• 한국구조물진단유지관리공학회 논문집
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• 제20권2호
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• pp.26-33
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• 2016

알칼리활성화 슬래그-레드머드 시멘트는 알칼리활성화 시멘트 연구의 일환으로서 시멘트 조성에서 알칼리자극제, 고로슬래그와 레드머드로 구성되어져 있으며, 포틀랜트 시멘트를 사용하지 않는 클링커 프리 시멘트(Clinker Free Cement)를 의미한다. 본 논문에서는 포틀랜트 시멘트를 전혀 사용하지 않고 고분자 유기화합물인 재유화형 분말 폴리머를 혼입한 알칼리활성화 슬래그 시멘트에 레드머드의 대체율을 달리하여 강도특성, 기공특성 등을 기존 포틀랜트 시멘트와 비교 평가하였다. 그 결과 알칼리활성화 시멘트에 레드머드를 대체할 경우 C-S-H 광물상과 에트린가이트가 주요 수화생성물로 포틀랜트 시멘트와 비교하여 조직이 치밀하고 대체율 10%까지는 압축강도 및 휨강도가 증가하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2018년도 추계 학술논문 발표대회
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• pp.169-170
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• 2018

In this study, TGA analysis of hardened cement paste with fire damage was performed. The mass reduction rate of 600 ℃ specimens was about 22 ~ 25%, and the sample of 800 ℃ showed the mass loss rate of 9 ~ 13%. As the target temperature and hold time increased, the mass reduction rate decreased. As the depth increased, the mass reduction rate decreased.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2009년도 정기 학술발표대회
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• pp.68.1-68.1
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• 2009

• 한국화재소방학회논문지
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• 제23권3호
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• pp.103-109
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• 2009

콘크리트의 온도에 의한 재료적 특성에 대한 저감은 두 가지 메커니즘에 기인한다. 첫 번째 메커니즘은 온도범위에 따른 구성성분의 상변화이다. 초기 구성성분들은 온도 증가로 인해 다른 성분들로 상변화를 일으킨다. 두 번째 메커니즘은 온도에 의한 각 구성성분의 역학적 특성 변화이다. 따라서 고온에 노출된 콘크리트의 재료적 특성에 관한 모델 역시 이 두 가지 메커니즘을 함께 고려하여 제시되어야 한다. 본 연구는 위에서 언급한 두 가지 메커니즘을 고려한 고온에 노출된 콘크리트의 재료적 특성 모델을 제안하기 위한 기반연구로서, 온도범위에 따른 상변화를 고려한 경화된 시멘트 페이스트의 공극률에 대한 이론적 모델을 제시한다.

• 한국세라믹학회지
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• 제36권12호
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• pp.1342-1349
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• 1999

In order to improve the density and the mechanical strength without change in chemical composition the hardened pastes of hydroxyapatite cement were reinforced with powders and/or whiskers of hydroxyapatite. The powders behaved as a seed of hydroxyapatite formation rather than a filler while the whiskers were mrerly dispersed in matrix and capillary pores of the hardened bodies leading to increase in mechanical strength. But the increase in strength But the increase in strength was nnt enough owing to the lack of homogeneous dispersion of the fibers. The highest diametral tensile strength of 18.5 MPa was measured at the hardened hydroxyapatite body in which well-dispersed whisker phase formed uniformly during hydro-thermal curing of power-added and dry-formed hydroxyapatite cement.

• 한국세라믹학회지
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• 제52권1호
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• pp.48-55
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• 2015

Hardened cement-based materials exposed to the high temperatures of a fire are known to experience change in the pore structure as well as microstructural changes that affect their mechanical properties and tend to reduce their durability. In this experimental investigation, hardened Portland cement pastes were exposed to elevated temperatures of 200, 400, 600, 800, and $1000^{\circ}C$ for 60 minutes, and the resulting damage was studied by thermogravimetry (TG), mercury intrusion porosimetry (MIP) and density measurements. These results revealed that the residual compressive strength is increased at temperatures greater than $400^{\circ}C$ due to a small pore size of 3 nm and/or rehydration of the dehydrated cement paste. However, a loss of the residual strength occurs at temperatures exceeding 500 and $600^{\circ}C$. This can be attributed to the decomposition of hydrates such as portlandite and to an increase in the total porosity.

