• Journal of the Korea institute for structural maintenance and inspection
• /
• v.21 no.3
• /
• pp.138-144
• /
• 2017

In order to reduce carbon dioxide emission in construction industry, less amount of cement use can be one of the alternatives to manufacture concrete. One of the non-sintered construction materials are limestone, which is the raw material to manufacture ordinary Portland cement(OPC). A large amount of limestone have already been used as binders such as blended cement in Europe and US. Even European countries were already established the standard of blended cement, where the limestone can be used up to 35 percent. In this study, experimental researches were conducted to investigate the effects of limestone replacement on the mechanical properties and durability of concrete with 15%, 25% and 35% of limestone substitution to use limestone in blended cement. 15 percent use of limestone in blended cement developed equivalent or even higher compressive strengths compared to Plain mixture. Porosity of limestone cement with 15 percent substitution was much lower than Plain mixture. Most durability tests such as concrete carbonation, freeze-thaw cycle and drying shrinkage strains were conducted to evaluate long-term performance, and the test results indicated that 15 percent of limestone use did not significantly influence on the concrete durability compared with plain concrete.

• Journal of the Korea Institute of Building Construction
• /
• v.9 no.4
• /
• pp.131-137
• /
• 2009

The rate of recycling of waste concrete, which represents the majority of construction-related waste, is increasing. However, a general recognition of the inferior qualify of recycled aggregates and their lower grade of compressive strength, bending strength, shear strength, frost resistance and ductility make the application of recycled aggregates to structures insufficient. Therefore, this study conducted material and member experiments by adding steel fiber for the purpose of improving the properties of recycled aggregate concrete. To synthesize the experimental results, it was found that specimens with a 30% steel fiber admixture had levels of compressive strength, tensile strength and frost resistance that were equivalent to or higher than the standard specimen, and that concrete that had a 30% replacement of recycled aggregates with steel fiber was suitable for application to actual structures.

• Journal of the Korea Concrete Institute
• /
• v.22 no.5
• /
• pp.685-694
• /
• 2010

As a eco-friendly material, Hwangtoh (red clay) has been studied for complete or partial replacement of portland cement. Most of existing studies focused on the material properties of the Hwangtoh concrete including the compressive strength, drying shringkage, and creep. In the present study, the shear strength of the beams made with the Hwangtoh concrete was tested. Further, bond strength of tension re-bars embedded in the Hwangtoh concrete was tested. One of the concrete tested consisted of activated Hwangtoh replacing 20% of the cement. The other consisted 100% activated. Hwangtoh replacing all the cement. The beam specimens were tested under two point static loading. The test result showed that the shear strength of activated Hwangtoh concrete beams replacing 20% and 100% of cement was equivalent to that of the ordinary portland cement concrete beam. However, the bond strength of activated Hwangtoh concrete replacing 100% of the cement was less than that of the ordinary portland cement concrete.

• 한국방재학회:학술대회논문집
• /
• 2008.02a
• /
• pp.305-308
• /
• 2008

This paper describes a research study on the durability and strength properties of thin quiet-permeable asphalt concrete. Such asphalt mixes have high porosity, which offers significantly better drainages than normal mix designs. However, these materials also exhibit poor durability and strength limiting their use in pavement application. To remedy this, fiber and polymer modifiers have been proposed. All samples were added to modified binder which were prepared with or without the modifiers and fiber using Marshall mix procedures and were experimentally tested using various standardized testing procedures including percent air void for porosity, cantabro test and marshall stability. In general, the results of marshall stability showed that modified mixtures were equivalent to unmodified mixtures. Especially, the result of cantabro tested modified mixtures was superior to unmodified mixtures.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2023.11a
• /
• pp.149-150
• /
• 2023

This study proposes the most suitable strength prediction model equation for UHPC by calculating the apparent activation energy of UHPC according to the curing temperature and deriving the integrated temperature and compressive strength prediction equation. The results are summarized as follows. The apparent activation energy was calculated using the Arrhenius function, which was calculated as 21.09 KJ/mol. A model equation suitable for UHPC was calculated, and when the Flowman model equation was used, it was confirmed that it was suitable for the properties of UHPC using a condensation promoting super plasticizing agent.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.5 no.2
• /
• pp.168-176
• /
• 2017

This study, as a research for using crushed sand as a fine aggregate of concrete for nuclear structures, we improved the performance of impact crusher in the existing crushed sand production process and adjusted grain size to conform to ASTM C 33 The shape and grain size characteristics of a crushed sand were examined and concrete was prepared according to the substitution ratio of the sand to investigate the properties of fresh concrete and hardened concrete. The experimental results show that most of the concrete characteristics are equivalent to those of concrete using only heavy sand. However, when the substitution rate of steel sand exceeds 50%, the amount of air, compressive strength and tensile strength are somewhat reduced.

