• Proceedings of the Korean Institute of Building Construction Conference
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• 2016.05a
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• pp.151-152
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• 2016

In this study, the shrinkage properties of concrete with the high-performance shrinkage admixture and the crack reinforcing materials applied to the high-flatness flooring of hypermarkets, outlets and warehouses was evaluated. The concrete with the popular shrinkage admixture is significantly reduced compared to the plain concrete without shrinkage admixture for the dry shrinkage deformation, and the difference of shrinkage ratio between the concretes has been shown to increase with increasing age.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.158-159
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• 2014

In general, the shrinkage occurring in the floor mortar is large the influence by the dry shrinkage. In order to reduce the cracks occurring in the floor mortar, studies of physical methods are often performed, but these methods is difficult to prevent cracking of the floor mortar essentially. Therefore, in this study, the dry shrinkage properties of floor mortar of gypsum and red clay type using alpha-hemihydrate gypsum had been evaluated. The experimental variables were cement mortar(CM), gypsum mortar(GM), red-clay mortar(RM), the evaluation items was conducted experiment to evaluate the setting time, the compressive strength, drying shrinkage cracks, the dry shrinkage. As a result, it was confirmed that condensation time of GM is shorter that that of CM, and GM satisfied the compressive strength of the floor mortar standard. Also shrinkage deformation of GM reduced more than the CM.

• Computers and Concrete
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• v.19 no.5
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• pp.443-449
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• 2017

Taking high geothermal tunnels as background, the deformation of concrete for shotcrete use was studied by simulating hot-humid and hot-dry environments in a laboratory. The research is made up by two parts, one is the influence of two kinds of high geothermal environments on the deformation of shotcrete, and the other is the shrinkage inhibited effect of fiber materials (steel fibers, polypropylene fibers, and the mixture of both) on the concrete in hot-dry environments. The research results show that: (1) in hot and humid environments, wet expansion and thermal expansion happened on concrete, but the deformation is smooth throughout the whole curing age. (2) In hot and dry environments, the concrete suffers from shrinkage. The deformation obeys linear relationship with the natural logarithm of curing age in the first 28 days, and it becomes stable after the $28^{th}$ day. (3) The shrinkage of concrete in a hot and dry environment can be inhibited by adding fiber materials especially steel fibers, and it also obeys linear relationship with the natural logarithm of curing age before it becomes stable. However, compared with no-fiber condition, it takes 14 days, half of 28 days, to make the shrinkage become stable, and the shrinkage ratio of concrete at 180-day age decreases by 63.2% as well. (4) According to submicroscopic and microscopic analysis, there is great bond strength at the interface between steel fiber and concrete. The fiber meshes are formed in concrete by disorderly distributed fibers, which not only can effectively restrain the shrinkage, but also prevent the micro and macro cracks from extending.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.521-529
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• 2002

A restraint coefficient for creep and dry shrinkage deformation of concrete in a composite section was derived to calculate the residual stress, and an equation for the loss rate of the pre-compression force was proposed. The derived restraint coefficient was computed by using the transformed section properties for the age-adjusted effective modulus of elasticity. The long-term behavior of complicate composite sections could be analyzed easily with the restraint coefficient. The articles of the current design code was examined for PSC and steel composite sections. The dry shrinkage strains of $150 ~ 200$\times$10^{-6}$ for the computations of the statically indeterminate force and the expansion joint could be under-estimated for less restrained sections such as the reinforced concrete. The dry shrinkage strain of $180$\times$10^{-6}$ for the computation of residual stress in the steel composite section was unreasonably less value. The loss rate of 16.3% of the design code for the PSC composite section in this study was conservative for the long-term deformation of the ACI 205 but could not be used safely for that of the Eurocode 2. For pre-compressed concrete slab in the steel composite section, the loss rate of prestressed force with low strength reinforcement was much larger than that with high strength tendon. The loss rate of concrete pre-compression increased, while that of pre-tension decreased due to the restraint of the steel girder.

