• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.194-195
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• 2022

The jointing of unsupported concrete on the parking lot floor is a process for cracking and stress relief due to concrete drying shrinkage and restraint, but curling occurs due to long-term drying shrinkage after the initial age. will be lowered Therefore, by using an expansion material and a shrinkage reducing agent, the dry shrinkage of concrete is realized to 200 με or less.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.621-626
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• 2004

The use of blast-furnace slag (BFS) in making not only normal concrete but also high-performance concrete has several advantages with respect to workability, long-term strength and durability. However, slag concrete tends to show more shrinkage than normal concrete, especially autogenous shrinkage. High autogenous shrinkage would result in severe cracking if they are not controlled properly. Therefore, in order to minimize the shrinkage stress and to ensure the service life of concrete structures, the autogenous shrinkage behavior of concrete containing BFS should be understood. In this study, small prisms made of concrete with water-binder (cement+BFS) ratio (W/B) ranging from 0.27 to 0.42 and BFS replacement level of $0\%$, $30\%$, and $50\%$, were prepared to measure the autogenous shrinkage. Based on the test results, thereafter, material constants in autogenous shrinkage prediction model were determined. In particular, an effective autogenous shrinkage defined as the shrinkage that contributes to the stress development was introduced. Moreover, an estimation formula of the 28-day effective autogenous shrinkage was proposed by considering various W/B's. Test results showed that autogenous shrinkage increased with replacement level of BFS at the same W/B. Interestingly, the increase of autogenous shrinkage is dependent on the W/B at the same content of BFS; the lower W/B, the smaller increasing rate. In concluding, it is necessary to use the combination of other mineral admixtures such as shrinkage reducing admixture or to perform sufficient moisture curing on the construction site in order to reduce the autogenous shrinkage of BFS concrete.

• Advances in materials Research
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• v.6 no.3
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• pp.257-278
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• 2017

A simple closed-form solution to calculate the interfacial shear and normal stresses of retrofitted concrete beam strengthened with thin composite plate under mechanical loads including the creep and shrinkage effect has been presented in this paper. In such plated beams, tensile forces develop in the bonded plate, and these have to be transferred to the original beam via interfacial shear and normal stresses. Consequently, debonding failure may occur at the plate ends due to a combination of high shear and normal interfacial stresses. These stresses between a beam and a soffit plate, within the linear elastic range, have been addressed by numerous analytical investigations. Surprisingly, none of these investigations has examined interfacial stresses while taking the creep and shrinkage effect into account. In the present theoretical analysis for the interfacial stresses between reinforced concrete beam and a thin composite plate bonded to its soffit, the influence of creep and shrinkage effect relative to the time of the casting, and the time of the loading of the beams is taken into account. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution over existing ones and to illustrate the main characteristics of interfacial stress distributions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.589-592
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• 2005

Molding shrinkage s variation is one of the problems to be solved in conventional injection molding. Despite many trying-out has been to solve these, intrinsic causes of shrinkage such as orientation and thermal exchange between melt and mold has yet not solved. For reducing shrinkage and residual stress on molding, injection compression molding process was invented. In this study, experiments about effect of injection compression molding's parameters on shrinkage of molding were conducted with PMMA and compared with conventional injection molding's shrinkage. Before the injection compression molding experiment, molding shrinkage rate was predicted by analyzing pvT graph and was compared with the results of experiment. The shrinkage rate of injection compression molding was lower than convention injection molding' one but was different from the predicted shrinkage. The reason was observed that experiment mold as not positive type, flowing backward of melt into nozzle and unreasonable mechanism of injection molding machine.

• Restorative Dentistry and Endodontics
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• v.25 no.1
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• pp.91-108
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• 2000

Most of cervical abrasion and erosion lesions show gingival margin where the cavosurface angle is on cementum or dentin. Composite resin restoration of cervical lesion shrink toward enamel margin due to polymerization contraction. This shrinkage has clinical problem such as microleakage and secondary caries. Several methods to diminish contraction stress of composite resin restoration, such as modifying cavity form and building up restorations in several increments have been attempted. The purpose of this study was to compare polymerization contraction stress of composite resin in Class V cavity subjected to cavity forms and placement methods. In this study, finite element model of 5 types of Class V cavity was developed on computer tomogram of maxillary central incisor. The types are : 1) Box cavity 2) Box cavity with incisal bevel 3) V shape cavity 4) V shape cavity with incisal bevel 5) Saucer shape cavity. The placement methods are 1) Incisal first oblique incremental curing 2) Bulk curing. An FEM based program for light activated polymerization is not available. For simulation of curing dynamics, time dependent transient thermal conduction analysis was conducted on each cavity and each placement method. For simulation of polymerization shrinkage, thermal stress analysis was performed with each cavity and each placement method. The time-temperature dependent volume shrinkage rate, elastic modulus, and Poisson's ratio were determined in thermal conduction data. The results were as follows : 1. With all five Class V cavifies, the highest Von Mises stress at the composite-tooth interface occurred at gingival margin. 2. With box cavity, V shape cavity and saucer cavity, Von Mises stress at gingival margin of V shape cavity was lower than the others. And that of box cavity was lower than that of saucer cavity. 3. Preparing bevel at incisal cavosurface margin decreased the rate of stress development in early polymerization stage. 4. Preparing bevel at incisal cavosurface margin of V shape cavity increased the Von Mises stress at gingival margin, but decreased at incisal margin. 5. At incisal margin, stress development by bulk curing method was rapid at early stage. Stress development by first increment of incremental curing method was also rapid but lower than that by bulk curing method, however after second increment curing final stress was the same for two placement methods. 6. At gingival margin, stress development by incremental curing method was suddenly rapid at early stage of second increment curing, but final stress was the same for two placement methods.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.238-245
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• 2000

