• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.3
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• pp.41-49
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• 2015

The repair of manhole raise has been caused much construction times and disruption of traffic flow, serious environmental pollution from crushed construction wastes, and budget waste due to the repeated repair construction works. In order to overcome such problems, we have developed the new manhole repairing composite structures by using a glass fiber-reinforced polymer (GFRP) pipe, which can raise manhole to the regular height of the overlayed road pavement with rapid construction and minimum traffic jams. This environmental-friendly technology is method completed by the methyl methacrylate monomer (MMA) double wide flanged GFRP pipe composite structures in order to raise manhole to the regular height. In this paper, two kinds of the compressive strength tests of MMA mortar composites were conducted and evaluated by a general compressive strength test, and compressive strength test after freezing-thawing resistance test. It was found that this MMA mortar composites will be used for the application of the double wide flanged GFRP pipe composite structures.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.3
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• pp.183-198
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• 2012

Dynamic buckling, also known as parametric resonance, is one of the dynamic instability phenomena which may lead to catastrophic failure of structures. It occurs when compressive dynamic loading is applied to the structures. Therefore it is essential to establish a reliable procedure to test and evaluate the dynamic buckling behaviors of structures, especially when the structure is designed to be utilized in compressive dynamic loading environment, such as supercavitating underwater vehicle. In the line of thought, a dynamic buckling test system is designed in this work. Using the test system, dynamic buckling tests including beam, plate, and stiffened plate are carried out, and the dynamic buckling characteristics of considered structures are investigated experimentally as well as theoretically and numerically.

• Journal of Korean Society of Rural Planning
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• v.11 no.3 s.28
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• pp.53-57
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• 2005

Up to recently building are constructed focusing on the convenience of residential condition. However, environmental-friendly materials is required for construction as people are spending more time inside buildings and causes of many problems like sick-building syndrome are known due to the noxious gases and polluted air originated from construction materials. Although loess(hwangtoh) is an environmental-friendly material, it has limitations in compressive strength far a construction material. The purpose of this study is to suggest the optimal ratio of loess(hwangtoh) mortar by tests of compressive strength comparing with standard strength of floor finishing mortar and evaluate the usability of loess(hwangtoh) mortar for floor finishing material through an impact test, a cracking test and a abrasion test. Based on the results of this study, 86% of loess(hwangtoh) and 14% of inorganic binder is suggested for the optimal mixture ratio of loess(hwangtoh) mortar. Moreover, the characteristics of loess(hwangtoh) is suitable for floor finishing material in impact, crack, abrasion.

• Advances in concrete construction
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• v.10 no.3
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• pp.237-245
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• 2020

Past research efforts already established geopolymer as an environment-friendly alternative binder system for ordinary Portland cement (OPC) and recycled aggregate is also one of the promising alternative for natural aggregates. In this study, an effort was made to produce eco-friendly mortar mixes using geopolymer as binder and recycled fine aggregate (RFA) partially and study the resistance ability of these mortar mixes against the aggressive environments. To form the geopolymer binder, 70% fly ash, 30% ground granulated blast furnace slag (GGBS) and alkaline solution comprising of sodium silicate solution and 14M sodium hydroxide solution with a ratio of 1.5 were used. The ratio of alkaline liquid to binder (AL/B) was also considered as 0.4 and 0.6. In order to determine the resistance ability against aggressive environmental conditions, acid attack test, sulphate attack test and rapid chloride permeability test were conducted. Change in mass, change in compressive strength of the specimens after the immersion in acid/sulphate solution for a period of 28, 56, 90 and 120 days has been presented and discussed in this study. Results indicated that the incorporation of RFA leads to the reduction in compressive strength. Even though strength reduction was observed, eco-friendly mortar mixes containing geopolymer as binder and RFA as fine aggregate performed better when it was produced with AL/B ratio of 0.6.

• Computers and Concrete
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• v.31 no.2
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• pp.97-110
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• 2023

This study investigates experimentally the impact of magnetized water (MW) on the fresh and hardened characteristics of concrete. Five types of MW are produced using magnetic fields of 1.4 and 1.6 Tesla for treating water with 100, 150, and 250 cycles. The concrete properties are assessed using the slump test, compressive strength test, scanning electron microscopy (SEM) analysis, energy dispersive X-ray analysis (EDX), and Fourier transform infrared spectrophotometry (FTIR). Furthermore, the chemical-physical characteristics of tap water (TW) and MW are evaluated. The results showed the magnetic field intensity has a significant impact on the magnetization effect; the best magnetizing conditions were found when TW was exposed successively to magnetic fields of 1.6 T and 1.4 T for 150 cycles. In addition, 150 MW cycles can be used to improve the compressive strength and workability of concrete by 40% and 17%, respectively. pH, total dissolved solids, and electrical conductivity improved by 15%, 17%, and 7%, respectively, when using MW. Additionally, MW can be used to enhance cement hydration chemical processes and made concrete's structure denser.

