Impacts of Water Saturation on the Mechanical Behavior of Basalt/Glass Fiber-Reinforced Recycled Aggregate Concrete Under Varying Stresses: Insights from Macro and Micro Perspectives
Recycled aggregate concrete (RAC) offers an effective approach to reducing the environmental burden associated with construction and demolition waste. In this study, a fiber-reinforced RAC was developed by replacing part of the cement with fly ash and ground granulated blast-furnace slag, while glass fibers or basalt fibers were incorporated as reinforcing materials. A systematic experimental program was conducted to evaluate the mechanical behavior of the proposed concrete under different saturation conditions. The results show that the best toughness performance was achieved in the natural moisture state. In comparison, compressive and flexural strengths reached their maximum values under dry conditions, whereas splitting tensile strength peaked in the natural state. Based on the experimental data, prediction equations were established for the splitting tensile and flexural strengths by considering both saturation degree and fiber content. A stress–strain model under uniaxial compression was also developed. In addition, scanning electron microscopy (SEM) was employed to examine the fiber–matrix interface and hydration products, thereby clarifying the microstructural characteristics of the concrete at different saturation levels.
The construction industry's reliance on ordinary Portland cement (OPC) is a major contributor to global anthropogenic CO₂ emissions, while plain concrete's inherent brittleness and low tensile capacity remain persistent structural limitations. This study presents an experimental investigation into a sustainable hybrid fiber-reinforced concrete (HFRC) of M30 grade, formulated by partially replacing cement with Ground Granulated Blast Furnace Slag (GGBS, 20–50% by weight) and silica fume (5–25% by weight), together with a fixed 2% (by volume of coarse aggregate) hybrid dosage of steel and polypropylene fibers. Six mix combinations were cast and evaluated for compressive, flexural, and split tensile strength at 7, 14, 28, and 60 days of water curing. Compressive strength increased consistently with binder replacement up to 50% GGBS and 20% silica fume, after which higher silica fume content (25%) reduced strength due to workability loss and particle agglomeration. The mix containing 50% GGBS, 20% silica fume, and 2% hybrid fiber (designated M5) produced the best overall performance, reaching 36 MPa compressive strength, 5.3 MPa flexural strength, and 4.1 MPa split tensile strength at 28 days, rising further to 40 MPa, 5.7 MPa, and 4.5 MPa respectively at 60 days. Relative to the mix with the lowest replacement level (M1: 20% GGBS, 5% silica fume), mix M5 showed gains of approximately 24% in compressive strength, 29% in flexural strength, and 41% in split tensile strength at 28 days. The results confirm that the combined pozzolanic action of silica fume and GGBS densifies the cementitious matrix, while the hybrid steel–polypropylene fiber system restrains crack propagation and improves post-cracking ductility. The study establishes 50% GGBS with 20% silica fume and 2% hybrid fiber as the optimum replacement level for producing high-performance, low-carbon M30 structural concrete.
Keywords: Sustainable concrete; Hybrid fiber reinforcement; Ground Granulated Blast Furnace Slag (GGBS); Silica fume; Compressive strength; Flexural strength; Split tensile strength.
Dasari Devika, Dr. Subash Chandra Bose· International Journal of Cre...· 0 citations
This study investigates the strength development, crack evolution and toughening mechanism of basalt fiber-reinforced desert sand high-strength concrete. An L9(33) orthogonal design was first used to optimize the reference mixture, after which basalt fibers with volume fractions of 0, 0.3%, 0.4% and 0.5% were incorporated. Mechanical testing, digital image correlation, SEM, XRD, TG and FTIR were combined to clarify the relationship among fiber dosage, crack propagation and microstructural reinforcement mechanisms. The optimized matrix mixture was obtained with a water-to-binder ratio of 0.32, a desert sand replacement ratio of 40% and a fly ash content of 20%. The incorporation of basalt fiber had little influence on the 28 d compressive strength, whereas the splitting tensile strength was markedly improved. The highest splitting tensile strength was observed in the 0.4% fiber group, reaching 5.46 MPa, which was 12.81% higher than that of the reference mixture. DIC results showed that basalt fiber reduced strain localization and limited crack opening. The 0.5% group had the lowest COD, while the 0.4% group showed a better balance among tensile strength, strain redistribution and crack-opening control. SEM observations showed fiber bridging and fiber–matrix interaction near the fracture region. Meanwhile, XRD, TG-DTG and FTIR showed no obvious changes in the main phases or functional groups, indicating that the improvement was mainly related to the physical crack-control effect of basalt fibers rather than chemical modification of the matrix. Overall, 0.4% basalt fiber was identified as the preferred dosage for the present system.
