• Journal of the Korean Geotechnical Society
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• v.40 no.1
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• pp.55-63
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• 2024

In this study, a thermomechanical numerical model was developed to evaluate the stability of energy slabs. First, a wall-type energy slab was installed in a residential underground parking lot, and thermal performance tests were conducted. Based on the tests, a numerical thermohydraulics model of the energy slab was developed to accurately simulate the thermal behavior in thermal performance tests. Finally, utilizing the temperature data acquired using the developed model, a thermomechanical numerical model of the energy slab was established. The thermomechanical model was then used to simulate the thermal stresses induced by operating the energy slab. The results demonstrated a maximum thermal stress of 5,300 kPa, which highlights the need to utilize cement mortar with sufficient tensile strength to realize stable operation of the energy slab.

• Journal of Korean Society of Disaster and Security
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• v.17 no.1
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• pp.27-35
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• 2024

This paper presents experimental research results to evaluate the applicability of chemical neutralization reaction and ultrasonic wave to remove cement paste and mortar attached to the surface of recycled aggregate. In order to derive optimal ultrasonic cleaning efficiency and chemical neutralization reaction, experiments were conducted using variables such as ultrasonic frequency and type of chemical solution. As a result, the optimal frequency was found to be 24 kHz, and immersion in a 15% hydrochloric acid solution for 30 minutes of stimulation showed the highest efficiency. In addition, the specific gravity, absorption rate, and wear rate of the quality-improved recycled coarse aggregate were similar to those of general aggregate and were found to satisfy all KS F 2527 standards. Therefore, it is believed that the recycled aggregate whose quality has been improved through the method proposed in this study can be used for concrete.

• Magazine of the Korean Society of Agricultural Engineers
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• v.11 no.4
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• pp.1798-1802
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• 1969

The experiment was carried out as one of the basic studies to improve the alkali-resistance of cement mortars and it was conducted to investigate some propetties of mortars relating to weight losses when exposed to 0.1 N salution of sodium hydroxide. The experiment and the results obtained are summarized as follow; 1. The specimens used in this experiment were made of 5 centi-meter cubes of mortar having such various ratios of mix by weight as 1 : 1, 1 : 3, 1 : 5, 1 : 7 and 1 : 10. 2. Physical tests included compressive strengths at 7 days, 28 days, 3 months, and 6 month, and 5 hour boiling absorption test. 3. In alkali test, every specimen was immersed into 0.1 N solutions of sodium hydroxide. The specimens exposed to the alkali solution were weighed to determine the weight losses of the alkail-corroded at one week interval for 7 week's exposure and the old alkali solutions were also changed to fresh solutions when weighed the weight losses by alkali attack at one week interval. 4. According to the alkail test after 7 week's exposure, no weight losses were observed on ratios of mix 1:1 and 1:3 and slight weight losses occurred on ratios of mix 1:5 and 1:7, but relatively large amount of weight losses were showed by 36.6 per-cent on ratios of mix 1:10. It was also found that the weight losses of the alkali-corroded were extremely lower than those of the acid-corroded at the some concentrations as 0.1 N of solutions. 5. In order to make better quality of alkali-resistant mortar it might recomend that a 1:7 mix or richemixes, use of small amount of mixing water for watertight, 20 per cent or less absorption by 5 hour boiling 1,600 kirogram per cubic meters or denser densities by absolute dry base are available for physical properties of mortar. It could conclude acid-resistant mortars were so high alkali-resistant, that it is expected to make and improve the acid-resistant mortars for getting rid of damages by alkali attack.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.101-111
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• 2016

