Effects of subsequent curing on chloride resistance and microstructure of steam-cured mortar

Hu, Yuquan,Hu, Shaowei,Yang, Bokai,Wang, Siyao Techno-Press 2020 Advances in concrete construction Vol.9 No.5

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.

Effect of Steam Curing on Concrete Piles with Silica Fume

N. Yazdani,F. ASCE, M. Filsaime,T. Manzur 한국콘크리트학회 2010 International Journal of Concrete Structures and M Vol.4 No.1

Silica fume is a common addition to high performance concrete mix designs. The use of silica fume in concrete leads to increased water demand. For this reason, Florida Department of Transportation (FDOT) allows only a 72-hour continuous moist cure process for concrete containing silica fume. Accelerated curing has been shown to be effective in producing high-performance characteristics at early ages in silica-fume concrete. However, the heat greatly increases the moisture loss from exposed surfaces, which may cause shrinkage problems. An experimental study was undertaken to determine the feasibility of steam curing of FDOT concrete with silica fume in order to reduce precast turnaround time. Various steam curing durations were utilized with full-scale precast prestressed pile specimens. The concrete compressive strength and shrinkage were determined for various durations of steam curing. Results indicate that steam cured silica fume concrete met all FDOT requirements for the 12, 18 and 24 hours of curing periods. No shrinkage cracking was observed in any samples up to one year age. It was recommended that FDOT allow the 12 hour steam curing for concrete with silica fume.

증기양생을 실시한 고강도 모르타르의 강도발현에 관한 실험적 연구

권희성,백민수,정상진 단국대 부설 리모델링연구소 2009 리모델링 연구소 논문집 Vol.7 No.1

Precast concrete produced in the industry is advantageous in a sense that it meets certain requiring standards and thus is easy to manage, and it saves construction period by shortening concrete curing time in the field. Nevertheless, studies on the strength evaluation of PC material by steam curing have rarely been done. In addition,as concrete becomes of high strength, it is speculated that relevant steam curing temperature history is also required. Therefore this study is on the steam curing method in manufacturing precast concrete products, and cement mortar has been used for experiments to exclude the possibility that concrete aggregate granularity and aggregate shape change may affect on strength development by cement hydration. In addition, this research is to provide the fundamental information of industrial manufacture of PC member by suggesting the optimal steam curing condition. The optimal steam curing condition has been investigated from the relations between temperature history condition and strength development, via modifying temperature patterns in various ways such as pre-tirne, curing maximaI temperature, maximaI temperature maintenance time which are factors that affect on high strength concrete product in steam curing.

증기양생을 실시한 고강도 모르타르의 강도발현에 관한 실험적 연구

권희성(Kwon Hee-Sung),김성진(Kim Sung-Jin),공민호(Gong Min-Ho),백민수(Paik Min-Su),정상진(Jung Sang-Jin) 대한건축학회 2008 大韓建築學會論文集 : 構造系 Vol.24 No.7

Precast concrete produced in the industry is advantageous in a sense that it meets certain requiring standards and thus is easy to manage, and it saves construction period by shortening concrete curing time in the field. Nevertheless, studies on the strength evaluation of PC material by steam curing have rarely been done. In addition, as concrete becomes of high strength, it is speculated that relevant steam curing temperature history is also required. Therefore this study is on the steam curing method in manufacturing precast concrete products, and cement mortar has been used for experiments to exclude the possibility that concrete aggregate granularity and aggregate shape change may affect on strength development by cement hydration. In addition, this research is to provide the fundamental information of industrial manufacture of PC member by suggesting the optimal steam curing condition. The optimal steam curing condition has been investigated from the relations between temperature history condition and strength development, via modifying temperature patterns in various ways such as pre-time, curing maximal temperature, maximal temperature maintenance time which are factors that affect on high strength concrete product in steam curing.

