a constant increase in load causes the specimen to experience progressive strain until it reaches its maximum load capacity. When the peak load is attained, the curve gradually drops due to a loss in load-carrying capacity known as post-peak softening. This behavior is attributed to steel’s ductility and is evident in specimens 75S25FA2 and 50S50FA2. Concrete with 75% slag and 25% fly ash demonstrated the highest peak load but the lowest ultimate displacement, indicating high strength but brittle behavior. In contrast, concrete with 75% fly ash and 25% slag showed the lowest peak load but the highest displacement. Across all binder ratios, the addition of steel fibers enhanced the flexural strength, initial stiffness, and toughness. This is attributed to the bridging action of steel fibers in concrete. Additionally, steel fiber-reinforced beams exhibited a ductile failure mode, characterized by multiple fine cracks throughout the midspan, whereas the control beams displayed a single vertical crack in the midspan, indicating a brittle failure mode. Full article
(This article belongs to the Section Building Materials, and Repair & Renovation)
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21 pages, 5307 KB  
Article
High-Performance Cementitious Composites with Tensile Strain Capacity Up to 18%
by Zongcai Deng and Wenzhe Li
J. Compos. Sci. 2025, 9(9), 502; https://doi.org/10.3390/jcs9090502 - 17 Sep 2025
Viewed by 434
Abstract
At present, the ductility of engineered cementitious composites (ECC) is not sufficient to achieve compatibility with steel, which limits the application of ECC in composite structures. To prepare ECC with ultra-high tensile strain, tensile tests on eighteen types of ECC with different mix [...] Read more.
At present, the ductility of engineered cementitious composites (ECC) is not sufficient to achieve compatibility with steel, which limits the application of ECC in composite structures. To prepare ECC with ultra-high tensile strain, tensile tests on eighteen types of ECC with different mix ratios were carried out. The effect of cementitious material composition, sand/binder ratio, and fiber hybridization on tensile properties was analyzed. Meanwhile, three types of ECC were developed and defined as ultra-high tensile property cementitious composites (UHTCC). UHTCC exhibits the characteristic of oversaturated cracking and obvious strain hardening during the tensile process. The tensile strain of UHTCC was up to 18.3% with an average tensile strength of 9.9 MPa. Meanwhile, UHTCC shows ultra-high flexural toughness and high compressive strength. In addition, the hybridization of PE fibers and macro-PP fibers has been proved to be beneficial to improve tensile strain capacity, with the cost of fibers decreased by 24.3%. To explore the causes of UHTCC’s ultra-high tensile strain, the state of the matrix and fibers after the tensile test was observed by scanning electron microscope. In addition, the cracking process of UHTCC was analyzed by comparing average crack spacing with the theoretical value. Further, a four-stage tensile constitutive model was proposed. And the new constitutive model has been verified to be applicable to three different types of UHTCC. Full article
(This article belongs to the Special Issue Recent Progress in Hybrid Composites)
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21 pages, 10515 KB  
Article
Comprehensive Study on Mechanical Properties of Rubberized Geopolymer Concrete Reinforced with Steel Fibers
by Xiaoping Wang, Feng Liu, Lei Luo, Baifa Zhang and Lijuan Li
Buildings 2025, 15(17), 3175; https://doi.org/10.3390/buildings15173175 - 4 Sep 2025
Viewed by 491
Abstract
To address challenges posed by waste tires and greenhouse gas emissions associated with ordinary Portland cement, exploring eco-friendly construction materials is critical for sustainability. This study examines the workability and mechanical properties of straight steel fiber-reinforced rubberized geopolymer concrete (SFRRGC), where rubber powder [...] Read more.