Separation strips are temporary joints to prevent crack due to stress induced by shrinkage. In this study, an analysis procedure considering separation strip is proposed to decide proper casting time of separation strip and cracking stresses of the example building slabs are calculated using this procedure. The result of the example high rise building shows that the percentage of cracking stress to the modulus of fracture is 43.4% when closing of separation strip are 30 days after placing the slab, so it is enough time for the separation strip in each floor to absorb the effects of shrinkage.

• Restorative Dentistry and Endodontics
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• v.36 no.3
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• pp.188-195
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• 2011

Objectives: The purpose of this study was to evaluate the polymerization shrinkage stress among conventional methacrylate-based composite resins and a silorane-based composite resin. Materials and Methods: The strain gauge method was used for the determination of polymerization shrinkage strain. Specimens were divided by 3 groups according to various composite materials. Filtek Z-250 (3M ESPE) and Filtek P-60 (3M ESPE) were used as a conventional methacrylate-based composites and Filtek P-90 (3M ESPE) was used as a silorane-based composites. Measurements were recorded at each 1 second for the total of 800 seconds including the periods of light application. The results of polymerization shrinkage stress were statistically analyzed using One way ANOVA and Tukey test (p = 0.05). Results: The polymerization shrinkage stress of a silorane-based composite resin was lower than those of conventional methacrylate-based composite resins (p < 0.05). The shrinkage stress between methacrylate-based composite resin groups did not show significant difference (p > 0.05). Conclusions: Within the limitation of this study, silorane-based composites showed lower polymerization shrinkage stress than methacrylate-based composites. We need to investigate more into polymerization shrinkage stress with regard to elastic modulus of silorane-based composites for the precise result.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.163-164
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• 2020

The purpose of this study was to evaluate the shrinkage properties of a tile reinforced with epoxy resin, which has the advantages of high adhesion and low shrinkage, and causes a hardening reaction by chemical bonding with cement mortar. As a result, since the epoxy resin adhesive suppresses the moisture evaporation of the mortar, the drying shrinkage of the mortar itself is reduced, accordingly, the shrinkage of the tile itself is greatly reduced, and it is thought that it is possible to prevent a decrease in adhesion due to shear stress.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.641-650
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• 2010

The concrete cracking from the restrained stress caused by the shrinkage may play significant cause of deterioration of concrete structures by allowing the permeation of sulphate and chloride ions which in turn triggers corrosion of steel reinforcement. In particular, the cracking becomes more critical as water binder ratio (W/B) is reduced and concrete strength increases. Therefore, it needs to evaluate correctly the comprehensive shrinkage behavior of concrete with high strength: high-strength concrete (HSC), ultra-highstrength concrete (UHSC). The unrestrained shrinkage tests, however, cannot estimate the net shrinkage effectively which affects cracking after full development of strength and stiffness because it does not consider the degree of restraint, strength development, stress relaxation, and so on. Therefore, in this study, both free and restrained shrinkage tests with variables of W/B (W/B of 30, 25 and 16%) and admixtures (fly ash (FA) and granulated blast-furnace slag (BFS)) for HSC, very-high-strength concrete (VHSC) and UHSC were performed. The test results indicated that the autogenous shrinkage and total shrinkage at drying condition were reduced as W/B increased and FA, BFS were added, and the cracking behavior was suppressed as W/B increased and FA was added.

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.59-68
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• 2009

Torsional behavior of concrete pavement slabs due to temperature and moisture effects is constrained by self weight and friction etc, and causes stress as the result. The stress due to humidity variation in the slab is difficult to calculate while that due to temperature variation can easily be calculated by a commercial structural analysis program. Thus, the slab behavior can be predicted more accurately if the humidity effect is converted to equivalent temperature and is used as an input of structural analysis. In this study, a concrete pavement slab was constructed and strains of the slab due to environmental loadings were measured for long-term period. Thermal strains were subtracted from the measured strains by using thermal expansion coefficient of the concrete measured in a laboratory. Shrinkage strains, the remained strains, was supposed as additional thermal strains to calculate imaginary temperature with equivalent effect of the shrinkage by dividing the shrinkage with the thermal expansion coefficient. An existing shrinkage model was modified by considering the self weight and friction to be used in another model which can convert differential shrinkage between top and bottom of the slab to equivalent temperature difference. Addition research efforts on tensile stress reduction according to steady increase in the compressive strains are warranted for more accurate stress calculation.