• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.343-350
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• 2022

In recent years, nanomaterials, such as nano-silica, carbon nanotubes, and graphene oxide (GO), have been suggested to improve the properties of the interfacial transition zone (ITZ) between aggregates and cement pastes, which has most adversely affected the strength of quasi-brittle concrete. Among the nanomaterials, GO with superior dispersibility has been reported to be effective in improving the properties of ITZ of normal-strength concrete by forming interfacial chemical bonds with Ca²⁺ ions abundant in ITZ. In this study, the effect of GO on the properties of ITZ in the high-strength mortar was elucidated by calculating the change in hydration heat release, ITZ thickness, and the porosity around ISO sand, which was obtained with isothermal calorimetry tests and scanning electron microscope image analysis, respectively.

• Geomechanics and Engineering
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• v.32 no.4
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• pp.427-443
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• 2023

Across the globe, rapid urbanization demands the construction of basements for car parking and sub way station within the vicinity of high-rise buildings supported on piled raft foundations. As a consequence, ground movements caused by such excavations could interfere with the serviceability of the building and the piled raft as well. Hence, the prediction of the building responses to the adjacent excavations is of utmost importance. This study used three-dimensional numerical modelling to capture the effects of twin excavations (final depth of each excavation, H_e=24 m) on a 20-storey building resting on (4×4) piled raft. Because the considered structure, pile foundation, and soil deposit are three-dimensional in nature, the adopted three-dimensional numerical modelling can provide a more realistic simulation to capture responses of the system. The hypoplastic constitutive model was used to capture soil behaviour. The concrete damaged plasticity (CDP) model was used to capture the cracking behaviour in the concrete beams, columns and piles. The computed results revealed that the first excavation- induced substantial differential settlement (i.e., tilting) in the adjacent high-rise building while second excavation caused the building tilt back with smaller rate. As a result, the building remains tilted towards the first excavation with final value of tilting of 0.28%. Consequently, the most severe tensile cracking damage at the bottom of two middle columns. At the end of twin excavations, the building load resisted by the raft reduced to half of that the load before the excavations. The reduced load transferred to the piles resulting in increment of the axial load along the entire length of piles.

• Economic and Environmental Geology
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• v.57 no.2
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• pp.219-231
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• 2024

A survey of concrete plants in Incheon Metropolitan City and Gyeonggi Province was used to conduct an analysis of aggregate transport distance and production forms, as well as to evaluate the features and current status of aggregates distribution. As a result, areas such as Incheon, Siheung, Bucheon, Gimpo, and Siheung, where the distance to the demand points is less than 20 km, exhibited bidirectional distribution whereas Paju, Yongin, Yangju, and Pocheon, with distances ranging from 20 to 50 km is showed a unidirectional distribution pattern supplying aggregates exclusively to Incheon. Survey on manufacturing forms, more than 85% of the gravel dispersed in the Incheon area is made up of crushed aggregates derived from rocks discharged at construction sites indicating a considerable skew in supply chain. These findings are predicted to have a detrimental influence on aggregate supply in the long run, necessitating policy changes targeted at building an optimal aggregate distribution market.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.335-343
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• 2010

Steel corrosion in reinforced concrete (RC) structures is a critical problem to structural safety and many researches are being actively conducted on developing methods to maintain the required performance of the RC structures during their intended service lives. In this study, concrete mixture proportioning technique through genetic algorithm (GA) for RC structures under carbonation, which is considered to be serious in underground site and big cities, is investigated. For this, mixture proportions and diffusion coefficients of $CO_2$ from the previous researches were analyzed and fitness function for $CO_2$ diffusion coefficient was derived through regression analysis. This function based on the 12 experimental results consisted of 5 variables including water-cement ratio (W/C), cement content, sand percentage, coarse aggregate content per unit volume of concrete in unit, and relative humidity. Through genetic algorithm (GA) technique, simulated mixture proportions were proposed for 3 cases of verification and they showed reasonable results with less than relative error of 10%. Finally, assuming intended service life, different exposure conditions, design parameters, intended $CO_2$ diffusion coefficients, and cement contents were determined and related mixture proportions were simulated. This proposed technique is capable of suggesting reasonable mix proportions and can be modified based on experimental data which consider various mixing components like mineral admixtures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.124-134
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• 2013

This study investigated the effect of surface water on concrete substrate on adhesive strength in tension of very high flowable SBR-modified cement mortar. The specimens were prepared with proportionally mixing SBR latex, ordinary portland cement, silica sand, superplasticizer and viscosity enhancing agent. Polymer cement ratio (P/C) were 10, 20, 30, 50 and 75% and the weight ratio of fine aggregate to cement were 1:1 and 1:3. The specimens obtained with different P/C and C:F were characterized by unit weight, flow test, crack resistance and adhesion test. After basic tests, two mixtures of P/C=20% and 30% in case of C:F=1:1, and one mixture of P/C=50% in case of C:F=1:3 were selected, respectively. These three selected specimens were studied about the effect of surface water evenly sprayed on concrete substrate by a amount of 0, 0.006, 0.012, 0.017, 0.024g per unit area ($cm^2$) of concrete substrate surface The results show that surface water on concrete substrate increases the adhesive strength in tension of high flowable SBR-modified cement mortar and improve the flowability compared to the non-sprayed case.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.3
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• pp.277-282
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• 2015