To address challenges posed by waste tires and greenhouse gas emissions associated with ordinary Portland cement, exploring eco-friendly construction materials is critical for sustainability. This study examines the workability and mechanical properties of straight steel fiber-reinforced rubberized geopolymer concrete (SFRRGC), where rubber powder is derived from recycled waste tires. The experimental variables included rubber powder (RP) content (0%, 6%, 12%, and 20% by volume of fine aggregate) and steel fiber (SF) content (0%, 0.5%, 1.0%, and 1.5% by volume). The results show that incorporating RP and SFs reduced the workability of SFRRGC but increased its peak strain. Specifically, RP addition decreased the elastic modulus, compressive strength, and toughness; increasing the SF content enhanced energy dissipation, while the effects of SF and RP contents on Poisson’s ratio were negligible. The specimens showed that a higher RP content would weaken the crack-bridging effect of SF. For example, specimens with 1.0% SF and 6% RP achieved 49.56 MPa compressive strength and 4.04 × 10−3 maximum peak strain; those with 0.5% SF and 20% RP had 118.40 J compressive toughness, which was 5.53% lower than that of the reference specimens (125.33 J). Furthermore, a constitutive model for SFRRGC was proposed, and its theoretical curves aligned well with the experimental results. This proposed model can reliably predict the stress–strain curves of geopolymer concrete with different SF and RP mixture proportions. Full article
(This article belongs to the Special Issue Next-Gen Cementitious Composites for Sustainable Construction)
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12 pages, 2832 KB  
Article
Study of Mechanical and Fracture Properties of Concrete with Different Lengths of Polypropylene Fibers
by Kristýna Hrabová, Jaromír Láník and Petr Lehner
Buildings 2025, 15(17), 3041; https://doi.org/10.3390/buildings15173041 - 26 Aug 2025
Viewed by 533
Abstract
This study investigates the effect of polypropylene fibers of different lengths (54 mm, 38 mm, 19 mm) on the mechanical and fracture properties of high-strength concrete. Unlike most existing research focusing on a single fiber length, this work evaluates a fixed hybrid ratio [...] Read more.
This study investigates the effect of polypropylene fibers of different lengths (54 mm, 38 mm, 19 mm) on the mechanical and fracture properties of high-strength concrete. Unlike most existing research focusing on a single fiber length, this work evaluates a fixed hybrid ratio of 4:1:1, thereby addressing the synergistic action of macro- and microfibers. Three dosages were tested and compared to a reference mixture without fibers. Validation was performed by repeated testing of multiple specimens and statistical evaluation of mean values and standard deviations. The results showed that the optimal hybrid mixture (2.0/0.5/0.5 kg/m3) increased compressive strength by 28.7% and splitting tensile strength by 30.1% relative to the reference. Fracture toughness and specific fracture energy also improved significantly, demonstrating enhanced crack resistance and energy absorption. The main contribution of this work is to provide experimental evidence that a hybrid combination of polypropylene fibers at a fixed ratio can improve both mechanical strength and fracture resistance, with direct implications for durability and service life. Full article
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21 pages, 7083 KB  
Article
Green Low-Temperature Activation and Curing for High-Toughness Geopolymer Binders from Diabase Tailings
by Yanan Hu, Yong Yao, Lingling Zhang, Xianming Hu and Xinchun Yang
Materials 2025, 18(16), 3815; https://doi.org/10.3390/ma18163815 - 14 Aug 2025
Viewed by 440
Abstract
This study addresses the low reactivity and poor toughness of diabase tailings (DT), a high-silica industrial byproduct, which restricts their large-scale application in geopolymer binders. To overcome these limitations, a dual-regulation strategy integrating stepwise low-temperature thermal activation (100, 200, and 300 °C) with [...] Read more.
