• Journal of the Mineralogical Society of Korea
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• v.14 no.2
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• pp.85-98
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• 2001

This study deals with the petrographic examination of aggregates(ASTM C 295) which is one of the methods to diagnose the quality of aggregates for concrete artifacts. A number of examinations including size and sieve analysis, test on the coating material, description of the weathering and contamination condition, petrographic description, and qualitative and quantitative analyses on the rocks and minerals potential to alkali-aggregates reactivity are carried out to examine the quality of aggregates. Petrographic description method examined on the fluvial aggregates from Maewhacheon A, B area, Uljin-gun, Kyungnam province shows that weathering grade ranges from F(fresh) to WS(slightly weathered) and coating material and contamination are not in a harmful condition. The weight percentage of the alkali-aggregates reactive minerals or structurally unstable rocks of the aggregates from study area covers 26% and 19% of all aggregates, respectively. So it is necessary to further identify their quality through the chemical(ASTM C 289) and mortar-bar method (ASTM C 227).

• Environmental Engineering Research
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• v.18 no.2
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• pp.95-101
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• 2013

Alternative sources of water are sought in some water stressed communities in the study area. The study focuses on the Aguata-Awka area of southeastern Nigeria. Aquifers occur at great depths, and surface waters may be far from homesteads. The scarcity of water has necessitated the people to adopt various local technologies for harvesting rainfall. The local technology includes collecting rainwater from roofs and channeling the water into large underground tanks, shallow wells and surface reservoirs. Large concrete tanks of $6m{\times}6m{\times}4m$ dimensions are often built underground and can store $144m^3$ of water. Surface reservoirs built on 4 m concrete pillar supports having dimensions of $10m{\times}10m{\times}4m$ and have a storage capacity of $400m^3$. Water samples were collected at 3 different locations of Agulu, Ekwulobia, and Awka and were analyzed for their physical, chemical, and bacteriological parameters. Results indicate a range of values for pH, 5.9 to 7.1; turbidity, 0.9 to 2.7; total dissolved solids, 80 to 170 mg/L; total hardness, 4.5 to 6.4 mg/L; magnesium, 1.2 to 1.4 mg/L; bicarbonate, 19.4 to 83.6 mg/L; and sulfate, 3.6 to 6.4 mg/L. Bacteriological analysis results were negative for fecal and total coliform counts. All parameters, with the exception of pH where aluminum and galvanized iron roofs are used for collection, fall within the recommended guidelines for drinking water quality of the World Health Organization, and the Standard Organization of Nigeria, new Nigerian standards for drinking water quality. Magnesium is above the maximum permitted level for consumer acceptability of the Nigerian standards for drinking water quality. The water can be classified as fresh moderately hard and soft. The water can be described as a calcium and bicarbonate type.

• Magazine of the Korea Concrete Institute
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• v.4 no.1
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• pp.107-118
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• 1992

In order to examine the mechanical properties of carbon fiber reinforced cement composites with silica powder PAN - based carbon fiber and Pitch- based carbon fiber, and polymer impregnators experimental studies on CFRC impregnated in polymer were carried out. The effects of types, length, and content~i of carbon fibers and matrices of fresh and hardened CFRC impregnated in polymer were examined. The test results show that compressive, tensile, and flexural strength of CFRC impregnated in polymer were much more iriCreased than those of air cured and autodaved CFIIC CFRC impregnated in polymer was also considerably effective in improving toughness, freeze thaw resistance, loss of shrinkage, and creep resist ance, compared with air cured and autoclaved CFRC.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.833-836
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• 2008

In this study, we would like to study on the apply properties to salt water environment of pre-hydrated bentonite for complement problem that water leakage to permit salt water that existing bentonite does not initial swelling. Accordingly, execute viscosity properties, swelling properties, permeability and confirmed apply properties to salt water environment. Did not permit initial permeable in test result salt water environment, and permeable did not happen until 72 hours by maximum $3kgf/cm^2$ water pressure. Fresh water environment enough progress of gelation confirm that viscosity and swelling properties confirmation result and as delamination phenomenon of platy formation looked in salt water environment but this as bentonite hydrates crystallization layer swelling that is done consider. Synthetic study results, if compaction condition such as press layer is formed to bentonite upper, applied to the salt water environment of the underground structures of expectations.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.358-366
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• 2019

The purpose of this study is to explore the possibility of estimating optimum surface finishing work time of the fresh concrete placed at the job site by applying a surface hardness test meter(Durometer). Tests are carried out by measuring and comparing the Proctor penetration resistance test and hardness test by Durometer. Correlations between Procter penetration test and hardness test by Durometer were obtained. Two different types Durometer were applied to estimate setting time. Test results indicate that the measurement of the Durometer and the test of the Proctor penetration resistance are highly correlated. When measuring the initial setting time with Durometer, initial setting time is reached when the hardness value by the type C Durometer is reached around 42HD, and when final setting is measured with the type D Durometer, the surface finishing work time limit and curing time can be estimated with 10HD of Durometer.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.23-30
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• 2008