• Explosives and Blasting
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• v.22 no.1
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• pp.81-91
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• 2004

Samples examined in this paper were selected from Samwoo building stone, Sinra building stone, Gana building stone, and Chung gin building stone in Kyunggi province and Whakwang industry, Gomoch building stone, and Sejin building stone in Kyungbuk province. The point of this study is to examine the physical and mechanical features of Pochun rock, Munkyung rock and Ildong rock through specific gravity, porosity, absorption, point load test, triaxial compressive test Brazilian test, petrology test and chemical analysis test.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.782-788
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• 2002

Several non-destructive test methods have been developed to estimate compressive strength of concrete in other countries. However, their applications are limited in domestic concrete due to their inaccuracies. The purpose of this study is to propose an aging coefficient of compressive strength of structural concrete in rebound number method and ultrasonic pulse velocity method for domestic concrete. The test variables include type of aggregate, curing condition, and compressive strength. Two approaches are used to estimate aging coefficient. One is evaluated by uniform linear regression equation for all ages and shows uniform strength reduction coefficient regardless of material properties and the other is evaluated by individual regression equation for each ages and shows nonuniform strength reduction and rebound increasing coefficients which decrease with increasing of rebound number and compressive strength. The latter result which can include the effect of rebound number and compressive strength is more resonable than the former.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.102-109
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• 2016

This paper presents mechanical properties and chloride diffusivity of the recycled aggregate concretes(RAC) in which natural coarse aggregate was replaced by recycled coarse aggregate(RCA) by compressive strength levels(20, 35, 50 MPa). A total of 9 RAC were produced and classified into three series, each of which included three mixes designed with three compressive strength levels of 20 MPa, 35 MPa and 50 MPa and three RCA replacement ratios of 0, 50 and 100%. Engineering properties of RAC were tested for slump test, air content, compressive strength, chloride penetration depth and chloride diffusion coefficient. The test results indicated that the workability of RAC could be improved or same by RCA replacement ratios, when compared with that containing no RCA. This is probably because of the RCA shape improving the workability of RAC. Also, the test results showed that the compressive strength was decreased by 9~10% as the RCA replacement ratios increase. Furthermore, the result indicated that the measured chloride diffusion coefficient increases by 144% with the increase of the RCA replacement. In the case of the concrete having low level compressive strength, the increase of chloride diffusion coefficient tends to be higher when using the RCA. However, the trend of chloride diffusion coefficient in high level compressive strength concrete is similar to that obtained in general concrete. This is because that the effect of the RCA replacement could be a decrease with increase of compressive strength. Therefore, an advance on the admixture application and mix ratio control are required to improve the chloride resistivity when using the recycled aggregate in large scale.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.157-165
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• 1999

When the ultimate strength of a concrete flexural member is evaluated, the effect of member size is usually not considered. For various types of loading, however, the strength always decreases with the increment of member size. In this paper the size effect of a flexural compression member is investigated by experiments. For this purpose, a series of C-shaped specimens subjected to axial compressive load and bending moment was tested using three different sizes of specimens with a compressive strength of 528 kg/$cm^2$. According to test results the size effect on flexural compressive strength was apparent, and more distinct than that for uniaxial compressive strength of cylinders. Finally a model equation was derived using regression analyses with experimental data.

• International Journal of Concrete Structures and Materials
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• v.10 no.2
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• pp.205-219
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• 2016

High-early-strength-concrete (HESC) made of Type III cement reaches approximately 50-70 % of its design compressive strength in a day in ambient conditions. Experimental investigations were made in this study to observe the effects of temperature, curing time and concrete strength on the accelerated development of compressive strength in HESC. A total of 210 HESC cylinders of $100{\times}200mm$ were tested for different compressive strengths (30, 40 and 50 MPa) and different curing regimes (with maximum temperatures of 20, 30, 40, 50 and $60^{\circ}C$) at different equivalent ages (9, 12, 18, 24, 36, 100 and 168 h) From a series of regression analyses, a generalized rate-constant model was presented for the prediction of the compressive strength of HESC at an early age for its future application in precast prestressed units with savings in steam supply. The average and standard deviation of the ratios of the predictions to the test results were 0.97 and 0.22, respectively.