• Journal of the Korean Ceramic Society
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• v.44 no.11
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• pp.633-638
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• 2007

The setting time of alkali activated slag cement tends to be much faster than ordinary Portland cement, and its compressive strength had been higher from the 1 day but became lower than that of the cement on the 28 days. According to the results of the surface observation, weight loss, compressed strength, and erosion depth tests on the sulphuric acid solution. It has been drawn that alkali activated slag cement has a higher sulphate resistance than ordinary Portland cement, and in particular, the alkali activated slag cement added 5 wt% alumina cement has little deterioration on the sulphuric acid solution. The reason why the alkali activated slag cement has higher sulphate resistance than other hardened cement pastes is that it has no $Ca(OH)_2$ reactive to sulphate ion, and there is little $CaSO_4{\cdot}2H_2O$ production causing volume expansion, unlike other pastes. And it is supposed that $Al(OH)_3$ hydrates with high sulphate resistance, which is produced by adding the alumina cement increases the sulfate resistance.

• Advances in concrete construction
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• v.9 no.1
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• pp.55-70
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• 2020

In this research article, acid resistance, sulphate resistance and sorptivity of self compacted concrete (SCC) prepared from C&D waste have been discussed. To improve the above properties of self compacted recycled aggregate concrete (SCRAC) along with mechanical and durability properties, different two stage mixing approaches (TSMA and TSMAsfc) were followed. In the proposed two stage mixing approach (TSMAsfc), silica fume, a proportional amount of cement and a proportional amount of water were mixed in premix stage which fills the pores and cracks of recycled aggregate concrete (RAC). The concrete specimen prepared using above mixing approaches were immersed in 1% concentration of sulphuric acid (H2SO4) and magnesium sulphate (MgSO4) solution for 28, 90 and 180 days for evaluating the acid resistance of SCRAC. Experimental results concluded that the proposed two stage mixing approach (TSMAsfc) is most suitable for acid resistance and sulphate resistance in terms of weight loss and strength loss due to the elimination of pores and cracks in the interfacial transition zone (ITZ). In modified two stage mixing approach, the pores and cracks of recycled concrete aggregate (RCA) were filled up and make ITZs of SCRAC stronger. Microstructure analysis was carried out to justify the reason of improvement of ITZs by electron probe micro analyser (EPMA) analysis. X-ray mapping was also done to know the presence of strength contributing elements presents in the concrete sample. It was established that SCRAC with modified mixing approach have shown improved results in terms of acid resistance, sulphate resistance, sorptivity and mechanical properties.

• ALGAE
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• v.22 no.3
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• pp.229-234
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• 2007

This study was to determine the extent of bacteria contamination and resistance to various antibiotics used commonly in microalgal culture. Seven different dose levels of chloramphenicol, dihydrostreptomycin sulphate, neomycin, penicillin G, streptomycin sulphate, penicillin G + streptomycin sulphate, and penicillin G + streptomycin sulphate + chloramphenicol were added to each culture of microalgae. The lethal effects on microalgae and bacteria were the highest in chloramphenicol and the lowest in penicillin G. The axenic culture of bacillariophyceae and dinophyceae was more difficult than that of chlorophyceae and haptophyceae because of their complicate external morphology. The efficient antibiotics and their concentrations for axenic cultures varied with microalgal species. The optimum quantity for antibiotic treatments were 2,000 ppm of dihydrostreptomycin for Chlorella ellipsoidea, neomycin 500 ppm of Isochrysis galbana and Heterosigma ahashiwo, hloramphenicol 500 ppm of Cyclotella didymus, and dihydrostreptomycin sulphate and neomycin 6,000 ppm of Thalassiosira allenii.

• Steel and Composite Structures
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• v.9 no.1
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• pp.77-87
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• 2009

This paper reports the results of an experimental investigation of the polyvinylpyrrolidone (PVP) influence on the steel reinforcement corrosion and compressive strength of concretes in sulphate medium. The effect of admixture of PVP in concrete on the corrosion resistance of steel reinforced concrete was assessed by measuring electrochemical test during 60 days immersion in two different external solutions. AC impedance spectrum indicated that the resistance of PVP mixed electrodes were higher than those without PVP. The compressive strength of concrete specimens containing PVP was measured and an increase of 19%~24% was observed.

