• Advances in nano research
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• v.15 no.5
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• pp.467-484
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• 2023

Despite the significant features of fiber-reinforced cementitious composites (FRCCs), including better mechanical, fractural, and durability performance, their high content of cement has restricted their use in the construction industry. Although ground granulated blast furnace slag (GGBFS) is considered the main supplementary cementitious material, its slow pozzolanic reaction stands against its application. The addition of nano-sized mineral modifiers, including nano-silica (NS), is an alternative to address the drawbacks of using GGBFS. The main object of this empirical and numerical research is to examine the effect of NS on the strain-hardening behavior of cementitious composites; ten mixes were designed, and five levels of NS were considered. This study proposes a new method, using a four-point bending test to assess the use of nano-silica (NS) on the flexural behavior, first cracking strength, fracture energy, and micromechanical parameters including interfacial friction bond strength and maximum bridging stress. Digital image correlation (DIC) was used for monitoring the initiation and propagation of the cracks. In addition, to attain a deep comprehension of fiber/matrix interaction, scanning electron microscope (SEM) analysis was used. It was discovered that using nano-silica (NS) in cementitious materials results in an enhancement in the matrix toughness, which prevents multiple cracking and, therefore, strain-hardening. In addition, adding NS enhanced the interfacial transition zone between matrix and fiber, leading to a higher interfacial friction bond strength, which helps multiple cracking in the composite due to the hydrophobic nature of polypropylene (PP) fibers. The findings of this research provide insight into finding the optimum percent of NS in which both ductility and high tensile strength of the composites would be satisfied. As a concluding remark, a new criterion is proposed, showing that the optimum value of nano-silica is 2%. The findings and proposed method of this study can facilitate the design and utilization of green cementitious composites in structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.81-90
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• 2008

This paper concerns the flexural capacity of reinforced concrete beams with ultra-high performance cementitious composites(UHPCC). It was investigated if the existing equations to estimate the flexural capacity of reinforced fiberous concrete beams are applicable with the experiments including lightly reinforced concrete beams. The reinforcing effect when the steel fiber reinforced concrete was used in beams was also estimated. The results showed that the equation to predict the flexural capacity of reinforced steel fiber concrete by ACI 544 committee didn't have a good agreement with the test results and underestimated the flexural capacity in especially lightly reinforced beams with under 1.5% reinforcement ratio. the enhancement of flexural capacity was quite considerable in lightly reinforced beams when the steel fiber reinforced concrete was used. A equation to predict the reinforcing effect of steel fiber in reinforced steel fiber beams was developed. the equation was proposed as a function of both the characteristics of steel fiber and reinforcement ratio.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.29-32
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• 2004

An experimental investigation of the behavior of steel cords(SC) and SC and Polyethylene(PE) hybrid fiber reinforced cementitious material under compressive and tensile loading is presented. In this experimental research, the tensile and compressive strength and strain capacity of high performance fiber-reinforced cementitious composites(HPFRCC) were selected using the cylindrical specimens. Uniaxial compressive and tensile tests have also been carried out at varying strain rates to better understand the behavior of. HPFRCC and propose the standard loading rate for compressive and tensile tests of new HPFRCC materials. The results show that there is a substantial increase in the ultimate compressive and tensile strength with increasing strain rate.

• Advances in concrete construction
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• v.12 no.6
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• pp.451-459
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• 2021

The mechanical behaviors and chloride resistance performance of fiber reinforced cementitious composites (FRCC) with hybrid polyethylene (PE) and steel fiber (in total 2% by volume) were investigated. Based on micro-mechanics and fracture mechanics, the reason why the tensile strain capacity of FRCC changed obviously was obtained. Besides, the effects of the total surface area of fiber in FRCC on compressive strength and chloride content were clarified. It is found that the improvement of the tensile strain capacity of FRCC with hybrid fiber is attributed to the growth of strain-hardening performance index (the ratio of complementary energy to crack tip toughness). As the total surface area of fiber related with the interfacial transition zone (ITZ) between fiber and matrix increases, compressive strength decreases obviously. Since the total surface area of fiber is small, the chloride resistance performance of FRCC with hybrid PE and steel fiber is better than that of FRCC containing only PE fiber.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.101-109
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• 2008

Many researchers have reported that adding steel fiber to concrete improved its tensile and flexural strength significantly, but relatively few studies have been made on the compressive behavior of steel fiber-reinforced concrete. It is still less in case of high strength steel fiber-reinforced cementitious composites(SFRC). The main objective of this research is to examine the effect of adding steel fiber on the compressive strength of high strength SFRC using fiber reinforcing index(RI, $V_f(I_f/d_f)$). It was found from the study that compressive strength was noticeably increased in proportion to RI. In conclusion, the relationship between Reinforcing Index(RI) and compressive strength in case of high strength steel fiber-reinforced cementitious composites was suggested.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.577-580
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• 2004

