• Tunnel and Underground Space
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• v.19 no.4
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• pp.304-317
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• 2009

Most crystalline rocks have much higher compressive strength than tensile strength and show brittle failure. In-situ rock mass, strong enough in general sense, often fails in brittle manner when subjected to high stress exceeding strength in due of geometrically induced stress concentration or of high initial stress. Therefore, it is necessary to verify the brittle failure characteristics of rock and rock mass for proper stability assessment of underground structures excavated in great depths. In this study, damage controlled tests were conducted on biotite-granite and granitic gneiss, which are the two major crystalline rock types in Korea, to obtain the strain dependency characteristics of the cohesion and friction angle. A Cohesion-Weakening Friction-Strengthening (CWFS hereafter) model for each rock type was constructed and a series of compression tests were carried out numerically while varying confining pressures. The same tests were also conducted assuming the rock is Mohr-Coulomb material and results were compared.

• International Journal of Highway Engineering
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• v.11 no.3
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• pp.1-11
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• 2009

This study focuses on evaluating the applicability of an acryl based polymer concrete to the thin bridge deck pavements. The acryl concrete developed in this study is composed of Methyl Methacrylate(MMA) resin, benzol peroxide and fillers. To study the effects of the types and amounts of the components on the physical characteristics of the acryl concrete, viscosity, compressive strength and bending tests were conducted. The optimum mixture design was then determined based on the testing results. Several different types of laboratory tests, such as water and chlorine ion penetration tests, shrinkage and thermal coefficients tests, and tensile bonding strength tests were performed for the optimum acryl concrete and conventional cement concrete. The testing results show that water and chroline ion resistance, bonding strength between acryl and cement concrete and crack resistance of the acryl concrete is better than those of the conventional cement concrete. There are shortcomings that the conventional acryl concrete has a higher shrinkage and thermal coefficients. However, it was confirmed that to use newly developed rubberized MMA resin in this study reduces the crack resistance with substantially increased ductility.

• Applied Chemistry for Engineering
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• v.8 no.6
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• pp.920-926
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• 1997

The catalytic glycolysis process is the method of chemical recycling where the polyol and carbamate compounds recovered by transesterification reaction are reused to produce new polyurethane foams. In this work, ethylene glycol, diethylene glycol, and 1,4-butanediol were used to decompose polyurethane foams and various metallic acetates were provided as catalysts. The catalytic glycolsis of polyurethane foams was taken place in the reaction temperature of $180{\sim}200^{\circ}C$. The reaction rates of catalytic glycolysis reaction were indicated by the viscosity of the reaction products at different reaction times. IR and GPC analysis showed the types and the molecular weight distributions of the products. The catalytic glycolysis was profitable for using ethyleneglycol at high temperature. The activities of the catalysts are suitable for K, Na, Tl acetate, and the products are composed of comparatively high-contained amine compounds and carbamate compounds. In the case of Sr acetate and Quinoline, the reaction rate was somewhat low. However, the content of polyol was high and the content of the side-products was low. The foams which were prepared by blending up to 20wt% of recovered polyol with virgin polyols showed better physical properties in tensile strength, hardness, tear strength, and compressive strength compared to those of polyurethane foams from virgin polyol.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.221-231
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• 2011

Thinner and lighter structural members can be designed by utilizing the high stiffness and toughness, and high compressive strength of UHPC(ultra high performance concrete), which reaches up to 200MPa. The punching shear capacity of UHPC was investigated in this paper aiming for the application of UHPC to bridge decks. Six square slabs were fabricated and punching shear test was performed under fixed boundary condition. Different thicknesses of test slabs, which were 40mm and 70mm, were selected. The shape ratio of loading plates were ranged between 1.0~2.5. 40mm thickness slabs showed longer softening region after the peak load and, on the other hand, 70mm thickness slabs revealed a more brittle shear failure. Experimental results were analyzed using various existing punching shear predicting equations. Ductal$^{(R)}$ equation and JSCE equation better predicted for 40mm slabs, and Harajli et al. equation and ACI-Ductal$^{(R)}$ equation better suited for 70mm slabs. Nevertheless generally they didn't well predict the test results. A new punching shear equation which was derived based on the actual failure mechanism was proposed. The proposed equation appeared to better predict the punching shear strength of UHPC than other available equations.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.169-177
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• 2017

Recently, as the size of transportation vessels has increased, there is a growing need for securing the front-water depths of existing port facilities. The method of deepening front-water depth is securing the depth of the port facility, and it is reinforced by grouting after excavating the rubble-mound to the required depth. The purpose of this study is to investigate the reinforcing performance and filling performance of thixotropic grout as a grouting material for reinforcing rubble-mound. Compressive strength tests were carried out for two types of thixotropic grout, and 5 specimens with a diameter of 400 mm and a height of 530 mm were manufactured and evaluated for filling performance. The required strength of reinforced rubble-mound required to ensure the safety of the structure is 6 MPa. All the thixotropic grouts used in this study were found to satisfy the required strength over 9 MPa at 7 days of age. As a result of visual observation of filling state of the filling performance test specimens, it was confirmed that the thixotropic grout was well filled up to the desired fillet height.