• Cement Symposium
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• no.19
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• pp.26-30
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• 1991

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.315-325
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• 2017

The purpose of the paper is to determine the influence of two widely used steel fibers and polypropylene fibers on the sulphate crystallization resistance, freeze-thaw resistance and surface wettability of ultra-high performance concrete (UHPC). Tests were carried out on cubes and cylinders of plain UHPC and fiber reinforced UHPC with varying contents ranging from 0.25 to 1% steel fibers and/or polypropylene fibers. Extensive data from the salt resistance test, frost resistance test, dynamic modulus of elasticity test before and after freezing-thawing, as well as the contact angle test were recorded and analyzed. Fiber hybridization relatively increased the resistance to salt crystallization and freeze-thaw resistance of UHPC in comparison with a single type of fiber in UHPC at the same fiber volume fraction. The experimental results indicate that hybrid fibers can significantly improve the adhesion properties and reduce the wettability of the UHPC surface.

• Advances in concrete construction
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• v.10 no.3
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• pp.237-245
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• 2020

Past research efforts already established geopolymer as an environment-friendly alternative binder system for ordinary Portland cement (OPC) and recycled aggregate is also one of the promising alternative for natural aggregates. In this study, an effort was made to produce eco-friendly mortar mixes using geopolymer as binder and recycled fine aggregate (RFA) partially and study the resistance ability of these mortar mixes against the aggressive environments. To form the geopolymer binder, 70% fly ash, 30% ground granulated blast furnace slag (GGBS) and alkaline solution comprising of sodium silicate solution and 14M sodium hydroxide solution with a ratio of 1.5 were used. The ratio of alkaline liquid to binder (AL/B) was also considered as 0.4 and 0.6. In order to determine the resistance ability against aggressive environmental conditions, acid attack test, sulphate attack test and rapid chloride permeability test were conducted. Change in mass, change in compressive strength of the specimens after the immersion in acid/sulphate solution for a period of 28, 56, 90 and 120 days has been presented and discussed in this study. Results indicated that the incorporation of RFA leads to the reduction in compressive strength. Even though strength reduction was observed, eco-friendly mortar mixes containing geopolymer as binder and RFA as fine aggregate performed better when it was produced with AL/B ratio of 0.6.

• Journal of the Korean institute of surface engineering
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• v.22 no.4
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• pp.161-167
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• 1989

Effects of bath composition on electroless deposition of Ni-W-B from sulphate solution were invesrigated in terms of deposition kinetics, electro resistivity and composition of deposit film. The microstruigated and crystataine structure of the films were also studied using a scanning electron microscope and X-ray diffractometer. The deposition rate increased linearly with increasing the concentration of nickel sulphate in bath solution, wheras the rate decreasing with sodium citrate. The rate was also affected by sodium tungstate, which was maaximum at the concentration of 0.06 M/1 in sodium tungstate, The content of W in the deposit increased with increased with increasing the sodium citrate had on opposite effect on the composition of W and B in the deposit. The crystal change film from armorphous to cryatallicne nature by heat treatments was proved by the reduction of specific resistance and X-ray diffration.

• Korean Journal of Soil Science and Fertilizer
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• v.22 no.3
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• pp.239-244
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• 1989

This work was for the elucidation of heterogeneity in a natural population of Rhizobium japonicum existing in Seoul National University's Experiment Field and of sensitivities of R. japonicum isolates for several antibiotics by using a method based on intrinsic antibiotic resistance (IAR). In addition, the suitability of IAR method for the recognition of R. japonicum strain was elucidated. Twenty seven isolates from various soybean cultivars cultivated at SNU's Experiment Field were tested to 4 antibiotics (streptomycin sulphate, kanamycin sulphate, ampicillin, oxytetracycline);There were 21 different IAR patterns among 27 isolates. It demonstrated diverse distribution of R. japonicum strains in SNU's Experiment Field. Their growth was inhibited at from a low concentration of about $1{\mu}g/ml$ to a high concentration of $400{\mu}g/ml$ for streptomycin sulphate, ampicillin, and oxytetracyclin. For kanamycin sulphate, on the contrary, all 27 isolates showed their growth inhibitances at below the concentration of $12.5{\mu}g/ml$. Two isolates identified as different strains from each other by the previous seroimmunological tests showed the same sensitivities for 4 antibiotics, and it seemed that IAR method was not perfect for the exact recognition of R. japonicum strain.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04a
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• pp.161-166
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• 1998

The main object of this study is to examine the basic properties of fresh concrete as well as hardened concrete using several types of cement such as ordinary portland cement, sulphate resisting portland cement, blast furnace slag cement, ternary blended cement. In addition, effects of each cement on the durability including drying shrinkage, freeze-thawing resistance, resistance of chloride ion penetration, carbonation of concrete were investigated. As the results of this study, it was proved that most of the properties of concrete using each cement were similar, but there were some differences in bleeding, setting time, resistance of chloride ion penetration and carbonation.