• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.323-328
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• 2002

Rapid set accelerators are widely used in tunnel construction, however quality criteria of and dosage are not well established. The density and solid content of admixtures, setting time and compressive strength of paste and mortar with admixtures were investigated to establish the quality criteria. While the early strength of mortar with sodium-silicate, sodium-aluminate and calcium aluminate type admixtures that have high alkali content are very high, but long-term strength are low. Aggregates of shotcrete has to be carefully selected. Sodium-silicate type admixture need longer setting time than the others.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.583-586
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• 2005

Strength of concrete is very important factor in design and quality management and may represent overall quality of concrete. Such strength of concrete may differ depending on amount of cement mixed, water and fine aggregate ratio. Classic concrete products have been produced mainly with ordinary portland cement(hereinafter 'cement'), water and fine aggregate as shown above, but various additives and mixture materials have been used for concrete manufacturing, along with development of high functional concrete and diversification of structures. Various kinds of chemical mixtures agents and mixture materials have been used as it requires concretes with other features which cannot be solved with existing materials only, such as high strength, high flexibility and no-separation in the water. Such addition of various mixture agents may cause change in cement hydrate, affecting strength. Hydration of cement is the process of producing potassium hydroxide, C-S-H, C-A-H and Ettringite, while causing heat generation reaction after it is mixed with water, and generation amounts of such hydrates play lots of roles in condensation and hardening. This study aims to analyze its strength and features with hydrates by making specimen according to curing temperature, types of mixture agent, mixing ratio and ages and by analyzing such hydrates in order to analyze role of cement hydrate on early strength of concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.1
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• pp.76-81
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• 2016

Recycled aggregate is a valuable resource in Korea in lack of natural aggregate. Government recognizes the importance and suggests various policies enhancing its use for higher value-added application. Most of recycled aggregate produced currently in Korea, however, is applied for low value-added uses such as embankment, reclamation, etc. Its higher valued application such as for structural concrete is very limited. Although domestic manufacturing technology of recycled aggregate is at the world level, recycled aggregate is not applied for structural concrete. Primary reasons for the limited use of the recycled aggregate include bonded mortar and cracks occurred during crushing and hence it is very difficult to predict and control the quality of recycled aggregate concrete. This research intended to grasp combined characteristics of recycled aggregate, high early strength cement, maximum temperature and time duration of steam curing and then, analyze the effects of factors. Also, it suggested the method to improve field applicability of recycled aggregate concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.1023-1028
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• 2001

This study focused on the investigation of strength development and permeability of LMC(latex modified concrete) and RSLMC(rapid-setting cement latex modified concrete) as the latex content, cement types and w/c ratio variated. The compressive strength of latex modified concrete decreased slightly and the flexural strength increased quitely at the latex content of 15%. This may due to the flexibility of latex filled in voids and interconnections of hydrated cement and aggregates by a film of latex particles, respectively. The permeability test results showed that the permeability of LMC was considerably lower than that of conventional concrete. In the RSLMC's tests of permeability to chloride ion indicated very low permeability at an early age, which nay be due to the early formation of needle-shape ettringites and latex film.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.5
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• pp.459-470
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• 2014

Now-a-days, the trend in constructing tunnels is to build more deeper, more longer tunnels of greater cross-sections. That's why, the demand of "Early-high-strength shotcrete" is very high because of their advantage of attaining higher strength immediately after excavation, which controls the ground subsidence. So, this study reveals the supporting phenomena of early-high-strength shotcrete, using three-dimensional numerical analysis. The crux of this study can be applied practically in construction sites also. Support Performance of two different qualities of shotcrete was checked out, by keeping the general shotcrete's thickness constant and comparing it with early-high-strength shotcrete's thickness decreasing it gradually in five steps, and analysing/comparing the support performance in all cases. Effect of using early-high-strength shotcrete was analysed to save the cost of steel sets, which are widely used for supporting the ground before the hardening of general shotcrete. The results of numerical analysis on the performance of early-high-strength shotcrete show that, it behaves more effectively under worse ground conditions and it can support the ground more conveniently than steel sets, before the shotcrete is hardened.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.53-58
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• 2003