This study addresses the low reactivity and poor toughness of diabase tailings (DT), a high-silica industrial byproduct, which restricts their large-scale application in geopolymer binders. To overcome these limitations, a dual-regulation strategy integrating stepwise low-temperature thermal activation (100, 200, and 300 °C) with standard curing (20 ± 2 °C, 95% RH) was developed. This approach aimed to enhance mineral dissolution kinetics and facilitate the formation of a dense, interconnected gel network. XRD, FTIR, and SEM analyses revealed significant decomposition of amphibole, pyroxene, and olivine, accompanied by increased release of reactive Si and Al species, leading to the formation of a compact N–A–S–H/C–A–S–H gel structure. Under optimized conditions (Si/Al = 2.6; activator modulus = 1.2), the geopolymer achieved a 7-day compressive strength of 42.3 ± 1.8 MPa, a flexural strength of 12.76 ± 1.6 MPa, and a flexural-to-compressive strength ratio of 0.308, demonstrating significant improvements in toughness compared with conventional binders. This green, energy-efficient strategy not only reduces energy consumption and CO2 emissions but also provides a technically feasible pathway for the high-value reuse of silicate-rich mining wastes, contributing to the development of sustainable construction materials with enhanced mechanical performance. Full article
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21 pages, 4980 KB  
Article
Strength Development of Bottom Ash-Based Geopolymer-Stabilized Recycled Concrete Aggregate as a Pavement Base Material
by Menglim Hoy, Chokchai Traiyasut, Suksun Horpibulsuk, Avirut Chinkulkijniwat, Apichat Suddeepong, Apinun Buritatum, Teerasak Yaowarat, Mantana Julvorawong and Thanaset Savetviwat
Coatings 2025, 15(8), 935; https://doi.org/10.3390/coatings15080935 - 11 Aug 2025
Viewed by 602
Abstract
This study investigated a 100% waste-derived material system, using bottom ash (BA) and recycled concrete aggregate (RCA) for sustainable pavement base applications. This innovative approach diverts both construction and power plant waste from landfills while replacing conventional natural aggregates and cement-based binders. Five [...] Read more.
This study investigated a 100% waste-derived material system, using bottom ash (BA) and recycled concrete aggregate (RCA) for sustainable pavement base applications. This innovative approach diverts both construction and power plant waste from landfills while replacing conventional natural aggregates and cement-based binders. Five RCA:BA replacement ratios (90:10 to 50:50) were evaluated with three Na2SiO3:NaOH alkaline activator ratios (1:1, 1:1.5, and 1:2) through unconfined compressive strength (UCS) testing, scanning electron microscopy, energy dispersive X-ray spectroscopy (SEM-EDX), and X-ray diffraction (XRD) analysis. The RCA90BA10 composition with a G/N ratio of 1:2 achieved exceptional performance, reaching 9.14 MPa UCS at 7 days while exceeding the Department of Highways, Thailand, requirement of 2.413 MPa. All geopolymer-stabilized mixtures substantially surpassed minimum specifications, validating the technology for high-traffic pavement applications. Toughness evaluation confirmed superior energy absorption capacity of 107.89 N·m for the optimal formulation. Microstructural characterization revealed that higher G/N ratios promoted extensive sodium aluminosilicate hydrate and calcium silicate hydrate gel formation, creating dense, well-integrated matrices. XRD patterns confirmed successful geopolymerization through pronounced amorphous gel development between 20° and 35° 2θ, correlating directly with mechanical performance improvements. The RCA90BA10 formulation demonstrated optimal balance between reactive aluminosilicate content and structural aggregate framework. This technology offers significant environmental benefits by diverting construction and power plant waste from landfills while achieving mechanical properties superior to conventional materials, providing a scalable solution for sustainable infrastructure development. Full article
(This article belongs to the Section Environmental Aspects in Colloid and Interface Science)
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14 pages, 2047 KB  
Article
Fracture Behavior of Steel-Fiber-Reinforced High-Strength Self-Compacting Concrete: A Digital Image Correlation Analysis
by Maoliang Zhang, Junpeng Chen, Junxia Liu, Huiling Yin, Yan Ma and Fei Yang
Materials 2025, 18(15), 3631; https://doi.org/10.3390/ma18153631 - 1 Aug 2025
Viewed by 411
Abstract
In this study, steel fibers were used to improve the mechanical properties of high-strength self-compacting concrete (HSSCC), and its effect on the fracture mechanical properties was investigated by a three-point bending test with notched beams. Coupled with the digital image correlation (DIC) technique, [...] Read more.