This study is conducted to utilize waste concrete powder (WCP) made as a by-product manufacturing high quality recycled aggregate. The blaine fineness of the used waste concrete powder was $928cm^2/g$. As the main characteristic of waste concrete powder, it showed an angular type similar to cement, but hydrated products were attached on the surface of particles. In addition, the size of the particles of waste concrete powder was larger than OPC and in terms of chemical components it had higher $SiO_2$ contents. For using WCP in soil cement-based pavement, the qualities, physical and chemical properties, of WCP should be researched. In the first step, the specified compressive strength of mortar for two types of clay sand soil and clay soil respectively was experimented to be 15 MPa and then optimum mixing ratio of chemical solidification agent were decided in the range of 1.5 - 3.0% in the replacement with cement weight content. In the second step, based on the prior experimental results, recycling possibility of WCP in soil cement-based pavement was studied. In the result of experiment the mixing ratio of WCP were 5, 10, 15 and 20% in the replacement with soil weight and the compressive strength of mortar was somewhat decreased according to the increase of the mixing ratio of WCP.

• Korean Journal of Agricultural Science
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• v.24 no.2
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• pp.194-206
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• 1997

This paper was performed to evaluate the properties of no-coarse lightweight concrete using perlite and expanded polystyrene bead on fine aggregate. The results were shown that w/c and unit weight was affected by absorption ratio and unit weight of using aggregate itself. The compressive strength of no-coarse lightweight concrete was showed $187kgf/cm^2$ by using natural sand, $170kgf/cm^2$ by using perlite. Tensile and bending strength were showed the same tendency of compressive strength, but when expanded polystyrene bead concrete dose not have strength nearly. The pulse velocity and static modulus of elasticity of no-coarse lightweight concrete were smaller than that of normal cement concrete. And stress-strain curves were shown that was increased with increase of stress, and when the stress-strain curve using expanded polystyrene bead was repeated at short intervals increase and decrease irregularly.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.3
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• pp.192-201
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• 2023

In this paper, the strength properties of porous concrete containing natural fine aggregates and bottom ash aggregates were investigated, The material properties of natural fine aggregates and bottom ash were identified then used as aggregates for porous concrete. The water-binder ratio was constant at 0.25, and the com paction level of 0.5, 1.5, and 2.5 MPa was applied to produce a porous concrete specimen. Test of unit weight, ultrasonic velocity, compressive strength, and flexural tensile strength were perform ed and analyzed. The unit weight, ultrasonic velocity, com pressive strength, and flexural tensile strength increased as the compaction level increased and also the replacement rate of bottom ash with sand(fine aggregate) increased. In addition, through regression analysis, the correlation between the unit weight, compressive strength, and flexural tensile strength of bottom ash porous concrete was presented. Unit weight and strength properties are proportional to each other and showed an increasing correlation. In addition, the correlation coefficient (R²) value of regression analysis was calculated based on the experimental results of this study and those of other research papers.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.54 no.1
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• pp.25-31
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• 2018

In this study, the differences of holding power according to the shape and weight distribution of concrete weight used in shellfish shell fishery were investigated through the experiments. To investigate the differences in shape, five bar-shaped concrete weights with the same length and different cross-sectional shapes were produced. The sectional shape of each weight was square, triangle, circle, small cross, and large cross (SQ, TR, CI, CR-S, CR-L). Ten rectangular parallelepiped weights with different bottom area and cross-sectional area were produced. To investigate the differences by the weight distribution, the holding power on the square model (SQ) with six 50 g weights at different positions was investigated. All the holding power was obtained by measuring the tensile force generated when the concrete weight was pulled at a constant speed on the sand. As a result, there were no differences in holding power between the ten rectangular weights. However, the experiment on weights with different cross-sectional shapes showed differences in holding power. The holding power was higher in the order of CR-L > CR-S > CI > TR > SQ. In the weight distribution test, the holding power was higher as the front side of the weight was heavier. Generally, the frictional force is the same even if the shape is different, when two objects have the same value in the weight and the roughness. On the other hand, it seems to have a large impact when the shape of the bottom is deformed in the course of pulling the object. Particularly, the larger the degree of protrusion like cruciform weights, the more the holding power increased while deeply digging the bottom. It is also likely that the holding power increases as the front weight increases.

• Economic and Environmental Geology
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• v.39 no.3 s.178
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• pp.285-299
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• 2006

The Mireuksaji stone pagoda in Iksan is the largest stone pagoda existing in Eastern Asia. It was assumed that originally it had been established in the shape of nine-storied pagoda but as time went by only six-storied pagoda remained partially due to collapsing, repair and reconstruction. According to the reference, we can't make sure when its modification happened. The form that the pagoda is having now, was modified with concrete by the Japanese during the 1910s. The materials mixed in concrete were mixture of Portland cement, all sorts of stone, sand, and a little bit of new building stone, additive and compound. And also these materials were applied to cultural assets without any experiment at the time of 1910s as maintenance, which are still used recently. To prevent the change of its shape, the west side, south side and the north side which is partially destructed was rebuilt and reinforced with concrete and some of the deformed parts were also filled. The amounts of concrete used were about 200 tons. Such method had prevented the pagoda from destructing, however, by choosing a wrong repair method, its surface of the stone has secondary contaminants and precipitation caused by concrete. This kind of contamination speeds up the weathering which accelerates the aging mechanism of the stone to make it even harder to revive the absence of historical nature. Therefore, we are to find the best cleaning method to remove the secondary hazard contaminants.