Vol.37/No.2 (144) (2022)

Vol.37/No.2(144) (2022)

Special Issue: Advanced Concrete 
Guest Editor: Chung-Chan Hung

TitleStudy on Seismic Retrofit of Concrete Frames using High-strength Fiber Resin Mortar
AuthorFu-Pei Hsiao, Pu-Wen Weng, Chia-Chen Lin, Takanori Kawamoto, Yi-Ching Lin, Asahi Oogami, Chia-Yi Ho
KeywordsHigh-strength Fiber Resin Mortar, Earthquake-proof Furniture, Seismic Assessment and Retrofitting
AbstractThe traditional seismic retrofitting methods often affect the regular operation of the building, and it takes a lot of time during the construction period. So it isn’t easy to carry out reinforcement work in private houses. This research aims to develop seismic retrofitting methods, so we use high-strength fiber resin mortar for existing reinforced concrete structures. It can effectively improve the performance of seismic retrofitting methods. By using the high-strength fiber resin mortar, its expected strength can be achieved within two weeks. Therefore, it takes just a small impact during construction, which does not affect the existing functions of the building. It has high application value for hospitals, commercial buildings, and private residences. In this research, the different kinds of seismic retrofitting methods will be tested at the NCREE Laboratory. There are three kinds of seismic retrofitting methods, such as steel frame bracing, shear wall, stub column. The experimental specimens were tested in horizontally cyclic loading to compare the seismic behavior and the difference of seismic retrofitting methods. It uses popular seismic assessment methods for each test and compares them with the experimental results in this research.
TitleFeasibility study on the Early-High-Strength
Repairing Geopolymer Materials at Bridge Expansion Joints
AuthorMohammad Rizwan Bhina, Kuang-Yen Liu, Chih-Ta Tsai
KeywordsGeopolymer material, early-high-strength, rapid repairing, expansion joint.
AbstractGlobal warming has become a serious issue worldwide and it was evident that the greenhouse gases are mainly responsible for global warming. CO2 is considered as the major greenhouse gas. Among all the industries, cement industries contributed 5-7 ℅ CO2 emissions to the environment. Demand for concrete is increasing by 3% per year as concrete is the material used worldwide next to the water. If the engineering materials can be exempted from the use of cement, the purpose of carbon reduction can be achieved. Additionally, expansion joints play an important role in the stability of the bridge deck and also in accommodating thermal, lateral, and rotational moments. Hence, bridge industries demanded a high-strength, rapid setting material to replace the joints quickly and reopen the traffic. Considering all these issues, the early-high-strength repairing geopolymer material by using fly-ash and ground granulated blast-furnace slag (GGBS) are developed in this study. The high calcium inorganic polymer material was prepared by mixing fly-ash (Class-F) and GGBS (S4000) as a bonding agent with a varied ratio, NaOH alkali solution with 10 molarity (SiO2/Na2O=1.28) as an activator and pre-heated river sand as a fine aggregate to enhance the polymerization reaction. The main objectives of the present investigation were to develop a high strength geopolymer material (GPM) to provide 35MPa in 5 hours and examined the properties with regard to the effect of pre-heated fine aggregate, compressive strength (hot air-cured for 1,3 and 5 hours) and bond strength of GPM with ultra-high-performance material (UHPM) as well as high-strength non-shrinkage material (HS-NSM) from the slant shear test. The experiment was also carried out by varying the fly-ash to GGBS ratio and water to NaOH ratio. A total of 36 GPM specimens with an aspect ratio of 1 were tested. Results revealed that the hot mix procedure of GPM with the fly-ash to GGBS and water to NaOH ratio 1:3 and 10%, respectively produced greater compressive strength (52.67 MPa/5 hours) and fly-ash to GGBS and water to NaOH ratio 1:2 and 10%, respectively indicated excellent bond strength of 34.93 MPa. Results of the present investigation revealed that by increasing the amount of GGBS, the initial and final setting time and the flow rate of GPM have decreased. It was suggested that by applying GPM on the actual construction site, strength and workability should be considered simultaneously.
TitleA Study on the Static and Dynamic Mechanical Behaviors of Recycled Carbon Fiber Reinforced Concrete
AuthorYeou-Fong Li, Jin-Yuan Syu, Shu-Mei Chang, Ming-Yuan Shen, Fa-Jun Huang, Li-Chen Lin, Pei-Jun Huang, Jia-Lu Yu
KeywordsRecycled carbon fiber, microwave-assisted pyrolysis, carbon fiber concrete
AbstractFiber reinforced concrete can improve the flexural strength and toughness of concrete, and also can reduce the shrinkage and cracking of concrete. In this study,  microwave-assisted pyrolysis was used to recycle carbon fibers from the waste carbon fiber polymer composites to make recycled carbon fiber- reinforced concrete. The lengths of the recycled carbon fibers were 5-10 mm, 15-20 mm, and 30-50 mm, respectively, and the fiber to cement weight rations were 0.5%, 1.0%, and 1.5%, respectively. The water-cement ratio was 0.6, and the aggregate fineness modulus (F.M.) was 6.78. The mechanical performances of recycled carbon fiber-reinforced concrete (RCFRC) were investigated by using compression, bending, splitting and impact tests. The test results show that when the fiber to cement weight ratio is 1.5%, the mechanical performance of the recycled carbon fiber- reinforced concrete is the best compared to other fiber to cement weight ratios. Compare to the benchmark specimen, for 1.5% fiber to cement ratio and fiber length from short to long, the compressive strengths of the RCFRC increase 48.71%, 56.15% and 48.88% respectively; the flexural strengths of RCFRC increase 55.76%, 43.63% and 27.31%; the splitting strengths of RCFRC increase 28.96%, 45.70% and 47.58% respectively. The impact test results show that with 1.0% fiber to cement ratio and an impact energy of 50 joules, the impact times of RCFRC with a fiber length of 30-50 mm increased by 3,615% compared to benchmark specimen. The above results show RCFRC can effectively improve the mechanical properties of concrete.
