• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.33-40
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• 2001

In this research, the cracking of tunnel concrete lining was investigated and analyzed through long-term measurement and nonlinear numerical analysis. For one year after the casting of lining, the stresses and strains were measured by the sensors installed in hard rock tunnel lining. The measurements showed that only small stresses which were less than cracking stress occurred in every survey sections regardless of sensor directions. It could be induced that the external load applied to the lining was small or ignorable. Also, it was carried out short-term numerical analysis based on such site condition as ambient temperature, the- degree of overbreak and mold staying period. Long-term numerical analysis based on creep & shrinkage and nonlinear cracking was carried out. The output showed that construction condition and ambient environments could make the lining concrete crack without external loads. The cracks formed in this process does not indicate the structural instability of the tunnel.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.785-788
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• 2005

In this paper, the influence of many factors related to the concrete mixture and the weather condition on plastic shrinkage cracking are analyzed through parametric studies using the numerical models introduced in the companion paper. First of all, through a systematic calculation of bleeding, the relationship between the bleeding constants and concrete mixture is proposed on the basis of the experimental data obtained by many researchers. Moreover, an equation, which can directly determine a critical point at which the evaporation and bleeding is balanced, is introduced, and the efficiency of the introduced equation is verified through the correlation study between the obtained results by the introduced equation and those by the rigorous analyses. The introduced equation can effectively be used to predict and to prevent plastic shrinkage cracking without any rigorous analysis and, in advance, to cope with the sudden changes in the concrete mixture and/or weather condition.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.409-410
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• 2009

The eco-cement concrete using fly-ash was produced for the improvement of the compressive strength of the eco-cement concrete under the long term age, and compressive strength test, drying shrinkage test, uniaxial restraint shrinkage cracking test, and bond test were carried out. In this study, the cracking resistance performance was investigated.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.661-664
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• 2006

Recently, various concrete reinforcing fibers have been used to reduce the plastic shrinkage cracking which occurs before the concrete hardens. In this study, the physical properties of nylon fiber reinforced concrete such as slump, air content, compressive strength and tensile strength were investigated. In addition, the performance of nylon fiber in the plastic shrinkage cracking reduction of concrete has been estimated in comparison with polypropylene, poly vinyl alcohol fiber and cellulose fiber. Nylon fiber showed considerable advantages in terms of the workability of concrete and the plastic shrinkage cracking reduction of concrete compared with polypropylene fiber and cellulose fiber.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.211-212
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• 2022

In this study, the cracking control performance of ultra-low shrinkage concrete was investigated by the field application. As a result, drying shrinkage crack occurred in normal concrete wall, but no crack occurred in ultra-low shrinkage concrete wall. It is determined that the drying shrinkage crack control effect of the ultra-low shrinkage concrete is excellent.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.104-110
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• 2019

Shrinkage is one of typical characteristics of concrete with cement paste and aggregates. A lot of studies on this has been conducted with an assumption that the concrete is a homogeneous material. However, as shrinkage acts on only one of the components that consist of concrete, it is hard to be characterized only by the average effective properties. Therefore, in this paper, the concrete shrinkage, which is one of the typical characteristics and still has a lot of uncertainty, is simulated considering its heterogeneous properties. Using a meso model, concrete is modeled with the combination of mortar and aggregates, and the shrinkage is simulated by applying the shrinkage strain on the mortar only. According to the results, it is shown that the cracking of shrinking concrete is largely influenced by the types of aggregates and the degree of restraint. Also, the shrinkage cracking cannot be represented only by the single values such as tensile strength since the stiffness of aggregates and the degree of restraint influence the cracking.

• 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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.5
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• pp.19-26
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• 2014

Concrete guide rail and median barrier are an attached RC member, however they are vulnerable to cracking due to slip form construction and large surface of member. In this study, causes and pattern of cracking are analyzed through assessment and NDT (Non-Destructive Technique) evaluation for concrete guide rail and median barrier on highway structure. For this work, analysis on drying shrinkage and hydration heat are performed considering installation period, and plastic shrinkage is also analyzed considering their environmental conditions. From the evaluation, plastic settlement around steel location, drying/ plastic shrinkage, and aggregate segregation are inferred to be the main causes of cracking in the structures. The crack causes and patterns are schematized and techniques of crack-control are suggested. Furthermore concrete guide rail/ median barrier in the bridge on the sea are vulnerable to cracking at early age so that special attentions should be paid at the stages of material selection and construction.

• Journal of the Korea Institute of Building Construction
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• v.16 no.3
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• pp.211-217
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• 2016

In this research, the performance of surface covering technique using a white-colored bubble sheet on reducing the cracking due to the plastic, and drying shrinkages for high rise building construction were evaluated by comparing the exposed surface without any surface treatment. From the results of the experiment conducted during fall season, desired results of decreased numbers, length, maximum width, and area of cracking were obtained without a significant difference on heat of hydration and cumulative temperature. Therefore, it is considered that the surface covering technique using bubble sheet is an appropriate method for preventing plastic and drying shrinkage cracking at fall season concrete construction.

• Journal of the Korea Concrete Institute
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• v.28 no.5
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• pp.519-525
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• 2016

This paper reports on analyzing the free and restrained shrinkage characteristic of ternary grout used cementitious admixture. In this study, the cementitious admixture was used such as fly ash, ziricania silica fume by combination of expansive additive (a, b) and shrinkage reducing agent. And a number of basic performance tests were conducted to investigate bleeding, volume change, fluidity and compressive strength behavior. According to the results, within appropriate mixing ratio, even the fluidity is not influenced by expansive additive and shrinkage reducing agent, the resistant properties of bleeding, volume change, shrinkage and compressive strength are increased. Comparing with plain grout, the free shrinkage reduced by a minimum of 29% which specimens are added expansive additive and shrinkage reducing agent. The combination of expansive additive a and shrinkage reducing agent is the most effective for reduction of shrinkage. And increasing the mixing ratio of expansive additive and shrinkage reducing agent extended cracking time. Nevertheless, combined addition of expansive additive a 2.0% and shrinkage reducing agent 0.50% has best shrinkage reduction behavior and not appeared cracking. From the above, the mixing ratio of 2.0% of expansive additive a and 0.50% of shrinkage reducing agent is high performance ternary grout for PSC bridge.