Peng-Yu Wang, Qiao-Xia An, Ling-Yan Xu et al.· Materials· 0 citations
This study investigates the combined use of waste glass aggregate (WGA, 0–60% volumetric replacement of natural coarse aggregate) and silica fume (SF, 0–15% replacement of cement) in steel fiber-reinforced self-compacting concrete. The experimental program covered fresh, mechanical, and durability properties, along with production cost, embodied CO₂, and scanning electron microscopy (SEM) observations. The results showed that 15% SF improved strength and durability, whereas WGA contents above 45% reduced fresh performance. The optimum mixture, containing 15% SF and 30% WGA, increased the 90-day compressive, splitting-tensile, and flexural strengths by 23.72%, 28.90%, and 16.50%, respectively, compared with the control. This mixture also maintained surface water absorption below 7.81% and ultrasonic pulse velocity (UPV) values of 3532–3974 m/s. Even at 60% WGA and 15% SF, production cost and embodied CO₂ were reduced by 4.59% and 5.03%, respectively. SEM observations showed that high WGA contents increased voids, microcracks, and ettringite formation, which contributed to strength loss. Gene Expression Programming (GEP) models were developed using WGA, SF, and durability-related indicators as input variables. The models showed reliable predictive performance for strength, absorption, and water penetration depth. Overall, the findings support the practical use of WGA and SF for producing more sustainable and cost-effective self-compacting concrete.
N. Safaeian Hamzehkolaei, Iman Afshoon, Amirhossein Davarpanah Tanha Ghochan· Multiscale and Multidiscipli...· 1 citation
The shift from Ordinary Portland Cement (OPC) to geopolymer concrete offers significant environmental advantages. However, its application to shear-critical structural elements, such as reinforced deep beams, remains insufficiently researched. This experimental study investigates the mechanical properties and structural performance of Ground Granulated Blast-furnace Slag (GGBS)-fly ash geopolymer concrete with alkaline liquid-to-geopolymer (AL/GS) ratios of 0.7, 0.8, and 0.9. The compressive strength, indirect tensile strength, and behavior of reinforced deep beams were evaluated under ambient and heat-cured conditions. The results showed that an AL/GS ratio of 0.7 yielded the highest compressive strength, 65.7 MPa at 90 days, under ambient curing. The deep beam tests revealed that a reduction in the 28-day compressive strength from 59 MPa (AL/GS = 0.7) to 42 MPa (AL/GS = 0.9) caused a dramatic 68% drop in the ultimate load-carrying capacity (from 325 to 108 kN). This pronounced sensitivity is attributed to the primary strut-and-tie mechanism, where higher compressive strength significantly enhances the efficiency of the concrete strut. The geopolymer concrete also exhibited more brittle tensile behavior compared to conventional predictive models. These findings highlight the importance of optimizing the AL/GS ratio to achieve high and uniform compressive strength for the safe structural application of GGBS-fly ash geopolymer concrete in shear-critical structural members.
Nguyen Thien Thanh, Tran Cao Thanh Ngoc, N. T. Khoa et al.· Engineering, Technology &...· 0 citations
ABSTRACT Alkali-activated materials (AAM), which are derived from aluminosilicate substances and activators, represent a sustainable and low-carbon alternative to ordinary Portland cement (OPC). The incorporation of fibers helps mitigate brittleness and enhance toughness. An orthogonal experimental approach was used to systematically examine the impact of silica fume (SF) content, the volume fraction of basalt fiber (BF) and polypropylene fiber (PPF), and alkali contents on the mechanical properties of slag-based cementitious materials. The synergistic enhancement mechanism of SF modification and its combination with hybrid fibers were revealed through macroscopic mechanical testing, digital image correlation (DIC) for deformation field analysis, pore structure testing, and microstructural observation. The orthogonal experimental results indicated that the optimal mix ratio for comprehensive mechanical properties was SF of 6 wt.%, BF of 0.2 vol.%, PPF of 0.1 vol.%, and alkali of 9 wt.%. Under this optimal mix ratio, the uniaxial compressive and splitting tensile properties were significantly improved compared to the control group. Combined SF and hybrid fibers promoted crack propagation and multi-cracking. DIC results demonstrated that hybrid fibers effectively redistributed strain concentration and delayed crack initiation. Microstructural analysis shows that SF optimizes pore distribution through physical filling and participates in chemical reactions to form C-A-S-H gel. Fibers acted to hinder crack propagation and bridge cracks. The synergy not only reduced harmful pores in the matrix but also promoted microstructural densification, thereby significantly enhancing the mechanical properties of the material.
The replacement of conventional aggregates in concrete with alternative and waste-based materials has become an important research area for sustainable construction. This study experimentally investigated the effects of natural perlite aggregate replacement and fiber reinforcement on the mechanical and microstructural properties of concrete. Natural perlite aggregate was used to replace conventional crushed stone aggregate at replacement levels of 0%, 30%, 70%, and 100%, while hemp shives, recycled plastic waste fibers, and polypropylene (PP) fibers were incorporated at volume fractions of 0.0%, 0.5%, 1.0%, and 1.5%. After 28 days of curing, compressive strength, modulus of elasticity, flexural strength, splitting tensile strength, ultrasonic pulse velocity (UPV), compressive stress–strain behavior, and scanning electron microscopy (SEM) analyses were performed. The results showed that 30% perlite replacement increased the compressive strength and modulus of elasticity by approximately 6.67% and 4.08%, respectively, compared with the reference mixture. In contrast, replacement levels of 70% and 100% reduced the mechanical performance due to the porous structure of perlite and the weaker interfacial transition zone. Among the fiber-reinforced mixtures, the optimum fiber content was found to be 1.0%, while PP fibers provided the best overall performance in terms of crack-bridging ability and energy absorption. Overall, the combination of 30% natural perlite aggregate replacement and 1.0% PP fiber was identified as an effective approach for producing low-carbon concrete with balanced mechanical properties.