• Steel and Composite Structures
• /
• v.17 no.3
• /
• pp.339-358
• /
• 2014

Exodermic deck systems are new composite steel grid deck systems which have been used in various projects during the past decade. One of the eminent features of this system is considerable reduction in the structure weight compared to the ordinary reinforced concrete decks and also reduction in construction time by using precast Exodermic decks. In this study, dynamic properties of the Exodermic deck bridges with alternative perfobond shear connectors are investigated experimentally. In order to evaluate the dynamic properties of the decks, peak picking and Nyquist circle fit methods are employed. Frequencies obtained experimentally are in good agreement with the results of the finite-element solution, and the experimental results show that the first mode is the most effective mode among the obtained modes. The first four modes are the rigid translational motion modes, and the next two modes seem to be rigid rotational motion modes around a horizontal axis. From the 7th mode onwards, modes are flexible. The range of damping ratios is about 0.5%. Furthermore, the static behavior of the Exodermic decks under a static load applied at the center of the decks was investigated. Failure of the decks under positive bending was punching-shear. The bending strength of the decks under negative bending was about 50 percent of their strength under positive bending. In addition, the weight of an Exodermic deck is about 40% of that of an equivalent reinforced concrete slab.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.18 no.1
• /
• pp.53-61
• /
• 2014

RC shear wall sections which have irregular shapes such as T, ㄱ, ㄷ sections are typically used in low-rise buildings in Korea. Pushover analysis of building containing such members costs a lot of computation time and needs professional knowledge since it requires complicated modeling and, sometimes, fails to converge. In this study, a method using an equivalent column element for the shear wall is proposed. The equivalent column element consists of an elastic column, an inelastic rotational spring, and rigid beams. The inelastic properties of the rotational spring represent the nonlinear behavior of the shearwall and are obtained from the section analysis results and moment distribution for the member. The use of an axial force to compensate the difference in the axial deformation between the equivalent column element and the actual shear wall is also proposed. The proposed method is applied for the pushover analysis of a 5- story shear wall-frame building and the results are compared with ones using the fiber elements. The comparison shows that the inelastic behavior at the same drift was comparable. However, the performance points estimated using the pushover curves showed some deviations, which seem to be caused by the differences of estimated yield point and damping ratios.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.3 no.2
• /
• pp.132-139
• /
• 2015

In this study, the different unit cement content by the ratio of water absorption and water-cement ratio are applied to examine the properties of the concrete used the aggregate recycled by the crushing treatment. According to the experimental results, in the mix of low strength and high water-cement ratio, both of the compressive strength is almost equal in the concrete using the recycled aggregate by the crushing treatment and the concrete using broken stones. It means that the recycled aggregate has the low effect of the amount of bonded mortar. But, in the mix of high strength and low water-cement ratio, the concrete using the recycled aggregate by the crushing treatment has 40% less of the compressive strength than that using broken stones by the effect of the amount of bonded mortar. On the other hand, after 8 weeks, the dry shrinkage of the recycled aggregate with 7% of the ratio of water absorption doubles that of the broken stones with 1% ($-350{\times}10^{-6}$), in other words $-700{\times}10^{-6}$. Thus, the dry shrinkage should be prior to any other conditions in recycling waste concrete for the aggregate for concrete. When the recycled aggregate with 3% of the ratio of water absorption is used, the compressive strength of the rich mix concrete ($450kg/m^3$ of the unit cement content) is equivalent to that of the concrete using broken stones, while in using the recycled aggregate with 7% of the ratio of water absorption, the rich mix concrete has 7% lower compressive strength than the concrete using broken stones. But, the compressive strength of the ordinary mix concrete ($350kg/m^3$ of the unit cement content) is far lower than that using broken stones.

• Journal of the Korea Concrete Institute
• /
• v.15 no.2
• /
• pp.335-343
• /
• 2003

In the previous experimental study, it is verified that the ultimate strain of concrete (${\varepsilon}$$_{cu}$=0.003) and coefficient of equivalent stress block (${\beta}$$_1$) can be used for the analysis of RC beams under biaxial and uniaxial bending moment. However, the characteristics of stress distribution of non rectangular compressed area in the RC columns are different to those of rectangular compressed area. The properties of compressive stress distribution of concrete have minor effect on the pure bending moment such as beams, but for the columns subjected to combined axial load and biaxial bending moment, the properties of compressive stress distribution are influencing factors. Nevertheless, in ACI 318-99 code, the design tables for columns subjected to axial loads with bidirectional eccentricities are based on the parameters recommended for rectangular stress block(RSB) of rectangular compressed areas. In this study the characteristics of stress distribution through both angle and depth of neutral axis are observed and formulated rationally. And the modified parameters of rectangular stress block(MRSB) for non rectangular compressed area is proposed. And the computer program using MRSB for the biaxial bending analysis of RC columns is developed and the results of MRSB are compared to RSB and experimental results respectively.