• Steel and Composite Structures
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• v.43 no.4
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• pp.419-429
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• 2022

In response to the sustainability requirements set in the EU Commission's "Green Deal" towards reduction of the greenhouse gas emissions, it is estimated that the structural design for deconstruction is going to contribute considerably to the sustainable development of the built environment. The demountability of multi-material structural systems basically depends on the shear connectors used in the structural system. This paper focuses on a type of demountable injected shear connector with an injected steel-reinforced resin (iSRR) which consists of spherical steel particles embedded in a resin. Its application to steel-to-concrete and steel-to-Fiber Reinforced Polymer (FRP) decks is presented along with its benefits. In parallel, an overview of the experimental and numerical research on the evaluation of the mechanical properties of the demountable bolted connectors with iSRR is discussed. Last, detailed finite element (FE) models and a parametric study are performed to quantify the confinement level of the SRR material influenced by the oversized hole diameter.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.611-618
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• 2008

CFRP (carbon fiber reinforced polymer) tendons can be used as an alternative to solve the corrosion problem of steel tendons. Since CFRP tendons are vulnerable to transverse pressure and stress concentration, the conventional anchorage system used for steel tendons can create an unreliable load carrying capacity and may result in a premature failure. Therefore, it is necessary to develop the anchorage system that is well suited for CFRP tendons. There are many types of anchorage systems for CFRP tendons, which can be classified into three types: wedge-type anchorage, bond-type anchorage, and compression-type anchorage. This paper deals with the compression-type anchorage system manufactured through swaging technology. Based on the previous test results performed by the authors, the dimension of anchorage sleeve, the use and non-use of the insert, and the compression pressure on the sleeve have been selected as the major parameters affecting the performance of the compression-type anchorage. Some anchorage sleeves have been tapered to reduce the stress concentration. Test results revealed that the performance of the anchorage system depends mainly on the dimension and the compression pressure. It has been verified that the tapered sleeve can effectively reduce the stress concentration.

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.303-312
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• 2006

The main objective of this experimental study is to examine the feasibilities of each testing method with various kinds of grip systems for the analysis of tensile strength of GFRP(glass fiber reinforced polymer) reinforcing bars. Three types of grip systems were examined such as resin-sleeved pipe-type grip proposed by CSA(Canadian Standard Association), frictional resistance type metal grip by ASTM(American Standard for Testing and Materials) and wedge-inserted cone-type grip normally used in prestressing tendons. Also, mechanical properties of GFRP rebars with different surface deformations were investigated for each different type of testing grip used in this study. All testing procedures including specimens preparation, set-up of test equipments and measuring devices were made according to the CSA S806-02 recommendations. From the test results, it was found that the highest tensile strengths of GFRP rebars were observed when tested by resin-sleeved grip system regardless of their different surface deformations. But tensile strengths of GFRP rebars by ASTM grip system are only 10% less than those by CSA grip system. On the other hand, CSA grip is not only difficult to prepare but also not disposable. Therefore, ASTM grip system is recommended as a practical alternative to estimate the tensile strength of GFRP rebars.

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.801-809
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• 2006

Epoxy resin has widely been used as adhesives and corrosion-resistant paints in the construction industry for many years, since it has desirable properties such as high adhesion and chemical resistance. Until now, in the production of conventional epoxy cement mortars, the use of any hardener has been considered indispensable for the hardening of the epoxy resin. However we have noticed the fact that even without any hardener, the hardening process of the epoxy resin can proceed by the action of hydroxides in cement mortars. As a result the disadvantages of the two-component mixing of the epoxy resin and hardener have been overcome. The purpose of this study is to evaluate the mechanical properties and durability of epoxy cement mortar without a hardener exposed at indoor and outdoor for one year. The epoxy cement mortars without and with a hardener were prepared with various polymer-cement ratios, and tested for weight change, flexural and compressive strengths, water absorption, carbonation depth and pore size distribution. Especially, the basic properties of the epoxy cement mortars without hardener are discussed in comparison with ones with the hardener. From the test results, it is concluded thai the epoxy cement mortars without a hardener exposed at indoor and outdoor for one year have higher strength and better durability than ones with the hardener within the polymer-cement ratios of 10 to 20%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.4
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• pp.235-242
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• 2005

This study is on the evaluation of performance of polymer cement mortar which is used for pre-wetting spray method. Pre-wetting spray method is an epoch-making method to repair concrete structures damaged, which is added a small quantity water preciously to dry mortar to reduce dust and rebound and spray mortar mixed with fixed quantity water at nozzle before spray. The result showed that physical performance such like compressive, flexural and adhesive strength of polymer cement mortar, TS 100 used for pre-wetting spray method was superior to other repair mortar. Also durable performance such as resistance on permeability of chloride ion, carbonation, chemical and freezing-thawing was excellent.

• Journal of the Korea Institute of Building Construction
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• v.15 no.6
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• pp.579-587
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• 2015

In this paper, microencapsulated healing agent was embedded in the polymer matrix to obtain self healing properties. Microencapsulation of methacrylate using polyurea-formaldehyde as a shell material and studied the effect of agitation rate on capsule characteristics such as size, shell thickness, and surface morphology. The formation of microcapsules was confirmed by FTIR and TGA, and capsule characteristics were studied by optical microscopy and SEM. The self-healing effect was evaluated using permeability measurements and further confirmed by surface analytical tools including optical microscope. According to the experimental results, the microencapsulated healing system has the self-heaing ability for artificial cracks.