• Journal of the Korean Geotechnical Society
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• v.20 no.3
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• pp.75-83
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• 2004

The Indiana Department of Transportation (INDOT) has permitted the use of Lime Kiln Dust (LKD) as a low-cost construction material in creating a workable platform for soil modification (not for soil stabilization) since the early 1990s on selected projects. However, the enhanced strength of soils with LKD has not been accounted for in the subgrade stability calculations in the design process. This study was initiated to evaluate how the lime kiln dust is a comparable material to hydrated lime. A series of laboratory tests were performed to assess the mechanical benefits of lime kiln dust in combination with various predominant fine grained soils encountered in the State of Indiana, such as A-4, A-6 and A-7-6. In the course of this study, several tests such as the Atterberg limits, standard Proctor, unconfined compression, CBR, volume stability, and resilient modulus were performed. As a result, mixtures of fine grained soils with 5% lime or 5% LKD substantially improve unconfined compressive strength up to 60% - 400%. CBR values for treated soils are in the range of 25 to 70 while those for untreated soils range from 3 to 18. In general, significant increase in resilient moduli of the soils treated with lime and LKD was observed. This indicates that lime kiln dust may be a viable, cost effective alternative to hydrated lime in enhancing the strength of fine grained soils.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.473-481
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• 2013

The purpose of this research is to evaluate the improvements in the strength and injection range of loose ground after injecting $CaCO_3$(created by microorganism reaction). For this purpose, three cases of single-layer (Sand, SP, SW) specimens were made in a 150mm D ${\times}$ 200mm H space and two cases of multi-layer specimens (SW/SP, SP/SW) were made in a 150mm D ${\times}$ 300mm H space. The specimens were made with a relative density of 30% of soft ground and an injection was given over a time of one day. The uniaxial compression strength was measured with a cone penetrometer and the injection range was observed by checking the bulb formation around the injection nozzle. Also, the compositions of the specimens were assessed through XRD analyses. Based on the test results, a compressive strength of 500kPa and 15cm thick cementation were noted due to the cementation of the soil. This implies that there are significant effects of the pore condition and size on bio-grouting technology.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.4
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• pp.18-24
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• 2012

In this study, hybrid method using polyvinyl acetate (PVAc) which has a strong adhesion and flexibility in which acrylic copolymer chemical-reaction reacts with cement, and is eco-friendly, is to improve the watertightness. The hybrid method is applied applied primarily waterproof stuff comprising silicate system and secondary mortar mixed with PVAc on the concrete surface. And then, in order to evaluate the performance, the properties of bond strength and amount of water absorption were measured. Based on the above experiments, mock-up specimens for field application were fabricated, and then the properties were evaluated as laboratory experiments. As the results, specimens cast from hybrid method using PVAc showed the best results on watertightness and bond strength. And also, with respect to experiment of mock-up specimens, the properties were in agreement with laboratory results. Especially, it could know that PVAc has strengthening effect from the results of the compressive strength. Due to outstanding results of carbonation depth and resistance to chloride ion penetration, it may be applied in weak areas such as underground and marine structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.72-80
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• 2020

The purpose of this study is to secure the same or more structural performance and constructability for the details of hooks cross-constructed at 135 degrees used as external-ties standard detail in RC columns, therefore, to the purpose of improving constructability, the clip-type binding implement was suggested and A total of 28 pull-out specimens were prepared with the parameters of concrete compressive strength and clip-embeded length, clip installation location to examine the anchorage behavior of the clip-type binding implement. The experiment was carried out. The results of the experiment confirmed that the anchorage strength of the clip-type binding implement was higher than the details of hooks cross-constructed at 135-degree regardless of the diameter of tie and concrete strength, embeded clip length, clip installation. and The 90-degree end hook with clip-type binding implement was showed a similar an anchorage behavior of 135-degree end-hooked transverse reinforcement, consequently, The 90-degree end hooked with clip-type binding implement is evaluated to be the same anchorage behavior and performance as standard 135-degree end hook detail.

• Composites Research
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• v.18 no.3
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• pp.38-46
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• 2005

In order to characterize the outstanding performance of three-dimensional (3D) composites, the low velocity impact test has been carried out. 3D fiber structures have been achieved by using the automated tape placement (ATP) process and a stitching method. Materials for the ATP and the stitching process were carbon/epoxy prepreg tapes and Kevlar fibers, respectively. Two-dimensional composites with the same stacking sequence as 3D counterparts have also been fabricated for the comparison of damage tolerance. For the assessment of damage after the impact loading, specimens were subjected to C-Scan nondestructive inspection. Compression after impact (CAI) tests were conducted to evaluate residual compressive strength. The damage area of 3D composites was greatly reduced $(30-40\%)$ compared with that of 2D composites. Although the CAI strength did not show drastic improvement for 3D composites, the ratio of retained strength was $5-10\%$ higher than 2D samples. The effect of stitching on the impact performance was negligible above the energy level of 35 Joules.