• Computers and Concrete
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• v.16 no.6
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• pp.865-880
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• 2015

Standard test method for bulk electrical conductivity (ASTM C1760) provides a rapid indication of the concrete's resistance to the penetration of chloride ions by diffusion. In this paper a new approach for assessing the bulk electrical conductivity of saturated specimens of hardened concrete is presented. The test involves saturating concrete specimens with a 5 M NaCl solution before measuring the conductivity of the samples. By saturating specimens with a highly conductive solution, they showed virtually the same pore solution conductivity. Different concrete samples yield different conductivity primarily due to differences in their pore structure. The feasibility of the method has been demonstrated by testing different concrete mixtures consisting ordinary and blended cement of silica fume (SF) and calcined perlite powder (CPP). Two standard test methods of RCPT (ASTM C1202) and Bulk Conductivity (ASTM C1760) were also applied to all of the samples. The results show that for concretes containing SF and CPP, the proposed method is less sensitive towards the variations in the pore solution conductivity in comparison with RCPT and Bulk Conductivity tests. It seems that this method is suitable for the assessment of the performance and durability of different concretes containing supplementary cementitious materials.

• Archives of design research
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• v.18 no.4 s.62
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• pp.35-44
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• 2005

In the world, most of the metal technologists were as called as adornment artists than other field of industrial arts strongly industrial characters functional materials and manufacturing technology many used in the present age. In the study, one of adornments researched and material character analyzed about Art Clay Silver. The shrinkage rate of shape was about 0.24%. A shrinking phenomenon drying time thought of evaporation of water linking bonding agents and powders. After calcination of Art Clay Silver, the EDX used that just Ag 100% analyzed a result from the surface assay in the room temperature. A binder with powder in the room temperature considered to disappear, because it was been fume and smoke at high calcined temperature. A study showed when handicrafted necklaces make by these characteristic as using in difficult and delicated operations rather than naturally and beautifully expressive products.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.148-151
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• 1994

Up to now, sea sand without complete removal of salt is being used in the construction works because there is little satisfactory counterplan for the substitute aggregate. In the case that such sea sand is used in the reinforced concrete, the residual salt gives rise to deterioration phenmenon and iron corrosion, reducing durability of the ferro-concrete structures. The paper, an experimental study on the effect of corrosion protection by tighting concrete used SF and FA, is to investigate general steel bar's corrosion and to develop concrete using sea sand economically after it is analyzed and examinated ratio of the corrosion area affected by the autoclave cycle. As a test results, as for corrosion area ratio, it is very effective to use admixrutes such as SF and FA which decrease corrosion area remarkably with increasing the amounts of admixtures. Accordingly the use of admixtures is advantageous for tightening concrete and has an effect of salt damage prevention and rust protection in concrete used sea sand.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.97-102
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• 2006

In this study, the effect of supplementary materials(GGBS, PFA, SF) on sulfuric acid corrosion resistance was assessed by measuring the compressive strength, corroded depth and weight change at 7, 28, 56, 91, 180 and 250 days of immersion in sulfuric acid solution with the pH of 0.5, 1.0, 2.0 and 3.0. Then, it was found that an increase in the duration of immersion and a decrease in the pH, as expected, resulted in a more severe corrosion irrespective of binders: increased corroded depth and weight change, and lowered the compressive strength. 60% GGBS mortar specimen was the most resistant to acid corrosion in terms of the corroded depth, weight change and compressive strength, due to the latent hydraulic characteristics and lower portion of calcium hydroxide. The order of resistance to acid was 60% GGBS>20% PFA>10% SF>OPC. In a microscopic examination, it was found that acid corrosion of cement matrix produced gypsum, as a result of decomposition of hydration products, which may loose the structure of cement matrix, thereby leading to a remarkable decrease of concrete properties.

• International Journal of Concrete Structures and Materials
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• v.9 no.2
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• pp.207-217
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• 2015

The influence of powdered and colloidal nano-silica (NS) on the mechanical properties of cement mortar has been investigated. Powdered-NS (~40 nm) was synthesized by employing the sol-gel method and compared with commercially available colloidal NS (~20 nm). SEM and XRD studies revealed that the powdered-NS is non-agglomerated and amorphous, while colloidal-NS is agglomerated in nature. Further, these nanoparticles were incorporated into cement mortar for evaluating compressive strength, gel/space ratio, portlandite quantification, C-S-H quantification and chloride diffusion. Approximately, 27 and 37 % enhancement in compressive strength was observed using colloidal and powdered-NS, respectively, whereas the same was up to 19 % only when silica fume was used. Gel/space ratio was also determined on the basis of degree of hydration of cement mortar and it increases linearly with the compressive strength. Furthermore, DTG results revealed that lime consumption capacity of powdered-NS is significantly higher than colloidal-NS, which results in the formation of additional calcium-silicate-hydrate (C-S-H). Chloride penetration studies revealed that the powdered-NS significantly reduces the ingress of chloride ion as the microstructure is considerably improved by incorporating into cement mortar.

