Evaluating Concrete Compaction: A Multi-modal Approach

Compaction of concrete plays a crucial role in ensuring the strength and durability of concrete structures. Proper compaction is essential for expelling entrapped air and achieving target density. Under-compaction leaves excessive entrapped air, reducing strength and durability. Conversely, over-compaction leads to uneven density distribution due to segregation, also impacting strength and durability. The quality of compaction is thus dependent on balancing the reduction of entrapped pores with minimal segregation. This thesis investigates methods to assess the quality of concrete compaction by examining both segregation and entrapped pores. The research encompasses four key areas: monitoring segregation during compaction, evaluating segregation in hardened concrete, analyzing theemergence of surface bubbles during compaction, and characterizing entrapped pores in hardened concrete. To monitor segregation during compaction, an AC impedance spectroscopy (ACIS) measurement system was developed. It showed a strong correlation with aggregate distribution, demonstrating its effectiveness in real-time segregation detection. For evaluating segregation in hardened concrete, three indices were proposed based on density measurements and aggregate distribution analysis. These indices provide a comprehensive assessment of segregation levels, offering a practical tool for segregation assessment. The long-standing practice of relying on the rise of bubbles to the surface as an indicator for optimal compaction time was critically examined. Video analysis of surface bubbles during compaction revealed that bubble emergence continues even after segregation occurs, challengingthe reliability of this traditional method. This finding emphasizes the need for more objective compaction quality assessment techniques. X-ray computed tomography (XCT) was employed to analyze entrapped pores in hardened concrete. The study investigated the effects of concrete workability and compaction time on pore characteristics. Results showed that increasing concrete workability reduces entrapped porosity but increases segregation sensitivity during extended vibration. Concentrated regions of entrapped pores were observed within specimens, highlighting the complex relationship between compaction parameters and pore distribution. This thesis concludes that improving compaction quality control requires considering two key factors: segregation extent and entrapped air content. Traditional indicators like surface bubble emergence proved ineffective, showing the importance of advanced monitoring techniques such as ACIS. The proposed segregation indices and XCT analysis methods provide valuable tools for evaluating and improving the quality of compaction. The findings enable future research to develop more effective compaction methods and quality control procedures, potentially leading to improved concrete durability and performance in construction practice.