증기이송튜브를 적용한 CIPP관의 증기 유동해석

이중연,홍기남,지상원 한국복합신소재구조학회 2020 복합신소재구조학회논문집 Vol.11 No.5

This paper reports the results of computational fluid dynamics analysis on a steam transfer tube designed to eliminate the uncured end point of the cured-in-place pipe (CIPP) that is used to reinforce sewer pipes. For the flow analysis of the designed steam transfer tube, analysis was performed using SolidWorks Flow Simulation. Flow and temperature distributions for steam transport tubes with diameters of 100, 150, and 200mm were investigated by using flow analysis. The analysis results confirmed that as the diameter of the steam transfer tube is increased, the inner length of the CIPP satisfying the curing temperature increased. Additionally, it was confirmed that a steam backflow phenomenon occurred at the inlets of all steam transfer tubes except for the diameter of 200mm. Accordingly, the optimum diameter for the steam transfer tube was determined to be 200mm. Further, through flow analysis, it was confirmed that the curing temperature was satisfied for all lengths of CIPP after 350s of steam injection. 본 논문은 하수관 보강 방법 중 보강튜브경화공법(CIPP)의 종점부 미경화 문제를 해결하기 위해 설계된 증기이송튜브 시스템에 대한 유동해석 결과를 보고한다. 설계된 증기이송튜브의 유동해석을 위해 SolidWorks Flow Simulation을 이용하여해석을 수행하였다. 100mm, 150mm, 200mm의 직경을 갖는 증기이송튜브에 대한 유동 흐름 및 온도 분포가 유동을 해석을 통해검토되었다. 해석 결과를 통해 증기이송튜브의 직경이 증가함에 따라 경화온도를 만족하는 CIPP 내부 길이가 증가하는 것이 확인되었다. 또한, 직경 200mm를 제외한 모든 직경의 증기이송튜브의 입구에서 증기 역류 현상이 나타남을 확인하였다. 이에 증기이송튜브의 최적 직경은 200mm로 결정되었으며, 이에 대한 유동해석을 통해 증기주입을 시작하고 350초 경과 이후에 CIPP 내 모든 길이에서 경화온도를 만족하는 것을 확인하였다.

고강도콘크리트용 혼화재를 사용한 콘크리트의 물성에 관한 연구

이승한 한국콘크리트학회 1995 콘크리트학회지 Vol.7 No.2

본 연구는 증기양생을 실시하는공장제품을 대상으로 석고계 고강도콘크리트용 혼화재를 사용하여 콘크리트를 고강도화하는데 그 목적이 있다. 목표 슬럼프는 원심력 성형제품을 대상으로 슬럼프 $6{\pm}1cm$가 되도록 고성능감수제로 조절하였으며, 아울러 양생방법에 다른 고강도콘크리트용 혼화재를 사용한 콘크리트의 강도발현 특성을 검토하고자 증기 및 수중양생을 실시 비교하였다. 실험결로부터 고강도 콘크리트용 혼화재는 증기양생이 효과적이며 압축강도 발현은 단위결합재량 $530{\sim}600kg/m^3$의 조건에서 10%치환으로 무치환에 비하여 1.3배 증가된 $650kgf/cm^2$ 이상, 15-30% 치환시 1.4-1.5배 증가된 $700kgf/cm^2$이상을 얻었다. 따라서 고강도콘크리트용 혼화재는 증기양생시의 고강도콘크리트 제조에 효과적으로, 시멘트2차제품 제조에 오오토클레브 양생을 하지 않고 증기양생만으로 고강도콘크리트를 얻을 수 있는 유효한 혼화재임을 나타냈다. This study was performed to get high strength of the precase concrete adopting a steam curing by using a gypsum-admixture for the high strength concrete. The superplasticizer was used to compensate low slump of base concrete keeping its slump up about $6{\pm}1cm$. To examine the property for strength revelation of concrete using admixtures for a high strength concrete, steam and standard curing were compared each other. Test results were shown that admixtures for high strength concrete were more effective in steam curing than standard curing. On the condition that the unit cement content is about $530{\sim}600kg/m^3$, the compressive strength of concrete replacing by 10% of the admixture was obtained over $65Okgf/cm^2$, which was increased as 1.3 times as that for the nonreplacement. When the admixture was replaced to 15-30%, the compressive strengh was obtained over $700kgf/cm^2$ which was increased as 1.4 - 1.5 times. Therefore, the admixture for high strength concrete, being effective in steam curing, was more efficient to get a high strength concrete using only steam curing instead of an autoclave curing for the secondary products of cement.

CO2 저감형 건자재 개발을 위한 양생방법과 결합재 종류에 따른 모르타르의 강도 특성

김하석,백대현,전찬수,이세현 한국폐기물자원순환학회 2013 한국폐기물자원순환학회지 Vol.30 No.8

Carbon dioxide generated from construction materials and construction material industry among the fields ofconstruction is approximately 67 million tons. It is about 30% of the carbon dioxide generated in the fields of construction.In order to reduce carbon dioxide in the fields of construction, it is necessary to control the use of fossil fuel consumedand decrease carbon emission by reducing the secondary and tertiary curing generating carbon dioxide in constructionmaterial industry. Therefore, this study manufactured mortar by having cement as the base and substituting three bindingmaterials up to 50% and then adopted different curing methods to analyze congelation and strength characteristics. According to the result of strength characteristics by the types of binding materials and replacement ratio, the specimensubstituting ESA (Early Strength Admixture) and FPC (Fine Particle Cement) showed active strength improvement. Inparticular, the specimen substituting ESA as 25% indicated the greatest strength improvement, and as the number of curingincreased, the strength grew higher, too. And when the binding material was used by substitution, it showed strengthcharacteristics similar to or higher than the specimen conducting tertiary autoclave curing as the secondary steam curing.

