• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.859-866
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• 2003

When calcium sulfoaluminate-based expansive cement was hydrated, ettringite and monosulfate were mainly formed. The crack of hardened cement was prevented by compensating drying shrinkage due to formation of the above hydrates. In order to study the hydration properties of calcium sulfoaluminate-based expanding cement, 3CaOㆍ3Al$_2$O$_3$ㆍCaSO$_4$(C$_4$A$_3$S) was prepared by chemical synthesis, and then the hydration of $C_4$A$_3$S-Ca(OH)$_2$-CaSO$_4$.$2H_2O$-C$_3$A system_was characterized. Good $C_4$A$_3$S phase was prepared at $1300^{\circ}C$ by chemical synthesis, and the main hydration product of $C_4$A$_3$S-Ca(OH)$_2$-CaSO$_4$.2$H_2O$ system was ettringite. In the case of hydration $C_4$A$_3$S-Ca(OH)$_2$-CaSO$_4$ㆍ 2$H_2O$-C$_3$A system, ettringite was formed in the early period and it was transformed into monosulfate while consumed gypsum.

• Journal of the Korean Institute of Landscape Architecture
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• v.46 no.6
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• pp.120-126
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• 2018

The study conducted an experiment in which residual aggregate and polypropylene fibers are mixed in concrete, and an experiment in which granite and polypropylene fibers are mixed. Two types of experiments, in particular, changed the amount of polypropylene fibers, and examined the mechanical properties of slump, compressive strength, tensile strength and the like. To establish a light and easy-to-use material for landscape construction and packaging material development by comparing two kinds of experimental results, comparing and analyzing residual aggregate as experimental materials and materials using granite soil to prevent partial destruction due to cracks in drying shrinkage. The more the amount of the PP fibers increases in concrete, the more the volume of the PP fibers increases, the less the slump is determined. As a result of the compressive strength, the cast-down earth concrete is measured to be about 59% to 71% of the concrete strength. As the amount of PP fibers mixed in increased, the compression strength showed a relative decrease. As a result of tensile strength, it is found that the granite concrete is about 68-67% of concrete tensile strength. It was found that the compression strength decreased as the amount of PP fibers mixed in concrete or fire-gant concrete was increased. Then, when polypropylene fibers are mixed in the concrete and the concrete, it is found that tensile strength is increased. By analyzing these results, a fixed amount of PP fiber is mixed in the concrete mixed with the granite soil and utilized for various structures in the field of landscape construction or materials related to packaging, the prevention and improvement effect of the structure is determined.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.498-505
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• 2020

Aggregate occupies about 70-85% of the concrete volume and is an important factor in reducing the drying shrinkage of concrete. However, when constructing high-rise buildings, it acts as a problem due to the high load of natural aggregates. If the load becomes large during the construction of a high-rise building, creep may occur and the ground may be eroded. Material costs increase and there are financial problems. In order to reduce the load on concrete, we are working to reduce the weight of aggregates. However, artificial lightweight aggregates affect the interface between the aggregate and the paste due to its higher absorption rate and lower adhesion strength than natural aggregates, affecting the overall strength of concrete. Therefore, in this study, in order to grasp the interface between natural aggregate and lightweight aggregate by type, we adopted a method of measuring electrical resistance using an EIS measuring device, which is a non-destructive test, and lightweight bone. The change in the state of the interface was tested on the outside of the material through a blast furnace slag coating. As a result of the experiment, it was confirmed that the electric resistance was about 90% lower than that in the air-dried state through the electrolyte immersion, and the electric resistance differs depending on the type of aggregate and the presence or absence of coating. As a result of the experiment, the difference in compressive strength depending on the type of aggregate and the presence or absence of coating was shown, and the difference in impedance value and phase angle for each type of lightweight aggregate was shown.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.314-320
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• 2022

