An Experimental study on Chloride Binding Capacity of Cement Mortar with Different CaAl2O4-CaAl4O7 Ratio

Abstract

Abstract

This experimental study was conducted with objectives to figure out the mechanical properties and the hydration properties and chloride binding capacity of cement mortar incorporated calcium aluminate clinker (CA and CA2) according to the CA-CA2 ratio as part of the exploration to expand the use of CA2, which improves the chloride resistance of the concrete structure. Also, the study presents the fundamental data on the optimal ratio. The Portland cement based-paste and mortar specimens were prepared by incorporating calcium aluminate clinkers with different CA-CA2 ratios. The clinker mixture were replaced 0, 5, and 10% by weight of cement, respectively. After immersed in the distilled water and NaCl solution, the strength, micropore structure, hydration products, chloride binding capacity and chloride penetration depth of specimens were analyzed. Compressive strength test and micropore structure analysis showed that Portland cement mixed with CA and CA2 can be used as structural material when the proportion of CA is less than 39% in clinker mixture within the range of less than 10% replacement ratio. Above the range, the strength decreased due to the quick freezing and the formation of large capillary pores by CA. In the analysis of hydration products, the formation of AFm phase and Friedel’s salt generally increased with higher proportion of calcium aluminate clinker. In addition, it was confirmed that the chloride binding capacity of specimens improved and the chloride penetration depth decreased as the ratio of calcium aluminate clinker increased. U10 was found to have a relatively deeper chloride penetration depth in the cement matrix compared to its chloride binding capacity because of the formation of large capillary pores. Moreover, It was confirmed that the chloride binding capacity tended to be more depend on CA-CA2 ratio than the amount of Al2O3 in the 10% replaced group. Through these results, it was found that chloride binding capacity generally improved as the increase of calcium aluminate clinker ratio. According to the ratio of CA-CA2, there were changes of hardening rate and hydration reactivity, causing the difference in chloride binding capacity and chloride penetration depth according to pore structure and AFm production.|국 문 요 지

본 연구는 콘크리트 구조물의 염해저항성을 향상시킬 수 있는 CA2의 활용을 넓히기 위한 탐구의 일환으로써 칼슘 알루미네이트 시멘트를 혼입한 포틀랜드 시멘트 모르타르 내 CA-CA2의 비율에 따른 물리·화학적 특성 및 염소이온 고정능력 평가에 목적을 두며 최적의 비율에 대한 기초적 데이터를 제시한다. 실험체는 포틀랜드 시멘트 베이스에 각각 0, 5, 10% 씩 각기 다른 CA-CA2 비율을 갖는 칼슘 알루미네이트 클링커를 혼입하여 모르타르 실험체와 페이스트 실험체를 제작하였으며, 실험체를 증류수 및 염소이온수용액 환경에 침지하여 압축강도, 미세공극구조, 수화생성물, 염소이온고정능력 및 침투깊이를 분석하였다. 압축강도 테스트와 미세 공극 구조 분석결과, 혼입율 10%이하 범위 내에서 CA가 클링커 내 39% 이하일 때 CA 와 CA2를 혼입한 포틀랜드 시멘트가 구조재료로써 사용가능하다고 판단되었다. 제한범위 이상에서는 CA에 의한 급결현상 및 조대공극 형성에 의해 강도저하가 나타났다. XRD 및 TG/DTA를 통한 수화물 분석결과, 칼슘 알루미네이트 클링커 혼입율이 증가할수록 일반적으로 AFm 상 및 프리델 염 형성이 증가하는 것으로 확인되었다. 또한, 침지실험결과에서도 혼입률이 증가함에 따라 염소이온고정능력이 향상하고 염소이온 침투깊이가 감소하는 것을 확인할 수 있었다. 하지만, U10은 조대공극형성에 의해 염소이온고정능력 대비 시멘트 매트릭스 내 염소이온침투깊이가 큰 것으로 나타났다. 또한, 칼슘 알루미네이트를 10% 혼입한 실험군에서 염소이온고정능력이 실험체 내 Al2O3의 양보다 CA-CA2 비율에 의존하는 것을 확인 할 수 있었다. 본 실험 수준 내에서 CA-CA2 비율이 39:60인 칼슘 알루미네이트 클링커를 10% 혼입한 시멘트 모르타르 실험체의 염해저항성이 가장 우수한 것으로 나타났다. 이 연구에서 본 연구결과, 칼슘 알루미네이트 클링커 혼입율이 증가함에 따라 일반적으로 염소이온 고정능력이 향상함을 파악할 수 있었고, CA-CA2비율에 따라 초기경화속도와 수화반응성에 차이가 있어 공극구조와 AFm 생성량에 따른 염소이온고정능력 및 염소이온침투억제능력에 차이를 보임을 확인하였다. 따라서, 보다 넓은 CA-CA2 비율의 범위에서 염소이온 고정능력 평가가 필요하다고 여겨지며 저열시멘트 및 중용열 시멘트에 적용을 위해 수화열분석도 필요하다고 판단된다.; Abstract

This experimental study was conducted with objectives to figure out the mechanical properties and the hydration properties and chloride binding capacity of cement mortar incorporated calcium aluminate clinker (CA and CA2) according to the CA-CA2 ratio as part of the exploration to expand the use of CA2, which improves the chloride resistance of the concrete structure. Also, the study presents the fundamental data on the optimal ratio. The Portland cement based-paste and mortar specimens were prepared by incorporating calcium aluminate clinkers with different CA-CA2 ratios. The clinker mixture were replaced 0, 5, and 10% by weight of cement, respectively. After immersed in the distilled water and NaCl solution, the strength, micropore structure, hydration products, chloride binding capacity and chloride penetration depth of specimens were analyzed. Compressive strength test and micropore structure analysis showed that Portland cement mixed with CA and CA2 can be used as structural material when the proportion of CA is less than 39% in clinker mixture within the range of less than 10% replacement ratio. Above the range, the strength decreased due to the quick freezing and the formation of large capillary pores by CA. In the analysis of hydration products, the formation of AFm phase and Friedel’s salt generally increased with higher proportion of calcium aluminate clinker. In addition, it was confirmed that the chloride binding capacity of specimens improved and the chloride penetration depth decreased as the ratio of calcium aluminate clinker increased. U10 was found to have a relatively deeper chloride penetration depth in the cement matrix compared to its chloride binding capacity because of the formation of large capillary pores. Moreover, It was confirmed that the chloride binding capacity tended to be more depend on CA-CA2 ratio than the amount of Al2O3 in the 10% replaced group. Through these results, it was found that chloride binding capacity generally improved as the increase of calcium aluminate clinker ratio. According to the ratio of CA-CA2, there were changes of hardening rate and hydration reactivity, causing the difference in chloride binding capacity and chloride penetration depth according to pore structure and AFm production.