UHPC has high performance, high strength and excellent mechanical properties. Moreover UHPC(Ultra High Performance Cementitious Composite) has advantage to reduce cross section under the same load compared with other kinds of concrete. But silica fume which is imported from foreign country has a abundant portion in UHPC mixture in comparison with normal concrete. This is one of the main reason to raise the construction cost. Superior mechanical properties of UHPC due to the optimum filling composition can be changed by replacing the very fine ingredient. The purpose of this research is to grasp the characteristic of UHPC which silica fume and silica flour is replaced with limestone powder. This experiment can be divided into three classes according to the kinds of replacement. The compressive strength and flow of all types were measured and microstructure and hydration phenomena for comparing RPC were analyzed by SEM, XRD, NMR method. As a result, the replacement can be considered to be effective by for the decrease of the UHPC structure construction cost and improvement of the fresh UHPC.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.5
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• pp.25-34
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• 2012

It has been well known that concrete structures exposed to acid and sulfate environments such as sewer etc. show significant decrease in their durability due to chemical attack. Such deleterious acid and sulfate attacks lead to expansion and cracking in concrete, and thus, eventually result in damage to cement mortar by forming expansive hydration products due to the reaction between cement hydration products and acid and sulfate ions. In this study, the effect of fly ash and blast furnace slag on the bond performances of structural synthetic fiber in latex modified cement mortar under sulfate environments. Fly ash and blast furnace slag contents ranging from 0 % to 20 % are used in the mix proportions. The latex modified cement mortar specimens were immersed in fresh water, 8 % sodium sulfate ($Na_2SO_4$) solutions for 28 and 50 days, respectively. Pullout tests are conducted to measure the bond performance of structural synthetic fiber from latex modified cement mortar after sulfate environments exposure. Test results are found that the incorporation of fly ash and blast furnace slag can effectively enhance the PVA fiber-latex modified cement mortar interfacial bond properties (bond behavior, bond strength and interface toughness) after sulfate environments exposure. The microstructural observation confirms the findings on the interface bond mechanism drawn from the fiber pullout test results under sulfate environments.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.4
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• pp.149-158
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• 2003

It is customary that tendons and sectional dimensions are calibrated and tendon forces are applied at once at the initial stage to keep the subsequent stresses occuring at different loading stages within the allowable stresse in prestressed concrete (PSC) bridge design. However, this traditional tensioning method usually results in a too conservative sectional depth in view of ultimate capacity of a girder. A new design method which can realize the reduction of sectional depth of PSC girder is theoretically suggested in this study. Tendons are tensioned twice at different loading stages: the initial stage and the stage after fresh slab concrete is cast. It can be shown that according to this technique, sectional depth can be significantly reduced and larger span can be realized compared to traditional ones. In this paper, there is an example about the design of bridge by means of new PSC design theory, having a longer span than a existing railway bridge. Also, a new method by continuous tendon profiles is presented to be continuous a IPC bridge.

• Earthquakes and Structures
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• v.16 no.5
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• pp.625-639
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• 2019

The concept of the combined seismic and energy retrofitting of existing reinforced concrete (RC) buildings was examined in this paper through a number of case studies conducted on model buildings (simulating buildings of the '60s-'80s in southern Europe) constructed according to outdated design standards. Specifically, seismic and thermal analyses have been conducted prior to and after the application of selected retrofitting schemes, in order to quantify the positive effect that retrofitting could provide to RC buildings both in terms of their structural and energy performance. Advanced materials, namely the textile reinforced mortars (TRM), were used for providing seismic retrofitting by means of jacketing of masonry infills in RC frames. Moreover, following the application of the TRM jackets, thermal insulation materials were simultaneously provided to the RC building envelope, exploiting the fresh mortar used to bind the TRM jackets. In addition to the externally applied insulation material, all the fenestration elements (windows and doors) were replaced with new high energy efficiency ones. Afterwards, an economic measure, namely the expected annual loss (EAL) was used to evaluate the efficiency of each retrofitting method, but also to assess whether the combined seismic and energy retrofitting is economically feasible. From the results of this preliminary study, it was concluded that the selected seismic retrofitting technique can indeed enhance significantly the structural behaviour of an existing RC building and lower its EAL related to earthquake risks. Finally, it was found that the combined seismic and energy upgrading is economically more efficient than a sole energy or seismic retrofitting scenario for seismic areas of south Europe.

• Journal of the Korean GEO-environmental Society
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• v.23 no.11
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• pp.5-11
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• 2022

The objective of this study is to evaluate the mechanical properties of high-flowable retaining wall material (RWM) incorporated with ground granulated blast-furnace slag (SG) and steel fiber (SF) based on a comparison with those of ordinary portland cement (OPC). To produce the specimens of RWM, some chemical agents such as superplasticizer (SP), air-entrained agent (AEA) and viscosity modifying agent (VMA) are added in the fresh RWM. The compressive, split tensile and flexural strength measurements were performed on the hardened RWM specimens. Additionally, surface electric resistivity and absorption tests according to ASTM standards were carried out at predetermined periods after water curing. It was found that the mechanical properties of slag cement concrete (SGC) RWM mix are better than those ordinary portland cement concrete (OPC) RWM mix. The effect of SF is remarkable to improve the mechanical properties of RWM mixes. It is noted that the usage of SG shows a beneficial effect to resist water penetration as well as long-term strength development of RWM mixes.