In this study, steel fibers were used to improve the mechanical properties of high-strength self-compacting concrete (HSSCC), and its effect on the fracture mechanical properties was investigated by a three-point bending test with notched beams. Coupled with the digital image correlation (DIC) technique, the fracture process of steel-fiber-reinforced HSSCC was analyzed to elucidate the reinforcing and fracture-resisting mechanisms of steel fibers. The results indicate that the compressive strength and flexural strength of HSSCC cured for 28 days exhibited an initial decrease and then an enhancement as the volume fraction (Vf) of steel fibers increased, whereas the flexural-to-compressive ratio linearly increased. All of them reached their maximum of 110.5 MPa, 11.8 MPa, and 1/9 at 1.2 vol% steel fibers, respectively. Steel fibers significantly improved the peak load (FP), peak opening displacement (CMODP), fracture toughness (KIC), and fracture energy (GF) of HSSCC. Compared with HSSCC without steel fibers (HSSCC-0), the FP, KIC, CMODP, and GF of HSSCC with 1.2 vol% (HSSCC-1.2) increased by 23.5%, 45.4%, 11.1 times, and 20.1 times, respectively. The horizontal displacement and horizontal strain of steel-fiber-reinforced HSSCC both increased significantly with an increasing Vf. HSSCC-0 experienced unstable fracture without the occurrence of a fracture process zone during the whole fracture damage, whereas the fracture process zone formed at the notched beam tip of HSSCC-1.2 at its initial loading stage and further extended upward in the beams of high-strength self-compacting concrete with a 0.6% volume fraction of steel fibers and HSSCC-1.2 as the load approaches and reaches the peak. Full article
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28 pages, 14358 KB  
Article
Three-Dimensional Mesoscopic DEM Modeling and Compressive Behavior of Macroporous Recycled Concrete
by Yupeng Xu, Fei Geng, Haoxiang Luan, Jun Chen, Hangli Yang and Peiwei Gao
Buildings 2025, 15(15), 2655; https://doi.org/10.3390/buildings15152655 - 27 Jul 2025
Cited by 1 | Viewed by 611
Abstract
The mesoscopic-scale discrete element method (DEM) modeling approach demonstrated high compatibility with macroporous recycled concrete (MRC). However, existing DEM models failed to adequately balance modeling accuracy and computational efficiency for recycled aggregate (RA), replicate the three distinct interfacial transition zone (ITZ) types and [...] Read more.