Recently, DFRCCs (Ductile Fiber Reinforced Cementitious Composites), materials with remarkable ductility when compared to ordinary fiber-reinforced concrete (FRC), have been developed and studied actively in the US, Japan, and many European countries. The transformation of failure behavior from brittle to ductile is achieved by incorporating with fracture mechanics concept especially micro-mechanical models approach of cementitious composite materials in manufacturing ordinary fiber-reinforced composites. The purpose of this study is to accurately understand the shear behavior of DFRCC repaired RC beams. Using a four-point bending test, the shear strengths and shear stress-deflection relations of DFRCC repaired RC specimens are obtained. The results show that DFRCC can be effectively used for repairing materials for concrete structures.

• Earthquakes and Structures
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• v.14 no.3
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• pp.261-271
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• 2018

Fiber reinforced cementitious composites (FRCC) materials that exhibit strain-hardening and multiple cracking properties under tension were recently developed as innovative building materials for construction. This study aims at exploring the use of FRCC on the seismic performance of coupling beams with conventional reinforcement. Experimental tests were conducted on seven FRCC precast coupling beams with small span-to-depth ratios and one ordinary concrete coupling beam for comparison. The crack and failure modes of the specimens under the low cycle reversed loading were observed, and the hysteretic characteristics, deformation capacity, energy dissipation capacity and stiffness degradation were also investigated. The results show that the FRCC coupling beams have good ductility and energy dissipation capacities compared with the ordinary concrete coupling beam. As the confinement stirrups and span-to-depth ratio increase, the deformation capacity and energy dissipation capacity of coupling beams can be improved significantly. Finally, based on the experimental analysis and shear mechanism, a formula for the shear capacity of the coupling beams with small span-to-depth ratios was also presented, and the calculated results agreed well with the experimental results.

• Computers and Concrete
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• v.29 no.5
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• pp.347-360
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• 2022

Fiber-reinforced cementitious composites (FRCC) have emerged as a response to the calls for strong, ductile and sustainable concrete mixes. FRCC has shown outstanding mechanical properties and ductility where special fibres are used in the mixes to give it the strength and the ability to exhibit strain hardening. With the possibility of designing the FRCC mixes to include sustainable constituents and by-products materials such as fly ash, FRCC started to emerge as a green alternative as well. To be able to design mixes that achieve these conflicting properties in concrete, there is a need to understand the composition effect on FRCC and optimize these compositions. Therefore, this paper aims to investigate the influence of FRCC compositions on the properties of fresh and hardened of FRCC and then to optimize these mix compositions using factorial design approach. Three factors, water-to-binder ratio (w/b), mineral admixtures (total of fly ash and metakaolin by cement content (MAR)), and metakaolin content (MK), were investigated to determine their effects on the properties of fresh and hardened FRCC. The results show the importance of combining both FA and MK in obtaining a satisfactory fresh and mechanical properties of FRCC. Models were suggested to elucidate the role of the studied factors and a method for optimization was proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.625-628
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• 2006

In this study, the beam which is repaired as high toughness cementitious composites evaluated on flexural performance. As for the test results, it was found that high toughness performance of beams of the repair as high toughness cementitious composites showed more better than the existing repair method and demonstrated about 95% semi-reinforcement to compare with reinforcement of carbon fiber sheets of one layer without interface and brittle failure. Therefore, appling on using PVA fiber reinforced high toughness cementitious composites, the repaired concrete structures can be increased to flexural performance.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.323-330
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• 2023

The development of an analysis model that reflects the microstructure characteristics of polyvinyl alcohol (PVA) fiber-reinforced cementitious composites, which have a highly complex microstructure, enables synergy between efficient material design and real experiments. PVA fiber orientations are an important factor that influences the mechanical behavior of PVA fiber-reinforced cementitious composites. Owing to the difficulty in distinguishing the gray level value obtained from micro-CT images of PVA fibers from adjacent phases, fiber segmentation is time-consuming work. In this study, a micro-CT test with a voxel size of 0.65 ㎛³ was performed to investigate the three-dimensional distribution of fibers. To segment the fibers and generate training data, histogram, morphology, and gradient-based phase-segmentation methods were used. A U-net model was proposed to segment fibers from micro-CT images of PVA fiber-reinforced cementitious composites. Data augmentation was applied to increase the accuracy of the training, using a total of 1024 images as training data. The performance of the model was evaluated using accuracy, precision, recall, and F1 score. The trained model achieved a high fiber segmentation performance and efficiency, and the approach can be applied to other specimens as well.