• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.937-940
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• 2008

Recently, the recycling and reusing of construction and demolition waste concrete is urgently required because generation quantity of construction and demolition waste concrete is greatly increased according to the rapid increasing of urban redevelopment project. On the other hand, the problem solution for demand and supply unbalance of fine aggregate is urgently required because of the restriction of collecting sea fine aggregate by intensification of environment influence evaluation and the shortage of river fine aggregate. but a quality of aggregate as building structure is not demonstrated. Therefore it is the objective of this study to estimate plastic and early dry shrink crack of fiber reinforced concrete using a recycled aggregate by plat-ring test and mock-up test of exposure to the air. as a result, in case of plat- ring test, developing crack is wider using recycled aggregate concrete than natural aggregate concrete, is wider using fiber reinforced concrete than non fiber. in case of mock-up test of exposure to the air, it is similar to plat-ring test.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.371-379
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• 2013

This paper investigates the cracking and tension-stiffening behavior of 100 MPa shrinkage-compensated strain-hardening cement composite (SHCC) and conventional concrete tie elements in monotonic and cyclic tension. Strain and surface crack formation of tension ties were monitored with two strain displacement transducers and a photo microscope with a lens of magnification 50 times. Three different cement composites such as conventional concrete, shrinkage-compensated SHCC, and normal SHCC were used in the tie specimens to investigate the influence of the cement composite type on the tension stiffening and cracking behavior. Test results indicated that initial shrinkage of the ultra high-strength cement composites is greatly reduced as the 10% replacement of cement by the shrinkage-compensating admixture based on calcium sulfo-aluminate (CSA). The test results on the SHCC tension ties showed that the first cracking load decreases proportionally to the initial shrinkage strain. Reinforced ultra high-strength SHCC ties with the initial shrinkage compensation exhibited improved tension stiffening and smaller crack spacings, i.e. the reduction in crack width. Cyclic loading did not have a significant effect on tension stiffening and cracking behavior of tension ties with normal concrete and SHCC materials.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.2
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• pp.75-86
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• 2012

This paper presents some research results on the shrinkage characteristics and frost resistance before and after cracking of FR-ECC(Fire Resistance-Engineered Cementitious Composite). Also, a waterstop performance and exfoliating resistance of multi-layer lining specimens using FR-ECC and flexural performance of beam member by repaired FR-ECC are estimated in this paper. Experimental results indicate that the plastic shrinkage crack and length change ratio of FR-ECC have been reduced as compared with that of the existing repair mortar, and that its crack resistance on the dry shrinkage is improved under the confining stress. As well as FR-ECC has been great in the frost resistance and its tensile properties under the cracked state have been not reduced by freezing and thawing reaction. In addition, beam member by repaired FR-ECC have been increased in the flexural properties such as initial crack moment, yeild moment, and its crack width has been controled in a stable by the frexural failure.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.82-83
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• 2014

Concrete with self-healing admixture can reduce the crack width by using a compound for chemical reaction with incoming water and carbon dioxide through the crack. Also, concrete with self-healing admixtures can reduce early-age shrinkage crack by using a inorganic expansive agent. In this research, we perform the basic workability test and compressive test. Also, We measure the drying shrinkage of concrete specimen. Finally, we make mock-up (3m X 3m X 0.23m) and monitor the crack width and length for 3 months.

• Journal of the Korea Institute of Building Construction
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• v.17 no.3
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• pp.245-252
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• 2017

Recently, structures such as large retailers, outlets and warehouses have been increasing in accordance with changes in consumption patterns. Since these structures include ultra-flat slab members, they are thoroughly managed to control slab cracking by the plastic and drying shrinkage. In order to control the cracking of the slab member, a chemical crack reduction method is used. In particular, the use of the shrinkage reducing agent has been examined. However, domestic research results are limited. In this study, the shrinkage properties of concrete using shrinkage reducing agent and the drying shrinkage properties according to the mixing factors were investigated. The performance of domestic shrinkage reducing agent was appeared similar to that of overseas high-grade shrinkage reducing agent. As the shrinkage reducing agent usage increased, the drying shrinkage reduction effect increased. At the age of 100 days, the dry shrinkage rate of specimen with the shrinkage reducing agent of 1.5%was shown about half that of the specimen without the shrinkage reducing agent. The shrinkage reducing agent was gound to have no specific performance change for the use of the admixture.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.296-302
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• 2016

Studies aimed at reducing the occurrence of cracks by the shrinkage of concrete are in demand because the repair and reinforcement for cracks caused by declining concrete durability costs the user to maintain the concrete structure. In particular, in underground power facilities for power transmission, the cost is a heavy burden to repair and reinforce. For this reason, underground power facilities demanded effective methods for crack reduction at the engineering design step. This study, as a part of the development of shrinkage reducing agent for low shrinkage concrete on underground power facilities, investigated TEA to complement the shrinkage reducing agent to improve the early strength of concrete. In the case of TEA 3% as a shrinkage reducing agent, the early strength was improved significantly, and the shrinkage reducing effect was excellent. In addition, TEA 3.0 % and the shrinkage reducing agent 2.0 % showed excellent shrinkage property and compressive strength. On the other hand, more study of shrinkage reducing materials, including performance reviews on the shrinkage reducing materials with variable factors and type of materials, will be needed to generalize these results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.3
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• pp.30-37
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• 2023