The mesoscopic-scale discrete element method (DEM) modeling approach demonstrated high compatibility with macroporous recycled concrete (MRC). However, existing DEM models failed to adequately balance modeling accuracy and computational efficiency for recycled aggregate (RA), replicate the three distinct interfacial transition zone (ITZ) types and pore structure of MRC, or establish a systematic calibration methodology. In this study, PFC 3D was employed to establish a randomly polyhedral RA composite model and an MRC model. A systematic methodology for parameter testing and calibration was proposed, and compressive test simulations were conducted on the MRC model. The model incorporated all components of MRC, including three types of ITZs, achieving an aggregate volume fraction of 57.7%. Errors in simulating compressive strength and elastic modulus were 3.8% and 18.2%, respectively. Compared to conventional concrete, MRC exhibits larger strain and a steeper post-peak descending portion in stress–strain curves. At peak stress, stress is concentrated in the central region and the surrounding arc-shaped zones. After peak stress, significant localized residual stress persists within specimens; both toughness and toughness retention capacity increase with rising porosity and declining compressive strength. Failure of MRC is dominated by tension rather than shear, with critical bonds determining strength accounting for only 1.4% of the total. The influence ranking of components on compressive strength is as follows: ITZ (new paste–old paste) > ITZ (new paste–natural aggregates) > new paste > old paste > ITZ (old paste–natural aggregates). The Poisson’s ratio of MRC (0.12–0.17) demonstrates a negative correlation with porosity. Predictive formulas for peak strain and elastic modulus of MRC were established, with errors of 2.6% and 3.9%, respectively. Full article
(This article belongs to the Special Issue Advances in Modeling and Characterization of Cementitious Composites)
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17 pages, 3437 KB  
Article
Effects of Heavy-Metal-Sludge Sintered Aggregates on the Mechanical Properties of Ultra-High-Strength Concrete
by Weijun Zhong, Sheng Wang, Yue Chen, Nan Ye, Kai Shu, Rongnan Dai and Mingfang Ba
Materials 2025, 18(14), 3422; https://doi.org/10.3390/ma18143422 - 21 Jul 2025
Viewed by 321
Abstract
To investigate the effects of heavy-metal-sludge sintered aggregates on the workability, mechanical properties, and fracture toughness of ultra-high-strength concrete (UHSC), this study systematically evaluated the influence of different aggregate replacement ratios and particle gradations on the fluidity, flexural strength, compressive strength, and fracture [...] Read more.
To investigate the effects of heavy-metal-sludge sintered aggregates on the workability, mechanical properties, and fracture toughness of ultra-high-strength concrete (UHSC), this study systematically evaluated the influence of different aggregate replacement ratios and particle gradations on the fluidity, flexural strength, compressive strength, and fracture energy of UHSC. Microstructural characterization techniques including SEM, XRD, TG, and FTIR were employed to analyze the hydration mechanism and interfacial transition zone evolution. The results demonstrated the following: Fluidity continuously improved with the increase in the sintered aggregate replacement ratio, with coarse aggregates exhibiting the most significant enhancement due to the “ball-bearing effect” and paste enrichment. The mechanical properties followed a trend of an initial increase followed by a decrease, peaking at 15–20% replacement ratio, at which flexural strength, compressive strength, and fracture energy were optimally enhanced; excessive replacement led to strength reduction owing to skeletal structure weakening, with coarse aggregates providing superior improvement. Microstructural analysis revealed that the sintered aggregates accelerated hydration reactions, promoting the formation of C-S-H gel and Ca(OH)2, thereby densifying the ITZ. This study identified 15–20% of coarse sintered aggregates as the optimal replacement ratio, which synergistically improved the workability, mechanical properties, and fracture toughness of UHSC. Full article
(This article belongs to the Section Construction and Building Materials)
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23 pages, 8675 KB  
Article
Research on the Deterioration Mechanism of PPF Mortar-Masonry Stone Structures Under Freeze–Thaw Conditions
by Jie Dong, Hongfeng Zhang, Zhenhuan Jiao, Zhao Yang, Shaohui Chu, Jinfei Chai, Song Zhang, Lunkai Gong and Hongyu Cui
Buildings 2025, 15(14), 2468; https://doi.org/10.3390/buildings15142468 - 14 Jul 2025
Viewed by 428
Abstract
Significant progress has been made in the low-temperature toughness and crack resistance of polypropylene fiber-reinforced composites. However, there is still a gap in the research on damage evolution under freeze–thaw cycles and complex stress ratios. To solve the problem of durability degradation of [...] Read more.