고로슬래그와 환원슬래그를 기반으로 한 저에너지양생용 혼합재를 사용한 압출성형패널의 강도특성

김하석,이세현 한국폐기물자원순환학회 2014 한국폐기물자원순환학회지 Vol.31 No.7

Carbon dioxide generated from construction materials and construction material industry among the fields ofconstruction is approximately 67million tons. It is about 30% of the carbon dioxide generated in the fields of construction.In order to reduce carbon dioxide in the fields of construction, it is necessary to control the use of fossil fuel consumedand decrease carbon emission by reducing the secondary and tertiary curing generating carbon dioxide in constructionmaterial industry. Therefore, this study produced an extrusion panel by using cement as the base materials and substitutingbinding materials up to 40% to analyze strength characteristics. According to the results of strength characteristics bythe replacement binder (Low energy curing Admixture) showed an apparent active strength improvement. In particular,specimens substituting binder as 45% indicated the greatest strength improvement. When binding materials was used withsubstitution, it showed strength characteristics similar or higher than specimens made from tertiary autoclave curing assecondary steam curing.

先붙임 工法을 이용한 PC 타일의 性能評價에 關한 細究

박희곤,정상진 단국대 부설 리모델링연구소 2006 리모델링 연구소 논문집 Vol.4 No.1

Exterior tile setting can be divided into two types: post-bonding method, and pre-bonding method. Pre-bonding method. In pre-bonding method, different from the post-bonding method, the process of background mortaring is eliminated, saving cost of materials, work hour, and labor expenses, and it doesn’t require time for curing. It is proved that pre-bonding method of manufactured PC tile is economical in terms of Life Cycle Cost, because it method is high in stability and reduces a term of work, and cost low in maintaining and repairing. There are many problems in applying pre-bonding method to real construction work, including the efflux of cement pastes during the process of vibration tampering, and the falling off or breaking of PC tile caused by the contact of vibrator, the cost increase that results from manufacturing overly strength-revealing concrete regardless of the strength of concrete used in the manufacturing of PC cotton wall. The purpose of this study, therefore, is to present ways to resolve above problems by using fluidized concrete in PC manufacturing, and, to find out an appropriate mixture of high fluidized concrete used for PC manufacturing, targeting 280kgf/cm² of specified concrete strength by conducting fundamental experiments, and to provide basic data for bringing pre-bonding method of high fluidized concrete tile into practical use. For this purpose, this study compares adhesive strengh between tiles attached on mock experimental structure, with different mixture rate and curing method, and review and compares marginal concrete deformation rate with the drying shrinkage of concrete by imposing vertical compressive loading until the falling-off of concrete

증기양생이 필요 없는 프리캐스트 콘크리트 개발에 관한 기초적 연구

민태범(Mim, Tae-Beom),조인성(Cho, In-Sung),이한승(Lee, Han-Seung) 대한건축학회 2012 大韓建築學會論文集 : 構造系 Vol.28 No.12

The purpose of this study is to develop the precast concrete without steam curing. Generally, it is necessary that the precast concrete must cure in steam condition. If we make a precast concrete without steam curing, we could save the manufacturing energy and CO₂ emission. In this experiment, the high early strength cement containing massive C₃S quantity was used to enhance the early strength of cement mortar using admixtures which can accelerate C₃S hydration reaction in the condition of room temperature. The measuring items are zero flow, setting times, compressive strength and analysis of MIP & SEM. From the results of this experiment, hardening catalyst is very effective to increase the high early strength of cement mortar according to the early formation of C-S-H hydrate. The compressive strength of mortar is increased that it increases in the amount of consumption of hardening catalyst. The increasing cause of the compressive strength of mortar is decrease in a pore ratio and pore size of mortar due to the acceleration of C₃S hydration with hardening catalyst. Also, the generation of C-S-H was confirmed by use of a hardening catalyst according to an SEM analysis. When the strength and workability of mortar are considered, the appropriate amount of hardening catalyst dosage is about 1.0%.