It is possible that aggregates add on to geopolymer based fly ash to mix mortar and concrete like cement. This is necessary to evaluate mineral composition, particle shape, surface, size distribution, density and absorption ratio for fine aggregates due to few detailed research to examine influence of fine aggregates properties on unhardened geopolymer concrete. In this research, used two different fine aggregates, Jumunjin sand(having quartz, mica, feldspar, pyroxene in mineral composition, more than 96% of total size between -0.60 and +0.30mm, angular shape and rough surface) and ISO sand(having almost all quartz in mineral composition, more than 51% size between -1.40 and +0.60mm, simultaneously varied size distribution, spherical shape and smooth surface). After an experimental result of the varied ratio of Si/Al=1.0-4.1 geopolymer paste, mix proportion respectively applied Si/Al=1.5 having the highest compressive strength to mortar and Si/Al=3.5 having the highest consistency to concrete. Geopolymer mortar by mixing with Jumunjin and ISO sand in varied range of 20-50wt.% showed flow size increase between 69.5 and 112.0mm, between 70.5 and 126.0mm respectively. Geopolymer concrete at an addition of 77wt.% of total aggregates ratio showed that average compressive strength was 32MPa and the consistency was favorable to molding. Since ISO sand observing varied size distribution, spherical shape, smooth surface, low absorption ratio resulted in advantageous properties on consistency of geopolymer, geopolymer concrete can be suitable for using the fine aggregates similar to ISO sand.

• International Journal of Highway Engineering
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• v.13 no.3
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• pp.51-63
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• 2011

Surface of fine-size exposed aggregate portland cement concrete pavements(FS-EAPCC) is consist by exposed coarse aggregate to remove upper 2~3mm mortar of concrete slabs. Advantages of FS-EAPCC are maintaining low-noise and adequate skid-resistance level during the performance period. However, FS-EAPCC is required rational management criteria for field application, since it is early stage for application. Design construction and quality control criteria of FS-EAPCC was temporary laboratory tests which including optimum mix and exposing method, selection of adequate aggregate, resistance against, environmental loading and etc. However, these criteria need to be validated base on field application. In this study, experimental constructions were performed and construction procedure and quality control criteria were suggested based on the performance of the FS-EAPCC.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.670-678
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• 2003

Recently, since industrial waste and life waste leaped into a pollution source, the building material used now a days is striking the limit. The purpose of this paper is to investigate an application of recycled coal ash using non-sintering method in the construction field. Accordingly, compressive strength, elastic modulus and drying shrinkage were experimentally studied for hardened coal ash using the non-sintering method. Also, Lineweaver and Burk method were applied to the regression analysis of drying shrinkage for the proposal equation. Elastic modulus, compressive strength of material become the basis properties of structural design. And these properties by age for hardened coal ash are important because of change by pozzolan reaction. This hardened coal ash is weak for tensile stress like that of concrete. And drying shrinkage is very important factor to make huge tensile force in early age. In the results, although some differences were shown when comparing coal ash with mortar or concrete, the application as a building material turned out to be possible if further researches were carried out. And the shrinkage characteristic of hardened coal-ash reveals to be similar to that of moderate heat cement.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.547-557
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• 2010

This paper presents a study on the development of next generation smart concrete in an eco-friendly manner using micro-biologically induced calcite precipitation (MICP) via microbial biomineralization. It seems that currently, the reformation and functional improvement of concrete using MICP can be achieved using Sporosarcina pasteurii, which is a representative microorganism that produces calcite precipitation. Based on previous studies on MICP the biochemical tests and crystallinity evaluation of cement using sporoasrcina pasteurii and four additional micro-organisms from the concrete structures as identified by 16S rDNA sequence analysis were conducted. Also by applying the Sporosarcina pasteurii and separated four effective micro-organisms from the concrete structures to mortar, the compressive strength improvement by varying curing conditions, repair of crack were examined, and plans for future study were suggested. The effect of the application of effective micro-organisms can lead to the development of a new material that will contribute to resolution of environmental problems and facilitate repair work, and this can also serve as a new research theme in the future. In addition, the importance of this study is to use micro-organism, which is found common in concrete structures, this new microbial is not only environmentally safe but also persists in the natural environment for an extended period of time. Therefore, it seems to have a great potential to became a new environmentally low-burdened functional material.