TitleFeasibility of additive manufacturing technology for structural components: the case study of 3D printing using cementless binders
AuthorChia-Yun Huang, Wei-Ting Lin, An Cheng, LUKÁŠ FIALA
Keywordscementless blended material; 3D printing technology; printing flow; viscosity
AbstractIn recent years, 3D printing of structural components or elements for construction has been a popular construction automation technology. 3D printing technology has the advantages of fast construction, saving construction materials and stable quality, and the diversity of printing spraying materials is the key to its development. In this study, three industrial by-products (fly ash, ultra-fine fly ash and ground-granulated blast-furnace slag) were mixed to form a ternary cementless blended material without the addition of alkaline activators. The test results were compiled through viscosity tests, setting time tests, syringe injection tests and flowability tests. The results revealed that a viscoelastic solid paste with a viscosity of over 6000 cP could be used as a spraying material for liquid deposition modeling 3D printers. The results confirmed that a ternary cementless blended material made from 10% slag, 40% ultra-fine fly ash and 50% fly ash, at a water to binder ratio of 0.25, could be used as a spraying material for 3D printing and that the spraying flow rate of the printer should be set at 40% to achieve the best aesthetic integrity of the sprayed specimens. The compressive strength tests were conducted to verify that the 3D printed specimens have higher compressive strength and casting quality than the conventional molded specimens. The cementless blended material developed in this study is suitable for use as a 3D printing spraying material and is in line with the promotion of high-value industrial by-product technology.
Title High-Fidelity Nonlinear Cyclic Response Simulations of Squat RC Shear Walls
Author Tzu-Han Wen, Chung-Chan Hung, Hexin Zhang, Phu Anh Huy Pham, Terry Y.P. Yuen*
Keywords Constitutive model, anisotropy, shear-slip and re-contact, mesh-sensitivity, non-proportional loading, concrete, finite element
Abstract As stipulated by most of the prevailing structural design standards, nonlinear response analysis with high-fidelity numerical models would be inevitable for
designing unconventional reinforced concrete structures under extreme seismic loading. The core of nonlinear numerical models is the constitutive modelling of materials, particularly for concrete materials. Nevertheless, many of the existing concrete constitutive models could not resolve some critical issues that involve crack-induced anisotropy, change of stress transfer mechanisms under non-proportional loading, shear-slip and re-contact behaviour, mesh-size sensitivity, and balance between computational efficiency and modelling the detailed responses. To this end, this paper presents a robust and experimentally validated constitutive model that was developed recently (Yuen et al., 2022) for high-fidelity nonlinear response analysis of reinforced concrete elements. The key features include (1) the total-strain based formulation with loading-history dependent internal variables, (2) cyclic normal and tangential stress-strain responses prescribed on crack planes, (3) fixed 3D crack plane coordinate that is uniquely determined by a novel crack plane searching algorithm, (4) multi-axial strain interaction modelled by the equivalent uniaxial-strains transformation method, (5) shear-slip and re-contact of the crack planes modelled by the modified shear retention model, and (6) mesh-size sensitivity mitigation through the model parameter regularisation. The proposed model was already implemented into ABAQUS through the user-subroutine and successfully applied to simulate reserved-cyclic loading tests on shear panels and a full-scale shear-controlled column (Yuen et al., 2022). This paper presents a further validation study of the proposed model on a high-strength squat RC wall. The high-fidelity model can again well capture the damage evolutions and complete load-deflection hysteresis response of the tested wall. Hence, with the demonstrated performances, the proposed model could be a competent candidate for the high-fidelity nonlinear analysis of next generations of concrete structures that feature unconventional design.
AuthorSturm, A.B.
AbstractDespite being a small country Australia has long maintained independent reinforced concrete design standards with significant differences to the US and European standards which most people outside of Australia would be familiar. This is in part due to the long history of high-level research into reinforced concrete within Australia. Therefore, in this paper I will review the latest edition of the Australian design standards and contrast this with ACI 318-19. From this I will draw implications for reinforced concrete design in Taiwan. Unique aspects of this standard include the approach to time effects, shear as well as fibre reinforced concrete.