• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.355-374
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• 2022

Soil conditioning improves the performance of EPB (earth pressure balance) shield TBMs (tunnel boring machines) by reducing shear strength, enhancing workability of the excavated soil, and supporting the tunnel face during EPB tunnelling. The mechanical and rheological behavior of the excavated muck mixed with additives should be properly evaluated to determine the optimal additive injection condition corresponding to each ground type. In this study, the laboratory pressurized vane test apparatus equipped with a vane-shaped rheometer was developed to reproduce the pressurized condition in the TBM chamber and quantitively evaluate rheological properties of the soil specimens. A series of the pressurized vane tests were performed for an artificial sand soil by changing foam injection ratio (FIR) and polymer injection ratio (PIR), which are the injection parameters of the foam and the polymer, respectively. In addition, the workability of the conditioned soil was evaluated through the slump test. The peak and yield stresses of the conditioned soil with respect to the injection parameters were evaluated through the rheogram, which was derived from the measured torque data in the pressurized vane test. As FIR increased or PIR decreased, the workability of the conditioned soil increased, and the maximum torque, peak stress, and yield stress decreased. The peak stress and yield stress of the specimen from the laboratory pressurized vane test correspond to the workability evaluated by the slump tests, which implies the applicability of the proposed test for evaluating the rheological properties of excavated soil.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.814-821
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• 2015

The purpose of this study is to estimate crack reduction properties of covering concrete with fibers in basement. Air contents, slump, compressive strength, tensile strength and plastic shrinkage has been tested to conduct the optimum addition ratio and type of fiber. The results is a following. For the properties of air contents, all of the specimens added fibers shown the higher than plain concrete. For the flowability, slump decreased about 40-80% when all of the specimens added fibers. For the strength properties, the specimens added nylon fiber shown higher compressive and tensile strength about 5-15% comparing with other concrete. For the plastic shrinkage, cracking decreased when the fiber added comparing with plain concrete. Especially, when nylon fiber added in the concrete, the plastic shrinkage did not occurred. For the overall consideration, when the addition ratio of nylon fiber is 0.6%, the press concrete is identified as showed optimum properties.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.178-185
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• 2011

Recently depletion of natural resources makes a deficiency of sand aggregation in the concrete works. In this study, the quality characteristics of concrete and aggregate according to blending fine aggregate in the river sand and the crash sand was analyzed by Normal method and Driscoll method which has used mixing of fine aggregate for asphalt mostly. Application of Discoll method to blend fine aggregate for concrete was studied in the first step to blend fine aggregates concrete. The fineness modulus, grading, slump, air content and compressive strength were tested by the two method, the results of Driscoll method was very similar to degree of err limits in comparison with those of Normal method in the same condition. As a result, Driscoll method is reasonable to use the fine aggregates mixture for concrete in river sand and crash sand.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.22-29
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• 2015

In this study, we tested to develop and apply structural insulation performance improvement concrete to field, which had compressive strength in 24 MPa and thermal conductivity twice as much as normal concrete. After experiment about slump and air contents, combination product of Plain and calcined diatomite powder showed reduction of slump and air contents and combination product with micro foam cell admixture, we cannot find result of slump and air contents reduction. Unit weight of combination product with insulation performance improvement materials decreased more than that of Plain. In the test of compressive strength, compressive strength of insulation performance improvement concrete decreased more than that of Plain but was content with 24 MPa. thermal conductivity of insulation performance improvement concrete tended to decrease. Freezing and thawing resistance of insulation performance improvement concrete was similar to that of Plain. In carbonation resistance test, combination product with calcined diatomite powder showed the result which was similar to that of Plain. In carbonation resistance test, combination product with micro foam cell admixture showed a increase compared to that of Plain and length variation of combination product generally increased.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.5
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• pp.171-180
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• 2007

The quality of ready-mixed concrete(henceforth abbreviated remicon) is influenced by various factors such as ingredient of material, difference of property, mixing ratio, mixing time, mixing error, conditioning of construction, method of curing and temperature, humidity time in transportation. These factors make it hard to confirm the quality of remicon till placing in site. As the quality control in field is very important to ensure the quality of building. Moreover in modern building production, the more important the inquiry of performance improvement, the more important the manufacture and the quality control of remicon. In this study, to examine and analyze the quality of remicon we used slump, air content and compressive strength in 7, 28 days as to remicon which placed during on year. As a result, we found that the slump and air content were satisfied with reference code and the compressive strength was more than the design standard strength so we concluded that the quality control of remicon was to be agreeable.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.4
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• pp.545-560
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• 2019

