A Comparative Study on Crack-bridging and Microstructural Densification Mechanisms Governing the Mechanical Properties of Fly-ash-based M25 Concrete Modified with MWCNT AND SiO2 NPS
Jun 2026· Journal of Environmental Nanotechnology· Vol 15, pp. 616-631· 0 citations
Abstract
This study examines the mechanical, microstructural, and hydration-related improvements in concrete modified with fly ash, multi-walled carbon nanotubes (MWCNTs), and nano silica. A comprehensive experimental program, comprising compressive, split tensile, and flexural strength tests along with SEM and XRD analyses, was conducted to evaluate the combined and individual effects of these additives. Fly ash improved the sustainability and long-term performance of concrete through its pozzolanic reaction, although its early-age strength contribution remained moderate. The inclusion of MWCNTs produced the most pronounced mechanical enhancements, with the 0.45% dosage yielding peak strength values due to efficient crack-bridging, improved stress transfer, and accelerated hydration. Nano silica also contributed to performance enhancement by refining pore structure and promoting the formation of a dense C–S–H matrix, with strength increasing progressively with higher dosages. The SEM images confirmed the development of a dense and compact microstructure, while XRD patterns displayed reduced portlandite peaks and enhanced amorphous C–S–H formation in nano-modified mixes. The findings demonstrate that nano-engineered additives, especially MWCNTs, significantly enhance the microstructure, mechanical strength, and durability of the concrete, highlighting their potential for producing high-performance and advanced composite materials.
To improve the mechanical performance and crack resistance of coal gangue–slag geopolymer concrete, basalt fiber-reinforced geopolymer concrete was prepared using calcined coal gangue powder and slag as composite precursors. The effects of nano-SiO2 dosage on strength, water absorption, and crack evolution under splitting tensile loading were investigated. Digital image correlation (DIC), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were further employed to characterize the crack evolution and microstructural changes associated with nano-SiO2 incorporation. The results show that the performance of the specimens was strongly dependent on the nano-SiO2 dosage, with the NS0.5 mixture (0.5% nano-SiO2) exhibiting the most pronounced improvement. Compared with the reference mixture, the 28 d compressive strength and splitting tensile strength of NS0.5 reached 86.80 MPa and 6.02 MPa, corresponding to increases of 17.67% and 39.97%, respectively; meanwhile, the 24 h water absorption decreased from 4.78% to 4.25%. The DIC results indicate that 0.5% nano-SiO2 delayed the localization of maximum principal strain and the penetration of the main crack, reducing the peak crack width from 0.487 mm to 0.222 mm, with a reduction of 54.4%. The microstructural results show that an appropriate nano-SiO2 dosage reduced the total porosity from 13.93% to 5.03%, shifted the pore structure from macropore-dominated to fine-pore-dominated, and decreased the proportion of coarse connected pores and crack-like pores. In contrast, the reduced enhancement observed at higher nano-SiO2 dosages may be associated with poorer nanoparticle dispersion and increased local heterogeneity, although particle agglomeration was not directly verified in this study. Overall, the improvements obtained with 0.5% nano-SiO2 are directly consistent with matrix densification and pore-structure refinement. Micro-filling, heterogeneous nucleation, and additional gel formation are proposed as plausible contributing mechanisms rather than directly verified processes.
Weizi Wang, Lianyong Zhu, Tao Li et al.· Materials· 1 citation
This study investigates the influence of high-entropy oxide (HEO) fine powder with submicron agglomerates (Mg₀.₂Ni₀.₂Co₀.₂Cu₀.₂Zn₀.₂O) on the mechanical performance, microstructural development, and durability characteristics of cement-based mortars. HEO was synthesized via a modified sol–gel method and incorporated into mortar mixtures as an additional additive at dosages of 0–1.0 wt% relative to the cement content. The experimental results demonstrate a strong dosage-dependent behavior. The optimum performance was obtained at 0.25 wt% HEO, where compressive and flexural strengths increased by up to approximately 3–4% compared to the control sample. In contrast, higher dosages (≥ 0.75 wt%) resulted in a gradual reduction in mechanical performance, indicating a threshold beyond which HEO begins to negatively affect hydration-related processes. Microstructural analysis (XRD and SEM–EDS) revealed that HEO particles contribute to matrix densification through a filler effect and act as nucleation sites for hydration products, leading to a more compact cementitious structure at optimal content. However, excessive incorporation appears to disrupt hydration continuity due to particle agglomeration and dilution effects. Durability tests showed improved resistance to water absorption, chloride ion penetration, and corrosion current with increasing HEO content, attributed to pore refinement and reduced ion transport pathways. The most balanced performance in both mechanical and durability properties was achieved at low HEO dosage. Overall, high-entropy oxides demonstrate significant potential as nano-scale additives for cementitious systems; however, their effectiveness is highly dependent on dosage, with low replacement levels providing the most beneficial performance balance.
