• Journal of the Korean Recycled Construction Resources Institute
• /
• v.11 no.3
• /
• pp.210-217
• /
• 2023

Various performances of ultra-high performance concrete (UHPC) applied with microplastics and expanded polystyrene (EPS) beads were evaluated. CompressIve and flexural strength, performance after ignition, flow-down in fresh state, and effective bond strength were evaluated. Designed weight of the cement panel with these mixtures was calculated based on the flexural strength. As a result of the experiments, it was confirmed that the EPS could reduce the density of UHPC with largest range. By maximum addition of EPS beeds, the density of UHPC decreased to 1300 kg/m³, and the compressive and flexural strengths for this mixtures were in ranges of 20-30 MPa and 15-20 MPa, respectively. On the other hand, lightest cement panel could be designed with UHPC having a density ranges about 2.0 g/cm³.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.5
• /
• pp.85-92
• /
• 2016

The eight mixes and artificial soil aggregates were prepared for evaluating the practical application of lightweight foamed concrete as soil aggregates. The main parameter was unit binder content ranged between from 100 to $800kg/m^3$. In lightweight foamed concrete, flow, slurry and dried density, and compressive strength at different ages were measured. In Artificial soil aggregates crushed from lightweight foamed concrete, particle size distribution, pH, coefficient of permeability, cation exchange capacity(CEC), and ratio of carbon to nitrogen(ratio of C/N), were measured. The test results showed that flow, slurry and dried density, and compressive strength at different ages of lightweight foamed concrete increased with the increasing of unit binder content. Compressive strength at age of 28, of lightweight foamed concrete with unit binder of more than $500kg/m^3$, was more than 4 MPa. The ammonium phosphate immersion time of more than age of 3, was effective to decrease pH of artificial soil aggregates. In addition, artificial soil aggregates was evaluated as high class in terms of cation exchange capacity(CEC), while satisfied with value of ratio of carbon to nitrogen(ratio of C/N) recommended by landscape specification.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.9
• /
• pp.414-423
• /
• 2020

Fiber-reinforced polymer (FRP) laminate sheets, which are lightweight with high strength, are commonly used to reinforce concrete structures. The bonding strength is vital in structural design. Therefore, experiments and analytical studies with differing variables (concrete compressive strength and tensile strength, the elastic modulus of concrete and FRP, thickness of concrete and FRP, width of concrete and FRP, bond length, effective bond length, fracture energy, maximum bond stress, maximum slip) have been conducted to obtain an accurate numerical model of the bond strength between an FRP sheet and concrete. Although many models have been proposed, no validated model has emerged that could be used easily in practice. Therefore, this study analyzed the parameters that influence the bond strength that were used in 23 of the proposed models (Khalifa model, Iso model, Maeda model, Chen model, etc.) and compared them to the test results of 188 specimens via the numerical results of each model. As a result, an easy-to-use practical model with a simple and high degree of expression was proposed based on the Iso model combined with the effective bond length model that was proposed by Holzenkӓmpfer.

• KIEAE Journal
• /
• v.10 no.3
• /
• pp.89-96
• /
• 2010

In comparison with ordinary or heavy-weight concrete, light-weight air void concrete has the good aspects in optimizing super tall structure systems for the process of design considering wind load and seismic load by lightening total dead load of buildings and reducing natural resources used. Light-weight air void concrete has excellent properties of heat and sound insulating due to its high amount porosity of air voids. So, it has been used as partition walls and the floor of Ondol which is the traditional Korean floor heating system. Under the condition of which the supply of light-weight aggregates are limited, the development of light-weight concrete using air voids is highly required in the aspects of reduced manufacturing prices and mass production. In this study, we investigated the physical properties and thermal behaviors of specimens that applied different mixing ratios of foaming agent to evaluate the possibility of use in the structural elements. We proposed the estimating equation for compressive strength of each mix having different ratio of foaming agent. We also confirmed that the density of cement matrix is decreased as the mixing amount of foaming agent increase up to 0.6% of foaming agent mixing ratio which was observed by SEM. Based on porosity and compressive strength of control mortar without foaming agent, we built the estimating equations of compressive strength for mortars with foaming agent. The upper limit of use in foaming agent is about 0.6% of the binder amount. Each air void is independent, and size of voids range from 50 to $100{\mu}m$.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2019.05a
• /
• pp.215-216
• /
• 2019

Recently, due to abnormal climate phenomena caused by greenhouse gas, flood damage such as local torrential rain has been emerging in Korea. Accordingly, there is a growing need for porous blocks capable of permeability in concrete, but there are limitations in commercialization due to problems such as high unit weight and flexural strength development limitations. This study investigates the unit weight and strength properties of porous blocks using bottom ash as an alternative to aggregate as part of a study to improve the light weight of porous blocks.