Many researchers have rigorously studied the nonlinear behavior of stress-strain relationship of concrete using mathematical curves. Most of model equations for stress-strain relationship, however, have been focused on old age concrete, and were not able to adequately represent the behavior of concrete at an early age. A wide understanding on the behavior of concrete from early age to old age is very important in evaluating the durability and service life of concrete structures. In previous study by authors of this paper, a stress-strain model equation for low- and medium-strength concretes was suggested. In this paper, to extend the application region of compressive stress-strain curve to high-strength concrete, an analytical research was performed. An analytical expression of stress-strain curve with strength and age was developed using regression analyses on the experimental results. For the verification of the proposed model equation, it was compared to the experimental data. The result showed that the proposed model equation was not only compatible with the experimental data quite satisfactorily but also describing well the effect of strength and age on stress-strain curve.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.11a
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• pp.23-26
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• 2003

This study is intended to investigate the properties of early strength development by application of TEA to the field. According to the results, when TEA is added, fluidity is almost same to base concrete, and increases upto aimed slump after field flowing. Setting time does not differ in the case of base and TEA, but retarded after flowing. The time when compressive strength gains 5 MPa, which side form can be removed, is 23 hours, and so the removal time is shortened by I hours in comparison with plain concrete. But compressive strength is almost same to that of plain concrete at 28 days. The rebound value of P type schmidt hammer show similar tendency to compressive strength, and the rebound value of structure is higher than that of standard curing specimen due to heat capacity effect and drying by the air outside. Therefore, it is thought that if the rebound value of P type schmidt hammer is controled. by about 26 in consideration of open air environment, it is very effective to determine the removal time of side forms.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2003.05a
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• pp.23.1-26
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• 2003

This study is intended to investigate the properties of early strength development by application of TEA to the field. According to the results, when TEA is added, fluidity is almost same to base concrete, and increases upto aimed slump after field flowing. Setting time does not differ in the case of base and TEA, but is retarded after flowing. The time when compressive strength gains 5 MPa, which side form can be removed, is 23 hours, and so the removal time is shortened by 1hours in comparison with plain concrete. But compressive strength is almost same to that of plain concrete at 28 days. The rebound value of P type schmidt hammer show similar tendency to compressive strength, and the rebound value of structure is higher than that of standard curing specimen due to heat capacity effect and drying by the air outside. Therefore, it is thought that if the rebound value of P type schmidt hammer is controled. by about 26 in consideration of open air environment, it is very effective to determine the removal time of side forms.

• Journal of the Korea Institute of Building Construction
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• v.9 no.6
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• pp.175-181
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• 2009

In this research, experiments were conducted to find out whether polycarboxylate could be used as a crude steel admixture for practical work, depending on the change in the replacement level of the compound mixed into polycarboxylate. Its fluidity was satisfactory, its airspace was a bit smaller than the KS standard, and its unit volume weight was proven to meet the standard. The amount of bleeding was smallest in B2, and in terms of the solidification time, the first and the last solidification was faster in A1, B1, and C1. With regard to the compressive strength in early days as acharacteristic of hardened concrete, all addition rates of 7-day C2 displayed the highest strength value, among which the addition rate of 1.3% had the biggest strength performance tendency. The seal strength also showed the strength performance rate which was about one tenth as big as that of the compressive strength. The length change rate resulting from dryness and contraction was proven to be good, and once the appropriate AE air entraining agent is used, it is evaluated to be a very useful and practical compound out in the field.

• Structural Engineering and Mechanics
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• v.16 no.1
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• pp.83-99
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• 2003

The aim of this paper is to develop the ISCOSTFUN (Intelligent System for Prediction of Concrete Strength by Functional Networks) in order to provide in-place strength information of the concrete to facilitate concrete from removal and scheduling for construction. For this purpose, the system is developed using Functional Network (FN) by learning functions instead of weights as in Artificial Neural Networks (ANN). In serial functional network, the functions are trained from enough input-output data and the input for one functional network is the output of the other functional network. Using ISCOSTFUN it is possible to predict early strength as well as 7-day and 28-day strength of concrete. Altogether seven functional networks are used for prediction of strength development. This study shows that ISCOSTFUN using functional network is very efficient for predicting the compressive strength development of concrete and it takes less computer time as compared to well known Back Propagation Neural Network (BPN).