• Polymer(Korea)
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• v.34 no.5
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• pp.434-441
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• 2010

Sodium polyacrylate (PAANa) was synthesized by inverse emulsion polymerization method to absorb excess water in concrete. Liquid paraffin was used as a continuous phase. Acrylic acid (AA) was neutralized by aqueous sodium hydroxide solution (8 M). Different amount of N,N'-methylene bisacrylamide (MBA) was used as a crosslinking agent to change crosslinking density of the synthesized PAANa. The size distribution of synthesized particles was measured by particle size analyzer. Swelling ratio of crosslinked PAANa was evaluated from the equation in D. I. water, cement aqueous solution, and $Ca(OH)_2$ aqueous solution. The FTIR spectroscopy was used to characterize $Ca^{2+}$ ion interaction with PAANa. Incorporation of 1.0 wt% PAANa into cement increased compressive and flexural strength approximately 30% and 10%, respectively, compared with those of ordinary portland cement.

• Computers and Concrete
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• v.29 no.2
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• pp.107-115
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• 2022

With the improvements in computer technologies, utilization of image processing techniques has increased in many areas (such as medicine, defence industry, other industries etc.) Many different image processing techniques are used for surface analysis, detection of manufacturing defects, and determination of physical and mechanical characteristics of composite materials. In this study, cementitious composites were obtained by addition of Grounded Granulated Blast-Furnace Slag (GGBFS), Styrene Butadiene polymer (SBR), and Grounded Granulated Blast-Furnace Slag and Styrene Butadiene polymer together (GGBFS+SBR). Expanded Polystyrene (EPS) beads were added to these cementitious composites in different ratios (20%, 40% and 60%). The mechanical and physical characteristics of the composites were determined, and homogeneity indexes of the composites were determined by image processing techniques to determine EPS distribution forms in them. Physical and mechanical characteristics of the produced samples were obtained by applying consistency, density, water absorption, compressive strength (7 and 28 days), flexural strength (7 and 28 days) and tensile splitting strength (7 and 28 days) tests on them. Also, visual examination by using digital microscope, and image analysis by using image processing techniques with open source coded ImageJ program were performed. As a result of the study, it is determined that GGBFS and SBR addition strengthens the adhesion sites formed as it increases the adhesion power of the mixture and helps to get rid of the segregation problem caused by EPS. As a result of the image processing analysis it is demonstrated that GGBFS and SBR addition has positive contribution on homogeneity index.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.6
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• pp.451-461
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• 2010

Utilization of the fiber reinforced polymer (FRP) material has been enlarged as a substitution material to the general construction materials having certain long-term problems such as corrosion, etc. However, it could be difficult to apply the FRP material, which has a linear shape generally, to an arch-shaped tunnel structure. Therefore, an attempt has been made in this study to develop a device to form a designed cross section of FRP material by pulling out with a curvature. A sample of the circled FRP product was successfully produced and then the sample has been tested to identify its physical characteristics. Then, intensive feasibility studies on the circled FRP panel to be used for a tunnel lining structure have been carried out by numerical analyses. As a result, it appears that the new circled FRP-concrete composite panel has a high capability to be used for a tunnel lining material without any structural problem.

• Steel and Composite Structures
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• v.51 no.5
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• pp.509-527
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• 2024

Bonding carbon fiber-reinforced polymer (CFRP) laminates have been extensively employed in the restoration of steel constructions. In addition to the mechanical properties of the CFRP, the bond strength (P_U) between the CFRP and steel is often important in the eventual strengthened performance. Nonetheless, the bond behavior of the CFRP-steel (CS) interface is exceedingly complicated, with multiple failure causes, giving the P_U challenging to forecast, and the CFRP-enhanced steel structure is unsteady. In just this case, appropriate methods were established by hybridized Random Forests (RF) and support vector regression (SVR) approaches on assembled CS single-shear experiment data to foresee the P_U of CS, in which a recently established optimization algorithm named Aquila optimizer (AO) was used to tune the RF and SVR hyperparameters. In summary, the practical novelty of the article lies in its development of a reliable and efficient method for predicting bond strength at the CS interface, which has significant implications for structural rehabilitation, design optimization, risk mitigation, cost savings, and decision support in engineering practice. Moreover, the Fourier Amplitude Sensitivity Test was performed to depict each parameter's impact on the target. The order of parameter importance was t_c> L_c > E_A > t_A > E_c > b_c > f_c > f_A from largest to smallest by 0.9345 > 0.8562 > 0.79354 > 0.7289 > 0.6531 > 0.5718 > 0.4307 > 0.3657. In three training, testing, and all data phases, the superiority of AO - RF with respect to AO - SVR and MARS was obvious. In the training stage, the values of R² and VAF were slightly similar with a tiny superiority of AO - RF compared to AO - SVR with R² equal to 0.9977 and VAF equal to 99.772, but large differences with results of MARS.