Significant progress has been made in the low-temperature toughness and crack resistance of polypropylene fiber-reinforced composites. However, there is still a gap in the research on damage evolution under freeze–thaw cycles and complex stress ratios. To solve the problem of durability degradation of traditional rubble masonry in cold regions, this paper focuses on the study of polypropylene fiber-mortar-masonry blocks with different fiber contents. Using acoustic emission and digital image technology, the paper conducts a series of tests on the scaled-down polypropylene fiber-mortar-masonry structure, including uniaxial compressive tests, three-point bending tests, freeze–thaw cycle tests, and tests with different stress ratios. Based on the Kupfer criterion, a biaxial failure criterion for polypropylene fiber mortar-masonry stone (PPF-MMS) was established under different freeze–thaw cycles. A freeze–thaw damage evolution model was also developed under different stress ratios. The failure mechanism of PPF-MMS structures was analyzed using normalized average deviation (NAD), RA-AF, and other parameters. The results show that when the dosage of PPF is 0.9–1.1 kg/m3, it is the optimal content. The vertical stress shows a trend of increasing first and then decreasing with the increase in the stress ratio, and when α = 0.5, the degree of strength increase reaches the maximum. However, the freeze–thaw cycle has an adverse effect on the internal structure of the specimens. Under the same number of freeze–thaw cycles, the strength of the specimens without fiber addition decreases more rapidly than that with fiber addition. The NAD evolution rate exhibits significant fluctuations during the middle loading period and near the damage failure, which can be considered precursors to specimen cracking and failure. RA-AF results showed that the specimens mainly exhibited tensile failure, but the occurrence of tensile failure gradually decreased as the stress ratio increased. Full article
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23 pages, 11832 KB  
Article
Investigation of Flexibility Enhancement Mechanisms and Microstructural Characteristics in Emulsified Asphalt and Latex-Modified Cement
by Wen Liu, Yong Huang, Yulin He, Hanyu Wei, Ruyun Bai, Huan Li, Qiushuang Cui and Sining Li
Sustainability 2025, 17(14), 6317; https://doi.org/10.3390/su17146317 - 9 Jul 2025
Viewed by 621
Abstract
The inherent limitations of ordinary cement mortar—characterized by its high brittleness and low flexibility—result in a diminished load-bearing capacity, predisposing concrete pavements to cracking. A novel approach has been proposed to enhance material performance by incorporating emulsified asphalt and latex into ordinary cement [...] Read more.
The inherent limitations of ordinary cement mortar—characterized by its high brittleness and low flexibility—result in a diminished load-bearing capacity, predisposing concrete pavements to cracking. A novel approach has been proposed to enhance material performance by incorporating emulsified asphalt and latex into ordinary cement mortar, aiming to improve the flexibility and durability of concrete pavements effectively. To further validate the feasibility of this proposed approach, a series of comprehensive experimental investigations were conducted, with corresponding conclusions detailed herein. As outlined below, the flexibility properties of the modified cement mortar were systematically evaluated at curing durations of 3, 7, and 28 days. The ratio of flexural to compressive strength can be increased by up to 38.9% at 8% emulsified asphalt content at the age of 28 days, and by up to 50% at 8% latex content. The mechanism of emulsified asphalt and latex-modified cement mortar was systematically investigated using a suite of analytical techniques: X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TG-DTG), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through comprehensive analyses of microscopic morphology, hydration products, and elemental distribution, the enhancement in cement mortar toughness can be attributed to two primary mechanisms. First, Ca2+ ions combine with the carbonyl groups of emulsified asphalt to form a flexible film structure during cement hydration, thereby reducing the formation of brittle hydrates. Second, active functional groups in latex form a three-dimensional network, regulating internal expansion-contraction tension in the modified mortar and extending its service life. Full article
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18 pages, 5009 KB  
Article
Preparation of Glass Fiber Reinforced Polypropylene Bending Plate and Its Long-Term Performance Exposed in Alkaline Solution Environment
by Zhan Peng, Anji Wang, Chen Wang and Chenggao Li
Polymers 2025, 17(13), 1844; https://doi.org/10.3390/polym17131844 - 30 Jun 2025
Viewed by 471
Abstract
Glass fiber reinforced polypropylene composite plates have gradually attracted more attention because of their repeated molding, higher toughness, higher durability, and fatigue resistance compared to glass fiber reinforced thermosetting composites. In practical engineering applications, composite plates have to undergo bending effect at different [...] Read more.
