• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.326-329
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• 2003

In practice, recycled aggregate is not used for a structural member due to its high absorbability and abrasion. It is, however, highly expected that the usage of recycled aggregate increases as the processing technique of the recycled aggregate progresses. In this study herein, the compressive strength of the recycled aggregate concrete was investigated. Coarse aggregate was replaced with 100% of the recycled aggregate, and cement and fine aggregate was replaced with various amount. The specimen was steam-cured at $80^{\circ}C$. It was shown that the concrete can obtain desirable strength when fine aggregate was replaced with up to 60% of recycled fine aggregate, and when cement was replaced with up to 15% of fly ash.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.881-884
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• 2006

Wasted phosphogypsum is a by-product from the phosphoric acid process of manufacturing fertilizers. It consists mainly of $CaSO_4{\cdot}2H_2O$ and contains some impurities. The purpose of this study is to utilize wasted phosphogypsum into an admixture for concrete products cured by steam This paper is to investigate the strength properties of cement composites containing high volume phosphogypsum. The cement composites were composed of OPC, phosphogypsum, fly-ash and granulated blast-furnace slag with activators. As a result, the strength of cement composites containing high volume wasted phosphogypsum were shown high level when granulated blast-furnace slag was mixed. Therefore, PG could be used as a steam curing admixture for concrete 2th production with reduction of OPC.

• Advances in concrete construction
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• v.9 no.5
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• pp.449-457
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• 2020

The influence of subsequent curing on the performance of fly ash contained mortar under steam curing was studied. Mortar samples incorporated with different content (0%, 20%, 50% and 70%) of Class F fly ash under five typical subsequent curing conditions, including standard curing (ZS), water curing(ZW) under 25℃, oven-dry curing (ZD) under 60℃, frozen curing (ZF) under -10℃, and nature curing (ZN) exposed to outdoor environment were implemented. The unsteady chloride diffusion coefficient was measured by rapid chloride migration test (RCM) to analyze the influence of subsequent curing condition on the resistance to chloride penetration of fly ash contained mortar under steam curing. The compressive strength was measured to analyze the mechanical properties. Furthermore, the open porosity, mercury intrusion porosimetry (MIP), x-ray diffraction (XRD) and thermogravimetric analysis (TGA) were examined to investigate the pore characteristics and phase composition of mortar. The results indicate that the resistance to chloride ingress and compressive strength of steam-cured mortar decline with the increase of fly ash incorporated, regardless of the subsequent curing condition. Compared to ZS, ZD and ZF lead to poor resistance to chloride penetration, while ZW and ZN show better performance. Interestingly, under different fly ash contents, the declining order of compressive strength remains ZS>ZW>ZN>ZD>ZF. When the fly ash content is blow 50%, the open porosity grows with increase of fly ash, regardless of the curing conditions are diverse. However, if the replacement amount of fly ash exceeds a certain high proportion (70%), the value of open porosity tends to decrease. Moreover, the main phase composition of the mortar hydration products is similar under different curing conditions, but the declining order of the C-S-H gels and ettringite content is ZS>ZD>ZF. The addition of fly ash could increase the amount of harmless pores at early age.

• Journal of the Korean Society for Railway
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• v.17 no.5
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• pp.365-372
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• 2014

Technologies for rapid concrete curing using elevated temperature are important for saving cost and time when constricting concrete structures. Recently, a microwave heating form was developed. In this study the early strength of concrete cured by the developed form was experimentally investigated. Large scale mock up tests were conducted six times, and the results were analyzed based on the maturity theory. Logarithmic correlation curves were generated based on the measured strength and estimated maturity. It was confirmed that the strength development of the concrete cured by microwave heating form can be estimated by the equivalent age theory usually applied to steam-curing technology. By using the microwave heating form, one day at most is enough to get the required strength for the safe removal of forms, even in cold weather.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7910-7916
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• 2015

This paper examines the mechanical and autogenous shrinkage characteristics per curing condition of Ultra High Performance Concrete (UHPC) according to the change in the quantities of expansive admixture and shrinkage-reducing agent. In view of the mechanical properties according to the curing condition, all the UHPC specimens that experienced steam curing at $90^{\circ}C$ developed compressive strength higher than 190 MPa, and the specimens that experienced water curing at $20^{\circ}C$ developed compressive strength comparable to that developed at 91 days by the steam-cured specimens. The specimens steam-cured at $90^{\circ}C$ showed high tensile strength of 23.4 MPa whereas slight loss of the tensile strength was observed in those water-cured at 20. Besides, in view of the autogenous shrinkage according to the curing condition, no particular change could be found in the final shrinkage. The compressive strength developed by UHPC according to the use of expansive and shrinkage-reducing agents reached values higher than 190 MPa in case of steam curing at $90^{\circ}C$. Shrinkage reduced by about 45% when using both expansive and shrinkage-reducing agents without difference according to the curing condition.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.543-548
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• 2008

