• Computers and Concrete
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• v.13 no.3
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• pp.411-421
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• 2014

A central pullout test was conducted to investigate the bonding properties between high strength rebar and reactive powder concrete (RPC), which covered ultimate pullout load, ultimate bonding stress, free end initial slip, free end slip at peak load, and load-slip curve characteristics. The effects of varying rebar buried length, thickness of protective layer and diameter of rebars on the bonding properties were studied, and how to determine the minimum thickness of protective layer and critical anchorage length was suggested according the test results. The results prove that: 1) Ultimate pull out load and free end initial slip load increases with increase in buried length, while ultimate bonding stress and slip corresponding to the peak load reduces. When buried length is increased from 3d to 4d(d is the diameter of rebar), after peak load, the load-slip curve descending segment declines faster, but later the load rises again exceeding the first peak load. When buried length reaches 5d, rebar pull fracture occurs. 2) As thickness of protective layer increases, the ultimate pull out load, ultimate bond stress, free end initial slip load and the slip corresponding to the peak load increase, and the descending section of the curve becomes gentle. The recommended minimum thickness of protective layer for plate type members should be the greater value between d and 10 mm, and for beams or columns the greater value between d and 15 mm. 3) Increasing the diameter of HRB500 rebars leads to a gentle slope in the descending segment of the pullout curve. 4) The bonding properties between high strength steel HRB500 and RPC is very good. The suggested buried length for test determining bonding strength between high strength rebars and RPC is 4d and a formula to calculate the critical anchorage length is established. The relationships between ultimate bonding stress and thickness of protective layer or the buried length was obtained.

• Journal of the Korea Institute of Building Construction
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• v.17 no.4
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• pp.331-339
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• 2017

The purpose of this study is to evaluate the effect of curing age and thickness of coating material on the bond strength of polymer cement slurry(PCS)-coated rebar that can replace epoxy-coated rebar. The test specimens were prepared with two types of cement, two types of polymer dispersion as St/BA and EVA, two polymer-cement ratios, two coating thicknesses and three curing ages, and tested for bond strength test to cement concrete. The flexural behavior of RC beam that is made by optimum conditions such as polymer-cement ratio of 80%, coating thickness of $100{\mu}m$ and curing age of 7 days of PCS recommended from the bond strength test is also conducted. From the test results, The maximum bond strength of PCS-coated rebar at curing age of 7-day and coating thickness of $100{\mu}m$ was about 1.52 and 1.58 times respectively, the strength of plain and epoxy-coated rebar. The ultimate loads of RC beam using PCS-coated rebar were range of 81.1% to 102.3% of that of plain rebar, and 98.4% to 124.1% of that of epoxy-coated rebar. It is apparent that PCS-coated rebar with EVA, curing age at 7-day and $100{\mu}m$ can replace epoxy-coated rebar in construction field.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.73-80
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• 2013

Polymer cement slurry (PCS) made from organic polymer dispersion and cement has good adhesion to steel, waterproofness and acid resistance due to being of polymer films formed in cement slurry. The purpose of this study is to evaluate the mix design conditions at early curing age of PCS-coating material effected on improvement in bond strength of coated rebar. The test pieces are prepared with two types of polymer dispersions such as St/BA and EVA, four polymer-cement ratios, two types of cement, four coating thicknesses and three curing ages, and tested for the bond strength test. From the test results, in general, bond strength of PCS-coated rebar is better than that of uncoated rebar and epoxy-coated rebar. It is also high bond strength at curing ages of 7-day or less, and coating thicknesses of $75{\mu}m$ and $100{\mu}m$. The maximum bond strength of PCS-coated rebar at curing age of 3-hour is almost same as that of curing age of 1-day and 7-day. The maximum bond strength of PCS-coated rebar with ultra high-early strength cement and St/BA at polymer-cement ratio of 80%, and coating thickness of $100{\mu}m$ is about 1.52 and 1.58 times respectively, the strength of uncoated rebar and epoxy-coated rebar. It is apparent that the curing age, coating thickness, type of polymer and cement are very important factors to improve the bond strength of PCS-coated rebar to cement concrete. We can have basic information that PCS-coated rebar with curing age at 3-hour and coating thickness of $100{\mu}m$ can replace epoxy-coated rebar.

• Journal of the Korea Concrete Institute
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• v.27 no.6
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• pp.633-640
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• 2015

Polymer cement slurry (PCS) is made from organic polymer dispersion and cement has good adhesion to steel, waterproofness and acid resistance due to being of polymer films formed in cement slurry. The purpose of this study is to evaluate the bond strength of coated rebar by polymer cement slurry made of EVA and ultra high-early strength cement. The test pieces are prepared with EVA polymer dispersion and ultra high-early strength cement having four types of polymer-cement ratios, four types of coating thicknesses and four curing ages, and tested for the bond strength test. From the test results, in general, bond strength of PCS-coated rebar is better than that of uncoated rebar and epoxy-coated rebar. It is also high bond strength at curing ages of 7-day, and coating thicknesses of $75{\mu}m$ and $100{\mu}m$. The maximum bond strength of PCS-coated rebar with ultra high-early strength cement and EVA at polymer-cement ratio of 80%, and coating thickness of $100{\mu}m$ is about 1.32 and 1.38 times respectively, the strength of uncoated rebar and epoxy-coated rebar. It is apparent that the curing age, coating thickness, type of polymer and cement are very important factors to improve the bond strength of PCS-coated rebar to cement concrete. We can have basic information that PCS-coated rebar with polymer-cement ratio of 80% or 100% and coating thickness of $100{\mu}m$ at curing age of 1-day can replace epoxy-coated rebar.

