• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.589-596
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• 2002

In this paper, setting and strength performances of concrete containing saccharic type super retarding agents are investigated under various kinds and contents of super retarding agents. According to test results, as super retarding agents contents increase, slump shows to be increased, while air contents decrease about 1∼2％. Setting time shows to be retarded considerably with increase of super retarding agents. It takes 20 days after mixing to reach final setting in case of concrete containing gluconic acid more than 0.3％. And 10 days after mixing in case of enhancing sucrose, white and brown sugar. Compressive strength of concrete containing super retarding agents is lower than that of plain concrete at early age. However, it keeps up with and exceeds the compressive strength of plain concrete at later age. White sugar md brown sugar shows positive performances in delaying setting time and strength compared to existing super retarding agents. n further investigations on durability are conducted, it is thought that application of white sugar as super retarding agent is available.

• Cement Symposium
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• no.24
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• pp.96-101
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• 1996

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.269-275
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• 2022

In this study, the setting time and compressive strength of cement paste composites applied with nano-micro pozzolanic binders were experimental analyzed. The pozzolanic binder was reduced initial and final setting time and the compressive strength was increased. Micro silica was effective in decrease the initial setting and final setting time and impressing the compressive strength. When two or more cement binders were used, the using of silica fume and a small amount of nano silica at reduced the setting time to 62-64 % to OPC cement and the compressive strength was increased to 117 %. A small amount of mixing the nano silica was effect to pore filling and pozzolanic activation. However, the addition of a chemical admixture should be considered when mixing table design because pozzolanic binders high specific surface area causes a decrease in cement composites flow.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.51-52
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• 2022

The electro-mechanical impedance(EMI) behavior of piezoelectric sensor embedded in cement mortar was investigated to assess the setting times. EMI signal was continuously measured for 12 hours by the PZT sensor embedded in cement mortar with different ratio of sand. As a result, the setting times by the penetration resistance test were accelerated as the sand ratio increased. However, the setting times by EMI sensing technique were delayed as the sand ratio increased.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6890-6897
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• 2014

EAF reduction slag has unstable properties of expansion and destruction. Therefore, it cannot be used as a construction material. The purpose of this study was to use EAF reduction slag as a concrete admixture. EAF reduction slag contains $11CaO{\cdot}7Al_2O_3{\cdot}CaF_2$ and ${\beta}-C_2S$ (calcium aluminate compounds). To confirm the properties of EAF reduction slag as a concrete admixture, the condensation, compressive strength and activity factor due to substitution rate of EAF reduction slag were measured. Originally, EAF reduction slag was cured rapidly because of its chemical composition ($11CaO{\cdot}7Al_2O_3{\cdot}CaF_2$). On the other hand, when 8% gypsum was added, its properties of condensation and compressive strength were similar to the plain specimen. When 6% gypsum was added, the quality of the KS F 2536 standards (quality standard number 3) were met in terms of activity factor. Overall, 8% gypsum addition is the most appropriate by considering the activity factor in the long-term compressive strength.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5A
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• pp.307-315
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• 2012

Recently, ultra high performance fiber reinforced concrete (UHPFRC) having over 180 MPa compressive strength and 10 MPa tensile strength has been developed in Korea. However, UHPFRC represents different material properties with normal concrete (NC) and conventional high performance concrete (HPC) such as a high early age autogenous shrinkage and a rapid dry on the surface, because it has a low water-binder ratio and high fineness admixtures without coarse aggregate. In this study, therefore, to propose suitable experimental methods and regulations, and to evaluate mechanical properties at a very early age for UHPFRC, setting, shrinkage and tensile tests were performed. From the setting test results, paraffin oil was an appropriate material to prevent drying effect on the surface, because if paraffin oil is applied on the surface, it can efficiently prevent the drying effect and does not disturb or catalyze the hydration of cement. From the ring-test results, it was defined that the shrinkage stress is generated at the time when the graph tendency of temperature and strain of inner steel ring is changed. By comparing with setting test result, the shrinkage stress was firstly occurred as the penetration resistance of 1.5 MPa was obtained, and it was about 0.6 and 2.1 hour faster than those of initial and final sets. So, the starting time of autogenous shrinkage measurement (time-zero) of UHPFRC was determined when the penetration resistance of 1.5 MPa was obtained. Finally, the tensile strength and elastic modulus of UHPFRC were measured from near initial setting time by using a very early age tensile test apparatus, and the prediction models for tensile strength and elastic modulus were proposed.

• Journal of the Korean GEO-environmental Society
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• v.17 no.3
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• pp.13-19
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• 2016

The ultrasonic waves for monitoring concrete materials have been used to investigate the setting and hardening process of concrete. This paper presents the application of bender elements for monitoring the hardening properties of Controlled Low Strength Material (CLSM) and the characterization of shear waves in CLSM according to curing time. To ensure the early age properties and flow, the CLSM consists of CSA cement, sand, silt, water, fly ash, and accelerator. In addition, three different type specimens according to fine contents are mixed. A couple of bender elements are installed at the wall of measurement cell and the CLSM specimen are prepared at the measurement cell for 28 days. Experimental results show that the resonant frequency and shear wave velocities increase with an increase in the curing time, regardless of the fine contents. Up to ten hours, the amplitudes of shear waves also increase, and the resonant frequency and shear wave velocities at the same time increase as the fine contents increase. The shear wave measurement technique using the bender elements may be effectively used to evaluate the hardening properties of CLSM along the curing time.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.80-91
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• 2022

This study is to provide an prediction model of setting time of super retarding mortar based on equivalent age method under various super retarding agent contents, curing temperature, and water-binder ratio (W/B). An equation for predicting setting time using maturity was proposed. Test results indicated that the setting time can be predicted by determining the curing temperature, W/B, and super retarding agent contents and substituting it into the equation proposed in this study. The coefficient of determination of the equation is 0.9 or more, and the reliability was confirmed through the F-test. Finally, using the equation proposed in this paper, reasonable quality control is possible regarding the setting of super retarding concrete in practice.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.215-220
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• 1994

본 연구의 목적은 당사 콘크리트 배합설계 프로그램인 쌍용배합설계시스템(Ssangyong Mix Proportioning Design System ; 이하 SMPD라 칭한다)을 기본으로해서 슬래그시멘트에 대한 콘크리트 배합설계(안)을 제안함으로써 콘크리트 현장에서 합리적으로 콘크리트를 제조할 수 있도록 하는데 있다. 연구 내용은 슬래그시멘트와 보통시멘트간의 콘크리트 물성차이를 실험실적으로 규명하기 위해서 슬래그 함유량 및 양생 온도별로 슬래그시멘트의 콘크리트 강도발현특성, 물시멘트비, 단위수량변화 및 응결특성 등을 검토하였으며 그 결과를 이용하여 슬래그시멘트의 콘크리트 배합설계를 시행, 표준배합과 현장배합표를 제시하였다.

• Journal of the Korea Institute of Building Construction
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• v.16 no.5
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• pp.389-395
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• 2016

The evolution of electro-mechanical impedance (EMI) of the piezoelectricity (PZT) sensor was investigated to determine the setting times of cementitious materials in this study. The PZT sensor coated with non-conductive acrylic resin was embedded in cement paste before casting and the EMI signatures were continuously measured. Vicat needle test and semi-adiabatic calorimetry test were also conducted to justify the validity of EMI senssing technique in setting monitoring of cementitious materials. The results show that significant changes in EMI resonant peak magnitude and frequency during setting process were observed, and that the setting times determined by EMI sensing technique were relevant to the setting times measured by Vicat needle test and semi-adiabatic calorimetry test.