Solid hydrated by hydro-thermal synthesis reaction is cured two times, the first curing is the steam curing at atmospheric pressure and the second one is a high-pressure steam curing, that is autoclaving. Steam curing is to acquire the proper strength for the resistance of treatment in the first curing process, it was not evaluated properly so far. Because of ignorance about curing, some engineers even think that the dry curing is better than the steam curing. The relation between compressive strength of solid hydrated by hydrothermal synthesis reaction and curing condition are presented in this paper. In order to investigate the effect of curing on the strength properties of specimen, the hydration behavior of solid hydrated by hydro-thermal synthesis reaction has been studied over curing condition using XRD, DT-TGA and porosimeter, SEM analysis technique. The results show that the specimens which are cured with blended method of dry and steam curing appear to have better strength properties than that of dry curing and steam curing. Also, there are significant difference of hydration behavior among curing condition in the solid hydrated by hydro-thermal synthesis reaction.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.49-52
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• 2007

Recently, as architectural concrete structures become high-rise and megastructured, concrete become high-strengthened and, by ensuring products of more stability, air compression and rationalization of construction are required. In general, product management test of precast concrete member, specimen for management cured in the same condition with precast concrete member is substitutively used for strength test. However, large cross-sectional precast concrete members such as columns show large temperature increase in manufacturing process not only by external heating but also by concrete itself's hydration heating. Therefore, it is expected that specimen for management to predict strength and compression strength of precast concrete member shows different temperature history and strength characteristics. Concerning this, in order to suggest temperature history and strength characteristics of high strength mass concrete suitable for precast concrete application, this study comprises the inclusive investigations on the relations between management specimen with similar temperature history and core strength, and the strength characteristics per member cross-section dimensional value and per water-bonding material ratio value.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.613-620
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• 2005

There are some problems in utilizing recycled concrete aggregate go structural use because of the difficulties concerning about quality control and durability. It seems to be possible to utilize recycled concrete aggregate for making concrete products because quality control of concrete products is easier than ready-mixed concrete, but there are little studies about the properties of the steam-cured recycled aggregate concrete. In this study, various tests were performed such as compressive strength, flexural strength, splitting tensile strength, bonding strength and chloride ion penetration test to evaluate the effect of substitution of recycled concrete aggregate. The results of strength test showed that the concrete strength decreased with the increase of the substitution ratio of recycled concrete aggregate, but it was in the reasonable range and almost equal to that of normal concrete below the substitution ratio of $50\%$. On the other hand, strength test of furnace slag cement concrete shows that the strength of recycled concrete with furnace slag cement under curing condition lower than that of recycled concrete with ordinary portland cement under same condition. From the result of this study, it can be concluded that recycled concrete aggregate is able to be utilized for structural use but substitution ratio should be decided with care in each case. The result of this study could be used as the basic data for the structural use of recycled concrete aggregate.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.533-536
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• 2004

This study aims to manufacture and to evaluate lightweight cement composite using lightweight aggregate and expanded perlite. The expanded perlite and lightweight aggregates were mixed with cement, water, SP(superplasticizer), forming-agent and poly-propylene fiber. The specimens were cured at $20^{\circ}C$ for 24h and then at steam curing of $60^{\circ}C$, RH $100\%$ for 12h. As a result, We could make lightweight cement composite of satisfaction about ALC properties. However it is need to improve the properties of density and water absorption.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.34-35
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• 2019

In recent years, the construction industry has also applied the dry method that can be assembled in the field by industrialization and factory production, which is free from climatic effects and can reduce the cost due to mass production and simplify the work in the field. Among the building materials used in this dry method, ALC products are made by mixing calcium oxide, gypsum, cement, and water in silica and putting them in an autoclave to create voids in the interior through steam curing at high temperature and pressure. But it requires curing cycle conditions of warming, isothermal, and temperature curing. It depends on the performance of the product depending on the curing conditions, the economical efficiency due to high oil prices, the emission of greenhouse gases by the use of fossil fuels. Experiments were conducted to select an appropriate animal protein foam for lightweight foamed concrete block which was cured by applying a prefilling method to replace existing ALC products. As a result of investigating the characteristics of lightweight foamed concrete by type of animal protein foam, it is considered that FP3 is most suitable for manufacturing lightweight foamed concrete block.