• Journal of the Korea Institute of Building Construction
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• v.15 no.4
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• pp.359-365
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• 2015

Floor mortar experiences dry shrinkage by temperature and humidity difference of internal matrix with material type. Also, since floor mortar is influenced by environmental conditions during placing and curing period, cracks are likely to be occurred. In this study, it was evaluated the hardening and dry shrinkage properties of non-sintered binder based floor mortar utilizing alpha-hemihydrate gypsum which has expansibility in order to prevent crack of the floor mortar. It was applied to the construction site, and examined the effects of external environmental conditions on shrinkage deformation and cracking. Different types of slag accelerated initial and final setting in comparison with cement mortar and its compressive strength was satisfied standard compressive strength for floor mortar. Also shrinkage deformation behavior after the initial expansion exhibited a similar tendency with the cement mortar. From the field application result, no crack was found from slag mortar, and it is determined that the slag mortar has better dimensional stability than cement mortar caused by external environment conditions.

• Journal of the Korea Institute of Building Construction
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• v.15 no.5
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• pp.457-464
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• 2015

The alternative material for cement has been attracting attention in construction projects. Especially, the alkali activated slag(hereafter, AAS) concrete is able to use for a structural vertical member because of 40MPa of compressive strength, However, the research about time-dependent deformation such as creep which is important to strength member is insufficient. Therefore, in this study, experiments were performed with respect to time-dependent deformation including the drying shrinkage and creep deformation of AAS concrete. The creep deformed ratio of AAS concrete was more than OPC concrete by approximately 4.3% and the dry shrinkage deformation of AAS concrete was more than OPC concrete by approximately 69%. The large amount of sodium silicate, alkali activator, is added causing temperature crack than promoted drying and drying creep which is confirmed by water ration test and SEM.

• Journal of the Korean Ceramic Society
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• v.19 no.3
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• pp.241-249
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• 1982

Two dinnerware porcelain bodies involving partial replacement of feldspar and kaoline by about 35wt% domestic GYUNGJU-pottery stone were developed and their properties such as shrinkage, porosity, firing range, linear thermal expansion, pyroplastic deformation, degree of whiteness and mechanical strength were compared with those of a traditional clay-flint-feldspar body. The experimental results showed that one of the clay-flint-feldspar-pottery stone body with 1% ZnO addition had the firing range of 115$0^{\circ}C$~121$0^{\circ}C$, whereas the traditional body had the firing range of 12$25^{\circ}C$~129$0^{\circ}C$. The linear drying shrinkage and linear dry-to-fired shrinkage of all bodies were 2.5~4.5% and 15~18%, respectively. And the major crystalline phases of sintered bodies were $\alpha$-quartz and secondary mullite surrounded by glassy phases. The modulus of rutpture of sintered bodies was ranged from 860 to 870kg/$\textrm{cm}^2$, and the microhardness of sintered bodies was 680 kg/$\textrm{cm}^2$.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.146-147
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• 2020

In this study, creep deformation characteristics of high strength concrete under dry curing conditions were investigated. It was confirmed that the creep coefficient decreases as the compressive strength of concrete increases. In addition, a modified proposal for calculating the ultimate creep factor of the ACI 209 model can be derived using the measured values.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2000.10a
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• pp.471-476
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• 2000

Long-term behavior of reinforced clayey soil by model tests were performed to investigate the effect of reinforcement during loads and under static loads. In order to determine proper contents by weight of monofilament polypropylene fiber and calcium carbonate, the drying shrinkage and compressive strength tests had been conducted before model tests. Model tests were run on a clayey soil mixed with or without reinforcement and test specimen in test apparatus was placed in air dry for 7days before load application. In the case of fiber reinforced soil, the horizontal strain was lower than others during loads because the presence of fibers increased the soil's resistance to deformation. All of reinforced clayey soil, horizontal strain decreased as the water content decrease under static loads.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.136-143
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• 2006

In this study, recently it is urgently required that demolition waste concrete has to be recycled on the construction because urban development is accelerated and redevelopment project is rapidly expanded, production quantity of construction and demolition waste concrete is being increased. As a results of drying shrinkage test under restrained and unrestrained condition, although workability and mechanical properites of concrete using HQRS were similar to that of concrete using natural sand, there were a great difference in deformation characteristic of dry shrinkage according to replacement ratio of HQRS. And, it makes sure that use of HQRS instead of partial nature sand was effective because drying shrinkage of concrete using 30 volume percentage of HQRS was smaller than that using only natural sand. Therefore, it is the objective of this study to provide the fundamental data about the re-application as an analysis of the drying shrinkage characteristics of concrete using HQRS and it is able to creta a high value-added by using HQRS.