• International Journal of Concrete Structures and Materials
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• v.6 no.4
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• pp.221-230
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• 2012

Cracking of repair material due to restraint of shrinkage could hinder the intended extension of serviceability of repaired concrete structure. The availability of model to predict shrinkage stress under restraint condition will be useful to assess whether repair material with particular deformation properties is resistance to cracking or not. The accuracy in the prediction will depend upon reliability of the model, input parameters, testing methods used to characterize the input parameters, etc. This paper reviews a variety of models to predict shrinkage stress in patch repair system. Effect of creep and composite action to release shrinkage stress in the patch repair system are quantified and discussed. Accuracy of the models is examined by comparing predicted and measured shrinkage stress. Simplified model to estimate shrinkage stress is proposed which requires only shrinkage property of repair material as an input parameter.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.1033-1039
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• 2006

The purpose of this study are to evaluated bond, flexural properties and control of plastic shrinkage cracking of crimped type synthetic fiber with amplitude 6 mm and height 1.8 mm reinforced cement based composites. Bond and flexural test were conducted in accordance with the JCI-SF 8 and JCI SF-4 standard, respectively. The plastic shrinkage cracking test was conducted for evaluating the effect of fiber in reducing shrinkage cracking in cement based composites. Test results indicated that the crimped typel synthetic fibers performed significantly better than the straight type fiber in terms of interface toughness and pullout load and the crimped type synthetic fibers improved the flexural toughness of concrete. Also, the increasing the crimped type synthetic fiber volume fraction from 0.00% to 1.00% improved the plastic shrinkage cracking resistance. Specially, the effect of control of plastic shrinkage cracking is excellent at the more than 0.5% fibre volume fraction.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.293-296
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• 2004

In this study, to investigate autogenous shrinkage behavior of 120MPa UHSC at early ages, free and restrained shrinkage tests are performed for various strength levels(50MPa, 80MPa, 120MPa). For 120MPa, the effect of fly ash on autogenous shrinkage was also investigated. In order to assess the potential for early-age cracking in concrete and a mixtures susceptibility to shrinkage cracking, restrained ring test was carried out. Test results show that autogenous shrinkage of UHSC was much higher than that of HSC, VHSC and fly ash delayed cracking age in UHSC by decreasing autogenous shrinkage.

• Journal of the Korean Society of Safety
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• v.23 no.5
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• pp.84-90
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• 2008

The occurrence of longitudinal cracking in concrete deck of box girder bridge is affected by many factors, but the most important factors are the shrinkage and thermal gradient of deck slabs. In this study, therefore, the tensile stresses at the bottom of deck were calculated from the experimental data(autogeneous shrinkage, drying shrinkage, and thermal gradient of deck slab). Also, the possibility of longitudinal cracks at bottom of deck was estimated. For this purpose, full-scale box girder segments have been fabricated and tested. The thermal gradients and shrinkage strains of deck slabs were measured after placement of concrete. Also, analytic program was conducted for the evaluation of longitudinal cracking in bridge deck considering differential shrinkage induced from non-uniform moisture distributions in concrete.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.73-77
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• 2006

This paper shows a study of the efficiency of expansive additive and shrinkage reducing admixture in controlling restrained shrinkage cracking of high performance concrete at early age. Free autogenous shrinkage test of $100{\times}100{\times}400mm$ concrete specimens and simulated completely-restrained test with VRTM(variable restraint testing machine) were performed. Creep and autogenous shrinkage of high-performance concrete with and without expansive additive and shrinkage reducing admixture were investigated by experiments that provided data on free autogenous shrinkage and restrained shrinkage. The results showed that the addition of expansive additive and shrinkage reducing admixture effectively reduced autogenous shrinkage and tensile stress in the restrained conditions. Also, it was found that the shrinkage stress was relaxed by 90% in high-performance concrete with and without expansive additive and shrinkage reducing admixtures at early age.

• Journal of the Korea Institute of Building Construction
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• v.19 no.2
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• pp.123-130
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• 2019

As a cold-weather-concrete construction technique for enhancing the sustainability and improving efficiency of cold-weather construction, the cracking timing, the starting point of deterioration for concrete, due to the shrinkage of the blast furnace slag cement concrete including accelerator was evaluated. As a result, by using blast furnace slag and accelerator, the cracking was developed faster with higher cracking potential under the restrained conditions at constant age and free-shrinkage strain. It can be considered that the results of decreased stress relaxation by creep or increased restraint with increased free-shrinkage strain causes the increased cracking development speed. Hence, it should be considered the necessary of cracking due to the shrinkage when blast furnace slag or accelerator was used for cold-weather construction.

• International Journal of Concrete Structures and Materials
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• v.2 no.1
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• pp.9-14
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• 2008

The cracking problem in concrete is widespread and complex. This paper reviews the problem and focuses on those parts of the problem that are more readily solved. Polymer fibers are shown to have promise in several important areas of the cracking problem. To investigate one of these areas of the cracking problem more completely, an experimental research program focusing on the early-age properties of fibers was carried out. This study researched the properties of four polymer fibers; two of the fibers were macrofibers, and two were microfibers. Each fiber was tested at several dosage rates to identify optimum dosage levels. Early-age shrinkage, long-term shrinkage, compressive strength, and tensile strength were investigated. Long-term shrinkage and strength impacts from the polymer fibers were minimal; however, the polymer fibers were shown to have a great impact on early-age shrinkage and a moderate impact on early-age strength.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.631-635
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• 2005

Aggregate gradation effects on cracking-related displacements of concrete are investigated in the laboratory using the German cracking frame. Concrete workability was assessed by use of the slump and drop tests for two different concrete mixtures consisting of gap-graded and dense-graded aggregates. Shrinkage strain, cracking frame strain, and concrete strain were measured and used to compare to strength gain and creep development. The measured and calculated strains of the different aggregate gradations were compared each other. Gradation effects on strength and stress development relative to tensile cracking at saw-cut tip were also investigated. Test results revealed that the gap-graded concrete has indicated larger shrinkage and creep strains than dense-grade concrete perhaps because of its higher volume concrete of cement mortars in the mixture.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.575-578
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• 2005

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 mortar has been estimated in comparison with polypropylene fiber and cellulose fiber. Nylon fiber showed considerable advantages in terms of the workability of concrete and the plastic shrinkage cracking reduction of mortar compared with polypropylene fiber and cellulose fiber.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.789-792
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• 2005

Development of high-strength concrete and improved durability has brought new opportunities to the construction industry. However, some attention was given to characteristics of such concrete, in particular with respect to their cracking sensitivity. It has been argued and demonstrated experimentally that a low water/cement ratio concrete undergoes shrinkage due to self-desiccation. This so-called autogenous shrinkage cracking is a major concern for concrete durability. One possible method to reduce cracking due to autogenous shrinkage is the addition of expansive additive. Tests conducted by many researches have shown the beneficial effects of addition of expansive for reducing the risk of shrinkage-introduced cracking. This paper aimed at forecasting deformation of high strength cement paste with expansive additive for early age.