• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.108-117
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• 2013

Among the byproducts from thermal power plant using coal combustion, fly ash as mineral admixture is widely utilized in concrete manufacturing for its engineering merits. However residuals including bottom ash are usually reclaimed. This study presents an evaluation of engineering properties in cement mortar with pond ash (PA). For this work, two types of pond ash (anthracite and bituminous coal) are selected from two reclamation sites. Cement mortar specimens considering two w/c (0.385 and 0.485) ratios and three replacement ratio of sand (0%, 30%, and 60%) are prepared and their workability, mechanical, and durability performance are evaluated. Anthracite pond ash has high absorption and smooth surface so that it shows reasonable workability, strength development, and durability performance since it has dense pore structure due to smooth surface and sufficient mixing water inside. Reuse of PA is expected to be feasible since PA cement mortar has reasonable engineering performance compared with normal cement mortar.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.101-110
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• 2014

Expansion agent is a very effective admixture for prevention of cracking due to autogenous/drying shrinkage and this can induce internal chemical prestress to embedded reinforcement. In this paper, tension-softening and hardening in cement mortar with steel and CSA expansion agent are experimentally evaluated. Cement mortar with steel reinforcement is prepared and tensile strength test is performed for evaluation of cracking and tensile behavior. In spite of slightly reduced strength and elasticity in CSA mortar, significantly increased tension-hardening behavior is evaluated in CSA mortar with induced chemical prestress. Furthermore previous tension softening models are compared with the test results and improvement are proposed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.163-170
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• 2019

In recent years, various types of industrial wastes are rapidly increasing with the development of high-tech industries. Specially, high-density waste glass of CRT TV containing heavy metals are buried or disposed of due to reprocessing costs and environmental pollution problems. Thus, more basic research is needed to recycle waste such as CRT waste glass such. In this study, the fundamental properties and radiation shielding performance of mortar specimens substituted CRT waste glass as a fine aggregate were analyzed and their application to shielding materials was evaluated. According to the results, the bulk density of mortar specimen replaced with CRT waste glass was increased and the compressive strength and flexural strength were decreased. Meanwhile, the CRT waste glass substitute specimen containing a large amount of lead component showed a higher shielding performance than the general mortar specimen. Especially, the linear attenuation coefficient of CRT waste glass in $122KeV{\cdot}^{57}Co$ of the low energy field was 2.5 times higher than that of normal specimen.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.1
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• pp.102-109
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• 2024

In order to use limestone powder as a material for concrete, the mechanical and durability characteristics of cement matrices manufactured by varying the substitution rate were evaluated. In general, limestone powder did not contribute to the cement hydration reaction, so as a result of the compressive strength test of cement mortar using it, the compressive strength decreased as the substitution rate increased. However, as a result of evaluating the durability performance of cement mortar using limestone powder, such as chloride ion penetration resistance, carbonation resistance, and chemical attack resistance, small particles of limestone powder showed superior results compared to the unsubstituted control mortar due to the micro-filler effect of filling the fine pores inside the cement matrix. Therefore, limestone powder is expected to be used as an effective method for improving the durability of concrete. In this study, the durability was evaluated by changing the mixing amount of limestone powder to 0 %, 5 %, 10 %, and 15 %, but it is judged that it is necessary to study in more detail the effect on the durability by changing the end and mixing amount of limestone powder to various levels in the future.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.363-369
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• 2016

Enhancing mechanical strength of concrete has been fascinated using carbon-based nanomaterials such as CNT and graphene. The key to improving strength is a dispersion of nanomaterials. A novel method is required to investigate the dispersion inner concrete nondestructively. In this study, the optical optical properties such as refractive index and absorption coefficient are measured in nano-cement mortar specimens containing MWCNT and GO using THz electro-magnetic waves. From the results, the properties of nano-cement mortar are confirmed to be 1.0% to 2.5% higher in refractive index, and -14% to 28% higher in absorption coefficient than those of cement mortar at the average values. Using these characteristics, visualizing the dispersion of nano-concrete structures seems possible in future.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.8
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• pp.5636-5645
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• 2015

Physical characteristics of aggregates affect the workability and strength of mortar and concrete, which include their fineness ratio, particle size distribution and water absorption. The workability of construction materials decreases if the incorporated fine aggregates show improper size distribution of their particles. This study shows the particle size effect on the rheological behavior of mortar and provides basic information for evaluating its workability. A mini-slump flow test was adopted to evaluate the workability of mortar. In addition, its plastic viscosity and yield stress were measured using a rheometer for building materials. The sand samples were prepared by sieving river sand and sorting out with their particle sizes. As a result, it was observed that the fines less than 0.7 mm increases the yield stress and plastic viscosity of the mortar samples. If the fines are less than 0.34 mm, the water absorption of the fines dominates change on the workability.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.377-383
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• 2007