The function of reinforcing fibers used in building materials is to maintain resistance to bending loads and to function for cracking caused by drying shrinkage. High-density fiber-cement composites are mainly used for linear plates and are used to increase bending resistance. Therefore, tensile properties, bonding strength with cement hydrate, alkali resistance, and the like are required. Recently, as the non-combustible performance has been strengthened, a function to minimize the occurrence of sparks during high-temperature heating has been added. Therefore, the use of organic fibers is limited. In this study, a study was conducted to replace polypropylene used as reinforcing fiber with hemp fiber with excellent heat resistance. Hemp fibers have excellent heat resistance, good affinity with cement, and excellent alkali resistance. Based on the total volume of polypropylene fibers used in the existing formulation, the non-combustible performance was compared and evaluated by using hemp fibers instead of the polypropylene fibers, and basic physical properties such as flexural strength were tested. As a result of conducting a non-combustibility and physical property test using hemp fibers with a fiber length of 7 mm using 2 % and 3 % by weight, it was found that there is no remaining time of the flame, and the flexural strength can be secured at 95 % level of the existing polypropylene fiber.

• Journal of Conservation Science
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• v.37 no.2
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• pp.135-143
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• 2021

Conservation treatment that involved filling the lifting parts of wooden cultural heritage is carried out by obtaining wood or wood powder of the same species and mixing it with synthetic resin or natural glue to charge the blank area. Various concentrations and mixing ratios of adhesives and additives are used, depending on the type and condition of the target. Accordingly, in this study, we determined the conditions of the filler suitable for conservation treatment of wooden sculptures with lifted or separated bark in the National Museum of Modern and Contemporary Art. The optimal filler conditions for each adhesive were selected based on drying speed, shrinkage and expansion rates, and physical deformation degree. Then, to verify their actual applicability, these fillers were applied to wood and exposed to high-humidity environment and their cross-sections were observed. The fillers showed stable application in the following order: animal glue, PVAc adhesive, acrylic adhesive. In conclusion, a 1:2 mixture of animal glue and wood powder is a suitable filler for conservation treatment of wooden sculpture with lifted bark. The results of this study suggest appropriate ways to stabilize the bark that was lifted or separated from a wooden sculpture, thus enabling the future conservation treatment of the artworks under similar conditions.

• Journal of the Korea Institute of Building Construction
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• v.21 no.3
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• pp.181-188
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• 2021

In this study, the various performance of dry cement mortar for Korean floor heating system depending on water-to-dry mortar ratios (W/DM) applied in project site was evaluated. According to the experiment conducted, the importance of mixing water for dry cement mortar was revealed by resultant performance or quality of the dry cement mortar for floor finishing by changing W/DM controlled in project site by workers. As the general trend, the flow was increased, and the unit volume weight was decreased with increasing W/DM. Additionally, compressive strength and drying shrinkage were significantly influenced by W/DM. Hence, it can be stated that the adding water for dry cement mortar should be managed precisely since excessively increased W/DM for workability improvement can cause performance degradation of floor mortar with the failures such as excessive bleeding, and severe segregation during the fresh state. As a summary of the study, to achieve a desirable performance of dry cement mortar, approximately 20 % of W/DM can be suggested to be managed in project site.

• Journal of the Society of Disaster Information
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• v.20 no.1
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• pp.20-31
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• 2024

Purpose: Research and development of high-strength concrete enables high-rise buildings and reduces the self-weight of the structure by reducing the cross-section, thereby reducing the thickness of beams and slabs to build more floors. A large effective space can be secured and the amount of reinforcement and concrete used to designate the base surface can be reduced. Method: In terms of field construction and quality, the effect of reducing the occurrence of drying shrinkage can be confirmed by studying the combination of low water bonding ratio and minimizing bleeding on the concrete surface. Result: The ease of site construction was confirmed due to the high self-charging property due to the increased fluidity by using high-performance water reducing agents, and the advantage of shortening the time to remove the formwork by expressing the early strength of concrete was confirmed. These experimental results show that the field application of ultra-high-strength concrete with a design standard strength of 100 MPa or higher can be expanded in high-rise buildings. Through this study, we experimented and evaluated whether ultra-high-strength concrete with a strength of 130 MPa or higher, considering the applicability of high-rise buildings with more than 120 floors in Korea, could be applied in the field. Conclusion: This study found the optimal mixing ratio studied by various methods of indoor basic experiments to confirm the applicability of ultra-high strength, produced 130MPa ultra-high strength concrete at a ready-mixed concrete factory similar to the real size, and tested the applicability of concrete to the fluidity and strength expression and hydration heat.