Glass fiber reinforced polypropylene composite plates have gradually attracted more attention because of their repeated molding, higher toughness, higher durability, and fatigue resistance compared to glass fiber reinforced thermosetting composites. In practical engineering applications, composite plates have to undergo bending effect at different angles in corrosive environment of concrete, including bending bars from 0~90°, and stirrups of 90°, which may lead to long-term performance degradation. Therefore, it is important to evaluate the long-term performance of glass fiber reinforced polypropylene composite bending plates in an alkali environment. In the current paper, a new bending device is developed to prepare glass fiber reinforced polypropylene bending plates with the bending angles of 60° and 90°. It should be pointed out that the above two bending angles are simulated typical bending bars and stirrups, respectively. The plate is immersed in the alkali solution environment for up to 90 days for long-term exposure. Mechanical properties (tensile properties and shear properties), thermal properties (dynamic mechanical properties and thermogravimetric analysis) and micro-morphology analysis (surface morphology analysis) were systematically designed to evaluate the influence mechanism of bending angle and alkali solution immersion on the long-term mechanical properties. The results show the bending effect leads to the continuous failure of fibers, and the outer fibers break under tension, and the inner fibers buckle under compression, resulting in debonding of the fiber–matrix interface. Alkali solution (OH ions) corrode the surface of glass fiber to form soluble silicate, which is proved by the mass fraction of glass fiber decreased obviously from 79.9% to 73.65% from thermogravimetric analysis. This contributes to the highest degradation ratio of tensile strength was 71.6% (60° bending) and 65.6% (90° bending), respectively, compared to the plate with bending angles of 0°. A high curvature bending angle (such as 90°) leads to local buckling of fibers and plastic deformation of the matrix, forming microcracks and fiber–resin interface bonding at the bending area, which accelerates the chemical erosion and debonding process in the interface area, bringing about an additional maximum 10.56% degradation rate of the shear strength. In addition, the alkali immersion leads to the obvious degradation of storage modulus and thermal decomposition temperature of composite plate. Compared with the other works on the long-term mechanical properties of glass fiber reinforced polypropylene, it can be found that the long-term performance of glass fiber reinforced polypropylene composites is controlled by the corrosive media type, bending angle and immersion time. The research results will provide durability data for glass fiber reinforced polypropylene composites used in concrete as stirrups. Full article
(This article belongs to the Section Polymer Composites and Nanocomposites)
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22 pages, 6793 KB  
Article
Effect of Nano-Modified Recycled Wood Fibers on the Micro/Macro Properties of Rapid-Hardening Sulfoaluminate Cement-Based Composites
by Chunyu Ma, Liang Wang, Yujiao Li, Qiuyi Li, Gongbing Yue, Yuanxin Guo, Meinan Wang and Xiaolong Zhou
Nanomaterials 2025, 15(13), 993; https://doi.org/10.3390/nano15130993 - 26 Jun 2025
Viewed by 470
Abstract
Recycled wood fiber (RWF) obtained through the multi-stage processing of waste wood serves as an eco-friendly green construction material, exhibiting lightweight, porous, and high toughness characteristics that demonstrate significant potential as a cementitious reinforcement, offering strategic advantages for environmental protection and resource recycling. [...] Read more.
