RCD 공법을 적용한 CSG 댐의 표면보호 콘크리트 배합설계 연구

다국어 초록 (Multilingual Abstract)

Most agricultural reservoirs in domestic are constructed in the form of embankment dams composed mainly of soil and sand. Although this type of dam is advantageous in terms of economic efficiency and constructability, it exhibits relatively low structural stability and is therefore vulnerable to overtopping and piping. In addition, many agricultural reservoirs lack adequate flood-control facilities, resulting in limited capability for flood mitigation and disaster response.
To overcome these limitations, the development of Cemented Sand and Gravel (CSG) construction technology, which enables rapid construction while providing improved structural stability compared to conventional embankment dams, has been increasingly required. However, due to the scarcity of domestic construction cases, systematic studies tailored to domestic conditions are still needed.
A CSG dam is constructed by mixing locally available riverbed aggregates or excavated soils with a small amount of cement and water, without additional gradation adjustment, and compacting the mixture using vibratory rollers. Conventional protection systems for CSG dams have primarily adopted precast concrete methods; however, these methods involve complicated construction processes and relatively low construction efficiency.
In contrast, the Roller Compacted Dam Concrete (RCD) method has construction procedures similar to those of CSG dams, allowing integrated construction using the same equipment and resulting in a simplified construction process with improved construction speed. Accordingly this study aimed to determine the optimum mix proportion of protection concrete for CSG dams applying the RCD method, with improved economic efficiency, environmental performance, and structural stability compared to the conventional precast method.
Unit water content, fine aggregate ratio, and unit cement content were selected as the primary mix design variables, and their effects on Vebe time (Vebe consistency), density, air content, and compressive strength were comprehensively evaluated. In addition, predictive equations for age-dependent compressive strength development based on the optimal mix design and for compressive strength estimation under steam curing conditions were proposed. Furthermore, by analyzing the time-dependent variation of Vebe time, workability control limits for field application were established.
The overall conclusions drawn from the experimental program of this study are summarized as follows:

1. Based on the evaluation of unit water content in the range of 150-170kg/m3, the Vebe time exhibited a decreasing trend with increasing unit water content, indicating that unit water content is a key parameter exerting a significant influence on Vebe time. The density of all mixtures exceeded the specified design density, confirming that sufficient compaction was achieved. In contrast, both air content and compressive strength showed decreasing trends as the unit water content increased. Considering these results comprehensively, a unit water content of 150kg/m3, which was closest to the target Vebe time of 20 s while providing the highest compressive strength, was determined to be the optimum unit water content.

2. When the unit water content was fixed at 150kg/m3 and the fine aggregate ratio was varied from 60% to 80%, the Vebe time showed an increasing trend with increasing fine aggregate ratio. This behavior is attributed to the dominant effect of increased mortar matrix content and the resulting reduction in workability. The density of all mixtures exceeded the specified design density, indicating that adequate compaction was achieved. The air content increased with increasing fine aggregate ratio, whereas the compressive strength exhibited an opposite trend; however, the reduction in compressive strength was relatively small, suggesting the investigated range was limited. Based on these results, the fine aggregate ratio range of 65-70% was found to be closest to the target Vebe time of 20 s, and an optimum fine aggregate ratio of 67% was determined from regression analysis.

3. When the unit water content and fine aggregate ratio were fixed at 150kg/m3 and 67%, respectively, and the unit cement content was varied from 140 to 240kg/m3, the Vebe time exhibited an increasing trend with increasing unit cement content. Similar to the results obtained from variations in unit water content and fine aggregate ratio, the density of all mixtures exceeded the specified design density, indicating that sufficient compaction was achieved. Both air content and compressive strength increased with increasing unit cement content, confirming that unit cement content is key paramenter governing compressive strngth development. Based on these findings, theunit cement content range satisfying both the target Vebe time of 20 s and the target compressive strength of 18 MPa was identified as 200-240kg/m3. Considering economic efficiency and test variability, a unit cement content of 200kg/m3 was was determined to be the optimum value.

4. The optimum mix proportion of protection concrete for CSG dams applying the RCD method was determined as a water-cement ratio of 79%, a unit content of 150kg/m3, a fine aggregate ratio of 67%, and a unit cement content of 200kg/m3 by comprehensively evaluating the results of Vebe time, density, air content, and compressive strength. To overcome the time-related constraints associated with long curing periods, a strength development prediction equation based on the optimum mix proportion was proposed, along with a steam curing–based compressive strength prediction equation. These prediction approaches are expected to effectively mitigate time-related and practical limitations encountered in mix design and quality control. In addition, by analyzing the time-dependent variation in Vebe time, the workability management limit was determined to be 220 minutes. Furthermore, using the proposed steam curing–based compressive strength prediction equation, it was confirmed that elapsed time has a direct influence on the development of compressive strength.

If future studies, incorporate various mineral admixtures, such as fly ash and limestone powder, to reduce the heat of hydration and carbon emissions, together with additional evaluations of long-term durability, the field applicability and practical implementation of protection concrete for CSG dams applying RCD method are expected to be further enhanced.

목차 (Table of Contents)

• List of Tables ⅲ
• List of Figures ⅳ
• Ⅰ. 서론 1
• Ⅱ. 연구사 4
• 2.1 CSG 댐 4
• 2.2 CSG 댐의 표면보호 및 RCD 공법 적용 8
• Ⅲ. 재료 및 실험방법 12
• 3.1 배합설계 방법 12
• 3.1.1 국내외 RCD 배합설계 방법 12
• 3.1.2 RCD 공법을 적용한 CSG 댐의 표면보호 콘크리트 배합설계 방법 17
• 3.2 사용재료 21
• 3.2.1 시멘트 21
• 3.2.2 골재 22
• 3.3 실험방법 28
• 3.3.1 Vebe 시간 및 밀도 28
• 3.3.2 공기량 30
• 3.3.3 압축강도 31
• Ⅳ. 결과 및 고찰 34
• 4.1 단위수량 결정 34
• 4.1.1 Vebe 시간 및 밀도 34
• 4.1.2 공기량 37
• 4.1.3 압축강도 39
• 4.2 잔골재율 결정 40
• 4.2.1 Vebe 시간 및 밀도 40
• 4.2.2 공기량 43
• 4.2.3 압축강도 44
• 4.3 단위시멘트량 결정 46
• 4.3.1 Vebe 시간 및 밀도 46
• 4.3.2 공기량 50
• 4.3.3 압축강도 51
• 4.4 최적 배합비 도출 53
• 4.5 CSG 댐의 표면보호 콘크리트 압축강도 예측 모델 제안 54
• 4.5.1 재령별 압축강도 발현 예측식 제안 54
• 4.5.2 증기 양생 기반 압축강도 예측식 제안 57
• 4.5.3 경시변화에 따른 관리한계 및 증기 양생 기반 압축강도 예측 59
• Ⅴ. 요약 및 결론 62
• 참 고 문 헌 65
• ABSTRACT 70