• The Korean Journal of Ceramics
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• 제3권4호
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• pp.235-238
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• 1997

Basic properties of new cement pastes based on the system $CaO-Al_2O_3-P_O_5-H_2O$were studied Phosphoric acid solutions and calcium dialuminate clinkers synthesized by the hydration-burning method were used for liquid and powder components of the paste, respectively Variation in the compositions of the paste was achieved by changing the liquid/powder ratio and the concentration of phosphoric acid solution. The hardening rate of the paste was so largely affected by the amount of phosphoric acid that hardening was inhibited with the low-concentrated solution but was explosively accelerated with the high-concentrated solution. The phosphoric acid solutions of concentration of 45~50% and the liquid/powder ratio of 0.5~1.5 were favoured for the high early-strength cement paste with the reasonable hardening rate and high strength. The binding phase of hardened paste was the dense amorphous gel of the system $CaO-Al_2O_3-P_O_5-H_2O$. in which the unreacted calcium dialuminate grains were embeded.

• 한국세라믹학회지
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• 제31권3호
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• pp.330-336
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• 1994

High strength cement composites (W/C=0.1) were prepared by using various blending materials such as SiC whisker and white carbon (hydrated silica: SiO2·nH2O). The effect of various blending materials on the microstructure and strength of the hardened cement paste were investigated in the view of fracture mechanics. The plain specimen showed 101 MPa of flexural strength, 81 GPa of Young's modulus and 1.32 MPam1/2 of fracture toughness. When the blending materials were added to the composites, their values were enhanced to about 110∼138 MPa, 95∼146 GPa and 1.32∼1.87MPam1/2 respectively. The improvement of the mechanical strength for the hardened cement paste may be due to the removal of macropores, the reduction of total porosity, pozzolanic reaction and the increase of various fracture toughening effect.

• Computers and Concrete
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• 제32권6호
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• pp.567-576
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• 2023

In this study, a 3D microstructure-based model is established to simulate the effective thermal conductivity of cement paste, covering varying influencing factors associated with microstructure and thermal transfer mechanisms. The virtual cement paste divided into colloidal C-S-H and heterogeneous paste are reconstructed based on its structural attributes. Using the two-level hierarchical cement pastes as inputs, a lattice Boltzmann model for heat conduction is presented to predict the thermal conductivity. The results suggest that due to the Knudsen effect induced by the nanoscale pore, the thermal conductivity of air in C-S-H gel pore is significantly decreased, maximumly accounting for 3.3% thermal conductivity of air at the macroscale. In the cement paste, the thermal conductivities of dried and saturated cement pastes are stable at the curing age larger than 100 h. The high water-to-cement ratio can decrease the thermal conductivity of cement paste.

• Advances in concrete construction
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• 제7권3호
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• pp.175-181
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• 2019

Low-calcium fly ash (LCFA) were used to prepare cement/LCFA specimens in this study. The basic physical properties including water demand, fluidity, setting time, soundness and drying shrinkage of cement/LCFA paste were investigated. The effects of curing time, immersion time and wet-dry cycles in 3% $Na_2SO_4$ solution on the compressive strength and the microstructures of specimens were also discussed. The results show that LCFA increases the water demand, setting time, soundness of cement paste samples. 50% and 60% LCFA replacement ratio decrease the drying shrinkage of hardened cement paste. The compressive strength of plain cement specimens decreases at the later immersion stage in 3% $Na_2SO_4$ solution. The addition of LCFA can decrease this strength reduction of cement specimens. For all specimens with LCFA, the compressive strength increases with increasing immersion time. During the wet-dry cycles, the compressive strength of plain cement specimens decreases with increasing wet-dry cycles. However, the pores in the specimens with 30% and 40% LCFA at early ages could be large enough for the crystal of sodium sulfate, which leads to the compressive strength increase with the increase of wet-dry cycles in 3% $Na_2SO_4$ solution. The microstructures of cement/LCFA specimens are in good agreement with the compressive strength.