Recycled wood fiber (RWF) obtained through the multi-stage processing of waste wood serves as an eco-friendly green construction material, exhibiting lightweight, porous, and high toughness characteristics that demonstrate significant potential as a cementitious reinforcement, offering strategic advantages for environmental protection and resource recycling. In this study, high-performance sulfoaluminate cement (SAC)-RWF composites prepared by modifying RWFs with nano-silica (NS) and a silane coupling agent (KH560) were developed and their effects on mechanical properties, shrinkage behavior, hydration characteristics, and microstructure of SAC-RWF composites were systematically investigated. Optimal performance was achieved at water–cement ratio of 0.5 with 20% RWF content, where the KH560-modified samples showed superior improvement, with 8.5% and 14.3% increases in 28 d flexural and compressive strength, respectively, compared to the control groups, outperforming the NS-modified samples (3.6% and 8.6% enhancements). Both modifiers improved durability, reducing water absorption by 6.72% (NS) and 7.1% (KH560) while decreasing drying shrinkage by 4.3% and 27.2%, respectively. The modified SAC composites maintained favorable thermal properties, with NS reducing thermal conductivity by 6.8% through density optimization, whereas the KH560-treated specimens retained low conductivity despite slight density increases. Micro-structural tests revealed accelerated hydration without new hydration product formation, with both modifiers enhancing cementitious matrix hydration product generation by distinct mechanisms—with NS acting through physical pore-filling, while KH560 established Si-O-C chemical bonds at paste interfaces. Although both modifications improved mechanical properties and durability, the KH560-modified SAC composite group demonstrated superior overall performance than the NS-modified group, providing a technical pathway for developing sustainable, high-performance recycled wood fiber cement-based materials with balanced functional properties for low-carbon construction applications. Full article
(This article belongs to the Special Issue Nanocomposite Modified Cement and Concrete)
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40 pages, 4122 KB  
Article
Stress–Strain Relationship of Rubberized Geopolymer Concrete with Slag and Fly Ash
by Sunday U. Azunna, Farah N. A. A. Aziz, Raizal S. M. Rashid and Ernaleza B. Mahsum
Constr. Mater. 2025, 5(3), 42; https://doi.org/10.3390/constrmater5030042 - 25 Jun 2025
Cited by 1 | Viewed by 676
Abstract
Rubberized concrete is a more environmentally friendly material than natural concrete as it helps to reduce rubber disposal issues and has superior impact resistance. Geopolymer concrete, on the other hand, is an economical concrete with higher mechanical properties than nominal concrete that uses [...] Read more.
Rubberized concrete is a more environmentally friendly material than natural concrete as it helps to reduce rubber disposal issues and has superior impact resistance. Geopolymer concrete, on the other hand, is an economical concrete with higher mechanical properties than nominal concrete that uses fly ash and slag, among other industrial solid wastes, to lower carbon footprints. Rubberized geopolymer concrete (RuGPC) combines the advantages of both concrete types, and a thorough grasp of its dynamic compressive characteristics is necessary for its use in components linked to impact resistance. Despite the advantages of RuGPC, predicting its mechanical characteristics is sometimes difficult because of variations in binder type and combination. This research investigated the combined effect of ground granulated blast furnace slag (GGBFS) and fly ash (FA) on the workability, compressive strength, and stress–strain characteristics of RuGPC with rubber at 0%, 10%, and 20% fine aggregate replacement. Thereafter, energy absorption and ductile characteristics were evaluated through the concrete toughness and ductility index. Numerical models were proposed for the cube compressive strength, modulus of elasticity, and peak strain of RuGPC at different percentages of crumb rubber. It was found that RuGPC made with GGBFS/FA had similar stress–strain characteristics to FA- and MK-based RuGPC. At 20% of crumb rubber aggregate replacement, the workability, compressive strength, modulus of elasticity, and peak stress of RuGPC reduced by 8.33%, 34.67%, 43.42%, and 44.97%, while Poisson’s ratio, peak, and ultimate strain increased by 30.34%, 8.56%, and 55.84%, respectively. The concrete toughness and ductility index increased by 22.4% and 156.67%. The proposed model’s calculated results, with R2 values of 0.9508, 0.9935, and 0.9762, show high consistency with the experimental data. RuGPC demonstrates high energy absorption capacity, making it a suitable construction material for structures requiring high-impact resistance. Full article
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