In recent years the field application of high performance concrete has been increased to improve the quality and reliability of concrete structures. The mix design of the high performance concrete includes the 2 set-off mixture theory of mortar and coarse aggregate and that of paste and aggregate. The 2 set-off mixture theory of mortar and coarse aggregate has a problem of having to determine its value through repeated experiments in applying the rheological characteristics of mortar. The 2 set-off mixture theory of paste and aggregate has never been applied to high performance concrete since it doesn't take into account the relationship between optimum fine aggregate ratio and unit volume of powder nor does it consider the critical aggregate volume ratio. As the mixture theory of these high performance concretes, unlike that of general concrete, focuses on flowability and charge-ability, it does not consider intensity features in mix design also, the unit quantity of the materials used is determined by trial and error method in the same way as general concrete. This study is designed to reduce the frequency of trial and error by accurately calculating the optimum fine aggregate ratio, which makes it possible to minimize the aperture of aggregate in use by introducing the maximum density theory to the mix design of high performance concrete. Also, it is intended to propose a simple and reasonable mix design for high performance concrete meeting the requirements for both intensity and flowability. The mix design proposed in this study may reduce trial and error and conveniently produce high performance concrete which has self-chargeability by using more than the minimum unit volume of powder and optimum fine aggregate with minimum porosity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.10-19
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• 2013

Recently, researches related to precast modular construction have been actively conducted for nuclear power plant, LNG gas tank, and small-medium PCCV as well as bridges and buildings. In this study, the precast panel cast with steel mesh reinforced mortar (SRM) which is similar reinforced ferrocement was developed for efficient precast construction, construction time reduction, and easy transportation. Mortar mixture with high strength and flowability was obtained from various case studies using silica fume and GGBS. Also, $1,200{\times}600{\times}150mm$ SRM and reinforced concrete (RC) panels were manufactured with reinforcing ratio of 2% and 4%. To verify structural performance of the SRM specimen, the basic material tests, free shrinkage test, and 3-point flexural test with a line loading were carried out. From the test results, it was determined that SRM specimens showed outstanding flexural capacity and ductility. However, the 4% reinforced SRM specimens must consider shear reinforcing to be used as a precast modular member.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.473-476
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• 2008

The use of the recycled fine aggregate to the material of structural concrete is not easy currently because there are some problems, such as the difficulty of quality control and the badness of chemical and physical property other than river sand, crushed fine aggregate. To use of recycled fine aggregate, many researches on the recycling of recycled fine aggregate have been studying until today. However, the result of the research is little except for some results. Therefore, the purpose of this study is to confirm the possibility of use of recycled fine aggregate for raw material of plaster mortar. In this study, various tests were performed such as flow, air content, unit weight, bond strength, and compressive strength test to evaluate the effect according to the substitution of recycled concrete aggregate. The results of strength test showed that the concrete strength improved with the increase of replacement ratio of recycled fine aggregate. In the other side, flow and air content are decreased according to replacement ratio of recycled fine aggregate. The result of this study could be used as the basic data for the recycling of recycled fine aggregate.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.973-981
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• 2002

Recently, the use of high strength concrete (HSC) has increased dramatically md however, few studies have been conducted on the early-age properties of HSC such as setting. The penetration resistance test (specified by KS F 2436) that is the standard test method for determining initial and final setting times of concrete, may not be appropriate for HSC because of the high viscosity of the mortar mixture. To address this issue, an ultrasonic pulse velocity (UPV) monitoring system was used to investigate the setting behavior of mortar and concrete. The experimental study was carried out to measure the UPV's of mortars and concretes having various water/binder ratios (W/B) and various fly ash replacement levels, during the first 24 hours of testing. Test results showed that the UPV in concrete was developed faster than that of mortar with the same W/B, and that of ordinary concrete was greater than that of fly ash concrete. Typical values of UPV were suggested that correspond to the initial and final setting times, based on following criteria: (1) the penetration resistance method; (2) the instant when the UPV begins to develop; and (3) the instant when the UPV development rate is maximum. The method and UPV monitoring device used in this study is promising for the setting assessment of concrete, particularly for HSC.