• Journal of Ocean Engineering and Technology
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• v.10 no.4
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• pp.103-108
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• 1996

To syudy the change of prtential in the mortar-embedded precorroded rebar, a half cell method was adapted. The rebar was corroded by the salt spray and then the rebar embedded in the mortar. A saturated copper sulfate feference electrode was used. The corrosion potential of the rebar in the mortar specimen cured in air was increased, whereas that of the rebar cured in water was decreased with aging. The corrosion potential of the rebar in the mortar was decreased with corroded time by the salt spray. As the mortar thickness covered the rebar was increased, the corrosion potential of the rebar in the mortar was increased.

• International conference on construction engineering and project management
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• 2022.06a
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• pp.312-318
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• 2022

Robot-based layout automation has been recently promoted for the purpose of improving productivity and quality. Marking robots have various functional demands to secure marking precision and environmental adaptability. In particular, in order to automate marking work of building structure, correction of the marking line through position recognition of rebars placed is required. Because the rebars must maintain a constant cover thickness from the formwork surface, if the rebars are out of planned position, the rebar or marking line need to be corrected to secure the cover thickness. Thus, the marking robot for structural work needs to have the function for determining the position correction of the rebar or the marking line. In order to judge the correction of marking line, it is required to measure the distance between the planned marking line and the rebar placed. Therefore, this study proposes an algorithm that can measure the distance between the planned line and the rebar, and correct marking line for the automatic operation of the marking robot. The results of this study will be utilized as a core function for unmanned operation of the marking robot and contribute to securing precise marking by reflecting construction errors.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.66-71
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• 2019

In this paper, a study was conducted on the method of using GPR data to predict rebar thickness inside a facility. As shown in the cases of poor construction, such as the use of rebars below the domestic standard and the construction of reinforcement, information on rebar thickness can be found to be essential for precision safety diagnosis of structures. For this purpose, the B-scan data of GPR was obtained by gradually increasing the diameter of rebars by making specimen. Because the B-scan data of GPR is less visible, the data was converted into the heatmap image data through migration to increase the intuition of the data. In order to compare the results of application of commonly used B-scan data and heatmap data to CNN, this study extracted areas for rebars from B-scan and heatmap data respectively to build training and validation data, and applied CNN to the deployed data. As a result, better results were obtained for the heatmap data when compared with the B-scan data. This confirms that if GPR heatmap data are used, rebar thickness can be predicted with higher accuracy than when B-scan data is used, and the possibility of predicting rebar thickness inside a facility is verified.

• Computers and Concrete
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• v.18 no.1
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• pp.139-154
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• 2016

Since the concrete strength around the reinforcement rebar affects the tension stiffening, the tension stiffening effect of ultra high performance concrete on the concrete members reinforced by steel rebar is examined by testing the specimens with circular cross section with the length 850 mm reinforced by a steel rebar at the center of a specimen's cross section in this research. Conducting a tensile test on the specimens, the cracking behavior is evaluated and a curve with an exponential descending branch is obtained to explain the post-cracking zone. In addition, this paper proposes an equation for this branch and parameters of equation is obtained based on the ratio of cover thickness to rebar diameter (c/d) and reinforcement percentage (${\rho}$).

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.761-768
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• 2012

The purpose of this study is to investigate bond properties of GFRP used in SFRC (Steel fiber reinforced concrete) and normal concrete. The experimental variables were rebar diameter (D13, D16), steel fiber volume fraction (0~2%) and cover thickness ($1.5d_b$, $5.4d_b$). The experimental results showed a different failure mode depending on the cover thickness. Through the tested specimens, splitting failure occurred for the specimens with small cover thickness and pull out failure occurred in the specimens with large cover thickness. Introduction of steel fiber caused the specimens to have more ductile behavior of bond stresss-lip after peak stress, but they did not increase the bond strength significantly. These failure modes were shown in both steel reinforcement and GFRP. However, from the difference of micro structure of bond failure mechanism between steel rebar and GFRP rebar, more ductile behavior was observed in GFRP-specimens after maximum bond strength was reached.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.2
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• pp.107-115
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• 2003

Nondestructive testing was carried out in order to evaluate the structural integrity and construction quality of the slurry wall of the underground LNG storage tank. 9 test points were selected, and the wall thickness, rebar spacing, and compressive strength of the slurry wall were evaluated by stress wave impact-resonance method, GPR, sonic velocity, and rebound testing, respectively. As results, the wall thickness, rebar sparing and estimated compressive strength satisfy the design criteria.