Hongseob Oh

Experimental Study on the Material Characteristics of Slag Cement with Various Phosphogypsum Materials

In this study, it is experimentally verified a feasibility of the wasted phosphogypsum () that is a byproduct from the phosphoric acid process of manufacturing fertilizers can be applied as an admixture in slag cement. For the test, phosphogypsum is modified as dihydrate, hemihydrate, type III anhydrite, and type II anhydrite, and then chemical characteristics and mechanical properties of various slag cements containing above mentioned gypsum materials were analyzed. The test results show that the gypsum made at high temperature has better quality with decrease of water-soluble phosphoric acid () which has an effect on the quality of cement. And type II anhydrite shows superior quality in terms of drying shrinkage and the compressive strength of cement paste with hemihydrate at 56 days is higher than other gypsum material.

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.

Static and fatigue performance of the bolt-connected structural jointed of deep corrugated steel plate member

Corrugated steel plate culvert bridge has been more commonly used as soil steel bridges because it is the cost-effective alternative for railway-highway crossings. The corrugated steel plate culvert bridge is considered the most suitable for quick rebuilding of bridges compared with the conventional bridges. This study intends to experimentally investigate the static and fatigue performance of the bolted connection of deep corrugated steel plate. Test variables are the thickness of deep corrugated steel plate and the types of bolted connection such as bolted-only, gasket, slot hole, and washer. For static test, the failure is mainly caused by a local buckling of deep corrugated steel plate member and bearing failure of bolts. Type of gasket and slot hole showed the largest stiffness so that they may be recommended for structural safety and redundancy under a static flexural behavior. For fatigue test, the bolted-only specimen exhibited no increase in the strain until failure and the highest fatigue life among the test variables. For structural safety under cyclic loading, bolted-only connection is recommended. According to AASHTO LRFD Bridge Design Specification, fatigue life category can be determined as category D level and the fatigue limit was estimated to be 48.3 MPa. The deep corrugated steel plate members tested in this study can provide a sufficient fatigue performance in compliance with the design specification.

Experimental Verification on the Structural Safety of Cantilever Beam Connected with Post-installed Adhesive Anchor Bolts

Recently, there has been a growing interest in expanded sidewalks for existing bridges. The cantilever beam system applied to expanded sidewalks for existing bridges are connected with the concrete structure by adhesive anchor bolts. However, the extended sidewalks are currently constructed without standardized regulations, which lead to excessive design of the beam spacing and installation and the construction difficulties due to the excessive over-weight. Moreover, there is only limited analysis and experiment data on the post-installed adhesive anchor bolts, so the excessive number of bolts is used for the connection. This paper deals with a method to increase the effectiveness of beam sections and anchor bolts geometry for expanded sidewalk of existing bridge. The study results showed that the failure of cantilever beam connected by adhesive anchor bolts was dominated by bond failure of interface between concrete and bolt. Also, the results indicated the possibilities of improving serviceability as well as safety of the sidewalks by changing of beam section and prestressing the bolts.

Experimental Assessment on the Flexural Bonding Performance of Concrete Beam with GFRP Reinforcing Bar under Repeated Loading

This study intends to investigate the flexural bond performance of glass fiber-reinforced polymer (GFRP) reinforcing bar under repeated loading. The flexural bond tests reinforced with GFRP reinforcing bars were carried out according to the BS EN 12269-1 (2000) specification. The bond test consisted of three loading schemes: static, monotonic, and variable-amplitude loading to simulate ambient loading conditions. The empirical bond length based on the static test was 225 mm, whereas it was 317 mm according to ACI 440 1R-03. Each bond stress on the rib is released and bonding force is enhanced as the bond length is increased. Appropriate level of bond length may be recommended with this energy-based analysis. For the monotonic loading test, the bond strengths at pullout failure after 2,000,000 cycles were 10.4 MPa and 6.5 MPa, respectively: 63–70% of the values from the static loading test. The variable loading test indicated that the linear cumulative damage theory on GFRP bonding may not be appropriate for estimating the fatigue limit when subjected to variable-amplitude loading.

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 Combined Effect of Concrete Environment and High Temperature on Interlaminar Shear Strength of FRP Reinforcement

Most experimental studies on durability of FRP reinforcements subjected to high temperature have focused on the effect of high temperature only on tensile properties. But FRP reinforcement used in newly constructed concrete structure is first degraded by moisture and alkaline environment of concrete. When the structure is subjected to fire, the degraded FRP reinforcement is exposed to high temperature. Therefore, the effects of concrete environment and high temperature should be simultaneously considered for evaluation of FRP reinforcement damaged by fire. In this study, FRP reinforcements submerged in simulated solutions of pH 12.3 and 7 for extended period of time were subjected to temperatures of , , , and to be examined. In order to investigate the effect of the high temperature, interlaminar shear strengths were measured and compared to those of control ones. The experimental results demonstrated that the combined effect of concrete environment and high temperature on properties of FRP reinforcement was more significant than the effect of high temperature or concrete environment solely.

Improved Biaxial Flexure Test (BFT) for Concrete with the Optimum Specimen Geometry

For designing concrete structures, engineers are provided data from unidirectional flexure test in most cases. But real structural components such as pavements and deck panel are subjected to multiaxial stress throughout their body. Therefore, biaxial flexure test for concrete may be considered as a gage of the performance of concrete in service. In this paper, we propose the optimum biaixial flexture test (BFT) to measure the biaxial flexural strength of concrete. This method are an improved version of the ring-on-ring test which have been used extensively in the fields of ceramics and biomaterials. The optimum geometry of the test specimen was determined by using a three-dimensional finite element analysis. A series of test data obtained from the pro- posed test method is provided to show that the proposed optimum biaxial flexure test method can be used to identify the biaxial tensile strength of concrete.

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.