• Advances in concrete construction
• /
• v.11 no.2
• /
• pp.151-161
• /
• 2021

The major shortcoming of concrete in most of the applications is its high self-weight and thermal conductivity. The emerging trend to overcome these shortcomings is the use of foam-concrete, which is a lightweight concrete consisting of cement, filler, water and a foaming agent. This study aims at the development of a cost-effective high-volume fly-ash foam-concrete insulation wall cladding for existing buildings using natural fiber like rice straw in different proportions. The paper reports the results of systematic studies on various mechanical, acoustic, thermal and durability properties of foam-concrete with and without replacement of cement by fly-ash. Fly-ash replaces 60 percent by weight of cement in foam-concrete. The water-solid ratio of 0.3, the filler ratio of 1:1 by weight, and the density of 1100 kg/㎥ (approx.) are fixed for all the mixes. Rice straw at 1%, 3% and 5% by weight of cement was added to improve the thermal and acoustic efficiency. From the investigations, it was inferred that the strength properties were increased with fly-ash replacement up to 1% rice straw addition. In furtherance, addition of rice straw and fly-ash resulted in improved acoustic and thermal properties.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.11a
• /
• pp.749-752
• /
• 2006

Autoclaved lightweight concrete (ALC) have high water absorption, low compressive strength and popout the origin of the low surface strength in its properties. These properties make troubles under construction such as cracking and popout. Thus, this study is to improve the fundamental strength by control of $SO_3$ ratio's and Sand Sulrry grain size. From the test result, Improved ALC have a good fundamental properties. Compressive strength, and abrasion's ratio were improved depending on increasing $SO_3$ ratio's and Sand Sulrry grain size control.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2023.11a
• /
• pp.217-218
• /
• 2023

This study is to develop porous concrete using super absorbent polymer, which possesses insolubility and high absorption capacity, as a substitute material for lightweight soil. Various mixtures were prepared using aggregates, cement, mixing water, and super absorbent polymer, and the absorption ratio and compressive strength were examined for each mixture. As the amount of super absorbent polymer added increased, the absorption ratio also increased, reaching up to 35-105%. However, the compressive strength decreased by 49.5% to 65.3%. This is believed to be due to the inherent properties of super absorbent polymer, which led to an increase in the absorption ratio but, in turn, reduced the binding strength of cement paste particles, resulting in a decrease in compressive strength.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.9 no.3
• /
• pp.268-275
• /
• 2021

The three factors that determine the strength of concrete are the strength of cement paste, aggregate and ITZ(Interfacial Transition Zone) between aggregate and cement paste. Out of these, the strength of ITZ is the most vulnerable. ITZ is formed in 10~50㎛, the ratio of calcium hydroxide is high, and CSH appears low ratio. A high calcium hydroxide ratio causes a decrease in the bond strength of ITZ. ITZ is due to further weak area. The problem of ITZ appears as a more disadvantageous factor when it used lightweight aggregate. The previous study of ITZ properties have measured interfacial toughness, identified influencing factors ITZ, and it progressed SEM and XRD analysis on cement matrix without using coarse aggregates. also it was identified microstructure using EMPA-BSE equipment. However, in previous studies, it is difficult to understand the microstructure and mechanical properties. Therefore, in this study, a method of measuring electrical resistance using EIS(Electrochemical Impedance Spectroscopy) measuring equipment was adopted to identify the ITZ between natural aggregate and lightweight aggregate, and it was tested the change of ITZ by surface coating of lightweight aggregate with ground granulated blast furnace slag. As a result, the compressive strength of natural aggregate and lightweight aggregate appear high strength of natural aggregate with high density, surface coating lightweight aggregate appear strength higher than natural aggregate. The electrical resistivity of ITZ according to the aggregate appeared difference.

• Structural Engineering and Mechanics
• /
• v.83 no.3
• /
• pp.387-400
• /
• 2022

The practice of using encased steel-concrete columns in medium to high-rise structures has expanded dramatically in recent years. The study evaluates existing methodologies and codal guidelines for estimating the ultimate load-carrying characteristics of concrete-encased short columns experimentally. The present condition of composite column design methods was analyzed using the Egyptian code ECP203-2007, the American Institute of Steel Construction's AISC-LRFD-2010, Eurocode EC-4, the American Concrete Institute's ACI-318-2014, and the British Standard BS-5400-5. According to the codes, the axial load carrying characteristics of both the encased steel and concrete sections was examined. The effect of load-carrying capacities in different forms of encased steel sections on encased steel-concrete columns was studied experimentally. The axial load carrying capacity of twelve concrete-encased columns and four conventional reinforced columns were examined. The conclusion is that the confinement was not taken into account when forecasting the strength and ductility of the encased concrete, resulting in considerable disparities between codal provisions and experimental results. The configuration of the steel section influenced the confining effect. Better confinement is achieved with the laced and battened section than with the infilled steel tube reinforced and conventionally reinforced section. The ECP203-2007 code reported the most conservative results of all the codes used.