During EPB TBM tunnelling, an appropriate application of additives such as foam and polymer is an essential factor to secure the stability of TBM as well as tunnelling performance. From the '90s, there have been many studies on the optimal injection of additives worldwidely contrary to the domestic situation. Therefore, in this paper, the foam, which is widely adopted for soil conditioning, was selected as an additive in order to investigate the effect of foam injection on TBM performance through a series of laboratory excavation tests. The excavation experiments were carried out on artificial sandy soil specimens with consideration of the variance of FIR (Foam Injection Ratio), FER (Foam Expansion Ratio) and $C_f$ (Surfactant Concentration), which indicate the amount and quality of the foam. During the tests, torque values were measured, and the workability of conditioned soil was evaluated by comparing the slump values of muck after each experiment. In addition, a weight loss of the replaceable aluminum cutter bits installed on the blade was measured to estimate the degree of abrasion. Finally, the foam injection ratio for the optimal TBM excavation for the typical soil specimen was determined by comparing the measured torque, slump value and abrasion. Note that the foam injection conditions satisfying the appropriate level of machine load, mechanical wear and workability are essential in the EPB TBM operational design.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.435-444
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• 2012

High performance concrete mixes are selected and corresponding test specimens are made for the study of chloride diffusion coefficient at reference time. The concrete mixes were same designs as those used in construction of bridges located in a marine environment. Mix design variables included binder type, water-to-binder ratio, mineral admixtures to total binder weight substitution ratio, fine aggregate source, chemical water reducer admixture type for high strength and high flowability, and target slump or slump flow. The test results showed that the diffusion coefficients at reference time varied significantly according to the type of mineral admixtures and their substitution ratios. A model for diffusion coefficient at reference time considering the type of mineral admixture and the substitution ratio was developed. Diffusion coefficients from the developed model were compared with those from literature review, a previous model, and additional test results. All of the comparisons verified that the developed model can reasonably predict diffusion coefficients and the application of the model to the durability design against chloride penetration is appropriate.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.923-926
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• 2008

Currently more high flow and high performance concrete is used for construction of buildings in the world. However, when high flow and high performance concrete put high performance water reducing agent in quantity to improve flow, it has a negative effect on concrete structures since segregation arises from it though flow will be improved. There are naked-eye observation, coarse aggregate washing test, L Flow test for permeation among reinforcing rods and measurement of viscosity to judge concrete segregation resistance. However, it is difficult to apply them to practical affairs since they are very complicated and troublesome. Therefore, the study analyzed EIS dividing slump flow value into slump value, how to valuate concrete segregation resistance more easily, on the basis of the existing reference materials to propose EIS. As the results, in the event of high flow concrete, it is desirable that EIS value is prescribed to be less than 2.5 at the time of managing segregation. Also, at the time of prescribing EIS with performance, it is judged that it is desirable to manage segregation as less than 2.2 (Grade 1), 2.2$\sim$2.4 (Grade 2) and more than 2.6 (Grade 3).

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.445-451
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• 2019

In this study, we evaluated the durability of concrete produced with recycled polymer that could replace synthetic polymer, which is the main raw material of bridge deck concrete pavement. As a result of the slump and air content test, the requirements of the Korea Highway Corporation Standard were satisfied with all mixing conditions. The slump was lowered when incorporating the recycled bio-polymer, compared to other mix proportions concrete. In contrast, the compressive strength was increased by 6.3~24.4% when the recycled bio-polymer was mixed, compared to the concrete produced with synthetic polymer. It should be noted that the compressive strength was lowered when synthetic polymer was added to concrete mixture. Durability test results showed the best durability when incorporating synthetic polymer. The durability of concrete also increased as the amount of recycled bio-polymer increased, however, the impact was slightly smaller than that of synthetic polymer.

• Journal of the Korea Concrete Institute
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• v.18 no.6 s.96
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• pp.777-783
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• 2006

This study has focused on the possibility for recycling of tailings from the Sangdong tungsten mine as powder(TA) of self-compacting concrete(SCC). The experimental tests for slump-flow, time required to reach 500 mm of slump flow(sec), time required to flow through V-funnel(sec) and filling height of U-box test(mm) were carried out in accordance with the specified by the Japanese Society of Civil Engineering(JSCE). The results of this study, slump-flow of SCC was satisfied a prescribed range. And time required to reach 500 mm of slump flow(sec) and time required to flow through V-funnel(sec) decreased with increasing replacement of TA. But filling height of U-box test(mm), replacement of TA up to 30% were satisfied a prescribed range. The mechanical properties including compressive strength, splitting tensile strength and elastic modulus were checked with the requirements specified by Korean Industrial Standards(KS). The compressive strength of SCC decreased with increasing replacement of TA, splitting tensile strength and elastic modulus were similar to those of normal concrete. The fundamental durability was reviewed through the dry shrinkage rate and accelerated carbonation tests. As the result dry shrinkage rate and accelerated carbonation depth increased with increasing replacement of TA.