• International Journal of Concrete Structures and Materials
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• v.6 no.3
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• pp.177-186
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• 2012

The temperature distributions of concrete structures strongly depend on the value of thermal conductivity of concrete. However, the thermal conductivity of concrete varies according to the composition of the constituents and the temperature and moisture conditions of concrete, which cause difficulty in accurately predicting the thermal conductivity value in concrete. For this reason, in this study, back-propagation neural network models on the basis of experimental values carried out by previous researchers have been utilized to effectively account for the influence of these variables. The neural networks were trained by 124 data sets with eleven parameters: nine concrete composition parameters (the ratio of water-cement, the percentage of fine and coarse aggregate, and the unit weight of water, cement, fine aggregate, coarse aggregate, fly ash and silica fume) and two concrete state parameters (the temperature and water content of concrete). Finally, the trained neural network models were evaluated by applying to other 28 measured values not included in the training of the neural networks. The result indicated that the proposed method using a back-propagation neural algorithm was effective at predicting the thermal conductivity of concrete.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.65-66
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• 2012

The cement used in the construction industry of the manufacturing process, large amounts of the greenhouse gas, CO₂ and is currently being studied for cement substitutes that reduce greenhouse gas issue. Therefore, the this study as a replacement for cement industrial by-product of blast furnace slag, red mud, silica fume and alkali-activator, using only inorganic composites without high-temperature calcination process were manufactured. The waste gypsum board micro powder added to compensate for the shrinkage cracks, the compressive strength and flow, and length change characteristics were investigated. Consequently, The setting time was shortened as GB added And liquidity was reduced. GB 2%, 7 days curing the added strength of specimens was the highest. Came out, and change the length of the Plain least.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.18 no.3
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• pp.300-306
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• 2009

Welding technology is applicable in many kinds of fields, with the help of its advantages such as easy operational procedure and structural simplification. However, in the process of welding, hazardous materials and fumes cause huge fire broke-outs, explosions, and health-conscious problems. Also, as heavy metals in fumes have a harmful effect on the environment, recently, this has emerged as a urgent social issue. This study has been aimed at the recommendation of the most environment-friendly, among materials currently used in plumbing welding, and it has been done at the result of the analysis of amount, ingredient, and size in collected fumes created in the experiment of welding five rods to galvanized steel pipes and steel pipe ones. At the test result, due to the effect of Zn-coating, galvanized steel pipes, when welded to rods, created more fumes than steel pipe ones. In the mean time, when it comes to welding rods, among five, WR-03 produced fumes the least. Therefore, a combination of the test results clearly indicates that the case of welding WR-03 to cast-iron pipes turned out to be the most environment-friendly.

• Tunnel and Underground Space
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• v.8 no.1
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• pp.8-16
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• 1998

The first purpose of this study is to verify the application of computer modelling to a enclosed space fire. The second one is to determine temperature distribution for the three different ventilation types in case of a enclosed space fire. The third one is to find out the ventilation direction and ventilation quantity to remove effectively heat and combustion products generated by a fire in variable air volume(VAV) system. Firstly, compared with experimental results of Lawrence Livermore National Laboratory(LLNL), numerical results show good agreements. Secondly, among three different ventilation types, the numerical analyses show the highest temperature distribution in occupied zone(up to 1.8 m from bottom) from firing moment to 100 sec. when supply ducts are placed in ceiling and extract duct is placed close to the bottom on side walls. This is due to disadvantageous position of extract duct in ventilating high temperature air which rise because of buoyancy force. Thirdly, this study finds out effective ventilation direction and ventilation quantity to remove heat and combustion products generated by a fire by using VAV system. $CO_2$ concentration is used as a fire fume removal index. As soon as a fire happens, ventilation direction is changed in order to gather and drive out fire fumes. In case of three times ventilation quantity of ordinary one, $CO_2$ concentration and temperature have begun to decrease at 120 sec. after firing, i.e.fire fumes have begun to be removed.

• Journal of Welding and Joining
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• v.23 no.1
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• pp.69-76
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• 2005

Recently, application of arc welding to galvanized carbon steel sheet is on the increasing Ould in the fields of automobile and construction industries. In arc welding process, zinc is evaporated in weld pool, even under the appropriate welding condition and produce blowhole and/or pit. Zinc gas cause instability of arc and increase spatter and fume. This research is purposed to minimize the heat-input and the formation of porosities in the welded joint of the galvanized carbon steel sheet using variable polarity AC wave pulse MIG welding system. An appropriate welding condition which showed low spatter and good bead appearance was acquired by applying the AC pulse MIG welding machine to DC duplicated MIG welding with the solid wire. When oxygen gas was added to shield gas of MIG welding for galvanized steel sheet, arc length was increased and arc stability was improved. In the AC duplicated welding, the loss of galvanized layer was decreased as the amount of heat-input was decreased when the EN ratio was increased under the condition that average welding current was evenly set.