• Structural Engineering and Mechanics
• /
• v.64 no.2
• /
• pp.243-257
• /
• 2017

Investigating the properties and durability of high-strength concrete exposed to sulfuric acid attack for the purpose of its application in structures exposed to this acid is of outmost importance. In this research, the resistance and durability of high-strength concrete containing macro-polymeric or steel fibers together with the pozzolans of silica fume or nano-silica against sulfuric acid attack are explored. To accomplish this goal, in total, 108 high-strength concrete specimens were made with 9 different mix designs containing macro-polymeric and steel fibers at the volume fractions of 0.5, 0.75, and 1.0%, as well as the pozzolans of silica fume and nano-silica with the replacement levels of 10 and 2%, respectively. After placing the specimens inside a 5% sulfuric acid solution in the periods of 7, 21, and 63 days of immersion, the effect of adding the fibers and pozzolans on the compressive properties, ultrasonic pulse velocity (UPV), and weight loss of high-strength concrete was investigated and the respective results were compared with those of the reference specimens. The obtained results suggest the dependency of the resistance and durability loss of high-strength concrete against sulfuric acid attack to the properties of fibers as well as their fraction in concrete volume. Moreover, compared with using nano-silica, using silica fume in the fibrous concrete mix leads to more durable specimens against sulfuric acid attack. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized was found using response surface method (RSM).

• International Journal of Highway Engineering
• /
• v.7 no.2 s.24
• /
• pp.45-55
• /
• 2005

It is known that the Q/C(Quality Control) in the early age of portland cement concrete(PCC) pavement gives a huge effect on long term pavement performance. Thus, many studies regarding the construction of PCC pavement have focused on how to assure construction quality at the early age stage. Curing is one of the most important factor in Q/C of PCC pavement. Membrane curing that protects the evaporation of moisture by placing an impermeable layer on the slab surface is the most common practice for curing the PCC pavement. In order to improve the membrane curing practice, the rate of curing compound should be optimized. However, the optimum rate of curing compound considering Korean weather and environmental conditions has not been specified in the pavement construction specifications. In this study, a proper application rate was recommended in terms of minimizing evaporation with several full-scale tests where various rates of curing compound have been applied. Four test sites on the expressway were enlisted during the summer of 2002 and 2003. Application rates tested were in the range of $0. The rate of evaporation, the temperature pattern of the slab and the pulse velocity of concrete surface have been monitored at each test construction. The result from this study showed that the rate of current construction was approximately $160ml/m^2$ and that approximately $400ml/m^2$ of curing application was recommended as the proper rate for minimizing the moisture evaporation.

• Journal of Sericultural and Entomological Science
• /
• v.16 no.1
• /
• pp.67-75
• /
• 1974

The studies are to know how much cocoon crops is damaged by the stained leaf with nicotine produced from the tobacco field cultivated in mulching system in spring season and by residual nicotine in autumn season. Furthermore, the new knowledges are to make both industries keep up with their development. In spring season mulberry Held is located higher on the West-North of tobacco held below 20 degrees of slope and with 36 per cent of East-South wind and 18 per cent of South wind blowing from tobacco fold to the mulberry fold. In addition, silkworm larvae are fed with the mulberry leaf produced in the different plots placing by the different distances, l0m, 25m, 50m, 80m, and loom far from the tobacco Held as a control and it is also considered that narcotic larvae including the dead larvae are not observed. On the other hand, it is noted that better leaf quality and abundant growth of mulberry tree is produced from the mulberry fold closer to the tobacco field and with a low slope. 1) Maximum weight of larval body at the 5th stage is damaged by the stained leaf with the nicotine up to 25m far from the tobacco held. 2) The larvae fed with the mulberry leaf in mulberry Held up to 25m far from the tobacco fold produce small number of the fresh cocoons per 1 liter. 3) Low single cocoon weight and low cocoon shell weight are produced by the poison damaged larvae fed with the mulberry. leaf up to 25m far from the tobacco field and weight of cocoon shell is damaged higher than the single cocoon weight. It is resulted in low percentage of cocoon shell. 4) Cocoon yield including the double cocoon from 10,000 larvae is decreased by the larvae fed with the stained leaf in the mulberry fold up to 25m far from the tobacco fold and 19 per cent of cocoon yield is decreased with 2.4kg of cocoon yield in l0m plot and with 2.5kg of cocoon yield in 25m plot at the first season and at the 2nd season with 1.8kg o( cocoon yield in l0m plot and with 11.5kg of cocoon yield in 25m plot, 11 per cent and 9 per cent of cocoon yield including double cocoon from 10,000 larvae is decreased, as compared with the control, respectively. With these results, it is observed that nicotine damage is occurred to the silkworm larvae if the larvae are fed with the leaf in the mulberry Held within 25m-50m far from the tobacco field.