• Korean Journal of Heritage: History & Science
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• v.50 no.4
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• pp.148-165
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• 2017

Mural paintings drawn inside ancient tombs are very sensitive to changes in the environment such as temperature and humidity, especially the finish layer of the tomb murals differ in preservability depending on the material properties and humidity conditions. In this study, I examined the mural painting of Songsan-ri Tomb No.6, where the finish layer was made of earth, and identified the physical changes that can occur due to drying, depending on the material properties of the finish layer. I found out through particle size analysis that the finish layer of the mural painting in Songsan-ri Tomb No.6 is about 85.0wt% below silt, about 14.0wt% clay therein, mostly composed of silt and below clay. I also found out through physical property evaluation that surface change rate of samples showed the largest change at 15.5% in reproduced finish layer sample made up of bentonite, followed by 7.8% of reproduced finish layer sample made up of celadon soil, 6.3% of reproduced finish layer sample made up of loess, 6.2% of reproduced finish layer sample composed of white clay and the same order of change in appearance was confirmed in each sample consisted of soil. In addition, it showed the same trend of surface change rate, and the bentonite condition showed the largest change, in the measurement of shrinkage rate and expansion rate. The experiment shows that the finish layer composed of soil is affected by cohesion among particles according to the content of fine parts and the relationship between the agglomeration due to the content of the differentiated part and the stress due to the expansibility depending on the kind of the clay mineral etc. Therefore, it can be concluded that the physical damage occurred in the mural painting finish layer of the Songsan-ri Tomb No.6 is related to the factors such as the material characteristics of the soil and the highly humid environmental change inside the tomb.

• International Journal of Highway Engineering
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• v.8 no.2 s.28
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• pp.55-62
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• 2006

Transverse cracks in continuously reinforced concrete pavement (CRCP) occur at early ages due to temperature and moisture variations. The width and spacing of transverse cracks have a significant effect on pavement performance such as load transfer efficiency and punchout development. Also, crack widths in CRCP depend on 'zero-stress temperature,' which is defined as a temperature where initial concrete stresses become zero, as well as drying shrinkage of concrete. For good long-term performance of CRCP, transverse cracks need to be kept tight. To keep the crack widths tight throughout the pavement life, zero-stress temperature must be as low as practically possible. Thus, temperature control at early ages is a key component In ensuring good CRCP performance. In this study, concrete temperatures were predicted using PavePro, a concrete temperature prediction program, for a CRCP construction project, and those values were compared with actual measured temperatures obtained from field testing. The cracks were also surveyed for 12 days after concrete placement. Findings from this study can be summarized as follows. First, the actual maximum temperatures are greater than the predicted maximum temperature in the ranges of 0.2 to 4.5$^{\circ}C$. For accurate temperature predictions, hydration properties of cementitious materials such as activation energy and adiabatic constants, should be evaluated and accurate values be obtained for use as input values. Second, within 24 hours of concrete placement, temperatures of concrete placed in the morning are higher than those placed in the afternoon, and the maximum concrete temperature occurred in the concrete placed at noon. Finally, from the 12 days of condition survey, it was noted that the rate of crack occurrence in the morning placed section was 25 percent greater than that in the afternoon placed section. Based on these findings, it is concluded that maximum concrete temperature has a significant effect on crack development, and boner concrete temperature control is needed to ensure adequate CRCP performance.