Jongsung Sim

Compressive strength and resistance to chloride ion penetration and carbonation of recycled aggregate concrete with varying amount of fly ash and fine recycled aggregate.

Construction and demolition waste has been dramatically increased in the last decade, and social and environmental concerns on the recycling have consequently been increased. Recent technology has greatly improved the recycling process for waste concrete. This study investigates the fundamental characteristics of concrete using recycled concrete aggregate (RCA) for its application to structural concrete members. The specimens used 100% coarse RCA, various replacement levels of natural aggregate with fine RCA, and several levels of fly ash addition. Compressive strength of mortar and concrete which used RCA gradually decreased as the amount of the recycled materials increased. Regardless of curing conditions and fly ash addition, the 28 days strength of the recycled aggregate concrete was greater than the design strength, 40 MPa, with a complete replacement of coarse aggregate and a replacement level of natural fine aggregate by fine RCA up to 60%. The recycled aggregate concrete achieved sufficient resistance to the chloride ion penetration. The measured carbonation depth did not indicate a clear relationship to the fine RCA replacement ratio but the recycled aggregate concrete could also attain adequate carbonation resistance. Based on the results from the experimental investigations, it is believed that the recycled aggregate concrete can be successfully applied to structural concrete members.

Experimental assessment of bridge deck panels strengthened with carbon fiber sheets

Abstract Concrete bridge decks supported by main girders develop initial cracks in the longitudinal or transverse direction by applied loads. Therefore, it is important to consider the crack patterns and deflections if such decks are to be strengthened. This study investigated the effectiveness of strengthening using carbon fiber sheets. The experimental variables were the direction and the amount of strengthening material. To simulate the real behavior of the bridge deck, static structural tests were conducted on six specimens, with a built-in concrete girder on each side. The structural behavior was then observed through the crack pattern and the load–displacement relationship of each specimen. Also, the yield line theory that adopts the modified Johansens yield criterion was applied to estimate the ultimate strength.

FATIGUE LIFE OF DAMAGED BRIDGE DECK PANELS STRENGTHENED WITH CARBON FIBER SHEETS

This article presents the results of an experimental investigation that was conducted to evaluate bridge decks strengthened with carbon fiber sheets (CFS) and subjected to repeated load applications. The authors also explored the suitability of a simplified cumulative damage theory for reinforced concrete structural members as a tool to decide on strengthening strategies. To simulate fatigue damage to the bridge deck slabs, cyclic loading was applied to test panels, which were then reinforced with CFS using two different methods. The strengthened panels were then tested again under cyclic loads. The authors note that the observed response to fatigue loads differed markedly from the results of static tests. Isotropic reinforcement was found to be more effective than unidirectional strengthening. The proposed simple damage theory can be used to estimate the residual life of bridge decks with unknown damage, even if these are strengthened with CFS. The authors caution, however, that the proposed model is based on a small number of tests and is therefore limited to the range of parameters governing those tests.

New Suggestion of Effective Moment of Inertia for Beams Reinforced with the Deformed GFRP Rebar

To fundamentally solve the problem of deterioration of concrete structures, it has been researched that the high durable concrete structure reinforced with the FRP rebar can be one of major solution to the newly-developed concrete structure. FRP rebar has lots of advantages such as non-corrosive, high performance and light weight against the conventional steel rebar. Among these kinds of FRP rebars, GFRP rebar has usually been considered as the best reinforcement because of its economic point of view. Even though the material capacity of the GFRP rebar was already investigated, there are some problems such as low modulus of elastic that will be cause for degrade of the serviceability of flexural concrete member reinforced with the GFRP rebar. Thus, the deflection characteristics of the GFRP rebar reinforced concrete structure should be considered then investigated. In this study, ACI 440 guideline (2003), ISIS Canada Design Manual (2001) and Toutanji et al. (2000) was considered for predicting the moment of inertia of the concrete beam reinforced with the GFRP rebar. And it was also evaluated that load-deflection relationship had a good accordance with the test and analysis result. In the result of this study, it could be estimated that the load-deflection relationship using the suggested equation of moment of inertia in this study indicated better accordance with the test result than that of the others until failure.

Semiempirical Methodology for Estimating the Service Life of Concrete Deck Panels Strengthened with Fiber-Reinforced Polymer

Deterioration of concrete bridge decks affects their durability, safety, and function. It is therefore necessary to conduct structural rehabilitation of damaged concrete decks by strengthening them with fiber-reinforced polymer. Of the recent studies on the strengthened structures, most have focused on static behavior; only a few studies have investigated fatigue behavior. Accurate analysis of fatigue in concrete deck performance requires a more realistic simulated moving load. This study developed a theoretical live-load model to reflect the effect of moving vehicle loads, based on a statistical approach to the measurement of real traffic loads over various time periods in Korea. It assessed the fatigue life and strengthening effect of bridge decks strengthened with either carbon fiber sheets or grid carbon fiber polymer plastic using probabilistic and reliability analyses. It used extrapolations and simulations to derive maximum load effects for time periods ranging from 1 day to 75 years. Limited fatigue tests were conducted and probabilistic and reliability analyses were carried out on the strengthened concrete bridge deck specimens to predict the extended fatigue life. Analysis results indicated that strengthened concrete decks provide sufficient resistance against increasing truck loads during the service life of a bridge.

