Fresh and Hardened Properties of Fly Ash-Based Roller Compacted Concrete (RCC) for Dam Construction: a Proposed Alternative Guideline Integrating Concrete and Soil Approach in RCC Mix Design

Laurence Alberto, Charles Alberto (2025) Fresh and Hardened Properties of Fly Ash-Based Roller Compacted Concrete (RCC) for Dam Construction: a Proposed Alternative Guideline Integrating Concrete and Soil Approach in RCC Mix Design. Masters thesis, Tunku Abdul Rahman University of Management and Technology.

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Abstract

Since the early 1980s, roller-compacted concrete (RCC) has been widely used in dam construction, replacing conventional mass concrete, due to its speed of construction and competitive cost. To date, more than 900 RCC dams have been completed or are under construction worldwide. In the design of mixture proportioning for RCC, two approaches are widely adopted, namely, the concrete approach and the soil approach. In the concrete approach, the assumed premise is “impermeability is the single most important property.” Hence, the relationship between water-binder ratio and compressive strength forms the basis in the mixture proportioning method. In the soil approach, the assumed premise is “greater impermeability can be achieved by a combination of increased cementitious content, greater compaction, sufficient well-graded fine aggregates, all of which reduces voids in the RCC.” So, the basis in mixture proportioning is the relationship between water content and density of the RCC. In the construction of RCC dams, both concrete and soil approaches were adopted separately (rather than complement each other), and over the years due to its excellent performance, the concrete approach to mixture proportioning is preferred over soil approach as it is perceived that mixtures from soil approach have higher risks of segregation and compaction during placement. However, the material cost of concrete approach is higher when compared to soil approach. Hence, this study aims to integrate both concrete and soil approach in the mixture design and proportioning for fly ash-based RCC, leveraging on the advantages provided by both approaches and dispelling the concern that RCC espousing the soil approach has placement issues. In this study, the addition of Class F fly ash at 25%, 50% and 70% was based on the mixture designs of completed RCC dams, where the addition of pozzolans, especially fly ash, was between 20% to 70%. Furthermore, the use of fly ash was widespread in about 500 RCC dams world-wide, especially in MCRCC and HCRCC, to reduce the heat of hydration and increase the volume of paste, thereby improving the mixture consistency. This study was carried-out in three phases. In Phase 1, the optimum compaction time per layer for cylindrical specimens was established. In Phase 2, the optimum water content (soil approach) and the relationship between optimum water content and water-binder ratio (concrete approach) of the RCC mixtures, were determined. The outcome from Phase 1 (Optimum compaction time per layer) and Phase 2 (Optimum water content and relationship between optimum water content and water binder ratio) was used in Phase 3, where the fresh and hardened properties of the RCC mixtures were tested to corroborate the integrated concrete and soil approach to RCC mixture design and proportioning. The findings from the study indicate that the fresh properties (consistency, density, and air content) and hardened properties (compressive strength, split tensile strength and modulus of elasticity) meet the requirements of Bulletin 177 ICOLD, ACI 207.5R-11 and Ulu Jelai Hydroelectric Project, validating the proposed alternative guideline integrating concrete and soil approach to RCC mixture design and proportioning.