• Journal of the Korea Institute of Building Construction
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• v.15 no.5
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• pp.483-489
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• 2015

The Purpose of this study was to establish the basic data on the mechanical properties of PCM in the high temperature range. To this end, an experiment was conducted on the characteristics of the residual compressive strength by temperature (100, 200, 400 and $600^{\circ}C$) with a fixed temperature heating. An after heating test was performed to investigate the properties after fire damage. The result showed that the residual compressive strength of PCM had a tendency to decrease, regardless of the type of polymer. It was also found that when the contents were low, the residual compressive strength started to greatly decrease from the high temperature range of $400^{\circ}C$, and that the specimen containing PAE showed a steeper slope than the specimen containing EVA. However, since little studies have been conducted on the mechanical properties of PCM with the high temperature, it is considered that, in addition to this study, basic studies must be preceded, including studies on the repairing methods.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.557-563
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• 2008

Recently, the amount of disposed construction materials like demolished concrete is growing fast and the shortage of natural concrete aggregate is becoming serious. Therefore, recycling of aggregate extracted from the demolished concrete is getting important and use of the recycled aggregate for concrete has been seriously considered. However, the use of the recycled aggregate even for low performance concrete is very limited because recycled aggregate which contains large amount of old mortar has very low quality. Therefore, removing the paste sticked to the recycled aggregate is very important in the manufacturing of high quality recycled aggregate. We have studied a series of research according to complex crushing method, which is removed the ingredient of cement paste from recycled fine aggregate using both the low speed wet abrasion crusher as mechanical process and the acid treatment as chemical processes. This paper is to analyze the quality of the recycled fine aggregate produced by those complex method and investigate optimum manufacturing condition for recycled fine aggregate by the design of experiments. The experimental parameters considered are water ratio, coase aggregate ratio, and abrasion time. As a result, data concerning the properties of recycled sand were obtained. It was found that high quality recycled fine aggregate could be to obtain at the condition of the fifteen minute of abrasion-crusher time and the over 1.0 of recycled coarse aggregate ratio.

• Journal of Korean Society of Rural Planning
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• v.13 no.3
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• pp.83-90
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• 2007

The purpose of main entrance was to protect the house with the wall and working for the house-gate where people come in and go out. On the other hand, the type of main entrance is changed variously depended on the materials for house and method of construction. Eleven villages in the Chungyang-Gun where the environment of rural villages is well maintained was chosen and researched to make data. These data of visual landscape elements were analysed by using the SPSS 12.0 for Windows. Relations of the visual component elements were analysed by the analysis for frequency and analysis for crosstab. From the above research we could conclude below results. Through review of the pre-researching and researching literatures, 11 types of visual component elements were selected such as the types of the gate, the looking through degree of the gate, the material of the gate, the color of the gate, the plan of the house, the material of the roof, a material of the wall, a color of the wall, the form of the penetration, the area to put, the area of a site, the year of the constructing a building. For the types of the gate, the gate from without the roof has been the most popular since it appeared 41.5%. For the looking through degree of the gate, a complete blockade form has been the most popular since it appeared 63.2%. For the material of the gate, the iron plate has been the most popular since it appeared 32.1%. For the color of the gate, color has been the most popular since it appeared 68.4%. For the plan of the house, 'ㄷ' form has beneath most popular since it appeared 38.3%. For the material of the roof. The Zinc has been the most popular since it appeared 51.9%. For a material of the wall, A cement mortar has been the most popular since it appeared 47.7%. For a color of the wall, Without tile color has hem the most popular since it appeared 67.0%. For the form of the penetration. The plain form has been the most popular since it appeared 54.0%. For tile area of a site, $100m^2{\sim}200m^2$ has been the most popular since it appeared 39.0%. The results of this study can provide to use of indicates four rural-housing reform. From now on, the results look forward to offering the meaning directions for the improvement of rural house gates.