굴패각, 플라이애쉬 및 메타카올린을 적용한 모르타르의 상온 및 고온 후 성능 평가 연구 = Performance Evaluation of Mortar Incorporating Oyster shells Powder, Fly Ash, and Metakaolin at Ambient and Elevated Temperatures

다국어 초록 (Multilingual Abstract)

Performance Evaluation of Mortar Incorporating Oyster shells Powder, Fly Ash, and Metakaolin at Ambient and Elevated Temperatures Jaegon Lee Advisor : Prof. Lee Heeyoung, Ph. D. Department of Civil Engineering Graduate School of Chosun University Residual mechanical performance and internal deterioration characteristics of mortars containing oyster shell powder (OS), fly ash (FA), and metakaolin (MK) after exposure to elevated temperatures were evaluated. In order to evaluate the feasibility of using eco-friendly replacement materials under high-temperature conditions, OS was used as a partial replacement for fine aggregate, while FA and MK were used as partial replacements for cement. A total of six mortar mixtures were prepared: OPC, FA-20, MK-10, OS-10, OS-FA, and OS-MK. Cube specimens with dimensions of 50 × 50 × 50 mm were fabricated and cured for 28 days under controlled moist conditions. After curing, the specimens were exposed to target temperatures of 200, 400, 600, 800, and 1000℃, maintained for 60 minutes at each target temperature, and then furnace-cooled to room temperature. The residual performance of the mortars was evaluated through compressive strength, residual strength ratio, mass loss ratio, and water absorption. In addition, X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), and heat transfer analysis using ABAQUS were conducted to examine phase transformation, microstructural deterioration, thermal decomposition behavior, and internal temperature distribution. The results showed that most mixtures exhibited an increase or retention in compressive strength in the range of 200–400℃, which was attributed to moisture removal and temporary matrix densification caused by microstructural rearrangement. Among the mixtures, MK-10 showed the highest absolute compressive strength from room temperature to 800℃, indicating the beneficial effects of metakaolin on matrix densification. In contrast, OS-10 exhibited relatively lower room-temperature strength, but showed the highest residual strength ratio in the range of 200– 800℃, suggesting favorable strength retention under elevated temperatures. Above 600℃, all mixtures showed clear degradation, including increased mass loss, increased absorption, pore expansion, and the development of connected cracks, which led to significant reductions in compressive strength. The TGA and XRD results indicated that the thermal behavior of OS-containing mixtures differed from that of OPC due to the presence of CaCO3-based phases, while FE-SEM observations confirmed severe microstructural damage at 1000℃. The heat transfer analysis further showed that the OS mixture exhibited slightly delayed temperature rise at the core and larger surface-to-center temperature differences than OPC under the same heating condition, implying that the internal thermal state of the specimens was not identical even under identical furnace exposure. Overall, MK-10 was found to be advantageous in terms of absolute compressive strength, whereas OS-10 was favorable in terms of residual strength retention after high-temperature exposure. However, the combined replacement mixtures did not show a simple additive improvement, indicating that the high-temperature behavior of blended eco-friendly mortars is governed by complex interactions among thermal decomposition, phase change, and microstructural deterioration.

목차 (Table of Contents)

• 제 1 장 서 론 1
• 1.1 연구 배경 1
• 1.2 연구 목적 4
• 1.3 연구 범위 및 방법 5
• 제 2 장 국·내외 연구동향 및 연구 가설 6
• 2.1 굴패각을 활용한 시멘트계 재료 관련 연구 6
• 2.2 플라이애쉬 및 메타카올린 적용 관련 연구 8
• 2.3 시멘트계 재료의 고온 손상 메커니즘 및 잔류강도 평가 10
• 2.4 연구 가설 및 분석 방향 12
• 제 3 장 실험 계획 및 방법 13
• 3.1 재료 및 배합 조건 13
• 3.1.1 사용 재료 13
• 3.1.2 배합 계획 15
• 3.2 시험체 제작 및 고온 노출 조건 17
• 3.2.1 시험체 제작 및 양생 17
• 3.2.2 고온 가열 조건 및 승온 곡선 19
• 3.3 역학적 특성 평가 방법 21
• 3.3.1 압축강도 시험 방법 21
• 3.3.2 잔류강도비 산정 방법 23
• 3.3.3 질량 변화율 측정 방법 24
• 3.3.4 흡수율 측정 방법 25
• 3.4 미세구조 및 열적 특성 분석 방법 26
• 3.4.1 전계방출형 주사전자현미경 분석 26
• 3.4.2 X선 회절 분석 28
• 3.4.3 열중량 분석 30
• 제 4 장 실험 결과 및 분석 32
• 4.1 상온 압축강도 결과 32
• 4.2 고온 노출 후 압축강도 결과 35
• 4.3 잔류강도비를 통한 내화성능 비교 39
• 4.4 질량 변화율 분석 42
• 4.5 흡수율 분석 44
• 4.6 내부 구조 분석 결과 46
• 4.6.1 전계방출형 주사전자현미경 분석 46
• 4.6.2 X선 회절 분석 51
• 4.6.3 열중량 분석 55
• 제 5 장 열전달 관점에서의 고온 거동 해석 61
• 5.1 열해석 모델 개요 61
• 5.2 해석 조건 및 물성치 설정 64
• 5.3 열해석 결과 및 실험 결과와의 비교 67
• 제 6 장 결 론 71
• 참 고 문 헌 74