An Experimental Study on the Multi-Deterioration Resistances of Concrete containing Waste-glass Sludge

Subsidiary concrete structures such as a barrier and a side-channel suffer from rapid deterioration due to the excessive use of an de-icing in Korea. Consequently, the needs for replacement and/or repair of the structures has increased significantly, resulting in the increase of the maintenance cost. The preliminary study strongly indicates that it is necessary to improve the durability and visibility of the subsidiary structures in order to reduce the maintenance cost of the structures. Hence, the purpose of this research project is to develop a concrete with high durability by incorporating waste-glass or polymer admixture in concrete. And in order to develop concrete of high durability by utilizing waste glass, a research was focused on an effect of waste glass sludge mixing over concrete strength and durability and measurement for compression strength by each material age performed together with chloride ion penetration resistance and scaling resistance test for properties of multi-deterioration.

The Suggestion of Testing Method for Analysis of Tensile Strength of Multi-Directional GFRP Plate

In this study, a standardized test method to analyze tensile properties of multi-directional GFRP plate was proposed. Presently, tensile strength test of FRP composite reinforced with isotropic and orthotropic fiber is standardized according to ISO standard. Also, even though many studies were performed on test method to analyze the dynamic properties, the properties of tensile strength for multi-directional GFRP plate were not clearly identified. Currently, the domestic test method in accordance with ASTM, which is applicable to unidirectional FRP plate, gave tensile test results greater than actual properties. Thus, in this study, GFRP tensile test was conducted using the method found to be commonly applicable to all standards based on literature review of domestic and international references. Then, anchorage length experiments were performed using the proposed tension test method to evaluate validity of the method. Finally, optimal anchorage length was estimated from the numerical analysis to propose the standardized tensile strength method for GFRP multi-directional composite evaluation.

Fundamental Performance Evaluation of Recycled Aggregate Concrete with Varying Amount of Fly Ash and Recycled Fine Aggregate

This study investigates fundamental properties of recycled aggregate concrete which incorporated recycled coarse aggregate and various amount of recycled fine aggregate. In addition, for the purpose of the improvement of long term strength and durability, a part of cement was replaced with fly ash. Compressive strength and resistance to chloride ion penetration and carbonation were investigated. When the coarse aggregate was completely replaced with the recycled the replacement ratio of the fine aggregate with the recycled was recommended to be limited below in the consideration of strength. The strength of the steam-cured specimen was very comparable to the wet-cured at 28 days. As fly ash content increased the resistance to chloride ion penetration was increased. The chloride ion penetrability based on the charge passed was found to be low at 21 days and very low at 56 days, respectively. Carbonation depth and carbonation velocity coefficient increased as the fly ash content increased and the relationship between the carbonation depth and recycled fine aggregate replacement ratio was not clear. Up to 28days, however, the measured carbonation depth was mostly less than 10mm which could be considered as low

Prediction of the Shear Strength of FRP Strengthened RC Beams (I) - Development and Evaluation of Shear strength model -

This study developed a shear strength prediction model of FRP strengthened reinforced concrete beams in shear. The primary design parameters were shear crack angle and shear span to depth ratio of FRP reinforcement. Of primary concern In the suggested model was the FRP debonding failure, which Is a typical fracture mode of RC beams strengthened with FRP, The proposed model used a crack sliding model based on modified plasticity theory. To address the effect of the shear span to depth ratio, the arch action was considered in the proposed model. The proposed model was applied to RC beams strengthened with FRP. The results showed that the proposed model agree with test results.

A Modified Model for Deflection Calculation of Reinforced Concrete Beam with Deformed GFRP Rebar

The authors carried out experimental and analytical research to evaluate the flexural capacity and the moment-deflection relationship of concrete beams reinforced with GFRP bars. The proposed model to predict the effective moment of inertia for R/C beam with GFRP bars was developed empirically, based on Branson’s equation to have better accuracy and a familiar approach to a structural engineer. For better prediction of the moment-deflection relationship until the ultimate strength is reached, a nonlinear parameter () was also considered. This parameter was introduced to reduce the effect of the cracked moment of inertia for the reinforced concrete member, including a lower reinforcement ratio and modulus of elasticity of the GFRP bar. In a comparative study using six equations suggested by others, the proposed model showed better agreement with the experimental test results. It was confirmed that the empirical modification based on Branson’s equation was valid for predicting the effective moment of inertia of R/C beams with GFRP bar in this study. To evaluate the generality of the proposed model, a comparative study using previous test results from the literature and the results from this study was carried out. It was found that the proposed model had better accuracy and was a familiar approach to structural engineers to predict and evaluate the deflection behavior.