Mustafa Eken, H. Eskalen, Hakan Yaykaşlı· Scientific Reports· 0 citations
As modern civil engineering demands increasingly higher strength, toughness, and long-term stability from concrete materials, the performance limitations of ordinary concrete in complex service environments have become increasingly apparent. The dual-blending modification of nanomaterials and steel fibers (SF) has emerged as an effective technical approach to overcome these limitations. The ratio design of the TiC-NC-SF dual-blending system has largely relied on empirical methods, lacking systematic quantitative optimization. The synergistic mechanisms among multiple factors remain unclear, hindering the engineering application of modified concrete. This study employs Box-Behnken experimental design and response surface methodology to systematically investigate the influence patterns of three factors on concrete's 28-day compressive strength, splitting tensile strength, and flexural strength. Scanning electron microscopy (SEM) characterization reveals microstructural mechanisms, while model optimization validates optimal ratios. Results indicate the dominance order of the three factors on concrete mechanical properties is SF > NC > TiC (with NC and TiC having similar effects on compressive strength). A significant synergistic enhancement effect exists between TiC and NC (interaction term P < 0.05). Both TiC and NC enhance concrete strength by optimizing matrix density through "hydration regulation and multi-level filling," while SF dominates crack control via "bridging crack propagation and energy dissipation toughening." No significant interaction was observed between TiC-SF or NC-SF (P > 0.05). Concrete compressive strength exhibits a quadratic variation with increasing dosage of all three factors, with SF exerting greater influence on splitting tensile strength and flexural strength. The response surface model optimization yielded the optimal mix design of TiC 2.12%, NC 2.14%, and SF 1.19%. Its 28-day compressive strength, splitting strength, and flexural strength reached 69.83 MPa, 7.22 MPa, and 9.34 MPa, respectively (measured values). The response surface optimization values were 70.50 MPa, 7.52 MPa, and 9.60 MPa, respectively. According to the experimental results, these values increased by 22.66%, 26.44%, and 15.02%, respectively, compared with the control group (CG). The performance deviation from the optimal experimental group was less than 0.5%, and the deviation from the optimization target was within 10%. SEM characterization revealed that the cement matrix in the CN10 and CN18 groups exhibited significantly higher densification than the CG group, with SF tightly bonded to the matrix interface.
Tian Bai, Xin Yang, Zhengjun Wang et al.· Scientific Reports· 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
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.
Jie Zhou, Tengfei Guo, Xiang Li et al.· Buildings· 0 citations
To mitigate the inherent drawbacks of Recycled Aggregate Concrete (RAC) produced from Construction and Demolition Waste (C&DW)—such as relatively low strength and pronounced microstructural defects—this study proposes the incorporation of a low content of Flake Graphite Powder (GP) to improve its mechanical properties. Through uniaxial compressive, splitting tensile, and three-point bending tests coupled with Acoustic Emission (AE) monitoring, the effects of varying GP contents on RAC’s strength, fracture toughness, and damage modes were investigated. Results reveal a non-monotonic effect of GP on concrete mechanical properties—enhancing them at low dosages but degrading them at high dosages. Notably, GP yields a significantly greater improvement in RAC compared to Natural Aggregate Concrete (NAC). With the addition of 1.0 wt% GP, the compressive strength and splitting tensile strength of RAC increase by 14.71% and 27.18%, respectively. Microstructural analysis reveals that GP improves interfacial bonding by filling surface pores and forming reinforcing elements within the Interfacial Transition Zone (ITZ). Furthermore, the bridging effect and crack deflection mechanism of the graphite platelets significantly enhance the fracture energy. AE parameters indicate that an optimal dosage of GP induces a transition in the failure mode of RAC from sudden brittle failure to a more progressive, damage-tolerant failure process, substantially broadening the pre-peak damage evolution interval. This study not only demonstrates the simultaneous enhancement of the strength and toughness of recycled concrete, but also provides a theoretical basis and technical pathway for the high-value utilization of construction and demolition waste.
Wei He, Bin Wang, Lei He et al.· Journal of composite materia...· 0 citations