The PSCB girder bridge is a closed cross-section in which the top and bottom flanges and the web are integrated, and the structural characteristics are generally different from the bridges in which the girder and the floor plate are separated, so a maintenance plan that reflects the characteristics of the PSCB girder bridge is required. As a result of analyzing damage types by collecting detailed safety diagnosis reports of highway PSCB girder bridges, most of the deterioration and damage occurring during use is concentrated on the top flange. In particular, cracks in the bridge direction on the underside of the top flange occurred in about 70 % of the PSCB girder bridges to be analyzed, and these cracks were judged to be caused by indirect loads such as heat of hydration and drying shrinkage rather than structural cracks caused by external loads. In order to improve durability and reduce maintenance costs of PSCB girder bridges in use, it is necessary to control restraint drying shrinkage cracks from the design stage. Therefore, in this paper, the cracks caused by drying shrinkage under restraint, which is the main cause of cracks under the flanges of the top part of the PSCB girder bridge, were directly calculated using the Gilbert Model, and the influencing factors such as the amount of reinforcing bars, diameter and spacing of reinforcing bars were analyzed. As a result of the analysis, it was found that the crack width caused by restraint drying shrinkage exceeded the allowable crack width of 0.2 mm for reinforcing bars with a reinforcing bar ratio of 0.01 or less based on the H16 reinforcing bar and a reinforcing bar with a diameter greater than H19 based on the reinforcing bar ratio of 0.01. Finally, based on the results of the crack width review, a method for controlling the crack width of the top flange of the PSCB girder bridge was proposed.

• Journal of the Korean Society for Railway
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• v.17 no.4
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• pp.270-280
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• 2014

In this study, to examine the causes of cracks in continuously reinforced concrete tracks (CRCTs) and the main factors affecting cracking, a field survey on the status of cracks and crack patterns in the Gyeong-bu high speed line was conducted, and the crack patterns of CRCT due to the temperature difference between the top of the slab (TCL) and the bottom of the subbase (HSB) and the drying shrinkage of concrete were predicted by a nonlinear finite element model considering the structure of CRCT. The results of the numerical analysis show that cracks will be developed at the interface between the sleeper and the TCL, and under the sleeper due to the temperature difference and concrete shrinkage. This corresponds well to the crack locations found in the field. Also, it is found that the most significant factors are the coefficient of thermal expansion with respect to the temperature difference, and the drying shrinkage strain with respect to shrinkage. According to the results, the reinforcement ratio should be carefully determined considering the structures of CRCT because the crack spacing is not always proportional to the reinforcement ratio due to the sleepers embedded in the TCL.

• Journal of the Korea Institute of Building Construction
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• v.23 no.5
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• pp.547-558
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• 2023

This research delves into the fabrication of an ultra-high-strength concrete, enriched with oxidized graphene nanoplatelet(GO) and hollow glass powder(HGP), notably eschewing the conventional inclusion of silica fume(SF). The primary objective was to scrutinize the autogenous shrinkage characteristics of this innovative formulation. It was discerned that the NewMix specimen, which incorporated the cGO(sourced from Company C) and HGP, and intentionally bypassed SF, showcased a commendable 13% reduction in autogenous shrinkage relative to the benchmark(Ref) specimenthat incorporated SF. Moreover, the proclivity for crack formation owing to autogenous shrinkage in the NewMix was observed to manifested by NewMix at the juncture of cracking emerged as the apex value. Attributed to the expansive specific surface area and exemplary dispersibility of cGO, it was postulated that the concrete's pore structure benefitted from enhanced infill, leading to a reduction in autogenous shrinkage. Additionally, the cGO integration fortified the concrete's resistance to crack initiation. Consequently, such an enhancement is posied to be pivotal in mitigating crack propagation resulting from autogenous shrinkage in ultra-high-strength concrete.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.693-699
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• 2016

In this study, the replacement effects of cementitious materials (fly ash, blast furnace slag, and blended mixtures) were assessed for normal strength concrete with very low shrinkage properties under $350{\mu}{\varepsilon}$ strain using a powder type shrinkage reducing agent. In addition, through mock-up tests of actual size walls restrained with four sides, the shrinkage characteristics using the power type shrinkage reducing agent were measured and the crack reducing ability was assessed. The slump and air contents were measured as the properties of fresh concrete, and the length changes of the prismatic specimens, $100{\times}100{\times}400mm$ in size, were measured for the shrinkage characteristics. To reduce the shrinkage of concrete, the maximum replacing ratio of the fly ash is effective to 20 percent; however, the use of blast furnace slag and ternary mixtures did not reduce the shrinkage.